The Effects And The Mechanism Of Ethylene On ABA-and Dark-induced Stomatal Closure

Some studies found that plant hormone ethylene could promote stomatal closure,other results indicated that ethylene prevented ABA-and dark-induced stomotal closure,so the effect of ethylene on stomatal movement was still unclear.The previous investigation proved that ABA and dark induced stomotal closure by enhancing the levels of H₂O₂ and NO,implying that the ethylene might prevent ABA-and dark-induced stomotal closure by reducing the levels of H₂O₂ and NO. However,this inference needed to be proved.By epidermal strip bioassay and laser-scanning confocal microscopy,the effects and the mechanism of ethylene on ABA-and Dark-induced stomotal closure in Vacia faba L.were studied in the present work.The main results were as follows:1.Like H₂O₂ scavenger Vc and CAT,the inhibitor of H₂O₂ generating enzyme NADPH oxidase DPI,NO scavenger cPTIO and Hb,the inhibitor of NO generating enzyme NOS L-NAME, ACC,a precursor of ethylene synthesis,and ethephon,an ethylene releasing agent,prevented ABA-and dark-induced stomatal closure significantly.These results suggested that ethylene could prevent ABA-and dark-induced stomatal closure through reducing H₂O₂ and NO in guard cells.2.Like Vc,CAT and DPI,ACC and ethephon did significantly reduce the ABA-and Dark-induced H₂O₂ in guard cells.Like cPTIO,Hb and L-NAME,ACC and ethephon did significantly reduce ABA-and dark-induced NO in guard cells.These results showed that ethylene indeed prevented ABA-and dark-induced stomatal closure by reducing H₂O₂ and NO in guard cells.3.Like Vc,CAT,cPTIO and Hb,ACC and ethephon significantly promoted the closed stomata induced by ABA and dark to reopen,but DPI and L-NAME did not.These results suggested that ethylene could promote the closed stoma induced by ABA and the darkness to reopen by scavenging H₂O₂,and NO in guard cells.4.Like Vc and CAT,ACC and ethephon indeed decreased H₂O₂ levels of guard cells induced by ABA and dark,but DPI did not.Like cPTIO and Hb,ACC and ethephon indeed decreased NO levels of guard cells induced by ABA and dark,but L-NAME did not.These results showed that ethylene promoted the closed stoma induced by ABA and dark to open assuredly by scavenging H₂O₂ and NO in guard cells.5.Like Vc and CAT,ACC and ethephon significantly inhibited exogenous H₂O₂-induced stomatal closure,but DPI did not.Like cPTIO and Hb,ACC and ethephon significantly inhibited SNP-induced stomatal closure,but L-NAME did not.These results suggested that ethylene inhibited exogenous H₂O₂-and SNP-induced stomatal closure probably by scavenging H₂O₂ and NO in guard cell.6.Like Vc and CAT,ACC and ethephon indeed significantly reduced H₂P₂ fluorescence of guard cells induced by exogenous H₂O₂,but DPI did not.like cPTIO and Hb,ACC and ethephon indeed significantly reduced NO fluorescence of guard cells induced by exogenous NO donor SNP, but L-NAME did not.These results showed that ethylene inhibited exogenous H₂O₂-and SNP-induced stomatal closure indeed by scavenging H₂O₂ and NO in guard cells.In summary,the results of the present studies showed that ethylene inhibited stomatal closure and abolished H₂O₂ and NO fluorescence caused by exogenous H₂O₂ and SNP,and also reopened stomatal closed by ABA and dark,and removed H₂O₂ and NO fluorescence that had been generated by ABA and dark.Combined with the facts that ethylene prevented ABA-and dark-induced stomatal closure and decreased H₂O₂ and NO levels of guard cells caused by ABA and dark,we conclude that ethylene probably initiate H₂O₂- and NO- scavenging mechanisms to reduce the levels of H₂O₂ and NO in guard cells,and then prevent ABA- and dark-induced stomatal closure.