The uncoupling protein and the potassium channel are activated by hyperosmotic stress in mitochondria from durum wheat seedlings

The plant uncoupling mitochondrial protein (PUMP) and the plant mitochondrial potassium channel (PmitoK(ATP)) are two recently discovered energy-dissipating systems present in plant mitochondria, which may play a role as defence systems under environmental stress. To verify whether hyperosmotic stress affects the two dissipating systems in durum wheat (Triticum durum Desf.), their functioning was studied in early etiolated seedlings maintained under moderate and severe salt (NaCl) and osmotic (mannitol) stress. As measures of mitochondrial stress mitochondrial integrity, membrane potential maintenance and oxygen uptake coupled with ATP synthesis during succinate and proline oxidation were investigated. Both PUMP and PmitoK(ATP) were activated under stress conditions. Activation was clearly evident even under moderate stress when proline oxidation was inhibited, although mitochondrial integrity and succinate oxidation were still unaffected. Under severe stress, which significantly affected all the tested indicators of mitochondrial integrity and functionality, PUMP and PmitoK(ATP) activation was further enhanced. Interestingly, both systems were activated by reactive oxygen species and were able to control mitochondrial superoxide anion production. These results suggest that PUMP and PmitoK(ATP) serve as early antioxidant defence systems in response to hyperosmotic stress and that they are involved in a prolonged response to stress.