Polyamines inhibit abscisic acid-induced stomatal closure by scavenging hydrogen peroxide

Stomatal closure is regulated by plant hormones and some small molecules to reduce water loss under stress conditions. Both abscisic acid (ABA) and polyamines alone induce stomatal closure; however, whether the physiological functions of ABA and polyamines are synergistic or antagonistic with respect to inducing stomatal closure is still unknown. Here, stomatal movement in response to ABA and/or polyamines was tested in Vicia faba and Arabidopsis thaliana, and the change in the signaling components under stomatal closure was analyzed. We found that both polyamines and ABA could induce stomatal closure through similar signaling components, including the synthesis of hydrogen peroxide (H₂ O₂ ) and nitric oxide (NO) and the accumulation of Ca²⁺ . However, polyamines partially inhibited ABA-induced stomatal closure both in epidermal peels and in planta by activating antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), to eliminate the ABA-induced increase in H₂ O₂ . These results strongly indicate that polyamines inhibit abscisic acid-induced stomatal closure, suggesting that polyamines could be used as potential plant growth regulators to increase photosynthesis under mild drought stress.