LIGHT-INDUCED ION TRANSPORT IN GLUTARALDEHYDE-FIXED CHLOROPLASTS - STUDIES WITH NIGERICIN

The effect of nigericin and glutaraldehyde treatment of spinach chloroplasts was investigated in order to examine the role of conformation and permeability on mechanisms of ion transport. Glutaraldehyde-fixed chloroplasts retain the capacity to manifest light-dependent H+ uptake, but the movement of other ions such as weak acid anions or weak base cations which efflux or influx, respectively, into chloroplasts, is largely eliminated because the fixed chloroplasts have lost the capacity to undergo changes in volume by an osmotic mechanism. It is concluded that the transport of H+ ion does not require gross conformational changes of chloroplasts and that the uptake of other ions is secondary to H+ uptake, depending upon volume changes for net uptake or efflux to occur. Nigericin induced an increase in permeability of H+, K+, Na+, and NH4+ ions in illuminated chloroplasts. The stoichiometry between cation uptake and H+ uptake varied with the concentration of nigericin and/or chloroplasts employed and, under appropriate conditions, cation uptake can far exceed the maximum obtainable for H+. At high nigericin and low K+ or Na++ concentrations, H+ gradients collapse, which can explain its powerful activity in the uncoupling of photophosphorylation. © 1968.