Intraspecific differences in physiological response of 20 wheat cultivars to enhanced ultraviolet-B radiation under field conditions.

Field studies were conducted to determine the potential for alterations in physiology and the intraspecific variation in sensitivity of 20 wheat (Triticum aestivum) cultivars to enhanced ultraviolet-B (UV-B, 280-315 nm) radiation. The supplemental UV-B radiation was 5 kJ m(-2), simulating a depletion of 20% stratospheric ozone. Out of 20 wheat cultivars (from South China, North China and Mexico) tested, 13 showed significant changes in total chlorophyll content. In most of these sensitive species, chlorophyll a content was strongly reduced, and chlorophyll b content decreased in a lesser extent, leading to a decrease in chlorophyll a/b ratio. However, some species had an increased chlorophyll a/b ratio under enhanced UV-B. The effect of UV-B on flavonoid content also showed intraspecific differences, a significant increase for one cultivar, decreases in 12 cultivars and no effect on the other seven cultivars. Superoxide dismutase (SOD) activity of five cultivars was significantly increased, and that of six cultivars significantly decreased. Membrane permeability of 12 cultivars significantly increased, while only that of Dali 905 was significantly decreased. Malonaldehyde (MDA) contents of eight cultivars were increased significantly, while that of three cultivars was significantly decreased. Although large intraspecific differences were found for the different parameters measured, there was no clear correlation between them under UV-B radiation.