Changes in Physiological and Biochemical Parameters of Gourd (Cucurbita pepo L.) Two Varieties under Drought and UV-B Radiation. Nobar Hajihosseinlo*, Siavash Hosseini Sarghein and Rashid Jamei

It emerged recently that there is an inter-relationship between drought and Ultraviolet-B (UV-B) radiation in plant responses, in that both stresses provoke an oxidative burst. The objective of the present investigation was to study the effect of drought stress, UV-B radiation and the combined effects of UV-B and drought stresses on two cultivars of gourd seedling. The gourd plants were grown with diurnal regime of 16h light and 8h dark and temperature of 22/26°C (night/day). The relative humidity 60% and average of photosynthetically active radiation was 150 µmol.m-2.s-1. Treatments was started 25 days after planting. Then, 25-days-old seedlings were divided in to four groups. The control and three groups subjected to stress conditions: UV-B radiation, drought stress conditions, UV-B radiation and drought stresses combined. The results of measurement on compounds which absorbs UV including flavonoids, anthocyanins, phenol and antioxidant enzymes activity including catalase, guaiacol peroxidase showed that these parameters increased when plant irradiated with UV-B, drought stress and their combination. Biochemical parameters indicate that with this experiment situation UV-B stress has stronger stress effectors than drought on the growth of seedling of both cultivars. The present results suggested that, under soil drought conditions, enhanced UV-B radiation had not let to greater decrease gourd biochemical markers. The results suggested that co-stresses of supplementary UV-B radiation and drought synergistically functioned and one of them could alleviate the inhibitory effects of another under the condition of arid and semiarid loessial soils.