Allelochemicals: Role in Agriculture and Forestry

Chapter 43

Structural and Genetic Variation of Natural Pesticides in Pigment Glands of Cotton (Gossypium) Alois A. Bell , Robert D. Stipanovic , Gary W. Elzen , and Howard J. Williams, J r . 1

1

2

2

National Cotton Pathology Research Laboratory, Agricultural Research Service, U.S. Department of Agriculture, College Station, TX 77841 Department of Entomology, Texas A & M University, College Station, TX 77841

1

Downloaded by FUDAN UNIV on January 17, 2017 | http://pubs.acs.org Publication Date: January 8, 1987 | doi: 10.1021/bk-1987-0330.ch043

1

Cotton (Gossypium) and other plants in the tribe Gossypieae contain lysigenous pigment glands in leaves and stems. The glands contain high concentrations of biologically active terpenes, including v o l a t i l e terpenes known to repel or attract insects and nonvolatile terpenoid aldehydes that have a wide range of antibiotic activity. We surveyed over 30 Gossypium species for structural and quantitative variations in these terpenes, and made interspecific crosses to analyze genetically the structural variations of terpenes. The results of these experiments and their implications for future research are discussed. The genus Gossypium includes four species cultivated for cotton fiber and over 30 wild species. The major cultivated species, G_. hirsutum, is referred to as Upland cotton and is grown throughout the world. G_. barbadense is grown mainly for thread and high quality textiles. In different countries or regions i t is known as Egyptian, Pima, Tanguis, or Sea Island cotton. G_. arboreum and G_. herbaceum are grown mostly in Asia on small acreages in marginal production areas with minimal use of agrochemicals; these species are referred to as Asiatic or Old World cottons. Gossypium and the other seven genera of the tribe Gossypieae are distinguished from other species of the Malvaceae by the production of lysigenous pigment glands (JJ. The spherical glands consist of a central cavity filled with yellow oil surrounded by a single layer of flattened epithelial cells. In green tissues the epithelial cells contain chrysanthemin and other anthocyanin pigments giving them a dark appearance (2J. In leaves and young stems the glands are located below the palisade and hypodermal cells, respectively. In old stems and roots the glands also are scattered throughout the bark. The importance of pigment glands as sources of toxins in cottonseed was suspected early in the twentieth century. In 1915 Withers and Carruth QJ showed that the toxicity of cottonseed to animals was due to the compound gossypol localized in pigment glands. 0097-6156/87/0330-0477$06.00/0 © 1987 American Chemical Society

Waller; Allelochemicals: Role in Agriculture and Forestry ACS Symposium Series; American Chemical Society: Washington, DC, 1987.


478

ALLELOCHEMICALS: ROLE IN AGRICULTURE AND FORESTRY

The s t r u c t u r e of g o s s y p o l (G; Scheme 1 ) , however, was not d e t e r m i n e d u n t i l the 1 9 4 0 ' s and was confirmed by t o t a l s y n t h e s i s i n 1958 (_4J. Gossypol i s a d i m e r i c p r o d u c t formed from hemigossypol (HG; Scheme 1) by the a c t i o n of p e r o x i d a s e (5). A l l species of Gossypieae produce g o s s y p o l i n pigment g l a n d s o f e i t h e r the seed or f o l i a g e . The i m p o r t a n c e o f p i g m e n t g l a n d s i n c o t t o n - p e s t i n t e r a c t i o n s became apparent w i t h the d i s c o v e r y o f g l a n d l e s s c o t t o n s i n t h e l a t e 1950's. These c o t t o n s s u b s e q u e n t l y were d e v e l o p e d w i t h t h e a i m o f i n c r e a s i n g the use o f c o t t o n s e e d i n animal f e e d s and i n human f o o d . In f i e l d t r i a l s , however, g l a n d l e s s p l a n t s were damaged more s e v e r e l y than glanded p l a n t s by s e v e r a l c o t t o n p e s t s , and t h e y were a t t a c k e d by s e v e r a l h e r b i v o r e s ( b e e t l e s , c u t w o r m s , p i l l b u g s , r o d e n t s , and p h e a s a n t s ) t h a t d i d not n o r m a l l y feed on glanded p l a n t s (6_). Based on t h e s e d i s c o v e r i e s , s e v e r a l p r o g r a m s were i n i t i a t e d t o d e v e l o p h i g h l y glanded (and presumably h i g h - g o s s y p o l ) c o t t o n s w i t h i n c r e a s e d r e s i s t a n c e to i n s e c t s . The t o x i c i t y o f f l o w e r buds f r o m c e r t a i n c o t t o n s , however, was g r e a t e r than c o u l d be a c c o u n t e d f o r b a s e d on t h e i r g o s s y p o l c o n t e n t s ( 7 J , w h i c h i n d i c a t e d t h a t o t h e r compounds were i n v o l v e d . C o n s e q u e n t l y , i n t h e 1 9 7 0 ' s we began a s e r i e s o f s t u d i e s to i d e n t i f y the a l l e l o c h e m i c a l s i n pigment g l a n d s . In g e n e r a l , two groups o f c h e m i c a l s , t e r p e n o i d a l d e h y d e s and v o l a t i l e t e r p e n e s , were f o u n d . D e t a i l e d d e s c r i p t i o n s of the s t r u c t u r e s , b i o l o g i c a l a c t i v i t y , b i o s y n t h e s i s , and g e n e t i c c o n t r o l o f t h e s e compounds are g i v e n i n the f o l l o w i n g s e c t i o n s . T e r p e n o i d Aldehydes

(TA)

and D e r i v a t i v e s

i n Pigment

Glands

TA i n Upland and A s i a t i c c o t t o n . When e x t r a c t s f r o m g l a n d e d and g l a n d l e s s c o t t o n s were c o m p a r e d by t h i n - l a y e r c h r o m a t o g r a p h y , we found s i x y e l l o w pigments and one r e d p i g m e n t u n i q u e l y a s s o c i a t e d with glands. Each y e l l o w pigment gave a t y p i c a l a l d e h y d e r e a c t i o n w i t h a c i d i c p h l o r o g l u c i n o l or 2 , 4 - d i n i t r o p h e n y l h y d r a z i n e . One o f the y e l l o w pigments was i d e n t i f i e d as g o s s y p o l , w h i l e the o t h e r f i v e were i d e n t i f i e d as h e m i g o s s y p o l o n e (HGQ; Scheme 2) and t h e d e r i v e d T A , h e l i o c i d e s Η , H , H , and FL ( Η Η , H H « , H h k , H H , ; Scheme 2) (8 11). H e l i o c i d e s H, a n d H , a r e t h e i s o m e r s d e r i v e d f r o m t h e D i e l s - A l d e r r e a c t i o n o f h e m i g o s s y p o l o n e w i t h t r a n s - β - o c i m e n e , and h e l i o c i d e s FL and FL are s i m i l a r l y f o r m e d f r o m h e m i g o s s y p o l o n e and myrcene (Scheme 2 ) . N e i t h e r r e a c t i o n r e q u i r e s an enzymatic c a t a l y s t , b e c a u s e t h e y o c c u r s p o n t a n e o u s l y a t room t e m p e r a t u r e . The c o n c e n t r a t i o n s o f h\ and are always two t o t h r e e times t h o s e o f and F L , r e s p e c t i v e l y , a p p a r e n t l y b e c a u s e s t e r i c h i n d r a n c e o f t h e methyl group on hemigossypolone f a v o r s the former p r o d u c t s . The r e d p i g m e n t , named g o s s y r u b i 1 one (GR; Scheme 2 ) , i s t h e c o n d e n s a t i o n p r o d u c t o f hemigossypolone and i s o p e n t y l a m i n e (12). Hemigossypolone a l o n g w i t h i t s d e r i v a t i v e s o c c u r o n l y i n t i s s u e s w i t h d i f f e r e n t i a t e d c h l o r o p l a s t s (12_). Nongreen t i s s u e s such as seed embryos, r o o t s , f l o w e r p e t a l s , stamenal t i s s u e , and i n n e r s t e m b a r k c o n t a i n o n l y g o s s y p o l as t h e p r o m i n e n t T A . T h u s , t h e key enzyme involved in d i v e r t i n g t e r p e n o i d b i o s y n t h e s i s from h e m i g o s s y p o l to hemigossypolone may be formed d u r i n g d i f f e r e n t i a t i o n o f c h l o r o p l a s t s . χ

2

3

χ


43.

BELL ET AL.

HG MHG

Natural

(R=H) (R=CH ) 3

G (R R =H) MG ( R ^ H . R = C H ) DMG (R R = C H ) v

2

2

1f


479

Pesticides in Pigment Glands of Cotton

2

3

3

Scheme 1

Scheme 2


A L L E L O C H E M I C A L S : R O L E IN A G R I C U L T U R E A N D F O R E S T R Y

480

TA i n G . barbadense c o t t o n . A n a l y s e s o f TA i n G.. barbadense c u l t i v a r s r e v e a l e d f i v e compounds n o t f o u n d i n U p l a n d or A s i a t i c c o t t o n s (12). These compounds were i d e n t i f i e d as t h e 6 - m e t h y l and 6 , 6 ' - d i m e t h y l e t h e r s of g o s s y p o l (Scheme 1; MG, DMG) and the 6-methyl e t h e r s of hemigossypolone (Scheme 2; MHGQ) and of h e l i o c i d e s and H-. The l a t t e r two c o m p o u n d s , w h i c h a r e f o r m e d f r o m o c i m e n e and MHGQ, were g i v e n the t r i v i a l names h e l i o c i d e B, and B , (Scheme 2 ; H B , , H B , ) ; the Β symbols were used f o r the m e t h y l a t e d h e l i o c i d e s t o i n a i c a t e t h e i r d i s c o v e r y i n G_. barbadense. No h e l i o c i d e d e r i v a t i v e s o f myrcene ( i . e . , H H , HH^, HB,, and HB^) were f o u n d , i n d i c a t i n g t h a t G_. barbadense does not s y n t h e s i z e a p p r e c i a b l e myrcene. Apparently m e t h y l a t i o n i s i n t r o d u c e d e a r l y i n the t e r p e n o i d b i o s y n t h e s i s pathway o f _G. barbadense, because s i m i l a r p e r c e n t a g e s of m e t h y l a t i o n (50-70%) a r e f o u n d i n a l l o f t h e d i f f e r e n t t y p e s o f TA f o u n d i n pigment glands of l e a v e s . High l e v e l s o f g o s s y p o l methyl e t h e r s a l s o are found i n nongreen t i s s u e s , i n d i c a t i n g t h a t the m e t h y l a t i n g enzyme i s not u n i q u e l y a s s o c i a t e d w i t h c h l o r o p l a s t s .


2

TA i n w i l d c o t t o n s . Many w i l d c o t t o n s have TA c o n t e n t s s i m i l a r t o t h o s e of G_. barbadense. T h u s , 30-80% m e t h y l a t i o n of t e r p e n o i d s and a p r e d o m i n a n c e o f o c i m e n e - d e r i v e d h e l i o c i d e s a l s o o c c u r s i n _G. anomalum, G_. b i c k i i , G,. c a p i t i s - v i r i d i s , GL. d a r w i n i i . G_. l o n g i c a l y x . G^. tomentosum and G_. s t u r t i a n u m (12). In the l a t t e r two s p e c i e s , the TA q u i n o n e c o n c e n t r a t i o n s a r e much g r e a t e r t h a n t h e heliocide c o n c e n t r a t i o n s , i n d i c a t i n g t h a t v e r y l i t t l e o c i m e n e or m y r c e n e i s formed i n t h e s e s p e c i e s . The w i l d New World d i p l o i d c o t t o n s c o n t a i n two TA p a t t e r n s n o t found i n o t h e r s p e c i e s . T e n o f t h e s e 12 s p e c i e s contain only g o s s y p o l or g o s s y p o l and i t s methyl e t h e r s i n p i g m e n t g l a n d s o f a l l t i s s u e s (12_). T h u s , t h e enzyme n e c e s s a r y f o r f o r m a t i o n o f TA quinones a p p a r e n t l y i s absent from g r e e n t i s s u e s i n t h e s e s p e c i e s . G_. r a i m o n d i i u n i q u e l y produces the TA raimondal (R; Scheme 3) as t h e o n l y major TA i n pigment glands (13.). This structural variation, l i k e TA quinone f o r m a t i o n , i s l i m i t e d t o g r e e n t i s s u e ; g o s s y p o l is the predominant TA i n nongreen t i s s u e . GL. a o s s v p i o i d e s i s t h e o n l y New World d i p l o i d s p e c i e s t h a t produces abundant h e m i g o s s y p o l o n e and h e l i o c i d e s H^-H^ s i m i l a r t o Upland c o t t o n . V o l a t i l e Terpenes

i n Pigment

Glands

Terpenes i n c u l t i v a t e d Upland c o t t o n s . E l z e n e t _ _ a l . (14) compared the v o l a t i l e t e r p e n e c o n t e n t o f f i v e p a i r s o f g e n e t i c a l l y s i m i l a r glanded and g l a n d l e s s c o t t o n c u l t i v a r s and s t r a i n s . In a l l pairs, the v o l a t i l e t e r p e n e c o n t e n t o f l e a v e s f r o m t h e g l a n d e d p l a n t s was more t h a n 100 t i m e s t h a t f r o m t h e g l a n d l e s s ones. Glandular l o c a l i z a t i o n o f v o l a t i l e t e r p e n e c o n t e n t was c o n f i r m e d by s t u d i e s which showed t h a t over 3% o f the o i l c o l l e c t e d from glands c o n s i s t e d o f v o l a t i l e t e r p e n e s i n a p p r o x i m a t e l y t h e same r a t i o s as f o u n d i n t o t a l p l a n t e x t r a c t s , w h i l e f l u i d s from s u r r o u n d i n g c e l l s were d e v o i d of t h e s e compounds. The t o t a l c o m p o s i t i o n o f v o l a t i l e terpenes c o l l e c t e d d i r e c t l y from pigment glands o f c a l y x e s o f ' A c a l a S J - 1 ' i s shown i n T a b l e I; s t r u c t u r e s of v o l a t i l e t e r p e n e s e m i t t e d by c o t t o n are shown i n F i g . 1.



43.

BELL ET AL.

Natural

cis. trans-farnesvl pyrophosphate

7 - O H desHG

j+CH

3

481

Pesticides in Pigment Glands of Cotton

H

Q

A

des HG

1+0

MH

Q

a

des MHG

j+O

Scheme 3


ALLELOCHEMICALS: ROLE IN AGRICULTURE AND FORESTRY


482

spathulenol

F i g u r e 1.

Volatile

gossonorol

Terpenes Emitted

from

Cotton.


43.

B E L L ET

AL.

Natural

Pesticides in Pigment Glands of

Cotton

T a b l e I. V o l a t i l e Terpene C o n c e n t r a t i o n s in O i l Pigment Glands o f C a l y x e s o f G., h i r s u t u m ' A c a l a S J - 1

Compound

ppm

11580 1929 2572 252 643 955 1286


a-Pinene β-Pinene Myrcene Ocimene Limonene a-Copaene a-Humulene

483

Collected

from

1

ppm

Compound

3-Caryophyllene 3-Caryophyllene Y-Bisabolene β-Bisabolol Spathulenol Gossonorol TOTAL

3215 129 643 7074 386 386 31050

oxide

T e r p e n e s i n G. b a r b a d e n s e and U p l a n d r a c e s t o c k s . Different c u l t i v a r s of Upland c o t t o n have s i m i l a r p r o f i l e s of volatile t e r p e n e s , but G.. barbadense and c e r t a i n i n s e c t - r e s i s t a n t T e x a s r a c e s t o c k s o f G.. h i r s u t u m (15 - 17) have p r o f i l e s d i f f e r e n t f r o m t h e cultivars. _G. barbadense lacks myrcene, γ - b i s a b o l e n e and B - b i s a b o l o l , which are major components i n c u l t i v a t e d U p l a n d c o t t o n , but i t has g r e a t e r c o n c e n t r a t i o n s o f α-copaene (18; T a b l e II).

Table II. Percentage D i s t r i b u t i o n o f V o l a t i l e T e r p e n e s Glands o f Leaves o f C u l t i v a r s and T e x a s Race S t o c k s o f and o f £ . barbadense 'Seabrook Sea I s l a n d 12B2'

Cultivars

Compound

*Data f o r

five

5-8 8-12 5-8 1-2 9-12 26-34

Allelochemicals: Role in Agriculture and Forestry

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