Differential rates of sucrose and hexose transport by asparagus cell cultures

Abstract

Cell cultures of asparagus ( Asparagus officinalis L.) grew well on media containing 3% (w/v) sucrose, glucose or fructose. However, optimal growth occurred with sucrose. The objective of this work was to characterize sugar transport and to determine the presence of sugar carriers in these cells. Cell cultures preferentially transported fructose, glucose, 3- O-methyl glucose (3-OMG), sucrose and l-glucose, in that order. Both sucrose and 3-OMG uptake was inhibited by carbonylcyanide chlorophenyl hydrazone (CCCP) and p-chloromercuribenzene sulfonic acid (PCMBS). Due to high cell wall invertase activity, sucrose was efficiently hydrolyzed so that no sucrose was detected in the culture medium after 5 days and cells accumulated more hexose than sucrose. Furthermore [ 14C]sucrose uptake was partially inhibited in the presence of unlabeled 3-OMG. Cell cultures transported 1′-fluorosucrose, a sucrose analog not subject to invertase hydrolysis, at rates similar to that of sucrose. The evidence indicated that despite the presence of high cell wall invertase activity and efficient hexose transport, a sucrose carrier is present at the plasmalemma of asparagus cell cultures. Therefore, sucrose hydrolysis by invertase is not essential for transport into these cells.