Chemical Agents as Regulators of Biological Responses in Plants

Chapter 21

Chemical Agents as Regulators of Biological Responses in Plants H. Yokoyama and J. H. Keithly

Downloaded by UNIV OF GUELPH LIBRARY on June 23, 2012 | http://pubs.acs.org Publication Date: December 7, 1991 | doi: 10.1021/bk-1991-0443.ch021

Fruit and Vegetable Chemistry Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Pasadena, CA 91106 A number of chemical agents regulate tetraterpenoid synthesis i n a wide array of carotenogenic plants and microorganisms. Structure-activity c o r r e l a t i o n studies indicated that a nitrogen atom nucleus is e s s e n t i a l for a stimulatory influence on isoprenoid biosynthetic pathways. On the basis of these findings, studies were extended to investigation of compounds which affect cis-polyisoprene biosynthesis i n the guayule plant (Parthenium argentatum Gray). And out of t h i s study on regulation of rubber synthesis, a number of chemical agents were discovered to have general e f f e c t s on plant and microbial systems. Genes determine the enzymic p o t e n t i a l of the plant, and it i s within t h i s framework that a bioregulatory agent appears to exert i t s influence. Thus, responses observed i n the tomato plant (Lycopersicon esculentum) would d i f f e r from those seen i n the soybean plant (Glycine max).

In work on the regulation of b i o l o g i c a l responses by chemical agents, the early studies were directed to regulation of biosynthesis of the tetraterpenoids. This phenomenon of regulation of the isoprenoid biosynthetic pathway was demonstrated i n a wide array of carotenogenic plants and microorganisms (1)· Structure a c t i v i t y correlations indicated a requirement of nitrogen atom nucleus as an essential s t r u c t u r a l feature for induction of carotenogenic a c t i v i t i e s {V). The studies then were extended to the regulation of synthesis of other isoprenoids, c i t r a l i n the lemon f r u i t {2) and cis-polyisoprene rubber i n the guayule plant (3). Significant increases i n rubber synthesis were observed, accompanied by enhancement of a c t i v i t i e s of the key enzymes involved i n the mevalonate pathway i n guayule plants treated with DCPTA (4).

This chapter not subject to U.S. copyright Published 1991 American Chemical Society

In Synthesis and Chemistry of Agrochemicals II; Baker, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.


256

SYNTHESIS AND CHEMISTRY OF AGROCHEMICALS Π

Early investigations by Bonner (5) showed that f o r rubber synthesis to occur, the l e a f must be attached t o the stem. The l e a f appears t o be the carbon source f o r the increased formation of rubber i n the guayule plant. This i n turn implicated the photosynthetic system as the carbon source f o r rubber synthesis i n the parenchyma c e l l s of the stem. These observations were strongly suggestive of a bioregulatory e f f e c t a t the l e v e l of basic biochemical processes common t o a l l green plants. Thus, through implications of these preliminary observations on photosynthetic system as carbon source f o r increased rubber synthesis, attention was directed to bioregulatory e f f e c t s of DCPTA on plants which produce constituents biogenetically unrelated to cis-polyisoprenes, p a r t i c u l a r l y those related to a g r i c u l t u r a l crops· BIOREGULATION OF AGRICULTURAL CROPS Soybean. Studies with the soybean (Glycine max L. M e r r i l l , cv Centennial) showed that when the plant i s treated by f o l i a r application with DCPTA and other bioregulatory agents (Figure 1), there i s observed a general e f f e c t ; an increase i n y i e l d accompanied by enhancement of protein and l i p i d content as shown i n Table I (6). Table I . E f f e c t of Bioregulatory Agents at 80 ppm on L i p i d and Protein Content and Y i e l d of Soybean Mean*

Treatment Control 1 2 3 4

Lipid (% Dry Wt.) 13.77 16.55 14.75 15.26 19.97

D Β C C A

Protein (% Dry Wt.) 21.73 36.56 35.05 31.38 30.80

C A A Β Β

Yield (G P l o t " Dry Wt.) 1

3131.35 4232.95 3667.85 3872.10 4091.05

Β A ΒΑ A A

1. 2-Diethylaminoethyl-3,4-dichlorophenylether (DCPTA) 2. 2-Diethylaminoethy12,4-dichlorophenylether 3. 2-Diethylaminoethyl-3,5-diisopropylphenylether 4. 1,1-Dimethylmorpholinium iodide •Duncan's Multiple Range Test f o r Variable L i p i d and Protein Content and Y i e l d . Means with same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p 0.05). Gel electrophoresis of protein components indicated no changes i n the pattern observed. However, the amounts were affected (Yokoyama, H.; DeBenedict, C , unpublished data). I t was reasoned that because the



21. YOKOYAMA AND KEITHLY

Regulators ofBiological Responses

257

Figure 1. Chemical structures of four bioregulatory agents. Key: A, 2-diethylaminoethyl-3,4-dichlorophenylether (DCPTA); B, 2-diethylaminoethyl-2,4-dichlorophenylether; C, 2diethylaminoethyl-3,5-diisopropylphenylether; D, 1,1dimethylmorpholinium iodide

biosynthetic systems were no longer operating under the l i m i t a t i o n of a f i n i t e amount of photosynthetic carbon there are no s h i f t s i n the pattern of carbon u t i l i z a t i o n and consequently no negative correlations among the l i p i d and protein content and y i e l d are observed. Plant breeders have produced improved c u l t i v a r s f o r higher protein content, but t h i s i s usually accompanied by a decrease i n the l i p i d content. Y i e l d increases are usually accompanied by decreases i n the protein and l i p i d content (6_ ) · No such negative relationships are observed when the plant i s treated with DCPTA. In c u l t i v a r development by cross-breeding d i f f e r e n t c u l t i v a r s of soybean plants, negative relationships probably r e s u l t from the f i n i t e amount of o v e r a l l photosynthetic carbon available f o r the synthesis of protein and and l i p i d constituents. With no increase i n the supply of photosynthetic carbon from the l e a f , the source of carbon f o r an increase i n protein synthesis, f o r example, must be l i p i d s and other storage materials. The f a c t that DCPTA influenced the synthesis of biogenetically unrelated constituents i n two plant species (Parthenium argentatum Gray and Glycine max L. M e r r i l l cv. Centennial) and a t the same time increased the y i e l d c h a r a c t e r i s t i c s without any negative relationships, suggested that the photosynthetic apparatus i s affected, r e s u l t i n g i n increased o v e r a l l supply of carbon f o r synthesis of storage materials. Additionally, there appeared t o be general and balanced e f f e c t s on the biosysnthetic and metabolic


258

SYNTHESIS AND CHEMISTRY OF AGROCHEMICALS II

systems of the i n d i v i d u a l soybean plant which leads t o increased u t i l i z a t i o n of larger amounts of carbon and, as a consequence, r e s u l t s i n enhanced content of constituents and improved y i e l d . Cotton. The influence of DCPTA a t a concentration of 125 ppm on uptake (photosynthesis) of cotton leaf discs 34 days a f t e r planting resulted i n o v e r a l l average of about 24.0 mg dm~ h~ as compared with 19.0 mg dm" h" f o r the c o n t r o l . This 21% DCPTA-induced increase i n C 0 2 uptake was s t a t i s t i c a l l y s i g n i f i c a n t a t ρ 0.001 (7^). The photosynthetic rate of field-grown cotton i s on the order of 40 t o 45 mg C 0 2 dm" h*" . The rates reported here are representative of greenhouse-grown cotton plants. Studies were conducted on the influence of DCPTA on various aspects of the growth and physiology of the cotton plant (7_, 8). Total plant biomass determined 62 days a f t e r planting increased s i g n i f i c a n t l y (p 0.001) from 26 g f o r control plants t o 40 g f o r DCPTA-treated (12.5 ppm) plants (7)· The DCPTA-induced biomass increase i s consistent with the DCPTA-induced increase i n CO2 a s s i m i l a t i o n . A d d i t i o n a l l y , DCPTA s i g n i f i c a n t l y (p 0.05) affected growth, f r u i t i n g , and phenology of the cotton plant, as compared with control plants [Table I I , (7^)]. 1 4

C02

2

2

1

1

1 4


2

1

Table I I . E f f e c t of DCPTA on Vegetative, Phenological, and F r u i t i n g C h a r a c t e r i s t i c s of Cotton Plants Mean (6 r e p l i c a t e s ) Observations/ Measurement Dry Wt., g Leaf Stem Total Plant Growth, cm. Height Stem Diam. F r u i t i n g , no. Squares Phenology, no. Nodes

Control

DCPTA (12.5 ppm)

Increase (%)

1.23 0.90 2.13

3.95 2.88 6.83

69 68 69

47.00 0.43

73.00 0.62

36 27

0 10.50

12.00 16.50

36


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YOKOYAMA AND KEITHLY

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Regulators of Biological Responses


For example, leaf and stem dry weights were increased 69 and 68% respectively, and plants height was increased 36%. Moreover, the number of nodes was increased 36%: control plants averaged 10.5 nodes, and DCPTA-treated plants averaged 16.5 nodes. The e f f e c t s of DCPTA reported above, ranging from formative e f f e c t s to increased biomass and photosynthesis, added to the growing pool of information r e l a t i v e to possible enhancement of q u a l i t y and crop y i e l d by other than genetic means, thus opening the way f o r investigations of other crops. Sugar Beet. Seedling sugar beet plants treated with DCPTA showed increased rates of taproot growth over a narrow range of DCPTA concentrations (Keithly, J . H.; Yokoyama, H., Plant S c i . , i n press). Application of 10 ug/ml DCPTA was optimal f o r taproot development and increased both fresh weight and taproot diameter 250% and 53%, respectively, of plants harvested 82 days after seed planting as compared to values of c o n t r o l . Taproot growth and development of DCPTA-treated plants using 50 ug/ml active ingredient was s a t i s t i c a l l y i n s i g n i f i c a n t when compared with the taproot development of control plants. Applications of DCPTA i n concentrations of 100 ug/ml or greater was phytotoxic to seedlings of sugar beet. Taprootdevelopment a f t e r DCPTA-treatment was s t a t i s t i c a l l y s i g n i f i c a n t (p 0.05) only a f t e r extended periods of plant growth regardless of the concentration of DCPTA employed. No gross changes i n taproot morphology were observed when compared to the development of control taproots. Treatment of sugar beet seedlings with DCPTA not only increased the rate of taproot development during e a r l y exponential growth, but also increased the taproot biomass attained by sugar beet plants grown to 115 days a f t e r after planting (DAP) i n container (Table I I I ) . Table I I I .

Effect of DCPTA upon Taproot Development and Sucrose Y i e l d of Sugar Beet Mean

DCPTA

Sucrose Vascular Yield Development (ug/ml) (g fr.wt.) (% fr.wt.) (g/plant) (3-4, mm) (Total Ring 0 1 10 100

Taproot

340.6 454.8 563.7 394.5

Sucrose

C Β A BC

8.3 A 8.8 A 9.1 A 8.5 A

28.3 40.0 51.3 33.5

C Β A C

5.6 6.2 6.3 5.5

A A A A

8.8 9.2 11.3 10.0

#)

Β Β A AB

Values represent the means obtained from at l e a s t f i f t e e n taproots i n each treatment group. Means followed by the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t (p 0.05) according to Duncan's Multiple Range Test.



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SYNTHESIS AND CHEMISTRY OF AGROCHEMICALS Π

Taproot sucrose content of DCPTA-treated plants harvested 115 DAP was maintained at a l l DCPTA concentrations tested (Table IV). F o l i a r application of 10 ug/ml DCPTA increased t o t a l sucrose y i e l d per plant 81% as compared with sucrose y i e l d of control plants. When based upon taproot biomass, 1 and 50 ug/ml DCPTA treatments increased sucrose y i e l d 41% and 18%, respectively, as compared with sucrose y i e l d s of controls. Total number of taproot vascular rings within 10 ug/ml DCPTA-treated taproots showed a s i g n i f i c a n t (p 0.05) increase over the vascular rings of controls. S t a t i s t i c a l l y s i g n i f i c a n t increases i n leaf dry weight and t o t a l leaf area of DCPTA-treated plants both 42 and 63 DAP were observed using 10 ug/ml f o l i a r application of DCPTA (Table IV).

Table IV.

E f f e c t of DCPTA upon Root and Shoot Development of Sugar Beet 1

Mean DAP

2

DCPTA (ug/ml)

42 Days

63 Days

0 1 10 50 0 1 10 50

Root Dry Wt. (g)

0.17 0.22 0.33 0.12 9.22 9.96 12.08 5.87

Β AB A Β Β AB A C

Leaf Dry Wt. (g)

2.33 2.83 3.87 2.84 15.77 17.69 24.29 13.62

Β AB A AB BC Β A BC

Leaf Area 2 ( d m

}

4.40 5.02 7.12 5.40 15.67 18.69 25.90 13.81

Β Β A AB BC Β A C

Root/Shoot Ra

3

SLW

t i o

0.07 0.08 0.09 0.07 0.59 0.56 0.50 0.43

A A A A A A A A

0.53 0.55 0.53 0.53 1.01 0.95 0.94 0.99

A A A A A AB AB A

1

Data represnts the mean from s i x randomly selected r e p l i c a t e plants from each treatment grosup. Means followed by the same l e t t e r are not s t a t i s t i c a l l y s i g n i f i c a n t (p 0.05) according to Duncan's Multiple Range Test. Days After Planting S p e c i f i c Leaf Weight 2

3

Consistent with root development, l e a f development was less e f f e c t i v e l y increased employing 1 ug/ml DCPTA. Again, leaf growth of 50 ug/ml DCPTA-treated plants was i n s i g n i f i c a n t when compared to the l e a f growth of control plants. S p e c i f i c l e a f weight of DCPTA-treated plants was maintained 42 DAP. However, the s p e c i f i c l e a f weight of 1 and 10 ug/ml DCPTA-treated plants was s l i g h t l y decreased 63 DAP. Total chlorophyll (chl) accumulation i n leaves of 10 ug/ml DCPTA-treated plants increased 39% r e l a t i v e to the amount recovered from leaves of control plants as shown i n Table V.


21. YOKOYAMA AND KEITHLY

Table V.


261

E f f e c t of DCPTA upon The Chlorophyll Content of Mature Sugar Beet Leaves 2

(mg chl/dm )


DCPTA (ug/ml)

Chltotal

0 1 10 50

4.4 5.7 6.1 4.7

+ + + +

0.3 0.3 0.2 0.2

Chl

3.1 4.3 4.6 3.4

+ + + +

Chlb

a

0.2 0.2 0.5 0.2

1.3 1.4 1.5 1.3

Chl /b a

+ 0.2 ± 0.2 + 0.2 ±0.2

2.4 3.1 3.1 2.7

± 0.4 ± 0.3 + 0.3 ±0.1

1

Leaf samples were obtained from leaves nine and ten numbered sequentially from the f i r s t v i s i b l e l e a f at the l e a f meristem. Leaves were harvested 65 DAP. Data represents the mean + SE of three independent l e a f harvests. C h l content i n 10 ug/ml treated plants increased 48% while the chlb content was increased 15%. The r e s u l t i n g c h l t o c h l ^ r a t i o [chla/b ratio] was increased 29% when compared t o the c h l / b r a t i o of controls. The c h l content of 50 ug/ml DCPTA-treated plants was s i m i l a r to the c h l content of controls. Chloroplasts i s o l a t e d from 10 ug/ml DCPTA-treated plants showed a 23% increase i n t o t a l soluble protein to t o t a l c h l r a t i o as shown i n Table VI which resulted i n a 23% increase i n Rubisco a c t i v i t y per u n i t c h l . a

a

a

Table VI.

E f f e c t of DCPTA upon Soluble Protein and Activated Rubisco A c t i v i t y Recovered from Chloroplast Preparations of Sugar Beet Leaves. 1

DCPTA Soluble Prot/Chl R a t i o A c t i v a t e d Rubisco A c t i v i t y (ug/ml) (mg prot/mg chl) I II III 2

0 1 10 50

13.62 13.41 16.80 12.11

+ + + +

1.68 1.59 1.77 0.92

3.02 3.04 3.00 3.05

+ + + +

0.20 0.15 0.10 0.13

41.13 40.72 50.40 36.94

+ + + +

3.62 3.11 3.47 2.97

3

164.52 232.39 307..44 173.62

Ί

Τβη to f i f t e e n leaves (leaf number eight t o eleven) were harvested from each DCPTA-treatment group 72 DAP. Isolated chloroplast preparations contained at l e a s t 80% i n t a c t chloroplassts. Values represent the mean + SE of three independent leaf harvests. 1 . mg C02/mg protein/h I I . mg C02/mg chl/h I I I . mg C02/dm /h C a l c u l a t e d from t o t a l c h l data i n Table VI. 2

2



262


Application of DCPTA t o sugar beet seedling had no e f f e c t upon Rubisco s p e c i f i c a c t i v i t y (umole C02/mg soluble protein/h) i n chloroplast lysates of mature leaves. Based on the increased c h l concentration of 10 ug/ml DCPTA-treated leaves, Rubisco a c t i v i t y per unit l e a f area was increased 87% compared t o controls. Increased Rubisco a c t i v i t y i n chloroplasts i s o l a t e d from DCPTA-treated leaves exhibited the same DCPTA concentration dependence that was observed for plant growth. Ten ug/ml of DCPTA applied t o sugar beet plants resulted i n increased l e a f canopy development during exponential plant growth. Increased l e a f rosette development of10 ug/ml DCPTA-treated plant was due t o a s i g n i f i c a n t (LSDo.05) increase i n the area of i n d i v i d u a l mature leaves. The t o t a l l e a f area duration of 10 ug/ml DCPTA-treated plants appeared t o increase due t o the delayed natural senescence of older mature leaves. Light saturated carbon exchange rates were determined for each l e a f of control and 10 ug/ml DCPTA-treated plants. For t h i s study, plants were grown widely spaced t o minmize leaf shading between i n d i v i d u a l plants. Both control and DCPTAtreated plants showed s i m i l a r CER values during l e a f development (leaves 5 through 9). Mature leaves of control exhibited a steady decline i n CER with increasing l e a f age (9). However, the mature leaves of 10 ug/ml DCPTA-treated plants maintained carbon exchange rates of 32 t o 36 mg C02/dm /h over a broad range of l e a f ages (leaves 10 through 18) which resulted i n a 48% increase i n CER over controls when based upon equal l e a f area per plant. Based upon t o t a l leaf area and light-saturated CER, the net carbon assimilation of treated plants was doubled when compared t o the values of controls (9). 2

There i s observed a strong negative c o r r e l a t i o n between taproot growth and taproot sucrose accumulation when synthetic plant growth regulators are used t o p o t e n t i a l l y increase sugar beet taproot growth and sucrose y i e l d (J£, 21). Application of mepiquat chloride [1,1dimethylpiperidinium chloride] t o sugar beet seedlings increased p a r t i t i o n i n g of photosynthate t o root tissues (12). However, application of synthetic plant growth regulators t o seedling plants often r e s u l t s i n shoot stunting and impaired l e a f development (^2 ). Moreover, the increased amounts of photosynthetic carbon p a r t i t i o n e d to roots may be allocated exclusively to root growth which r e s u l t s i n decreased sucrose y i e l d per taproot (JKO. Wyse ( VY) showed that sugar beet taproot growth and taproot sucrose accumulation are the r e s u l t s of balanced p a r t i t i o n i n g of photosynthate allocated t o shoot growth, root growth, and sucrose storage throughout exponential plant growth. Sucrose age i n taproots i s regulated by the o v e r a l l physiology of t f ^ o o t development and functions independently of photosynthate supply {YV). Increased plant growth due t o DCPTA treatment i s characterized by the increased biomass of a l l parts without any adverse e f f e c t s



21.



263

upon plant morphology, taproot vascular anatomy, and sucrose accumulation i n taproots. The rate of taproot development i n DCPTAtreated plants appeared to p a r a l l e l l e a f development which resulted i n no change i n the o v e r a l l root to shoot dry weight r a t i o during exponential plant growth. Consistent with the f i n d i n g of Wyse (11), sucrose accumulation i n taproots appeared to function as a r e s u l t of general and balanced e f f e c t s and independently of photosynthate supply i n DCPTA-treated plants. Thus, the the regulation of sugar beet productivity by DCPTA does not appear to a l t e r the balanced p a r t i t i o n i n g of photosynthate to a l l parts of the plant during exponential plant growth and taproot development. In our study, chloroplasts i s o l a t e d from mature leaves of DCPTAtreated sugarbeet plants, compared to controls, show an increase i n the t o t a l soluble protein t o chlorophyll r a t i o which p a r a l l e l s the increase i n t o t a l activated i n v i t r o Rubisco a c t i v i t y per u n i t chlorophyll and per unit l e a f area. These r e s u l t s suggest that DCPTA may regulate chloroplast compartment s i z e thereby increasing Rubisco a c t i v i t y per unit area i n DCPTA-treated sugar beet plants. Direct microscopic examination of DCPTA-treated sugar beet leaves was not undertaken. However, when compared to control leaves, electron micrographs show mature leaves of 10 ug/ml DCPTA-treated bush bean (Healey, Mehta, Yokoyama, unpublished data) and spinach (Keithly, Yokoyama, unpublished data) to contain mesophyll chloroplasts of a larger cross-sectional area and with increased thylakoid membrane development. The number of chloroplasts per mesophyll c e l l , mesophyll c e l l s i z e , and l e a f thickness were unchanged i n treated plants when compared to controls. The combined increases i n stromal volume and thylakoid development could t h e o r e t i c a l l y increase the enzymes of the Calvin cycle, ATPase coupling factor proteins, the components of electron transport, and the pigment-protein complexes both the l i g h t harvesting "antenna" and the photochemical reaction centers. In t h i s manner, the e f f e c t s of DCPTA upon photosynthesis would be "balanced" over the many component " l i g h t " and "dark" reactions. Benedict et a l (JjO has shown that the induction of carotenoid biosynthesis by analogs of t e r t i a r y amines requires the de novo nuclear gene t r a n s c r i p t i o n i n treated t i s s u e s . The photoregulation of nuclear Rubisco small subunit [rbcS] and l i g h t harvesting chlorophyll-a/b-binding protein [cab] gene t r a n s c r i p t i o n by phytochrome has been widely documented (14-16). I t has also been shown that the 5' flanking regions to both rbcS and cab genes function as promoter sequences and play a p i v o t a l regulatory r o l e i n gene t r a n s c r i p t i o n (14-16). The regulation of gene expression by DCPTA and phytochrome may conceivably operate through a common molecular route r e s u l t i n g i n altered rates of t r a n s c r i p t i o n of i n d i v i d u a l rbcS and cab genes. Carbon exchange rate [net carbon assimilation] has been correlated to the synthesis and maintenance of l i g h t saturated



264


Rubisco enzyme a c t i v i t y i n developing and i n mature leaves ( V7, JjJ). In our study, DCPTA-treated sugar beet plants exhibited a maximum increase of 47% i n t o t a l dry weight over controls during mid exponential growth. Assuming photosynthate production to be l i m i t e d only by Rubisco a c t i v i t y , a minimum 50% increase i n l i g h t saturated Rubisco a c t i v i t y would be required to sustain the photosynthate demands of CPTA-treated plants. Per u n i t leaf area of 10 ug/ml DCPTA-treated plants, t o t a l activated i n v i t r o Rubisco a c t i v i t y was increased 87% i n mature leaves r e l a t i v e to controls which appears to account for the biomass increase of DCPTA-treated plants. However, t h i s c a l c u l a t i o n may severely overestimate Rubisco enzyme a c t i v a t i o n (18, 19) and i n v i t r o Rubisco a c t i v i t y due to leaf shading i n the lower l e a f canopy (20). Carbon dioxide a v a i l a b i l i t y also strongly colimits CER (J_7, _18) which may p a r t i a l l y explain the s i m i l a r i t y of maximum CER of both control and treated plants. Yet, the sustained CER of 32 to 36 mg C02 dm~ h" over a broad range of leaf ages i n 10 ug/ml DCPTA-treated plants resulted i n s u b s t a n t i a l l y increased net carbon assimilation per plant. The cumulative e f f e c t s of increased leaf canopy development and delayed natural leaf senescence may increase photosynthesis i n DCPTA-treated plants when compared to controls. Thus, DCPTA-regulated photosynthesis i n sugar beet appears to involve regulatory e f f e c t s upon chloroplast biogenesis. In a previous report (21), i t was reported that DCPTA has no e f f e c t or an i n h i b i t o r y e f f e c t on c h l content and net photosynthesis of bean leaves. Bean plants were analyzed 3 and 6 days a f t e r application of 200uM to 20 mM DCPTA. Our study showed that the e f f e c t s of DCPTA upon plant photosynthesis are manifested only a f t e r extended periods of plant growth and i n f u l l y expanded mature new leaves which develop subsequent to DCPTA-treatment. A d d i t i o n a l l y , increased l e v e l s of Rubisco enzyme and c h l accumulation i n mature leaves of DCPTA-treated sugarbeet plants are observed only within the range of 3.0 to 30 uM applied DCPTA (1 to 10 ug/ml DCPTA). Our r e s u l t s appear to explain the disappointing r e s u l t s of e a r l i e r studies. The e f f e c t of DCPTA upon o v e r a l l plant productivity i n sugar beet i s consistent with the crop improvements i n net photosynthesis, crop y i e l d , and crop q u a l i t y demonstrated i n other DCPTA-treated crops ( 1-4, 6, 2 ' j?2., *D · 2

1

Tomato. When compared with controls, application of DCPTA as a pregermination seed treatment to tomato (Lycopersicon esculentum M i l l . cv. Pixie) increased r e l a t i v e rates (22) of roots and shoots during exponential plant growth. The mean r e l a t i v e growth rates (R) determined between 25 and 35 days a f t e r seed planting of 30 uM DCPTAtreated roots, leaves, and stems were increased 20.1%, 36.8%, and 15.6%, respectively, when compared to controls. The r e l a t i v e growth rates of 3 and 150 uM DCPTA-treated plants were numerically s i m i l a r to controls (Keithly and Yokoyama, unpublished data). Primary stem developemnt (plant height) was numerically s i m i l a r i n a l l DCPTA-


21.


265


treament groups during exponential plant growth (Keithly and Yokoyama, unpublished data). The cumulative dry weights of roots, leaves, and stems of 30 uM DCPTA-treated plants harvested 72 days a f t e r seed planting were increased 116%, 90.0%, and 69.8%, respectively, when compared with controls. The cumulative dry weights of roots and shoots of 3 and 150 uM DCPTA-treated plants were s t a t i s t i c a l l y i n s i g n i f i c a n t (p 0.05) r e l a t i v e to controls (Keithly and Yokoyama, unpublished data). Specific leaf weights (g dry wt. per dm leaf area] and the root to shoot r a t i o s (dry wt. basis) were s t a t i s t i c a l l y s i m i l a r i n a l l DCPTA-treatmentgroups (Table V I I ) . Downloaded by UNIV OF GUELPH LIBRARY on June 23, 2012 | http://pubs.acs.org Publication Date: December 7, 1991 | doi: 10.1021/bk-1991-0443.ch021

2

Table VII.

1

DCPTA (UM) 0 3 15 30 150

E f f e c t of DCPTA on the Growth and Development of Tomato (Lycopersicon esculentum M i l l , cv. Pixie)

2

SLW

2

g (dm" ) 0.73 0.73 0.74 0.79 0.72

A A A A A

Root to Shoot

A x i l l a r y Branches

Ratio

# (plant" )

0.16 0.16 A 0.12A 0.17 A 0.16 A

1

7.2 6.8 9.4 12.3 10.0

Β Β AB A AB

Truss 1

# (plant" ) 12.5 15.5 21.5 24.5 17.0

Β Β A A Β

'Tomato seeds were soaked f o r 16 h i n solutions odf DCPTA containing Tween 80 (o.1%, w/v) as a surfactant. Plants were greenhouse grown i n 5.5 1 pots. Plant growth parameters were determined 72 days a f t e r seed planting. Means (n=8) followed by same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t according to Duncan's Multiple Range Test, 5% level. S p e c i f i c Leaf Weight, based on leaf dry weights. 2

The increased cumulative growth of 30 uM DCPTA-treated roots and stems was due to increased secondary root development and to increased a x i l l a r y branch development (Table V I I ) . Flower c l u s t e r (truss) number per plant p a r a l l e l e d secondary branch development (Table V I I ) . Truss development i n 30 uM DCPTA-treated plants was doubled when compared with controls (Table V I I ) . The e f f e c t of DCPTA on f r u i t y i e l d p a r a l l e l e d the e f f e c t s of DCPTA upon plant growth (Table V I I I ) .


266


Table VIII. 1

DCPTA (uM) 0


Total F r u i t # (plant" 1) 28.7 26.7 40.3 40.0 25.8

3 15 30 150

E f f e c t of DCPTA on the Y i e l d Productivity of Tomato

Β * Β A A Β

Ripe Fr (%) 57.5 59.0 76.6 65.7 85.2

Β Β A A A

Total Fr Y i e l d (plant" 1) g

752.7 841.4 1303.0 1351.6 652.7

Β Β A A C

Fr Size g (fr" ) 1

26.2 31.5 32.3 33.8 25.3

Fr Dry Wt. /Fresh Fr

Β A A A Β

0.063 0.069 0.066 0.085 0.065

Β Β Β A Β

tomato seeds were soaked f o r 6 h i n solutions of DCPTA containing Tween 80 (0.1%, w/v) as a surfactant. Tomato plants were harvested 72 days a f t e r seed planting. Means (N=8) followed by same l e t t e r are not s i g n i f i c a n t l y differewnt according to Duncan's Multiple Range Test, 5% l e v e l . 2

The t o t a l f r u i t y i e l d of 30 uM DCPTA-treated plants was increased 80% when compared with controls. Individual f r u i t s i z e and t o t a l f r u i t per plant were s i g n i f i c a n t l y increased i n 30 uM DCPTAtreated plants. The dry weight to fresh weight r a t i o of r i p e f r u i t s was s i g n i f i c a n t l y increased i n 30 uM DCPTA-treated plants when compared with controls. The increased fructose and glucose contents of r i p e tomato f r u i t s were s i g n i f i c a n t within the 15, 30, and 150 uM DCPTA-treatment groups when compared with controls as shown i n Table IX. Table IX.

1

DCPTA (UM) 0 3 15 30 150

E f f e c t of DCPTA on The Composition of Ripe Tomato F r u i t 2

TSS % fr.wt. 3.75 3.58 4.42 4.58 4.68

B Β A A A

3

Fructose % fr.wt.

Glucose % fr.wt.

Lycopene /3-Carotene ug(g f r . wt.)"

1.68 1.62 1.82 1.91 2.00

1.43 1.49 1.67 1.81 1.64

58.46 81.21 98.18 11.83 110.10

Β Β A A A

Β Β A A A

1

C Β AB A A

2.20 3.18 4.33 5.24 5.67

C Β AB A A

''Tomato seeds were soaked f o r 6 h i n solutions of DCPTA containing Tween 80 (0.1%) as a surfactant. F r u i t s were harvested 72 days a f t e r seed planting. Six random samples of r i p e f r u i t were used f o r f r u i t constituent analysis. T o t a l Soluble Solids 2

J

Means (N=6) followed by the same l e t t e r are not s i g n i f i c a n t l y d i f f e r e n t according t o Duncan's Multiple Range Test, 5% l e v e l .



21.



267

Glucose and fructose were i d e n t i f i e d as major sugar constituents of r i p e f r u i t and represented 78 to 87% of the t o t a l soluble s o l i d content within a l l DCPTA-treatment groups. Sucrose was detected only i n trace amounts i n a l l P i x i e f r u i t s that were analyzed. Lycopene and beta-carotene were i d e n t i f i e d as the major pigment constituents of r i p e tomato f r u i t (Table IX). The combined lycopene and betacarotene contents of r i p e f r u i t were increased about two f o l d i n the 30 and 150 uM DCPTA-treatment groups. The observed biomass gains of a l l plant parts i n DCPTA-treated tomato plants would indicate s i g n i f i c a n t l y increased rates of net carbon assimilation and a v a i l a b i l i t y and supply of photosynthetic carbon i n mature leaves. Previous studies have shown the observed biomass gains of DCPTA-treated cotton (7^) # spinach (24), and sugarbeet (Keithly, J . H.; Yokoyama, H. Plant S c i . , i n press ) plants to be associated with increases i n chloroplast compartment s i z e and increased net carbon a s s i m i l a t i o n per u n i t l e a f area i n mature leaves. These r e s u l t s indicate that i n DCPTA-treated plants, crop productivity i s p r i m a r i l y determined by regulation of chloroplast development during leaf expansion. However, the s i g n i f i c a n t l y increased l e a f and root meristem a c t i v i t i e s of DCPTAtreated plants (]_* 2

Chemical Agents as Regulators of Biological Responses in Plants

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