Specificity of Action of Allelochemicals: Diversification of Glycosides

C h a p t e r 25

Specificity of Action of Allelochemicals: Diversification of Glycosides Kevin C. Spencer

Downloaded by UNIV OF LEEDS on August 24, 2016 | http://pubs.acs.org Publication Date: January 8, 1987 | doi: 10.1021/bk-1987-0330.ch025

Department of Medicinal Chemistry and Pharmacognosy, University of Illinois at Chicago, Chicago, IL 60612

Diversification of structure of glycosides often ac companies coradiation of plant and herbivore species. In the evolutionary development of insecticidal chem i s t r i e s , plants u t i l i z e differences in glycosylation patterns as well as aglycone structure to deter herbivory. Examples of glucosinolate, cyanogenic glyco side and triterpene glycoside ramification in the Passifloraceae, Brassicaceae and Cactaceae are cor related to insect host-plant s p e c i f i c i t y . Evidence for the presence of a specific glucosidase-mediated toxification mechanism is presented, and is consi dered to represent the proximal basis for the selec tion of altered glycosylation patterns. Glycosides are elaborated by a large number of plants, and within families are often diversified in structure considerably. This diversification seems correlated with the coevolution of groups of plants with specialist herbivores. Examples are found in the Passiflora-Heliconius interaction (J_,2j and in the association of Pieris and Brassica (3.>Μ· The same phenomenon has recently been determined to occur in the Drosophila-cactus-yeast coevolved system (5,6) and may be present in the Danaiid-Asclepias and other systems Glycosides themselves are generally regarded as representing simple storage products, accumulable derivatives of the aglycone moiety (8). The fact of glycosidation is often disregarded as irrelevant in terms of potential biological a c t i v i t y , except in reducing same (9). It is certainly appreciated that glycosidasemediated enzymatic hydrolysis of glycosides (8J releases the agly cone whereby these glycosides may become active plant toxic principles, but this process is also regarded as essentially a storage-release phenomenon. 3-Glucosidases and other glycosidases have been determined to often show an exceedingly high degree of s p e c i f i c i t y toward a par ticular substrate (J_0,rj_). In recent work (_Γ2,_Π) specificity has been shown to be attributable to the structure of the aglycone. t n i s

0097-6156/87/0330-0275$06.00/0 © 1987 American Chemical Society

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

276

ALLELOCHEMICALS: ROLE IN AGRICULTURE AND FORESTRY


Several recent reviews (14-16) have i n d i c a t e d t h a t one can gener a l l y expect t o f i n d a s p e c i f i c g l y c o s i d a s e c o r r e s p o n d i n g t o a spe c i f i c g l y c o s i d e s t r u c t u r e being p r e s e n t i n t h e same p l a n t . How e v e r , t h i s necessary c o e l a b o r a t i o n has been f r e q u e n t l y o v e r l o o k e d as a f u n c t i o n a l mechanism o f e v o l u t i o n a r y change i n d i v e r s i f i e d systems o f c o e v o l v e d p l a n t s and i n s e c t s . I w i l l argue i n t h i s c h a p t e r t h a t t h e very p r o c e s s o f h y d r o l y s i s i s an event under t h e e v o l u t i o n a r y c o n t r o l o f t h e competing i n t e r e s t s o f p l a n t and i n s e c t s p e c i e s , and t h a t " t o x i c " p l a n t g l y c o s i d e s should be regarded as such o n l y i n terms o f an i n s e p a r a b l e , t a r g e t e d g l y c o s i d e - g l y c o s i d a s e system. I w i l l extend t h i s argument t o encompass t h e d i v e r s i f i c a t i o n o f such systems i n l i n e a g e s o f p l a n t s i n an e f f o r t t o c o r r e l a t e enzyme-mediated g l y c o s i d e t o x i c i t y w i t h t h e e v o l u t i o n o f host p l a n t s p e c i f i c i t y and t h e c o e v o l u t i o n o f p l a n t s and i n s e c t s . The

Passiflora-Heliconius

Interaction

The s p e c i f i c i t y o f 3 - g l u c o s i d a s e s toward t h e i r s u b s t r a t e s has been c o n f i r m e d i n t h e p r o d u c t i o n o f c y a n i d e from cyanogenic g l y c o s i d e s of Passiflora and i t s r e l a t i v e s (Table i ) . While e c o l o g i c a l l y s i g n i f i c a n t q u a n t i t a t i v e v a r i a t i o n i n s p e c i f i c i t y e x i s t s (J_>2.)> t h e more o b v i o u s degree o f s p e c i f i c i t y shown by these enzymes toward cyanogenic g l y c o s i d e s w i l l s u f f i c e f o r t h e present d i s c u s s i o n . The s p e c i f i c i t y i s such t h a t even a c r u d e l y p u r i f i e d enzyme p r e p a r a t i o n (2,15) can be used t o i d e n t i f y b i o s y n t h e t i c and s t r u c t u r a l types o f cyanogens. The p e c u l i a r o b s e r v a t i o n t h a t p a r t i c u l a r c o m b i n a t i o n s o f 3g l u c o s i d a s e s from v a r i o u s r e l a t e d s p e c i e s , o r c o m b i n a t i o n s o f 8glucosidases and s u b s t r a t e substitutes, frequently prevented expected h y d r o l y s i s (Table n ) , gave t h e f i r s t i n d i c a t i o n t h a t t h e i n t e r a c t i o n o f p l a n t enzymes c o u l d be o f importance i n t h e Passiflora-Heliconius system. The same i n h i b i t o r y i n t e r a c t i o n has s i n c e been observed i n i n s e c t - p l a n t g l u c o s i d a s e c o m b i n a t i o n s ( 1 7 ) . The c y c l o p e n t e n o i d cyanogenic g l y c o s i d e s undergo h y d r o l y s i s a c c o r d i n g t o t h e r e a c t i o n i l l u s t r a t e d i n F i g u r e 1. T h i s two-step p r o c e s s i s e n t i r e l y c o n s i s t e n t w i t h t h a t determined f o r o t h e r cyan ogenic g l y c o s i d e s ( T8). The second step i s t h e r m o d y n a m i c a l l y f a v o r e d , and o c c u r s r a p i d l y a t normal c e l l pH even i n t h e absence o f α - h y d r o x y n i t r i l e lyase. The p r o d u c t i o n o f a 2-cyclopenteny1 ketone i s unique t o c y c l o p e n t e n o i d h y d r o l y s i s . T h i s f a c t i s o f b i o l o g i c a l importance, as the ketone i s an a,β-unsaturated compound, and has been determined t o be a powerful a l k y l a t i n g agent ( F i g u r e 2) ( 6 , ^ 9 ) . While HCN i s a g e n e r a l t o x i n which reduces f i t n e s s i n many organisms (6,J_7,20_ and r e f e r e n c e s t h e r e i n ) , i t i s t h e ketone moiety which c o n f e r s s p e c i f i c t o x i c i t y upon t h e Passiflora cyanogenic g l y c o s i d e s . Preliminary data i n d i c a t e t h a t t h e a l k y l a t i o n r e a c t i o n i s so r a p i d and non s p e c i f i c as t o t h e o r e t i c a l l y p r e c l u d e t h e s u c c e s s f u l development o f a s p e c i f i c p o s t - h y d r o l y s i s r e s i s t a n c e i n an h e r b i v o r e . The i n s e c t s p e c i e s i s t h e r e f o r e h i g h l y induced t o produce a d e f e n s i v e c a p a b i l i t y that prevents h y d r o l y s i s a l t o g e t h e r . This s e l e c t i v e pressure i s not a t a l l n e c e s s a r i l y t h e same as would induce t h e development of a defense a g a i n s t HCN.


25.

SPENCER

Table I.

Specificity

S p e c i f i c i t y of

of Action

of

β-Glucosidases

o f Passif'lora


Enzyme P r e p a r a t i o n

Species

eu

ω

ulmifolïa

-

-

-

+++

foetida

+++

Passiflora

and R e l a t e d

Compound

ω Turnera

277

Allelochemicab

+ -

+

-

-

-

-

-

-

-

-

-

+++

-

-

+++

P. caeruJea

-

-

+++

Ρ·

trifasciata

-

-

-

-

-

-

Ρ·

suberosa

-

-

-

-

-

-

-

-

+++

+

P. coriacin

-

-

-

-

-

-

-

-

+

+++

Emulsin

-

+++

-

+++

-

P. X alatocaerulea

(Sigma)

+++

-

+ +

-

+

+

-

-

+++

-

-

-

L i namarase Gynocardia

-

odorata


+++

278

Table


II.

Inhibition

o fNatural

β-Glucosidase A c t i v i t y by A d d i t i o n o f S i m i l a r of Competing Substrates


C o m b i n a t i o n s o f Enzyme P r e p a r a t i o n s and C y a n o g e n i c Compounds

Compound

T. ulmifolia

+ P. X alatocaerulea

T. ulmi folia

+ emu 1 s i η

T. ulmifolia

+ linamarase

(+)

T. ulmifolia

+ P. foetida

-

P. X alatocaerulea P. foetida

+ emulsin

P. biflora

+ P. trifasciata

+

+ P. foetida

-

(+)

-

G.

+ P. trifasciata + amygdalin

+ tetraphyllin

Β

H

C

N

(+)

-

-

+ prunasin

^

HO*

-

-

-

odorata + l i n a m a r i n

P. X alatocaerulea

-

-

P. coriacea

Emulsin

-

(+)

-

ulmifolia

-

-

P. suberosa + P. biflora

T.

Glucosidases

-

Plant

ff-glucosid^se

glucose

'O-glucose

N>

(Unstable)

Toxic

H o J

LCN

α-hydroxynitrile^

H

0

J

Ί

Q

+

Toxic

Figure

1.

3-Glucosidase-mediated cyanogenic

hydrolysis

HCN

T

of

o

x

i

c

cyclopentenoid

glycosides.



25.

SPENCER

Specificity

of Action of

Allelochemicab

279

in vitro s t u d i e s i n t h i s l a b o r a t o r y have e s t a b l i s h e d t h a t s p e c i f i c r e s i s t a n c e s to t o x i f i c a t i o n by c y c l o p e n t e n o i d cyanogenic g l y c o s i d e s e x i s t i n Heliconius and i t s r e l a t i v e s , and t h a t the process i n v o l v e s the s p e c i f i c i n h i b i t i o n of the h y d r o l y s i s of the compounds present i n the host p l a n t ( ] _ , 2 j . While the a c t u a l mechanism has not been s a t i s f a c t o r i l y q u a n t i t a t i v e l y demonstrated, our data a r e c o n s i s t e n t w i t h the models i l l u s t r a t e d i n F i g u r e 3 · In the f i r s t r e a c t i o n , the Heliconius 8-g1ucosidase b i n d s t o the p l a n t substrate-enzyme complex, e i t h e r d u r i n g or a f t e r complex f o r m a t i o n , in a c o m p e t i t i v e manner. The o n e - s u b s t r a t e , two-enzyme complex p r e c i p i t a t e s out o f s o l u t i o n . In the second r e a c t i o n , the Heliconius 8 - g l u c o s i d a s e and/or o t h e r g l y c o s i d a s e s a c t u a l l y a t t a c k and h y d r o l y z e the p l a n t 8 - g l u c o s i d a s e . Both r e a c t i o n s have been measured in vitro and appear t o occur i n vivo ( 6 , 1 7 ) » Both r e a c t i o n s a r e h i g h l y s u b s t r a t e s p e c i f i c , and both r e s u l t i n the i n a c t i v a t i o n of the p l a n t 8 - g l u c o s i d a s e and prevent h y d r o l y s i s . The s p e c i f i c i t y o f the r e a c t i o n i s such t h a t the p r o d u c t i o n o f Heliconius i n h i b i t o r y enzymes must be regarded as a c o e v o l v e d response t o the s p e c i f i c Passiflora tox i f i c a t i o n system (cyanogenic g l y c o s i d e p l u s 8 - g l u c o s i d a s e ) which i s t a r g e t e d a g a i n s t i t . The i n t e r a c t i o n o f the Passiflora 8 - g l u c o s i d a s e and cyanogenic g l y c o s i d e w i t h a s p e c i a l i z e d Heliconius h e r b i v o r e i s summarized i n Figure 4. Glucose i s assumed as the model sugar moiety. Here, i n response t o the development o f an i n s e c t 3-g'lucosidase c a p a b l e o f i n a c t i v a t i n g the p l a n t t o x i f i c a t i o n syndrome, the p l a n t s p e c i e s may e v o l v e any one or more o f the f o l l o w i n g changes: 1) m o d i f i c a t i o n o f aglycone s t r u c t u r e . T h i s o c c u r s i n Passiflora through the a t t a c h ment o f d i f f e r e n t s u b s t i t u e n t s or replacement of the double bond w i t h a s i n g l e bond or e p o x i d e , or through changes i n symmetry. 2) M o d i f i c a t i o n o f the sugar m o i e t y , through a change i n number, type or l i n k a g e of sugar s u b s t i t u e n t s . 3) Change i n cyanogenic g l y c o s i d e s k e l e t a l type through an a l t e r a t i o n i n the b i o s y n t h e t i c pathway t o another p r e c u r s o r t o y i e l d an a l t e r n a t e type cyanogenic g l y c o s i d e ( i . e . c y c l o p e n t e n o i d becomes a r o m a t i c as 2 - c y c l o p e n t e n y l g l y c i n e i s r e p l a c e d w i t h p h e n y l a l a n i n e as p r e c u r s o r ) , k) P r o duction of ionically destabilized cyanogenic g l y c o s i d e s ; in Passiflora by attachment o f a s u l f a t e a t C-4. 5) P r o d u c t i o n o f c y a n o h y d r i n s through the o m i s s i o n of the f i n a l g l y c o s y l a t i o n s t e p in b i o s y n t h e s i s . T h i s r e s u l t s i n an e x c e e d i n g l y u n s t a b l e form o f cyanogenic compound ( a - h y d r o x y n i t r i l e ) which, having no sugar m o i e t y , no longer r e q u i r e s a 8 - g l u c o s i d a s e f o r h y d r o l y s i s . 6) Change i n s t r u c t u r e of the p l a n t 8 - g l u c o s i d a s e complement: a) t o f a c i l i t a t e h y d r o l y s i s o f an a l t e r e d s t r u c t u r e , b) t o r e s i s t b i n d i n g and i n a c t i v a t i o n by a g i v e n i n s e c t 8 - g l u c o s i d a s e , c) t o h y d r o l y z e i n s e c t 8 - g l u c o s i d a s e s (not y e t o b s e r v e d ) . The

Pierid-Cruciferae

Interaction

Given the r a p i d r a d i a t i o n o f many s p e c i f i c p l a n t g l u c o s i d a s e - s u b s t r a t e systems and the c o r a d i a t i o n o f s p e c i f i c i n s e c t a d a p t a t i o n s in the Passiflora-Heliconius c o e v o l u t i o n a r y i n t e r a c t i o n , i t seems q u i t e r e a s o n a b l e t o expect t h a t such a process would occur i n o t h e r systems. As the d i s c o v e r y of the d i v e r s i f i c a t i o n o f cyanogenic g l y c o s i d e s i n Passiflora was the p r e r e q u i s i t e f o r i n t e r p r e t i n g the co-



280

RN 2

R C:" 3

H

H

if

R"

R RN 2

R"


F i g u r e 2.

3 - A l k y l a t i n g property of 2-cyclopentenones derived from h y d r o l y s i s o f c y c l o p e n t e n o i d cyanogenic g l y c o s i des.

Hel iconius /3-gl ucosidase

P a s s i f l o r a /3-glucosidase (may be glycoprotein)

HO,

HO,

1.

+

glucose

+

HCN

p r e c i p i t a t i o n , no hydrolysis

HO H

H

=0

d-glu

H

° ^ k > H^

i n a c t i v a t i o n , no hydrolysis C

N

O-glu

F i g u r e 3·

Two h y p o t h e t i c a l mechanisms by which Heliconius may p r o t e c t i t s e l f from t o x i f i c a t i o n by Passiflora cyanogen i c g l y c o s i d e s .



SPENCER

Figure 4 .

Specificity

of Action

ofAllelochemicals

Chemical responses o f Passif'lora t o s p e c i a l i z a t i o n by Heliconius . See t e x t f o r e x p l a n a t i o n o f numbered responses.



282


e v o l u t i o n o f Passiflora and Heliconius, a s i m i l a r coevolved system w i t h a d i v e r s i f i e d g l y c o s i d e c h e m i s t r y should p r o v i d e a l o g i c a l comparison o f t o x i f i c a t i o n p r o c e s s e s . The c r u e i f e r - P i e r i d i n t e r a c t i o n i s p a r t i c u l a r l y w e l l s t u d i e d (2>ÎL>iLL) and i s thought t o r e p r e s e n t an i n t r i c a t e l y coevolved system. Species i n t h e C r u c i f e r a e c h a r a c t e r i s t i c a l l y e l a b o r a t e g l u c o s i n o l a t e s ( t h i o g l u c o s i d e s ) . A l a r g e number ( > 7 5 ) have been d e s c r i b e d from t h e f a m i l y ( 2 2 , 2 3 _ ) , r e p r e s e n t i n g a c o n s i d e r a b l e d i v e r s i f i c a t i o n i n s t r u c t u r e when compared t o g l u c o s i n o l a t e prod u c t i o n in o t h e r f a m i l i e s ( 4 ) . These compounds are b i o s y n t h e s i z e d i n a pathway e n t i r e l y a n a l ogous t o t h a t o f cyanogenic g l y c o s i d e s ( 2 4 ) , and a r e h y d r o l y z e d t o t o x i c (25) i s o t h i o c y a n a t e s by 3 - t h i o g l u c o s i d a s e i n a p r o c e s s a n a l o gous t o t h e h y d r o l y s i s o f cyanogenic g l y c o s i d e s ( 2 6 ) . The subs t r a t e and enzyme may a l s o be compartmentalized w i t h i n t i s s u e s i n the same way as cyanogenic g l y c o s i d e s and g l u c o s i d a s e ( 2 8 - 3 1 ) . $ T h i o g l u c o s i d a s e (myrosinase) has long been c o n s i d e r e d , a t l e a s t de facto* t o c o n s i s t o f o n l y a s i n g l e enzyme a c t i v i t y ( 4 ) . However, myrosinase has been determined t o be a f a m i l y o f isoenzymes ( a l s o glycoproteins) ( 2 7 ) . While t h e host s p e c i f i c i t y o f Pieris and i t s r e l a t i v e s t o c r u c i f e r s p e c i e s has been i n t e r p r e t e d as a stepwise r e c i p r o c a l s e l e c t i v e response t o e v o l u t i o n a r y changes i n g l u c o s i n o l a t e chemi s t r y ( 3 2 ) , f u r t h e r s y n t h e s i s has proved d i f f i c u l t . Because o f t h e i n t e r p r e t a t i o n o f t h e t o x i c a c t i v i t y as r e s i d i n g i n t h e g l u c o s i n o l a t e s a l o n e , as r e l e a s e d by a n o n s p e c i f i c a c t i v a t i n g enzyme, a n a l y s e s become compounded by t h e a p p a r e n t l y widespread d i s t r i b u t i o n o f many compounds i n v a r i o u s c o m b i n a t i o n s . The d e f e n s i v e v a l u e o f the g l u c o s i n o l a t e a r r a y s , and t h e i r importance as s e l e c t ive agents i n t h e c o e v o l u t i o n o f t h e C r u c i f e r a e and t h e P i e r i d a e , have been w e l l e x p l o r e d ( 3 3 - 3 5 ) . However, a p l a u s i b l e mechanism f o r r e c o g n i t i o n and t o l e r a n c e o f these compounds remains e l u s i v e . I s o l a t i o n s were made o f t h i o g l u c o s i d a s e f r a c t i o n s from e i g h t p l a n t s i n the C r u c i f e r a e and s e v e r a l o t h e r s known t o produce g l u c o s i n o l a t e s . Each showed a number o f s p e c i f i c t h i o g l u c o s i d a s e a c t i v i t i e s t o be present upon s e p a r a t i o n by g e l e l e c t r o p h o r e s i s and assay f o r SCN~ r e l e a s e a f t e r treatment w i t h a v a r i e t y o f s u b s t r a t e s Combinations o f enzymes i n h i b i t e d expected h y d r o l y s i s o f a s u b s t r a t e i n an experiment c o n s t r u c t e d a c c o r d i n g t o Table I I . Enzyme f r a c t i o n s from d i f f e r e n t p l a n t s p e c i e s r e l e a s e SCN~ a t d i f f e r e n t r a t e s when s i n i g r i n , s i n a l b i n , benzyl g l u c o s i n o l a t e , and g l u c o s i n o l a t e - c o n t a i n i n g f r a c t i o n s o f each p l a n t were used as substrate. The spécificités showed were s i g n i f i c a n t b u t were n o t as r e s t r i c t e d as was observed f o r g l u c o s i d a s e s m Table I . This i s t o be expected as a f a r g r e a t e r number o f g l u c o s i d e s and enzymes appear t o be present in the l a t t e r samples than i n the p r e v i o u s experiment. Enzyme p r e p a r a t i o n s o f t h r e e Pieris s p e c i e s each c o n t a i n e d 3t h i o g l u c o s i d a s e a c t i v i t y , a f a c t p r e v i o u s l y r e p o r t e d ( 3 6 . ) , and each i n h i b i t e d h y d r o l y s i s i n one o r more c o m b i n a t i o n s w i t h a p l a n t enzyme-substrate system. These data a r e being q u a n t i f i e d and extended t o i n c l u d e i n s e c t / p r e f e r r e d h o s t - p l a n t p a i r s . The Pieris-crucifer i n t e r a c t i o n t h e r e f o r e seems t o i n v o l v e t h e same b i o c h e m i c a l parameters as t h e Passiflara-Heliconius intera c t i o n , and i t i s proposed t h a t t h e e v o l u t i o n o f host p l a n t s p e c i f i c i t y has proceeded i n an analogous f a s h i o n i n both systems.


25.

SPENCER

Specificity

of Action


The Drosophila-Cactus-Yeast

of

Allehchemicab

283

Interaction

The i n t e r a c t i o n between Drosophila, y e a s t s and columnar c a c t i o f the Sonoran Desert has been the s u b j e c t o f much recent i n t e r e s t (37)« As a c o e v o l v e d system, perhaps more i s known about t h i s i n t e r a c t i o n than any o t h e r . The c h e m i s t r y o f the c a c t i (70 spp.) has been p o s t u l a t e d t o p l a y a s i g n i f i c a n t r o l e i n the e s t a b l i s h m e n t of t h i s system (38), but t h i s was based upon r e p o r t s o f a r e l a t i v e l y small number o f r e l a t i v e l y s i m p l e a l k a l o i d s , and a small number o f t e r p e n o i d compounds. Only r e c e n t l y , the d i v e r s i f i c a t i o n o f p l a n t compounds has been d i s c o v e r e d t o be much g r e a t e r (5.). In t h e i r s e c t i o n on a l k a l o i d s i n t h e above work, B a j a j and McLaughlin r e p o r t the presence o f some t h i r t y - f i v e s t r u c t u r e s . In a d d i t i o n , I have been a b l e t o i s o l a t e some s i x t y t r i t e r p e n o i d g l y c o s i d e s ( s t r u c t u r e s were not determined) and more were d e t e c t e d but not i s o l a t e d . P r e v i o u s l y (39.), some s i x t e e n d i s t i n c t t r i t e r p e n e s k e l e t o n s i n two c l a s s e s were i s o l a t e d and r e p o r t e d from t h i s group o f c a c t i . Standard i s o l a t i o n procedure f o r these compounds r e q u i r e s h y d r o l y s i s of sugars, so the g l y c o s i d i c s t r u c t u r e s have not been d e s c r i b e d . As the data p r e s e n t e d p r e v i o u s l y imply, i n d i v i d u a l g l y c o s i d e s a r e t h e compounds o f e c o l o g i c a l i n t e r e s t . A l a b o r a t o r y study was undertaken t o determine the l i k e l i h o o d t h a t c a c t u s t r i t e r p e n o i d g l y c o s i d e s a r e important f a c t o r s i n t h e h o s t - p l a n t c h o i c e o f d e s e r t Drosophila (6). A f e e d i n g experiment was conducted u s i n g f i e l d c o n c e n t r a t i o n s of t h e a l k a l o i d a l f r a c t i o n and the t o t a l t r i t e r p e n o i d g l y c o s i d e f r a c t i o n o f t h i r t y r e l a t e d s p e c i e s o f columnar c a c t i (most i n t h e Pachycereeae). S u r v i v o r s h i p was measured as + o r - and i n d i c a t e s s u c c e s s f u l development, p u p a t i o n and emergence a f t e r eggs were l a i d by s e v e r a l D. melanogaster o r D . mojavensis f e m a l e s . The l a t t e r s p e c i e s i s a d e s e r t f l y known t o s p e c i a l i z e on s e v e r a l s p e c i e s o f Pachycereeae; t h e former i s a n o n s p e c i a l i z e d , nondesert s p e c i e s . Heliothis zea l a r v a e were a l s o used i n a separate b i o a s s a y o f t o x i c i t y where compounds were added t o commercial d i e t . T r i t e r p e n o i d g l y c o s i d e s are hydrolyzed to y i e l d aglycone ketones and d i o l s by 3 - g l u c o s i d a s e s . Assays o f p l a n t m a t e r i a l s showed these enzymes t o be p r e s e n t . It i s known t h a t c a c t o p h i l i c y e a s t s a r e a b l e t o h y d r o l y z e t e r p e n o i d g l y c o s i d e s (38J. I t was determined t h a t p l a n t s and y e a s t s h y d r o l y z e d i f f e r e n t g l y c o s i d e s a t different rates. In the p r e s e n t experiment, commercial baker's y e a s t was u t i l i z e d f o r Drosophila f e e d i n g t r i a l s . I t was p o s s i b l e t o d e t e c t h y d r o l y s i s o f g l y c o s i d e s and a r r a y s o f g l y c o s i d e s i n t r i t e r p e n o i d f r a c t i o n s through the p r o d u c t i o n o f f r e e sugars and the d e g r a d a t i o n o f i n d i v i d u a l compounds as r e v e a l e d by s p e c i f i c c o l o r reagents and TLC. Many t r i t e r p e n o i d s underwent h y d r o l y s i s , but a l k a l o i d s d i d n o t . S p e c i f i c d i f f e r e n c e s i n t o x i c i t y toward each t e s t s p e c i e s were d i s c o v e r e d between t h e v a r i o u s p l a n t chemical a r r a y s . Table I I I l i s t s s u r v i v o r s h i p f o r these species f o r a l k a l o i d - p r o d u c i n g c a c t i . A d d i t i o n a l l y , data was o b t a i n e d f o r 20 s p e c i e s i n which a l k a l o i d s were not d e t e c t e d . The t h r e e i n s e c t s p e c i e s showed c o n s i s t e n t d i f f e r e n c e s i n t o l e r a n c e toward g i v e n p l a n t s p e c i e s , w i t h no c l e a r phylogenetic pattern accounting f o r t h i s . I n s e c t s a l s o responded d i f f e r e n t l y t o a l k a l o i d a l f r a c t i o n s versus t r i t e r p e n o i d g l y c o s i d e f r a c t i o n s . A l k a l o i d s were found t o be g e n e r a l l y not t o x i c t o D.


284



Table I I I . S u r v i v o r s h i p o f Drosophila and Heliothis Upon A l k a l o i d a l and T r i t e r p e n o i d G l y c o s i d e E x t r a c t s o f A l k a l o i d - P r o d u c i n g Columnar C a c t i

TRI

ALK D mel

Stenocereus

D moj

D moj

stellatus treleasei

+

beneckei

+

quevedonis

+

duwortieri

+

Pola skia

chende

+

Escontria

chiotilla

+

Lemaireocereus

H zea D mel

hollianus

+

humilis Pterocereus

gauneri


H zea


25.

SPENCER

Specificity of Action of Allebchemicals

285

mojavensis ( t o l e r a t e d 90$ o f p l a n t s p e c i e s ) , y e t t r i t e r p e n o i d g l y c o s i d e s from 60$ o f t h e a l k a l o i d - p r o d u c i n g and from 80$ o f nona l k a l o i d - p r o d u c i n g p l a n t s were l e t h a l . D. melanogaster grew suc c e s s f u l l y upon 40$ o f a l l t r i t e r p e n o i d f r a c t i o n s , and somewhat l e s s (30$) o f a l k a l o i d f r a c t i o n s . H. zea performed c o n s i s t e n t l y b e t t e r on t r i t e r p e n e f r a c t i o n s (60$+) than on a l k a l o i d f r a c t i o n s (40$+). In terms o f c o m p a r a t i v e performance upon e x t r a c t s from i n d i v i dual p l a n t s p e c i e s , D· melanogaster and D. mojavensis showed d i f f e r e n t t o l e r a n c e on 80$ o f p l a n t s p e c i e s whether t e s t e d a g a i n s t t r i t e r p e n o i d s or a l k a l o i d s . From t h e s e p r e l i m i n a r y d a t a , i t can be c o n c l u d e d t h a t : 1) t r i t e r p e n o i d g l y c o s i d e s are h y d r o l y z e d by y e a s t s t o y i e l d a g l y c o n e s t h a t a r e s e l e c t i v e l y t o x i c t o D· mojavensis a t f i e l d l e v e l s . 2) Cactus a l k a l o i d a r r a y s a r e not g e n e r a l l y t o x i c t o D. mojavensis a t f i e l d levels. 3) Non-adapted and n o n - s p e c i a l i z e d i n s e c t s do not e x h i b i t s e l e c t i v e t o l e r a n c e toward any g i v e n compound a r r a y s , and are s u s c e p t i b l e t o t o x i f i c a t i o n by e i t h e r a l k a l o i d s o r t r i t e r p e n o i d g l y c o s i d e s or both. 4) T r i t e r p e n o i d g l y c o s i d e s may be s p e c i f i c a l l y t a r g e t e d a g a i n s t Drosophila more than o t h e r i n s e c t s , and a l k a l o i d s may be l e s s s p e c i a l i z e d t o x i n s . T h i s would t h e r e f o r e be analogous t o t h e s e p a r a t i o n o f s p e c i f i c ( a g l y c o n e ) and general (HCN) t o x i c p r i n c i p l e s i n the Passiflora-Heliconius interaction. F u r t h e r work i s being conducted u s i n g s p e c i a l i z e d y e a s t s and other s p e c i e s o f Drosophila and q u a n t i f y i n g d i f f e r e n c e s i n h y d r o l y s i s and t o x i c i t y o f g l y c o s i d e s under these c o n d i t i o n s . We may h y p o t h e s i z e f o r the p r e s e n t t h a t columnar c a c t i produce a l k a l o i d s as a general d e t e r r e n t t o h e r b i v o r y , and t r i t e r p e n o i d g l y c o s i d e s and a s s o c i a t e d h y d r o l y t i c g l y c o s i d a s e s as a s p e c i f i c t o x i f i c a t i o n mechanism a g a i n s t s p e c i a l i s t Drosophila species. R a d i a t i o n and d i v e r s i f i c a t i o n o f t r i t e r p e n o i d s may have o c c u r r e d i n response t o c o n t i n u e d i n t e r a c t i o n between the c a c t i and Drosophila · T h i s p r o c e s s i s dependent upon c o e v o l u t i o n w i t h s p e c i a l i z e d y e a s t s which may i n t e r f e r e w i t h h y d r o l y s i s o f t r i t e r p e n o i d s o r h y d r o l y z e i n d i v i d u a l compounds s e l e c t i v e l y . Other Systems G l y c o s i d e d i v e r s i f i c a t i o n a l s o has o c c u r r e d i n t h e c o e v o l u t i o n o f monarch b u t t e r f l i e s and milkweeds (7.). I t may be d e s i r a b l e t o r e l a t e the t o x i c i t y of cardenolides t o the h y d r o l y t i c c a p a b i l i t i e s o f s u s c e p t i b l e and n o n s u s c e p t i b l e insects. Cardenolides from Asclepias s p e c i e s can be h y d r o l y z e d by 3 - g l u c o s i d a s e s p r e s e n t i n the p l a n t (β), y e t s p e c i a l i z e d Danaus s p e c i e s are a b l e t o s e q u e s t e r these compounds, a process which r e q u i r e s c o n t r o l o f h y d r o l y s i s . P l a n t 3 - g l u c o s i d a s e s a l s o cause h y d r o l y s i s o f i r i d o i d g l y c o s i d e s , and a r e h i g h l y s p e c i f i c i n a c t i v i t y (6). S e v e r a l i n s e c t s p e c i e s t h a t a r e a b l e t o t o l e r a t e i r i d o i d s have been found t o con t a i n i n h i b i t o r y 3-glucosidases. These and o t h e r systems a r e under continuing investigation in this laboratory. Ecoregulatory

Processes

Recent work (kQ) has shown t h a t p l a n t t a n n i n s are c a p a b l e o f i n a c t i v a t i n g p l a n t 3-glucosidases in vitro. I t has been determined (6) t h a t i n s e c t 3 - g l u c o s i d a s e s are a l s o i n a c t i v a t e d by p l a n t t a n n i n s a t


286



f i e l d l e v e l s ( F i g u r e 5 ) . Heliconins 3-glucosidase f r a c t i o n s have been assayed f o r t h e i r a b i l i t y t o i n h i b i t in vitro Passiflora 3g l u c o s i d a s e h y d r o l y s i s o f e y e l o p e n t e n o i d cyanogenic g l y c o s i d e s (£, 17) » A f t e r treatment w i t h t a n n i n s , t h e i n s e c t enzyme f r a c t i o n s were d i a l y z e d t o recover s o l u b l e g l u c o s i d a s e a c t i v i t y . The remain ing i n h i b i t o r y a b i l i t y was determined through q u a n t i t a t i v e measure ment o f HCN r e l e a s e i n t h e t e s t r e a c t i o n . It i s p o s s i b l e t h a t t h e s e e c o r e g u l a t o r y enzymes, used by t h e i n s e c t t o i n h i b i t t a r g e t e d p l a n t t o x i f i c a t i o n systems, may them s e l v e s be t h e p r i n c i p a l t a r g e t o f t h e p r o d u c t i o n o f t a n n i n s by plants. The d i s c o v e r y o f o t h e r examples o f secondary chemical i n t e r a c t i o n s w i t h enzymes d e d i c a t e d t o t h e r e g u l a t i o n o f t o x i f i c a t i o n and d e t o x i f i c a t i o n mechanisms may be expected as our knowledge o f c h e m i c a l l y mediated ρ I a n t - i n s e c t i n t e r a c t i o n expands.

8.0-1

7-oH

Relative 66.0 r a t e of hydrolysis of 55.0H Passiflora cyanogens as 44.0H HCN r e l e a s e d (yg * 10) 3.0H

2.0H

0

0.01

0.1

Tannin

1.0

10.0 100.0

(mg/mL)

(Quebracho, w a t t l e , see R e f . 40) F i g u r e 5.

Tannin i n h i b i t i o n o f Heliconius i n t e r f e r e w i t h cyanogènes is o f

chestnut,

3-glucosidases Passiflora.


that

SPENCER

25.

Specificity of Action of Allelochemicals

287


Summary Plant lineages exhibiting diversification of glycosides should more properly be regarded as having produced a diverse set of glycoside/glycosidase systems. These are generally toxic, owing their toxicity to the structures of one or more of the hydrolysis products and to the fact of successful hydrolysis. The effectiveness of the glycoside-derived toxin also depends upon inhibitory glycosidases present in the target insect digestive system which can inhibit hydrolysis through competitive interaction with the substrateenzyme complex, or through direct hydrolytic action against the plant enzyme. Plant tannins may interact directly with the enzymes responsible for hydrolysis, and may therefore be targeted against insect ecoregulatory enzymes. This underscores the importance of regarding plant allelochemicals as one part of complex targeted toxification systems. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18.

Spencer, K.C. In "Chemical Mediation of Coevolution"; Spencer, K.C., Ed.; Pergamon Press: New York, 1986; in preparation. Spencer, K.C. Ph.D. Thesis, University of Illinois, Urbana, 1984. Feeny, P. Ann. Missouri Bot. Gdn. 1977, 64, 221-234. Rodman, J.E. In "Phytochemistry and Angiosperm Phylogeny"; Young, D.A.; Seigler, D.S., Eds.; Praeger Press: New York, 1981; p. 43. Gibson, A.C.; Spencer, K.C.; Bajaj, R.; McLaughlin, J.L. The Everchanging Landscape of Cactus Systematics. Ann. Missouri Bot. Gdn., in press. Spencer, K.C, in preparation. Brower, L.P. In "Chemical Mediation of Coevolution"; Spencer, K.C., Ed.; Pergamon Press: New York, 1986; in preparation. Hosel, W. In "the Biochemistry of Plants"; Stumpf, P.K.; Conn, E.E., Eds.; Academic Press: New York, 1981 ; Vol. 7, p. 725. Pridham, J.B. Ann. Rev. Plant Physiol. 1965, 16, 13-36. Hosel, W.; Nahrstedt, A. Hoppe Seyler's Z. Physiol. Chem. 1975, 356, 1265-1275. Nahrstedt, Α.; Hosel, W.; Walther, A. Phytochemistry 1979, 18, 1137-1141. Hosel, W.; Conn, E.E. Trends Biochem. Sci. 1982, 7, 219-221. Dale, M.P.; Emsley, H.E.; Kern, K.; Sastry, K.A.R.; Byers, L.D. Biochemistry 1985, 24, 3530-3539. Nisizawa, K.; Hashimoto, J. In "The Carbohydrates"; Pigman, W.; Horton, D., Eds.; Academic Press: New York, 1970; 2nd ed., Vol. 2A, Ch. 33. Spencer, K.C.; Seigler, D.S. Phytochem. Bull. 1984, 16, 13-21. Conn, E.E. In "Herbivores: Their Interaction with Secondary Plant Metabolites"; Rosenthal, G.A.; Janzen, D.H., Eds.; Academic Press: New York, 1979; p. 387. Spencer, K.C.; Smiley, J.T., in preparation. Hosel, W. In "Cyanide in Biology"; Vennesland, B.; Conn, E.E.; Knowles, C.J.; Westley, J.; Wissing, F., Eds.; Academic Press: New York, 1981; p. 217.


288

19. 20. 21. 22. 23. 24. 25.


26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38.

39. 40.

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

H a l l , I.H.; Lee, K.H.; Mar, E.C.; Starnes, C.O.; Waddell, T.G. J. Med. Chem. 1977, 20, 333-337. Jones, D.A. In "Cyanide in Biology"; Vennesland, B.; Conn, E.E.; Knowles, C.J.; Westley, J . ; Wissing, F., Eds.; Academic Press: New York, 1981; p. 509. Chew, F.S.; Rodman, J.E. In "Herbivores: Their Interaction with Secondary Plant Metabolites"; Rosenthal, G.A.; Janzen, D.H., Eds.; Academic Press: New York, 1979; p. 271. Kjaer, Α.; Larsen, P.O. Biosynthesis 1973, 2, 71-105. Kjaer, Α.; Larsen, P.O. Biosynthesis 1976, 4, 179-203. Conn, E.E. Naturwissenschaften 1979, 66, 28-34. Van Etten, C.H.; Tookey, H.L. In "Herbivores: Their Interac tion with Secondary Plant Metabolites"; Rosenthal, G.A.; Janzen, D.A., Eds.; Academic Press: New York, 1979; Ρ. 471. U n d e r h i l l , E.W.; Wetter, L.R.; Chisholm, M.D. Biochem. Soc. Symp. 1973, 38, 303-326. Bjorkman, R. In "The Biology and Chemistry of the Cruciferae"; Vaughan, J.G.; MacLeod, A.J.; Jones, B.M.G., Eds.; Academic Press: New York, 1976; p. 191. H o l l e r , R.A.; Jones, J.D. Can. J. Bot. 1985, 63, 521-526. Kojima, M.; Poulton, J.E.; Thayer, S.S.; Conn, E.E. Plant Physiol. 1979, 63, 1022-1028. Fahn, A. In "Secretory Tissues in Plants"; Academic Press: New York, 1979; p. 147. Pihakaski, K.; Iversen, T.H. J. Exper. Bot. 1976, 27, 242258. E h r l i c h , P.R.; Raven, P.H. Evolution 1965, 18, 586-6Ο8. Erickson, J.M.; Feeny, P. Ecology 1974, 55, 103-111. Blau, P.Α.; Feeny, P.; Contardo, L.; Robson, D.S. Science 1978, 200, 1296-1298. Larsen, P.O. In "The Biochemistry of Plants"; Stumpf, P.K.; Conn, E.E., Eds.; Academic Press: New York, 1981; Vol. 7, p. 502. MacGibbon, D.B.; A l l i s o n , R.M. N.Z.J. S c i . 1971, 14, 134-140. Barker, J.S.F.; Starmer, W.T. "Ecological Genetics and Evolu t i o n " ; Academic Press: New York, 1982. Kircher, H.W. In "Ecological Genetics and Evolution"; Barker, J.S.F.; Starmer, W.T., Eds.; Academic Press: New York, 1982; p. 143. Djerassi, C. In "Festschr. Arthur S t o l l " ; Birkhauser-Verlag: B e r l i n , 1957; p. 330. Goldstein, W.S.; Spencer, K.C. J . Chem. Ecol. 1985, 7, 847858.

RECEIVED December 23, 1985


Specificity of Action of Allelochemicals: Diversification of Glycosides

Recommend Documents