Effects Of Chloroquinoline (Quinmerac) On Stomatal Movement In Arabidopsis Thaliana And Its Mechanism

Quinmerac is one of auxin herbicides. Since 1988, it has been widely used to control dicot weeds. Because quinmerac is relatively well soluble in water and hardly degradable, it has been found in groundwater, surface water and drinking water, and endanger plant life. Thus, the effect and action mechanism of quinmerac on plant growth and development, including stomatal movement, need to be studied. In the present work, role and relationship of ethylene, abscisic acid ?ABA?, hydrogen dioxide ?H₂O₂? and nitric oxide ?NO? during quinmerac-induced stomatal closure in Arabidopsis were studied by means of pharmacological approach and laser scanning confocal microscopy. The main results are as follows:1. Quinmerac closed stomta in dose-dependent manner, and its maximum biological response concentration is 400?M.2. Quinmerac induced ethylene production and stomatal closure in wild-type ?WT, Col-0?. However, the effects of quinmerac in WT ?Col-0? were fully abolished in the acs5-1, acs6-1 and acs5-1/acs6-1 mutants. These data clearly show that ethylene is involved in quinmerac-induced stomatal closure.3. Quinmerac induced the expression of ABA-specific promoter and stomatal closure in WT ?Col-0?, the effects were largely prevented in aba2-1, aba2-4 and pyr1pyllpyl2pyl4 mutants, indicating that ABA mediates quinmerac-induced stomatal closure.4. Quinmerac induced H₂O₂ production and stomatal closure in WT ?Col-0?, but did not in AtrbohF and AtrbohD/F mutants, indicating that AtrbohF-dependent H₂O₂ production is requered by quinmerac-induced stomatal closure.5. Quinmerac induced NO sythesis and stomatal closure in WT ?Col-0, Ler?, but did not in Nia1-2 and Nia2-5/Nia1-2 mutants, indicating that Nial dependent NO sythesis is essential for quinmerac-induced stomatal closure.6. ACC induced H₂O₂ production and stomatal closure in WT ?Col-0? and AtrbohD mutant, but did not in AtrbohF and AtrbohD/F mutants. The data indicate that ethylene closes stomata via inducing AtrbohF-dependent H₂O₂ production.7. ACC induced NO production and stomatal closure in WT ?Col-0, Ler? and Nia2-1 mutant, but did not in Nia1-2 and Nia2-5/Nia1-2 mutants. The data indicate that ethylene closes stomata via inducing Nial-dependent NO synthesis.8. ABA induced H₂O₂ production and stomatal closure in WT ?Col-0? and AtrbohD mutant, but did not in AtrbohF and AtrbohD/F mutants. The data indicate that ABA closes stomata via inducing AtrbohF-dependent H₂O₂ production.9. ABA induced NO production and stomatal closure in WT ?Col-0, Ler? and Nia2-1 mutant, but did not in Nial-2 and Nia2-5/Nia1-2 mutants. The data indicate that ABA induces stomatal closure via inducing Nial-dependent NO synthesis.10. ACC closed the stomata in WT ?Col-0?, but did not in aba2-1, aba2-4 and pyrlpyllpyl2pyl4 mutants, indicating that ABA syntesis is required by ethylene-induced stomatal closure. ACC promotion of ABA-specific promoter expression supports the conclusion above.11. Quinmerac did not induce NO synthesis in AtrbohF and AtrbohD/F mutants, but induced H₂O₂ production in Nial-2 and Nia2-5/Nial-2 mutants. The results indicate that H₂O₂ mediates quinmerac-induced stomatal closure through inducing NO synthesis.Together, our results strongly suggest a signaling pathway in which quinmerac activates ethylene production, thereby inducing ABA synthesis, and then promotes AtrbohF-dependent H₂O₂ production and subsequent Nial-catalyzed NO accumulation, and finally closes stomata.