Characterization of S tester lines in Brassica oleracea: Polymorphism of restriction fragment length of SLG homologues and isoelectric points of S-locus glycoproteins

Forty three S tester lines of Brassica oleracea were characterized using DNA and protein gel-blotting analyses. DNA gel-blot analysis of HindIII-digested genomic DNA with class-I and class-II SLG probes revealed that 40 lines could be classified as class-I S haplotypes while three lines could be classified as class-II S haplotypes. The band patterns in the S tester lines were highly polymorphic. Although the S tester lines typically showed two bands corresponding to SLG and SRK in the analysis with the class-I SLG probe, only one band was observed in the S²⁴ homozygote. This band was identified as SRK, suggesting that this haplotype has no class-I SLG band. In the analysis using the class-II SLG probe, one plant yielded a different band pattern from the known class-II haplotypes, S², S⁵ and S¹⁵. Unexpectedly, this plant was reciprocally cross-incompatible with the S² haplotype. Therefore, it was designated as S(2-b). We found an S¹³ haplotype having a restriction fragment length polymorphism different from that of the S¹³ homozygotes of the S tester line. These findings indicate that S homozygous lines with the same S specificity do not necessarily show the same band pattern in the DNA gel-blot analysis. Soluble stigma proteins of 32 S homozygotes were separated by isoelectric focusing and detected using anti-S²²SLG antiserum. S haplotype-specific bands were detected in 27 S homozygotes but not in five S homozygotes, including the S²⁴ homozygote. This is consistent with the observation that the S²⁴ haplotype had no SLG band.