Control of ion absorption by phytochrome.

Phosphate absorption by segments excised from hypocotyls of Phaseolus aureus Roxb. was inhibited by either continuous or short-term illumination with red light. Maximal inhibition was observed at pH 6.5. Illumination with 800 erg cm(-2) s(-1) of red light for 5 min was sufficient to obtain maximal inhibition. The effect of red light was completely counteracted by illumination.with 4500 erg cm(-2) s(-1) of far red light for 3 min, indicating that the effect was mediatedy by phytochrome. The efflux of phosphate from the segments was not altered by illumination. Similar effects of red and far-red light on potassium influx and efflux were also found.