Cytoplasmic Dimorphism within Pollen Grains

Abstract

MATURE pollen grains contain a vegetative nucleus and either a generative nucleus or two sperm nuclei (derived by mitotic division of the generative nucleus). It has been generally accepted that the generative nucleus has an associated cytoplasm containing basic cell organelles^1,2 and is separated from the vegetative cell cytoplasm by plasma membranes. While Venema and Koopmans³ have recently reported that a phase-contrast study of germinating pollen yielded no evidence for the ‘bicellular’⁴ nature of pollen grains, confirmation has been achieved by Safijovska² utilizing light microscopy, and in a definitive manner in the electron microscopic examination reported by Bopp-Hassenkamp⁵. In addition to demonstrating the presence of a generative cell, the investigation by Bopp-Hassenkamp indicated that vegetative and generative cell cytoplasms differ in relative organelle numbers, and to a degree in organelle morphologies as seen in profile. Safijovska has observed that generative cell cytoplasm is longer-lived than vegetative cell cytoplasm in both aged pollen tubes and following pollen tube rupture. A comparative investigation of the fine structure of pollen cytoplasm now being conducted by me has made possible the observation of generative cells within pollen grains of a number of plant species.