Active and passive ion transport in relation to transpiration in Helianthus annuus.

The effect of transpiration on the uptake of K, Ca, NO3 and SO4 from two strengths of culture solution by Helianthus plants was investigated. In the dilute solution transpiration had no effect on the uptake of all the ions studied. In the more concentrated solution the uptake of K, NO3 and SO4 were found to be sensitive to changes in water flux across the root. Calcium uptake was found to be completely independent of water uptake in all the experiments.The results are interpreted in the light of the results from an earlier study on excised Helianthus roots. It is suggested that transpiration only affects the nonmetabolic transport of the ions across the root.