13:15 〜 14:00
[P3-40] The Effect of N-application on cpHSP70-2 Accumulation to Improve Rice (Oryza sativa L.) Grain Chalkiness
High temperature (HT) increases chalky rice grains which lower grain quality, market value, and substantial yield. Although nitrogen (N) application is a promising technique to enhance transpiration, carbohydrate supply, and then reduce chalkiness but it lowers eating and cooking quality as well. Thus, the underlying molecular mechanism of chalkiness along with N nutrition should be clarified. Recently we isolated conditional chalky grain mutant flo11-2, its causative gene encodes amyloplast molecular chaperone (cpHSP70-2) and found a negative correlation between its expression and chalkiness. In this study, we examined the effect of N-application on chalkiness and cpHSP70-2 accumulation using near-isogenic lines with an erect panicle (EP) trait showing low available carbohydrate per spikelet, and a non-EP (NEP) trait. Experiments were conducted in Kyoto, 2020 using 7 cultivars; Aki(EP, NEP), LG5(EP, NEP), flo11-2, Nipponbare, and Kinmaze under pot and field conditions with low and high (ambient) temperatures (LT, HT) and/or different N levels, namely low and high N (LN, HN) for pots and 0, 6, 20 gN m-2 (0N, 6N, 20N) for fields. The results showed flo11-2 had the highest chalky ratio under HT, while early heading cultivars [Aki(EP), Aki(NEP)] had the lowest due to escaping from a HT season. LN-HT and 0N treatments produced the highest chalky ratio. Chalky ratio was positively correlated with averaged daily maximum temperature during 20 days after flowering. N-application reduced chalky ratio and tended to increase cpHSP70-2 accumulation irrespective of genotypic differences.