Effects of Drought Stress on the Metabolic Properties of Active Oxygen Species, Nitrogen and Photosynthesis in Cucumber 'Jinchun No. 5' Seedlings

To gain a physiological understanding of the effect of drought stress on the cucumber (Cucumis sativus L.), we subjected 'Jinchun No. 5' seedlings to three treatments: control (C), moderate drought stress (MDS) and severe drought stress (SDS) during exposure to high temperature and strong light. We then investigated the metabolic properties of active oxygen species, nitrogen and photosynthesis in leaves from the 3rd to 15th days of treatment. The amounts of active oxygen species superoxide anion (O-2(center dot-)) and hydrogen peroxide (H2O2) increased with increasing drought stress in C, MDS and SDS. The malondialdehyde (MDA) content, which reflects the excess metabolism of active oxygen was increased on the 12th and 15th days of treatment with increasing drought stress. The nitrate-reductase (NR) activity of nitrogen metabolism indicators decreased on the 3rd to 15th days of treatment, while soluble protein content increased on the 9th to 15th days of treatment with increasing drought stress. With respect to the photosynthetic properties, stomatal conductance (g(s)) decreased from the 6th to 15th days of treatment with increasing drought stress, no significant difference was seen in sub-stomatal CO2 concentration (C-i) between all three treatment plots, transpiration rate (E) was lower in SDS than C, and the net photosynthesis rate (A) decreased with increasing drought stress. A significant correlation between g(s), H2O2 and E with A, and secondly between MDA and NR with A was observed. These findings suggest that drought stress during periods of high temperature and strong light results in the generation and accumulation of abundant active oxygen species, and inhibition of nitrogen and photosynthesis metabolism in cucumber 'Jinchun No. 5' seedlings.