THE PLANT CELL, Vol 5, Issue 7 747-755, Copyright © 1993 by American Society of Plant Biologists
Karyogamy after Electrofusion of Single Egg and Sperm Cell Protoplasts from Maize: Cytological Evidence and Time Course
J. E. Faure, H. L. Mogensen, C. Dumas, H. Lorz and E. Kranz
Reconnaissance Cellulaire et Amelioration des Plantes, UMR 9938 CNRS-INRA, Ecole Normale Superieure de Lyon, 69364 Lyon Cedex 07, France
In maize, in vitro fusion of isolated male gametes with isolated egg cell
protoplasts can be induced by electric pulses. Until now, karyogamy has not
been demonstrated. In this study, we cytologically examined fusion products
fixed at different times after electrofusion with phase contrast microscopy
and transmission electron microscopy. We obtained a precise timetable from
23 samples studied during the first 3 hr. The sperm nucleus was integrated
within the egg cell protoplast, migrated toward the egg cell nucleus, and
fused with it within 1 hr, as demonstrated by ultrastructural observations,
three-dimensional reconstructions of nuclei, and subsequent nuclear volume
estimates. Fusion of nuclei occurred before zygotic mitosis, as is the case
in vivo. These findings demonstrate karyogamy during in vitro fertilization
of maize.