Water limitation mitigates high-temperature stress injuries in grapevine cultivars through changes in photosystem II efficiency and antioxidant enzyme pathways

Plants, via physiological and molecular processes, respond to unsuitable environmental conditions, resulting in stress tolerance. Most previous studies have focused on plant responses to a single abiotic stress, but the effects of combined water deficit and high temperature stresses are more severe and complex than those due to a single stress. Therefore, our study aimed to explore the differences in the damage caused by combined vs. single stresses. Grapevines were subjected to water deficit, high temperature, and water deficit plus high temperature treatments. The transcript levels of heat- and drought-stress genes, activities of photosystem II (PS II) and antioxidant enzymes (superoxide dismutase, catalase, and peroxidase), and changes in abscisic acid (ABA) biosynthesis were evaluated. The activities of PS II and antioxidant enzymes were lower under the water deficit plus high temperature treatment than under the heat treatment alone. The concentration of ABA and the transcript levels of ABA biosynthesis-related genes increased under both types of stress. The enhanced thermo-tolerance observed under drought stress could be attributed to increased PS II efficiency, as well as to changes in antioxidant pathways, mediated by a common regulatory system or including a substantial cross talk between heat- and drought-stress signaling.