Mechanism of Arginine Transport inVitis viniferaL. Protoplasts

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Abstract
Protoplasts were isolated from leaves of in vitro grown axenic shoots of grapevine (Vitis vinifera L. cv. Soultanina) and used to study the characteristics of arginine transport. Uptake was linear up to at least 60 min and the rate did not differ significantly between light and dark assaying conditions whereas incubation in darkness for 24 h caused a 70% reduction in uptake rate, which was probably not due to an energy dependent factor. Kinetics analysis revealed a biphasic uptake curve. The high affinity component had a Km, of 2.2 mol m−3. Optimum pH value was 5.5. Two carrier systems, one for basic and neutral and one for acidic amino acids were identified. Use of inhibitors revealed that those associated with ATP metabolism inhibited arginine uptake; more specifically, the proton motive force appeared to be the predominant energy source. Metabolic products of labelled arginine were consistent with the operation of the Krebs-Henseleit cycle.