Photosynthetic Characteristics and Antioxidative Metabolism of Flag Leaves in Responses to Shading during Grain Filling in Winter Wheat Cultivars with Different Spike Types

Abstract

Shading post flowering caused by cloudy weather and the surrounding protective trees often occurs in the Huang-HuaiHai Plain of China.The objective of this study was to suggest cultivars acclimated to insufficient light intensity post flowering in this region through evaluating the impact on photosynthesis and antioxidation.Two winter wheat(Triticum aestivum L.) cultivars,Tainong 18(a large-spike cultivar) and Jinan 17(a multiple-spike cultivar),were treated with 100%(control,S0),75%(S1),50%(S2),and 10%(S3) of full radiation from anthesis to maturity.The chlorophyll content,net photosynthetic rate(P n),contents of soluble protein and sugar,activities of antioxidative enzymes,and malondialdehyde(MDA) content were measured from 0 to 28 d post flowering.Compared to S0 treatment,the chlorophyll content and maximal efficiency of photosystem II(PSII) photochemistry(F v /F m) of flag leaves were enhanced in treatments S1 and S2.From 0 to 6 d post flowering,the chlorophyll content and F v /F m in S3 were also higher than those in S0,but significantly lower than these in controls,thereafter.With the increase of shading intensity,the effective quantum yield of PSII(Φ PSII) was promoted;whereas,the ratio of Chl a/b was declined.Compared to S0,treatments S2 and S3 significantly suppressed the activities of superoxide dismutase(SOD) and peroxidase(POD),P n,and contents of soluble protein and total soluble sugar,but S1 treatment showed positive effects on above parameters.Under the same shading condition,Jinan 17 had larger chlorophyll content and higher activities of PSII and antioxidative enzymes,but lower MDA content than Tainong 18.This result indicated that multiple-spike cultivar was more suitable than large-spike cultivar in the Huang-Huai-Hai Plain with shading problem at late growth period,because there were less damage of flag leaf and better photosynthetic function in multiple-spike cultivar.Wheat plants under S1 shading condition had relatively high activities of antioxidative enzymes and low degree of membrane lipid peroxidation,which was in favor of stress resistance,maintaining high P n duration,and accumulation of photosynthate in wheat plants.