ABSTRACT
The more heavy metals are used by plants in the soil, the greater the stress is in plant growth. A series of physiological changes are existed in stress or plants aging, such as intracellular reactive oxygen metabolism balance is destroyed, leading to accumulation of active oxygen, which can cause or aggravate membrane lipid peroxidation, damaging cell membrane system and severity will lead to plant cell death. Malondialdehyde (MDA) is one of the products, and the more MDA is, the greater stress level is. Free radicals in plant cells hurt the plant itself, which can be eliminated mainly by related enzymes and organic molecules reacting with free radicals and producing stable products (Gou & Wang. 1995). Superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) are important protective enzymes of plant enzymatic defense system. SOD can scavenge oxygen free radical, protecting cells from damaging, and the higher the activity is, the stronger stress resistance of plants is. CAT and APX can eliminate H2O2 produced in strengthening process of active oxygen metabolism, and its activity is closely related with plant stress tolerance. The higher CAT and APX activity are, the stronger the stress resistance of plants is.
