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 sensitivity of cucumber (Cucumis sativus L.) was studied using UV-B-sensitive cv Poinsett 76 and UV-B-resistant cv Ashley grown under control and elevated (300 mW m-2) UV-B radiation levels. Using both cotyledon and leaf discs, the ability of the tissue to reduce triphenyl tetrazolium chloride (TTC) was determined after treatment at 50[deg]C for various times. Semilogarithmic plots of TTC reduction as a function of time at 50[deg]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[deg]C for 24 h or of tissue 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 withstand elevated temperatures.