The Role Of AtMPK6 In UV-B Radiation-induced Stomata Closure In Arabidopsis And Its Relationship With H₂O₂, NO And Ethylene

Ultraviolet-B(UV-B)radiation functions is a key environmental signal directing plant growth and development.Thus,understanding the mechanism of UV-B signal transduction in cells has important theoretical and practical significance.Previous studies have shown that UV-B can induce stomatal closure,and this UV-B effect is mediated by hydrogen peroxide(H2O2),nitric oxide(NO)and ethylene.Pharmacological evidence also show the involvement of MAPKK in UV-B-induced stomatal closure.However,up to date,it is still not clear that which specific MPK participates in the UV-B-induced stomatal closure,and that what are the interrelationships between MPK and signaling molecules H2O2,NO or ethylene in the UV-B quard cell signaling.In this study,by stomatal analysis and laser scanning confocal microscope,the Arabidopsis wild-type,AtMPK6 T-DNA insertion homozygous mutants and ethylene signaling mutants for EIN2,EIN3 and ARR2 were used to address the following questions:(1)AtMPK6 involved in UV-B-induced stomatal closure;(2)The interrelationships between AtMPK6 and H2O2,NO,EIN2,EIN3 or ARR2 in the UV-B quard cell signaling.The following are the main results and conclusions of this research:1.0.5 W m-2 UV-B radiation induced stomatal closure in wild-type,but did not in AtMPK6 mutants,suggesting that MPK6 is involved in UV-B-induced stomatal closure in Arabidopsis leaves.2.Exogenous ethephon could induce stomatal in wild type,but not in AtMPK6 mutants under either light or UV-B radiation,suggesting that ethylene functions upstream of MPK6 in UV-B quard cell signaling.3.Exogenous H2O2 could induce stomatal closure in wilt type,but not in AtMPK6 mutants under light,UV-B radiation or exogenous ethephon treatment;UV-B radiation and ethephon treatment induced H2O2 generation not only in wild-type quard cells,but also in AtMPK6 mutants quard cells.These results indicate that H2O2 acts downstream of ethylene and upstream of MPK6 in UV-B guard cell signaling.4.Exogenous NO donor sodium nitroprusside(SNP)induced stomatal closure in wild type,also in AtMPK6 mutants under either light,UV-B radiation,ethephon or H2O2 treatment;Treatments of UV-B,ethephon or H2O2 could induce NO production in wild-type quard cells,but not did so in quard cells of AtMPK6 mutants.Together,these results indicate that NO works downstreeam of ethylene,H2O2 and MPK6 in the UV-B quard cell signaling.5.0.5 W m-2 UV-B radiatioL and exogenous ethephon could not induce stomatal closure in mutants of ethylene signaling components EIN2,EIN3 and ARR2,suggesting that EIN2,EIN3 and ARR2 are involved in UV-B-and ethylene-induced stomatal closure.6.Exogenous H2O2 could induce stomatal closure in wilt type,but not in mutants EIN2,EIN3 and ARR2 under light,UV-B radiation or exogenous ethephon treatment;UV-B radiation and ethephon treatment induced H2O2 generation in quard cells of mutants EIN2,EIN3 and ARR2.These results indicate that H2O2 acts downstream of ethylene and upstream of EIN2,EIN3 and ARR2 in UV-B guard cell signaling..7.SNP induced stomatal closure in mutants EIN2,EIN3 and ARR2 under either light,UV-B radiation,ethephon or H2O2 treatment;Treatments of UV-B,ethephon or H2O2 could not induce NO production in quard cells of mutants EIN2,EIN3 and ARR2.Together,these results indicate that NO works downstreeam of ethylene,H2O2,EIN2,EIN3 and ARR2 in the UV-B quard cell signaling.Taken together,the results in this study indicate:(1)MPK6 is involved in 0.5 W m-2 UV-B-induced stomatal closure in Arabidopsis leaves;(2)0.5 W m-2 UV-B induces stomatal closure by a linear signaling pathwat is UV-B(?)ethylene(?)H2O2(?)EIN2,EIN3,ARR2,MPK6(?)NO(?)stomatal closure.