Uptake of Dinitrophenol & its Effect on Transpiration & Calcium Accumulation in Barley Seedlings

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Abstract
There was considerable accumulation of C14 labeled 2,4-dinitrophenol (DNP) in the shoot and much more accumulated at pH 4 than at pH 6. In agreement with this, DNP was more effective in reducing transpiration and Ca accumulation at pH 4 than at pH 6. The effect on transpiration appeared to be determined by the presence of the inhibitor in the shoot, whereas Ca accumulation in the shoot was affected by the action of DNP on the roots. When the integrity of the barrier (probably the plasmalemma) in the root was slightly altered by non-aeration or by short exposure to DNP, Ca uptake was reduced. When the barrier was drastically altered by heating, freezing or prolonged exposure to DNP, Ca taken up by the shoot was markedly increased, and DNP uptake was markedly de- 23583-23599 PLANT PHYSIOLOGY [Vol. 42] 1870 creased. Under these drastic conditions the Ca barrier was essentially removed, allowing Ca to move freely with the transpirational water, and since the lipid phase of the barrier was apparently disrupted, the uptake by the shoot of the lipophilic and relatively large DNP molecules was reduced. These and other data support the concept that an energy-requiring step is involved in the transport of Ca from the external solution to the xylem vessels of the root.