[Changes in cell ultrastructure during sexual determination of litchi staminate flower]

The ultrastructural changes of meristematic cell during the degeneration of gynoecium primordium leading to the formation of staminate flower of litchi were followed. Degradation of the cells and transport of the dissolved cytoplasmic components were well ordered. Configurations of rough endoplasmic reticulum (RER) changed significantly. ER played an important role in degenerative processes of gynoecium primordiuml cells. The degenerative processes started with the appearance of long RER cisternae throughout the cytoplasm. Some long RER cut or enclosed the cytoplasm. Some RER connected nucleus and mitochondria of adjacent cells, formed a ridge-like connection. Later the RER formed concentric patterns and then became irregular stacks. RER and golgiosome produced many vesicles, which were importance to protoplasmic degradation and intercellular transport of the cellular debris. The number of mitochondria increased up to the time when they began to degrade in batches. Peroxisomes appeared temporarily at the middle stage near the nucleus. The nucleolus disintegrated at the beginning of degeneration of nucleus. Then fragments of chromatin aggregated at the periphery of nuclear membrane and diffused outward. In some nuclei the perinuclear membrane became dilated and puffs were formed. As cell degeneration progressed, the protoplasm disintegrated and dissipated in an orderly fashion, i.e. ribosomes became disorganized first, followed by peroxisomes, ER, golgiosoms, mitochondria and nucleus. Eventually, gynoecium primordium cells digested all of the cytoplasm, leaving only cell wall with high electron density. Most of the products of degeneration of gynoecium primordium cells were removed through either symplastic or apoplastic pathways. Programmed cell death (PCD) may be involved in the degeneration of meristematic cells at the gynoecium primodium.