| Self-incompatibility (SI) is a genetically controlled phenomenon preventing seed set in self pollinated plants producing functional gametes. Orlando tangelo (Citrus paradisi Macf. x C. reticulata Blanco) is a gametophytically self incompatible variety and is cross compatible with Dancy tangerine (C. reticulata Blanco). Developmental, physiological and biochemical events resulting in SI were studied by comparing Orlando pollen in both self incompatible pollinations and cross compatible pollinations with Dancy tangerine.;Up to day 3, most pollen tubes followed the same route and timing. Pollen germinated in stigmatic exudate, grew between papillae cells, and between parenchymatous cells to stylar canals. By day 6 most pollen tubes reached the ovary in compatible pollinations but those from incompatible pollinations were still in the upper style. Pollen tube growth rates varied over time in vivo and were linear in vitro. They decreased at 3 days in both the self-incompatible pollination and in vitro. In the compatible cross, the generative cell divided between 1 and 3 days after pollination. Generative cell division occurred by day 3 in a few pollen tubes in the incompatible cross and in vitro, but most pollen tubes were still bicellular.;Stigma protein changes were compared using SDS-PAGE. Major and minor protein bands, from 15 to over 200 kD, were common to both unpollinated stigmas. The band above 200 kD was an arabinogalactan-protein(AGP). AGPs were localized in the stigma papillae, exudate, and stylar canal epithelial cells of both varieties. Protein changes of both unpollinated and pollinated stigmas over time were mostly quantitative; however, there were qualitative changes specific either to incompatible or to compatible pollinations.;Number of pollen tubes was compared in Orlando and Dancy gynoecia at stigma surface, upper style, lower style, ovary and ovule entrance. In incompatible pollinations, the stigma was the primary region of pollen tube arrest. In compatible pollinations some pollen tubes penetrated ovules between 9 and 12 days after pollination; however, other pollen tubes were arrested in the stigma. Pollen tubes penetrating ovules differed morphologically from those arrested in both compatible and incompatible situations. |
