Regulation Of Polyamines And Ethylene To The Grain Filling Of Rice

Both polyamines (PAs) and ethylene are important plant growth regulators, and play important roles in cell division, morphogenesis, embryogenesis, fruit set and growth, senescence, and responses to environmental stresses. As PAs and ethylene share a common biosynthetic precursor S-adenosyl-L-methionine (SAM), so it would be possible that they interact in mediating plant growth and development. However, the synchronous changes of PA and ethylene levels and their relationships with grain filling are yet to be investigated. This study chose different rice varieties as materials, and changes in contents of putrescine (Put), spermidine (Spd), spermine (Spm), and1-aminocylopropane-1-carboxylic acid (ACC) and ethylene evolution rate were observed during the grain filling period, and their relationship with grain filling rate was analyzed. The effects of nitrogen fertilizer on the content of endogenous PAs and ACC were also observed. The main results are as follows.1. Six rice cultivars, two inbred cultivars (Yangdao6, Zhendao88), two super rice cultivars (Liangyoupeijiu, Ⅱ you084), and two new plant type (NPT) lines [(IR65598-112-2(NTP-1), IR66738-118-1-2(NTP-2)], were field-grown. The changing patterns of PAs and ACC levels, ethylene evolution rate, and grain filling rate in both superior and inferior spikelets during grain filling and their relations with grain filling rates were investigated. The results were verified by application of exogenous Put, Spd, Spm, methylgly-oxal-bis (MGBG, an inhibitor of Spd and Spm synthesis), ethephon, ACC and aminoethoxyvinylglycine (AVG, an inhibitor of ethylene synthesis by inhibiting ACC synthesis) at the early of grain filling stage. The results showed that,(1) compared with superior spikelets, inferior spikelets had lower grain filling rate and grain weight, and the time reaching maximum grain filling rate was much longer. For inferior spikelets, grain filling rate and grain weight showed significant differences among three kinds of rice cultivars:the two inbred cultivars> the two super rice cultivars> the two NTP lines. For superior spikelets, however, difference in grain filling rate and grain weight was rather small among cultivars. At the early of grain filling stage, concentrations of free-Put in both superior and inferior spielets was very higher, and quickly declined with the procession of grain filling. Inferior spielets showed a higher free-Put concentration than superior spikelets, especially at early and mid grain filling stages. For superior spikelets, free-Spd or free-Spm concentrations showed no significant differences among the six cultivars; while for inferior spielets, they exhibited the two inbred cultivars> the two super rice cultivars> the two NTP lines, and similar to the grain filling rate. (2) At the early grain filling stage, ethylene evolution rate and ACC concentration in both superior and inferior spikelets were very higher, and declined with the procession of grain filling. For superior spikelets, ethylene evolution rate and ACC concentration showed no significant differences among the six cultivars. For inferior spielets, ethylene evolution rate and ACC concentration were the two NTP lines> the two super rice cultivars> the two inbred cultivars, which was opposite to the grain filling rate and the changing patterns of free-Spd or free-Spm.(3) During the active grain filling period, grain filling rate was very significantly and positively correlated with concentration of free-Spd, free-Spm, Spd/ACC and Spm/ACC, and very significantly and negatively correlated with concentrations of free-Put, ACC, and ethylene evolution rate. Application of Spd or Spm significantly reduced ethylene evolution rate and ACC concentration, and significantly increased activities of sucrose synthase, ADP glucose pyrophosphorylase, and soluble starch synthase, mean grain filling rate, and grain weight of inferior spielets. Application of MGBG, ethephon, or ACC exhibited the opposite effects. It implies that potential metabolic interaction/competition between PAs (Spd and Spm) and ethylene biosynthesis may regulate the processes of grain filling in rice. A higher ratio of free-Spd or free-Spm to ethylene (Spd/ACC, Spm/ACC) could enhance grain filling, leading to an increase in grain weight.2. Four rice cultivars, IR24, Yangdao6, Yangliangyou6and Yangjing4038, were field grown, and two nitrogen levels, no nitrogen application (ON:0kg/ha) and nitrogen application (180N:180kg/ha), were conducted to investigate the changing patterns of PAs and ACC concentrations in both superior and inferior spikelets. The result showed that effects of application of nitrogen on PA and ACC concentrations were more for inferior spikelets than for superior spikelets. Application of nitrogen increased PA concentration and decreased ACC concentration, and increased the ratio of PAs to ACC (Put/ACC, Spd/ACC, Spm/ACC). These results suggest that application of nitrogen could reduce the difference in PA concentrations between superior and inferior spikelets, and increase the ratio of PAs to ethylene, leading to enhancement in grain filling of inferior spikelets.