Exogenous abscisic acid inhibits leaf elevation during shade avoidance response in Arabidopsis thaliana

Plant shade avoidance response includes elongated hypocotyls and petioles as well as increased leaf elevation angles. Our time-course image analyses indicate that the phytohormone abscisic acid (ABA) affects leaf elevation angles in Arabidopsis. While mutants with impaired ABA production ( <i>aba1-6</i> ) or with insensitivity to ABA ( <i>abi5-10</i> ) did not fully increase the angles under shade avoidance conditions, a higher concentration of exogenous ABA inhibited leaf elevation under the same conditions. These suggest that certain levels of ABA production and sensing are required for leaf elevation during shade avoidance response, whereas higher concentrations of ABA can inhibit the process.