Self-incompatibility in Antirrhinum

Abstract

Self-incompatibility (SI) systems have been reported in almost half of the families of all flowering plants (de Nettancourt, 1977). Most commonly, SI is regulated by a single multiallelic locus, with the compatibility of the pollen with respect to the stigma being controlled by the haploid nucleus (East, 1940). The genus Antirrhinum possesses such a gametophytically-regulated monofactorial SI system and, when pollen and pistil share SI (S) alleles, tube growth is arrested in the style. The significance of SI systems to plant breeders, combined with the fact that they represent some of the best defined systems of intercellular interaction in plants has resulted in their being intensively studied (Anderson et al., 1986; Nasrallah et al., 1985). For example, molecular and biochemical research has identified the female S-allele products of members of the Solanaceae as being highly charged glycoproteins with molecular weights of between 20–35 kDa (for review, see Ebert et al., 1989). Many putative S-alleles have been cloned and sequenced, and it has been recently discovered that all of the S-glycoproteins in the Solanaceae have ribonuclease activity (McClure et al., 1990), leading to the proposal that this type of SI may involve a step in which pollen tube RNA is selectively degraded. Although progress has been made in our understanding of the S-allele products of the pistil in gametophytically-controlled SI (GSI), and also in the sporophytically-controlled systems where pollen compatibility is regulated by two alleles (Bateman, 1952; Nasrallah et al., 1970), little is known of the organisation of the S-locus and of S-allele expression in the pollen.