Shoot activity has been reported to affect rates of ion uptake by plant roots in other ways than merely through supply of assimilates. To elucidate the mechanisms by which a signal from the upper part of the plant controls the rate of K+ and NO3− uptake by roots, both uptake of K+ and NO3− and secretion into the xylem of young sunflower plants (Helianthus annuus L.) were measured after changes in light intensity. No close correlation was observed between the uptake of NO3− and that of K+; an increase in light intensity produced a much greater stimulation of NO3− uptake than of K+ uptake. On the other hand, secretion of NO3− into the xylem was tightly coupled to that of K+, and this coupling was strongly disturbed by excision of the root. The results suggest the involvement of the K2‐malate shuttle on the regulation by the shoot of K+ and NO3− secretion in the xylem, which is linked to NO3− uptake, while K+ uptake is independent of this regulation mechanism.
|Number of pages||7|
|Publication status||Published - 1 Jan 1995|