Roles Of Ethylene?Nitric Oxide And Auxin Regulating Magnesium Deficiency-Induced Root Hair Development In Arabidopsis

Magnesium(Mg)is an essential macronutrient for plants,and it is involved in many fundamental biochemical processes.However,Mg limitation is often a critical constraint for crop production and quality,because of the easily leaching in acid or sandy soils and its absorption is intensively antagonized by that of other cations.Understanding the mechanism underlying plants to Mg deficiency in roots is critially of importance for the the breeding of crops with high Mg-uptake efficiency.In this study,we used Arabidopsis and ethylene or NO or auxin related mutants as a test species to investigate ethylene,NO and auxin in the regulating the induction of root hair development under Mg deficiency.The main findings are as follows:Mg deficiency induced root hair development,elevated the accumulations of ethylene,NO and auxin in roots by activating the activities of ACC synthase(ACS)and ACC oxidase(ACO),nitrate reductase(NR)and NOS like enzyme(NOS-L),and by stimualting the expression of auxin transporter AUX1,PIN1 and PIN2,respectively.In Mg-sufficiency Col-0 plants,either ACC,or SNP,or NAA clearly elevated the root hair development,whereas the induction of root hair development by Mg-deficiency was significantly restrained by either STS or c-PTIO or NPA,This result was in concert with the observation that Mg-deficiency-induced root hair growth was clearly compromised in ethylene insensitive ein2-5 and ein3-1 mutants,or NO defective nial,2 and noal mutants,or auxin transport defective aux1-7,pinl-1 and pin2 mutants.These results suggested that ethylene,NO and auxin were all involved in the Mg-deficiency-induced root hair development.We then investigated whether there is an interaction between ethylene,NO and auxin in regulating Mg-deficiency-induced root hair development.We found that Mg deficiency induced ethylene,NO and auxin accumulation in roots,with each positively influenced the accumulation of the other two by stimulating the activities of ACS and ACO,NR and NOS-L,or the expression of AUX1,PIN1 and PIN2 in roots..These results suggested that there existed a positive correlation between ethylene,NO and auxin accumulation in Mg-deficiency roots.Furtehermore,ACC partially alleviated the inhibited root hair development in c-PTIO-treated Col-0 plants,in nial,2 and noal mutants under Mg deficiency.In turn,SNP partially antagonized the impaired root hair development in STS-treated Col-0 plants,in ein2-5 and ein3-1 mutants under Mg deficiency.These results suggested that ethylene and NO interactively involved in the regulation of root hair development under Mg deficiency.Interestingly,the Mg-deficiency-induced root hair development in Col-0 plants by either STS or c-PTIO or in nia1,2,noal,ein2-5 and ein3-1 mutants was completely reversed by NAA;nevertheless,ACC or SNP did not rescue the impared root hair development in NPA-treated Col-0 plants or in auxl-7,pin1-1 and pin2 mutants.These results suggested auxin acts downstream of ethylene and NO involving in the regulation of root hair development.