Morphogenesis and developmental ultrastructure of Nicotiana tabacum short glandular trichomes

Abstract

The anatomy and ultrastructure of the short glandular trichomes occurring on young expanding leaves of Nicotiana tabacum were investigated using light and transmission electron microscopy. The objective of the present research was to characterize the cellular changes that occur during morphogenesis of short glandular trichomes, from initiation to senescence. Ultrastructural analysis of their secretory cells revealed characteristics common to gland cells: numerous mitochondria in highly organized cytoplasm, large nuclei, and an elaborate network of endoplasmic reticulum. Initial changes in nuclear and plastidial organization were observed at a more advanced secretory stage, marking the onset of senescence. During trichome senescence, gradual reduction of the cytoplasm density occurred along with structural changes of the plastids and the tonoplast. As a result of inward blebbing of the cytoplasm into the vacuole, membrane bound vesicular structures appeared in the vacuolar space. At the late secretory stage, marked by an increase in vacuolation and extraplasmic space, degenerative changes included further fragmentation of the cytoplasm and deterioration of the tonoplast. Multimembrane myelin bodies observed in the vacuolar space were indicative of membrane digestion although plasma membrane did not appear massively degraded.

Glandular Trichomes on the Leaves of Nicotiana tabacum: Morphology, Developmental Ultrastructure, and Secondary Metabolites

“…Head cells of fully developed short glandular trichomes at the early secretory stage display characteristics typical of secretory tissues with high metabolic activity, as found in mature glandular trichomes of a number of species: the abundance of mitochondria in highly organized cytoplasm, large nuclei with prominent nucleoli, and an elaborate network of endoplasmic reticulum (Fig. 9a) [4,38,56,64,88].…”

“…Akers et al [56] described large accumulations of the secretory product in the extraplasmic space, between the cells or within the space formed by the juncture of the cell walls with the outer cutinized wall. Large accumulations of secretory product were never observed in short glandular trichomes of in vitro grown tobacco plants, where substantial amount of relatively small droplets was found in the extraplasmic and intercellular spaces [64]. Osmiophilic material was also detected in the extraplasmic space and between the cuticle and cell wall proper in short glandular trichome heads of N. sylvestris [45].…”

“…Periclinal divisions of the stalk cell eventually give rise to a multicellular stalk of variable length, made up of highly vacuolated cells with centrally positioned nuclei. Both short and tall glandular trichomes develop rapidly on leaf primordia, and fully developed forms can be observed already on young, not fully differentiated tobacco leaves [58,64].…”

“…Slight detachment of the cuticle forms a small subcuticular space atop the secretory cells, where the secreted material accumulates temporarily, until its release through cuticular micropores [24,31]. Subcuticular space has never been detected in either glandular trichome type of N. tabacum [45,[56][57][58]64]. Subcuticular space had also never been found in terpene-producing long-stalked trichomes of Cucurbita pepo [36] or short-stalked capitate trichomes of Pogostemon auricularius [85], where the secretion process was indicated by lipid droplets on the apical head cell.…”

“…The onset of the secretory stage is marked by the formation of the extraplasmic space between the cell wall and the plasma membrane, as a result of the plasma membrane withdrawal from the cell wall (Fig. 9c) [56,64]. Large central vacuole restricts the cytoplasm to the cell periphery, where long cisterns of ER, mitochondria, and plastids are found (Fig.…”