Etude ultrastructurale de la gamétogenèse mâle dans une espèce à floraison cléistogame: Oxalis corniculata, suivie de quelques considérations générales sur la cléistogamie

Abstract

In male gametophytes of chasmogamous and cleistogamous flowers of Oxalis corniculata, the development of the tube cell at the ultrastructural level shows that gametogenesis is almost the same in both cases: the dictyosomes, in particular, go through an inactive period accompanied by an intense production of microvesicles. This rest phase, present in pollen grains of numerous Angiosperms, is thus well marked in the two types of flowers. However, the similarity between the two types of gametogenesis is less obvious with regard to cell reserves: in pollen grains of cleistogamous flowers, starch formation is slightly retarded. At maturity, they contain numerous starch grains comparable with those found in chasmogamous flowers. In both types of flowers, the generative cell of the mature gametophyte gives rise to two sperms.Earlier studies on male gametogenesis in chasmogamous and cleistogamous flowers of Streptoearpus nobilis and Viola sp. compared with results on Oxalis corniculata show that cleistogamy determines more or less strongly the ontogeny of pollen grains as well as the morphology of the vegetative and floral parts. Thus, different degrees of cleistogamy exist from very specialized states (Streptocarpus nobilis) to very little modified ones (Oxalis corniculata).