Rapid phytochrome-mediated changes in the uptake by bean roots of sodium acetate [1-(14)C] and their modification by cholinergic drugs.

4 min of red light increases the uptake of sodium acetate[1-(14)C] by excised, etiolated secondary roots of Phaseolus aureus Roxb. 4 min of far-red light reveres this effect. AMO-1618, which inhibits acetylcholinesterase activity, enhances the red-light effect, while d-tubocurarine, which blocks the animal acetylcholine receptor, inhibits it. Red light also increases basipetal translocation of the label. When the metabolic fate of the label was determined in dark-held roots, 36% of the label remained as acetate, 48% evolved as [(14)C]CO2, 3% partitioned with acetylcholine, and 3% effluxed from the roots. The rest of the label was associated with the coarse residue left after extraction. The major effect of red light was to increase the uptake of the label in the acetate fraction.We interpret these observations to mean that the phytochrome mechanism immediately causes an increase in uptake of the label during brief irradiation with red light. Because of our previous demonstration that both red light and acetylcholine increase respiration, it is probable that the increased absorption of the label is a process requiring respiratory energy. These data support the concept of phytochrome as a membrane-bound functional system that in bean roots is mediated by the acetylcholine mechanism.