Abstract
BackgroundType VI glandular trichomes represent the most abundant trichome type on leaves and stems of tomato plants and significantly contribute to herbivore resistance, particularly in the wild species. Despite this, their development has been poorly studied so far. The goal of this study is to fill this gap. Using a variety of cell imaging techniques, a detailed record of the anatomy and developmental stages of type VI trichomes in the cultivated tomato (Solanum lycopersicum) and in a related wild species (S. habrochaites) is provided.ResultsIn both species, the development of these structures follows a highly reproducible cell division pattern. The two species differ in the shape of the trichome head which is round in S. habrochaites and like a four-leaf clover in S. lycopersicum, correlating with the presence of a large intercellular cavity in S. habrochaites where the produced metabolites accumulate. In both species, the junction between the intermediate cell and the four glandular cells constitute a breaking point facilitating the decapitation of the trichome and thereby the quick release of the metabolites. A strongly auto-fluorescent compound transiently accumulates in the early stages of development suggesting a potential role in the differentiation process. Finally, immuno-labelling with antibodies recognizing specific cell wall components indicate a key role of pectin and arabinogalactan components in the differentiation of type VI trichomes.ConclusionsOur observations explain the adaptive morphologies of type VI trichomes for metabolite storage and release and provide a framework for further studies of these important metabolic cellular factories. This is required to better exploit their potential, in particular for the breeding of pest resistance in tomato.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0678-z) contains supplementary material, which is available to authorized users.
Highlights
Type VI glandular trichomes represent the most abundant trichome type on leaves and stems of tomato plants and significantly contribute to herbivore resistance, in the wild species
The difference in external appearance of type VI glandular trichomes in S. habrochaites and S. lycopersicum is reflected by a distinct internal architecture There are a number of reports that document a higher metabolic productivity of glandular trichomes in the wild tomato species S. habrochaites compared to its cultivated relative S. lycopersicum [18, 23]
We estimated the number of type VI glandular trichomes per leaflet (n = 5) on the adaxial side at 2573 ± 161 cm−2 in S. habrochaites versus 611 ± 171 cm−2 in S. lycopersicum as measured on leaflets that have an area of 1.6 ± 0.2 cm2 and 2.1 ± 0.9 cm2 respectively
Summary
Type VI glandular trichomes represent the most abundant trichome type on leaves and stems of tomato plants and significantly contribute to herbivore resistance, in the wild species Their development has been poorly studied so far. Type VI trichomes represent the most abundant trichome type in several tomato species, including S. lycopersicum, and have a specific architecture with four glandular cells arranged on one plane atop one intermediate cell and a single stalk cell They are the site of biosynthesis of a variety of compounds including terpenes and methyl ketones, whose diversity distinguishes species and accessions within a species [8,9,10]. One can anticipate that the extensive knowledge on Arabidopsis trichome development and differentiation may not be directly transferable to species with glandular trichomes
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