Abstract:

Cytokinin and abscisic acid (ABA) are two kinds of important plant hormones. Their roles in the grain filling and quality of rice, however, are not fully understood. The objective of this study was to determine changes in concentrations of zeatin (Z) + zeatin riboside (ZR) and ABA in both the roots and grains during grain filling, grain filling characteristics and the indexes for cooking quality using ten rice cultivars (including hybrids and lines) grown in nutrient solution. The results showed that the change in concentrations of Z+ZR and ABA in roots and grains exhibited a single peak curve during the grain filling period. The Z + ZR concentration in roots was very high at early grain filling stage and reached a peak at 3–9 d after anthesis (DAA), and that in grains at 9–12 DAA. ABA concentrations in roots and grains were rather low at early grain filling stage, then increased with grain filling, and reached a peak at 15–18 DAA in roots and at 15–21 DAA in grains. Concentrations of Z + ZR in roots and grains at early grain filling stage (0–12 DAA) and ABA at the mid stage (13–26 DAA) were significantly or very significantly correlated with the initial grain growth potential, mean grain filing rate, maximum grain filling rate and brown rice weight (r=0.726* ~ 0.984**), whereas significantly and negatively correlated with active grain filling period (r=－0.749* ~ －0.834**). Z+ZR concentrations at the mid or late grain filling stage (27–40 DAA) significantly or very significantly correlated with active grain filling period (r=0.689* ~ 0.932**) but those at the late stage negatively correlated with grain filling rate (r=－0.826** ~ －0.927**). The gel consistency and alkali spreading value of rice were significantly or very significantly correlated with Z+ZR concentrations in roots and grains at mid and late grain filling stages (r = 0.722* ~ 0.896**), whereas significantly and negatively correlated with ABA concentrations at mid grain filling stage (r=－0.883**~－0.913**). The correlations between amylose content and the concentrations of Z+ZR and ABA were reversed to the correlations of gel consistency with the two hormones. When roots were treated with 10^-7 mol/L ZR or with 10^-7 mol/L ABA at 0-6, 14–20 and 24–30 DAA, respectively, the effects of the exogenous hormones on grain filling and the cooking quality were consistent with the relationships of the two endogenous hormones with the grain filling parameters and indexes for cooking quality. The results suggest that cytokinin and ABA play important roles in the regulation of grain filling and quality of rice, and the direction of effects may dependent on grain filling stages.

Key words: Rice, Root, Cytokinin, Abscisic acid, Grain filling, Cooking quality