The Relationship Of G Protein And H₂O₂ In Guard Cell Signal Transduction

G Protein and H2O2 were found to be involved in the guard cell signal transduction, and they could induce stomatal closure. But the molecular mechanisms about how they induced stomatal closure and what were the relationship between them has not been resolved. Here, by using Arabidopsis heterotrimeric G protein alpha subunit - null mutants gpa1-1 and gpa1-2, overexpression lines wGa and cGa, and atrbohD/F double mutant, which corresponding to the mutation of two guard cell special-expressed NADPH oxidase gene AtrbohD and AtrbohF, together with epidermal strip bioassay, CLSM, and RT-PCR techniques, we gained data to show the relationship between G Protein and H2O2. Our results were as follows:Firstly, ABA or ExtCaM failed to induce gpa1-1 and gpa1-2 stomatal closing, but stomatal closure was fastened in wGa and cGa, which indicated that Gα was involved in ABA or ExtCaM guard cell signal transduction at molecular level. atrbohD/F double mutants impaired ExtCaM induced stomatal closing, which suggested the genetic roles of H2O2 in ExtCaM signal transduction.Furthermore, gpa1-1 and gpa1-2 impaired in ABA or ExtCaM induction of H2O2 generation in guard cells, in contrast, H2O2 induced by ABA or ExtCaM was accelerated in wGa and cGa, which suggested Gα was involved in ABA or ExtCaM inducing H2O2 generation in guard cells at molecular level, and H2O2 was located in the downstream of Gα during the process.The expressions of Arabidopsis Gα gene-GPA1 in WT and atrbohD/F double mutants were almost at the same level, which suggested GPA1 was not affected by AtrbohD, AtrbohF genes and AtrbohD, AtrbohF were perhaps located in the downstream of GPAl. While expression level of AtrbohD, AtrbohF were higher in WT than that in gpal-2, indicating expression of AtrbohD,AtrbohF might be regulated by GPA1, induction of H2O2 through NADPH oxidase was inhibited. These results shows AtrbohD, AtrbohF were located in the downstream of GPA1.So far, we presumed the process that H2O2 induction by ABA and ExtCaM in guard cells might be: ABA and ExtCaM binded to their receptors, then activated a G-protein a subunit, the Gα subunit regulated AtrbohD, AtrbohF transcription and activited of NADPH oxidasse , so H2O2 is induced by NADPH oxidase, and the H2O2 induces stomatal closing. However, what are the components involved in stomatal closing by H2O2?For the first time, our results showed that gpa1-1 and gpa1-2 greatly impaired stomatal closure by H2O2, which suggested Gα is necessary in stomatal closing by H2O2. Combined with some results above, we could conclude that the action of H2O2 in guard cell signal transduction depended on the activation of Gα.