The Role Of CO-mediated H₂O₂ In ABA-induced Stomatal Closure And The Effect Of FC On Stomatal Closure Caused By ABA

Previous studies showed that CO, H₂O₂ and NO are involve in ABA-induced stomatal closure, and stomatal opening is induced by fusicoccin (FC). However, the role of CO-mediated H₂O₂ in ABA-induced stomatal closure remains unclear. Also, the effect and action mechanism of FC on ABA-induced stomatal closure are unkown. In the present study, by means of the epidermal strip bioassay and the laser scanning confocal microscopy(LSCM), it was investigated that the relationship of CO and H₂O₂ in ABA-induced stomatal closure and the effects and action mechanism of FC on stomatal closure induced by ABA. The main results are as followed:1. Stomatal closure were induced by ABA, CO synthesis substrate Hematin (Ht), CO aqueous solution and H₂O₂, ABA-induced stomatal closure was restrained by ZnPPIX (CO specific synthetic inhibitor), CAT(catalase), Vc(H₂O₂ scavenger) and DPI(an inhibitor of H₂O₂ generating enzyme NADPH oxidase), Ht-induced stomatal closure was also prevented by CAT, Vc and DPI. The results suggest that CO Synthesis may mediate ABA-induced H₂O₂ production and stomatal closure. The examination results of endogenous H₂O₂ showed that ABA and Ht induce increase of H₂O₂. However, ABA-induced the production of endogenous H₂O₂ was significantly prevented by ZnPPIX. These results were in accordance with the epidermal strip bioassay.2. Like CAT. Vc and DPI, FC inhibited ABA-induced stomatal closure and reduced the level of endogenous H₂O₂ in guard cells, which indicated that FC inhibited ABA-induced stomatal closure by reducing endogenous H₂O₂ level. Like CAT and Vc, FC not only prevented stomatal closure induced by exogenous H₂O₂, reduced H₂O₂ fluorescence of guard cells treated by exogenous H₂O₂, but also promoted the closed stoma induced by ABA to reopen, abolished H₂O₂ that had been generated by ABA. However, DPI had no the effects mentioned above. Taken together, our results indicate that FC probably reduce the levels of H₂O₂ in guard cells by scavenging, not restraining H₂O₂ generation, and then prevent ABA-induced stomatal closure.3. Like c-PTIO(NO scavenger) and L-NAME(NO synthase inhibitor), FC prevented ABA-induced stomatal closure and reduce the level of endogenous NO in guard cells, which indicated that FC prevented ABA-induced stomatal closure by reducing the level of endogenous NO. Like c-PTIO, FC not only prevented SNP-induced stomatal closure, reduced NO fluorescence of guard cells treated by SNP, but also promote the closed stoma induced by ABA to reopen, abolished NO that had been generated by ABA. However, L-NAME had no the effects mentioned above. Hence, it is concluded that FC reduce probably the levels of NO in guard cells via scavenging, not preventing NO generation, and then prevent ABA-induced stomatal closure.