Male Gametophyte Development.

Pollen development offers the opportunity to study cell fate, cell patterning, cell polarity, and cell signaling-in this sense, pollen development can serve as a microcosm for all the in- teresting questions facing plant biologists today. The events that culminate in the formation and release of the pollen grain from the plant begin with meiosis and involve an intricate and tightly controlled set of structural and molecular changes, requiring gene expression in both the gametophytic and sporo- phytic tissues of the anther. The biochemistry of angiosperm pollen development was first reviewed comprehensively 18 years ago (Mascarenhas, 1975), and severa1 subsequent reviews have appeared (e.g., Mascarenhas, 1989,1990,1993, this issue; McCormick, 1991; Bedinger, 1992). Although a great deal of progress has been made, it is notable that two of the areas for future research noted by Mascarenhas (1975) remain today: What are the differ- ences in the two cytoplasms that determine the different cell fates of the generative and vegetative cells? What are the func- tions of pollen-specific proteins? In this review, I will give an overview of the current state of knowledge of microsporogen- esis, minimizing repetition of the topics covered in other recent reviews, and I will try to point out promising avenues of re- search for the future.