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| The phenomenon of female sterility on all male-sterile plants was observed in a genic male-sterile (GMS) Brassica napus line designated as FM195AB (A represents sterile plants and B refers to its wild type ones). For the purpose of clarifying the causal mechanism of this female sterility, we contrastively studied the morphological characteristics of reproductive structures and procedures involved in seed formation between FM195A and FM195B. First, Scanning electron microscopy (SEM) investigations on stigma papilla cells showed no apparent difference between the fertile and sterile plants. Second, alien pollen grains can normally germinate and pollen tubes can enter the stigma papilla cells of both FM195A and FM195B; however, pollen tubes in FM195A pistils appear morphologically abnormal in comparison with FM195B, even if they can normally elongate and reach the ovules. Furtther observations of the paraffin-sectioned pistils revealed that early magasporogenesis in FM195A is similar to that of FM195B; however, mono-nucleate and the subsequent developmental stages of the female gametophytes can hardly seen in the ovules of FM195A, suggesting. Approximately at the eight-nucleate embryo sac stage in FM195B, five major types of the abnormal embryo sacs in FM195A can be observed. Similarly, we found that microsporogenesis in FM195A is also stopped before the entrance of meiosis. Because both of the male and female sterility occur at the same plant, it can be assumped that the male sterility gene, Ms, may play an important role in prompting the transition from maintaince of the spore mother cells into meiosis. |
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| Keywords:Crop genetics and breeding; Brassica napus; Genic male sterility; Female sterility; Megagsporogenesis; Microsporogenesis |
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