Short- and long-term effect of sulphite on sucrose transport in grapevine (Vitis vinifera L.) leaves. An electrophysiological study

Sucrose is the main carbohydrate translocated in grapevine and its transport may be restricted or inhibited by a number of factors such as the pollutant sulphur dioxide. The present study investigated, for the first time in grapevine, the effects of sulphite on membrane electrical response of sucrose transport in the mesophyll cells. Co-transport of sucrose across the membrane is linked to the free energy in a electrochemical proton gradient. Without the pollutant, electrophysiological traces displayed a metabolic-dependent sucrose electrical response in which an initial depolarization was followed by complete repolarization. In the presence of sulphite, instead, there were different trends depending on time of contact with the tissue of the pollutant. In the short-term, a slower repolarization was observed and in the long-term (after 6 and 12 h) the extent of depolarization (Delta mV) was also reduced. Transmembrane electrical potentials, measured in the presence of sulphite, became significantly (P < 0.01) more positive with increasing time of incubation of the tissue. On the whole, electrophysiological results highlight a direct or indirect effect of the pollutant on the activity of proton pump H+/ATP ase. Since carbohydrate translocation has a central role in the balance between source and sinks in the plant, the results of the research suggest that sulphite can modify the above balance with negative implications for the export of carbohydrate from the leaves.