ANALYSIS OF POLLEN S-HAPLOTYPE DETERMINANT IN BRASSICA SELF-INCOMPATIBILITY

Many higher plants have evolved self-incompatibility (SI) systems to prevent self fertilization. In Brassica, SI recognition is controlled by the S-locus which contains highly polymorphic genes： S-receptor kinase gene (SRK and S-locus protein 11 gene (SP11). Recent functional studies have shown that SRK and SP11 control stigma and pollen S-haplotype specificity, respectively. However, the expression and localization of SP11 protein in the anther during its developmental process and the translocation of SP11 from pollen to a stigmatic papilla cell during the pollination process have never been demonstrated. Here, we analyzed the localization of SP11 in the anther or the pollinated stigma by immunostaining. We first showed that the major oxidised form of S8-SP11 functions as the pollen S-haplotype determinant and used this form to produce specific S8-SP11 antibody. The immnostaining with this antibody showed that the S8-SP11 is localized to the tapetum and the loculus of anther at early developmental stage, and to the pollen coat of mature pollen grains at late stage. Furthermore, after pollination . S8-SP11 was detected in the cell wall of the papilla cell just beneath the pollinated site. Thus, it was suggested that the SP11 translocated from pollen coat to papilla cell and penetrated into its cell wall to induce the self-incompatible response.