The Chemistry of Allelopathy - American Chemical Society

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12 Effects of Allelochemicals on Plant-Water Relationships F. A. EINHELLIG, M. STILLE MUTH, and M. K. SCHON

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Department of Biology, University of South Dakota, Vermillion, SD 57069

Bioassays with grain sorghum [Sorghum bicolor (L.) Moench.]seedlings grown under summer glasshouse conditions demonstrated that leaf diffusive resistance increased and water potential decreased following treatments with ferulic acid, p-coumaric acid, and extracts from several allelopathic weeds. During the week f o l lowing treatment with 0.5 mM ferulic or p-coumaric acid, sorghum leaf resistances indicated that stomates were almost closed. Effects on water potential were found at a lower treatment level, with 0.25 mM ferulic or p-coumaric acid-treated sorghum having midday leaf water potentials of approximately -10 bars, compared to -5 bars for controls. Water potential changes resulted from reductions in both osmotic potential and turgor pressure. Aqueous extracts from Kochia scoparia, Helianthus tuberosus, and Xanthium pensylvanicum caused growth reductions in sorghum that correlated with high diffusive resistances and low water potentials, with these effects found using extracts from 1 g fresh-leaf material in 60 ml of nutrient medium. Growth of sorghum in soil containing dried residue from these weeds was also reduced. The data suggest one mechanism of allelopathic action is a disruption of plant water balance.

The p r o c e s s o f a l l e l o p a t h y i m p l i e s t h a t compounds ( a l l e l o c h e m i c a l s ) o f p l a n t o r i g i n a r e r e l e a s e d i n t o the environment, subsequently m o d i f y i n g t h e growth and development o f o t h e r p l a n t s . Definitive e x p l a n a t i o n s o f t h i s p r o c e s s r e q u i r e an u n d e r s t a n d i n g o f how a l l e l ochemical f u n c t i o n . Some i n h i b i t o r y a l l e l o c h e m i c a l s i n d i r e c t l y i n f l u e n c e t h e growth o f v a s c u l a r p l a n t s by t h e i r e f f e c t s on n i t r i f i c a t i o n and n i t r o g e n f i x a t i o n 2), d i s e a s e r e s i s t a n c e o r s u s c e p t i b i l i t y ( 3 ) , o r m y c o r r h i z a l f u n g i ( 4 ) . A l t e r n a t i v e l y , more d i r e c t a l l e l o c h e m i c a l e f f e c t s may o c c u r . 1

Current address: Mount Marty College, Yankton,SD57078 0097-6156/ 85/0268-0179506.00/ 0 © 1985 American Chemical Society

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T H E C H E M I S T R Y OF A L L E L O P A T H Y

P l a n t s s u s c e p t i b l e to i n h i b i t o r y a l l e l o c h e m i c a l s t y p i c a l l y have r e d u c e d o r d e l a y e d g e r m i n a t i o n and s t u n t e d s e e d l i n g growth. Some e v i d e n c e i n d i c a t e s s e e d l i n g growth is more s e n s i t i v e t o a l l e l o c h e m i ­ c a l s than seed g e r m i n a t i o n ( 5 ) , and l o n g - t e r m s e e d l i n g growth may be the b e s t i n d i c a t o r o f s e n s i t i v i t y t o a c h e m i c a l (6). However, i d e n t i f y i n g the growth r e g u l a t o r y mechanisms a t tfie system o r c e l l u ­ l a r l e v e l has been e l u s i v e . A l l e l o c h e m i c a l s appear t o a l t e r a v a r i ­ e t y o f p h y s i o l o g i c a l p r o c e s s e s (Λ 8 ) , and i t is d i f f i c u l t to sepa^ r a t e p r i m a r y from secondary e f f e c t s . D e t e r m i n i n g the mechanisms o f a l l e l o p a t h i c a c t i o n i n a p a r t i c u l a r f i e l d s i t u a t i o n is f u r t h e r c o n ­ f u s e d by t h e f a c t t h a t s e v e r a l d i f f e r e n t a l l e l o c h e m i c a l s may be i n ­ volved. While t h e s e s u b s t a n c e s may a c t i n c o n c e r t to reduce growth (5^ 9^ 1 0 ) , i n most cases the i n t e r a c t i o n o f c o m b i n a t i o n s o f a l l e l o ­ c h e m i c a l s on growth o r p h y s i o l o g i c a l p r o c e s s e s has not been d o c u ­ mented. I n v e s t i g a t i o n o f a l l e l o p a t h y has o f t e n i m p l i c a t e d p h e n o l i c d e ­ r i v a t i v e s o f c o u m a r i n , c i n n a m i c a c i d , and b e n z o i c a c i d as growth i n h i b i t o r s (7^ 1J_). E a r l y e v i d e n c e i n d i c a t e d t h a t s c o p o l e t i n and s e v e r a l p h e n o l i c a c i d s r e g u l a t e growth by c o n t r o l l i n g the l e v e l o f i n d o l e - 3 - a c e t i c a c i d (12^ 1 3 ) . While t h e r e has been no comprehensive assessment o f the p h y s i o l o g i c a l e f f e c t o f a s i n g l e s u b s t a n c e , com­ pounds from t h i s group o f chemicals have been r e p o r t e d t o a l t e r s e e d ­ l i n g m e t a b o l i s m i n a v a r i e t y o f o t h e r ways. These i n c l u d e changes i n p h o t o s y n t h e t i c r a t e (24, 1 5 ) , s t o m a t a l f u n c t i o n (16), chlorophyll c o n t e n t ( 1_7), r e s p i r a t o r y r a t e ( 1 8 , 1 9 ) , f l o w o f carbon (2Ό), m i n e r a l uptake ( 2 1 - 2 4 ) , and membrane p e r m e a b i l i t y ( 2 5 ) . G l a s s and Dunlop (25) r e p o r t e d t h a t s e v e r a l p h e n o l i c a c i d s cause membrane d e p o l a r i z a ­ t i o n , an a c t i o n t h a t would l o g i c a l l y have a d i r e c t e f f e c t on i o n uptake and p l a n t w a t e r b a l a n c e . These a c t i o n s c o u l d then t r i g g e r o t h e r m e t a b o l i c e f f e c t s , as s u g g e s t e d i n F i g u r e 1. WATER SOLUBLE INHIBITORS

GROWTH AND DEVELOPMENT Figure

1.

CONTENT

H y p o t h e t i c a l a c t i o n sequence s u g g e s t i n g a l l e l o c h e m i c a l i n ­ volvement i n p l a n t p r o c e s s e s . Each arrow s u g g e s t s a nega­ t i v e impact.

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Effects of Allelochemicals on Plant- Water Relationships

EINHELLIG ET AL.

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Experiments were d e s i g n e d t o t e s t the h y p o t h e s i s t h a t p h e n o l i c a c i d s a l t e r t h e w a t e r b a l a n c e o f s e e d l i n g s , and t h a t changes i n p l a n t w a t e r s t a t u s would be c o r r e l a t e d w i t h i n h i b i t i o n o f s e e d l i n g growth. The a l l e l o p a t h i c p o t e n t i a l o f s e v e r a l weeds common t o a g r i ­ c u l t u r a l f i e l d s was a l s o t e s t e d u s i n g s e e d l i n g b i o a s s a y s , and w a t e r r e l a t i o n s h i p s o f t h e b i o a s s a y p l a n t s were m o n i t o r e d . Materials

and Methods

P l a n t m a t e r i a l s and growth c o n d i t i o n s . G r a i n sorghum [Sorghum b i c o l o r ( L . ) M o e n c h . , h y b r i d 7 0 1 , G u r n e y ' s N u r s e r y , Y a n k t o n , S D . l was used f o r t h e t e s t s i n t h e s e e x p e r i m e n t s . G r a i n sorghum was chosen because i t is s e n s i t i v e t o p h e n o l i c a c i d s (9^ V 7 ) , and i t s growth may be i n f l u e n c e d by a l l e l o c h e m i c a l s from weeds i n a g r i c u l t u r a l f i e l d s (26). P l a n t s were grown under summer g l a s s h o u s e c o n d i t i o n s w i t h n o r ­ mal v a r i a t i o n s i n t e m p e r a t u r e and l i g h t , u s i n g s u p p l e m e n t a l l i g h t i n g t o o b t a i n a 16 h r p h o t o p e r i o d . Experiments w i t h p h e n o l i c a c i d s . S e e d l i n g s were grown i n n u t r i e n t s o l u t i o n augmented w i t h e i t h e r f e r u l i c a c i d (FA) o r £ - c o u m a r i c a c i d (pCA) f o r t e s t i n g e f f e c t s on w a t e r b a l a n c e . Seeds were g e r m i n a t e d i n v e r m i c u l i t e f o r a 6 t o 8 day p e r i o d , then i n d i v i d u a l s e e d l i n g s were t r a n s p l a n t e d i n t o o p a q u e - p l a s t i c v i a l s (80 ml) c o n t a i n i n g n u t r i e n t medium. The n u t r i e n t medium was o n e - t h i r d s t r e n g t h H o a g l a n d ' s (27) m o d i f i e d t o c o n t a i n 2 . 5 times t h e normal i r o n s u p p l i e d as sodium f e r ­ r i c diethylenetriamine pentaacetate (Sequestrene 330). Seedlings were s e l e c t e d f o r u n i f o r m i t y and p h e n o l i c a c i d t r e a t m e n t s were i n i t i ­ a t e d 2 o r 3 days f o l l o w i n g t r a n s p l a n t . In each e x p e r i m e n t t h e r e was a c o n t r o l and t h r e e p h e n o l i c a c i d regimes w i t h 25 s e e d l i n g s p e r group. Treatments were p r e p a r e d by d i s s o l v i n g pCA o r FA (Sigma Chemical C o . ) i n f r e s h n u t r i e n t medium t o o b t a i n c o n c e n t r a t i o n s o f O.25, O.5, and O.75 mM. The s o l u t i o n s were r e p l a c e d w i t h f r e s h l y p r e p a r e d medium 4 days a f t e r t r e a t m e n t . Growth and w a t e r s t a t u s o f s e e d l i n g s were m o n i t o r e d d a i l y f o r 6 days f o l l o w i n g t r e a t m e n t . Water s t a t u s o f t h e s e e d l i n g s was d e t e r m i n e d each a f t e r n o o n by o b t a i n i n g l e a f d i f f u s i v e r e s i s t a n c e , water p o t e n t i a l , and o s m o t i c potential. D i f f u s i v e r e s i s t a n c e was measured on both t h e a d a x i a l and a b a x i a l s u r f a c e s o f t h e y o u n g e s t f u l l y expanded l e a f f o r s i x randomly s e l e c t e d p l a n t s i n each t r e a t m e n t u s i n g a Lambda Model L I - 6 0 meter and a narrow a p e r t u r e s e n s o r . T o t a l l e a f r e s i s t a n c e (R) was c a l c u ­ l a t e d from t h e component r e s i s t a n c e s ( r ) as f o l l o w s : _ L R

=

r

ι abaxial

+

_

r

J adaxial

L i g h t c o n d i t i o n s each day were d e t e r m i n e d as an average o f t h e i n ­ t e n s i t y b e f o r e and a f t e r t a k i n g the r e s i s t a n c e r e a d i n g s . L e a f w a t e r p o t e n t i a l and o s m o t i c p o t e n t i a l were measured u s i n g a Wescor Dewpoint M i c r o v o l t m e t e r (Model HR-33) c o u p l e d w i t h C-51 and C-52 sample chambers. Two p l a n t s from each group were sampled each day by t a k i n g two 7-mm d i a m e t e r l e a f d i s k s from each p l a n t , one f o r w a t e r p o t e n t i a l and one f o r o s m o t i c p o t e n t i a l . P l a n t s from which l e a f d i s k s were o b t a i n e d were d i s c a r d e d . The w a t e r p o t e n t i a l o f a l e a f d i s k was r e a d f o l l o w i n g a 2 - h r e q u i l i b r a t i o n p e r i o d i n a sample

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chamber. Osmotic p o t e n t i a l o f the l e a f s o l u t i o n was d e t e r m i n e d a f t e r f r e e z e r u p t u r i n g t h e t i s s u e and s a t u r a t i n g a f i l t e r paper d i s k which was e q u i l i b r a t e d i n a sample chamber f o r 30 m i n . T u r g o r p r e s s u r e was c a l c u l a t e d as t h e d i f f e r e n c e between w a t e r p o t e n t i a l and o s m o t i c p o tential. The average f o r each water parameter was computed f o r the 6-day p e r i o d t o f a c i l i t a t e a n a l y s i s o f t h e e f f e c t s o f t h e t r e a t m e n t s . The d r y w e i g h t s (104 C , 48 h r ) o f t e n p l a n t s from each t r e a t m e n t group were taken a t the t e r m i n a t i o n o f each e x p e r i m e n t i n o r d e r t o compare growth e f f e c t s w i t h p l a n t w a t e r s t a t u s . Dry w e i g h t d a t a were a n a l y z e d u s i n g a n a l y s i s o f v a r i a n c e (AN0VA) and Duncan's m u l t i p l e range t e s t . D i f f u s i v e r e s i s t a n c e and w a t e r p o t e n t i a l were e v a l u a t e d using the t - t e s t . Each o f t h e s e and subsequent experiments was r e p licated. Aqueous-weed e x t r a c t e x p e r i m e n t s . F r e s h s h o o t m a t e r i a l from t h e l e a v e s and s m a l l stems o f K o c h i a {Kochia s c o p a r i a ( L . ) S c h r a d . ] , J e r u s a l e m a r t i c h o k e ( H e l i a n t h u s t u b e r o s u s L . ) , and c o c k l e b u r (Xanthium p e n s y l v a n i c u m W a l l r . ) were c o l l e c t e d from p l a n t s i n the field. Aqueous e x t r a c t s were made by b o i l i n g 10 g f r e s h w e i g h t o f p l a n t m a t e r i a l i n 100 ml o f w a t e r f o r 10 m i n . , g r i n d i n g i n a Waring b l e n d e r , f i l t e r i n g through c h e e s e c l o t h and Whatman No. 4 p a p e r , and a d j u s t i n g t h e f i n a l volume t o 100 ml ( 2 8 ) . Thus 1 ml o f the e x t r a c t c o n t a i n e d the w a t e r - s o l u b l e s u b s t a n c e s from O.1 g o f l e a f m a t e r i a l . The e x t r a c t pH was a d j u s t e d t o 5 . 5 . D i l u t i o n s o f an aqueous e x t r a c t were i n c o r p o r a t e d i n t o n u t r i e n t medium f o r growing s e e d l i n g s so t h a t the f i n a l r a t i o s o f f r e s h s h o o t o r l e a f w e i g h t t o n u t r i e n t mediurr (w/v) i n the e x p e r i m e n t s ranged from 1:20 t o 1:120. The n u t r i e n t medium was a m o d i f i e d f u l l - s t r e n g t h H o a g l a n d ' s as d e s c r i b e d by E i n h e l l i g and Schon ( 2 9 ) , and a l l t r e a t m e n t s had t h e same n u t r i e n t concentration. The medium h a v i n g the l o w e s t o s m o t i c p o t e n t i a l among t h e t r e a t m e n t s was t h e K o c h i a 1:20 t r e a t m e n t , which was - 1 . 4 b a r s . The o s m o t i c p o t e n t i a l s f o r o t h e r t r e a t m e n t s were i n a range from -1 bar t o - O . 6 b a r f o r t h e c o n t r o l . Preparation o f s e e d l i n g s f o r treatments with extract-amended n u t r i e n t s o l u t i o n was s i m i l a r t o t h a t d e s c r i b e d f o r t e s t i n g the e f f e c t s o f p h e n o l i c a c i d s , e x c e p t 40 p l a n t s were used p e r t r e a t m e n t and no r e p l a c e m e n t o f t h e n u t r i e n t s o l u t i o n was made d u r i n g the t r e a t m e n t period. Data c o l l e c t i o n p r o c e d u r e s were m o d i f i e d i n t h a t o n l y a b a x i a l l e a f r e s i s t a n c e was o b t a i n e d and w a t e r p o t e n t i a l was d e t e r m i n e d from f o u r p l a n t s each day. P r i o r work e s t a b l i s h e d t h a t a b a x i a l r e s i s t a n c e p r o v i d e d an adequate i n d i c a t o r o f s t o m a t a l e f f e c t s . The d a t a ware a n a l y z e d as d e s c r i b e d i n e x p e r i m e n t s w i t h pCA and FA, Experiments w i t h weed r e s i d u e i n soil. The e f f e c t s o f d r i e d s h o o t and l e a f m a t e r i a l from K o c h i a , J e r u s a l e m a r t i c h o k e , and c o c k l e b u r were d e t e r m i n e d by growing sorghum i n soil amended w i t h t h e s e r e s i dues. A c t i v e l y growing p l a n t s were c o l l e c t e d from t h e f i e l d i n A u g u s t , a i r d r i e d i n the g l a s s h o u s e f o r one week, and the l e a v e s and s m a l l e r stems ground t o pass t h r o u g h a 1-mm s c r e e n . T h i s r e s i d u e was mixed i n t o a f e r t i l e s i l t y - c l a y soil h a v i n g c h a r a c t e r i s t i c s p r e v i o u s l y r e p o r t e d (290. The p l a n t r e s i d u e was added t o a i r - d r i e d soil so t h a t t r e a t m e n t s o i l s c o n t a i n e d e i t h e r 2 . 5 , 1 . 2 5 , O.63, o r O.31% weed residue. These r a t e s were e s t i m a t e d on the b a s i s o f t h e amount o f plant material found from s a m p l i n g s e v e r a l q u a r t e r - m e t e r q u a d r a t s i n a r e a s where a p a r t i c u l a r weed was abundant. In t h e f i r s t o f t h e

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two t r i a l s c o n d u c t e d w i t h each r e s i d u e , t h e c o n t r o l soil was amended w i t h 2.5% sphagnum moss as a n o n t o x i c o r g a n i c m a t t e r c o n t r o l ( 2 8 ) . The growth c o n t a i n e r s used i n t h e soil s t u d i e s were t h e same p l a s t i c v i a l s (3.2-cm d i a m e t e r χ 10-cm deep) u t i l i z e d i n t h e o t h e r e x p e r i ­ m e n t s , and 80 g o f soil was added t o each c o n t a i n e r . T h i r t y t o 40 soil p o t s were used f o r each t r e a t m e n t g r o u p . Three sorghum seeds were p l a n t e d 1-cm deep i n t h e soil o f each p o t , and s e e d l i n g s were t h i n n e d t o one p e r p o t a f t e r emergence. The soil p o t s were watered t o f i e l d c a p a c i t y each day by a w e i g h t p r o c e d u r e . Sur­ f a c e e v a p o r a t i o n was reduced by c o v e r i n g t h e soil s u r f a c e w i t h a plastic disk. A f t e r emergence o f t h e s e e d l i n g s , a h o l e was punched in the p l a s t i c f o r the shoot. The growth p e r i o d from g e r m i n a t i o n t o h a r v e s t was two weeks. A b a x i a l l e a f r e s i s t a n c e , w a t e r p o t e n t i a l , and o s m o t i c p o t e n t i a l were o b t a i n e d from sorghum on two o r t h r e e days d u r i n g t h e second week o f g r o w t h . The w a t e r used by each p l a n t was r e c o r d e d and a f t e r h a r v e s t t h e t r a n s p i r a t i o n r a t i o was computed. A l l d a t a were a n a l y z e d as p r e v i o u s l y d e s c r i b e d . Results Experiments w i t h p h e n o l i c a c i d s . Treatments w i t h pCA and FA caused s i m i l a r e f f e c t s on t h e growth o f g r a i n sorghum s e e d l i n g s . Seedlings grown f o r s e v e r a l days w i t h e i t h e r O.75 o r O.5 mM pCA o r FA i n t h e medium had a w i l t e d a p p e a r a n c e , some c h l o r o s i s o f t h e lower l e a v e s , more v i s i b l e a n t h o c y a n i n a c c u m u l a t i o n than c o n t r o l s , and s t u n t e d growth. These c o n d i t i o n s were most e x t e n s i v e i n t h e O.75 mM t r e a t ­ ments, and t h e s e p l a n t s had f o l d e d l e a v e s and p r o l i f e r a t i o n o f a d ­ v e n t i t i o u s r o o t s as t h e e x p e r i m e n t p r o g r e s s e d . The h a r v e s t d r y w e i g h t s show t h a t both O.75 and O.5 mM l e v e l s o f t h e two p h e n o l i c a c i d s s i g n i f i c a n t l y i n h i b i t e d growth and t h i s i n h i b i t i o n was c o n c e n ­ t r a t i o n dependent ( T a b l e I ) . The w e i g h t s o f p l a n t s t r e a t e d w i t h O.25 mM pCA o r FA were n o t s i g n i f i c a n t l y below t h e c o n t r o l s a t t h e end o f the 6 days o f t r e a t m e n t , b u t a comparison t o c o n t r o l s i n d i c a t e s t h a t the O.25 mM pCA and FA t r e a t m e n t s may have had a s l i g h t e f f e c t . The e f f e c t s o f pCA on p l a n t water s t r e s s were s i m i l a r i n t h e r e p l i c a t e e x p e r i m e n t s , thus o n l y t h e d a t a from t h e second t r i a l has been p r e s e n t e d ( T a b l e I I ) . Treatments w i t h O.75 and O.5 mM pCA e l e ­ v a t e d l e a f r e s i s t a n c e o f t h e sorghum s e e d l i n g s a f t e r one day o f t r e a t m e n t , and h i g h r e s i s t a n c e s p e r s i s t e d through t h e d u r a t i o n o f t h e experiment. Only a minor i n c r e a s e was i n d u c e d by O.25 mM pCA. Some o f t h e day t o day v a r i a t i o n i n r e s i s t a n c e r e f l e c t s d i f f e r e n c e s i n l i g h t i n t e n s i t y and t e m p e r a t u r e . A l l pCA t r e a t m e n t s d e p r e s s e d s o r ­ g h u m - l e a f w a t e r p o t e n t i a l f o r t h e d u r a t i o n o f t h e e x p e r i m e n t . The summary d a t a o f t h e 6 days shows t h a t even O.25 mM p C A - t r e a t e d s e e d ­ l i n g s had water p o t e n t i a l s t w i c e as n e g a t i v e as t h e c o n t r o l s , and t h e o t h e r t r e a t m e n t s f u r t h e r lowered w a t e r p o t e n t i a l . This depression o f l e a f w a t e r p o t e n t i a l was due t o both a l o w e r i n g o f o s m o t i c p o t e n ­ t i a l and t u r g o r p r e s s u r e . The o c c a s i o n a l n e g a t i v e t u r g o r p r e s s u r e c a l c u l a t e d a p p a r e n t l y o c c u r r e d from t h e combined e r r o r a r i s i n g i n the measurement p r o c e d u r e s , but t h e o v e r a l l d a t a c o n f i r m t h e l o s s o f t u r ­ g o r t h a t t h e w i l t e d appearance o f s e e d l i n g s t r e a t e d w i t h O.5 and O.75 mM pCA s u g g e s t e d . The e f f e c t s o f FA on t h e water s t a t u s o f g r a i n sorghum s e e d l i n g s were s i m i l a r t o t h a t o b s e r v e d from pCA t r e a t m e n t s , as i l l u s t r a t e d i n

Note:

2 1 7 . 6 + 13.7a

2

7.1a

213.6+

9.2a

1 5 9 . 7 + 11.2a

135.8+

270.2 + 15.1a

mg + SE

u . 2 5 mM

mM

125.9 +13.6b

1 0 6 . 3 + 6.9b

86.3 + 4.9b

114.4 + 8.3b

O.5

Sorghum

mM

91.3+

5.9c

9 2 . 7 + 6.1b

65.1 + 3 . 0 c

69.3 + 4.8c

-

O.75

Values i n a row not f o l l o w e d by t h e same l e t t e r a r e s i g n i f i c a n t l y d i f f e r e n t , P < O . 0 5 , AN0VA and Duncan's m u l t i p l e - r a n g e t e s t .

1 7 3 . 1 + 10.6a

1

1 5 1 . 3 + 28.9a

2

FA

2 9 1 . 8 + 22.4a

1

pCA

Control

Trial

Treatment

on the Dry Weights o f G r a i n

Phenolic Acid

of Phenolic Acids

Cpd.

Effects

TABLE I

12.

EINHELLIG ET AL.

Effects of Allelochemicals on Plant- Water Relationships

185

TABLE II Effects

o f £-Coumaric A c i d on t h e Water S t a t u s o f G r a i n Sorghum pCA Treatments

Days Treatment

Control

O.25 Total

1 2 3 4 5 6 _ 6-day X

4.2+O.4 5.3+1.0 4.6+O.3 4.6 + O.3 5.6+O.7 3.3+O.3 4.6+O.3

-

5.5 5.9 3.7 4.1 2.8 5.4 4 . 6 + O.5

O.5

Leaf Resistance 5.7+O.2 6.1+O.6 19.3+7.4 5.2 + O.4 7.3+O.7 6.5+3.4 8.4+2.2 b

Water 1 2 3 4 5 6 6-day X

mM

Potential

-10.9 -11.3 -10.4 -10.7 - 9.2 - 8.7 - 1 0 . 2 + O.4

b

a

-14.2 -12.7 -16.1 -13.3 -15.1 -12.8 κ - 1 4 . 0 + O.6 b

1 2 3 4 5 6 6-day X

5.4 5.4 6.7 6.6 6.4 3.3 5.6 + O.5

47.7+2.3? 48.0+1.7? 31.1+7.O. b 3 6 . 0 + 5.4, 45.2 + 3 . 5 7.7+1.2° 36.0+6.3°

(bars)

" · b - 1 1 . 8 + O.8° 9

U

mM

(Sec /cm + SE)

-14.2 -13.6 -12.7 -10.4 -10.4

-11.0 -11.0 -14.2 - 9.0 - 9.7 - 8.3 - 1 0 . 6 + O.9

Turgor

O.75

32.5 + 6 . 5 15.1+4.3* 28.2 + 6 . l u 10.3 + 1.6° 20.2+8.0 3.3+O.2 18.3 + 4 . 5

Osmoti c P o t e n t i a l 1 2 3 4 5 6 6-day X

mM

7

-15.7 -16.0 -10.2 - 8.1 -10.5 - 9.5 b - 1 1 . 7 + 1.4'

(bars)

-12.4 -12.4 -11.3 -12.4 -15.1 -12.5 - 1 2 . 7 + O.4° b

-14.0 -15.4 -14.1 -12.8 -14.1 -14.1 >b - 1 4 . 1 + O.3'

P r e s s u r eÎ ( b a r s )

3.2 1.6 1.9 4.3 5.4 4.5 3.5 + O.6

Û

- 1.8 - 1.2 - 1.4 2.0 4.7 2.8 . O.9 + 1 . 1 °

- 1.7 - O.6 3.9 4.7 3.6 4.6 2.4

1.2 a

Note — V a l u e s each day a r e t h e mean o f s i x s e e d l i n g s f o r r e s i s t a n c e and two f o r w a t e r p o t e n t i a l . R e s i s t a n c e d a t a and t h e 6-day mean f o r w a t e r p o t e n t i a l were a n a l y z e d w i t h t h e t - t e s t . a

Differs

significantly

from t h e c o n t r o l ,

Ρ