Atmospheric CO ₂ Alters Resistance of Arabidopsis to Pseudomonas syringae by Affecting Abscisic Acid Accumulation and Stomatal Responsiveness to Coronatine

摘要

Atmospheric CO_(2)influences plant growth and stomatal aperture. Effects of high or low CO_(2)levels on plant disease resistance are less well understood. Here, resistance of Arabidopsis thaliana against the foliar pathogen Pseudomonas syringae pv. tomato DC3000 ( Pst ) was investigated at three different CO_(2)levels: high (800 ppm), ambient (450 ppm), and low (150 ppm). Under all conditions tested, infection by Pst resulted in stomatal closure within 1 h after inoculation. However, subsequent stomatal reopening at 4 h, triggered by the virulence factor coronatine (COR), occurred only at ambient and high CO_(2), but not at low CO_(2). Moreover, infection by Pst was reduced at low CO_(2)to the same extent as infection by mutant Pst cor~(-) . Under all CO_(2)conditions, the ABA mutants aba2-1 and abi1-1 were as resistant to Pst as wild-type plants under low CO_(2), which contained less ABA. Moreover, stomatal reopening mediated by COR was dependent on ABA. Our results suggest that reduced ABA levels at low CO_(2)contribute to the observed enhanced resistance to Pst by deregulation of virulence responses. This implies that enhanced ABA levels at increasing CO_(2)levels may have a role in weakening plant defense.