The Mode of Action of Kinetin in Maintaining the Protein Content of Detached Tropaeolum Majus Leaves

S ummary Kinetin maintains the protein content of detached leaves, but the reason is not clear. This work attempted to find out whether the effect arises from maintenance of protein synthesis or retardation of protein breakdown. Protein synthesis and degradation in detached Tropaeolum majus leaves were estimated by measuring the incorporation into amino acids and protein of photo‐synthetically fixed 14 C, and by determining the total amounts of amino acids and protein present in ageing leaves. Protein synthesis in kinetin‐treated leaves kept in darkness was higher than in the control. Rough calculation showed, however, that enhancement of protein synthesis by kinetin cannot directly account for the higher protein level found after this treatment. It seems to result from decreased degradation rather than from the maintenance of protein synthesis.