Effects of Phenolic Acids on Growth and Activities of Membrance Protective Enzymes of Cucumber Seedlings

Shandong Mici cucumber was taken as experimental plant variety. The applied phenolic acids were P hydroxy benzoic acid and cinnamic acid which were designed to four concentration (0 μmol/L, 50 μmol/L, 100 μmol/L, 150 μmol/L)treatments to study the effects of phenoic acids on the growth and the activities of protective enzymes of cucumber seedlings. The results showed that the two types of phenolic acids both inhibited the plant growth. The inhibitory effects were enhanced with increasing concentration of phenolic acids and prolonging time of treatment. Compared with the control, the growth of the cucumber under the treatments of A150(P hydroxy benzoic acid, 150 μmol/L),B50(cinnamic acid, 50 μmol/L),B100(cinnamic acid, 100 μmol/L), B150(cinnamic acid, 150 μmol/L) showed significant difference in the plant height and leaf area, and the inhibitory effect of cinnamic acid was more stronger than that of P hydroxy benzoic acid. For protective enzymes system [peroxidase (POD),catalase (CAT)], the results indicated that the POD activity increased firstly, then decreased , increased again finally under lower concentrations of phenolic acids but decreased at last under highter concentrations, and that the CAT activity increased firstly, then decreased, increased again finally under lower concentrations of phenolic acids, however, the activities decreased firstly, then increased a little, decreased continuously at last under higher concentrations. In addition, the treatments of phenolic acids led to a decrease of superoxide dismutase (SOD) activity and an increase of malonic aldehyde (MDA) content in the seedlings compared with the check. It proved that lot of activited oxygen were produced and protective enzymes were destroyed under highter concentrations of phenolic acids.