ORGANIZATION, COMPOSITION, AND FUNCTION OF THE GENERATIVE CELL AND SPERM CYTOSKELETON

This chapter focuses on the organization, composition, and function of the generative cell and sperm cytoskeleton. Microtubule (MT) organization in generative and sperm cells (GSP) contrasts sharply with that in the surrounding vegetative cytoplasm. MT is composed of heterodimers of α- and β-tubulin, which share sequence homology at the DNA and protein levels with counterparts in animals. Vegetative MTs in hydrated pollen grains and pollen tubes do not occur in similar thick bundles but instead comprise much thinner elements organized in various patterns. In pollen tubes MTs are arranged primarily in helical to longitudinal arrays in the outer cortex. The cortical elements consist of single MTs or planar groups that are cross-bridged to each other and to the plasma membrane. The MT bundles in GSP are also unlike somatic cell arrays. While cortical MTs are linked to the plasma membrane and associate with each other in somatic cells, the kind of large, flexuous bundles that ramify through the cytoplasm of GSP are not observed. Instead, the MTs are largely limited to a single layer next to the plasma membrane. © 1992, Academic Press Inc.