Abstract
To reveal the physiological role of polyamines and the mechanism involved in grain-filling of rice ( Oryza sativa L.) superior and inferior spikelets, the relationship between grain-filling rate and polyamine concentrations was analyzed and verified using 4 super rice cultivars and 2 high-yielding cultivars (controls). Compared with the controls, super rice had similar maximum grain-filling rate, mean grain-filling rate, and brown rice weight in superior spikelets and significantly lower values in inferior spikelets. The concentrations of putrescine (Put), spermidine (Spd), and spermine (Spm) varied in single-peak curves in both inferior and superior spikelets during grain-filling period. The peak and mean concentrations of Put were greater in inferior spikelets than in superior spikelets. However, the peak and mean concentrations of Spd and Spm were greater in superior spikelets than in inferior spikelets. The control cultivars had higher concentrations of polyamines than super rice. The mean grain-filling rate and brown rice weight were negatively correlated with Put concentration, and positively correlated with Spd and Spm concentrations and the ratios of Spd/Put and Spm/Put. Spraying of Spd or Spm to panicle at early grain-filling stage significantly enhanced activities of sucrose synthetase, adenine diphosphoglucose pyrophosphorylase, and soluble starch synthetase in inferior spikelets, resulting in improvement of grain-filling rate, seed-setting rate, and grain weight. Application of Put or methylglyoxal-bis (guanylhydrazone) (MGBG, an inhibitor of S-adenosyl- L-methioninedecarboxylase) exhibited an opposite effect. These results indicated a regulative function of polyamines during grain filling. The low grain-filling rate and grain weight in inferior spikelets of super rice are probably in relation to the low concentrations of Spd and Spm and the small ratios of Spd/Put and Spm/Put in inferior spikelets.
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