The development of extractable peroxidase activity in the mustard seedling is controlled by phytochrome (Pfr; operationally: Continuous far-red light) in an organ specific manner (enhancement in the cotyledons and taproot, inhibition in the hypocotyl; Tables I, II). Detailed kinetics of peroxidase accumulation in the cotyledons (Figs. 2, 3) reveal the existance of a two-step induction mechanism: 1. Formation of a stable transmitter during a period of competence to Pfr (“determination phase“), and 2. development of peroxidase activity mediated by the transmitter during a later period of competence to the transmitter (“realization phase“). These two periods of seedling development are completely separated in time.
Organ-specific phytohormone synthesis in two Geranium
species with antithetical responses to far-red light enrichment
