Cytologie ultrastructurale de l'anthère de Saxifraga. I. Période d'initiation des précurseurs des sporopollénines au niveau des principaux types exiniques

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Abstract
The period of initiation of sporopollenin precursors studied by transmission electron microscopy in the anthers of three species of the genus Saxifraga (S. cymbalaria ssp. huetiana, sempervivum and clusii) reveals two main phases. They are characterized successively by the elaboration of the ectexine (outer layer of the exine composed of sporopollenin) and endexine (inner layer of the same wall). This phenomenon has been observed in the tapetal periplasm and the sporal periplasm; the latter has been chosen as the reference point in establishing the chronology of the ontogenetic stages as well as the terminology of the sporopollenin structures. Proectexine and proendexine are distinctly stratified in the microspore while they become intermingled in the proorbicules. Proendexine could be elaborated according to a fluid mosaic model in relation to the plasmalemma. During this period, the relationships revealed between the plasmalemma–glycocalyx system (glycolemma) and the cytoskeleton (microtubules, microfilaments, and microfibrils) are emphasized. Thus, their functional role in the setting up of sporopollenin precursors is suggested.

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