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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.

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Lignin from aspen {Populus tremuloides Michx.) tissue cultures containing only mature vessels and undifferentiated parenchymatous cells is exclusively of the guaiacyl type normally associated with gymnosperms. This supports the theory that the guaiacyl and syringyl lignin in angiosperm wood is compartmentalized, with guaiacyl lignin in vessels and syringyl lignin in fibers and ray cells.

The stimulation of lightwood formation (oleoresin soaking) in Pinusresinosa Ait. treated with the bipyridylium salt, paraquat (1,1′-dimethyl-4,4′-bipyridylium dichloride), affected various physiological parameters. Respiration, transpiration, and ethylene synthesis were markedly increased and were correlated with the increased production of rosin and turpentine. Photosynthesis, however, was severely inhibited, and phloem transport was not necessary for oleoresin deposition. These marked changes in function reflect a typical wounding response. Ethylene (supplied as Ethrel (2-chloroethylphosphonic acid)) was capable of replacing the stimulatory effect of paraquat, with a 14-fold increase in rosin over controls and a 25-fold increase in turpentine. This increase in turpentine content was accomplished by a significant enhancement in β-pinene content. Ethrel-treated trees also showed an increased abietic acid content, with a concomitant decrease in levopimaric acid.