Synthesis and Chemistry of Agrochemicals II - American Chemical

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.


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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


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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

Synthesis and Chemistry of Agrochemicals II - American Chemical

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