13 Potato Glandular Trichomes: A Physicochemical Defense Mechanism Against Insects 1,3
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Peter Gregory , Ward M. Tingey , Dirk A. Ave , and Pierre Y. Bouthyette Downloaded by NORTH CAROLINA STATE UNIV on December 14, 2012 | http://pubs.acs.org Publication Date: January 16, 1986 | doi: 10.1021/bk-1986-0296.ch013
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Department of Plant Breeding and Biometry, Cornell University, Ithaca, NY 14853 Department of Entomology, Cornell University, Ithaca, NY 14853
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A wild potato species, Solanum berthaultii Hawkes, is resistant to insect pests by virtue of two types of glandular trichomes on its foliage. Type A is a short trichome with a four-lobed membrane-bound gland at its apex. Type Β is a longer, simple trichome with an ovoid gland at its tip which continuously exudes a clear viscous exudate. Studies of this physicochemical resistance mechanism suggest the following series of events: (a) the insect lands upon the foliage and encounters Type Β trichomes, (b) Type Β trichomes coat the insect with a sticky exudate and, due to sesquiterpenoid action, agitate the insect, (c) the struggling insect disrupts the heads of Type A trichomes, and an oxidation reaction between a unique polyphenoloxidase enzyme (PPO) and phenolic substrate(s) results in quinone formation, (d) these events result in insect immobilisation, cessation of feeding and death. The relevance of this mechanism to breeding for improved potato resistance to insect pests is discussed. Over t h e c o u r s e o f t h e i r a s s o c i a t i o n , p l a n t s have e v o l v e d many tactics t o contend with herbivorous i n s e c t s . Among t h e b e s t known a r e c h e m i c a l p r o d u c t s o f s e c o n d a r y m e t a b o l i s m which c o n f e r an a d a p t a t i v e advantage t o t h e p l a n t by a c t i n g a s t o x i c a n t s and repellents (1). No less important i n protection from insect-induced stress i s t h e p l a n t ' s indumentum. Pubescence, once thought o f o n l y as a means f o r p l a n t s t o m i n i m i z e w a t e r l o s s , i s now known t o p r o v i d e a d e f e n s i v e b a r r i e r a g a i n s t many species o f herbivorous insects (2). The t y p e s o f pubescence a c t i v e i n defense are diverse, r a n g i n g from t h e s i m p l e , unbranched o r s t e l l a t e e p i d e r m a l h a i r s 3
Current address: International Potato Center (CIP), Apartado 5969, Lima, Peru. Current address: Allied Corporation, Solvay Research Laboratory, P.O. Box 6, Solvay, NY 13209.
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0097-6156/86/0296-0160S06.00/0 © 1986 American Chemical Society
In Natural Resistance of Plants to Pests; Green, M., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
Downloaded by NORTH CAROLINA STATE UNIV on December 14, 2012 | http://pubs.acs.org Publication Date: January 16, 1986 | doi: 10.1021/bk-1986-0296.ch013
13.
GREGORY ET AL.
Potato Glandular
Trichomes
of maize, a l f a l f a , cotton, wheat, and soybean, to the s t r i k i n g secretory trichomes of solanaceous species (3). The glandular pubescence of potato defends against a broad complex of pest species, including aphids, leafhoppers, f l e a beetles, the Colorado potato beetle, the potato tubermoth complex, and spidermites (4,5,6,7). This wide spectrum of a c t i v i t y i n i t i a t e d considerable interest i n the mechanistic basis for defense by glandular trichomes (8) and stimulated e f f o r t s to exploit these structures in potato breeding for pest resistance (9,10,11). Hybrid potatoes bearing glandular trichomes from the wil
