Comparative studies on the properties of spinach chloroplasts prepared by media containing choline chloride or sucrose

Abstract

Spinach chloroplasts were isolated and stored in a medium containing 0.5 M choline chloride. The properties of these chloroplasts were compared with those of chloroplasts prepared in an ordinary sucrose medium. In marked contrast to sucrose-prepared chloroplasts, choline-prepared chloroplasts did not show “conventional uncoupling” (stimulation of ferricyanide reduction paralleling the inactivation of phosphorylation) after transient warming in the temperature range between 20° and 55°C. The thermal stability of the oxygen evolving system, the vulnerability of the lipophilic structure in the thylakoids to alcohol during the warming treatment, and the effects of amine on photophosphorylation were similar in both chloroplast preparations. After the warming treatment, the degree of swelling in chloroplasts was larger and the intermediate electron transport systme (from reduced 2,6-dichlorophenolindophenol to methyl viologen) was more stable against uncoupling, in choline-prepared chloroplasts than in sucrose-prepared ones. The presence and absence of “conventional uncoupling” in two chloroplast preparations were ascribed to differences in thermal stability. In choline-prepared chloroplasts the uncoupling temperature of the electron transport system was higher than the inactivation temperature of the oxygen evolving system, but it was lower in the sucrose-prepared ones.