Post-Anthesis Changes in Concentrations of Polyamines in Superior and Inferior Spikelets and Their Relation with Grain Filling of Super Rice

Abstract

Success in super rice breeding has been considered a great progress in rice production in China. However, many un-filled inferior spikelets limit the realization of great yield. As polyamines have been frequently described as endogenous plant growth regulators or intracellular messengers mediating physiological processes, this study investigated whether and how poly-amines are involved in the regulating post-anthesis development of rice spikelets. Four super rice cultivars, Liangyoupeijiu and II you 084 (indica hybrids), Huaidao 9 and Wujing 15 (japonica), and two high-yielding check cultivars, Shanyou 63 (indica hybrid) and Yangfujing 8 (japonica), were field grown. Concentrations of putrescine (Put), spermidine (Spd) and spermine (Spm) in both inferior and superior spikelets during the grain filling period and grain filling rate were determined. The relationship between polyamine concentrations and grain filling rate were analyzed, and chemical regulators were applied to verify the roles of poly-amines in grain filling. The results showed that the maximum grain filling rate, mean grain filling rate, and brown rice weight for superior spikelets showed small difference between the super rice and check rice, but those of inferior spikelets were significantly lower for super rice than for check rice cultivars. Changes in concentrations of polyamines in grains exhibited single peak during the grain filling period. The peak and mean concentrations of Put were greater in inferior than in superior spikelets. The peak and mean concentrations of Spd and Spm were greater in the superior than in the inferior, and greater in the check rice than in the su-per rice. The mean grain filling rate and brown rice weight were negatively and very significantly correlated with the Put concen-trations, and positively and very significantly correlated with Spd and Spm concentrations, Spd/Put, and Spm/Put. Application of Spd or Spm to panicle at the early grain filling stage significantly enhanced activities of sucrose synthetase, adenine di-phosphoglucose pyrophosphorylase, and soluble starch synthetase in inferior spikelets, and significantly increased grain filling rate, seed setting rate and grain weight of inferior spikelets. Application of Put or methylglyoxal-bis (guanylhydrazone) (MGBG, an inhibitor of S-adenosyl-L-methionine decarboxylase) exhibited an opposite effect. The results suggest that polyamines play a role in regulating grain filling. Low concentrations of Spd and Spm and low Spd/Put and Spm/Put may be an important physiological reason for the small grain filling rate and low grain weight of inferior spikelets in super rice.