Photometrically Assayable Phytochrome in vivo in Callus Tissue Cultured from Nicotiana tabacum

Phytochrome was photometrically detected in callus tissue cultured from tobacco stem pith. Our previous work with such tissues showed a growth response to red light, and a nullification of the effect of red by far-red light. Tissues that were subcultured for 4 or 20 months were assayed. Tissues of the younger clone had the most detectable phytochrome. Also, tissues cultured in darkness and those exposed to 5 minutes of red light each day bad more detectable phytochrome than tissues grown under 16-hour photoperiods of low intensity white light. We gratefully acknowledge Drs. H. A. Borthwick and J. E. Scheibe for use of facilities and assistance in operating the dual-wavelength photometer at the U.S.Department of Agriculture Pioneering Research Laboratory for Plant Physiology at Beltsville, Maryland.