Ultrastructural abnormalities in pollen and anther wall development may lead to low pollen viability in jasmine (Jasminum sambac (L.) Aiton, Oleaceae)

Jasmine [Jasminum sambac (L.) Aiton] rarely sets seed, and its poor pollen fertility significantly influences fecundity. In this study, pollen development of jasmine was investigated at an ultrastructural level, examining the dynamic changes of microspore-tetrads and tapetum and their possible effects on pollen viability. Normally developed microspores are released at the late tetrad phase, whereas the abnormal ones formed large complexes of two to five tetrads with plasmodesmata. Ultrastructural observation also revealed that sterility of some pollen grains might result from defective development of cell walls that failed to absorb their surrounding sporopollenin to form the exine. The secretory type of jasmine tapetum, the usually degenerated middle layer and thickened endothecium were confirmed during the process of pollen development. The epidermis, middle layer and endothecium exhibited no adverse effects on pollen development and dispersal. However, the asynchronous division and delayed degradation of tapetal cells resulted in abnormal development of some microspores and the formation of massulae and empty and flat pollen grains. This is the first ultrastructural characterization of pollen development in J. sambac leading to a better understanding of embryology and poor pollen fertility of this important horticultural species.