Sucrose and Glycine Uptake in Stems and Roots of Cuscuta Seedlings

Abstract

Entire seedlings and excised stems of Cuscuta lupuliformis Krock, induced an acidification of the incubation medium and an alkalinization during substrate uptake. Sucrose and glycine uptake were proportional to their concentration in the medium showing both a saturable and a linear component which predominate at high substrate concentration (above 10 mM sucrose). Sucrose uptake was temperature and pH-dependent. The stem cell membrane potential was strongly depolarized by dinitrophenol, K+, Na+, and substrates. A maximum value of the depolarisation was reached at 25 mM sucrose and 10 mM glycine. All these data demonstrated that the cell potential results from two components, one of a diffusive nature and one generated by an electrogenic ion pump. Excised roots induced neither acidification nor alkalinization. The root membrane potential, unaffected by dinitrophenol and substrates, is considered as a diffusion potential. In stems, the involvement of a proton pump was evidenced by the effect of two inhibitors: carbonyl cyanide m-chlorophenylhydrazone and parachloromercuribenzene sulfonic acid. Inhibition of sucrose uptake was dependent on sucrose concentration. These results are interpreted in terms of an active, carrier-mediated component of substrate uptake in the stems of Cuscuta seedlings.