CYTOCHROME AND ALTERNATIVE PATHWAY RESPIRATION IN TOBACCO - EFFECTS SALICYLIC-ACID

In suspension cultures of NT1 tobacco (Nicotiana tabacum L. cv Bright Yellow) cells the cytochrome pathway capacity increased between d 3 an d d 4 following subculturing and reached the highest level observed on d 7. The capacity decreased significantly by d 10 and was at the same level on d 14. Both alternative pathway capacity and the amount of th e 35-kD alternative oxidase protein increased significantly between d 5 and d 6, reached the highest point observed on d 7, remained constan t until d 10, and decreased by d 14. The highest capacities of the alt ernative and cytochrome pathways and the highest amount of the 35-kD p rotein were attained on the day that cell cultures reached a stationar y phase of growth. Addition of salicylic acid to cell cultures on d 4 caused a significant increase in alternative pathway capacity and a dr amatic accumulation of the 35-kD protein by 12 h. The alternative path way capacity and the protein level reached the highest level observed by 16 h after salicylic acid addition, and the cytochrome pathway capa city was at about the same level at each time point. The accumulation of the 35-kD alternative oxidase protein was significantly decreased b y addition of actinomycin D 1 h before salicylic acid and was blocked by addition of cycloheximide. These results indicate that de novo tran scription and translation were necessary for salicylic acid to cause t he maximum accumulation of the 35-kD protein.