Potassium antimonite was used to investigate the localisation of calcium in developing wheat anthers to examine the relationship between Ca and pollen development. During anther development, calcium precipitate formation increased in anther wall cells prior to microspore mother cell meiosis and appeared in microspores, suggesting the presence of a calcium influx from anther wall cells into the locule. Initially, the precipitates in microspore cytoplasm primarily accumulated in the mitochondria and destroyed their inner membranes (cisterns) to become small vacuoles, which expanded and fused, ultimately becoming a large vacuole during microspore vacuolisation. After microspore division and large vacuole decomposition, many calcium precipitates again accumulated in the small vacuoles, indicating that calcium from the large vacuole moved back into the cytoplasm of bicellular pollen.

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SummaryIsolated gametes can be used to investigate fertilization mechanisms, and probe distant hybridization between different species. Pollen grains of wheat and Setaria viridis are tricellular, containing sperm cells at anthesis. Sperm from these plants were isolated by breaking open pollen grains in a osmotic solution. Wheat ovules were digested in an enzyme solution for 20 min, and then transferred to an isolation solution without enzymes to separate egg cells from ovules. The fusion of wheat egg cells with wheat and S. viridis sperm was conducted using an electro-fusion apparatus. Under suitable osmotic pressure (10% mannitol), calcium concentration of 0.001% (CaCl2·2H2O), and a 30–35 V alternating electric field for 15 s, egg cells and sperm adhered to each other and became arranged in a line. Electroporation of the plasma membrane of egg cells and sperm using a 300–500 V direct-current electric field (45 µs amplitude pulse) caused them to fuse.

Summary In higher plants, fertilization induces many structural and physiological changes in the fertilized egg that reflect the transition from the haploid female gamete to the diploid zygote – the first cell of the sporophyte. After fusion of the egg nucleus with the sperm nucleus, many molecular changes occur in the zygote during the process of zygote activation during embryogenesis. The zygote originates from the egg, from which some pre-stored translation initiation factors transfer into the zygote and function during zygote activation. This indicates that the control of zygote activation is pre-set in the egg. After the egg and sperm nuclei fuse, gene expression is activated in the zygote, and paternal and maternal gene expression patterns are displayed. This highlights the diversity of zygotic genome activation in higher plants. In addition to new gene expression in the zygote, some genes show quantitative changes in expression. The asymmetrical division of the zygote produces an apical cell and a basal cell that have different destinies during plant reconstruction; these destinies are determined in the zygote. This review describes significant advances in research on the mechanisms controlling zygote activation in higher plants.