玉米花粒期不同阶段遮光对籽粒品质的影响

选用高淀粉玉米费玉3号和普通玉米泰玉2号，大田条件下分别于花粒前期（授粉后1~14 d），中期（15~28 d）和后期（29~42 d）遮光（透光率45%）处理，研究了对籽粒品质和籽粒中蛋白质、淀粉合成关键酶活性的影响，以及影响品质的关键时期。结果表明，花粒期遮光显著降低了籽粒产量、容重、淀粉直/支比、淀粉及其组分含量，遮光后淀粉RVA谱特征值峰值黏度（PV）、热浆黏度（HV）及崩解值（BD）下降，而籽粒含水率、粗蛋白及其各组分含量、谷/醇比、粗脂肪含量、亚油酸含量、亚麻酸含量、亚油酸/亚麻酸比值以及不饱和脂肪酸含量均升高；遮光显著降低了籽粒蛋白质和淀粉合成关键酶活性，腺苷二磷酸葡萄糖焦磷酸化酶（ADPGPPase）、尿苷二磷酸葡萄糖焦磷酸化酶（UDPGPPase）、淀粉合酶（SSS）、束缚态淀粉合酶（GBSS）活性与籽粒淀粉含量、容重、峰值黏度和崩解值呈显著正相关，谷氨酰胺合酶（GS）和谷氨酸合酶（GOGAT）活性与蛋白质含量和谷/醇比也呈显著正相关。不同时期遮光对两品种玉米品质性状的影响基本一致，前期遮光处理对籽粒商品品质(容重，含水率)影响大，而中期遮光对籽粒营养品质影响大。可见花粒中前期的光照强度对籽粒品质形成具有关键作用，后期光强对其影响较小。

Effect of Shading on Grain Quality at Different Stages from Flowering to Maturity in Maize

Light deficiency from pollination to maturity is a common problem in summer maize(Zea mays L.) production in Huang-Huai-Hai-River region in China.Some researches on rice(Oryza sativa L.),wheat(Triticum aestivum L.), and soybean Glycine max(L.) Merr.] have reported that light deficiency limited carbohydrate accumulation,and result in protein content increase in grain.However,the conclusion on maize is uncertain due to rare studies.To investigate the effects of low light intensity at different stages after pollination on grain quality and the activities of key enzymes of starch and protein syntheses,we conducted a field experiment by shading treatment in 2005-2006 with two maize cultivars,Feiyu 3(high starch content) and Taiyu 2(low starch content).The black fabric net was used for making light defiency with 45% sunlight transmission.The shading periods were 1-14(S1),15-28(S2),and 29-42(S3) days after pollination (DAP),respectively.Only medium position grains of the ear were sampled at 7,14, 21,28,35,and 42 DAP to determinate the enzyme activities.Grain yield and quality parameters were measured after maturity.Compared with the control(no shading treatment,S0),the S1,S2,and S3 treatments showed obvious difference in grain quality and activities of tested enzymes,and the two cultivars had similar results.The grain yield,test weight,and starch content in the three shading treatments were significantly lower than those in control,while the water content,protein content and oil content were relatively higher.The grain nutrition quality indexes such as four protein component contents,glutenin/gliadin ratio, amylopectin /amylose ratio,sub-oleic acid content,flax acid content,un-saturated fatty acid content and sub-oleic acid/Oleic acid ratio increased by shading,these suggesting shading improved the grain nutrition quality.However,the grain starch RVA eigenvalues such as peak viscosity(PV),hot viscosity(HV) and breakdown(BD) decreased by shading,resulting in the decline of cooking and eating quality.The activities of the tested enzymes were significantly reduced by shading treatment,in which the activities of adenosine diphosphate glucose pyrophosphorylase(ADPG),uridine diphosphate glucose pyrophosphorylase(UDPG),soluble starch synthases(SSS),and granule bounded starch synthases(GBSS) were significantly and positively correlated with grain starch content,test weight,peak viscosity,and breakdown.The activities of glutamine synthase(GS) and glutamate synthase(GOGAT) were significantly and positively correlated with grain protein content and Glu/Gli ratio.Among three shading treatments,the commodity quality(test weight and water content) of maize grain was affected mostly by S1,moderately by S2,and least by S3,respectively.However,the effect of S2 treatment on grain nutrition quality was more decisive as compared with those of S1 and S3.This result suggested that the early and middle terms from flowering to maturity are the key stage for the impact of shading on grain qualities,with little effect for the light condition at the later stage from flowering to maturity stage.