Cytoskeleton during pollen development in Tradescantia virginiana: a study employing chemical fixation, freeze-substitution, immunofluorescence, and colchicine administration

Abstract

A correlated chemical fixation and freeze-substitution electron microscopic, immunofluorescence, and colchicine administration study of the structure and behavior of the cytoskeleton during pollen development in Tradescantia virginiana revealed a dynamic picture of the cytoskeleton. In contrast with chemical fixation, freeze-substitution consistently showed a higher number of microtubules, and preserved microfilaments. Higher populations of cortical microtubules occurred before and after the formation of exine pattern whereas lower populations occurred during the period of exine formation and in late bicelled pollen. Coincident with the reduced population of microtubules during the tetrad stages, immunofluorescence preparations showed a diffuse fluorescence, perhaps indicating the presence of unpolymerized tubulin. Cortical microfilaments occurred throughout the period of exine formation and in late bicelled pollen. Perinuclear and cytoplasmic bundles of microfilaments were also recorded in the late bicelled pollen. Pollen grains grown in colchicine during the period of exine formation developed normal exines, but failed to acquire their normal shape. It is suggested that during tetrad stages, the microfilament – plasma membrane interactions may be involved in exine-pattern formation, and that cortical microtubules are largely a determinant of pollen shape.