Effects Of Cadmium On Pea Growth Under Hypoxia

Cadmium toxicity and waterlogging cause detrimental effect in the coastal areas of south China.Each year causes incalculable economic losses in food crops.Therefore,it is of great significance to understand the mechanism of cadmium toxicity tolerance under waterlogging stress.As a result,screening the varieties of crops with superior tolerance to cadmium and waterlogging stress is critical to improve crop resistance and crop yield in breeding programme.ROS appears in the case of numerous stress condition inducing oxidative stress in plants.However,it is also an essential signal molecule,playing an important role in many signal pathways especially associated with cadmium accumulation under hypoxia condition.Accordingly,to investigate the physiological aspects of cadmium toxicity tolerance under hypoxia condition,the following specific objectives were addressed:（1）to develop a rapid screening method and screen a large number of pea varieties;（2）to quantify the relative contribution of hypoxia condition to Cd accumulation;（3）to identify the effect of Cd toxicity on ROS production in pea root.Working along these lines,pea was subjected to cadmium treatment with multiple concentrations gradient（0,1,3,6,10,20μM）,and further applied 0.2%agar solution which simulated as anoxia environment.To screen Cd toxicity tolerance associated with waterlogging stress tolerance,biomass and other physiological traits of pea were measured.The potential mechanism of Cd accumulation under hypoxia condition was study.With the ascent of the Cd concentration,an inhibition was observed on plant growth,and a significant decrease occurred to plant biomass.Under the treatment of high concentration of cadmium,pea leaves appeared to be dry and yellow.At the same time,yellowingand thickening could be found in taproot.Occurrence of lateral root was dramatically inhibited.Each variety showed significant differences at different concentrations,6μM Cd²⁺was found to best separate sensitive from tolerant genotypes.In this experiment,the tolerance of cadmium of 4 pea varieties was sequenced as Ps-100>Ps-4>Ps-7>Ps-203.Further 18 pea varieties were conducted under Cd toxicity treatment.Combining with the phenotype identification of shoot and root,Ps-2,33,36,61 and74 were found to perform a well tolerance to cadmium,while Ps-4 and 9 were cadmium-sensitive types.Ps-5,33 and 61 could maintain high biomass under hypoxia condition,while Ps-43 and 107 showed Cd sensitive performance.Under the complex stress of waterlogging and cadmium toxicity,the waterlogging stress tolerant varieties Ps-33 and 61 were less affected by cadmium than Ps-5,showing better tolerance to cadmium under the condition of hypoxia.Ps-38 and 82,107were more sensitive under this treatment,while waterlogging sensitive variety ps-107 was also sensitive to the present of cadmium under hypoxia condition.The root biomass under ps-4 and 21 hypoxia treatment was significantly higher than that under combined stress treatment.Under the treatment of Cd toxicity associated with hypoxia condition,there was no significant different observed in biomass of shoot and root subjected to hypoxia condition No significant symptom was found with the present of cadmium in the treatment solution.Therefore,in great possibility,the effects of cadmium toxicity of pea was suppressed by hypoxia condition.Under high concentration of cadmium treatment,a large generation of ROS were found to induce oxidative stress,causing a detrimental influence on permeability of cell membrane in root,finally leading to cell death.The ROS content in root tip was significantly higher than that in root mature zone.The relative ROS content of root mature zone（relative to that in root tip）in most of pea varieties was round 35%,while Ps-5,9,61,74,Ps-58 maintained a high ROS production in root mature zone with a relative content up to 75%.Cd-tolerant varieties have capacity to alleviate the impairment of ROS by sequestration or compartmentalization of Cd to reduce cellular Cd concentration,in order that root cell can maintain a proper level of ROS from induction of oxidative stress for plant survival.