Genetic control of meiosis in rice, Oryza sativa L. IV. Cytogenetical analyses of asynaptic mutants

Abstract

One complete asynaptic mutant, MM-19, and two partial ones, MM-4 and MM-16, of Oryza sativa L. induced by N-methyl-N-nitrosourea (MNU) were cytogenetically investigated. No chromosome pairing occurred from zygotene to pachytene and 24 univalents appeared at diakinesis and metaphase 1 in MM-19. On the other hand, a partial lack of chromosome pairing was observed from zygotene to pachytene and various numbers of univalents occurred at metaphase I in MM-4 and MM-16. The mean chiasma frequency per bivalent as well as per cell decreased to different extents in MM-4 and MM-16, and the correlation between both the amount of chromosome pairing from zygotene to pachytene and the chiasma frequency per cell at diakinesis was recognized. Judging from the development of anthers in each meiotic stage, the duration of the stage forming the synizetic knot, at which chromosome pairing took place, was longer in MM-4 and MM-16 than in the normal plant, and was in MM-19 almost as long as in the normal plant. The results of gene analyses indicate that each of the three asynaptic mutants is controlled by a recessive gene and that, at least for MM-4 and MM-16, these genes are located at different loci.Key words: asynaptic, rice, Oryza, chiasma frequency, synizesis.