Delayed Autonomous Self-pollination in Saxifraga hirculus L.(Saxifragaceae)

Through continuous observation of six stages of floral morphology and development,and continuous assay of pollen viability and stigma receptivity,we identified a novel mechanism of delayed autonomous self-pollination driven by filaments in Saxifragahirculusin high arctic and alpine regions.The crack mode of anther and the stigma structure was studied by SEM,and using SudanⅢtested pollen histochemistry.The results showed that:(1)As the majority of anthers gathered above the stigma by filaments,pollen viability and stigma receptivity reach their peaks[(94±6)% and(96±13)%,respectively],then the spatiotemporal separation of pollen and stigma which termed as herkogamy came from stage 3[the pollen viability higher to(90±8)%,however,the stigmas receptivity only(6±17)%],were eliminated in stage 4.This autonomous self-pollination occurs after outcrossing,making S.hirculus a classical case of delayed autonomous selfing.(2)Deeply concave stigmas with abundant columned papillae and oily pollenkitt got pollen together and contacted with stigmas well,increasing pollination efficiency.(3)We examined the breeding system of this species,found that there was no difference between obligate self-pollination and hand self-pollination in seed production.Indexes of autonomous selfing in 2007 and 2008 were 0.92 and 0.91,respectively.It means that S.hirculus developed a capacity of self-pollination and no pollen lamination.Significant difference between hand self-pollination and hand outcross-pollination in seed production indicating that the quality of self-pollen is lower than that of outcross-pollen and self-pollination can result in inbreeding depression.Reproductive assurance measures were 0.92 in 2007 and 0.91 in 2008 indicating selfing provided reproductive assurance.No effective pollinators were found.These results showed that as a glacial relict,S.hirculus has developed a capacity for delayed autonomous selfing while retaining partial characteristics of outcrossing from its ancestors,and provided reproductive assurance in rough weather conditions.