| In order to investigate the effect of different nitrogen(N) rates on the starch granule size distribution in wheat(Triticum aestivum L.) kernels,two local wheat cultivars,Yangmai 16 and Yangmai 20,were grown in the field,under different N rates of 120 kg·hm-2(120N),180 kg·hm-2(180N),240 kg·hm-2(240N) and 300 kg·hm-2(300N) during the whole wheat season. The results showed that,with the increase of N application amount,the concentrations of free-spermidine(free-Spd) and free-spermine(free-Spm),activities of two starch synthase during grain filling period,and proportions of medium starch granule(5-50 μm) volume and surface area,starch accumulation and kernel weight at maturity in inferior kernels of the two wheat cultivars increased first and then decreased. No significant difference for these parameters in superior kernels of wheat was observed at different nitrogen rates. The free-putrescine(free-Put) concentration,proportions of small starch granule(< 5 μm) size distribution and medium starch granule number and length in kernels had no obvious responses to different N rates. The concentrations of free-Spd and free-Spm,activities of two starch synthase,starch accumulation and kernel weight were significantly and positively correlated with proportions of medium starch granule volume and surface area,but negatively correlated with proportion of large starch granule size distribution. Exogenous applications of synthetic Spd or Spm increased the concentrations of free-Spd or free-Spm,activities of two starch synthase,proportions of medium starch granule volume and surface area,starch accumulation and kernel weight,but reduced the proportions of large starch granule volume and surface area; the negative effect was obtained when the synthetic inhibitor was applied. The results indicated that N mainly influences on medium and large starch granule size distribution in inferior kernels of wheat,and the improvement of starch granule size distribution at reasonable N rate is attributed to the positive regulations of free-Spd and free-Spm on activities of two starch synthase. |
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