弱光条件下不同穗型小麦品种旗叶光合特性和抗氧化代谢

在大田试验条件下，比较了大穗穗型小麦品种泰农18和多穗型品种济南17的叶绿素含量、净光合速率(P_n)、可溶性蛋白和总糖含量、抗氧化酶活性及丙二醛(MDA)含量对不同程度弱光响应的差异，为黄淮麦区小麦高产稳产栽培及品种选用提供理论依据。从开花期至成熟期分别对两品种进行25%(S1)、50%(S2)和90%(S3)的弱光处理，以正常光照(S0)为对照。结果表明，S1和S2处理提高了小麦灌浆期内旗叶叶绿素含量和最大光化学效率(F_v/F_m)，而S3处理提高了花后0~6 d旗叶叶绿素含量和F_v/F_m，之后显著低于对照；随弱光程度增强旗叶花后实际光化学效率(Φ_PSII)升高，而叶绿素a/b比降低。S2和S3处理显著抑制了旗叶抗氧化酶活性，降低了旗叶P_n、可溶性蛋白和可溶性总糖含量；而S1处理增强了旗叶超氧化物歧化酶(SOD)和过氧化物酶(POD)活性，提高了小麦旗叶P_n、可溶性蛋白和可溶性总糖含量。相同处理条件下，与泰农18相比，济南17的旗叶叶绿素含量较高，光系统II (PSII)活性较强，同时抗氧化酶活性下降较慢，膜脂过氧化程度低，使叶片功能免受破坏，保证了光合作用的进行。75%光照条件下(S1)的小麦抗氧化酶具有较高活性，叶片膜脂化程度低，抗逆性较强，旗叶P_n高值持续期长，有利于光合产物的积累。多穗型品种比大穗型品种更能适应黄淮麦区小麦生育后期光照不足的生产条件。

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

Shading post flowering caused by cloudy weather and the surrounding protective trees often occurs in the Huang-Huai-Hai 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.