Abstract
Rice grains are matured in 40 days after flowering. During that time, intense changes can be seen such as storage protein and starch accumulation, decrease in water content etc. To identify aquaporins involved in these processes, mRNA expression levels were analyzed in a realtime-PCR method at each stage. As a result, many aquaporins were expressed in early ripening stage. In contrast, OsPIP2;1 and OsTIP3;1 accounted for the most part of aquaporin mRNA expression level in mid-ripening stage. Western blotting results showed that OsPIP2;1 and OsTIP3;1 proteins increased rapidly from mid-ripening stage. Furthermore, immunocytochemical analysis clarified that OsPIP2;1 was present throughout the organ, whereas OsTIP3;1 was present only in the aleurone layer. In conclusion, it is assumed that OsPIP2;1 and OsTIP3;1 showed correlation with the rapid decrease of water content in rice grains during mid-ripening stage. In particular, OsTIP3;1 was only expressed in rice grains and was not found to be expressed in other organs. These results suggest that OsTIP3;1 has a unique function related to the aleurone layer.
