Plant Bioregulators: Overview, Use, and Development - ACS

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P l a n t B i o r e g u l a t o r s : O v e r v i e w , Use, and Development JOHANNES JUNG

Downloaded by MONASH UNIV on September 18, 2015 | http://pubs.acs.org Publication Date: April 26, 1985 | doi: 10.1021/bk-1985-0276.ch007

BASF Agricultural Research Centre, D-6703 Limburghof, Federal Republic of Germany

The action of most exogenous plant bioregulators (PBRs) consists of interference with the plant's hormone system. Accordingly, the action of these substances may be related to the five phytohormone groups, known up to now, as homologs, synergists, antagonists, or inhibitors of hormone biosynthesis. Beside this group of PBRs there are, however, other important compounds which have not so far been shown to have a definite relationship to a phytohormone. On this basis, an overview of substances with bioregulatory effects is presented. The specific influence of exogenous PBRs on crop plants has in some cases already been integrated into the crop production system. Examples of this are the use of chlormequat chloride in cereal growing, ethephon for influencing the development and maturity of various crops, and mepiquat chloride in cotton. The development of PBRs is discussed under the aspect of relevant concepts for the synthesis and screening of new compounds and other factors involved. This state-of-the-art contribution on plant bioregulators (PBRs) is directed to the following four questions: 1. What are plant bioregulators and what is plant bioregulation? 2. What substances and what principle of action are available? 3. How have plant bioregulators been used so far in crop production and where are they employed in particular? 4. What factors will have a major influence on determining the development of new plant bioregulators and on opening up further possibilities for use in crop production?

0097-6156/ 85/0276-0095506.00/ 0 © 1985 American Chemical Society

In Bioregulators for Pest Control; Hedin, P., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

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BIOREGULATORS FOR PEST CONTROL


What are p l a n t b i o r e g u l a t o r s and

what i s p l a n t

bioregulation?

I t i s n e c e s s a r y t o d e f i n e the term " p l a n t b i o r e g u l a t o r s " i n o r d e r t o p r o v i d e a g e n e r a l c h a r a c t e r i z a t i o n o f t h e i r p r o p e r t i e s and mode o f a c t i o n , and t o d i s t i n g u i s h them from o t h e r a g r o c h e m i c a l s . An endoge nous s u b s t a n c e may be c o n s i d e r e d t o be a b i o r e g u l a t o r i f , at a low c o n c e n t r a t i o n ( f o r example below 1 mM) and w i t h o u t h a v i n g a b i o c i d a l e f f e c t , i t e x e r c i s e s an i n f l u e n c e on the growth, development, and composition of p l a n t s , without being a n u t r i e n t . T h i s term c o v e r s a b r o a d e r spectrum o f e f f e c t s on p l a n t s than the term " p l a n t growth r e g u l a t o r s " t h a t has been commonly used i n E n g l i s h - s p e a k i n g c o u n t r i e s . T h i s new d e f i n i t i o n s h o u l d do g r e a t e r j u s t i c e t o the v a r i e t y o f e f f e c t s t h a t are e x p e c t e d from t h i s c l a s s o f s u b s t a n c e s . These i n c l u d e not o n l y an i n f l u e n c e on the growth and development p r o c e s s e s o f c r o p p l a n t s or t h e i r s p e c i f i c organs, but a l s o the m o d i f i c a t i o n o f m e t a b o l i c p r o c e s s e s or the f o r m a t i o n o f c e r t a i n c o n s t i t u e n t s , as w e l l as a m o d i f i e d s t r e s s b e h a v i o r . Another c h a r a c t e r i s t i c o f a b i o r e g u l a t o r i s t h a t the m o d i f i c a t i o n s t h a t i t produces must not a f f e c t the genome, i . e . , i t s a c t i o n must be o f a temporary n a t u r e . N a t u r a l l y , phytohormones have a s p e c i a l p o s i t i o n among p l a n t b i o r e g u l a t o r s , because they a r e l e a d compounds f o r r e g u l a t o r y f u n c t i o n s i n the p l a n t system. S i n c e , however, t h e s e endogenous sub s t a n c e s have a l r e a d y been d e a l t w i t h by Thomas C. Moore i n the p r e v i o u s c h a p t e r , they are o n l y touched on as f a r as i n t e r a c t i o n s w i t h exogenous b i o r e g u l a t o r s and the c h a r a c t e r i z a t i o n o f t h e i r e f f e c t s are c o n c e r n e d . Namely, an i m p o r t a n t g u i d e l i n e , which c o n t i n u e s t o s u b s t a n t i a l l y govern the s e a r c h f o r new s y n t h e t i c b i o r e g u l a t o r s , i s i n f l u e n c i n g the p l a n t ' s hormone s t a t u s . T h i s can be a c h i e v e d not o n l y by an e f f e c t o f the a p p l i e d exogenous compound analogous t o t h a t o f the p a r t i c u l a r phytohormone, but a l s o by s y n e r g i s t i c and a n t a g o n i s t i c e f f e c t s , or by promoting or i n h i b i t i n g hormonal b i o s y n t h e s i s by means o f exogenous s u b s t a n c e s . A c l a s s i f i c a t i o n r e l a t e d t o the "phytohormonal i n t e r a c t i o n p r i n c i p l e " i s a l s o a p p r o p r i a t e i n a s y s t e m a t i c overview o f v a r i o u s groups o f exogenous PBRs. What s u b s t a n c e s and

what p r i n c i p l e s o f a c t i o n are

available?

T a b l e 1 shows a l i s t and c l a s s i f i c a t i o n o f the range o f exoge nous b i o r e g u l a t o r s p r e s e n t l y a v a i l a b l e , drawn up on the b a s i s o f the a s p e c t s a l r e a d y o u t l i n e d . Even i f t h e r e i s a s u b s t a n t i a l l i m i t a t i o n t o groups o f a c t i v e compounds r a t h e r t h a n t o i n d i v i d u a l s u b s t a n c e s , the overview g i v e n cannot be c o n s i d e r e d complete. I t does, however, c o n t a i n the m a j o r i t y o f s y n t h e t i c b i o r e g u l a t o r groups t h a t are a l ready i n use or a r e i n the developmental s t a g e . Of the analogous compounds r e l a t e d t o a p a r t i c u l a r hormone, a t t e n t i o n must be drawn t o the l a r g e group o f s y n t h e t i c a u x i n s , t o the s y n t h e t i c c y t o k i n i n s (- r e c e n t l y not o n l y adenine, but a l s o u r e a de r i v a t i v e s -) and t o the e t h y l e n e g e n e r a t o r s Q , 2^). An e x t e n s i o n o f the range o f analogous compounds i s i n d i c a t e d i n the c a s e o f a b s c i s i c a c i d , as w e l l (_3)· The groups o f s u b s t a n c e s t h a t e x h i b i t a n t a g o n i s t i c b e h a v i o r t o ward a phytohormone or i n h i b i t i t s b i o s y n t h e s i s a r e e x p e r i e n c i n g



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i n t e n s e and expanding d i v e r s i f i c a t i o n . Here, p a r t i c u l a r l y t h e group of g i b b e r e l l i n antagonists o r i n h i b i t o r s ( a n t i - g i b b e r e l l i n s ) should be emphasized. T h i s group r e p r e s e n t s the s o - c a l l e d growth r e t a r d a n t s , some o f which have a t t a i n e d c o n s i d e r a b l e importance i n p r a c t i c e . I t i s s u r p r i s i n g , b u t c h a r a c t e r i s t i c o f the p l a n t b i o r e g u l a t o r s p r e s e n t l y used i n c r o p p r o d u c t i o n , t h a t most o f the b e n e f i c i a l e f f e c t s r e s u l t from growth r e t a r d a t i o n r a t h e r than from growth s t i m u l a t i o n ( 4 ) . F o r t h i s r e a s o n , t h i s group o f PBRs i s d i s c u s s e d i n more d e t a i l . Of the s u b s t a n c e s t h a t i n t e r f e r e w i t h g i b b e r e l l i n b i o s y n t h e s i s , mention s h o u l d f i r s t be made o f the s o - c a l l e d onium compounds, which a r e s u b s t a n c e s w i t h a c h a r g e d c e n t r a l atom (_5, 6), They i n c l u d e t h e a l r e a d y e x t e n s i v e l y employed b i o r e g u l a t o r s chlormequat c h l o r i d e (CCC) and mepiquat c h l o r i d e (DPC) ( F i g u r e 1 ) . Other s u b s t a n c e s w i t h an a n t i - g i b b e r e l l i n a c t i o n a r e found i n the groups o f p y r i m i d i n e s ( a n c y m i d o l ) , n o r b o r n e n o d i a z e t i n e s ( t e t c y c l a c i s ) and t r i a z o l e s ( p a c l o b u t r a z o l ) , e t c . ( F i g u r e 2 ) . I t i s an i n t e r e s t i n g f a c t t h a t some o f t h e s e s u b s t a n c e s o r i g i n a t e from groups t h a t have produced p o t e n t i a l f u n g i c i d e s . The r e t a r d a t i o n e f f e c t o f a l l t h e s e s u b s t a n c e s c a n be r e v e r s e d by g i b b e r e l l i n s . F u r t h e r m o r e , i t has been p o s s i b l e , i n t h e c a s e o f some o f t h e s e s u b s t a n c e s , t o d e t e c t p r e c i s e l y t h e p o i n t o f a t t a c k o r s i t e o f a c t i o n i n t h e g i b b e r e l l i n b i o s y n t h e s i s sequence. As c a n be seen from F i g u r e 3, i t i s assumed t h a t t h e onium compounds i n h i b i t t h e c y c l i z a t i o n o f g e r a n y l g e r a n y l pyrophosphate t o c o p a l y l p y r o p h o s phate (_7), whereas i t has been demonstrated i n c e l l - f r e e systems t h a t pyrimidines, norbornenodiazetines, and t r i a z o l e s i n h i b i t t h e sequen t i a l o x i d a t i o n o f ent-kaurene t o e n t - k a u r e n o i c a c i d 9). Morphologically t h i s biochemical process manifests i t s e l f i n the " a n t i - g i b b e r e l l i n h a b i t u s " o f the t r e a t e d p l a n t s t h a t corresponds t o compact growth w i t h s h o r t e n e d i n t e r n o d e s and t o a more i n t e n s i v e c o l o r o f l e a v e s . However, i t i s a l s o worth m e n t i o n i n g the changes i n the s h o o t - r o o t r a t i o t h a t l e a d t o a pronounced s h i f t i n f a v o r o f r o o t growth, e s p e c i a l l y a f t e r t r e a t m e n t w i t h n o r b o r n e n o d i a z e t i n e s ( 1 0 ) . The i n d u c e d i n h i b i t i o n o f l o n g i t u d i n a l growth by t e t c y c l a c i s r e s u l t s both from i n h i b i t e d c e l l e l o n g a t i o n and from reduced c e l l d i v i s i o n . The r e l a t i v e p r o p o r t i o n s t o which c e l l e l o n g a t i o n and c e l l d i v i s i o n c o n t r i b u t e t o the s h o r t e n i n g e f f e c t v a r i e d i n t r i a l s w i t h maize, s u n f l o w e r s , and soybeans, i . e . , t h e i n f l u e n c e e f f e c t e d v i a c e l l d i v i s i o n i n c r e a s e d w i t h an i n c r e a s e i n c o n c e n t r a t i o n o f the PBR. The i n h i b i t o r y e f f e c t on c e l l d i v i s i o n d e t e c t e d i n i n t a c t p l a n t s has been c o n f i r m e d i n c e l l s u s p e n s i o n c u l t u r e s o f the same p l a n t s p e c i e s (11). A f t e r t h e s e d e t a i l e d remarks about a n t i - g i b b e r e l l i n s and t h e i r mode o f a c t i o n , i t s h o u l d be emphasized t h a t t h e a c t i o n o f not a l l b i o r e g u l a t o r y a c t i v e s u b s t a n c e s c a n be a s s i g n e d so p r e c i s e l y t o an i n t e r a c t i o n w i t h a s p e c i f i c phytohormone. T h i s p a r t i a l l y a p p l i e s t o daminozide ( s u c c i n i c a c i d 2 , 2 - d i m e t h y l h y d r a z i d e ) , which i s f r e q u e n t l y c l a s s i f i e d a s a r e t a r d a n t (J). An overview o f some r e p r e s e n t a t i v e s o f t h i s heterogeneous group i s g i v e n i n T a b l e I I . The f i r s t group a g a i n i n c l u d e s s u b s t a n c e s w i t h an i n h i b i t o r y a c t i o n , which may a l s o be used i n some c a s e s f o r s u c k e r c o n t r o l and f o r p i n c h i n g ( 1 2 ) . A t t e n t i o n s h o u l d a l s o be drawn t o t h e s u b s t a n c e s t h a t i n c r e a s e t h e sugar c o n t e n t o f sugarcane (13), espe c i a l l y those o f t h e g l y c i n e t y p e .



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Table I . Overview o f Exogenous P l a n t B i o r e g u l a t o r s C l a s s i f i e d a c c o r d i n g t o T h e i r Phytohormonal I n t e r a c t i o n ( A b s t r a c t ) Reference phytohormones

Compounds with homologous or synergistic activity

Compounds with an antagonistic activity or inhibitors of biosynthesis

Auxins

Synthetic Auxins

Triiodobenzoic acid Hydroxyfluorene carboxylates

Gibberellins

Phthalimides Steroids Steviol

Onium compounds (N, S, P) Pyrimidines Norbornenodiazetines Triazoles

Cytokinins

Benzyl- and Furfurylaminopurine Phenylurea derivatives

Pyrrolo- and Pyrazolepyrimidines

Abscisins

Terpenoic analogues of ABA Farnesol

Ethylene

Aminoethoxivinyl glycine Chloroethyl phosphonic acid Aminocyclopropane carboxylic acid

Table I I . Survey on S y n t h e t i c PBR's w i t h D i f f e r e n t Modes o f A c t i o n (Examples)

effect

Retardation of growth Dwarfing

Sucker control

compound

Succinic acid 2,2-dimethyl hydrazide (daminozide) Trifluormethanesulfonanilides 6-Azauracil Maleic hydrazide Maleic hydrazide higher alcohols and fatty acids (C -C ) Dikegulac-Na 8

Pinching Stimulation of growth

4-Hydroxybenzoic acid (phthalimides, steroids)

Enhancement of sucrose content (sugarcane)

Phosphonomethylglycine (glyphosine, glyphosate)

14

Enhancement of isoprenoids (Guayule) 2-Diethylamino-ethyl-3,4-dichlorophenylether Defoliation (cotton)

N-phenyl-N'-1,2,3-thiadiazol-5-yl urea S.S.S-tributylphosphorotrithioate

Pollen suppression

1 -(p-chlorophenyl)l ,4-dihydro-6-methyl4-oxopyridazine-3-carboxylate


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charged central atom

Ν

S

Ρ

ij3* /

C


V

C H

3 cr

Cl-CHjCH -N-CH CH ccc (Chlormequat chloride) 3

2

N

C

H

S-CH / \ CH CH 3

3

3

Bra-r"VcH -p-c H C Hg 2

DIS

C±7

811

LAB 109 274 8-(4-chlorophenyl)-3,4,8dec-3-ene triazatetracyclo-4,3,1,0 ,0 25

79

OH

Triazoles

Paclobutrazol (PP 333) (4-chlorophenyl)-4,4-dimethyl-2( 1,2,4-triazol-1 -yl)pentan-3-ol

.

H

°i o

Λ

r

Λ^Ο V '' N

LAB LAB 150 978 -trifluormethylphenyl)-2;,-g.4-triazol-1 -yl)-3-(5-methyldioxan-5-yl)-propen-3-ol 1,3-1

F i g u r e 2. Growth r e t a r d a n t s : Kaurene o x i d a s e

inhibitors.


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CYCLIZATION

MVA— —MPP—GPP^FPP (Mevalonic acid)

Copalyl-PP η

[CYCLI[ZATION Pyrimidines I Norbornenodiazetines Triazoles

Gibberellin GA 3

COOH Kdurenoicacid

CHO —j—-CHoOH , 26, 27). When d e v e l o p i n g p r o j e c t s i n t h i s f i e l d , one i s n a t u r a l l y con f r o n t e d w i t h the n e c e s s i t y o f a c o n c r e t e : r e s e a r c h and

development

(R + D)

concept

I f t h e q u a n t i t a t i v e a s p e c t , i . e . , the p e r s o n n e l and f i n a n c i a l r e s o u r c e s , i s i n i t i a l l y l e f t out o f account, i t i s the b a s i c approach t h a t must be g i v e n primary a t t e n t i o n , i . e . , t h e o b j e c t i v e s and the ways i n which they can be r e a l i z e d . The g o a l t h a t i s e a s i e s t t o d e f i n e , but h a r d e s t t o a c h i e v e , i s an i n c r e a s e i n y i e l d . A f t e r s e v e r a l y e a r s o f i n t e n s i v e R + D work i t i s d i f f i c u l t - i f not even i m p o s s i b l e - t o f i n d b i o r e g u l a t o r s t h a t i n c r e a s e t h e y i e l d d i r e c t l y , and t h a t any such i n c r e a s e w i l l have t o be a c h i e v e d by i n f l u e n c i n g p a r t i a l p r o c e s s e s i n a p l a n t ' s growth and development ( 4 ) . I n n o v a t i o n i n the s e a r c h f o r s y n t h e s i s o f a c t i v e s u b s t a n c e s . In t h i s c o n n e c t i o n , " e m p i r i c a l a p p r o a c h " and " b i o r a t i o n a l d e s i g n " a r e two r e l e v a n t c o n c e p t s f o r b i o r e g u l a t o r s . Up t o now, the e m p i r i c a l ap proach or mass s c r e e n i n g s o f c h e m i c a l s have been the dominant and most s u c c e s s f u l concept f o r d i s c o v e r i n g c a n d i d a t e s w i t h adequate a c t i v i t y , when a s p e c i f i c g o a l was r e c o g n i z e d . T h i s does not mean, however, t h a t t h e i n p u t o f c r o p p h y s i o l o g y , and thus t h e " b i o r a t i o n a l d e s i g n " , c o u l d not l e a d t o a s u b s t a n t i a l i n c r e a s e i n e f f i c i e n c y i n


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the s e a r c h f o r b i o r e g u l a t o r s . B a s i c a l l y , t h e need f o r a b i o r a t i o n a l d e s i g n a r i s e s l o g i c a l l y from t h e d i v e r s i t y o f s t r u c t u r a l v a r i a t i o n . However, b i o r e g u l a t o r r e s e a r c h i s s t i l l i n t h e i n i t i a l phase as f a r as b i o r a t i o n a l d e s i g n i s c o n c e r n e d . As G e i s s b u h l e r (29) p o i n t e d o u t , t h e r e i s not s u f f i c i e n t b a s i c i n f o r m a t i o n on t h e mode o f a c t i o n o f a g r o c h e m i c a l s a t t h e b i o c h e m i c a l and m o l e c u l a r l e v e l s t o be system a t i c a l l y employed f o r b i o r a t i o n a l improvements and m o d i f i c a t i o n s . At p r e s e n t , t h e r e a r e t h e f o l l o w i n g p o s s i b i l i t i e s and a l t e r n a t i v e s as g u i d e l i n e s f o r d i s c o v e r i n g a new PBR: G u i d e l i n e s f o r d i s c o v e r i n g a new PBR a) E m p i r i c a l approach Random c h e m i s t r y D i s c o v e r y o f a c t i v i t y v i a mass s c r e e n i n g O p t i m i z a t i o n and m o d i f i c a t i o n o f a l e a d s t r u c t u r e D i s c o v e r y and e v a l u a t i o n o f s i d e - e f f e c t s b) B i o r a t i o n a l d e s i g n D e t e r m i n a t i o n and u t i l i z a t i o n o f s t r u c t u r e activity relationships M o d i f i c a t i o n o f endogenous s u b s t a n c e s w i t h p h y t o h o r monal and m e t a b o l i c a c t i v i t y E f f i c i e n c y o f t h e s c r e e n i n g systems. The q u a l i t a t i v e and q u a n t i t a t i v e e f f i c i e n c y o f t h e s c r e e n i n g system i s o f g r e a t importance f o r t h e i d e n t i f i c a t i o n o f new PBRs among a l a r g e number o f i n d i v i d u a l chemi cals. The f o l l o w i n g c h a r a c t e r i z a t i o n by C.W. Raven (33) i s p r o b a b l y t y p i c a l o f t h e p r e s e n t s t a t u s o f PBR s c r e e n i n g t e c h n i g u e s : " S e l e c t i o n from and a m i x t u r e o f a number o f company p h i l o s o p h i e s , t h e o r i e s , s t r a t e g i e s , and e x p e r i e n c e forms t h e b a s i s o f t h e modern i n d u s t r i a l s c r e e n i n g o p e r a t i o n and make i t a p r o f e s s i o n o f i t s own!" B r i e f l y , t h e methods and t e c h n i q u e s used may be grouped as f o l l o w s : Methods and t e c h n i q u e s o f PBR s c r e e n i n g systems l a b o r a t o r y b i o a s s a y s i n c l u d i n g b i o c h e m i c a l enzyme a s s a y s , c e l l and t i s s u e c u l t u r e , d e t a c h e d p l a n t o r g a n s , e t c . ; i n d o o r b i o l o g i c a l e v a l u a t i o n s on major c r o p s p e c i e s ; advanced p o t and model e x p e r i m e n t s ( e . g . t h e M i t s c h e r l i c h s y s t e m ) ; field trials. The t e s t systems t h a t have been o u t l i n e d here a r e b e i n g con s t a n t l y m o d i f i e d and adapted t o t h e p a r t i c u l a r t a s k s . In g e n e r a l , however, they have a l r e a d y been d e v e l o p e d t o t h e e x t e n t t h a t t h e PBR e f f e c t s t h a t a r e o f i n t e r e s t can be r e l i a b l y r e a l i z e d w i t h them. The f o l l o w i n g a d d i t i o n a l d e t e r m i n i n g f a c t o r s i n t h e development and performance o f PBRs s h o u l d a l s o be mentioned: t h e e f f i c i e n t p r o j e c t i o n o f a PBR i n t o c r o p management and t h e c o o r d i n a t e d a d a p t i o n t o t h e s t a t e o f development i n p l a n t b r e e d i n g and t o t h e problems w i t h t h e p a r t i c u l a r p l a n t s p e c i e s t h a t have not y e t been s o l v e d by i t . P a r t i c u l a r emphasis s h o u l d be p l a c e d on t h e l a s t p o i n t , not l e a s t because t h e view i s o f t e n e x p r e s s e d t h a t t h e g e n e t i c approach t o m o d i f y i n g c r o p c h a r a c t e r i s t i c s may be s u p e r i o r t o t h e use o f PBRs -


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(30). This no doubt applies to many cases; on the other hand, there should be an interesting chance for chemical bioregulation precisely where the same modifications are possible and desirable over a broad spectrum of different varieties of a plant species or where geneti cally fixed negative correlations between certain properties can be compensated for by bioregulators. Finally, the question of the expenditure that must be expected in developing a PBR nowadays should not be neglected. The overall costs for research, development, and registration are estimated to be in the order of $ 30 million. A figure of this order of magnitude na turally limits the number of companies interested in PBR research and development, and selects not only in terms of innovative capability but also in terms of available resources. Acknowledgments My thanks are given to Dr. C. Rentzea from BASF's Central Re search Laboratory for the synthesis of the compound LAB 150 978 and his helpful co-operation and to Mr. B.E. Byrt for the translation of the manuscript. Literature Cited 1. 2. 3. 4. 5. 6. 7.

8. 9.

10. 11. 12. 13.

Moore, T.C. "Biochemistry and Physiology of Plant Hormones"; Springer-Verlag: New York, Heidelberg, Berlin, 1979. Luckwill, L.G. "Growth Regulators in Crop Production"; Studies in Biology 129, Edward Arnold Publishers Ltd.: London, 1981. Grossmann, K.; Jung, J . J . Agronomy & Crop Science 1984, 153, 14-22. Morgan, P.W. Bot. Gaz. 1980, 141 (4), 337-46. Zeeh, Β.; König, Κ.-Η.; Jung, J . Kemia (Helsinki), 1974, 1 (9), 621-3. Sauter, H. In "Bioregulators: Chemistry and Use"; Ory, R . L . ; Rittig, F.R., Eds.; ACS SYMPOSIUM SERIES No. 257, American Chem ical Society: Washington, D.C., 1984; pp. 9-21. Dicks, J.W. In "Recent Developments in the Use of Plant Growth Retardants"; Clifford, D.R.; Lenton, J.R., Eds.; British Plant Growth Regulator Working Group, MONOGRAPH 4, Wessex Press: Wantage, 1980; pp. 1-14. Graebe, J . E . In "Plant Growth Substances"; Wareing, P . F . , Ed.; Academic: London-New York, 1982; pp. 71-80. Rademacher, W.; Jung, J.; Hildebrandt, E.; Graebe, J . E . In "Regulation des Phytohormongehaltes und seine Beeinflussung durch synthetische Wachstumsregulatoren"; Bangerth, F . , Ed.; Ulmer-Verlag: Stuttgart, 1983; pp. 132-44. Jung, J . In "Bioregulators: Chemistry and Use"; Ory, R . L . ; Rittig, F.R., Eds.; ACS SYMPOSIUM SERIES No. 257, American Chemical Society: Washington, D.C., 1984, pp. 29-43. Nitsche, K. Diploma dissertation, University of Heidelberg, West Germany, 1983. Steffens, G.L. In "Plant Growth Regulating Chemicals"; Nickell, L . G . , Ed.; CRC Press: Boca Raton/FL, 1983; Vol. I, pp. 71-88. Nickell, L.G. In "Plant Growth Regulating Chemicals"; Nickell, L . G . , Ed.; CRC Press: Boca Raton/FL, 1983; Vol. I, pp. 185-205.



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14. Bridge, K. In "Plant Growth Regulating Chemicals"; Nickell, L . G . , Ed.; CRC Press: Boca Raton/FL, 1983, Vol. I pp. 41-58. 15. Yokoyama, H.; Hsu, W.J.; Hayman, E.; Poling, S.M. In "Plant Growth Regulating Chemicals"; Nickell, L . G . , Ed.; CRC Press: Boca Raton/FL, 1983; Vol. I, pp. 59-70. 16. St. John, J . B . ; Christiansen, M.N.; Terlizzi, D.E. In "Bioregulators: Chemistry and Use"; Ory, R . L . ; Rittig, F.R., Eds.; ACS SYMPOSIUM SERIES No. 257, American Chemical Society: Washington, D.C., 1984; pp. 65-73. 17. Nickell, L.G. "Plant Growth Regulators - Agricultural Uses"; Springer-Verlag: Berlin, Heidelberg, New York, 1982; pp. 15-18. 18. Jung, J . In "Plant Regulation and World Agriculture"; Scott. R.K., Ed.; Plenum Press: New York, London, 1979; pp. 279-307. 19. Jung, J.; Rademacher, W. In "Plant Growth Regulating Chemicals"; Nickell, L . G . , Ed.; CRC Press: Boca Raton/FL, 1983; Vol. I, pp. 253-71. 20. Oplinger, E.S. Beltsville Symposium in Agricultural Research VIII, 1983 (in press). 21. Jung, J.; Koch, H.; Rieber, N.; Würzer, B. J . Agronomy & Crop Science 1980, 149 128-36. 22. Schott, P.; Knittel, H.; Klapproth, H. In "Bioregulators: Chemistry and Use"; Ory, R.L.; Rittig, F.R., Eds.; ACS SYMPOSIUM SERIES No. 257, American Chemical Society: Washington, D.C., 1984; pp. 45-63. 23. Stutte, C.A.; Davis, M.D. In "Plant Growth Regulating Chemicals"; Nickell, L . G . , Ed.; CRC Press: Boca Raton/FL, 1983; Vol.11, pp. 99-112. 24. Lürssen, K. In "Chemical Manipulation of Crop Growth and Development"; McLaren, J . S . , Ed; Butterworth Scientific: London, 1982; pp. 67-78. 25. Tolbert, E. Plant Physiol. 1960, 35, 380-5. 26. Linser, Η.; Κühn, H. Z. Pflanzenern., Düng., Bodenk. 1962, 96, 231-47. 27. Jung, J.; Sturm, H. Landw. Forsch. 1964, 17, pp. 1-9. 28. Beyer, E.M. Proc. 8th Ann. Mtg. Plant Growth Soc. Amer., 1981, pp. 161-2. 29. Geissbühler, H.; Müller, U.; Pachlatter, J . P . ; Waespe, H.R. In "Chemistry and World Food Supplies"; Shemilt, L.W., Ed.; Pergamon Press: Oxford, 1983; pp. 643-56. 30. Lurssen, K. In "Aspects and Prospects of Plant Growth Regulators"; Jeffcoat, B., Ed.; British Plant Growth Regulator Working Group, MONOGRAPH 6, Wessex Press: Wantage, 1981; pp. 241-9. 31. Lever, B.G. In "Opportunities for Chemical Plant Growth Regulation", Brit. Crop Prot. Council MONOGRAPH 21, 1978; pp. 17-24. 32. Nickell, L.G. In "Chemistry and World Food Supplies"; Shemilt, L.W., Ed.; Pergamon Press: Oxford, 1983; 601-6. 33. Raven, C.W. In "Aspects and Prospects of Plant Growth Regulators"; Jeffcoat, B., Ed.; British Plant Growth Regulator Working Group, MONOGRAPH 6, Wessex Press: Wantage, 1981; pp. 229-40. 34. Sacher, R.M. In "Chemical Manipulation of Crop Growth and Development"; McLaren, J . S . , Ed.; Butterworth Scientific: London, 1982; pp. 13-15. RECEIVED November 23, 1984


Plant Bioregulators: Overview, Use, and Development - ACS

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