Tapetal plastids in Ornithogalum virens: From meristematic stage to pollencoat

We examined the ultrastructure of plastids during the development and degra dation (programmed cell death) of the secretory tapetum in Ornithogalum vir ens, a species with a pollen coat. Plastids present in meristematic tapetum cells differentiate into amyloplasts and function as amyloplasts during th e period of tapetal activity. They undergo two cycles of starch synthesis a nd hydrolysis before entering the degradation phase in which their structur e disintegrates and plastoglobules form, preceding pollen coat formation. W e showed that during these processes the plastids are nonrandomly distribut ed in tapetal cells and that the spatial relation between the plastids, cel l nuclei and ER depends on the stage of tapetum and pollen development. We also showed that polar distribution of the plastids and polar localization of starch hydrolysis activity characterized the phase of intensive tapetal secretion.