Yi Xiao-Ping, Zhang Ya-Li, Yao He-Sheng, Zhang Xiang-Juan, Luo Hong-Hai, Gou Ling, Zhang Wang-Feng
The Key Laboratory of Oasis Eco-agriculture, Xinjiang Production and Construction Group, Shihezi University, Shihezi, 832003, PR China.
Funct Plant Biol. 2014 Jul;41(7):737-747. doi: 10.1071/FP13269.
To clarify the photoprotective mechanisms of cotton leaves under water deficit in the field, leaf gas exchange, chlorophyll a fluorescence as well as the corresponding physiological responses were examined in cotton (Gossypium hirsutum L.) to evaluate electron flux distribution. With increasing water deficit, net photosynthetic rate (Pn) significantly decreased, the total electron flux through PSII [Je(PSII)] gradually decreased and the fraction of electron flux required to sustain CO2 assimilation [Je(PCR)] markedly declined. Simultaneously, the ratio of quantum efficiency of PSII [Φ(PSII)] to the quantum efficiency of CO2 fixation [Φ(CO2)] increased, accompanied by an increase in the alternative electron flux (Ja). The enhanced alternative electron flux of O2-dependent Ja(O2-dependent) indicated that electrons had been transported to O2 in the Mehler-peroxide reaction (MPR) and that the remaining alternative electron flux Ja(O2-independent) had been used for nitrate reduction, as indicated by an increase in nitrate reductase (NR) and glutathinone reductase (GR) activities. In addition, mild water deficit increased the proportion of electron flux for the photorespiratory carbon oxidation [Je(PCO)]. Water deficit significantly increased surperoxide radical production rate (O2-•) and hydrogen peroxide content (H2O2), and the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD) and catalase (CAT) in cotton leaves also increased under water deficit. Therefore, the Mehler-peroxidation reaction, photorespiration and nitrate reduction helped to dissipated excess light energy, being important photoprotective mechanisms for adapting the photosynthetic apparatus to mild and moderate water deficit in cotton.
为阐明田间水分亏缺条件下棉花叶片的光保护机制，对棉花（陆地棉）的叶片气体交换、叶绿素a荧光及相应生理响应进行了研究，以评估电子通量分布。随着水分亏缺加剧，净光合速率（Pn）显著降低，通过PSII的总电子通量[Je(PSII)]逐渐减少，维持CO2同化所需的电子通量分数[Je(PCR)]明显下降。同时，PSII量子效率[Φ(PSII)]与CO2固定量子效率[Φ(CO2)]的比值增加，伴随交替电子通量（Ja）增加。依赖O2的交替电子通量Ja(O2 - 依赖)增强，表明电子在梅勒过氧化物反应（MPR）中传递给了O2，其余交替电子通量Ja(O2 - 非依赖)用于硝酸盐还原，这可通过硝酸还原酶（NR）和谷胱甘肽还原酶（GR）活性增加得以证明。此外，轻度水分亏缺增加了光呼吸碳氧化的电子通量比例[Je(PCO)]。水分亏缺显著提高了棉花叶片中超氧阴离子产生速率（O2-•）和过氧化氢含量（H2O2），水分亏缺下超氧化物歧化酶（SOD）、抗坏血酸过氧化物酶（APX）、过氧化物酶（POD）和过氧化氢酶（CAT）的活性也增加。因此，梅勒过氧化物反应、光呼吸和硝酸盐还原有助于耗散过剩光能，是棉花光合机构适应轻度和中度水分亏缺的重要光保护机制。
