Functional Analysis Of The Gene Involved In The Regulation Of Heavy Metal Stress Responses In Arabidopsis

It was shown previously that Arabidopsis(Arabidopsis thaliana) desaturase 2(ADS2) cDNA was isolated,and that the expression of ADS2 was organ-dependent and up-regulated by low temperature.However,little is known about the role of ADS2 gene in heavy metal resistance in plants.In this study,we showed that ADS2 gene is involved in the regulation of cadmium(Cd) and lead(Pb) resistance.ADS2 was strongly repressed by Cd(â…¡),and ads2-1 mutant plants showed increased Cd(â…¡) resistance.A lower Cd content was detected in ads2-1 plants than in wild-type plants subjected to Cd(â…¡) treatment,which was associated,at least in part,with activation in expression of AtPDR8 gene,a pump excluding Cd(â…¡) and/or Cd(â…¡)-containing toxic compounds from the cytoplasm,suggesting that ADS2-mediated Cd(â…¡) resistance is AtPDR8 dependent.Surprisingly,we found that ads2-1 plants showed increased Pb(â…¡) sensitivity,and ADS2 was strongly repressed by H₂O₂ but not by Pb(â…¡).No significant difference in Pb content was detected between wild-type and ads2-1 plants subjected to Pb(â…¡). The ads2-1 mutant also showed increased sensitivity to oxidative stresses mediated by hydrogen peroxide(H₂O₂) and paraquat,and higher levels of H₂O₂ accumulation were observed in leaves of ads2-1 plants than those of wild-type plants when subjected to Pb(â…¡) and H₂O₂,indicating that ADS2 mediates Pb(â…¡) resistance indirectly by impaired ROS scavenging.Taken together,all these results suggest that ADS2 gene mediates Cd(â…¡) and Pb(â…¡) resistance,at least in part,through two distinct mechanisms,a AtPDR8-dependent mechanism and a ROS detoxification system-mediated mechanism,respectively.