Changes in NMR Relaxation Times, Gene Expression and Quality of Seeds : Response to Different Temperature Treatments before and after the Heading Stage of Rice Plants

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We investigated the effects of different temperature treatments on the ^1H-nuclear magnetic resonance (NMR) relaxation times (T_1 and T_2) before and after the heading stage of rice seeds. The T_1 values at temperatures of 25℃/30℃ and 30℃/25℃ before and after the heading stage were lower than those at 25℃/25℃ 21 days after heading (DAH). The T_2 values at 25℃/30℃ and 30℃/25℃ were abruptly shortened at 28 DAH, while that of under 25℃/25℃ treatment was hardly shortened. In addition, dehydration of rice seeds was accelerated by heat stress at 30℃ before or after the heading stage. The changes in T_1 values at 30℃ before or after the heading stage were similar to the changes in the degree of dehydration. These results indicate that T_1 and T_2 are useful diagnostic indicators for the water status during seed ripening of rice plants. A high level of expression of aquaporin gene OsPIP1;1 in seeds at 25℃/30℃ and 30℃/25℃ was detected using DNA microarray analysis at 14 DAH. Seed quality grown under 25℃/30℃ and 30℃/25℃ treatments was inferior to that of seeds under 25℃/25℃ treatment because of the occurrence of white immature kernels. These results suggested that thermal stress either before or after the heading stage led to a reduction in the quality of rice seeds as well as changes in NMR relaxation times and expression of aquaporin genes.
2013-10-15