The kinetics of the inactivation of thylakoid membranes by freezing and high concentrations of electrolytes

Abstract

The effect of electrolyte concentration, pH, and low temperature on the inactivation of cyclic photophosphorylation of isolated thylakoids from spinach has been investigated. Inactivation of membranes caused by electrolytes increased with increasing electrolyte concentration and with time. Temperature has a 2-fold effect on the rate at which inactivation of ATP synthesis occurs during freezing: lowering the temperature of a suspension of membranes in an electrolyte solution below the freezing point results in the concentration of electrolyte and membranes owing to the partial crystallization of water. The increased electrolyte concentration accelerates membrane inactivation. If viewed separately from the effect of electrolyte concentration, lowering the temperature decreases the rate of membrane inactivation by electrolytes. However, below about −35 °C inactivation occurs rapidly after freezing. pH shifts are not responsible for the inactivation of membranes by electrolytes during dehydration. The results pertain to the response of intact cells to dehydration by freezing or desiccation: inactivation is dependent on temperature, the extent of dehydration, and the time during which temperature and increased electrolyte concentration act on the membrane structures within the cell in vivo.