Morphological characterization of trichomes shows enormous variation in shape, density and dimensions across the leaves of 14 Solanum species

Abstract

Trichomes are the epidermal appendages commonly observed on plant surfaces including leaves, stem, and fruits. Plant trichomes have been well studied as a structural plant defense designed to protect plants against abiotic and biotic stressors such as UV rays, temperature extremities and herbivores. Trichomes are primarily classified into glandular and non-glandular trichomes, based on the presence or absence of a glandular head. The plant genus Solanum is the largest genus of family Solanaceae that houses ~25,000 species of ecological and economic importance have a diverse set of trichomes that vary in density and morphology. However, due to the incomplete and contradictory classification system, trichomes have subjective names and have been largely limited to be grouped into glandular or non-glandular types. Through this study, we did a complete workup to classify and characterize trichomes on both adaxial and abaxial leaf surface of 14 wild and domesticated species of the genus Solanum. Using electron microscopy, statistical analyses and artistic rendition, we examined finer details of trichomes and measured their density and dimensions to compile a detailed dataset which can be of use for estimating the variation in trichome types, and their density, with consequences for understanding their functional roles. Our study is the first of its kind that provides us with a better and well-defined classification, density, and dimension analysis to complete the morphological classification of trichomes on both leaf surfaces of a diverse range of members in Solanum genus.

Are epicuticular waxes a surface defense comparable to trichomes? A test using two Solanum species and a specialist herbivore

“…Previous work has used members of the Solanaceae family to understand the effects of inter and intraspecific variation in physical defenses, and their impact on mediating plant-herbivore interactions (Kariyat et al, 2013;Kariyat et al, 2017;Kariyat et al, 2019;Chavana et al, 2021;Watts and Kariyat, 2021b). More recently, we observed that, among 14 species in the Solanum genus, Solanum macrocarpon (Gboma) has glandular and non-glandular trichomes (Watts and Kariyat, 2021a), but almost no waxes on the leaf surface. On the other hand, Solanum glaucescens (Cuatomate) has a thick wax layer on its leaf surface, but almost no trichomes (Kaur et al, 2022).…”

“…Solanum glaucescens (Product code: Y5SSSOGL) and Solanum macrocarpon (Product code: Y5SSSOLG) from rarepalmseeds.com. For details of how the plants were grown, please see Watts and Kariyat (2021a).…”

“…To image leaves for trichome morphology, dimension, and density analysis (n= 3-11 plants per abaxial and adaxial leaf surface per species), a desktop Scanning Electron Microscope (DSEM; SNE-4500 Plus Tabletop; Nanoimages LLC, Pleasanton, California, USA; Watts et al, 2021) was used. For operational procedures and DSEM methodology, see Watts and Kariyat (2021a) and Watts et al (2021).…”

“…Chemical defenses include numerous secondary metabolites that can both directly and indirectly protect plants (Howe and Jander, 2008). Among physical defenses, trichomes are one of the most important and possibly the most studied of defenses (Levin, 1973;Kariyat et al, 2013;2017;Karabourniotis et al, 2019;Kaur and Kariyat, 2020a;Watts et al, 2021;Watts and Kariyat, 2021a;2021b).…”

“…A higher trichome density is usually associated with reduced herbivory (Watts and Kariyat, 2021b). While trichomes are primarily classified as glandular and non-glandular types, based on the presence or absence of a glandular head, deeper inspection has revealed both inter and intra specific morphological variation (Watts and Kariyat 2021a). This variation includes trichome size, shape, density, and dimensions on abaxial and adaxial leaf surfaces (Watts and Kariyat 2021a;.…”