XVI International Botanical Congess

Isolated sperm cells of Nicotiana tabacum differ in size and relationship with the vegetative nucleus. The smaller one (Svn) has an average diameter of 6.79 µm, whereas the larger one (Sua) is 7.76 µm. Microelectrophoresis of paired sperm cells from single pollen tubes demonstrates that the cells differ in electrophoretic motility. In all samples examined, the Sua has higher electrophoretic motility than the Svn, although the difference is not significant. Calculated surface charges of mature Svn and Sua based on electrophoretic motility are 2940 ± 170 esu/cm2 and 3030 ± 170 esu/cm2, respectively. Sperm cell surface charge varies at different developmental stages. Fusion frequency between egg and Sua cells is higher than that between the egg and Svn, suggesting potential preferential fertilization in tobacco.