EN
Calmodulin distribution was studied in the maturing male fertile and male sterile anther of Allium cepa L., using commercial monoclonal anti-CaM antibodies. The main sites of its occurrence were the tapetum and the generative cell lines. During microsporogenesis, calmodulin localization in the anthers of both onion lines was similar. Anti-CaM was localized in dividing microsporocytes, and low levels of it were found in the tapetum cytoplasm. Significant differences in calmodulin level and distribution between male fertile and male sterile anthers were observed after completion of meiosis. In the tapetum of the male fertile anther, throughout its existence, calmodulin level was higher than in the tapetum of the male sterile anther. The prematurely degenerating male sterile tapetum, starting from the free-microspore stage, did not bind anti-CaM. Differences in calmodulin localization between the functional and nonfunctional tapetum were found already in the tetrad stage, that is, before the start of degeneration of microspores. In functional tapetum cells, anti-CaM was concentrated in the cytoplasm on the loculus side; in the nonfunctional tapetum of the male sterile anther, calmodulin was evenly distributed over the cells. In the microspores of the male sterile line, calmodulin was dispersed in the cytoplasm. During pollen maturation, calmodulin was observed to undergo polarization - anti-CaM was localized mainly in the region of one of the pollen poles, near the plasma membrane. In the male sterile anther, progressive degeneration of microspores was associated with decreasing calmodulin level in the cytoplasm; microspores in the abortion stage did not bind anti-CaM.