Heat Shock Increases the Tolerance of Plants to UV-B Radiation: 1. Growth, Development, and Water Supply to Tissues

The effects of heat shock (HS); UV-B irradiation; and the consecutive action of these factors on the growth, development, and water supply of seven-day-old melon (Melo sativusSager., cv. Torpeda) seedlings were investigated. Depending on the HS severity, we observed growth stimulation (after treatment at 45°C for 1 h), growth retardation (after treatment at 45°C for 2 h or at 48°C for 1 h), or complete growth inhibition and cell death (after treatment at 45°C for 3 h or at 55°C for 1 h). UV-B irradiation (18.3 kJ/(m2h)), depending on its duration, stimulated (5–10 min), retarded (60 min), or resulted in complete growth inhibition and plant death (90 min). HS treatment (at 45°C for 1 h) prior to UV-B irradiation (for 1 h) favorably affected both the growth and water balance of seedlings. Apparently, the HS pretreatment increases the tolerance of seedlings to high doses of UV-B radiation.