Effects of chlorine dioxide on mitochondrial energy levels and redox status of ‘Daw’ longan pericarp during storage

Abstract

Mitochondrial redox status and adenosine triphosphate (ATP) production play a central role in responding to physiological and environmental changes and metabolic control. Changes in mitochondrial redox potential are intimately associated with oxidative stress which could lead to plant senescence. This study aimed to demonstrate the involvement of an alteration of the redox status in energy production and fruit senescence of longan (Dimocarpus longan Lour. cv. Daw) during storage and to investigate the effects of gaseous chlorine dioxide (ClO2) both on the redox and the energy status and on delaying senescence. Fresh longan fruit were fumigated with 5, 10 and 25mg/L ClO2 for 10min and then stored in a cardboard box at 25°C with 82% relative humidity for 7 days. ATP content and energy charge (EC), and activities of respiratory enzymes such as succinate dehydrogenase (SDH) and cytochrome c oxidase (CCO) were found to be steadily decreased in the untreated group during storage. These reductions coincided with a decrease in the redox status as determined by pyridine nucleotide (NAD/NADH) and ubiquinone (Q/QH2) ratios and with fruit senescence including browning and the onset of disease symptoms. However, in the ClO2 fumigated fruit, ATP content, EC, SDH and CCO activities as well as NAD/NADH ratio were immediately and markedly increased after treatment. The effects can be seen through the fourth day of storage. The Q/QH2 ratio remained unchanged before rising after Day 4. Higher concentrations of ClO2 (10 and 25mg/L) were more effective than the lower one (5mg/L) in altering the redox balance and increasing energy production. The altered redox state and increased energy by ClO2 were found to be closely associated with a delay in fruit senescence during storage. These findings support the notion that energy production and redox balance involve directly in longan senescence and demonstrated that ClO2 could restore ATP and the redox balance, leading to reduction and delay in fruit senescence.