Influence of rootstock on antioxidant system in leaves and roots of young apple trees in response to drought stress

Grafting rootstocks are widely used to enhance plants resistance to various biologic and abiotic stresses. We determined how the rootstock genotype might influence plant responses to drought, using 2-year-old 'Gale Gala' apple trees grafted onto Malus sieversii and M. hupehensis. Under water stress, trees with the former as their rootstock had smaller reductions in rates of relative growth and photosynthesis, total biomass, leaf area, levels of leaf chlorophyll, and relative water content compared with those grafted onto the latter. They also had greater maximum photochemical efficiency and water-use efficiency. On the other hand, trees growing on M. sieversii rootstock had less production of superoxide radicals and hydrogen peroxide in both leaves and roots than those growing on M. hupehensis in response to drought stress. Furthermore, under drought conditions, leaves and roots from trees grafted onto M. sieversii had greater synthesis of ascorbic acid and glutathione, as well as higher activities of superoxide dismutase, catalase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase. These results suggest that the choice of grafting rootstock can enhance drought resistance by improving the antioxidant system in a plant. Here, 'Gale Gala' trees grafted onto M. sieversii were more drought-resistant than those on M. hupehensis rootstock.