Effect of temperature on glandular trichome exudate composition and pest resistance in geraniums

Abstract

One inbred geranium line (71‐18‐6) which exhibits host plant resistance to the twospotted spider mite and foxglove aphid, becomes susceptible to these pests under some temperature conditions, while another resistant line (71‐17‐7) maintains its resistance. Resistance to these pests is conferred by the presence of glandular trichomes and the exudate they produce. The tall glandular trichome exudate of resistant geraniums has been identified as chiefly C22 and C24 unsaturated anacardic acids. Plants of a resistant line, a susceptible line and the temperature sensitive resistant line were exposed to three different temperature regimes and were analyzed chemically and for resistance using a foxglove aphid bioassay. Results indicate that the loss of resistance in the temperature sensitive line is not due to reduced production of the anacardic acids which comprise the exudate. Similarly, analysis of the exudate present on the leaf exterior indicate the loss of resistance in line 18‐6 with increasing temperature is not the result of reduced translocation of the exudate to the trichome tip. Evidence is presented to support the hypothesis that loss of resistance in line 18‐6 with increasing temperature is the result of an increased proportion of the shorter chain (C22) anacardic acid in the trichome exudate, which reduces the viscosity of the material and causes it to flow from the trichome tips as the temperature increases. Presentation of the material as an exudate droplet at the trichome tip is apparently required for resistance.

Glucosinolates are produced in trichomes of Arabidopsis thaliana

“…It is therefore not surprising that trichomes often contain defense metabolites (Levin, 1973). Multicellular glandular trichomes, which are found on the leaf surface of many plant species such as Solanum habrochaites (wild tomato), Nicotiana tabacum (tobacco), Ocimum basilicum (sweet basil), and Mentha piperita (peppermint) are able to synthesize and/or secrete various chemical compounds such as organic acids, polysaccharides, proteins, terpenes, phenolic compounds, glucose esters, and salts (Kelsey, 1984; Navasero and Ramaswamy, 1991; Walters et al, 1991; Gershenzon et al, 1992; McCaskill et al, 1992; Wang et al, 2001). By contrast, the leaf hairs of Arabidopsis thaliana are non-glandular single-cell hairs that develop from epidermal cells and are found on most aerial organs (Hülskamp and Schnittger, 1998).…”

An Investigation of the Storage and Biosynthesis of Phenylpropenes in Sweet Basil

“…geranium, tobacco, and cotton) possess specialized glands known as glandular trichomes on the surface of their leaves, and the presence of such glands is often correlated with exudation of defense compounds and pest resistance (Navasero and Ramaswamy, 1991;Walters et al, 1991). In the Lamiaceae, which includes basil and mint, two classes of secretory glandular trichomes can be found.…”

Remains of secretory cavities in pinnules of Stephanian pteridosperms from Blanzy-Montceau (Central France): a comparative study

“…Detto, 1903;Hshn & Elfert, 1957;Dell, 1977), biocidal properties against phytophagous animals (e.g. Fraenkel, 1959;Sutherst et al, 1982;Walters, Craig & Mumma, 1990;Walters et al, 1991;Karban & Baldwin, 1997) or microorganisms (e.g. Deans & Ritchie, 1987), and positive support for wound healing processes (e.g.…”