The Growth And Development Responses Of Arabidopsis To Different Concentrations Of Copper Ions

The microelement copper?Cu?is essential for plant growth and development.Though the appropriate concentration of copper can promote plant growth,excessive copper disrupts many biological functions in plants.To investigate the complex network controlling Cu²⁺sensitivity and adaptability,a wide range of CuSO₄ concentrations were tested for their differential impacts on primary root length of Arabidopsis.The results showed that 5?M Cu²⁺slightly promoted the growth of Arabidopsis primary roots.While 20?M and 60?M Cu²⁺moderately and dramatically inhibited root development,respectively.Thus,three Cu²⁺concentrations?5,20,60?M?were chosen for the following analyses since they resulted in three highly distinguishable phenotypic responses of Arabidopsis and represented three distinct adaptation patterns of plants challenged by Cu²⁺stress.Sixty?M Cu²⁺reduced the meristem size by affecting meristematic cell division ability and stem cell niche activity.As revealed by the DR5:GUS marker line,the Cu²⁺-triggered root phenotype was correlated well with the change in the levels of endogenous auxin in Arabidopsis.Therefore,the regulation mechanism of auxin in the root of Arabidopsis was analyzed based on the above experimental results.Then,Arabidopsis were treated with 1-naphthalene acetic acid?NAA?and Cu²⁺,and the results showed that NAA could increase the content of endogenous auxin in root tips.Besides,The role of auxin homeostasis in regulating the differential Cu²⁺responses was verified in Arabidopsis mutants defective in auxin production,signaling sensitivity or transport.This study also presented evidences for the involvement of an auxin/cytokinin crosstalk in regulating auxin biosynthesis upon Cu²⁺treatment and demonstrated that the decreased level of auxin was caused by the repressed expression of TAA1 and YUCCA family members in the indole-3-pyruvic acid pathway.Next,we investigated the effects of three different concentrations of Cu²⁺on reproductive growth,reactive oxygen species homeostasis and reactive oxygen species scavenging system of Arabidopsis.The results showed that Cu²⁺at 5?M promoted,but 20,60?M Cu²⁺retarded the onset of bolting and flowering.Besides,60?M Cu²⁺also negatively affected the silique size,however did not cause the change of the average seed weight.The leaves and roots of Arabidopsis were then examined for the changes in antioxidant enzyme activity and expression level of genes related to reactive oxygen species scavenging at different Cu²⁺levels.The results indicated that a significantly enhanced production of hydrogen peroxide was provoked by 60?M Cu²⁺in roots,which was correlated to the increased activity of superoxide dismutase and the deceased activities of catalase,ascorbate peroxidase.In the presence of 60?M Cu²⁺,glutataione and ascorbic acid supplementations protected Arabidopsis from Cu²⁺-induced chlorosis toxicity symptom by significantly increasing chlorophyll content in leaves.In summary,the growth and development responses of Arabidopsis to different concentrations of Cu²⁺were investigated in this research.This study laid the foundation for the new research strategy to protect plants from the excessive Cu²⁺damage.