抄録
Germination of seeds is a complex physiological process triggered by imbibition of water. Although germination does not occur even though the seeds on a mother plant are in a humid surrounding, wheat (Triticum aestivum L.) caryopses are characterized by relatively weak embryo dormancy and are susceptible to preharvest sprouting, vivipary. We focus on dynamic state of water in wheat seeds for the purpose of screening characteristics in wheat three cultivars having different susceptibility in preharvest sprouting. Although Shirogane-Komugi is known as one of the susceptible preharvest sprouting cultivars, there was no relationship of ABA sensitivity to vivipary since the mature seeds easily loose their dormancy. Spin-spin NMR relaxation times (T_2) in wheat indicated that cellular water in the dry seeds mainly consisted of tightly bound water. Although there are no influence of ABA on T_2 in non-sprouting seeds, ABA strongly reduced T_2 in endosperms for sprouting seeds. These results indicate that ABA prohibited both water uptake and water mobility in sprouting seeds while mobility of water bound with starch appears to remain unchanged in non-sprouting seed. The water in the endosperms of the ABA-treated seeds have more restricted mobility than in those treated by DW. Especially, the rate of long T_2 values reduced by ABA was the highest in Shirogane-Komugi and the tendency was consisted with their vivipary of three cultivars tested. Therefore, it is suggested that the T_2 reflected a primary event of sprouting for wheat grains. In conclusion, the water compartments determined by the T_2 in endosperms of sprouting seeds clearly reflected an ABA sensitivity and thus the parameters would be useful for vivipary screening in wheat cultivars.
