Effects of drought stresses on antioxidition capacity and Osmotic Adjustment of Chenopodium album L

Drought is one of the stress conditions that often severely effects plant growth. The loss of agricultural production due to drought stress is estimated to nearly equal the total losses caused by all other environmental stresses. In this study, the physiological and biochemical responses of Chenopodium album L. under artificially simulated drought stresses were examined to provide a theoretical basis for crops cultivation and effectively increasing agricultural production in arid areas. Chenopodium album L. was grown from freshly harvested seeds under natural light. Twelve pots of plants showing similar growth were divided into 4 groups and treated with different levels of drought stress by controlled irrigation: no stress (control), watered every morning to keep the 80% of field moisture capacity (well watered) for 20 days and then drought stressed 0 day before the measurement; mild stress: watered every morning to keep the 80% of field moisture capacity for 15 days and then drought stressed 5 days before the measurement; moderate stress watered every morning to keep the 80% of field moisture capacity for 10 days and then water stressed 10 days before the measurement and severe stress: watered every morning to keep the 80% of field moisture capacity for 5 days and then water stressed 15 days before the measurement, The following parameters were determined: relative water content (RWC), free water content(FWC), bound water content(BWC), soluble sugars, free proline, K+, Ca2+, malondialdehyde ( MDA) and free ascorbic acid (ASA), plasma membrane permeability , the production rate of O2-·, and activities of superoxide dismutase (SOD) and peroxidase (POD). The results showed that the relative water content in leaves of the control, mild-stressed, moderately-stressed and severely-stressed plants were 94.07%, 87.01%, 76.35% and 64.03%, respectively. The water content in soil 5-7 cm under the surface in the 4 groups of pots at the same time were 23.33%, 16.92%, 10.82% and 7.73%, respectively. Under moderate drought stress, the RWC and FWC in leaves were decreased while the BWC was increased. The activities of SOD and POD in leaves reached the highest level among the four treatments plasma membrane permeability, MDA content and the O2-·production rate in leaves declined; whereas osmoregulatory molecules such as soluble sugars, proline, K+and Ca2+in leaves accumulated rapidly, indicating that Chenopodium album L. has the ability to adapt to drought stress by regulating the internal osmolarity and protecting the membrane. Under severe drought stress, however, the O2-·production rate in leaves declined; whereas membrane damage and increased plasma membrane permeability. The activities of SOD and POD were initially increased as compared to those under the moderate drought stress and then declined; ASA content was also decreased. These results suggest that severe drought stress could cause some damage on the Chenopodium album L...