Physiological and biochemical mechanisms of taste decrease in high tasting japonica rice under warming at growth stages

In order to better understand the response of the taste of high-tasting japonica rice in cool regions to climate warming, we have set up warming treatments at six growth stages in the field in two years: the before heading stage (T1), the whole growth stage (T2), the grain-filling stage (T3), the early grain-filling stage (T4), the middle grain-filling stage (T5) and the late grain-filling stage (T6). Except for T6, which showed no significant changes, all other treatments had varying degrees of negative effects on the taste value of milled rice, with T2 and T3 being the most serious, followed by T1, and finally T4 and T5. The taste value of milled rice was positively correlated with amylopectin content, total starch content, peak viscosity (PV), breakdown (BD), and negatively correlated with protein content, amylose content, hot pasting viscosity (HPV) and setback (SB). There was a close relationship between carbon and nitrogen metabolism of rice grains. The protein content was negatively correlated with the total starch content and amylopectin content, and positively correlated with the activity of glutamic oxalo-acetic transaminase (GOT) and glutamate pyruvate transaminase (GPT). The total starch content had no significant relationship with ADP-glucose pyrophosphorylase (AGPP) activity. The amylopectin content was positively correlated with soluble starch synthase (SSS) activity, and not significantly correlated with starch branching enzyme (SBE) and starch debranching enzyme (DBE) activity. The amylose starch content was positively correlated with granule-bound starch synthase (GBSS) activity and negatively correlated with SSS activity. Under warming conditions, the increase of nitrogen metabolism level promoted the increase of protein content and the decrease of amylopectin content in milled rice, leading to a decrease in taste quality.