We examined the ultrastructure of plastids during the development and degradation (programmed cell death) of the secretory tapetum in Ornithogalum virens, a species with a pollen coat. Plastids present in meristematic tapetum cells differentiate into amyloplasts and function as amyloplasts during the period of tapetal activity. They undergo two cycles of starch synthesis and hydrolysis before entering the degradation phase in which their structure disintegrates and plastoglobules form, preceding pollen coat formation. We showed that during these processes the plastids are nonrandomly distributed in tapetal cells and that the spatial relation between the plastids, cell 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.
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