Efficiency of K+Utilization by Barley Varieties: Activation of Pyruvate Kinase

Abstract

Barley (Hordeum vulgare L.) varieties differed in their raponse to [K⁺]₀, in terms of their utilization efficiencies (UE = fresh weight. concentration of [K⁺]₁⁻¹). At low [K⁺]₀, Compana, an efficient-non-responder demonstrated superior utilization of absorbed K⁺. On the other hand, at high [K⁺]₀, Fergus (an efficient responder) and BT 334 (an inefficient responder) had higher UE values for K⁺ than Compana which performed poorly at this [K⁺]₀. Kinetic parameters for K⁺ activation of the enzyme pyruvate kinase from 12 barley varieties, representing a range of UE values, were determined. Varieties showed substantial differences in their V_max values (PV_max (31 μmol g⁻¹ fresh wt. h⁻¹) which was about 50% higher than that of Mingo, an inefficient variety. By contrast, K_m values for the enzymes were not significantly different among varieties The mean values for all varieties (3·9±0·15 mol m⁻³ K⁺) is far below the estimated cytoplasmic [K⁺] (100-200 mol m⁻³). It is, therefore, unlikely that differences in the utilization of K⁺ by these varieties can be explained on the basis of differential requirements for (K⁺) activation of these enzymes. Alternative possibilities for differences in the utilization of K⁺ are discussed.