Water Uptake during Rapid Changes of Transpiration Induced by the Presence of High Concentration of Growth Substances in Root Medium

Immediate response of water uptake by intact plants ofPisum sativum L. to the introduction of high concentrations of α-naphtaleneacetic acid (NAA), β-indoleacetic acid (IAA), 2,4-dichlorophenoxyacetic acid (2,4-D), 2-methyl-4-chlorophenoxyacetic acid (MCPA), coumarin was determined by a series of potometric measurements. Growth substances were present in the root medium in two concentrations: 10-3 m and 10-2 m; the concentration of coumarin was 5. 10-4 m and that of EDTA was 10-3 m. The response of water uptake to the application of the growth substances and coumarin was always negative. EDTA did not affect immediately the intensity of water uptake. The inhibition of water uptake brought about by the growth substances takes place immediately. Coumarin causes slow, progressively increasing inhibition of water uptake. A coincidence was found as to the time course of the changes in the water uptake intensity in the presence of high concentrations of growth substances and coumarin in the root medium with the time course of changes of transpiration intensity, found under analogous conditions by Allerup (1964). This may be considered as another justification for the hypothesis, according to which the rapid changes of transpiration intensity in the presence of high concentrations of growth substances in the root medium are caused by rapid changes of the intensity of water uptake.