Abstract:

【Objective】 Cinnamic acid is one of phenolic acids secreted by cucumber root, and it closely related to the continuous cropping barrier of cucumber. The aim of the experiment was to study exogenous nitric oxide on growth inhibition and active oxygen metabolism of cucumber seedlings under cinnamic acid stress and discuss physiological mechanism of effects alleviated by NO under cinnamic acid stress. 【Method】 The effects of exogenous nitric oxide on growth, antioxidant enzyme systems and active oxygen metabolism of cucumber seedlings were investigated under 200 μmol?L-1 cinnamic acid stress, taking two varieties of cucumber as test materials, by using plastic pot filled with nutrient soil to cultivate plants. 【Result】 The results showed that 100 μmol?L-1 of exogenous sodium nitroprusside (SNP), a nitric oxide donor, significantly alleviated the stress damage on cucumber plants with cinnamic acid, and increased the growth amount, activities of antioxidant enzymes, such as SOD, POD, CAT and APX, and contents of chlorophyll and Pro, reduced production rate and contents of MDA and H2O2 in cucumber seedlings. When treated with 50 or 200 or 400 μmol?L-1 of SNP, stimulative effect on growth, oxidative injure to leaves and antioxidant enzyme activities in cucumber seedling were obviously decreased as compared with 100 μmol?L-1 of SNP. 【Conclusion】 Exogenous NO evidently promoted the growth, increased the activities of antioxidant enzymes, decreased the metabolism of active oxygen in cucumber seedlings under cinnamic acid stress, the alleviated effect of 100 μmol?L-1SNP were the best. It was concluded that exogenous NO certainly can alleviate the damage of cinnamic acid stress to cucumber seedlings, improve the cinnamic acid tolerance of plants, and alleviate continuous cropping barrier caused by autointoxication.

Key words: NO, cinnamic acid stress, cucumber seedlings, antioxidant enzymes systems, active oxygen metabolism