STRUCTURAL-CHANGES IN THE POLLEN GRAIN OF BRASSICA-OLERACEA DURING DEHYDRATION IN THE ANTHER AND DEVELOPMENT ON THE STIGMA AS REVEALED BY ANHYDROUS FIXATION TECHNIQUES

An anhydrous fixation method has been used to examine the de- and rehydration of pollen grains of Brassica oleracea, and to follow their early development after both compatible and incompatible intraspecific pollinations. Conventional water-based fixation techniques were shown to present a very artefactual image. Using the anhydrous method, specific stages of de- and rehydration were recognized in the pollen cytoplasm, and the most dehydrated grains were found not to possess an organized plasma membrane, but rather a superficial mosaic composed of vesicles, membranes and granules. The surface of the stigmatic papillae and of the pollen grain coating appear to be structurally adapted for the passage of metered quantities of water into the pollen grain. Evidence is presented that the self-incompatibility mechanism operating in these plants consists of a recognition stage occurring at the interface between the stigmatic pellicle and a membrane-like investment of the pollen coating, and a response phase involving the translocation of an inhibitor into the pollen grain cytoplasm. Since this system may be overridden by changes either in the plant or in its environment, the mechanism would seem to be uniquely adapted to changes in breeding strategy. © 1985