Comparison of the Uptake Kinetics of Valine and Sucrose and their Light-reactivity in Mesophyll Cells of Commelina benghalensis

Abstract

Summary Eadie-Hofstee plots demonstrate that valine and sucrose uptake by isolated Commelina benghalensis L. mesophyll cells obeyed biphasic kinetics. The uptake of sucrose is presumably performed by two saturable systems (K m1 , K m2 : 10 −4 and 2,3 × 10 −4 M, respectively; V m1 , V m2 : 4.8 and 928 nmol h −1 /10 6 cells), valine uptake by two saturable systems (K m1 , K m2 : 3.8 × 10 −4 and 7 × 10 −3 M, respectively; V m1 , V m2 : 111 and 171 nmol h 1 /10 6 cells) imposed on a linear term. The differences between the uptake parameters of the sucrose uptake systems (ratios K m2 /K m1 , 1900–2700; V m2 /V m1 , 180–550) surpass by far those of valine uptake (K m2 /K m1 , 25–100; V m2 /V m1 , 1.8–7.5). Light did not affect the K m -values , but exerted a differential effect on the V m -values. Of valine uptake V m1 was promoted more by illumination than V m2 -valine whereas V m2 -sucrose reacted more strongly to light than V m1 -sucrose.