Grain weight and the concentrations of phenylpropanoid glycosides and γ‐oryzanol in response to heat stress during ripening in rice

Background and objectives Grain weight decreases by heat stress during ripening in rice. Phenylpropanoid glycosides and γ‐oryzanol are biomarkers for heat stress. The relationships between grain weight and the concentrations of these compounds should be understood in order to use biomarkers to improve the heat tolerance of rice. In the present study, we aimed to determine the relationships between grain weight and the concentrations of these compounds in the japonica cultivar Koshihikari and the indica cultivar Takanari. Findings In Koshihikari, the concentrations of 3',6‐di‐O‐sinapoylsucrose, 24‐methylenecycloartanyl ferulate, and total γ‐oryzanol had strong negative correlations with grain weight. Conversely, in Takanari, the concentrations of 3',6‐di‐O‐sinapoylsucrose and 3'‐O‐sinapoyl‐6‐O‐feruloylsucrose had negative correlations with grain weight, whereas those of 3',6‐di‐O‐feruloylsucrose and cycloartenyl ferulate had positive correlations with grain weight. Interestingly, the relationships between grain weight and the concentrations of 3',6‐di‐O‐sinapoylsucrose, 24‐methylenecycloartanyl ferulate, and total γ‐oryzanol appeared to be stronger in Koshihikari than in Takanari. Conclusions The metabolisms of 3',6‐di‐O‐sinapoylsucrose, 24‐methylenecycloartanyl ferulate, and total γ‐oryzanol may be strongly correlated with grain weight reduction caused by heat stress in Koshihikari. Significant and novelty The concentrations of 3',6‐di‐O‐sinapoylsucrose, 24‐methylenecycloartanyl ferulate, and total γ‐oryzanol may be powerful tools for improving the heat tolerance of japonica cultivars.