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

Laticiferous vessels of Hevea brasiliensis were isolated from stem seg ments by enzymatic digestion of the cell wall. The laticiferous vessel s keep their anastomosed network shape as in the intact tissue. After cell-wall hydrolysis, the isolated laticiferous protoplasts have a neg ative polarization (negative inside) and functional voltage sensitive inward K+ channels. The transplasmalemmal electric gradient is lower t han that for laticiferous vessels in place inside the tissue in the sa me medium (about - 35 mV instead of - 115 mV). In the absence of cell wall, and therefore of cell-wall invertase, we observe that sucrose in duces depolarization as in intact vessels. Whereas fructose and 3-0-me thylglucose do not produce any depolarization on intact laticiferous v essels, a depolarization of laticiferous vessel protoplasts is observe d upon addition of these sugars under the conditions used for glucose and sucrose. With sucrose, the depolarizing effect was blocked by phlo rizin as in intact vessels. Furthermore, the link between transport of different sugars and the function of the proton excretion pump endors es the hypothesis that electrogenic symports are present on the plasma lemma of the laticiferous vessels. Two specific symports, one to trans port hexoses and the other to transport sucrose, could be involved.