Effects of Interaction between Cadmium (Cd) and Selenium (Se) on

Oct 10, 2017 - ... 0.9 and 1.2 mg kg–1, which were generated by mixing C1S1 soil with appropriate quantities of Cd in the form of Cd(NO3)2·4H2O and...
1 downloads 12 Views 506KB Size
Subscriber access provided by UNIVERSITY OF ADELAIDE LIBRARIES

Article

Effects of interaction between cadmium (Cd) and selenium (Se) on grain yield and Cd and Se accumulation in a hybrid rice (Oryza sativa) system Baifei Huang, Junliang Xin, Hongwen Dai, and Wenjing Zhou J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b03316 • Publication Date (Web): 10 Oct 2017 Downloaded from http://pubs.acs.org on October 11, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Journal of Agricultural and Food Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 38

Journal of Agricultural and Food Chemistry

1

Effects of interaction between cadmium (Cd) and selenium (Se)

2

on grain yield and Cd and Se accumulation in a hybrid rice

3

(Oryza sativa) system

4

Baifei Huang, Junliang Xin*, Hongwen Dai, Wenjing Zhou

5

Research Center for Environmental Pollution Control Technology, School of Safety

6

and Environmental Engineering, Hunan Institute of Technology, Hengyang 421002,

7

China

8

*

9

Tel.: +86-734-3452399

10

Corresponding author

E-mail: [email protected]

1

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

11

Abstract

12

A pot experiment was conducted to investigate the interactive effects of cadmium (Cd)

13

and selenium (Se) on their accumulation in three rice cultivars, which remains unclear.

14

The results showed that Se reduced Cd-induced growth inhibition, and increased and

15

decreased Se and Cd concentrations in brown rice, respecially. Cadmium

16

concentrations in all tissues of the hybrid were similar to those in its male parent yet

17

significantly lower than those in its female parent. Selenium reduced Cd accumulation

18

in rice when Cd concentration exceeded 2.0 mg kg-1; however Se accumulation

19

depended on the levels of Cd exposure. Finally, Cd had minimal effect on Se

20

translocation within the three cultivars. We concluded that Cd concentration in brown

21

rice is a heritable trait, making crossbreeding a feasible method for cultivating

22

high-yield, low-Cd rice cultivars. Selenium effectively decreased the toxicity and

23

accumulation of Cd, and Cd affected Se uptake but not translocation.

24

Keywords: Cadmium; Selenium; Rice (Oryza sativa); Translocation; Hybridization

2

ACS Paragon Plus Environment

Page 2 of 38

Page 3 of 38

Journal of Agricultural and Food Chemistry

25

INTRODUCTION

26

Cadmium (Cd) is a non-essential metal, and is highly mobile and toxic to living

27

organisms.1 Cadmium in soil is easily taken up by crop roots and rapidly transported

28

to the edible parts. Cadmium enters agricultural soil mainly from anthropogenic

29

sources, such as industrial discharge and emissions, sewage used for irrigation, and

30

phosphate fertilizers, and can threaten human health through bioaccumulation and

31

biomagnification.2 Currently, approximately 7.0% of the land area of China has been

32

contaminated by Cd at different levels.3 Therefore, the need for reducing Cd

33

accumulation in agricultural products is urgent.

34

Rice (Oryza sativa L.) is the predominant cereal crop in China, and additionally, the

35

staple food for over 60% of the Chinese population. Undoubtedly, the yield and

36

quality of rice are closely related to social stability, economic development, and

37

human health. Previously, several physical, chemical, and biological methods have

38

been used to minimize Cd accumulation in rice, including soil removal and

39

replacement,4 chemical washing,5 phytoremediation,6 application of soil amendments,

40

7

41

cost-ineffectiveness and time-consumption nature, ion imbalance in the soil, low grain

42

yield, and inconvenience.9 Although transgenic approaches could similarly reduce Cd

43

accumulation in rice grains,10-12 they are less publicly acceptable owing to concerns

44

over genetically modified crops, as demonstrated by the recent “Golden Rice”

45

controversy.13 By comparison, the selection and breeding of low-Cd rice cultivars is

46

becoming an increasingly popular method for reducing Cd accumulation in grains, as

and water management.8 The major limitations of these measures are their

3

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

47

there are already substantial differences in the uptake and accumulation of Cd among

48

cultivars.14 However, the inherited patterns of Cd concentration in rice are still unclear,

49

and additionally, relevant information is quite limited.

50

In recent years, researchers have discovered that selenium (Se), which is an essential

51

micronutrient for humans, plays an important role in the enhancement of immunity,

52

protection against cancer, and reduction of heavy metal toxicity.15, 16 Nevertheless,

53

approximately 72% of the total land area in China is Se-deficient,17 and consequently,

54

Se concentration in the grains of the rice cultivated in this region is 20 µg kg-1 on

55

average.18 Therefore, average daily Se intake by the Chinese is only 28–40 µg, which

56

is less than the recommended daily intake of 55–85 µg for adults,19 and often results

57

in diseases or problems related to Se deficiency.20 Furthermore, at low levels, Se is

58

beneficial to plants,21, 22 and biofortification of rice using Se fertilizers not only

59

increases grain Se concentration, but also reduces grain Cd concentration.23, 24

60

Consequently, the application of Se to slightly-to-moderately Cd-contaminated paddy

61

soils may be a cost-effective approach to the production of Cd-deficient, Se-rich rice

62

grains.24 Se application to paddy soils not only decreases Cd concentration in brown

63

rice, but also reduces Cd accumulation in other tissues.24 However, Chen et al.

64

observed that Se did not reduce Cd accumulation in rice roots.25 Consequently, the

65

effects of Cd-Se interactions on the uptake, translocation, and accumulation of Cd in

66

rice, especially in hybrid rice systems, are not yet well understood, and require further

67

investigation.

68

Currently, brown rice constitutes a considerable part of human diets because of its

4

ACS Paragon Plus Environment

Page 4 of 38

Page 5 of 38

Journal of Agricultural and Food Chemistry

69

high nutritional value. We previously observed that brown rice contains more

70

nutrients than polished rice; however, it also has higher concentrations of heavy

71

metals (Table S1). In this study, three rice cultivars, including a female parent

72

(male-sterile line), a male parent (restorer line), and their F1 hybrid were grown in

73

nine soils with different concentrations of Cd and Se. The aims were to compare the

74

accumulation of Cd and Se among the tested cultivars to investigate the inherited

75

characteristics of grain Cd accumulation, and effects of Se-Cd interactions on the

76

translocation of Cd and Se within the rice plants. We hypothesized that: (1) Se

77

application substantially reduces Cd accumulation in all tissues; (2) grain Se

78

concentration is not affected by soil Cd levels. The results of this study would help in

79

further understanding the feasibility of reducing grain Cd concentration by

80

crossbreeding and the mechanisms of Cd-Se interactions underlying grain Cd

81

accumulation.

82

MATERIALS AND METHODS

83

Plant cultivation

84

Two rice cultivars, Zhongjiu A (female parent, F) and Huazhan R (male parent, M),

85

and their F1 hybrid (H) were used in this study. The seeds of the three cultivars were

86

surface-sterilized for 15 min with 0.5% NaClO solution, rinsed with deionized water

87

for 10 min, and then, germinated in moist, sterile quartz sand at 30°C. The

88

germination time of F was delayed by 25 days to synchronize its flowering time with

89

that of M. Three weeks after germination, uniform-sized seedlings were transferred to

90

soil-filled plastic pots.

5

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

91

Experimental site and soil

92

A pot experiment was conducted in the greenhouse of the Hunan Institute of

93

Technology (26°52′N, 112°41′E), Hunan Province, China at 28–35°C. Experimental

94

soil was collected from a nearby farmland, air-dried, ground, and passed through a

95

5-mm sieve. The physical and chemical properties of the soil were evaluated using the

96

analytical methods described by Lu.26 The soil pH, cation-exchange capacity, organic

97

matter content, and contents of total N, available P, available K, total Cd, and total Se

98

were 6.40, 89.2 mmol kg-1, 19.5 g kg-1, 1.5 g kg-1, 112 mg kg-1, 124 mg kg-1, 1.23 mg

99

kg-1, and 0.58 mg kg-1, respectively. According to the Farmland environmental quality

100

evaluation standards for edible agricultural products (HJ 332-2006), the maximum

101

level (ML) of Cd in soil should be 0.3 mg kg-1; however, the standards do not specify

102

any limitation for Se concentration. Therefore, the tested soil was considered as

103

Cd-contaminated, and served as a treatment group (C1S1) in this experiment. Eight

104

other treatment groups (C2S1, C3S1, C1S2, C2S2, C3S2, C1S3, C2S3, and C3S3)

105

contained soil with target Cd concentrations of 2.0 and 4.0 mg kg-1 and/or Se

106

concentrations of 0.9 and 1.2 mg kg-1, which were generated by mixing C1S1 soil

107

with appropriate quantities of Cd in the form of Cd(NO3)2·4H2O and Se in the form of

108

Na2SeO3. Each of the eight soil groups was placed in a large plastic basin, watered,

109

and allowed to equilibrate in the greenhouse for approximately 6 months. This period

110

allowed for the attainment of balance between the various sorption mechanisms in the

111

soils.27 The final total Cd concentrations were 2.01 mg kg-1 for C2S1, C2S2, and

112

C2S3, and 4.16 mg kg-1 for C3S1, C3S2, and C3S3. The final total Se concentrations

6

ACS Paragon Plus Environment

Page 6 of 38

Page 7 of 38

Journal of Agricultural and Food Chemistry

113

were 0.86 mg kg-1 for C1S2, C2S2, and C3S2, and 1.13 mg kg-1 for C1S3, C2S3, and

114

C3S3.

115

Experimental design

116

Plastic pots (diameter at the top, 25 cm; diameter at the base, 18 cm; height, 26 cm)

117

were filled with 6.0 kg (dry weight, dw) of prepared soil. For each cultivar, three

118

replicates of each treatment group (n = 3 pots) were cultivared. The prepared rice

119

seedlings were transplanted into the pots (two plants per pot) on April 28 (M and H)

120

and May 23, 2016 (F). The pots with the M and F seedlings were arranged alternately

121

to facilitate effective cross-fertilization between them. All the pots were submerged,

122

and a water depth of approximately 3 cm above the soil surface was maintained

123

throughout the cultivation period. A solid compound fertilizer (N:P:K = 15:15:15) was

124

applied to the pots at a rate of 3.5 g pot−1 every 2 weeks. Owing to male sterility in F,

125

manual pollination was performed thrice to increase the seed-setting rate of F during

126

the flowering period of M and F.

127

Sampling and chemical analysis

128

Each plant was harvested entirely at maturity. Grains, shoots (including leaves and

129

stems), and roots were rinsed separately with tap water to remove dust and soil, and

130

then, the roots were desorbed for 15 min in ice-cold 5 mM CaCl2 solution (5 mM

131

MES-Tris, pH 6.0). Thereafter, all the plant samples were washed thoroughly with

132

deionized water, and dried at 70°C to attain constant weight. The grains were dehulled

133

using a motorized dehusker (JLGJ4.5, TZYQ, Zhejiang, China) to yield brown rice.

134

The dried samples were ground, passed through a 0.149-mm sieve, and digested with

7

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

135

HNO3-H2O2 (10:3, v/v) using a microwave digester (XT-9900 A, Shanghai Xintuo

136

Analytical Instruments Co., Ltd., China). The concentrations of Cd and Se were

137

determined using ICP-MS (Agilent-7500, Agilent Technologies Co. Ltd, Palo Alto,

138

CA, USA). Certified Reference Materials (CRM) for plants, GBW07605 and soil,

139

GBW07410 (provided by the National Research Center for CRM, China) were used

140

for quality assurance and quality control of the analysis of Cd and Se. The detection

141

limits of Cd and Se in the plant samples were 0.002 and 0.003 mg kg-1 dw,

142

respectively. The recovery rates of Cd in the plant and soil samples were 96–105%

143

and 93–112%, respectively, and those of Se were 94–106% and 92–105%,

144

respectively.

145

Safety standards and statistical analysis

146

According to the Chinese National Food Safety Standard for Maximum Levels of

147

Contaminants in Food (GB 2762-2017,

148

http://bz.cfsa.net.cn/staticPages/D5921FFE-BD08-4D34-AE26-CF9CA4FEB001.html

149

), the maximum recommended Cd level in brown rice is 0.2 mg kg-1 (dw). This

150

standard was used to evaluate the safety of the tested rice cultivars. Translocation

151

factors (TFs) of Cd and Se from roots to shoots and from shoots to brown rice were

152

calculated using the following equation:

153

TFa to b = Cb-x/Ca-x

(1)

154 155 156

where a represents roots or shoots; b represents shoots or brown rice; x represents Cd or Se; Cb-x represents the concentration of Cd or Se in b; and Ca-x represents the

8

ACS Paragon Plus Environment

Page 8 of 38

Page 9 of 38

Journal of Agricultural and Food Chemistry

157

concentration of Cd or Se in a.

158

Data were analyzed for homogeneity of variances by Levene’s test, and showed no

159

heteroscedasticity. All data were analyzed statistically by three-way analysis of

160

variance (ANOVA) at p < 0.05. When the cultivar treatment was significant, the

161

differences in the same cultivar among the three Se concentrations at the same Cd

162

concentration and among the three Cd concentrations at the same Se concentration

163

were further evaluated by one-way ANOVA with Tukey's HSD (Honest Significant

164

Difference) test. All tests were performed using Microsoft Excel 2003 (Microsoft

165

Corp., Redmond, WA, USA) and SPSS 13.0 (IBM, Armonk, NY, USA). All

166

correlations were assessed using Pearson product-moment correlation.

167 168

RESULTS

169

Grain Biomass in Response to Cd and Se Treatments

170

Rice grain dw was significantly affected by cultivar type, Se treatment, Cd treatment,

171

and the interaction among the three factors (Figure 1), indicating that grain biomass

172

was determined not only by genetic factors, but also by Cd and Se levels in the soil.

173

The H plants invariably had the highest grain dw, followed by M and F in each

174

treatment group (Figure 1), showing heterosis in yield. Overall, the grain dw of M and

175

H increased significantly with increasing Se concentration in the treatment groups at

176

the same Cd concentration (Figure 1); therefore, Se may help promote grain biomass

177

accumulation. Additionally, the grain biomass of each cultivar did not decrease

178

significantly; rather it increased when soil Cd concentration increased to 2.01 mg kg-1;

9

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

179

however, it decreased significantly afterward, especially for H (Figure 1), implying

180

that the rice cultivars showed moderate tolerance to Cd toxicity.

181

Cadmium Accumulation in Response to Cd and Se Treatments

182

Generally, Cd accumulation in the brown rice, shoots, and roots was significantly

183

affected by the cultivar type, Se treatment, Cd treatment, and the interactions among

184

these factors (Figure 2A, B, and C). This demonstrated that Cd accumulation in rice is

185

determined by genetic factors, as well as exposure to Cd and Se. The ability of H to

186

accumulate Cd was similar to that of M, and significantly lower than that of F (Figure

187

2A), suggesting that the trait of high Cd accumulation of F was not inherited by H.

188

For each cultivar, Cd concentration in the brown rice increased significantly with

189

increasing Cd concentration in the treatment groups at the same Se concentration,

190

except in C2S3, which was similar to C1S3. In the treatment groups without

191

additional Cd2+ (i.e., C1S1, C1S2, and C1S3), Cd concentration in the brown rice did

192

not change significantly, and increased in F with increasing soil Se concentrations.

193

However, Se application significantly decreased the Cd concentration in the brown

194

rice in the treatment groups with additional Cd2+ (Figure 2A). Additionally, Cd

195

concentration in the H brown rice exceeded the maximum level (0.2 mg kg-1)

196

recommended by the Chinese food standard in C3S1; although not when Se was

197

added to the Cd-contaminated soils (i.e., C3S2 and C3S3).

198

Cadmium concentrations in the shoots and roots of each cultivar increased with

199

increasing Cd levels (Figure 2B and C). Furthermore, there was no significant

200

difference in Cd accumulation in the shoots and roots between M and H, and Cd

10

ACS Paragon Plus Environment

Page 10 of 38

Page 11 of 38

Journal of Agricultural and Food Chemistry

201

accumulation was invariably higher in F than the other two cultivars. In the treatment

202

groups without additional Cd2+, Cd concentrations in the shoots did not change

203

significantly in the two parents; however, they increased significantly in H with

204

increasing soil concentration of Se. Nevertheless, the increased Se levels in other

205

higher Cd-contaminated soils significantly decreased Cd concentrations in the shoots

206

in all cultivars. Cadmium concentrations in the roots of the three cultivars in the

207

treatment groups without additional Cd2+ increased significantly with increasing soil

208

concentration of Se. Contrastingly, root Cd concentrations in the three cultivars

209

decreased with increasing Se levels in the other higher Cd-contaminated soils;

210

however, this decrease was statistically significant only in F. Overall, Cd

211

concentrations in the brown rice showed significant positive correlations with Cd

212

concentrations in the shoots and roots (Figure 3A and B), demonstrating that low Cd

213

levels in the latter may give rise to low Cd levels in the former.

214

Selenium Accumulation in Response to Cd and Se Treatments

215

Selenium accumulation in the brown rice, shoots, and roots was significantly affected

216

by cultivar type, Se treatment, Cd treatment, and certain interactions among these

217

factors (Figure 4A, B, and C), demonstrating that Se accumulation in rice is controlled

218

by genetic factors, as well as exposure to Se and Cd. Generally, Se concentrations

219

were higher in the brown rice and shoots of F than those of M and H, although there

220

were no obvious differences between M and H (Figure 4A and B). Additionally, the Se

221

concentration was slightly higher in the roots of F than those of M in all the treatment

222

groups, except for C3S2 and C2S3; however, H showed no difference in root Se

11

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

223

concentrations from M and F (Figure 4C). This indicated that the characteristics of Se

224

accumulation in H were inherited from each parent.

225

For each cultivar, Se concentrations in the brown rice, shoots, and roots increased

226

significantly with increasing Se level in the treatment groups with the same Cd

227

concentration (Figure 4A, B, and C). However, generally, Se concentrations in all the

228

tissues first increased, and then, decreased dramatically with increasing Cd levels in

229

the treatment groups with the same Se concentration, demonstrating the importance of

230

Cd exposure for Se accumulation in rice. Additionally, Se concentration in the brown

231

rice was significantly, positively correlated with that in the shoots and roots (Figure

232

5A and B), implying that Se level in the brown rice depended on that in the shoots and

233

roots.

234

Cadmium Translocation within Rice Plants

235

Cadmium translocation from the roots to the shoots and from the shoots to the brown

236

rice varied greatly with cultivar type and levels of Cd and Se exposure (Table 1).

237

Overall, the Cd translocation factors (TFs) from the roots to the shoots in F and H

238

increased gradually with increasing Cd concentration; however, they were minimally

239

affected by Se addition. In the treatment groups without additional Cd2+, the lowest

240

Cd TFs from the roots to the shoots in M were observed in C1S1, and the increase in

241

Se level significantly inhibited Cd translocation from the roots to the shoots. However,

242

Cd translocation from the roots to the shoots in M did not changed noticeably with

243

increasing Se level in the other higher Cd treatment groups. Additionally, M had the

244

highest Cd TFs from the roots to the shoots, followed by F and H in C1S1, C1S2, and

12

ACS Paragon Plus Environment

Page 12 of 38

Page 13 of 38

Journal of Agricultural and Food Chemistry

245

C1S3; however, the TF was slightly lower in M than F in the C1S1 (Table 1). There

246

was no significant difference in the Cd TFs from the roots to the shoots among the

247

three cultivars in the other higher Cd treatment groups excluding C3S1.

248

For F, the Cd TF from the shoots to the brown rice was the highest in C2S3; however,

249

it did not differ significantly from those in other treatment groups with the lowest Cd

250

levels (Table 1). Furthermore, in the treatment groups with the same Cd levels,

251

excluding C2S3, the ability of shoot-to-brown rice Cd translocation of F remained

252

relatively stable with increasing Se concentration. It is noteworthy that the Cd TFs

253

from the shoots to the brown rice in M and H were noticeably affected by Se levels in

254

the highest Cd treatment groups (Table 1). Among the treatment groups without

255

additional Se (i.e., C1S1, C2S1, and C3S1), there were no significant differences in

256

the Cd TFs in either M or H. However, Cd translocation from the shoots to the brown

257

rice in both cultivars decreased slightly when Se was applied to the Cd-contaminated

258

soils. Additionally, the Cd TFs from the shoots to the brown rice were invariably,

259

significantly higher in H and M than F, excluding C1S1 and C1S2.

260

Selenium Translocation within the Rice Plants

261

Generally, the Se TFs from the roots to the shoots in F did not change significantly

262

with increasing Se level, and was not obviously affected by Cd application, except

263

that the TF was significantly lower in C3S3 than C1S1 and C2S1 (Table 2). For M

264

and H, Se translocation from the roots to the shoots was not significantly affected by

265

the Se and Cd levels. Additionally, there were no significant differences in the

266

root-to-shoot Se translocation among the three cultivars in any treatment group,

13

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

267

except that the ability of Se translocation of F was significantly higher than that of M

268

in C2S2 (Table 2).

269

In the treatment groups with the lowest Se levels, the Se TFs from the shoots to the

270

brown rice increased significantly in H with increasing Cd level (Table 2). Moreover,

271

in other treatment groups with higher Se levels, the ability of shoot-to-brown rice Se

272

translocation of the three cultivars did not change with increasing Cd level. A similar

273

phenomenon occurred similarly in other treatment groups with the highest Se levels.

274

However, the difference in Se translocation from the shoots to the brown rice among

275

the three cultivars was observed only in C2S1, and the TF of H was similar to that of

276

M; however it was significantly higher than that of F (Table 2).

277

DISCUSSION

278

Effects of Cadmium and Selenium on Grain Biomass

279

In this study, the grain biomass of the three rice cultivars increased at different

280

degrees when soil Cd concentration increased from 1.23 mg kg-1 (C1S1) to 2.01 mg

281

kg-1 (C2S1). This suggested that the rice cultivars had high tolerance to the Cd levels

282

detected in Chinese soils.3 The stimulatory effect of Cd on rice growth, which may

283

represent hormesis, was similarly observed in other studies.28-30 However, grain dw

284

decreased significantly in C3S1 (4.16 mg Cd kg-1 soil) compared with C1S1, possibly

285

because of Cd toxicity-induced reduction in photosynthetic efficiency.31 It is

286

noteworthy that grain dw increased significantly with increasing soil Se concentration

287

when Cd concentration remained constant (4.16 mg kg-1). This demonstrated that

288

exogenous Se addition can reduce the negative effects of Cd on rice growth, and

14

ACS Paragon Plus Environment

Page 14 of 38

Page 15 of 38

Journal of Agricultural and Food Chemistry

289

enhance the activity of the photosynthetic system. Similarly, Zhang et al. observed

290

that Se application enhances photosynthesis by increasing the net photosynthetic rate,

291

intercellular CO2 concentration, and transpiration efficiency of rice, thereby

292

increasing grain yield.32

293

We similarly observed that grain biomass increased gradually with increased soil Se

294

concentration without added Cd, excluding H in C1S2. Contrastingly, Liao et al.

295

reported that rice grain yield was reduced by 12.81% and 9.16% when Se was added

296

to the soil at 0.1 and 1 mg kg-1, respectively. 23 These inconsistent results may be

297

related to the rice cultivars, Se species, experimental conditions, or levels of Se

298

exposure. Additionally, one major reason for the lower grain yield of F than those of

299

M or H was the lower seeding rate; although H invariably had the highest grain dw,

300

suggesting heterosis in grain yield.

301

Effects of Selenium on Cadmium Accumulation in Rice

302

Cadmium accumulation was lower in H, similar to M, than F, indicating that this

303

characteristic of low Cd accumulation in rice is heritable, and probably controlled by

304

dominant gene(s). Similarly, Cd accumulation in durum wheat grains and water

305

spinach shoots is largely controlled by a single locus of multiple genes with low Cd

306

accumulation dominance.33, 34 It is noteworthy that OsNramp5 (natural

307

resistance-associated macrophage protein 5) is a major transporter responsible for Cd

308

uptake in rice,11 and OsHMA3 (heavy metal ATPase 3) is closely related to Cd

309

translocation.12 OsHMA3 in a low-Cd cultivar (Nipponbare) functionally limits

310

root-to-shoot Cd translocation by sequestering Cd in root vacuoles; however, the

15

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

311

transporter in a high-Cd cultivar (Anjana Dhan) loses its function.12 Further, Miyadate

312

et al. observed that OsHMA3 is dominant in controlling the phenotype of low

313

root-to-shoot Cd translocation.35 Moreover, the ability of low Cd accumulation in H

314

and M was not influenced by soil Se levels, and was stable. Therefore, it is feasible to

315

breed rice cultivars with low Cd accumulation and high yield using conventional

316

hybridization techniques.

317

In this study, Se application significantly decreased Cd concentrations in all the

318

tissues of the rice plants exposed to exogenous Cd. One reason may be that selenite is

319

reduced to Se2- in acidic soil, and further forms Se-Cd complexes in the rhizosphere,

320

which are unavailable to the plants.36 Selenite may also chelate with Cd2+ to form

321

CdSeO3 complexes, thus, reducing Cd bioavailability in the soil.37 In any case,

322

selenite limits root growth, and decreases the proportion of fine roots,38 which further

323

reduces Cd uptake. Therefore, Se is involved in antagonistic processes with Cd in rice

324

plants, and inhibits Cd uptake by the abovementioned mechanisms. Additionally, we

325

observed that Se application did not significantly affect root-to-shoot Cd translocation

326

in most cases, which is similar to the finding by Hu et al.24 Most of the selenite

327

absorbed by plant roots is rapidly assimilated into organic forms, such as SeOMet,

328

MeSeCys, and SeMet,39 which may not compete with Cd2+ in the xylem during

329

transport from roots to shoots. The difference in root-to-shoot Cd translocation among

330

the three cultivars appeared to depend on the levels of Cd and Se exposure. However,

331

the difficulty in Cd translocation from shoots to brown rice increased with increasing

332

soil Se levels in M and H, yet not in F. Hu et al. similarly observed that Se application

16

ACS Paragon Plus Environment

Page 16 of 38

Page 17 of 38

Journal of Agricultural and Food Chemistry

333

did not significantly affect Cd translocation from shoots to grains.24 This

334

demonstrated that the effect of Se on Cd translocation from shoots to grains may be

335

related to genotype. Furthermore, Cd was more easily transported to the brown rice

336

from the shoots in F than in M and H. Selenium was reported to significantly increase

337

leaf glutathione (GSH) levels in plants cultivated in the soil;40 further, GSH is a

338

substrate for phytochelatin (PC) synthesis, and crucial for the sequestration and

339

detoxification of Cd. Cytosolic Cd can form complexes with S-containing ligands,

340

such as GSH and PCs, and subsequently be transported into vacuoles, resulting in Cd

341

immobilization within the leaf.41 Therefore, further investigations are required to

342

evaluate the synthesis of GSH and PCs in the shoots of the three cultivars.

343

It is worth noting that by increasing Se levels, Cd accumulation increased in the rice

344

tissues, especially roots, in the treatment groups without additional Cd, partially

345

confirming our first hypothesis. Fargašová et al. similarly discovered that Se increases

346

Cd accumulation in the roots of Sinapis alba L.42 Therefore, the interaction between

347

Se and Cd depends on the ratio of concentration of the two elements; thus, certain

348

stimulating effects of increased Se concentrations on Cd uptake may be expected in

349

addition. As Arvy et al. mentioned, selenite addition to the cultivation medium

350

increases the capacity of root cells to accumulate heavy metals.43 In our study, Se

351

application decreased root-to-shoot Cd translocation in M, yet not in H and F in the

352

treatment groups without additional Cd. Consequently, the interaction between Cd and

353

Se is dose-dependent and probably, cultivar-dependent.

354

Effects of Cadmium on Selenium Accumulation in Rice

17

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

355

Cadmium enters root cells via ZIP (zinc/iron-regulated transporter protein) or other

356

cation channels,44 while selenite is absorbed by plant roots via phosphate

357

transporters,35 silicon influx transporters,45 and aquaporins.46 Theoretically, there is no

358

competition between Cd and Se on root surfaces, as they are absorbed via different

359

transporters or channels. However, in this study, Se concentrations in all the tissues of

360

the three cultivars, including roots, shoots, and grains, initially increased to different

361

levels, and then, decreased rapidly as Cd concentrations increased from 1.23 mg kg-1

362

to 2.01 mg kg-1, and then, to 4.16 mg kg-1, thereby disproving our second hypothesis.

363

Lin et al. observed that Cd2+ (50 µM) addition significantly decreased Se

364

accumulation in rice cultured in a nutrient solution containing 3 µM Se (Na2SO3).47

365

Meanwhile, the effects of Cd on Se accumulation in cucumber depended on the

366

concentrations of Cd and Se in the medium, and Cd addition strongly promoted Se

367

translocation from roots to shoots.48 Therefore, the effects of Cd-Se interactions on Se

368

accumulation in plants are related not only to the levels of Cd and Se exposure, but

369

also to plant species or cultivar types. The main reason for the Cd-promoted increase

370

in Se concentrations in the rice tissues may be that rice absorbs more Se to detoxify

371

Cd, since Se can reduce Cd-induced oxidative stress by increasing the accumulation

372

of proline and GSH.49 Furthermore, -SeH can replace the -SH group in GSH and PCs,

373

and protect against Cd toxicity by increasing thiol concentrations.36 Notably, Se

374

translocation from roots to shoots and from shoots to brown rice was minimally

375

affected by the levels of Cd exposure, particularly when soil Cd concentration

376

increased from 2.01 mg kg-1 to 4.16 mg kg-1. Thus, the obvious decrease in Se

18

ACS Paragon Plus Environment

Page 18 of 38

Page 19 of 38

Journal of Agricultural and Food Chemistry

377

concentrations in the three cultivars when the level of Cd exposure increased to 4.16

378

mg kg-1 was mainly due to the decrease in Se uptake via root surfaces. Possibly, high

379

Cd toxicity inhibited the activities of the transporters or water channels involved in Se

380

uptake; however, this requires further investigation of the mechanisms controlling Se

381

uptake in rice.

382

In conclusion, our results showed that F invariably had significantly higher grain Cd

383

concentration and higher shoot-to-brown rice Cd translocation than M or H. The trait

384

of low Cd accumulation in rice may be dominant, and thus, it is feasible to develop

385

new low-Cd, high-yield rice cultivars through crossbreeding. Selenium

386

biofortification not only increases grain Se concentration, which helps overcome Se

387

deficiency in humans, but also significantly decreases grain Cd concentration when

388

soil Cd concentration exceeds 2.0 mg kg-1. Additionally, these results suggested that

389

Se can reduce Cd-induced growth inhibition, improve photosynthesis, and increase

390

grain yield in rice. Furthermore, the effects of Cd-Se interactions on the accumulation

391

of Cd and Se in rice are related to the levels of Cd and Se exposure. Selenium

392

application inhibited shoot-to-brown rice Cd translocation in M and H; however, Cd

393

affected Se translocation in the rice plants negligibly.

394

Notes

395

The authors declare no competing financial interest.

396

ACKNOWLEDGMENTS

397

This study was supported by the Hunan Provincial Natural Science Foundation of

398

China (Grant 2016JJ5017) and the National Natural Science Foundation of China

19

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 20 of 38

399

(Grants 41101303 and 41201320).

400

Supporting Information

401

Table S1 Concentrations of different elements in rice husk, brown rice, and polished

402

rice

403

REFERENCES

404

1.

405

Cadmium in rice: transport mechanisms, influencing factors, and minimizing

406

measures. Environ Pollut 2017, 224, 622-630.

407

2.

408

Uptake

409

bioavailability/toxicity in human cell lines (Caco-2/HL-7702). J Agric Food Chem

410

2015, 63, 3599-3608.

411

3.

412

China: current status and mitigation strategies. Environ Sci Technol 2014, 49,

413

750-759.

414

4.

415

Nakagawa, H. Serial changes in urinary cadmium concentrations and degree of renal

416

tubular injury after soil replacement in cadmium-polluted rice paddies. Toxicol Lett

417

2008, 176, 124-130.

418

5.

419

Restoration of cadmium-contaminated paddy soils by washing with ferric chloride:

420

Cd extraction mechanism and bench-scale verification. Chemosphere 2008, 70,

Li, H.; Luo, N.; Li, Y. W.; Cai, Q. Y.; Li, H. Y.; Mo, C. H.; Wong, M. H.

Aziz, R.; Rafiq, M. T.; Li, T.; Liu, D.; He, Z.; Stoffella, P. J.; Sun, K.; Yang, X. of

cadmium

by

rice

grown

on

contaminated

soils

and

its

Zhao, F.-J.; Ma, Y.; Zhu, Y.-G.; Tang, Z.; McGrath, S. P. Soil contamination in

Kobayashi, E., Suwazono, Y., Honda, R., Dochi, M., Nishijo, M., Kido, T.,

Makino, T.; Takano, H.; Kamiya, T.; Itou, T.; Sekiya, N.; Inahara, M.; Sakurai, Y.

20

ACS Paragon Plus Environment

Page 21 of 38

Journal of Agricultural and Food Chemistry

421

1035-1043.

422

6.

423

capable of accumulating Cd at high levels: reduction of Cd content of rice grain.

424

Environ Sci Technol 2009, 43, 5878-5883.

425

7.

426

uptake in a contaminated paddy soil: a two-year field experiment. Bioresources 2011,

427

6, 2605-2618.

428

8.

429

management on cadmium and arsenic accumulation and dimethylarsinic acid

430

concentrations in Japanese rice. Environ Sci Technol 2009, 43, 9361-9367.

431

9.

432

cadmium-contaminated rice in China: a critical review. Environ Int 2016, 92-93,

433

515-532.

434

10. Uraguchi, S.; Kamiya, T.; Sakamoto, T.; Kasai, K.; Sato, Y.; Nagamura, Y.;

435

Yoshida, A.; Kyozuka, J.; Ishikawa, S.; Fujiwara, T. Low-affinity cation transporter

436

(OsLCT1) regulates cadmium transport into rice grains. Proc Natl Acad Sci 2011, 108,

437

20959-20964.

438

11. Sasaki, A., Yamaji, N., Yokosho, K., Ma, J. F. Nramp5 is a major transporter

439

responsible for manganese and cadmium uptake in rice. Plant Cell 2012, 24,

440

2155-2167.

441

12. Ueno, D.; Yamaji, N.; Kono, I.; Huang, C. F.; Ando, T.; Yano, M.; Ma, J. F. Gene

442

limiting cadmium accumulation in rice. Proc Natl Acad Sci USA 2010, 107,

Murakami, M.; Nakagawa, F.; Ae, N.; Ito, M.; Arao, T. Phytoextraction by rice

Cui, L.; Li, L.; Mail, A. Z.; Pan, G. Biochar amendment greatly reduces rice Cd

Arao, T.; Kawasaki, A.; Baba, K.; Mori, S.; Matsumoto, S. Effects of water

Hu,

Y.;

Cheng,

H.;

Tao,

S.

The

challenges

21

ACS Paragon Plus Environment

and

solutions

for

Journal of Agricultural and Food Chemistry

Page 22 of 38

443

16500-16505.

444

13. Qiu,

445

https://www.nature.com/news/china-sacks-officials-over-golden-rice-controversy-1.11

446

998 (accessed September 17, 2017).

447

14. Sebastian, A.; Prasad, M. N. V. Cadmium minimization in rice. A review. Agron

448

Sustain Dev 2014, 34, 155-173.

449

15. Drasch, G.; Schöpfer, J.; Schrauzer, G. N. Selenium/cadmium ratios in human

450

prostates. Biol Trace Elem Res 2005, 103, 103-107.

451

16. Reid, M. E.; Duffield-Lillico, A. J.; Slate, E.; Natarajan, N.; Turnbull, B.; Jacobs,

452

E.; Jr, G. F. C.; Alberts, D. S.; Clark L. C.; Marshall, J. R. The nutritional prevention

453

of cancer: 400 mcg per day selenium treatment. Nutr Cancer 2008, 60, 155-163.

454

17. Feng, R.; Wei, C.; Tu, S. The roles of selenium in protecting plants against abiotic

455

stresses. Environ Exp Bot 2013, 87, 58-68.

456

18. Fang, Y.; Wang, L.; Xin, Z.; Zhao, L.; An, X.; Hu, Q. Effect of foliar application

457

of zinc, selenium, and iron fertilizers on nutrients concentration and yield of rice grain

458

in China. J Agric Food Chem 2008, 56, 2079-2084.

459

19. Rayman, M. P. The use of high-selenium yeast to raise selenium status: how does

460

it measure up? Brit J Nutr 2004, 92, 557-573.

461

20. Tan, J.; Zhu, W.; Wang, W.; Li, R.; Hou, S.; Wang, D.; Yang, L. Selenium in soil

462

and endemic diseases in China. Sci Total Environ 2002, 284, 227-235.

463

21. Hartikainen, H. Biogeochemistry of selenium and its impact on food chain quality

464

and human health. J Trace Elem Med Bio, 2005, 18, 309-318.

J.

China

sacks

officials

over

Golden

22

ACS Paragon Plus Environment

Rice

controversy.

Page 23 of 38

Journal of Agricultural and Food Chemistry

465

22. Lyons, G. H., Genc, Y., Soole, K., Stangoulis, J. C. R., Liu, F., Graham, R. D.

466

Selenium increases seed production in Brassica. Plant Soil 2009, 318, 73-80.

467

23. Liao, G.; Xu, Y.; Chen, C.; Wu, Q.; Feng, R.; Guo, J.; Wang, R.; Ding, Y.; Sun, Y.;

468

Xu, Y. Root application of selenite can simultaneously reduce arsenic and cadmium

469

accumulation and maintain grain yields, but show negative effects on the grain quality

470

of paddy rice. J Environ Manage 2016, 183, 733-741.

471

24. Hu, Y.; Norton, G. J.; Duan, G.; Huang, Y.; Liu, Y. Effect of selenium fertilization

472

on the accumulation of cadmium and lead in rice plants. Plant Soil 2014, 384,

473

131-140.

474

25. Chen, M. X.; Cao, L.; Song, X. Z.; Wang, X. Y.; Qian, Q. P.; Liu, W. Effect of

475

iron plaque and selenium on cadmium uptake and translocation in rice seedlings

476

(Oryza sativa) grown in solution culture. Int J Agric Biol 2014, 16, 1159-1164.

477

26. Lu, R. Soil and agro-chemical analysis methods; Agricultural Science and

478

Technology Press: Beijing, China, 2000.

479

27. Alexander, P.; Alloway, B.; Dourado, A. Genotypic variations in the accumulation

480

of Cd, Cu, Pb and Zn exhibited by six commonly grown vegetables. Environ Pollut

481

2006, 144, 736-745.

482

28. Yu, H.; Wang, J.; Fang, W.; Yuan, J.; Yang, Z. Cadmium accumulation in different

483

rice cultivars and screening for pollution-safe cultivars of rice. Sci Total Environ 2006,

484

370, 302-309.

485

29. Zhang, H.; Zhang, X.; Li, T.; Fu, H. Variation of cadmium uptake, translocation

486

among rice lines and detecting for potential cadmium-safe cultivars. Environ Earth

23

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

487

Sci 2014, 71, 277-286.

488

30. Stebbing, A. R. D. Hormesis—the stimulation of growth by low levels of

489

inhibitors. Sci Total Environ 1982, 22, 213-234.

490

31. Nwugo, C. C.; Huerta, A. J. Effects of silicon nutrition on cadmium uptake,

491

growth and photosynthesis of rice plants exposed to low-level cadmium. Plant Soil

492

2008, 311, 73-86.

493

32. Zhang, M.; Tang, S.; Huang, X.; Zhang, F.; Pang, Y.; Huang, Q.; Yi, Q. Selenium

494

uptake, dynamic changes in selenium content and its influence on photosynthesis and

495

chlorophyll fluorescence in rice ( Oryza sativa L.). Environ Exp Bot 2014, 107, 39-45.

496

33. Clarke, J. M.; Leisle, D.; Kopytko, G. L. Inheritance of cadmium concentration in

497

five durum wheat crosses. Crop Sci 1997, 37, 1722-1726.

498

34. Xin, J.; Huang, B.; Yang, Z.; Yuan, J.; Dai, H.; Qiu, Q. Responses of different

499

water spinach cultivars and their hybrid to Cd, Pb and Cd–Pb exposures. J Hazard

500

Mater 2010, 175, 468-476.

501

35. Miyadate, H., Adachi, S., Hiraizumi, A., Tezuka, K., Nakazawa, N., Kawamoto, T.,

502

Katou, K., Kodama, I., Sakurai, K., Takahashi, H. OsHMA3, a P1B-type of ATPase

503

affects root-to-shoot cadmium translocation in rice by mediating efflux into vacuoles.

504

New Phytol, 2011, 189, 190-199.

505

36. Wan, Y.; Yao, Y.; Qi, W.; Qiao, Y.; Li, H. Cadmium uptake dynamics and

506

translocation in rice seedling: influence of different forms of selenium. Ecotox

507

Environ Safe 2016, 133, 127-134.

508

37. Badiello, R.; Feroci, G.; Fini, A. Interaction between trace elements: selenium and

24

ACS Paragon Plus Environment

Page 24 of 38

Page 25 of 38

Journal of Agricultural and Food Chemistry

509

cadmium ions. J Trace Elem Med Bio 1996, 10, 156-162.

510

38. Feng, R.; Wei, C.; Tu, S.; Liu, Z. Interactive effects of selenium and antimony on

511

the uptake of selenium, antimony and essential elements in paddy-rice. Plant Soil

512

2013, 365, 375-386.

513

39. Li, H.-F.; McGrath, S. P.; Zhao, F.-J. Selenium uptake, translocation and

514

speciation in wheat supplied with selenate or selenite. New Phytol 2008, 178, 92-102.

515

40. Schiavon, M.; Berto, C.; Malagoli, M.; Trentin, A.; Sambo, P.; Dall'Acqua, S.;

516

Pilonsmits, E. A. H. Selenium biofortification in radish enhances nutritional quality

517

via accumulation of methyl-selenocysteine and promotion of transcripts and

518

metabolites related to glucosinolates, phenolics, and amino acids. Front Plant Sci

519

2016, 7, 1371.

520

41. Salt, D. E.; Rauser, W. E. MgATP-dependent transport of phytochelatins across

521

the tonoplast of oat roots. Plant Physiol 1995, 107, 1293-1301.

522

42. Fargašová, A.; Pastierová, J.; Svetková, K. Effect of Se-metal pair combinations

523

(Cd, Zn, Cu, Pb) on photosynthetic pigments production and metal accumulation in

524

Sinapis alba L. seedlings. Plant Soil Environ 2006, 52, 8-15.

525

43. Arvy, M. P.; Thiersault, M.; Doireau, P. Relationships between selenium,

526

micronutrients, carbohydrates, and alkaloid accumulation in Catharanthus roseus

527

cells. J Plant Nutr 1995, 18, 1535-1546.

528

44. Lux, A.; Martinka, M.; Vaculík, M.; White, P. J. Root responses to cadmium in

529

the rhizosphere: a review. J Exp Bot 2011, 62, 21-37.

530

45. Xue, Q. Z.; Jian, F. M. Involvement of silicon influx transporter OsNIP2;1 in

25

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

531

selenite uptake in rice. Plant Physiol 2010, 153, 1871-1877.

532

46. Zhang, L.; Shi, W.; Wang, X. Difference in selenite absorption between high- and

533

low-selenium rice cultivars and its mechanism. Plant Soil 2006, 282, 183-193.

534

47. Li, L.; Zhou, W.; Dai, H.; Cao, F.; Zhang, G.; Wu, F. Selenium reduces cadmium

535

uptake and mitigates cadmium toxicity in rice. J Hazard Mater 2012, 235–236,

536

343-351.

537

48. Hawrylak-Nowak, B.; Dresler, S.; Wójcik, M. Selenium affects physiological

538

parameters and phytochelatins accumulation in cucumber ( Cucumis sativus L.) plants

539

grown under cadmium exposure. Sci Hortic-Amsterdam 2014, 172, 10-18.

540

49. Khan, M. I.; Nazir, F.; Asgher, M.; Per, T. S.; Khan, N. A. Selenium and sulfur

541

influence ethylene formation and alleviate cadmium-induced oxidative stress by

542

improving proline and glutathione production in wheat. J Plant Physiol 2015, 173,

543

9-18.

544

26

ACS Paragon Plus Environment

Page 26 of 38

Page 27 of 38

Journal of Agricultural and Food Chemistry

Figure captions Figure 1 Effects of cadmium (Cd) and selenium (Se) on the grain biomass of three rice cultivars. Error bars represent the standard deviation (n = 3). ns, not significant; *, significant at the p < 0.01 level. For the same cultivar, different lower-case letters indicate significant differences (p < 0.05) among different Se treatment groups with the same Cd concentration; different upper-case letters indicate significant differences (p < 0.05) among different Cd treatment groups with the same Se concentration. See the Materials and Methods section for the abbreviations.

Figure 2 Effects of selenium (Se) on the accumulation of cadmium (Cd) in brown rice (A), shoots (B), and roots (C) of three rice cultivars. Error bars represent the standard deviation (n = 3). *, significant at the p < 0.05 level; **, significant at the p < 0.01 level. For the same cultivar, different lower-case letters indicate significant differences (p < 0.05) among different Se treatment groups with the same Cd concentration; different upper-case letters indicate significant differences (p < 0.05) among different Cd treatment groups with the same Se concentration. See the Materials and Methods section for the abbreviations.

Figure 3 Correlations between brown rice cadmium (Cd) concentration and Cd concentrations in the shoots (A) and roots (B) of three rice cultivars.

Figure 4 Effects of cadmium (Cd) on the accumulation of selenium (Se) in brown rice

27

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

(A), shoots (B), and roots (C) of three rice cultivars. Error bars represent the standard deviation (n = 3). ns, not significant; *, significant at the p < 0.05 level; **, significant at the p < 0.01 level. For the same cultivar, different lower-case letters indicate significant differences (p < 0.05) among different Se treatment groups with the same Cd concentration; different upper-case letters indicate significant differences (p < 0.05) among different Cd treatment groups with the same Se concentration. See the Materials and Methods section for the abbreviations.

Figure 5 Correlations between brown rice grain selenium (Se) concentration and Se concentrations in the shoots (A) and roots (B) of three rice cultivars.

28

ACS Paragon Plus Environment

Page 28 of 38

Page 29 of 38

Journal of Agricultural and Food Chemistry

Table 1 Changes in cadmium (Cd) translocation from roots to shoots, and from shoots to brown rice at different levels of Cd and selenium (Se) exposure Treatment group

F

M

H TF root to shoot

C1S1

3.17 ± 0.40

d

A

2.78 ± 0.52

c

AB

2.20 ± 0.12

d

B

C1S2

3.79 ± 0.51

cd

B

6.34 ± 0.84

a

A

2.60 ± 0.04

cd

C

C1S3

3.89 ± 0.36

bcd B

5.29 ± 0.25

ab

A

3.03 ± 0.21

bcd C

C2S1

3.92 ± 0.55

bcd

4.09 ± 1.09

bc

3.71 ± 0.72

abc

C2S2

4.21 ± 0.74

bcd

3.63 ± 0.73

bc

4.15 ± 0.28

ab

C2S3

4.54 ± 0.33

abc

4.26 ± 0.48

bc

4.11 ± 0.32

ab

C3S1

4.66 ± 0.10

abc

3.44 ± 0.14

c

3.93 ± 0.55

abc B

C3S2

5.46 ± 0.26

a

4.08 ± 0.05

bc

4.91 ± 0.96

a

C3S3

5.11 ± 0.36

ab

4.18 ± 0.51

bc

4.57 ± 0.28

a

8.84 ± 1.80

ab

B

12.70 ± 2.14

a

A

A

B

TF shoot to brown rice C1S1

6.95 ± 0.84

ab

C1S2

6.52 ± 0.39

abc

C1S3

6.35 ± 1.78

abcd B

11.02 ± 0.91 abc A

11.49 ± 3.10

ab

A

C2S1

4.35 ± 0.69

cde

C

6.59 ± 0.63

d

B

9.00 ± 0.85

ab

A

C2S2

4.80 ± 0.52

bcde B

9.95 ± 2.31

bc

A

10.70 ± 2.07

ab

A

C2S3

7.93 ± 0.71

a

B

13.29 ± 1.07 a

A

12.78 ± 2.69

a

A

C3S1

4.30 ± 0.17

de

C

8.38 ± 0.50

cd

A

6.94 ± 0.51

b

B

C3S2

3.99 ± 0.19

e

B

12.09 ± 0.81 ab

A

12.58 ± 1.23

a

A

C3S3

4.31 ± 0.22

cde

C

9.82 ± 1.16

B

11.78 ± 0.70

ab

A

B

8.27 ± 0.38

cd

7.88 ± 0.90

cd

bc

Notes: Values shown are the mean ± SD (n = 3). Different lower-case letters in the same column indicate significant (p < 0.05) difference among treatment groups. Different upper-case letters in the same row indicate significant (p < 0.05) difference among cultivars. See the Materials and Methods section for the abbreviations.

29

ACS Paragon Plus Environment

Journal of Agricultural and Food Chemistry

Page 30 of 38

Table 2 Changes in selenium (Se) translocation from roots to shoots, and from shoots to brown rice at different levels of cadmium (Cd) and Se exposure Treatment group

F

M

H TF root to shoot

C1S1

4.59 ± 0.69

a

5.38 ± 0.75

4.89 ± 0.55

C2S1

4.49 ± 0.31

a

4.81 ± 1.32

4.97 ± 0.51

C3S1

4.24 ± 0.30

ab

4.95 ± 0.87

4.50 ± 0.43

C1S2

4.09 ± 0.33

ab

4.58 ± 0.65

4.47 ± 0.20

C2S2

4.38 ± 0.17

ab

C3S2

3.27 ± 0.71

ab

4.69 ± 0.81

4.67 ± 1.19

C1S3

3.33 ± 0.60

ab

4.13 ± 0.92

5.19 ± 1.14

C2S3

3.47 ± 0.39

ab

5.58 ± 1.15

4.60 ± 1.03

C3S3

3.07 ± 0.41

b

4.39 ± 0.82

4.04 ± 0.74

B

5.55 ± 0.76

A

4.67 ± 0.20

AB

TF shoot to brown rice C1S1

0.94 ± 0.08

ab

0.95 ± 0.07

ab

0.87 ± 0.05

b

C2S1

0.81 ± 0.12

b

1.10 ± 0.17

a

1.31 ± 0.10

a

C3S1

1.28 ± 0.23

a

1.19 ± 0.13

a

1.27 ± 0.13

a

C1S2

0.67 ± 0.08

b

0.59 ± 0.12

c

0.65 ± 0.10

b

C2S2

0.65 ± 0.13

b

0.62 ± 0.09

c

0.81 ± 0.16

b

C3S2

0.64 ± 0.10

b

0.76 ± 0.04

bc

0.69 ± 0.20

b

C1S3

0.77 ± 0.18

b

0.58 ± 0.04

c

0.54 ± 0.15

b

C2S3

0.59 ± 0.10

b

0.53 ± 0.04

c

0.61 ± 0.11

b

C3S3

0.70 ± 0.05

b

0.58 ± 0.10

c

0.72 ± 0.17

b

B

A

A

Notes: Values shown are the mean ± SD (n = 3). Different lower-case letters in the same column indicate significant (p < 0.05) difference among treatment groups. Different upper-case letters in the same row indicate significant (p < 0.05) difference among cultivars. See the Materials and Methods section for the abbreviations.

30

ACS Paragon Plus Environment

Page 31 of 38

Journal of Agricultural and Food Chemistry

210

Grain biomass (g, dw)

180

Cultivar F = 451.9* Cultivar × Se F = 1.1ns Se F = 41.5* Cultivar × Cd F = 1.5ns Cd F = 49.0* Se × Cd F = 1.7ns

150

C1S1 C2S1

C1S2 C2S2

C1S3 C2S3

C3S1

C3S2

C3S3 B

120

Cultivar × Se × Cd F = 3.2*

A

A

C

A

B

90

AB A

A A

AB

B

B

A

B

A

B

b a ab

b a a

B

60 b ab a

30

b ab a

b ab a

b b a

0 F

M Cultivar

Figure 1

31

ACS Paragon Plus Environment

H

Journal of Agricultural and Food Chemistry

A 1.0

C1S2

C1S3

C2S1

C2S2

C2S3

C3S1

C3S2

C3S3

Cultivar F = 362.3** Cultivar × Se F = 7.7** Se F = 95.8** Cultivar × Cd F = 42.9** Cd F = 228.8** Se × Cd F = 34.3** Cultivar × Se × Cd F = 4.5**

0.8

-1

Brown rice Cd concentration (mg kg dw)

0.9

C1S1

Page 32 of 38

0.7 0.6 C 0.5

B C

A B

B

A B

The maxmium level of Cd in brown rice (GB 2762-2017)

A

0.4 0.3

B

A B

0.2

C

A A

B

B B

A B

A

a b b

a b b

A A

A

a b b

a b b

0.1 0.0

b ab a

a b c

a b b

F

M

H

Cultivar

B

Cultivar F = 81.9** Cultivar × Se F = 2.8* Se F = 58.7** Cultivar × Cd F = 3.0* Cd F = 309.2** Se × Cd F = 33.0** Cultivar × Se × Cd F = 2.2*

3.5

-1

Shoot Cd concentration (mg kg dw)

3.0

2.5 C

B C

2.0

A B

B

C

A AB

A

B C

A B

C

B

A B

A

A C

A B

A

B

B

A

b a a

a b b

a b b

1.5

1.0

0.5

a ab b

a b b

a ab b

a b b

0.0 F

M Cultivar

32

ACS Paragon Plus Environment

H

Page 33 of 38

Journal of Agricultural and Food Chemistry

C

Cultivar F = 103.2** Cultivar × Se F = 3.2* Se F = 14.2** Cultivar × Cd F = 11.7** Cd F = 333.1** Se × Cd F = 21.8** Cultivar × Se × Cd F = 2.3*

15

-1

Root Cd concentration (mg kg dw)

12

9

C

B C

B

A B

B

C

A B

A

B B

B B

6

A B

A C

A

A B

A

B

B

b a a

a b b

A

3

b a a

a ab b

a ab b

b a a

0 F

M Cultivar

Figure 2

33

ACS Paragon Plus Environment

H

A

Journal of Agricultural and Food Chemistry

A

Root Cd concentration (mg kg dw)

2.5

-1

2.0

1.5 1.0 y = 3.2259x + 0.609 r = 0.877, n = 27, p < 0.01

0.5

B

14

-1

Shoot Cd concentration (mg kg dw)

3.0

Page 34 of 38

12 10 8 6 4

y = 16.148x + 2.0503 r = 0.895, n = 27, p < 0.01

2 0

0.0 0.0

0.2

0.4

0.6

0.0

0.8

0.2

0.4

0.6

0.8 -1

-1

Brown rice Cd concentration (mg kg dw)

Brown rice Cd concentration (mg kg dw)

Figure 3

34

ACS Paragon Plus Environment

Page 35 of 38

Journal of Agricultural and Food Chemistry

6

Cultivar F = 23.1** Se F = 482.0** Cd F = 102.5**

Cultivar × Se F = 2.7* Cultivar × Se × Cd F = 1.8ns Cultivar × Cd F = 5.1** C1S1 C2S1 Se × Cd F = 45.4**

5

C3S1

C1S2

C2S2

C3S2

C1S3

C2S3

C3S3

-1

Brown rice Se concentration (mg kg dw)

A

4

3

C

B B

2

A B

C

C

A B

A

C

B C

B C

B C

A

A B

C

A B

A

ab a b

a a b

A B

A

1

b a b

ab a b

b a b

b a b

a a b

b a c

0 F

M

H

Cultivar

B 3.0

Cultivar F = 27.9** Se F = 283.7** Cd F = 65.1**

Cultivar × Se F = 5.5** Cultivar × Se × Cd F = 0.6ns Cultivar × Cd F = 1.1ns Se × Cd F = 21.2**

-1

Shoot Se concentration (mg kg dw)

2.5

2.0 C 1.5

B C

A B

C

A B

A

C C

B B

A B

B

1.0

A AB

B B

A B

A

B

B

A

c a b

ab a b

ab a b

A

0.5 c a b

ab a b

b a b

b a ab

ab a b

0.0 F

M Cultivar

35

ACS Paragon Plus Environment

H

Journal of Agricultural and Food Chemistry

C

12

Cultivar F = 3.9* Se F = 417.1** Cd F = 167.3**

Page 36 of 38

Cultivar × Se F = 0.8ns Cultivar × Se × Cd F = 1.6ns Cultivar × Cd F = 0.4ns Se × Cd F = 45.6**

-1

Root Se concentration (mg kg dw)

10

8 B 6

A C

A B

B

C

A B

A

B C

A B

C

C

A B

A

B C

A B

C

4

A B

A

ab a b

b a c

2 b a b

a a b

b a b

b a ab

b a b

b a b

b a c

0 F

M Cultivar

Figure 4

36

ACS Paragon Plus Environment

H

Page 37 of 38

Journal of Agricultural and Food Chemistry

A

B

12

Root Se concentration (mg kg dw)

2.5

10

-1

-1

Shoot Se concentration (mg kg dw)

3.0

2.0 1.5 1.0

y = 0.5345x + 0.1521 r = 0.984, n = 27, p < 0.01

0.5

8 6 4 y = 2.1066x + 0.8548 r = 0.964, n = 27, p < 0.01 2 0

0.0 0

1

2

3

4

0

5

1

2

3

4 -1

-1

Brown rice Se concentration (mg kg dw)

Brown rice Se concentration (mg kg dw)

Figure 5

37

ACS Paragon Plus Environment

5

Journal of Agricultural and Food Chemistry

Effects of Cd-Se interaction on Cd and Se accumulation in rice 254x190mm (96 x 96 DPI)

ACS Paragon Plus Environment

Page 38 of 38