Ultraviolet-b radiation effects on water relations, leaf development, and photosynthesis in droughted pea plants

The effects of ultraviolet-B (UV-B) radiation on water relations leaf development and gas-exchange characteristics in pea (Pisum sativum L. cv Meteor) plants subjected to drought were investigated. Plants grown throughout their development under a high irradiance of UV-B radiation (0.63 W m-2) were compared with those grown without UV-B radiation and after 12 d one-half of the plants were subjected to 24 d of drought that resulted in mild water stress. UV-B radiation resulted in a decrease of adaxial stomatal conductance by approximately 65%, increasing stomatal limitation of CO2 uptake by 10 to 15%. However, there was no loss of mesophyll light saturated photosynthetic activity. Growth in UV-B radiation resulted in large reductions of leaf area and plant biomass which were associated with a decline in leaf cell numbers and cell division UV-B radiation also inhibited epidermal cell expansion of the exposed surface of leaves. There was an interaction between UV-B radiation and drought treatments: UV-B radiation both delayed and reduced the severity of drought stress through reductions in plant water-loss rates, stomatal conductance, and leaf area