Association of the Generative Cell and Vegetative Nucleus in Pollen Tubes of Rhododendron

Abstract

Mixed fluorescence/bright field microscopy of Rhododendron pollen tubes in the first 72 h after germination reveals a lens-shaped generative cell which divides to give two associated sperms within the original cell boundary. The generative cell is closely associated with the vegetative nucleus which precedes it in 92 per cent of pollen tubes. Three-dimensional reconstruction from serial thin sections of a pollen tube fixed 24 h after germination shows that the association between the generative cell and vegetative nucleus is extremely complex. Elongated tails of the generative cell physically enfold the vegetative nucleus and penetrate into enclaves within it. The association has been clarified by use of the periodic acid-phosphotungstic acid-chromic acid technique to enhance electron contrast of the plasma membranes surrounding the generative cell. In this bicellular system, the male germ unit association is apparently initiated after pollen maturity but prior to generative cell division.