Effect Of Shading During Late Growth Stage On Physiological Characteristics Of Yield And Quality In Maize (Zea Mays L.)

The experiment was carried out in the corn research garden of Shandong agriculture university and the State Key Laboratory of Crop Biology from 2005 to 2006. This paper is focused on resolving this problem that the overcast-rainy and low-light weather impact the yield and quality of maize after tasselling. Three maize cultivars, FY3 (High starch maize), TY2 (Normal maize), and GY115 (High oil maize) were used to investigate the respond of yield, quality and physiology traits under different stages by black overshading net simulating low-light weather. The main results as followed:1 Effect of shading on yield and grain filling character of maizeShading stress has significant effect on yield and grain filling trait of different genotypes maize. After shading, the grain yield, ear kernel numbers and 1000-kernel weight decreased significantly. Grain yield and ear kernel numbers behaves the change trend of CK>S3>S2>S1>S0, whereas 1000-kernel weight is CK>S0>S3>S2>S1. The three cultivars have different sensitivity to shading stress, and light stress has the greatest effect on grain yield of FY3, TY2 is the second, GY115 is the least. Shading on tassel-anthesis stage due to not meet of male and female flower is a limited factor to yield formation, while the main cause of shading at early, middle, later filling stage(S1, S2, and S3)decreasing yield is the depression of photosynthetic ability and grain filling in badness.After deficit light treatment T_max appeared later and W_max, G_max and G_mean all decreased. The earlier the treatment began, the later the T_max was, and the smaller the W_max,G_max, and G_mean were.2 Effect of shading on photosynthetic character of maize and the physiological mechanismsExposure of maize plants to low light resulted in decrease in chlorophyll content(chl(a+b)), chlorophyll a/b, photosynthetic rate(Pn), soluble protein, activity of RuBPPcase and PEPcase, light saturation point, the photosystemâ…¡(PSâ…¡)photochemical efficiency(Fv/Fm), actual quantum yield of PSâ…¡of electron transport(ΦPSâ…¡), But an significant increase in relative content of chlorophyll b(chlb), intracellular CO₂ concentration, and non-photochemical quenching(NPQ). There was insignificant effect of shanding on the pool size of xanthophyll cycle, significant reversible effect of state of xanthophyll cycle, the antenna dissipations was main thermal dissipation during shading. After shading, Chl(a+b), Chla/b, Pn, Fv/Fm,ΦPSâ…¡, Ci, and NPQ gradually approached CK level, while the relative content of Chlb decreased. PSâ…¡dissipated excess energy mainly by non-photochemistry dissipation at prophase recovery, non-stomatal limitations(primary reaction, electron transfer and C assimilation)were part of the reason why Pn decreased by stress, and the earlier stress began after tasselling, the more average photosynthetic rate decreased. The capacity of grain sink feedback restrained Pn enhancing in restoration period.3 Effect of shading on the quality of maize grainShadings had considerable impact on grain qualities. In comparison of their un-shading(CK)control, three shade treatments were significant lower in amylopectin/amylose index, total protein and its four components content, Glutenin/Gliadin index, oil content, Sub-oleic acid content, Flax acid and Un-saturated fatty acid and Sub-oleic acid/Oleic acid index; the similar trend was observed for the response of grain quality traits to different stage shadings between three maize cultivars. Among 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 on grain nutrition quality was more decisive compared to those of S1 and S3. This result suggested that the early and middle term after anthesis is a key stage for the impact of shading on grain qualities, with little effect for the light condition at the later stage after anthesis. Shading decreased the commodity quality of grain, but improved the nutrient quality of grain. Shading on the early filling stage has greatest effect on grain commodity quality, and grain nutrient quality is sensitive to light stress at middle filling stage. It indicated that the grain commodity and nutrient quality have different sensitivity stage period at shading condition.4 Effect of shading on protein accumulation and activity of protein synthesis key enzymeAfter shading, the protein content of grain increased, and the amplitude of S1 treatment is the highest, S2 treatment is second, and S3 treatment is the lowest. Comparing in cultivars, the increasing of GY115 is most, FY3 is second, and TY2 is lowest. The protein absolute content is depressed, and the soluble protein and dissociating amino acid is decreased, while after resuming illumination, those of S1 treatment are approaching to the control, and those of S2 have more decreased than those at shading stage. Shading condition decreased the activity of protein synthesize key enzymes (NR, GS and GOGAT), meanwhile, the ability of ammonia assimilation in plant depressed significantly. At recovery process, the Gs and GOGAT of S1 is near that of control in ear leaf. The NR activity, the GS and GOGOT of S1 treatment in grain and S2 treatment in grain and GS and GOGAT activity of ear leaf cannot recover, due to protein biosynthesis suffocating.Relative analysis indicated that there was an insignificant correlation between protein content of maize grain and GOGAT activity of ear leaf, and NR at 7d after pollination, GOGAT at 35d after pollination, GS of 21d after pollination to maturity and GOGAT of grain were significant correlated with protein content of grain. It indicated that the GS of leaf and the GOGAT of grain play a key role in maize protein formation.5 Effect of shading on starch accumulation and activity of starch synthesis key enzymeShading decreased the starch gross, amylase and amylopectin content. Under shading condition, the starch increasing rate in grain is slow and accumulation amount is reduced, it behaved that the smaller the production amount at the time of the most accumulation rate, the most accumulation rate and the average accumulation rate represent as the earlier the shading treatment begins. After shading, the constitution of starch in grain is altered, the percentage of amylopectin in total starch is enhanced, and the increasing extent is higher as the earlier the shading begins. Shading stress restrained the starch accumulation significantly.The different type enzymes activity show difference in shading conditions, the activities of SS, SSS, ADPGPPase, UDPGPPase, and GBSS is decreased, S1 treatment has the most decreasing extent of three genotype maize, and SBE is increased, it indicated that shading is not favorable for the starch synthesized. The correlated analysis indicated that SSS, ADPGPPase, UDPGPPase, GBSS are the key enzymes to synthesize starch of grain at natural illumination condition, but the correlation between grain starch and SS, ADPGPPase is increased, and SSS, UDPG, GBSS and SBE is decreased, especially the correlation of UDPGPPase and grain starch depressed mostly, it shows that shading has great effect on the UDPGPPase of grain.6 Effect of shading on dry matter and nitrogen accumulation, distribution, and translocationAfter shading, the dry matter accumulation of different genotype maize is significant decreased, shading at early filling stage to plant has distinct effect on matter accumulation, while shading at middle filling stage has great effect on matter translocation. Shading at the middle filling stage decreased the weight of plant nutrient organs(leaf+straw)distinctly, whereas shading at the early filling stage has great effect on plant reproductive organ(grain). Simultaneously, shading decreased the nitrogen accumulation of plant significantly, and shading at the early filling stage has a great influence on nitrogen production ability, but shading at the middle filling stage behaved great effect on the senescence process of plant nutrient organs, which consisted with the change of dry matter accumulation.Shading at the early filling stage decreased the ability of nitrogen transfer in leaf, but shading at middle filling enhanced the ability of nitrogen translocation in leaf, and the nitrogen translocation ability of straw is increased at all shading condition, so the translocated nitrogen to grain is highest at the middle filling stage shading, and the late filling stage shading is second. Shading depressed the nitrogen assimilation ability, the less the nitrogen in grain comes from assimilated nitrogen as the earlier the shading begins, and shading at the early filling stage has significant effect on the growth and yield formation of maize plant. Shading at different phases increased the nitrogen amount of formation 100kg grain, the more the increasing extent behaves, the earlier the shading begins, which due to affect the nitrogen assimilation and utilization ability at shading conditions.7 Effect of shading on Endosperm cell proliferation, and structureThere was revisable decline of dry matter accumulation of embryo, and endosperm after shading compared with the control, while the embryo/endosperm ratio increased. Different stage shadings all resulted in a significant decrease in the number of endosperm cell, the earlier shading began, the fewer the number of endosperm cell. The development of starch granules was retardation by shading, the filling degree endosperm cell also decreased. Among 3 shading treatments, the size and the filling degree of endosperm was affected mostly by middle stage shading treatment. This perhaps means the grain weight was mainly determined by the number of endosperm in the early stage of grain filling, while the determine factor was the endosperm filling status in the middle stage of grain filling. Shading also increased the number of protein body. The size of endosperm transfer cell of shading treatment was smaller, and the silk wall ingrowths was fewer and shorter, the link status of different cell layer was declined compared with control, the capability of nutrient reduced by shading which result in the decrease in the smooth degree of current8 Effect of shading on active oxygen metabolism and membrane lipid overoxidation in maizeEffect of shading on SOD, POD, CAT activities and MDA content in maize leaf is different at different stages. After shading, the ability of cleaning out active oxygen(SOD, POD, CAT)is depressed, and membrane lipid overoxidation is increased. The maize plant shows the ability of self-adjusting in a way after releasing from shading at early days of grain-filling stage. The self-adjusting ability of maize plant decreased as the senescence of plant was accelerated gradually, after shading at middle-later stage of filling, protecting enzyme system become debility and breakdown, and the growth and mechanism of plant become turbulence, shortening the time of filling stage. The adapted ability to shading stress is different among different cultivars, GY115 is the highest, TY2 is the second, and FY3 is the lowest.