Effect of Enhanced UV-B Radiation on Polyamine Content and Membrane Permeability in Cucumber Leaves

Cucumber plants (Cucumis sativus L., cv. Jingchun 3) were grown in a greenhouse under PAR illumination of 400–600 μmol/(m2 s) at 30/15°C (day/night) temperature. Two enhanced biologically effective UV-B radiation levels per day were applied: 8.82 kJ/m2 (T1) and 12.6 kJ/m2 (T2). Cucumber seedlings were irradiated 7 h per day for 25 days under T1 and T2. A comparative study of growth, membrane permeability, and polyamine content in cucumber leaves under T1 and T2 treatments was conducted. UV-B radiation resulted in the dose-dependent decrease in leaf area, dry weight of foliage, and plant height. The T1 and T2 treatments caused an increase in the contents of putrescine, spermine, and spermidine. However, the total polyamine content declined slightly when electrolyte leakage increased dramatically on the 18th day of treatment, especially after T2 treatment. It can be concluded that polyamine accumulation in the cucumber leaves is an adaptive mechanism to the stress caused by UV-B radiation.