Summary

Structural details of pollen development are quite uniform in most of the species studied. The main structural events associated with pollen development are (i) the formation of a syncytium of microspore mother cells (MMCs), also referred to as pollen mother cells (PMCs) or meiocytes, in each anther locule, followed by the isolation of each MMC and the resulting microspores encased in a callose wall; (ii) cytoplasmic reorganization resulting in the breakdown of most of the RNA and ribosomes of MMCs, and de-differentiation of plastids and mitochondria; (iii) release of microspores by the activation of callase; (iv) development of microspores accompanied by the synthesis and buildup of RNA, ribosomes, and proteins, and redifferentiation of plastids and mitochondria; (v) asymmetric division of the microspore; and (vi) desiccation and dispersal of pollen grains. The tapetum undergoes several changes and plays a crucial role in pollen development. Although the pistil shows tremendous morphological diversity, the surface of the stigma and the path of pollen tube growth in the pistil invariably contain extracellular components that come into contact with the pollen grain and the pollen tube. Pollination initiates a series of events leading to the discharge of sperm cells in the embryo sac and double fertilization. There is a close interaction between pollen and pistil throughout the postpollination period, and so far only a beginning has been made in understanding the details of these interactions.

Introduction

The development of normal, viable pollen grains, their transfer to the stigma, and pollen germination and successful completion of pollen–pistil interaction are prerequisites for fruit and seed development. Since the beginning of this century, extensive studies have been carried out on various aspects of pollen biology.