Pollen wall development in Vigna vexillata II. Ultrastructural studies

Abstract

Ultrastructural studies to determine the role of cytoplasmic organelles in pollen wall development in Vigna vexillata L. (Fabaceae) showed that plastids, mitochondria, and vacuoles do not directly participate in pollen wall morphogenesis, as inferred from their cytoplasmic distribution during microsporogenesis and pollen development. Spatial and temporal correlations between elements of the endomembrane system and pollen wall development suggest that dictyosomes, the endoplasmic reticulum, and multimembrane inclusions are involved in synthesis, processing, and/or transport of precursors for the various pollen wall layers. Large numbers of dictyosome‐derived vesicles appear during development of the primexine matrix, the patterned primexine, and the apertural Zwischenkörper, suggesting that dictyosomes are involved in development of these layers. Tubules of smooth endoplasmic reticulum, preferentially located under developing primexine ridges and extending to the vicinity of the plasma membrane, support the hypothesis of endoplasmic reticulum involvement in pollen wall pattern formation. Multimembrane inclusions, abundant in the cortical cytoplasm of developing microspores, may be involved in development of the lamellate endexine.