Some characteristics of anion transport at the tonoplast of oat roots, determined from the effects of anions on pyrophosphatedependent proton transport

✍ Scribed by Andrew J. Pope; Roger A. Leigh

• Publisher: Springer-Verlag
• Year: 1987
• Tongue: English
• Weight: 928 KB
• Volume: 172
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00403033

✦ Synopsis

The effects of anions on inorganicpyrophosphate-dependent H +-transport in isolated tonoplast vesicles from oat (Arena sativa L.) roots were determined. Both fluorescent and radioactive probes were used to measure formation of pH gradients and membrane potential in the vesicles. Pyrophosphate hydrolysis by the H +-translocating pyrophosphatase was unaffected by anions. Nonetheless, some anions (CI-, Br-and NOa-) stimulated H+-transport while others (malate, SO4 zand iminodiacetate) did not. These differential effects were abolished when the membrane potential was clamped at zero mV using potassium and valinomycin. Stimulation of H+-transport by C1showed saturation kinetics whereas that by NO3consisted of both a saturable component and a linear phase. For C1 and NOa , the saturable phase had a Km of about 2 m01. m-3. The anions that stimulated H+-transport also dissipated the membrane potential (A~,) generated by the pyrophosphatase. It is suggested that the stimulatory anions cross the tonoplast in response to the positive A ~u generated by the pyrophosphatase, causing dissipation of A~u and stimulation of ApH, as expected by the chemiosmotic hypothesis. The work is discussed in relation to recent studies of the effects of anions on ATP-dependent H+-transport at the tonoplast, and its relevance to anion accumulation in the vacuole in vivo is considered.