Ultrastructural characterization of male sterile33 (ms33) mutant in Arabidopsis affected in pollen desiccation and maturation

Abstract

The MS33 gene in Arabidopsis is required for stamen filament growth and for pollen maturation. The objective of this study was to characterize the effects of ms33 mutation on pollen development at the ultrastructural level. There were no differences between the wild type and ms33 mutant pollen development before the first mitotic division of microspores. At the bicellular pollen stage, the first signs of abnormalities were observed in the ms33 tapetum, which started to degenerate early and released osmiophilic material in the anther locule. In ms33 pollen, the endintine was thicker, and exintine thinner, than in the wild type, and the mutant pollen had large vacuoles. Later in development, the mutant pollen underwent second mitosis and produced two normal-looking sperm cells; however, the intine was precociously formed, and there were abnormalities in tryphine deposition on the pollen wall, in the size of vacuoles, and in the formation of lipid bodies in the vegetative cell cytoplasm. Based on these observations it is suggested that mutation in the MS33 gene interferes with intine formation and tryphine deposition, both of which negatively affect pollen desiccation resulting in large, highly vacuolate pollen that are nonviable.Key words: Arabidopsis, male sterility, mutant, pollen, tapetum, ultrastructure.