The Structural Diversity of Trichomes and Pubescence of Brassicaceae Burnett of the Flora of Ukraine with an Emphasis on Ecology

Abstract

Species of the Brassicaceae family (crucifers), which are of great scientific and practical importance, are inherent by a wide variety of trichome structures. Trichomes -specialized cells of the epidermis, modulate the response of plants to biotic and abiotic stresses. We investigated the structural diversity of trichomes and the features of pubescence of all (252 species, 73 genera) Brassicaceae species of the flora of Ukraine. Trichomes were studied on living plants and based on materials from seven herbaria, as well as on the basis of analysis of literature data. Stereoscopic and electronic scanning (JSM-6060 LA) microscopes were used in this investigation. To describe the structural diversity of trichomes, an original four-level hierarchical classification was developed, taking into account a complex of features, including functional specificity (covering or glandular), the nature and degree of hair branching, as well as the features of the orientation of their rays. The pubescence of plants was divided into isomorphic (consists of one type of trichomes) and heteromorphic (formed by two or more types of hairs with or without glandular structures). Hairs are completely absent in 23 species of 15 genera of the flora of Ukraine. Isomorphic pubescence is characteristic of the most (170 species) cruciferous plants and is represented by simple (120 species), Malpighian (23 species), stellate (23 species), dendroid (3) and fork-shaped (1 species) trichomes. The composition of heteromorphic pubescence is dominated by a combination of simple and fork-shaped hairs: it is observed in 44 species. There are glandular structures in the pubescence of 14 species. The structural diversity of Brassicaceae trichomes correlates, in general, with the temperate continental climate of Ukraine. Species without hairs or pubescent with simple trichomes, including those in combination with fork-shaped hairs, are observed in biotopes with sufficient moisture, optimal insolation, and satisfactory soil quality. Species with dense branched trichomes inhabit arid biotopes with intense insolation, insufficient moisture, and poor substrate. In the flora of Ukraine, the evolutionary-phylogenetic line LII included non-pubescent species or those with simple hairs. The cruciferous line LI is characterized by isomorphic and heteromorphic pubescence. In species LIV, heteromorphic pubescence predominates. Glandular structures are observed in the heteromorphic pubescence of taxa of line LIII.