Glandular trichome exudate

Table V. Activity of neonate Colorado potato beetle larvae on excised leaflets of either S. tuberosum, S. berthaultii PI 310927, or PI 310927 from which most of the glandular trichome exudate had been removed by wiping between tissue papers. Adapted from (24)...

Table II Mass Spectrometric Analysis of Anacardic Acids in Glandular Trichome Exudate...

Table IV Percentage Composition of Anacardic Acids in Geranium Glandular Trichome Exudate.

Immobilizing Chemicals. Some plants produce a sticky, gummy exudate from glandular trichomes. These exudates effectively immobilize small Insects. 

The wild tomato, Lycopersicon hirsutum f, glabratum is covered with trichomes which contain 2-tridecanone. The level of this compound is much lower in the domesticated tomato, U esculentum. This exudate proved to be toxic to Manduca sexta (tobacco hornworm) and to Heliothis zea (121). The density of glandular trichomes, which secrete 2-tridecanone, was influenced... 

Glandular trichomes of j>. berthaultii provide the greatest levels of resistance against immature life stages of pest species. Encasement of feet and mouthparts of the green peach aphid by trichome exudate is greatest on nymphs and least on adult aphids, parallelling the trends in mortality (6). 

Behavioral and sensory disturbance. Potato glandular trichomes, in addition to acting as a physical barrier to pests, manufacture and/or store a profusion of plant metabolic products, some of which profoundly influence insect behavior and metabolism (19,20). The sesquiterpene components of potato trichome glands (21,22,23) are potentially powerful semiochemicals and one of these, E-6-farnesene, is well known for its ability to initiate evasive behavior in aphids (24). The dramatic alteration of aphid feeding behavior on S. berthaultii reported by Lapointe and Tingey (25) may be due to allomonal sesquiterpenes in trichome exudate and will be discussed later. 

The sesquiterpenes of j>. tuberosum foliage are not present in sufficient quantities at the leaf surface interface to discourage aphid settling. By contrast, the exudate of the Type B glandular trichomes on S. berthaultii foliage contains sesquiterpenes, thus enhancing the external level of these insect-repellent compounds. 

The source of these materials in tobacco is the leaf end stem trichomes. Compounds exude from the glandular trichomes. the morphology of which differ from cultivar to cultivar. For example, tobaccos with simple, or nonglanded trichomes produce only cuticular hydrocarbons. The profusion of the trichome... 

Figure. 1. Nature of glandular trichome-mediated aphid resistance in 5. berthaultiL Key (1) Carboxylic acid sucrose esters (CASE), (2) Viscous type B trichome exudate, (3) Increased aphid movement and attempts to escape, (4) Adhesive aphid tarsi, (5) Enhanced rupture of type A trichome membrane , (6) Polyphenoloxidase + 02 + substrate, (7) Aphid alarm pheromone, E-(B)=famesene, (8) Encasement of tarsi by trichome exudate, (9) Greater effective tarsal size, (10) Decreased aphid mobility, (11) Occlusion of mouthparts by trichome exudate, (12) Starvation and death. Adapted from (38).

Although glandular trichomes can interfere with predators and parasitoids of aphids and the Colorado potato beetle, the inhibitory effect is largely associated with entrapment by type B exudate and is minimized on plants bearing moderate densities of these trichomes (42.43). 

Browning and hardening of exudate on the insect s mouthparts and tarsi is due to the enzymatic activity of an O2- requiring oxidase (12), and has been associated with both peroxidase and polyphenol oxidase activities (2/14-fl2.). We recently showed that these enzymatic activities are due to a 59 kD polyphenol oxidase (PPO) which is present in the type A trichomes of S. berthaultii at approximately 1 ng/trichome head (a concentration of approximately 0.3 mM) (lA). The specialization of the glandular trichome is reflected in the fact that PPO comprises approximately 60% of the total soluble protein of the organ. 

During the 1970 s the USDA Nicotiana tabacum germplasm collection was evaluated in field plots at the Clemson University Pee Dee Research and Education Center, Rorence, SC for their resistance to the tobacco hornworm, Manduca sexta (L,) (1), and the tobacco budworm, Heliothis virescens (F.) (2). During this investigation a large variation in leaf trichome types and density was observed. Johnson et al. (3,4) classified the major trichome types from the various tobacco types as simple trichomes without exudates, glandular trichomes without exudates, glandular trichomes with exudates, and... 

The exudate of the glandular trichomes of Solanum ber-thaultii are effective against aphids and similar insect pests. One part of the defense involves the immobilization of the insects in the exudate which hardens (Harbome, 1989). This exudate proved to be a mixture of sucrose esters, of which 3,4-di-0-isobutyryl-6-C>-caprylsucrose is a major component. These compounds also appear to provide resistance to potato blight (Harbome, 1989). A similar series of compounds is found in the trichomes of other solanaceous plants of the genera Datura, Lycopersicon, Nicotiana, and Petunia. A series of esters of sucrose with -p-coumaric acid (such as 104) and acetate from Prunus maximowiczii proved to be responsible for the very bitter taste of the fruits (Shimazaki et al., 1991) (Fig. 15.18). 

Di- and l,2,3-tri-Q-hexanoyl- -D-glucopyranose were the principal components in the exudate from glandular trichomes of Datura jmetel (Solanaceae), whereas the glandular trichomes of certain non-tuberous Solanum species furnished mainly 2-Q-acetyl-... 

---