Effects Of Zn/Mn On Growth, Pb Uptake And Transport In Rice (Oryza Sativa L) Seedlings Under Pb Stress

In recent years,heavy metal pollution in farmland has become increasingly serious due to the heavy use of sewage irrigation,agricultural chemicals and industrial wastewater and waste gas,et al.As the main food crop in China,rice is easily affected by Pb at seedling stage.Zn and Mn play a vital role in the growth and development of rice.In the same environmental system,Pb,Zn and Mn,which are all divalent metal cations,may interact with each other.In this study,“HuangHuazhan” was chosen as the test crop to investigate the changes of physiological and biochemical indexes of rice seedlings and the uptake and transport of Pb in different parts during short-term Pb stress,as well as the effects of Zn or Mn on the growth and uptake of Pb in rice seedlings through hydroponic,to explore whether Zn or Mn could alleviate or aggravate the poisoning of rice seedlings in the process of Pb stress,and whether this effect was related to the stress time,so as to provide experimental data and practical reference for the treatment of Pb pollution in rice seedlings.The main conclusions are as follows:(1)Pb had a dual effect on the growth and physiological characteristics of rice seedlings,manifested as “low promotion and high inhibition”,that is,3.5?M Pb could promote the growth of rice seedlings,while 5?M Pb could inhibit the growth of rice seedlings.(2)The distribution of Pb in different parts of rice seedlings was as follows: root >> stem > leaf.During the 3 days of Pb stress,the accumulation of Pb in rice roots was mainly concentrated day 1,while the accumulation of Pb in stems and leaves was mainly concentrated on day 3.The distribution rules of Zn,Mn and Cu in different parts of rice seedlings were as follows: stem > leaf > root,leaf > stem > root,and root > leaf > stem.Under Pb stress,the concentration of Zn,Mn and Cu in the main distribution parts decreased with the increase of treatment time.(3)The toxicity of Pb to rice seedlings could be alleviated by simultaneous addition of Pb and Zn,or simultaneous addition of Pb and Mn.After the pretreatment with Zn in advance,the toxicity of Pb to rice seedlings was enhanced.However,Mn could still play a mitigating role on Pb's poison to rice seedlings after Mn pre-treatment.(4)Under the two treatments with Zn,the inhibiting/promotion effect of Zn on Pb uptake in roots and stems was related to the Pb stress time.Zn inhibited the uptake of Pb within 2 days of Pb stress,and promoted the uptake of Pb after 4 days of Pb stress.Moreover,Zn inhibited the uptake of Pb in leaves during 10 days of Pb stress.When Pb and Zn were added simultaneously,the inhibition effect of Zn on the uptake of Pb was better.(5)Under the two treatments with Mn,the inhibition/promotion effect of Mn on Pb uptake in roots,stems and leaves was related to the Pb stress time.Mn inhibited the uptake of Pb in different parts of rice within 2 days of Pb stress,and after 4 days of Pb stress,Mn began to promote the uptake of Pb in different parts of rice.Moreover,when Mn and Pb were added simultaneously,the inhibition effect of Mn on the uptake of Pb in stems was better.