Reactive Oxygen Species Production by Potato Tuber Mitochondria Is Modulated by Mitochondrially Bound Hexokinase Activity

Abstract

Potato tuber (Solanum tuberosum) mitochondria (PTM) have a mitochondrially bound hexokinase (HK) activity that exhibits a pronounced sensitivity to ADP inhibition. Here we investigated the role of mitochondrial HK activity in PTM reactive oxygen species generation. Mitochondrial HK has a 10-fold higher affinity for glucose (Glc) than for fructose (K MGlc = 140 mM versus K MFrc = 1,375 mM). Activation of PTM respiration by succinate led to an increase in hydrogen peroxide (H 2 O 2 ) release that was abrogated by mitochondrial HK activation. Mitochondrial HK activity caused a decrease in the mitochondrial membrane potential and an increase in oxygen consumption by PTM. Inhibition of Glc phosphorylation by mannoheptulose or GlcNAc induced a rapid increase in H 2 O 2 release. The blockage of H 2 O 2 release sustained by Glc was reverted by oligomycin and atractyloside, indicating that ADP recycles through the adenine nucleotide translocator and F 0 F 1 ATP synthase is operative during the mitochondrial HK reaction. Inhibition of mitochondrial HK activity by 60% to 70% caused an increase of 50% in the maximal rate of H 2 O 2 release. Inhibition in H 2 O 2 release by mitochondrial HK activity was comparable to, or even more potent, than that observed for StUCP (S. tuberosum uncoupling protein) activity. The inhibition of H 2 O 2 release in PTM was two orders of magnitude more selective for the ADP produced from the mitochondrial HK reaction than for that derived from soluble yeast (Saccharomyces cerevisiae) HK. Modulation of H 2 O 2 release and oxygen consumption by Glc and mitochondrial HK inhibitors in potato tuber slices shows that hexoses and mitochondrial HK may act as a potent preventive antioxidant mechanism in potato tubers.Production of reactive oxygen species (ROS) is an unavoidable consequence of aerobic respiration (Chance et al., 1979). The mitochondrial electron transport system (ETS) is the major site of ROS production in mammalian and nonphotosynthesizing plant cells (Puntarulo et al., 1991;Halliwell and Gutteridge, 2007). Depending on the mitochondrial respiratory states, a small portion of the consumable oxygen is partially reduced to generate ROS (

Plant respiration under low oxygen

“…Under some conditions, when the availability of O 2 in roots is decreased, adaptation to stress may occur through two strategies; the first is a decrease in ATP consumption which leads to a metabolic crisis at the cellular level , and the second is an increase in the glycolytic flux (Mancuso and Marras, 2006). The latter is called the "Pasteur effect" (Gibbs et al, 2000), consisting of a progressive acceleration in carbohydrate metabolism that allows the plants to maintain their energy level, especially during the early phase of acclimation to oxygen deficiency (Turner, 1951;Greenway and Gibbs, 2003;Camacho-Pereira et al, 2009;Wegner, 2010).…”

“…The gin1 mutant is allelic to aba, which has been found to act on an enzyme that catalyses the last step in ABA biosynthesis, indicating that HXK level mediates signaling by the ABA pathway (Rolland et al, 2002). In addition, protective functions against ROS have also been attributed to a mitochondrial HXK through the generation of ADP for OXPHOS, avoiding limitations in the synthesis of ATP during respiration and facilitating the release of hydrogen peroxide (Camacho-Pereira et al, 2009). While HXK is found in the mitochondria, there is also evidence to indicate the presence of HXK in the cell nucleus (Kim et al, 2006).…”

Neutral invertase, hexokinase and mitochondrial ROS homeostasis

“…If mitochondrial AsA contents become too low to counteract ROS accumulation, Glc outflow and mtHXK activity would be promoted, stimulating ADP recycling and avoiding ATP synthesis-related limitation of respiration and subsequent H 2 O 2 release. 18 Such a fine regulatory mechanism would be particularly useful when other sources of Glc or ADP become limited.…”

“…We propose that a continuous and efficient supply of Glc to mtHXK is necessary to maintain its activity at a rather constant level, in order to control the flux through the mitochondrial electron transport chain (ETC), influencing mitochondrial ROS production 18 ( Fig. 3).…”

Oxygen Metabolism in Chloroplast

“…Hexokinase, the first enzyme in glucose catabolism can reduce the intracellular ROS levels (Sun et al, 2008). It was shown that mitohondrial hexokinases play a key role as a regulator of ROS levels (Camacho-Pereira et al, 2009). In the work (Bolouri-Moghaddam et al, 2010) it was postulated that chloroplastic hexokinases also can carry out this function.…”