Abstract: To understand the physiological mechanisms for the different tolerance of tropical forages and temperate forages to temperature stresses, the seasonal changes in antioxidant systems, soluble sugars and chlorophyll fluorescence parameters in leaves of Stylosanthes guianensis and Medicago sativa L. were comparatively investigated. Malondialdehyde (MDA) content increased of S.guianensis in the winter, but for M.sativa it increased in the summer. Superoxide dismutase (SOD) activity increased in S.guianensis before the winter and before the summer, whereas it was maintained high in M.sativa in the autumn and winter, and decreased to a low level in the spring and summer. Catalase (CAT) activity increased in both S.guianensis and M.sativa before winter, and maintained stable in S.guianensis in spring and summer, whereas for M.sativa it increased gradually in summer. Ascorbate-peroxidase (APX) activity was stable in S.guianensis throughout the investigations, whereas it increased gradually in M.sativa in the spring and summer. Ascorbic acid (AsA) and reduced glutathione (GSH) contents increased in S.guianensis before and after the winter, whereas in M.sativa they increased only before the winter and then maintained at a stable level. Soluble sugars content accumulated in both S.guianensis and M.sativa before winter, more soluble sugars accumulated and the accumulation peak appeared earlier in M.sativa than in S.guianensis, which could be beneficial for increased chilling resistance in M.sativa. Soluble sugars accumulated in great amounts again after the winter in S.guianensis, which may indicate the response to chilling injury. For S.guianensis, maximal photochemical efficiency (F_v/F_m) and non-photochemical quenching (NPQ) showed a slight decrease in the winter, but quantum efficiency of photosystemⅡ photochemistry(Ф_PSⅡ) and photochemical quenching (q_p) decreased significantly. For M.sativa, F_v/F_m, Ф_PSⅡ, and q_p were stable throughout the investigations, but NPQ decreased gradually in the winter and summer. The present data suggest that the different tolerance performance of S.guianensis and M.sativa to low temperature and high temperature is associated with their difference in seasonal changes in antioxidant systems, soluble sugars and PSⅡ photochemistry.

Key words: Stylosanthes guianensis, Medicago sativa, Antioxidant systems, Soluble sugars, Chlorophyll fluorescence, Seasonal changes

摘要： 为探讨热带和温带牧草对温度胁迫抗性差异的生理机制,本文比较研究了柱花草(Stylosanthes guianensis)和苜蓿(Medicago sativa)叶片抗氧化系统、可溶性糖和叶绿素荧光参数的季节性变化。结果表明:柱花草在冬季丙二醛(MDA)含量升高,苜蓿MDA含量在夏季升高;柱花草超氧化物歧化酶(SOD)活性在越冬前和越夏前升高,苜蓿SOD活性在秋冬季较高,春夏季较低;柱花草和苜蓿的过氧化氢酶(CAT)活性在越冬前均升高,但柱花草春夏季维持稳定,苜蓿CAT活性夏季升高;柱花草抗坏血酸-过氧化物酶(APX)活性全年较稳定,苜蓿的APX活性在春夏季不断升高;柱花草抗坏血酸(AsA)和还原型谷胱甘肽(GSH)含量在越冬前、后均升高,而苜蓿只在越冬前升高,越冬后维持稳定水平;柱花草和苜蓿的可溶性糖含量在越冬前均积累,柱花草积累高峰出现得较晚,且在越冬后再次大量积累,苜蓿在越冬前就大量积累,更有利于提高抗寒性;柱花草光系统Ⅱ(PSⅡ)最大光化学效率(F_v/F_m)和非光化学荧光猝灭(NPQ)在冬季有一定程度降低,PSⅡ光化学量子效率(Ф_PSⅡ)和光化学荧光猝灭(q_p)等叶绿素荧光参数明显降低,苜蓿F_v/F_m、Ф_PSⅡ和q_p等参数较稳定,但NPQ在春夏季不断降低。这说明,柱花草和苜蓿抗寒和抗热性的不同与其抗氧化系统、可溶性糖和PSⅡ季节性变化的差异有关。

关键词: 柱花草, 苜蓿, 抗氧化系统, 可溶性糖, 叶绿素荧光, 季节性变化