Ultrastructural and microbiological research of the double fertilization in angiosperm

点击翻译按钮获取中文摘要

Changes in the distribution of organelles and organelle-DNA in Pelargonium zonale from the mature egg cell stage to the first zygotic division during the early stages of embryogenesis were investigated using electron microscopy and fluorescence microscopy. The mature egg is a large, polarized bulbous-shaped cell tapering toward its micropylar end. The wide chalazal region has a large nucleus that is surrounded by cytoplasm containing many giant mitochondria and large amyloplasts. The mitochondria contain a large amount of mitochondrial DNA (mt-DNA) and appear as long stretched rods or complex rings, sometime consisting of several concentric or half-concentric circles in sections. The tme of pollination to cell fusion is approximately 6 to 9 h and is 20 to 24 h until the first zygotic division. The changes in the zygote and its organelles preparatory to division occur in 3 stages. At stage 1 (6-9 h after pollination), cell fusion occurs and the zygote bigins to elongate. Many vacuoles o … More f varying size appear surrounding the nucleus. At stage 2 89-15 h), the zygote nucleus migrates to a central position in the cell and the mitochondria form a single ring that becomes either irregularly crushed or appears as long thin strings. Amyloplasts exhibit a gradual decrease in the number of starch grains. At stage 3 (15-20 h), the vacuoles disappear, except for a few that remain in the micropyolar region and cell size decreases. Mitochondria become short, fine strings or small rings. Amyloplasts with starch grains are no longer observed, but are transformed into large proplastids. Following the first division of the zygote approximately equal-sized apical and basal cells are formed. Short rod-shaped or small ring-shaped mitochondria are randomly distributed near the nucleus of the apical cell, whereas mitochondria in the basal cell are long and rod-shaped. Inthe electron microscope, two types of plastids can be distinguished : dark oval plastids originating from the sperm cell, which are observed in both apical celland basal cell, and others with a less dense, amorphous matrix, believed to originate from egga amyloplasts, which are unevenly distributed in the micropylar region of the basal cell. fluorometry using video-intensified microscope photon counting system (VIMPICS) reveals that, correlated with changes in mitochondrial morphology, DNA amount within the mitochondrion decreases linearly during these stages. Less