The influence of the transpiration rate on uptake and transport of potassium ions in barley plants.

The influence of the transpiration rate on uptake and transport of K(+) in intact barley plants was investigated. The results indicate that both components of K absorption by the root, that is, accumulation into the vacuoles and binding in the cytoplasm, proceed independently of the transpiration rate, nor is there any influence on the length of the lag phase in K translocation to the shoot. It is concluded that the ion concentration in the xylem vessels, which is directly determined by the transpiration rate, limits the rate of transfer of K ions from the cytoplasmatic constituents of the root tissue to the xylem vessels.