Abstract: The aim of the experiment was to explore the physiological and biochemical mechanisms
of nitric oxide（NO）and abscisic acid（ABA）on alleviation to autotoxicity in pepper seedlings（Capsicum
annuum L.‘Longjiao 2’）. With soil and substrates extracts of 3 years continuous cropping pepper treated
pepper seedlings，then the effects of SNP（150 μmol · L-1）and ABA（100 μmol · L-1）on antioxidant
enzymes activity，antioxidant substances content，osmotic adjustment substance content，and membrane
lipid peroxidation in pepper seedlings leaves were investigated. The results showed that superoxide
dismutase（SOD），peroxidase（POD），catalase（CAT）activities，and dehydroascorbate（DHA）content
declined under all of soil and substrates extracts stress，while ascorbic acid（AsA），proline（Pro），soluble
protein ，malondialdehyde （MDA）contents，relative conductivity and AsA/DHA ratio increased.
Autotoxicity on pepper of soil extracts was serious greatly than that of substrates extracts. NO and ABA
significantly increased SOD，POD and CAT activities，Pro and soluble protein contents，while reduced
MDA content and relative conductivity significantly. At the same time，AsA/DHA ratio was significantly
higher through promoting significantly to increase AsA content and decrease DHA content. Alleviate effect
to autotoxicity of NO was significantly better than that of ABA in pepper seedlings. The above results
suggested that NO and ABA effectively prevented malondialdehyde accumulation and electrolyte leakage，
mitigated lipid peroxidation，through increasing antioxidant enzymes activities，osmotic adjustment
substance content and AsA/DHA ratio in pepper seedlings under autoxicity stress.

Key words: pepper, nitric oxide, abscisic acid, autotoxicity, antioxidant enzymes, antioxidant, substances, osmotic adjustment substance