[Regulation of peroxidase patterns during shoot differentiation in callus cultures of Nicotiana tabacum L].

Peroxidase activity and isoenzyme pattern were studied during dedifferentiation of tobacco stem-sections leading to callus formation and during redifferentiation of tobacco callus leading to formation of shoots. These processes are both accompanied by an increase in total peroxidase activity and by characteristic changes in isoenzyme pattern. The isoenzyme pattern of tobacco callus differs from that of tobacco stem-tissue. The plantlets differentiated from the callus show the same pattern as seedlings do.During the differentiation process, before any buds are visible, the callus shows a peroxidase pattern that is determined by a reduction of fast-migrating anodic isoenzymes and by an increase of activity in all the other peroxidase isoenzymes. The formation of this pattern is independent of the growth regulators responsible for the differentiation: only the kind of differentiation itself determines the pattern.By artificial inhibition of callus growth it is possible to induce an isoenzyme pattern very similar to that of differentiation; the fast-migrating anodic enzymes are reduced in activity but the others are not increased as they are during differentiation. Therefore the question arises whether there are two independent processes taking place in differentiating callus. The one process, inhibition of growth in the cells that do not differentiate, is accompanied by a reduction of fast-migrating anodic isoenzymes. The other process, formation of meristemoids in the callus, is accompanied by a sharp rise in peroxidase activity of the other anodic and cathodic isoenzymes.