2,4-Dichlorophenoxyacetic acid inhibition of potassium transport in barley seedlings

Growth, potassium uptake and translocation as well as transpiration rates were measured in intact low-salt barley seedlings ( Hordeum vulgare L. cv. Union) in the presence of different 2,4-D concentrations at pH 6.5. Growth was only affected at 10^-3 M .
Above 10^-7 M 2,4-D both uptake by the roots and transport to the shoots were inhibited. The inhibition at 10^-5 M remained constant for at least 24 h. Furthermore inhibition of uptake was measurable within 1 h. Excised roots and roots of intact plants showed the same uptake pattern.
It is suggested that the observed effects were caused by 2,4-D-induced changes in uptake and translocation systems in the roots. Pre-treatment with 10^-5 M 2,4-D had no effect upon subsequent potassium uptake. Transpiration was reduced within 1 h in 10^-4 or 10^-3 M 2,4-D, probably due to changes in water transport or root permeability.