SPERM IDENTIFICATION IN MAIZE BY FLUORESCENCE IN-SITU HYBRIDIZATION

The two sperm cells of common origin within the pollen tube of floweri ng plants are each involved in a fertilization event. It has long been recognized that preferential fusion of one sperm with the egg can occ ur in B chromosome-containing lines of maize. If the second pollen mit osis begins with a single B chromosome, nondisjunction will result in one sperm possessing two B chromosomes and the other containing no B c hromosomes, The B chromosome-containing sperm most often fertilizes th e egg, whereas the sperm nucleus with no B chromosomes fuses with the polar nuclei. Despite the obvious advantages of being able to recogniz e 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 ma ture pollen and pollen tubes, Our results are consistent with conclusi ons from previous genetic studies related to B chromosome behavior dur ing 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.