Peroxidases as Indicators of Growth and Differentiation in Aspen Callus Cultures

Aspen (Populus tremuloides Michx.) callus tissue grown on a synthetic medium containing either an auxin (2,4‐dichloro‐phenoxyacetic acid) or cytokinin [6‐(3‐methyl‐2‐butenylamino) purine] differed in growth rate, total peroxidase activity, peroxidase isoenzyme expression, and in lignin, cell wall sugars and extractive content. Tissue treated with auxin increased more rapidly in fresh weight, but stopped growing sooner than did the cytokinin‐treated tissues. Lignification also proceeded more rapidly, and lignin formed a greater fraction of the cell wall weight in auxin‐treated tissue. For both treatments, peroxidase activity and growth rate were positively related (r = 0.96). Polyacrylamide gel electrophoresis showed some quantitative, but few qualitative, isoenzyme differences with hormonal treatment and growth rate.