Introduction

Self-incompatibility (SI) is the single most important outbreeding device found in Angiosperms. It is a mechanism under genetic control which regulates the acceptance or rejection of pollen during fertilisation. In many species SI is controlled by a single, multi-allelic (S-) gene (Darlington & Mather, 1949; de Nettancourt, 1977). Self-fertilisation is prevented when pollen carrying an S-allele which is genetically identical to that carried by the stigma on which it lands is discriminated from pollen carrying an S-allele which is not carried by the stigma; the former is inhibited, whereas the latter grows normally to achieve fertilisation. As such, self-incompatibility systems play a fundamental and crucial role in the processes involved in Angiosperm sexual reproduction.

SI systems may be conveniently divided into two groups: one is under sporophytic control; the other, which appears to be much more wide-spread, is under gametophytic control. Over the last ten years there has been considerable accumulation of new information, revealing much about the molecular and cellular processes involved in the two major SI systems. Most of the work on SI has concentrated on Brassica (which is under sporophytic control) and Nicotiana, together with other Solanaceous species (which are under gametophytic control). We are primarily interested in the SI system of Papaver rhoeas, which is determined by a single, multi-allelic gametophytically controlled S-gene (Lawrence, Afzal & Kenrick, 1978). In recent years we have begun to dissect the molecular events involved in SI in Papaver rhoeas.