Male gametophyte development and formation of the male germ unit inPopulus deltoides following compatible pollination

Abstract

This study, combining the use of fluorescence and electron microscopy, is devoted to the behaviour of thePopulus deltoides male gametophyte following compatible crosses but prior to fertilization. Close association between the vegetative nucleus and the generative cell, initiated at pollen maturity, has been observed from the time of pollen activation at the stigma surface through early pollen tube growth and after generative cell division to form sperm cells. The elongated generative cell contains the normal set of cytoplasmic organelles with the exception of plastids. Microtubules are orientated along its longitudinal axis. In actively growing pollen tubes at the lower end of the style sperm cells are frequently observed. Paris of interconnected sperm cells derived from generative cell division are detected alone or in close association with the vegetative nucleus, forming a male germ unit. The two sperm of a pair are apparently not dimorphic. In this bicellular system, the male germ unit association is apparently initiated at pollen maturity and maintained during pollen tube growth within the style