Characterization of viviparous mutants in rice

Four single recessive viviparous mutants of rice, riv1-1, riv1-2, riv2 and enl1, were characterized. All riv mutants showed pre-harvest germination (v ivipary) during seed development but no defects in the other traits. Vivipa ry was also observed in the enl1 mutant that lacked endosperm in the seeds. Examination of the viviparous nature of the mutants under three rain condi tions, no rain, artificial rain and natural rain, revealed that the inducti on of vivipary in the riv mutants required a small amount of water. In cont rast, precocious germination in the enl1 mutant was caused by the absence o f endosperm in the seeds, but not by the external signal of rain. In riv mu tants, the precocious germination occurred simultaneously at late stages of seed development, The germination test in the presence of exogenous ABA re vealed that sensitivity to ABA was gradually reduced from 15 through 35 day s after pollination in the wild-type seeds, and was almost lost at 40 days after pollination. A similar tendency was observed in riv1 and riv2 seeds. However, at 15-35 days after pollination, riv1-1 and riv2 seeds had signifi cantly lower sensitivity to ABA than the wild-type seeds, In addition, the three riv mutants lost the sensitivity to ABA at an earlier stage of seed d evelopment than the wild type. These results indicate that riv1 and riv2 ha ve a lower sensitivity and shorter period of sensitivity to ABA.