Ultrastructural Features ofPrunus AviumL. Pollen Tubein Vivo

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Abstract
Ultrastructural features of the compatible pollen tube of Prunus avium (L.) growing in vivo are described. During its growth the tube has four different zones reflecting a functional specialization. The cytoplasm of the apical or growth zone contains two types of secretory vesicles probably involved in the formation of the tube wall. The sub-apical zone, in addition to the secretory vesicles, shows the presence of dilated rough endoplasmic reticulum (RER) cisterns containing electron-dense material which does not react to the test for polysaccharides. In the nuclear zone the vegetative nucleus and the generative cell can be observed; this zone is followed by the vacuolization and callosic plug formation one. The function of secretory vesicles, as well as other ultrastructural features, are discussed in relation to the self-incompatibility phenomenon.