Seasonal changes in enzymatic antioxidant system in roots of alpine perennial forage grasses related to freezing tolerance
高寒山区植物根抗氧化酶系统的季节变化与抗冷冻关系

Four plants, Poa sphyondylodes, Bromus inermis, Bromus sinensis and Elymus nutans established in apline in 1993, were investigated throughout the winter and spring between 1995 and 1996 by monitoring MDA content and antioxidant enzymatic activities of SOD , CAT, POD and APX Roots were sampled at approximately 15 days interval in both autumn and spring Leakage of ions and MDA content increased,while SOD and CAT activities declined markedly from September with the drop of temperature In contrast, in alive roots, MDA content increased markedly from September 1 to September 15,and then decreased to early October and was litter fluctuated from early Oct to December, also during spring Average activities of SOD, CAT, POD in roots of all species increased 170%, 130%, and 56%, respectively from September to early November Thereafter these enzymatic activities declined throughout winter, but still higher than that of September, and elevated again with rising of temperature from mid April to early May These results provided evidence for the ability of the alpine plant root to activate enzymatic defense mechanisms to limit the production of free radicals to protect membrane integrity In dead leaves, it is because antioxidant enzymes inactivated lead to accumulation of AOS initiating lipid peroxidation APX is not important scavengers for this study Freezing tolerance in alpine grasses correlated with an increased capacity to scavenge or detoxify activated AOS by antioxidant enzymatic system