Rendering grapevines more tolerant to drought can be achieved by developing effective measures in viticulture management. Here, the impact of naphthalene acetic acid (NAA) was evaluated on physiological and biochemical features, as well as growth, photosynthesis, and phytohormone levels in two grapevine cultivars under drought stress conditions. The results show that the grapevine cultivars experienced a significant inhibition of growth, impairment of cellular membranes, and suppression of photosynthesis under drought stress. Also, drought stress increased both grapevine cultivars’ osmolyte compounds and abscisic acid (ABA) concentration. By applying 50 mg L− 1 NAA, grapevines showed enhanced levels of growth when cultivated both in well-watered (90% FC) and drought-stress conditions (50% FC). NAA (50 mg L− 1) caused plants to increase osmolyte concentrations, including proline and total soluble carbohydrates, while maintaining more of their photosynthetic pigments and photosynthetic activity. Additionally, the same treatment improved the relative water content and water use efficiency, as well as IAA and ABA concentrations. Exogenous applications of 50 mg L− 1 NAA caused improvements in drought tolerance by promoting higher levels of antioxidant enzyme activity (e.g. catalase, peroxidase, ascorbate peroxidase, and superoxide dismutase) while reducing hydrogen peroxide content, electrolyte leakage, and malondialdehyde. In conclusion, NAA proved to be effective in mitigating the adverse effects of drought stress in grapevines.
