Physiological and Molecular Responses of Red Maple (Acer rubrum L.) Cultivars to Drought Stress

Acer rubrum (red maple) is one of the most important ornamental trees in North America. It is used in urban forestry and landscaping, as well as timber and syrup production. Drought is a major challenge that hinders the development and growth of maples and other tree species. The objective of the present study was to evaluate three red maple cultivars namely, October glory, Autumn red, and Red sunset for their physiological and molecular response to drought stress. Saplings of three cultivars of red maple were subjected to drought stress (up to 28 days unirrigated) in the summer of 2018 and 2019, and leaf samples were used to quantify physiological, biochemical, and expression changes under stress. Decrement of chlorophyll content significantly correlated with the soil moisture content observed in all three genotypes subjected to drought stress. Significant variation in proline concentration, Malondialdehyde levels, and increase in superoxide dismutase (SOD) activity at various stages of the experiments showed the ability of the maple plants to respond to drought stress. RT-qPCR analyses revealed higher and variable expression of drought-responsive genes GGAT1 encoding glutamate-glyoxylate aminotransferase, and CSD2 encoding SOD, in the red maple plants under drought stress. The results from this study indicate that the red maple plants alleviate drought stress by the possible mechanism involving decreased lipid peroxidation, and enhanced production of osmolyte and antioxidants.