Ultrastructural Alterations in Cells of Sunflower Linear Glandular Trichomes during Maturation

Abstract

Sunflower and related taxa are known to possess a characteristic type of multicellular uniseriate trichome which produces sesquiterpenes and flavonoids of yet unknown function for this plant. Contrary to the metabolic profile, the cytological development and ultrastructural rearrangements during the biosynthetic activity of the trichome have not been studied in detail so far. Light, fluorescence and transmission electron microscopy were employed to investigate the functional structure of different trichome cells and their subcellular compartmentation in the pre-secretory, secretory and post-secretory phase. It was shown that the trichome was composed of four cell types, forming the trichome basis with a basal and a stalk cell, a variable number (mostly from five to eight) of barrel-shaped glandular cells and the tip consisting of a dome-shaped apical cell. Metabolic activity started at the trichome tip sometimes accompanied by the formation of small subcuticular cavities at the apical cell. Subsequently, metabolic activity progressed downwards in the upper glandular cells. Cells involved in the secretory process showed disintegration of the subcellular compartments and lost vitality in parallel to deposition of fluorescent and brownish metabolites. The subcuticular cavities usually collapsed in the early secretory stage, whereas the colored depositions remained in cells of senescent hairs.

Developmental Programmed Cell Death Involved in Ontogenesis of Dictamnus dasycarpus Capitate Glandular Hairs

“…Early studies indicated that the synthesis and accumulation of secretions are followed by degeneration and autolysis in the secretory cells, including the autolysis of glandular cells, nuclear disorganization, cytoplasmic condensation, and the disruption of endoplasmic reticulum (ER) cisternae and multivesicular bodies [ 2 , 3 , 4 , 5 , 6 , 7 ]. Amrehn and Spring [ 8 ] reported that the deposition of fluorescent and brownish metabolites in the mature secretory cells of sunflower linear glandular trichomes is associated with the disintegration of their subcellular compartments. Recently, a comparative proteomic analysis of latex from Euphorbia kansui laticifers at different developmental stages was studied by Zhao et al [ 9 ], and the result showed that partial cytoplasmic degradation is positively correlated with secondary metabolite synthesis.…”