Activity of alternative oxidase and plant uncoupling mitochondrial protein in potato tubers stored at low temperature or submitted to artificial aging

Potato tubers (Solanum tuberosum L. cv. Binje) were stored at 18 and 4oC in order to verify changes in mitochondrial metabolism, especially in the activities of the alternative oxidase (AOX) and plant uncoupling mitochondria protein (PUMP). Tubers were also sliced and submitted to artificial aging. The oxygen consumption rate (OCR), respiratory control (RC) and ADP/O ratio for mitochondria obtained after storage at 18oC were not altered, regardless of the time of storage. Considerable increment in OCR, for both respiratory states 3 and 4, was observed after storing the tubers for five and ten days at 4oC; and it was accomplished by reductions in RC and ADP/O. The AOX activity was evident after five days at 4oC, and it was enhanced after ten days of storage at that temperature. No significant changes in PUMP activities were observed after one day at 18oC or at 4oC, neither after artificial aging. However, increased swelling of potato mitochondria was observed in the presence of valinomycin and linoleic acid when the tubers were kept at 4oC for five and ten days. Besides the changes in AOX and PUMP activities, slight alterations in ascorbate peroxidase (APX) and catalase (CAT) activities were observed after storing the tubers at 4°C for 5 days. The activities of these enzymes were higher after storage at 4°C for 10 days. The results suggest the combined effect of low temperature and time of exposure in promoting AOX activity, probably as a protective mechanism against cell damage in response to mitochondrial oxidative stress.