MICROSPOROGENESIS AND TAPETAL CELLS DEVELOPMENT IN <i>RHODODENDRON LUTEUM (ERICACEAE)</i>
The process of microsporogenesis was studied by light, scanning and transmission electron microscopes in Rhododendron luteum Sweet (Ericaceae) in order to recognize stages of pollen development in relation to period of low temperature. It is shown that development of flower generative organs starts in July and lasts 11 months. Meiotic stage leading to the formation of four daughter cells (tetrads) occurs in September. At that time, tapetum shows hypersecretory morphology: abundant cisternae of RER are branched and contact with lipid droplets and vacuoles containing dense substance. Decrease of the secretory activity of tapetal cells occurs at the early stages of exine formation. The low temperature period is passed by microsporocytes at vacuolization stage. The vesiculation of tapetal cell cytoplasm, decreased number of organelles, and formation of RER «stacks» characteristic for this period are specific features of the cell dormancy. In April, the structure of tapetal cells undergoes a number of changes showing the increase of their secretory activity: reorganization of RER cisternae, disappearance of vesicles and accumulation of substances for Ubisch bodies. Pollen grain is completely developed just before the flowering. Generative and vegetative cells are distinguished at the end of spring. Tapetum collapses at that time. Questions of functional morphology of tapetal cells are discussed.