![]() In maize lines carrying B chromosomes, the B centromere frequently undergoes nondisjunction at the second mitosis, so that one sperm cell of a pair acquires two B centromeres and the other acquires none (Rusche et al., 1997). Genetic evidence for fusion partner selectivity comes from studies of maize lines that carry supernumerary (so-called B) chromosomes. It will be interesting to determine if the sperm cell that is ‘‘in communication’’ with the vegetative nucleus is destined for a particular fusion partner (egg or central cell), a situation that has been documented in Plumbago (Russell, 1985). A cytoplasmic extension between one of the two sperm cells and the vegetative nucleus was already documented from transmission electron microscopy analyses in Plumbago (Russell, 1984), and extensions of the vegetative nucleus toward one of the two sperm cells are visible in 4 9 ,6-diamidino-2-phenylindole–stained pollen (Lalanne and Twell, 2002). Figure 4 shows a pollen grain from one line: note that one sperm has a long cytoplasmic extension that connects it to the vegetative nucleus (M. In transgenic lines harboring one such construct, the two sperm cells are brightly fluorescent. McCormick, unpublished data) to determine if any would confer sperm-specific expression to a reporter gene, eGFP. ![]() Accordingly, the promoters of the Arabidopsis homologs were tested (M. ![]() ![]() We reasoned that those might be good candidates for sperm-specific messages. For 4% of the maize sperm ESTs, the best database matches were to proteins that were annotated as hypothetical (i.e., not in other available EST databases). (2003) sequenced 5000 ESTs from a cDNA library prepared from sperm of maize that had been purified away from vegetative cytoplasm by fluorescence- activated cell sorting and used reverse transcriptase–mediated PCR and in situ hybridizations to characterize the expression patterns for some of these mRNAs. ![]()
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