PHOTOSYNTHESIS DEPENDENT ACIDIFICATION OF PERIALGAL VACUOLES IN THE PARAMECIUM-BURSARIA CHLORELLA SYMBIOSIS - VISUALIZATION BY MONENSIN

After treatment with the carboxylic ionophore monensin the Chlorella containing perialgal vacuoles of the "green" Paramecium bursaria swell. The Paramecium cells remain motile at this concentration for at least one day. The swelling is only observed in illuminated cells and can be inhibited by DCMU. We assume that during photosynthesis the perialgal vacuoles are acidified and that monensin exchanges H+ ions against monovalent cations (here K+). In consequence the osmotic value of the vacuoles increases. The proton gradient is believed to drive the transport of maltose from the symbiont into the host. Another but light independent effect of the monensin treatment is the swelling of peripheral alveoles of the ciliates, likewise indicating that the alveolar membrane contains an active proton pump.