The Interrelations of Cell Turgor Pressure, Gas-vacuolation, and Buoyancy in a Blue-green Alga

Abstract

The increase in pressure required to collapse gas vacuoles on suspending the cells of the blue green alga Anabaena flos-aquae in hypertonic sucrose solutions shows the turgor pressure to vary over the range of 265 to 459 kX m-2 under different culture conditions. The cell turgor increased at a rate of up to 94 kN m-2 h_1 on transferring the alga from low to high light intensity. This rise appears to be a result of the accumulation of photosynthate, as it is dependent on the presence of carbon dioxide in the gas phase and is inhibited by DCMU. Experiments using 14C02 indicate that the increased rate of photosynthesis during the high light exposure is easily sufficient to account for the observed turgor rise. The rise in turgor can bring about collapse of sufficient of the alga's gas vacuoles to destroy its buoyancy. Higher turgor pressures, and consequently a lower degree of gas vacuolation and buoyancy, were maintained when the alga was kept at high light intensities for a week and more. The significance of this behaviour is discussed in relation to stratification of planktonic blue-green algae in natural habitats.