Pollen-Stigma Interactions and S-Products in Brassica

Abstract

The cellular events that occur during pollen-stigma interactions and the mechanisms by which self-incompatibility is expressed have been the subjects of much research and hypotheses these past ten years (Heslop-Harrison .1975; Dumas et al. 1984). Recently, the initial interaction between male and female partners have been interpreted in terms of new concepts based on cellular and molecular recognition (Dumas et al. 1984). When pollen landed on the stigma, an information, specific of the species and genotypes, is read-out by the stigma or other pistil tissues. Both information and read-out system are encoded in a complex genetic system of which the commonest and simplest type is the monofactorial S locus with many alleles (see De Nettancourt 1984). Pollen acceptance or rejection is thus based on the results of a dialogue between the S-gene products. As a conseguence, if information and read-out are compatible, fertilization ensues. If not, the interactions lead to the incompatibility response. The Brassica model, controlled by a sporophytically inherited S gene system, with recognition reaction at the stigma surface, provides an ideal experimental model. In this article we will review the data available on stigma read-out system and pollen information in Brassica that constitutes certainly one of the best-defined processes of cell recognition found in higher plants.