The features of cytological defects during meiotic and mitotic progression of microsporogenesis in male sterile mutants Ms41 and Ms44

--Qinqin Liu and W. Zacheus Cande

The new dominant male steriles, Ms41 and Ms44, have been previously described as linked alleles on chromosome 4L (Albertsen, MC and Neuffer, MG, MNL 64:52). However, the cytological features of meiotic and mitotic progression during microsporogenesis in these mutants have not yet been studied. The presence of cytological defects in these mutants at different stages of microsporogenesis are identified using DAPI to stain chromatin. Normal meiotic divisions are observed in both mutants, but cytological defects occur before the first mitotic division in pollen development. These defects are correlated with nuclear and cytoplasmic disintegration.

In Ms41 (Fig. 1), the nuclei become reduced and degenerate during microspore vacuolation although normal tapetal cells and normal wall and pore development are observed during pollen maturation. The cytoplasm also breaks down at the same stage of development. In wildtype cells, vegetative and generative nuclei are observed after the first pollen mitosis (Fig. 2). Similar cytologi-

Figure 1a-d. Cytological defects before the first mitotic division in Ms41 pollen cells. 1a: A reduced nucleus, stained by DAPI, in the pollen cell. 1b: Cytoplasm degenerated in the same cell as Figure 1a. 1c: Degenerate nucleus with diffuse chromatin staining in the pollen cell. 1d: Disintegrated cytoplasm in the same cell as Figure 1c.

Figure 2a and b. Normal cytological features after the progression of the first pollen mitosis in wildtype cells of Ms41. 2a: Vegetative and generative nuclei stained with DAPI. 2b: Cytoplasm with normally developed vacuoles in the center of the pollen cells.

Figure 3. Cytological defects before the first mitotic division in Ms44 pollen cells. Nuclei become reduced and degenerate, but normal interphase nuclei in tetrads are present after meiosis.

cal defects in Ms44 also occur before the first pollen mitosis (Fig. 3). These results suggest that mitotic progression in both mutants is blocked before the first pollen mitosis.

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