Changes in Antioxidative Enzyme Activities in Cucumber Plants with Regard to Biological Control of Root-knot Nematode, Meloidogyne incognita with Cinnamomum cassia Crude Extracts

Cucumber plants were infected with the root-knot nematode Meloidogyne incognita and were then treated with Cinnamomum cassia crude extracts (CCE). The activities of antioxidative enzymes such as superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), and ascorbate peroxidase (APX, EC 1.11.1.11, class I peroxidase) were detected in the cucumber leaves. On day 28 after treatment of C. cassia (0, 1, 5, and 10 mg/mL), the relative galling formation decreased significantly in a dose-dependent manner. The C. cassia crude extracts also effectively inhibited the growth of M. incognita in soil and roots. The number of second-stage juveniles was significantly decreased as the concentration of the C. cassia crude extracts increased. Twenty-eight days after treatment with CCE, the SOD activities of plant leaves treated with 5 and 10 mg/mL CCE were greater than that of leaves treated with nematode (Ne) only. In addition, the CAT and ascorbate peroxidase (APX) activities increased as the concentration of CCE increased. The relative activities of the antioxidative enzymes decreased as the galling formation in the roots increased in response to M. incognita infection. Polyacrylamide gel electrophoresis (PAGE) with activity staining revealed active bands of SOD corresponding to at least five isozymes (93, 79, 71, 66, and 41 kDa), including three Fe-SOD bands (71, 66, and 41 kDa) and two Mn-SOD bands (93 and 79 kDa). Analysis of the cucumber leaves revealed one active band corresponding to the CAT isozyme (>97 kDa) on 10% native gels. At least four bands corresponding to APX were observed in 10% polyacrylamide, including one major band (>97 kW) and three minor bands (79, 71, and 66 kDa). Compared with the leaves of cucumber plants that received other treatments, SOD (41 kDa) and APX (70 kDa) isozymes in the leaves of plants treated with Ne only showed intensified bands in PAGE gels.