Abstract: Polyamines have been frequently described as endogenous plant growth regulators or intracellular messengers mediating physiological processes. This study investigated whether polyamines are related with the grain quality of rice. Twelve rice genotypes were grown in the field, and used to determine the concentrations of putrescine (Put), spermidine (Spd), and spermine (Spm) in the grains during the grain filling period. The relationship between polyamine concentrations and rice quality were analyzed, and chemical regulators were applied to verify the roles of polyamines in regulating rice quality. The results showed that a genotype with better milling and appearance qualities had higher concentrations of Spd and Spm, and lower put concentrations, in grains during the filling period. Concentrations of Spd and Spm in the grains were significantly or very significantly and positively correlated with grain plumpness, grain weight, brown rice, and milled rice, and negatively correlated with chalkiness. Concentrations of Put were significantly or very significantly and negatively correlated with grain plumpness, grain weight, brown rice, and milled rice, whereas positively correlated with chalkiness. Neither of Put nor Spd and Spm was significantly correlated with head rice and amylose content. Application of Spd or Spm to panicle at the early grain filling stage significantly increased the maximum endosperm cell number and activities of sucrose synthetase (SuS), adenine diphosphoglucose pyrophosphorylase (AGP), and soluble starch synthetase (SSS) in grains, and improved the milling and appearance qualities. Application of Put or methylglyoxal -bis (guanylhydrazone) (MGBG, an inhibitor of S-adenosyl-L-methionine decarboxylase) exhibited an opposite effect. The results suggested that the milling and appearance qualities would be improved to a certain degree by increasing Spd and Spm, or reducing Put, concentrations in the filling grains through variety breeding or application of chemical regulators.

Key words: Rice, Polyamines, Milling quality, Appearance quality, Grain plumpness