NUCLEAR BEHAVIOR IS DEFECTIVE IN THE MAIZE (ZEA-MAYS L) LETHAL OVULE2FEMALE GAMETOPHYTE

It has long been known that the maize lethal ovule2 mutation results i n ovule abortion but has a much smaller effect on pollen development o r function. The behavior of the nuclei, the microtubular cytoskeleton and other events were examined in normal and lo2 mutant female gametop hytes in order to obtain an understanding the role of this gene in emb ryo sac formation. The effect of the lo2 mutation is manifested follow ing meiosis. When the surviving single megaspore carries the mutant lo 2 allele, often both the megaspore and its nucleus greatly enlarge, bu t the nucleus either fails to divide or divides only once or twice; Mi cronuclei are frequently present, nuclei are often clustered and the a bundance and patterns of microtubules are abnormal in the mutant embry o sacs. The mutant female gametophytes are blocked at the one-, two- o r four-nucleate stage. Nearly all the embryo sacs containing the lo2 a llele fail to function as evidenced by the failure of transmission of closely linked loci. When mutant female gametophyte development is arr ested, the immature embryo sac degenerates, This mutation appears to i dentify a gene that is essential in the female gametophyte for normal nuclear division and migration and the normal accompanying tubulin cyt oskeleton behavior.