Effects of supplemental UV-B and drought stress on photosynthetic activity of sessile oak (Quercus petraea L.)

Abstract

Enhanced UV-B radiation may have many direct and indirect effects on physiology of plants. Different species exhibit varying degrees of resistance and susceptibility to UV-B radiation which change when other stresses are present. In the present study we investigate the responses of sessile oak seedlings exposed to supplemental UV-B radiation and water stress. One year old seedlings were grown and acclimated under white light of 300 m mol m-2 s-1) for 2 weeks and then treated with 150 m W cm-2 of UV-B radiation for 4 weeks. Then a set of seedlings both in control and UV-B chambers were exposed to water stress by withholding water for 2 weeks. Leaf gas exchange was measured by LCA2 analyser (ADC, UK), photochemical efficiency and occurrence of photoinhibition of PSII were determined by means of PAM 2000 modulated fluorometer (WALZ, Germany). For analysis of photosynthetic pigments, leaf samples were frozen in liquid N2 in field, and pigments were determined by spectrophotometric and HPLC methods. Seedlings of sessile oak showed relatively high and rapidly developing susceptibility to the enhanced UV-B radiation which appeared in lowering the chlorophyll content and maximum photochemical efficiency (Fv/Fm) during the treatment prior to the onset of water stress. With increasing water stress, seedlings grown without UV-B exhibited more significant decreases in Fv/Fm values than UV-B treated plants. Both UV-B radiation and water stress increased non-photochemical quenching with a parallel enhancement of zeaxanthin formation. The results suggest that exposure to UV-B radiation tends to increase the drought tolerance of sessile oak seedlings. This work was supported by INCO/Cop. No. IC15-CT98-0126.