Relationship Between Root Chemical Signals And Grain Quality Of Rice

This study was designed to elucidate the relationship between the root chemical signals (hormones, polyamines and organic acids) and the grain quality of rice. Various rice genotypes were used. The experiments were conducted in the paddy field, water-culture pools and in pots. The relationship between root chemical signals and the grain quality was studied, and the techniques to regulate root chemical signals and improve grain quality were investigated. The main results are as follows:1. Concentrations of zeatin (Z) + zeatin riboside (ZR) in roots were very significantly and positively correlated, whereas those of N6-isopentenyladenine (iP) + N6-isopentenyladenosine (iPA) were not significantly correlated, with the proliferation rates of endosperm cells, with r=0.88** and r=0.33, respectively. When roots were treated with 10-7 mol L-1 ZR at the early grain filling satge,the number of endosperm cells in both superior and inferior grains was significantly or very significantly increased, but the number was not significantly increased when roots were treated with 10-7 mol L-1 iPA, indicating that the endosperm development is regulated by Z+ZR levels in rice roots.2. Concentrations of Z+ZR in the roots at mid and late grain filling stages were significantly and positively correlated with the gel consistency and alkali spreading value (r=0.72* ~ 0.90**), whereas negatively correlated with the amylose content (r=-0.68* ~ -0.78**). Abscisic acid (ABA) concentrations in roots at mid grain filling stage were significantly and negatively correlated with gel consistency and alkali spreading value (r=-0.90** ~ -0.91**), and positively correlated with the amylose content (r=0.87**). Z+ZR or ABA concentrations at all the filling stages were not significantly correlated with rice appearance quality indexes (transparency, chalky kernel and chalkiness). The effects of ZR treatments at 0~6 and 14~20 DAA and ABA treatments at 0~6 and 24~30 DAA on cooking quality of rice were not significant. The amylose content increased, whereas the alkali spreading value and gel consistency were reduced when exogenous ABA was applied at 14~20d after anthesis. In contrast, the amylose content was reduced, whereas the alkali spreading value and gel consistency were increased when exogenous ZR was treated at 24~30 DAA.3. Concentrations of 1-aminocylopropane -1-carboxylic acid (ACC) in root exudates at mid grain filling stage were very significantly correlated with the percentage of chalky grains and chalkiness (r = 0.97**~ 0.98**), and those at late grain filling stage were significantly correlated with chalkiness and chalky size (r = 0.69*~ 0.96**). ACC concentrations in roots at early grain filling stage were not significantly correlated with the percentage of chalky grains, chalkiness and chalky size, and neither were significantly correlated between ACC concentrations and gel consistency, alkali spreading value and amylose content at each grain filling stage. The percentage of chalky grains, chalkiness and chalky size of rice were all significantly increased when rice roots were treated with 10-6 mol·L-1 ACC at 10~15 or 25~30 DAA. The results were reversed when 10-6 mol·L-1 amino-ethoxyvinylglycine, an inhibitor of ACC synthetase, was applied.4. Concentrations of malic acid and succinic acid secreted by roots were significantly and positively correlated with the breakdown value in starch-profile (r = 0.95**～0.97**), whereas negatively correlated with the setback value (r =-0.96**～-0.97**). The concentrations of tartaric acid and citric acid secreted by roots were significantly and negatively correlated with the breakdown value in starch-profile (r =-0.94**～-0.95**), whereas positively correlated with the setback value (r =-0.95**～-0.97**), the concentrations of lactic acid secreted by roots were significantly and negatively correlated with rice gel consistency and alkali spreading value (r = -0.76*～-0.78**), whereas positively correlated with amylose content (r = 0.81*). The concentrations of organic acids secreted by roots were not significantly correlated with other rice quality indexes.5. The root and plant obsorbed less amount of cadmium (Cd) for a cultivar with more lactic acid in root exudates, whereras obsorbed more amount of lead (Pb) for a cultivar with more the malic acid and succinic acid exuded from the roots. When rape cake was used as organic fertilizer in the basic fertilizers, the concentrations of malic acid and succinic acid in root exudates were increased, while the concentrations of tartaric acid and citric acid were decreased, and no significant changes in lactic acid were observed. Application of rape cake increased the breakdown value whereas reduced the setback value in starch-profile.6. Concentrations of spermine in rice roots were very significantly and negatively correlated with prolamine content in the grain (r = -0.85**), whereas significantly and positively correlated with the content of the globulin (r = 0.67*). The concentrations of putrescine secreted by roots were very significantly and positively correlated with prolamine content in grains (r = 0.84**),but significantly and negatively correlated with the globulin content (r =-0.87**). The ratio of spermine to putrescine (spermine/ putrescine) in roots was very significantly and negatively correlated with the content of the prolamine (r = -0.95**) and significantly and positively correlated with globulin (r = 0.90**).The results suggest that root chemical signals are closely associated with the grain quality of rice, and that the root chemical signals would be regulated and the grain quality of rice be improved via genetic improvement or chemical controlling or cultivation techniques.