MODIFICATION OF THE CELLULAR HEAT SENSITIVITY OF CUCUMBER BY GROWTH UNDER SUPPLEMENTAL ULTRAVIOLET-B RADIATION

The effect of ultraviolet B (UV-B) radiation on the thermal sensitivit y of cucumber (Cucumis sativus L.) was studied using UV-B-sensitive cv Poinsett 76 and UV-B-resistant cv Ashley grown under control and elev ated (300 mW m(-2)) UV-B radiation levels. Using both cotyledon and le af discs, the ability of the tissue to reduce triphenyl tetrazolium ch loride (TTC) was determined after treatment at 50 degrees C for variou s times. Semilogarithmic plots of TTC reduction as a function of time at 50 degrees C were curvilinear. They were monophasic for the control cucumber and biphasic for cucumber grown in the presence of elevated UV-B. Treatment of cucumber plants at 37 degrees C for 24 h or of tiss ue discs at acute UV-B levels for 1 h further modified their response to elevated temperature. These results suggest that growth of cucumber under enhanced UV-B radiation levels increased its ability to withsta nd elevated temperatures.