Post-anthesis Protein Expressions And Concentration Changes Of Polyamines In Superior And Inferior Spikelets Of Super Rice

Poor grain filling of the later-flowering inferior spikelets (in contrast to the earlier-flowering superior spikelets) is a serious proplem in rice production. This problem is more aggravated in new bred super rice. Causes for the poor grain filling of inferior spikelets have been studied from assimilate supply, hormonal balance, enzymatic activity, and gene expressions. However, the mechanism underlying the poor grain filling is yet to be understood. Using super rice cultivars as materials, this study investigated the difference in protein experessions between superior and inferior spikelets at the different grain filling stages, and the functions of some proteins were anylyzed. As polyamines have been frequently described as endogenous plant growth regulators or intracellular messengers mediating physiological processes, this study alaso investigated the concentration changes of putrescine (Put), spermidine (Spd) and spermine (Spm) in both superior and inferior spikelets during the grain filling period and anylyzed the relationship between polyamine concentrations and grain filling rate. The main results are as follows:1. Two super rice cultivars, Liangyoupeijiu (indica hybrids) and Huaidao9(japonica), were used to investigate the protein expressions in superior and inferior spikelets through two-demensional gel electrophoresis (SDS-PAGE) and the MALDI analysis. Compared with superior spikelets, inferior spikelets showed fewer spots of protein expressions at5d and10d post-anthesis, whereas they exhibited more spots at20d and30d post-anthesis. The forty one protein spots that showed significant difference in the expressions between superior and inferior spikelets were chosen for the MALDI analysis, and of which the functions of17protein spots were indentified and those of other24protein spots were not known. The identified proteins were devided into six groups according to their functions:(a) energy metabolism (ribulose-bisphosphate carboxylase large chain);(b) amino acid metabolism (triose-phosphate isomerase and putative pyruvate orthophosphate dikinase);(c) cell differentiation and aging (translation initiation factor5A);(d) energy metabolism (putative phosphoglycerate kinase, cytosolic and alpha-amylase/subtilisin inhibitor);(e) environmental adaptation (stromal70kDa heat shock-related protein and putative cysteine synthase); and (f) polyamine metabolism (putative polyamine oxidase). The deficient or lower expression in ribulose-bisphosphate carboxylase large chain, putative pyruvate orthophosphate dikinase, translation initiation factor5A and putative polyamine oxidaseand as well as high expression in stromal70kDa heat shock-related protein and putative cysteine synthase may contribute to the poor grain filling of inferior spikelets.2. Four super rice cultivars, Liangyoupeijiu and Ⅱ you084(indica), Huaidao9and Wujing15(japonica), and two high-yielding check cultivars, Shanyou63(indica hybrid) and Yangfujing8(japonica), were field grown. Concentrations of Put, Spd and 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 polyamines 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 super rice. The mean grain filling rate and brown rice weight were negatively and very significantly correlated with the Put concentrations, 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 diphosphoglucose 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.