低温下紫花苜蓿叶片的光破坏防御作用

The Photoprotection Mechanism of Alfalfa Leaves under Low Temperature

低温是影响植物正常生长发育的重要环境因素。本研究以‘新牧4号’紫花苜蓿(Medicago sativa L.‘Xinmu No.4’)和‘甘农5号’紫花苜蓿(Medicago sativa L.‘Gannong No.5’)为试验材料,探究低温下紫花苜蓿叶片光破坏防御作用的变化。结果表明,低温下紫花苜蓿叶片的光合速率、最大光化学效率(Fv/Fm)及核心蛋白下降;低温下非光化学淬灭系数(NPQ)降低,环式电子传递(CEF)上调,使用NPQ抑制剂后Fv/Fm显著下降;低温下交替氧化酶(AOX)呼吸速率以及蛋白含量降低,但AOX呼吸的占比升高,AOX抑制剂和光呼吸抑制剂的施用均加重Fv/Fm的下降;低温下超氧阴离子、过氧化氢和丙二醛含量上升,抗坏血酸酶(APX)活性上升。低温下NPQ被抑制,CEF的上调弥补了NPQ作用的下降从而保护叶片减少光破坏;AOX增加电子分流从而维持光呼吸正常运作;低温下活性氧的清除主要依靠APX,但仍有大量活性氧产生使光系统受到损伤,引起光抑制。

Low temperature is an important environmental factor affecting the normal growth and development of plants.In order to adapt to the low temperature environment,plants have developed a series of photoprotection mechanisms to protect photosynthetic apparatus from damage.In this study,alfalfa(Medicago sativa L.)‘Xinmu No.4’and‘Gannong No.5’were used as experimental materials to explore the changes of non photochemical quenching(NPQ),alternative oxidase(AOX)respiration rate,cyclic electron flow(CEF)and antioxidant system in alfalfa leaves under low temperature.The results showed that under low temperature,the photosynthetic rate of alfalfa leaves was decreased significantly,the maximum photochemical efficiency of photosystem II(Fv/Fm)was also decreased,and the core protein of PSII was degraded.At low temperature,NPQ decreased,CEF were increased,and the use of NPQ inhibitors caused a significant decrease in Fv/Fm.The AOX respiration rate and protein content were decreased at low temperature,but the proportion of AOX to total respiration was increased.The application of AOX inhibitors and photorespiration inhibitors aggravated the decrease of Fv/Fm.At low temperature,the contents of superoxide anion,hydrogen peroxide and malondialdehyde increased,and the activity of ascorbate peroxidase(APX)were increased.Therefore,at low temperature,the NPQ decreased,and the up-regulation of CEF makes up for the decrease of NPQ effect and protects leaves from light damage.AOX increases electron shunt to maintain the normal operation of photorespiration.The removal of reactive oxygen species at low temperature mainly depends on APX.However,there is still a large amount of reactive oxygen species was produced,which damages the photosystem and leads to photoinhibition.