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Evidence for stigmatic self-incompatibility, pollination induced ovule enlargement and transmitting tissue exudates in the paleoherb, Saururus cernuus L. (Saururaceae)

Pontieri, V., Sage, T.L.
Annals of botany 1999 v.84 no.4 pp. 507-519
stigma, pollination, ovules, gynoecium, crossing, pollen tubes, pollen germination, cell walls, tissue culture
Saururus cernuus, a species belonging to the primitive herbaceous angiosperm family Saururaceae, exhibits high rates of self-sterility. We investigated the structural and functional aspects of pollen-carpel interactions following cross and self pollination to assess the tissue specific site and timing of self-sterility and factors important for successful cross pollen tube growth. Self-sterility was due to inhibition of self pollen germination at a dry stigma. Self pollination was associated with anomalous foot formation, reduced cell wall expansion and secretory activity of stigmatic papillae, and callose production in stigmatic papillae. Following germination, cross compatible pollen tubes entered a solid core of transmitting tissue and grew to the base of a short style. Entry of cross pollen tubes into the ovary was coincident with ovule enlargement which placed the micropyle in the proximity of cross pollen tube tips. Ovule enlargement also occurred following self pollination. Cross pollen tubes either entered an exudate-filled micropyle directly from the style, or growth in the ovary was localized to the epidermis of the locule and outer integument prior to entry into the micropyle. Prior to pollination, the transmitting tract was void of secretions except for exudate in the micropyle. Growth of pollen tubes on the locule and integument was associated with exudate apparently arising from transmitting cells adjacent to growing pollen tubes. The present study provides the first evidence in a primitive herbaceous species of stigmatic self-incompatibility (SI) in association with a dry stigma, pollination-induced signalling events affecting development of carpellary tissues, and micropylar exudates.