Glycosylation of S-RNases may influence pollen rejection thresholds in Solanum chacoense.

A survey of Solanum chacoense plants expressing an authentic S(11)-RNase transgene identified a line with partial compatibility to S(11) pollen. By comparing fruit set to the S-RNase levels determined immunologically in single styles, the minimum level of S(11)-RNase required for full rejection of S(11) pollen was estimated to be 18 ng per style. The S(11)-RNase threshold levels are thus considerably lower than those previously reported for the S(12)-RNase. Interestingly, these two allelic S-RNases differ dramatically in the extent of glycosylation, with the number of glycosylation sites varying from one (S(11)-RNase) to four (S(12)-RNase). It is suggested that reduced glycosylation of the S(11)-RNase may be related to the lower threshold for pollen rejection.