Interaction Of Drought And Cadmium Stresses On Agronomic Traits,Physiology And Biochemistry Of Soybean

Water shortage is a significant environmental stress factor that negatively affects crop growth and development,resulting in reduced yield and poor seed quality.In recent years various types of contaminations in soils also caused the harmful impact on crop productivity.Among the environmental contaminants,heavy metals can disturb the natural ecological balance due to their non-biodegradable nature and toxicity to the living things.Mechanisms of Cd uptake and accumulation in plant parts have been studied extensively in recent years in an attempt to reduce Cd concentration in edible plant parts for safe food production and to improve Cd accumulation in plant parts for phytoextraction.Drought stress has been reported to reduce the uptake and translocation of Cd in soybean.Recent climatic changes and low water availability due to unpredictable precipitation have reduced the productivity of soybean?Glycine max[L.]Merr.?cultivars.Limited information is available on how drought affects the accumulation and translocation of cadmium?Cd?by affecting soybean roots.Excess amount of cadmium?Cd?in soils and shortage of good quality water are the major abiotic factors affecting the crop yield.Therefore,it is of great significance to identify the effects of drought stress on cadmium accumulation and translocation in crops for the safe production of food and the improvement of yield.In this study,several soybean cultivars were used to study the effect of Cd,drought and interaction of drought and Cd stresses on morpho-physiological responses,yield attributes and Cd accumulation.The main results were:1.Drought?5%and 10%?W/V?PEG?,Cd?0.2 and 0.5 mg L^-11 CdCl₂?and PEG+Cd stresses can significantly reduce plant height and root length of soybean plants compared with the control.However,there has no significant effect on root diameter,surface area and volume of soybean plants.Compared with the drought and stress group,PEG+Cd treated soybean plants shown higher root growth inhibition.Furthermore,the reduction in root length,area and diameter and increase in catalase activity was less in drought tolerant cultivars?Shennong20and Liaodou32?than in drought sensitive cultivars?Liaodou3 and Liaodou10?.PEG+Cd treatment significantly reduce Cd accumulation in soybean plants compared with Cd treatment.2.The activity of antioxidant enzymes?including SOD,POD,CAT?in soybean shoots and roots were significantly enhanced by drought?5%and 10%?W/V?PEG?,Cd?0.2 and 0.5 mg L^-11 CdCl₂?and PEG+Cd compared with the control.The activity of antioxidant enzymes in soybean roots were higher than these in shoots.However,there were no significant effect on the activity of antioxidant enzymes of soybean shoot and roots between drought,Cd or interaction of drought and Cd treatment.3.Compared with the control,drought?5%and 10%?W/V?PEG?,Cd?0.2 and 0.5 mg L^-11 CdCl₂?and PEG+Cd treatment significantly up-regulated the expression levels of genes involved in abscisic acid?ABA?degradation?Glyma17G242200??methyl jasmonate?MeJA?biosynthesis?Glyma11G007600??salicylic acid?SA?biosynthesis?Glyma02G063400?,hydrogen peroxide?H₂O₂?production?U51191.1?and Cd transportation?Glyma07G023600?,but down-regulated the expression levels of genes involved in biosynthesis of zeatin riboside?ZR??Glyma03G151800?XM₀03550461??indole 3-acetic acid?IAA??Glyma02G037600?and gibberellin?GA??Glyma03G019800?.The expression levels of these genes in drought tolerant cultivars?Shennong20 and Liaodou32?were significantly higher than these in drought sensitive cultivars?Liaodou3 and Liaodou10?.PEG+Cd treated soybean roots have shown higher gene expression levels of Glyma17G242200,Glyma02G037600,Glyma11G007600,Glyma03G019800 and U51191.1 than PEG/Cd treated soybean plants,but lower gene expression levels of Glyma07G023600.4.This study aimed to explore the effects of drought stress on cadmium?Cd?accumulation in soybean cultivars.Fifteen soybean cultivars were grown in a calcareous soil spiked with Cadmium(0,0.2 and 0.5 Cd?mg L-1?under well-watered,mild drought,and severe drought conditions.The results demonstrated that PEG,Cd and PEG+Cd treatment negatively affected the soybean photosynthesis,and caused oxidative stress in leaves with excess accumulation of Cd in leaves.Furthermore,PEG+Cd treatment significantly reduced the plant height,stem diameter,number of leaves,number of seeds per plant,100 seed,seed yield and Cd accumulation in seeds when compared with PEG or Cd treatment.The seed yield was less reduction in drought tolerant cultivars?Shennong20 and Liaodou32?than in drought sensitive cultivars?Liaodou3 and Liaodou10?.In addition,the results suggested that selected genotypes should be tested in the field to confirm their response to drought and cadmium stress.However,the results reported here help elucidate the agronomic and molecular aspects of plant response to drought and cadmium stress.Taken together,drought stress affected the growth and configuration of soybean roots and down-regulated the expression level of Cd transporter gene to reduce the Cd accumulation in soybean plants and seeds.The above results provide a theoretical basis for the safe production of food in Cd polluted areas through water management.