Changes in the capacity and operation activity of the alternative pathway under 1 O 2 and . OH treatments in tobacco callus

The effects of 1O2 and ·OH on alternative pathway respiration in tobacco (Nicotiana rustica L. cv. Gansu Yellow Flower) callus were examined. The addition of <15 mM exogenous 1O2 induced a pronounced increase in ρValt without affecting Valt. For example, upon treatment with 10 mM 1O2, ρValt increased by 1.5 times compared to control, while Valt changed little. When 1O2 was increased to 25 mM, this induction effect disappeared and both ρValt and Valt were suppressed by 59.5% and 40.2%, respectively. Both ρValt and Valt were diminished by the addition of exogenous ·OH, and this inhibition effect increased with ·OH concentration. At a concentration of 25 mM, for example, ρValt and Valt were reduced by 88.9% and 78.2%, respectively. ·OH scavengers, DMSO or MAN, could repress the ·OH-dependent inhibitory effect. The possible regulation mechanism of alternative pathway by 1O2 and ·OH are discussed.