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

The MS33 gene in Arabidopsis is required for stamen filament growth and for pollen maturation. The objective of this study was to characterize the eff ects of ms33 mutation on pollen development at the ultrastructural level. T here were no differences between the wild type and ms33 mutant pollen devel opment before the first mitotic division of microspores. At the bicellular pollen stage, the first signs of abnormalities were observed in the ms33 ta petum, which started to degenerate early and released osmiophilic material in the anther locule. In ms33 pollen, the endintine was thicker, and exinti ne thinner, than in the wild type, and the mutant pollen had large vacuoles . Later in development, the mutant pollen underwent second mitosis and prod uced two normal-looking sperm cells; however, the intine was precociously f ormed, and there were abnormalities in tryphine deposition on the pollen wa ll, in the size of vacuoles, and in the formation of lipid bodies in the ve getative cell cytoplasm. Based on these observations it is suggested that m utation in the MS33 gene interferes with intine formation and tryphine depo sition, both of which negatively affect pollen desiccation resulting in lar ge, highly vacuolate pollen that are nonviable.