Abstract: 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.

Key words: Maize, Quality, Shading, Flowering to maturity stage