Possible participation of active oxygen species in the induction of cyanide-resistant pathway at the initial senescence of tobacco callus

Changes in active oxygen species (AOS) and respiration, with special reference to the alternative pathway of respiration, were followed in callus of tobacco (Nicotiana rustica L.) during its growth and senescence. Two peaks of the total respiration rate were observed: the first one appeared on day 11, and the second one on day 19 (in senescing callus). H2O2 and O-2(-) contents increased gradually and reached the greatest values when callus senescence initiated (by day 11 and day 15, respectively), and then declined. The peaks of H2O2 and O-2(-) before the onset of senescence coincided with the peaks of capacity V-alt and activity rhoV(alt) of alternative pathway, respectively. After the onset of senescence, . OH accumulated abundantly and maintained at a relatively high level from then on, accompanied by the decrease in both V-alt and rhoV(alt). The conclusion is that these three active oxygen species operated coordinately to regulate the alternative pathway during growth and senescence of tobacco callus, as confirmed by the callus treatments with AOS scavengers, exogenous . OH, and inhibitors of antioxidant enzymes. The possibility of AOS-induced alternative pathway respiration at the initial senescence of tobacco callus is discussed.