KARYOGAMY AFTER ELECTROFUSION OF SINGLE EGG AND SPERM CELL PROTOPLASTS FROM MAIZE - CYTOLOGICAL EVIDENCE AND TIME-COURSE

In maize, in vitro fusion of isolated male gametes with isolated egg c ell protoplasts can be induced by electric pulses. Until now, karyogam y has not been demonstrated. In this study, we cytologically examined fusion products fixed at different times after electrofusion with phas e contrast microscopy and transmission electron microscopy. We obtaine d a precise timetable from 23 samples studied during the first 3 hr. T he sperm nucleus was integrated within the egg cell protoplast, migrat ed toward the egg cell nucleus, and fused with it within 1 hr, as demo nstrated by ultrastructural observations, three-dimensional reconstruc tions of nuclei, and subsequent nuclear volume estimates. Fusion of nu clei occurred before zygotic mitosis, as is the case in vivo. These fi ndings demonstrate karyogamy during in vitro fertilization of maize.