Physiological and biochemical responses of Chenopodium album to Drought Stresses

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 effectively increasing agricultural production in arid areas. C.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 once a week for 4 weeks;light stress,watered once a week for the first 3 weeks;moderate stress,watered once a week for the first 2 weeks;severe stress,watered once in the first week only.Each time the water was allowed to fully saturate the moisture capacity of soil.The pots were protected from exposure to rain.Leaf samples were taken after the fourth week(the final week) of the experiment.The following parameters were determined: relative water content(RWC),free water content(FWC),bound water content(BWC),soluble sugars,free proline,K~+,Ca~(2+),malondialdehyde (MDA) and free ascorbic acid(ASA),membrane permeability,the production rate of O~(·)_2,and activities of superoxide dismutase(SOD) and peroxidase(POD).The relative water content in leaves of the control,lightly-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.Membrane permeability,MDA content and the O~(·)_2 production rate in leaves declined;whereas osmoregulatory molecules such as soluble sugars,proline,K~+ and Ca~(2+) in leaves accumulated rapidly,indicating that C.album has the ability to adapt to drought stress by regulating the internal osmolarity and protecting the membrane.Under severe drought stress,however,the O~(·)_2 production rate and the MDA content increased remarkably,causing membrane damage and increasing membrane permeability of leaf cells.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 C.album is vulnerable to damage by severe drought stress.