MS32-regulated timing of callose degradation during microsporogenesis in Arabidopsis is associated with the accumulation of stacked rough ER in tapetal cells

In the male sterile32 (ms32) mutant in Arabidopsis thaliana, pollen develop ment is affected during meiosis of pollen mother cells (PMCs). Tn normal wi ldtype (WT) anthers, callose is deposited around PMCs before and during mei osis, and after meiosis the tetrads have a complete callose wall. Tn ms32, PMCs showed initial signs of some callose deposition before meiosis. but it was degraded soon after, as was part of the cellulosic wall around the PMC s. The early dissolution of callose in ms32 was associated with the occurre nce of extensive stacks of rough ER (RER) in tapetal cells. The stacks of R ER were also observed in the WT tapetum, but at a later stage, i.e., after the tetrads were formed and when callose is normally broken down for releas e of microspores. Based on these observations it is suggested that: (1) cal lose degradation around developing microspores is linked to the formation o f RER in tapetal cells, which presumably synthesize and/or secrete callase into the anther locule, and (2) mutation in,MS32 disrupts the timing of the se events.