The kinetics of [C-14]sucrose uptake by cotyledons of Araucaria araucana and the anatomy of these organs were previously studied. A further characterization of the uptake process has been performed in this present work to investigate the specificity of the uptake system for sucrose and the effect of metabolic poisons, bivalent ions, pH and temperature. The cotyledons take up sucrose as well as glucose, fructose and maltose, with a higher uptake velocity for glucose and fructose and lower for maltose as compared with sucrose. Competition experiments between sucrose and other sugars demonstrate that glucose, fructose and maltose inhibit sucrose uptake although maltose has less inhibitory effect. Glucose and fructose do not inhibit each other, suggesting that the sucrose uptake system could have a site for glucose and another for fructose. Metabolic poisons such as sodium azide, phenylhydrazone p-trifluoromethoxicarbonyl cyanide, 2,4-dinitrophenol, p-chloromercuribenzyl-sulphonic acid and N-ethylmaleimide decrease the velocity of the second saturable phase while Ca2+, Mg2+ and Mn2+ increase the velocity of the uptake process. Sucrose uptake is also modified by pH and temperature. The optimum pH of the uptake is 6.3 with a larger decrease in the uptake rate at basic pH than at acidic pH. A decrease in 10-degrees-C affects the V(max) but not the K0.5 of the first and second saturable phases.
