Pollen Dimorphism—Origin and Significance in Pollen Plant Formation by Anther Culture

Abstract

Pollen dimorphism during the ripening of Nicotiana tabacum anthers takes the form of differentiation at the binucleate pollen stage into normal (N) grains, characterized by their high frequency, larger size, densely–staining cytoplasm and high starch content and into smaller (S) grains characterized by their variable and low frequency and weakly–staining cytoplasm. Most of the S grains show distinctive vegetative and generative nuclei (A grains); a small number have two vegetative–type nuclei (B grains). Evidence is presented that when excised anthers are cultured, pollen plants arise only from S grains. It is suggested that the differentiation into N and S grains arises by an abnormal second meiotic division in the pollen mother cells.