MALE GAMETOPHYTE DEVELOPMENT IN PLUMBAGO-ZEYLANICA - CYTOPLASM LOCALIZATION AND CELL DETERMINATION IN THE EARLY GENERATIVE CELL

The behavior of the generative cell during male gametophyte developmen t in Plumbago zeylanica was examined by epifluorescence microscopy and electron microscopy with organelle nucleoid as a cytoplasm marker. Wh en the thin sections stained with 4',6-diamidino-2-phenylindole (DAPI) were observed under an epifluorescence microscope, two types of fluor escence spots were detected in the cytoplasm of the pollen cells befor e the second mitosis. The spots emitting stronger fluorescence were co nfirmed as plastid nucleoids and those emitting dimmer fluorescence we re mitochondrial nucleoids. Before the first mitosis, both plastid and mitochondrial nucleoids distributed randomly in the cytoplasm of the microspore. A small lenticular generative cell formed with attachment to the interior of the intine after the mitosis. Small vacuoles were f ound in the lenticular cell. In the cytoplasm of the lenticular cell, both plastid nucleoids and the small vacuoles were distributed randoml y at the very beginning but began to migrate in opposite directions im mediately. Plastid nucleoids aggregated to the side of the cell that f aces the pollen center and the small vacuoles aggregated to the side o f the cell that attaches to the intine. As the result, the lenticular generative cell appeared highly polarized in cytoplasm location soon a fter the first mitosis. In accordance with the definition of the cytop lasm polarization, the primary wall between the generative and the veg etative cells began to flex and the lenticular generative cell started to protrude towards the pollen center. When the generative cell peele d away from the intine, it was spherical in shape with the pole that a ggregated plastids towards the vegetative nucleus. But the cell direct ion appeared to be transformed immediately. The pole that aggregated s mall vacuoles turned to the position towards the vegetative nucleus an d the pole that aggregated plastid nucleoids turned to the position co untering to the vegetative nucleus. A cellular protuberance formed at the edge of the pole that aggregated small vacuoles and elongated into a tapered end that got into contact with the vegetative nucleus. The polarization of the cytoplasm kept constant throughout the second mito sis. The small vacuoles that apportioned to the sperm cell which attac hed the vegetative nucleus (the leading sperm cell) disappeared during sperm cell maturation. Plastid nucleoids were apportioned to the othe r sperm cell (the trailing sperm cell) completely. Mitochondrial nucle oids became undetectable after the second mitosis.