SUGAR ABSORPTION AND POTASSIUM CHANNELS IN PROTOPLASTS OF HEVEA-BRASILIENSIS LATICIFEROUS VESSELS

Laticiferous vessels of Hevea brasiliensis were isolated from stem segments by enzymatic digestion of the cell wall. The laticiferous vessels keep their anastomosed network shape as in the intact tissue. After cell-wall hydrolysis, the isolated laticiferous protoplasts have a negative polarization (negative inside) and functional voltage sensitive inward K+ channels. The transplasmalemmal electric gradient is lower than that for laticiferous vessels in place inside the tissue in the same medium (about - 35 mV instead of - 115 mV). In the absence of cell wall, and therefore of cell-wall invertase, we observe that sucrose induces depolarization as in intact vessels. Whereas fructose and 3-0-methylglucose do not produce any depolarization on intact laticiferous vessels, a depolarization of laticiferous vessel protoplasts is observed upon addition of these sugars under the conditions used for glucose and sucrose. With sucrose, the depolarizing effect was blocked by phlorizin as in intact vessels. Furthermore, the link between transport of different sugars and the function of the proton excretion pump endorses the hypothesis that electrogenic symports are present on the plasmalemma of the laticiferous vessels. Two specific symports, one to transport hexoses and the other to transport sucrose, could be involved.