Sulfite inhibition of sucrose transport into vacuoles of cottonwood leaves

Abstract

The mechanism of sucrose transport and the influence of various concentrations of sulfite on its activity was studied in the mesophyll vacuoles isolated from cottonwood (Populus deltoides Bartr. ex Marsh) leaves. Kinetic analysis of [14C] sucrose uptake by isolated vacuoles revealed the presence of a saturable component with Km for sucrose uptake = 23 mM and Vmax = 21.2 nmol sucrose 10-6 vacuoles min-1. The saturable component was inhibited by SH-blocker, p-chloromercuribenzenesulfonic acid (PCMBS) and was substrate specific. The transport of sucrose was not changed by ATP with or without Mg2+, by the ionophore, valinomycin and by protonophores, carbonylcyanide m-chlorophenyl hydrazone (CCCP) or dinitrophenol (DNP). Sulfite at concentrations of 0.01-2.5 mM inhibited the uptake of [14C] sucrose by isolated vacuoles. Inhibition was of the noncompetitive type with K; = 2.48 mM of sulfite (22oC).

Keywords

• isolated vacuoles
• Populus deltoides
• sucrose uptake mechanism