Regulation of respiration in rotenone-treated tobacco cell suspension cultures

Cells of Nicotiana tabacum L. suspension cultures were treated with the res piratory inhibitor rotenone, which specifically inhibits complex I activity of mitochondria. Rotenone retarded cell growth, as shown by decreases in f resh weight, dry weight and cell numbers on a suspension-volume basis. Howe ver, rates of the coupled respiration were higher in rotenone-treated compa red to control cells when expressed on a fresh-weight basis. Rates of the r otenone-insensitive respiration increased substantially on both a fresh-wei ght and extractable-cellular-protein basis 24 h after rotenone treatment. A TP/ADP ratios were not significantly different between control and rotenone -treated cells. Our results indicated that cells of tobacco suspension cult ures were able to maintain a slow rate of growth and adequate ATP/ADP ratio s without the operation of complex I.