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, thelight-induced pH shift (JpH) and the light scattering response(4LS) of isolated spinach chloroplasts were studied at temperaturesranging from 5 to 60°C. Activities which produce JpH and JLS under actinic illuminationdecreased with a rise in the reaction temperature above 30°Cand disappeared at 50°C. The ferricyanide-Hill reactionat pH 6.0 was stimulated by raising the reaction temperaturefrom 5 to 35°C, was slowed at higher temperatures and wasinactivated at 50°C. 4LS activity at temperatures below20°C depended on the activity of electron transport. With a rise in temperature of a suspension of chloroplasts whichexhibited JLS under actinic illumination, the scattering intensitydecreased. The decrease in scattering intensity was limited,at most, to an extent equal to ALS. The behavior of JLS whichdiffered from that of basal scattering is discussed in connectionwith a mechanism of JLS formation other than the shrinkage-swellingcycle. When activities were measured at 25°C with chloroplastswarmed transiently (2 min) at various temperatures (25–60°C),the dependence of JLS on the wanning temperature was identicalwith that on the reaction temperature, while the activitiesof both ferricyanide reduction and JpH formation were higherthan those measured at the corresponding reaction temperature.This suggested that the mechanism for 4LS formation could beirreversibly altered by a warming treatment and that it wasless stable against heat than the mechanisms of ferricyanidephotoreduction and 4pH formation. That is, transiently warmedchloroplasts showed a similar behavior to alkane-treated chloroplasts.The similarity is discussed in relation to the activity changethrough the possible and common cause of disordering of theorganized structures of lipophilic components in the lamellarmembranes. (Received June 5, 1971; )     

Biophysical studies on subcellular particles IV. The light scattering response and photosynthetic activities of spinach chloroplasts treated with n-alkanes

A suspension of isolated spinach chloroplasts was shaken withone of a series of liquid n-alkanes, from hexane to dodecane,for several sec. Physical and biological activities of alkane-treatedchloroplasts were compared with those of untreated ones. Thelight scattering response, the light-induced pH shift, the ferricyanide-Hillreaction and noncyclic phosphorylation were inhibited by shakingwith alkanes, with the exception of undecane and dodecane whichtemporarily stimulated the latter two reactions. The degreeof inhibition was inversely proportional to the chain-lengthof the n-alkane. This inhibition by alkane treatment was observed in the lightscattering response much more strongly than in any other reaction.Thus, we postulated that the light scattering response is attributableto changes in some internal structures that are sensitive topenetrated n-alkane molecules. Electronmicroscopy of alkane-treated chloroplasts revealed thatmost of the thylakoid sacs were swollen while partitions apparentlyremained intact. The degree of swelling was also inversely proportionalto the chain-length of the n-alkane. (Received April 22, 1971; )