Laudiene E. Meyer¹ ; Lilia B. Machado¹ ; Juliana Camacho Pereira;  Marcus F. Oliveira ¹; Antonio Galina ^1¶

The evolution of aerobic metabolism inevitably led to the production of reactive oxygen species (ROS) in mitochondria. It is estimated that 1-2% of total O2 consumed in plant tissues is diverted to ROS production. Several hexokinases with tissue specificity which is involved in the expression several genes by sugars have been described. There are convincing evidences that these hexokinases are located in plant mitochondria. Therefore, in the present work the relationship between mitochondrial membrane potential (ΔY_m)and ROS production with the mt-HK activity was evaluated in potato tuber mitochondria. The isolated mitochondria from potato tubers present significant levels of mt-HK activity. The rate of oxygen consumption was stimulated by glucose after the state 4 of respiration was reached. Under these conditions a small depolarization in ΔY_m (less than 3 %) was detected. Curiously, under glucose phosphorylating conditions, ROS formation was completely abolished. These effects on ROS production are comparable to those observed when the plant uncoupling protein (PUMP) is activated by linolenic acid. The presence of two different hexokinase inhibitors such as mannoheptulose or N-acetylglucosamine, leads to stimulation of ROS production. Taken together, these results suggest that mt-HK activity may be directly involved in the local ADP recycling mechanism, providing a novel physiological antioxidant role in potato tubers.