Trichome exudates

Inheritance of diterpene constituent in tobacco trichome exudates. Crop Sci 1992 32(5) 1148-1150. 

Mendoza, L. and Urzua, A., Minor flavonoids and diterpenoids in the resinous trichome exudates from Pseudognaphalium cheiranthifolium, P. heterotrichium, P. vira vira and P. robustum, Biochem. Syst. Ecol, 26, 469, 1998. 

Adheslve entrapment. Mortality and immobilization of aphids increases with a rise in density of Type A and Type B trichomes and with increased volume of Type A trichome glands. Insects landing on the foliage first encounter Type B trichome exudate which forms an adhesive coating on the tarsi. This accelerates... 

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. 

Se8qulterpenold semlochemlcals. The aphid-repellent effect of Type B trichomes of S. berthaultii (25) appears to be due to the presence of sesquiterpenes (22). Three major components, identified by GC-MS, were B-caryophyllene, B -cubebene and A-cadinene. E-B-farnesene was also identified, but was a minor component. GC-MS of the other major components in Type B trichome exudate indicated sesquiterpenold structures, but these have not been identified. 

Ovinoaitional properties of DVT diols and DVT ols. In 1978, it was proposed that a tobacco cultivar. Tobacco Introduction (TI) 1112, was resistant to tobacco budworm because it lacked certain trichome exudates (MO Also, there were fewer budworm eggs on TI 1112 leaves compared to egg masses found on two other flue-cured cultivars. Four years later, Johnson and Chaplin (17) reported that trichome secretions influenced budworm moth oviposit ion in certain cultivars and, furthermore, resistant cultivars were capable of producing antibiotic substances that affected first instar larvae. Later, the leaf surface chemistry of TI 1112 was studied in detail and compared with that of budworm susceptible NC 2326 (18). The cuticular substances of NC 2326 were composed of high levels ofeCand/3-DVT diols, a series of C25 to C30 saturated... 

Many species of small-bodied pests experience classical responses to host resistance phenomena during an encounter with foliage of 5. berthaultii. These include host avoidance and restlessness, reduced feeding, delayed development, reduced adult weight and reproductive performance, increased mortality, and diminished longevity. In several cases, these responses are associated with entrapment or immobilization by trichome exudate. 

Entrapment/Immobilization. Aphids and leafhoppers experience significant mortality by entrapment in trichome exudate. Initial contact with the foliage leads to an encounter with the tall Type B hairs which confer a high degree of adhesiveness to the tarsi (Fig. 1). Tarsi coated with this viscous materi are very effective in... 

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).

Type B trichome exudate of S. berthaultii also conditions abnormal behaviors in aphids and leafhoppers, particularly delay in host acceptance as measured by an increase in time to the first probe and a decrease in feeding time (Table I) (21.22V The avoidance/deterrance responses of aphids are conditioned by the presence of sucrose esters of short-chain branched carboxylic acids in the type B exudate (Table ID (23.24). Sensory receptors on the tarsi and/or antennae of aphids are the likely target sites of sucrose esters in type B exudate (24). 

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 I. Sugar Ester Composition of Trichome Exudates in the Solanaceae...

Stable Isotope Administration. The biosynthesis of I. penne 11 i i glucose esters was investigated using deuterium labeled precursors. Compound leaves of L. pennellii were removed and briefly rinsed in 100% EtOH before precursor administration. The preincubation sample of the trichome exudate was saved to establish fatty acyl composition prior to precursor feeding its removal served to increase the proportion of labeled glucose esters after precursor incubations. 

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

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

All other species which did not produce observable trichome exudates Nicotiana spp. Nos. 19,23,25,27,31,44,47,52,53,63,64, and 71) were not attractive to budworm oviposition. Excluding tabacum types, only N sylvestris produced significant levels of a- and jff-DVT-diols. 

Most of the Nicotiana species with observable trichome exudates produced sugar esters. However, as shown in Figure 2 and Table IV, large variations in sugar ester types and distribution of ester moieties were found. 

Gerhold, D. L., R. Craig, and R. O. Mumma, Analysis of trichome exudate from mite-resistant geraniums, J. Chem. Ecol., 10, 713-722 (1984). 

These studies clearly demonstrate a relationship between aphid resistance in V. tabacum and differences in the levels and composition of trichome exudates. Tobaccos which are resistant to the green morph of the tobacco aphid are also resistant to the red form (10, 11, 75). This indicates that both color forms of the tobacco aphid have similar response to plant surface chemistry. It also appears that, as seen in the tobacco budworm and tobacco homworm (72,77-79), the DVT-diols are preference compounds used by alate aphids to identify their host plants. The DVT-ols, cw-abienol, and SE are toxic to the tobacco aphid, and these compounds have potential as contact aphicides. Breeding of commercially acceptable N, tabacum cultivars with high levels of DVT-ols, cw-abienol and/or the SE would greatly decrease the level of tobacco aphid colonization and lessen the need to use conventional insecticides. 

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