Towards an in vitro bioassay for the self-incompatibility response in Brassica oleracea

Summary Eluates of stigmas of Brassica oleracea that were known to contain S locus-specific glycoproteins (SLSG) discriminated between self and cross pollen in vitro in three different media. Discrimination was equally evident in experiments that were the in vitro equivalents of reciprocal pollinations. In a TAPS-buffered medium, self eluates depressed pollen germination in a dose-dependent manner. TAPS medium allowed a bioassay of the effects of SLSG in eluates because it optimized germination in a way that eliminated the complicating features of the stimulatory substances in the eluates. Stigma eluates affected percentage pollen germination and optimum calcium concentrations in vitro whether or not SLSG were present in the eluates, but differently in different media, and depending on whether the eluates were cross or self with respect to the pollen tested. Thus, the effect of stigma eluates on the in vitro germination of pollen in Brassica depends on the balance of stimulatory versus inhibitory substances in the eluates.