Specific uptake of 6-deoxy-d-glucose and of 2-aminoisobutyric acid by sugar beet leaves and roots

Abstract

Sugar beet was grown in pots and the transport of 6-deoxy-d-glucose (6-dg) and of 2-aminoisobutyric acid (AIB) into leaf and root tissue segments was examined. The uptake of 6-dg into both tissues displayed two kinetic components, one apparently of diffusional nature, the other saturable (half-saturation constant 0.22 mM in leaves, 0.10 mM in roots; limiting rate 0.37 and 0.10 nmol mg-1 (fresh mass) h-1 for leaves and roots, respectively). It was suppressed by d-glucose and inhibited by diethyl-stilbestrol (DES), suloctidil (SUL) and 2,4-dinitrophenol (DNP), but little by D2O and not at all by sodium vanadate. It showed a temperature optimum at 30 °C and a pH optimum at 6.0 - 6.5 in both tissues. The uptake of AIB was also two-componental but even the specific component had an immeasurably high half-saturation constant although it was inhibited by high concentrations of AIB as well as by DES, SUL, DNP and D2O. However, vanadate stimulated the uptake by as much as 40% in both leaves and roots. The temperature optimum in leaves lay at 30 °C while in the roots no maximum was present; its pH optimum was at 5.5 in leaves and again no maximum was observed in roots. Both transport systems were unaffected by 0.1M NaCl or 0.1 M KCl and by the presence of cytokinin in the incubation vessel. However, spraying with the cytokinin N6-(m-hydroxybenzyl) adenosine decreased both the half-saturation constant and the limiting velocity of 6-dg uptake slightly in the leaves and substantially in the roots. Spraying had an insignificant effect on the uptake of AIB.