Effects of water stress on starch synthesis and accumulation of two rice cultivars at different growth stages

Rice is a water intensive crop and soil water conditions affect rice yield and quality. However, there is limited research on the starch synthesis and accumulation of rice under different soil water conditions at different growth stages. Thus, a pot experiment was conducted to explore the effects of IR72 (indica) and Nanjing (NJ) 9108 (japonica) rice cultivars under flood-irrigated treatment (CK, 0 kPa), light water stress treatment (L, -20 +/- 5 kPa), moderate water stress treatment (M, -40 +/- 5 kPa) and severe water stress treatment (S, -60 +/- 5 kPa) on the starch synthesis and accumulation and rice yield at booting stage (T1), flowering stage (T2) and filling stage (T3), respectively. Under LT treatment, the total soluble sugar and sucrose contents of both cultivars decreased while the amylose and total starch contents increased. Starch synthesis-related enzyme activities and their peak activities at mid-late growth stage increased as well. However, applying MT and ST treatments produced the opposite effects. The 1000-grain weight of both cultivars increased under LT treatment while the seed setting rate increased only under LT3 treatment. Compared with CK, water stress at booting stage decreased grain yield. The principal component analysis (PCA) showed that LT3 got the highest comprehensive score while ST1 got lowest for both cultivars. Furthermore, the comprehensive score of both cultivars under the same water stress treatment followed the trend of T3 > T2 > T1, and NJ 9108 had a better drought-resistant ability than IR72. Compared with CK, the grain yield under LT3 increased by 11.59% for IR72 and 16.01% for NJ 9108, respectively. Overall, these results suggested that light water stress at filling stage could be an effective method to enhance starch synthesis-related enzyme activities, promote starch synthesis and accumulation and increase grain yield.

Automated summary

Rice yield and quality are influenced by soil water conditions, but little research has been conducted on starch synthesis and accumulation under different soil water conditions at different growth stages. In this experiment, the effects of various water stress treatments on starch synthesis and accumulation, as well as rice yield, were investigated. The results showed that under light water stress treatment, the contents of soluble sugar and sucrose decreased, while amylose and total starch contents increased. Starch synthesis-related enzyme activities also increased. However, moderate and severe water stress treatments had the opposite effects. The 1000-grain weight and seed setting rate increased under light water stress treatment. Principal component analysis indicated that the highest comprehensive score was obtained under light water stress treatment during the filling stage. Additionally, the comprehensive score followed the trend of filling stage > flowering stage > booting stage. The drought-resistant ability of NJ 9108 was also found to be better than that of IR72. Overall, these findings suggest that light water stress during the filling stage can enhance starch synthesis-related enzyme activities, promote starch synthesis and accumulation, and increase grain yield.