THE PLANT CELL, Vol 8, Issue 5 815-821, Copyright © 1996 by American Society of Plant Biologists
Sperm Identification in Maize by Fluorescence in Situ Hybridization
L. Shi, T. Zhu, H. L. Mogensen and P. Keim
Department of Biological Sciences, Box 5640, Northern Arizona University, Flagstaff, Arizona 86011-5640
The two sperm cells of common origin within the pollen tube of flowering
plants are each involved in a fertilization event. It has long been
recognized that preferential fusion of one sperm with the egg can occur in
B chromosome-containing lines of maize. If the second pollen mitosis begins
with a single B chromosome, nondisjunction will result in one sperm
possessing two B chromosomes and the other containing no B chromosomes. The
B chromosome-containing sperm most often fertilizes the egg, whereas the
sperm nucleus with no B chromosomes fuses with the polar nuclei. Despite
the obvious advantages of being able to recognize and then track, separate,
and analyze one sperm type from the other, it has not been possible because
of the lack of sufficient detectable differences between the two types of
sperms. In this study, we used a B chromosome-specific DNA sequence (pZmBs)
and in situ hybridization to identify and track the B chromosome-containing
sperm cell within mature pollen and pollen tubes. Our results are
consistent with conclusions from previous genetic studies related to B
chromosome behavior during pollen formation. Within pollen tubes, the
position in which the B chromosome-containing sperm travels (leading or
trailing) in relation to the sperm cell lacking B chromosomes appears to be
random.
