Abstract
Water status in superior seeds of rice (Oryza sativa L.) panicles exposed to low temperature, 15℃ for seven days, at different maturing stages was evaluated by accumulation of dry matter, water content and NMR relaxation time (T_2). The dry weight of control seeds grown at field linearly increased after anthesis to 21 DAF and it proceeded without significant changes thereafter. On the other hand, that of seeds treated at 1st week-chilling linearly increased until 28DAF. The decay in dry matter increase was observed both at 2nd and the 3rd week-chilling treatments. The water content of control seeds linearly decreased at 7 to 14 DAF and it slightly decreased until 49 DAF while decreasing of water continent in child seeds occurred one week delay. The maintenance of higher water content in seeds was more emphasized in earlier stage of rice plants exposed to the chilling temperature. T_2 values of long and short fractions in rice seeds grown at field showed linear decrease until 21 DAF but abrupt decrease was observed in all seeds at 28 DAF. Changes in T_2 values indicated that low temperature at early stage maintained more mobile water in immature seeds seven days longer than control grown at field while the phenomena disappeared in seeds treated at middle stage. From these results, it was shown that the early stage of rice seed maturation was more sensitive to the chilling stress.
