The effect of magnesium nutrition on the antioxidant response of coffee seedlings under heat stress

High temperatures are already a current reality. If necessary attention is not given to plant nutrition, including magnesium nutrition, large losses in productivity can occur when plants are subjected to combinations of these heat and nutrient stresses. Thus, the goal of our work was to investigate the importance of adequate magnesium nutrition for an effective antioxidant response in coffee seedlings subjected to heat stress. As such, six-month-old Coffea arabica L. seedlings were transferred to plastic containers containing nutrient solutions with different concentrations of magnesium (Mg) and were cultivated at two different temperatures (25 or 35 degrees C). Fully expanded leaves and roots were evaluated at the beginning of the treatment and after 10, 20 and 30 days for the concentrations of magnesium, hydrogen peroxide, proline, ascorbate, malondialdehyde, protein and amino acids as well as the activities of the enzymes superoxide dismutase, catalase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase. The variables analyzed were mainly altered by the combination of stresses. Mg deficiency and heat stress caused an increase in hydrogen peroxide concentration that was accompanied by an increase in antioxidant metabolism and by greater production of praline and ascorbate. Nevertheless, antioxidant metabolism and osmoprotectants were insufficient at removing excess ROS, resulting in increased lipid peroxidation and protein degradation. When subjected to heat stress, coffee seedlings under adequate Mg nutrition showed lower production of hydrogen peroxide and, consequently, poor lipid peroxidation and protein denaturation compared with seedlings deficient in Mg. Therefore, adequate Mg nutrition is essential for minimizing oxidative damage caused by heat stress in coffee seedlings.