Biophysical studies on subcellular particles V. Effects of temperature on the ferricyanide-Hill reaction, the light-induced pH shift and the light scattering response of isolated spinach chloroplasts

Effects of temperature on the ferricyanide-Hill reaction, the light-induced pH shift (JpH) and the light scattering response (4LS) of isolated spinach chloroplasts were studied at temperatures ranging from 5 to 60°C. Activities which produce JpH and JLS under actinic illumination decreased with a rise in the reaction temperature above 30°C and disappeared at 50°C. The ferricyanide-Hill reaction at pH 6.0 was stimulated by raising the reaction temperature from 5 to 35°C, was slowed at higher temperatures and was inactivated at 50°C. 4LS activity at temperatures below 20°C depended on the activity of electron transport. With a rise in temperature of a suspension of chloroplasts which exhibited JLS under actinic illumination, the scattering intensity decreased. The decrease in scattering intensity was limited, at most, to an extent equal to ALS. The behavior of JLS which differed from that of basal scattering is discussed in connection with a mechanism of JLS formation other than the shrinkage-swelling cycle. When activities were measured at 25°C with chloroplasts warmed transiently (2 min) at various temperatures (25–60°C), the dependence of JLS on the wanning temperature was identical with that on the reaction temperature, while the activities of both ferricyanide reduction and JpH formation were higher than those measured at the corresponding reaction temperature. This suggested that the mechanism for 4LS formation could be irreversibly altered by a warming treatment and that it was less stable against heat than the mechanisms of ferricyanide photoreduction and 4pH formation. That is, transiently warmed chloroplasts showed a similar behavior to alkane-treated chloroplasts. The similarity is discussed in relation to the activity change through the possible and common cause of disordering of the organized structures of lipophilic components in the lamellar membranes.