CALCIUM AND OTHER POLYVALENT CATIONS AS ACCELERATORS OF ION ACCUMULATION BY EXCISED BARLEY ROOTS

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Abstract
Absorption expts. with excised barley roots capable of rapid ion accumulation from dilute solns. show that Ca, Mg, Sr, Ba and Al ions in KBr soln. can accelerate K and Br accumulation as detd. by analyses of the expressed sap from roots frozen and then thawed. Contrary to the concept of antagonism, Ca ions increase the K absorbed by as much as 100% and Br by 150%, the magnitude depending on the conc. of Ca used. At Ca concs. higher than 0.3iV, antagonism and root injury are noted. Ca is the most effective cation tested over a wide range of cones. of both KBr and calcium. Mixtures of CaSO4 and MgSO4 produce enhanced absorptions similar to equal cones, of the single salt indicating that the cations perform the same function, but with different efficiencies. Roots respond to Ca during concurrent K and Br absorption regardless of their initial Ca content, as modified by growth or pretreatment conditions. Increased absorption due to Ca is associated with a higher respiratory rate and loss of sugars. The Ca effect is apparent over a wide range of temps. Aerobic metabolism is essential to show the effect since roots treated with KCN or N2 during absorption from moderately high cones, of KBr are relatively impermeable to Br even when Ca is added to the soln. Two possible interpretations of the polyvalent cation effect are advanced: they may modify directly the oxidative metabolism supplying the energy for accumulation; and the primary effect may be on the plasma membrane or on some phase of surface metabolism intimately related to permeability.