优质小麦子粒淀粉组成与糊化特性对氮素水平的响应

Effects of nitrogen application rates on starch composition and pasting properties of high quality wheat

在大田条件下,选用3个不同类型优质小麦品种：豫麦47（强筋品种）、山农8355（中筋品种）和豫麦50（弱筋品种）,设置3个氮肥水平：施N 01、5和30 g/m2,研究了小麦子粒淀粉的粒度分布、直支链淀粉组成、糊化特性及其对氮素水平的响应。结果表明,优质小麦子粒中淀粉粒的粒径分布范围为14~5μm,其数目分布呈单峰或双峰曲线变化,体积和表面积分布均呈双峰曲线变化,峰谷位于10μm处 据此可将淀粉粒分为两种类型：A型大淀粉粒（104~5μm）和B型小淀粉粒（11~0μm）。优质小麦子粒淀粉粒组成存在显著的基因型差异。强筋品种豫麦47子粒中B型淀粉粒的比例较高,弱筋品种豫麦50子粒中A型淀粉粒的比例较高,中筋品种山农8355居中。施氮水平对优质小麦子粒中淀粉的粒度分布存在显著影响。在本试验条件下,随氮素水平的提高,强筋品种豫麦47子粒中A型淀粉粒的比例提高,而B型淀粉粒的比例下降 增施氮肥后弱筋品种豫麦50和中筋品种山农8355子粒中B型淀粉粒的比例增大,而A型淀粉粒的比例降低,且前者变化的幅度较大。适量增施氮肥提高优质小麦子粒中的淀粉含量,氮肥用量进一步增大后,淀粉含量降低 增施氮肥后优质小麦子粒中直链淀粉含量降低。增施氮肥对优质小麦子粒淀粉的糊化特性存在较大影响,且此影响的趋势因基因型和施氮量而异。其中强筋品种豫麦47表现为低谷粘度、最终粘度、反弹值、糊化温度和峰值时间提高,而高峰粘度和稀懈值降低 当氮肥用量增大至30 g/m2时,糊化温度和峰值时间降低,而以粘度为单位的参数均提高。弱筋品种豫麦50表现为增施氮肥后,RVA参数呈下降趋势,与之相对应中筋品种山农8355的呈上升趋势。相关性分析表明,B型淀粉粒的数目、体积和表面积比例与高峰粘度和稀懈值存在显著正相关 与低谷粘度、最终粘度和反弹值存在显著负相关。子粒中直链淀粉含量、支链淀粉含量和总淀粉含量与高峰粘度和稀懈值呈显著负相关,与低谷粘度、最终粘度、反弹值和峰值时间呈一定程度正相关 直链淀粉相对含量与RVA特征参数之间的相关趋势与子粒中直链淀粉含量的趋势一致,但均未达显著水平。由此可以认为,氮肥通过调控小麦子粒中淀粉的直、支链组成和粒度分布而影响其糊化特性。

In field conditions,3 typical cultivars,YM47（strong-gluten）,SN8355（medium-gluten） and YM50（weak-gluten） were used to investigate the starch granule distribution,composition of amylose and amylopection,and pasting characteristics of wheat starch under three nitrogen application rates（N 0,15 and 30 g/m2）.The results indicate that the range of starch granule diameters in wheat endosperm is from 1 to 45 μm.Wheat endosperm has a unimodal or bimodal curve in starch granule number distribution,and both starch granule volume and surface area distribution have a bimodal curve.The nadir of those bimodal curves is on the point of 10 μm,and therefore the starch granules in wheat endosperm could be divided into two groups,A-type granules（1-10 μm） and B-type granules（10-45 μm）.The composition of wheat starch granules in high quality wheat cultivars varies significantly with genotypes.The strong-gluten wheat YM47 has a much higher ratio of Btype starch granules,while the weak-gluten wheat YM50 has a higher ratio of A-type starch granules,and the distribution of starch granules in the medium-gluten wheat SN8355 has a central tendency.The N rates influence the distribution of starch granules in high quality wheat endosperm significantly.In the conditions of this study,increasing N fertilization improves the ratio of A-type starch granules and decreases the ratios of B-type starch granules in the endosperm of strong-gluten wheat YM47.The B-type starch granule ratios in the weak-gluten wheat YM50 and medium-gluten wheat SN8355 are increased under the N fertilization,on the contrary,the A-type starch ratios of those two cultivars are declined after using more N,and the amplitude of the variation of the weak-gluten wheat YM50 is much higher than that of the medium-gluten wheat SN8355.Increasing N fertilization appropriately could heighten the starch content in wheat grain,but as the amount of N continued to increase,grain starch content might decrease.The amylose content in wheat grain or in isolated wheat starch is decreased after increasing N applications.The pasting characteristics of isolated starches in high quality wheat cultivars are greatly affected by increasing N amounts,and the effects vary with genotypes and N rates.In strong-gluten wheat cultivar YM47,increasing N properly could increase the through viscosity,final viscosity,setback,pasting temperature and peak time,and decrease peak viscosity and breakdown.As the amount of N increasing to 30 g/m2,pasting temperature and peak time are decreased,and those parameters using RVU as unit are increased compared to the control.The RVA parameters of isolated starches of weak-gluten wheat YM50 are declined after using more N fertilizer,while those of the medium-gluten wheat SN8355 are increased.The correlation analysis between RVA parameters and components of wheat starches indicates that the number,volume and surface area ratios of B-type starch granules are significantly positively correlated with peak viscosity and breakdown,and are significantly negatively correlated with through viscosity,final viscosity and setback.The amylose,amylopectin and starch contents of wheat grains are significantly negatively correlated with peak viscosity and breakdown,and are positively correlated with through viscosity,final viscosity,setback and peak time.The correlation trend between amylose content of isolated wheat starch and parameters of RVA is similar to that of amylose content in wheat grain,but the former does not reach the significant level.From the above results,we conclude that the N fertilization affects the pasting characteristics of wheat starch with the changes in constitute of amylose and amylopectin,and starch granule distribution.