Enhanced UV-B radiation aggravates negative effects more in females than in males of Morus alba saplings under drought stress

Drought and UV-B radiation are two major environmental stresses which can either suppress or activate defense responses in plants. What is less clear is how these stresses, separately or combined, affect the male and female plants of dioecious species. Mulberry (Mows alba L.) saplings, a dioecious plant widely planted in China and Japan, was employed as a model species and subjected to two UV-B radiation regimes (3.43 kJ m(-2) day(-1) (ambient radiation) and 3.78 kJ m(-2) day(-1) biologically effective UV-B radiation (enhanced radiation)) and two watering regimes (100 and 30% of the field capacity) for 3 months, and then sex-related morphological, physiological, anatomical and ultrastructural responses of mulberry to enhanced UV-B radiation and drought were investigated. Compared with the control, both enhanced UV-B radiation and drought significantly inhibited growth of both sexes and the effects were not fully additive. This might indicate that one of the two stress factors activated defense responses in the plants which reduced the damage caused by the other. Furthermore, when exposed to the combination of enhanced UV-B radiation and drought stress, females exhibited significantly lower morphological increment of stem and root, biomass accumulation, net photosynthesis rate, antioxidative enzymes activities, anthocyanin content, total leaf area and relative water content, as well as more damage on mesophyll cells than did males. Therefore, these results indicated that enhanced UV-B radiation aggravates negative effects more in female saplings than in males under drought stress