Pollen ontogeny linked to tapetal cell maturation in Impatiens parviflora (Balsaminaceae)

Abstract

Microsporogenesis in Impatiens parviflora was studied with special attention to the mode of exine deposition and tapetum development. Our results are based on light, scanning electron and transmission electron microscopic observations of developing anthers of I. parviflora, from the microspore mother cell stage to anther dehiscence. In I. parviflora, the secretory tapetal cell layer is extended into the sporogenous tissue forming protrusions. The tapetal cytoplasm undergoes considerable changes during all stages of microsporogenesis such as fluctuations in volume densities of endoplasmic reticulum and plastids, occasional presence of two nuclei and the occurrence of a single very pronounced lipid droplet, which are indications that the tapetal cells are subject to cycles of different metabolic activity. Microsporogenesis in I. parviflora is simultaneous. Mature pollen is oblate, medium sized, 4-colpate, with a duplicolumellate reticulate sexine ornamentation. Anther dehiscence of I. parviflora involves accumulation of raphides in septal cells and the formation of a network of threads that retains and stabilises the pollen mass. The extreme sensitivity of Impatiens pollen to acetolysis can be explained by the loosely organised, tubular architecture of the intermingled foot layer/endexine.