Developmental cytology on gametic abortion caused by induced complementary genes gal and d60 in japonica rice

摘要

Genes for hybrid sterility have been found in crosses between distantly related rice species showing a reproductive barrier. The gametic lethal gene gal causes gametic abortion together with the semidwarfing gene d60 in crosses among closely related japonica varieties. The F_1 between mutant line Hokuriku 100 (genotype d60d60GalGal, Gal: nonlethal allele) and its original variety Koshihikari (D60D60galgal, D60: tall allele) showed 25% sterility because of the deterioration of both sex gametes havingthe genotype d60gal, Development processes of male gametes were cytologically observed using the F_4 progenies, Meioses, tetrads, stranded microspores, single-nucleate pollens, and first-pollen mitoses were normally observed in all plants. However, at the middle binucleate stage, when generative nuclei became enclosed in newly formed generative cells and were located opposite the pore side (apart from vegetative nuclei), some pollens discontinued development in the F_4 plants with 71.6% seed set. Beforeanthesis, two distinct types of pollen were observed: vacant pollens (median value 37 microns) with only a remnant of the generative cell wall and normal trinucleate pollens (51 microns) with well-developed cytoplasm. The frequency of the empty pollensaveraged 24.5%, which was expected for the haploid genotype d60gal.