Temperature dependence of chlorophyll a fluorescence in relation to the physical phase of membrane lipids algae and higher plants.

The temperature dependence of the yield of chlorophyll a fluorescence was measured at room temperatures in living algal cells and higher plant chloroplasts. 3-(3',4'-Dichlorophenyl)-1, 1-dimethylurea was added to the samples during the measurements in order to eliminate the influence of photosynthetic photochemical reactions on the fluorescence yield.In Anacystis nidulans the maximum in the curve for the fluorescence yield versus temperature occurred near the temperatures at which the transition of physical phase of the membrane lipids changes from the liquid crystalline to the mixed solid-liquid crystalline states. These findings suggest that the occurrence of a fluorescence maximum in the temperature-dependence curve is an indication of the thermal transition of physical phase of membrane lipids. Similar but less distinct maxima were found in Cyanidium caldarium and Euglena gracilis. No maxima were seen in the curves for chlorophyll a fluorescence versus temperature in Chlorella pyrenoidosa, Plectonema boryanum, Stichococcus bacillaris Phaeodactylum tricornutum, or in chloroplasts of the higher plants, spinach, lettuce, tomato, and Tidestromia oblongifolia.The fluorescence yield of allophycocyanin in Anacystis did not show such a maximum, but did show a steep increase with decreasing temperature below 5 C. the fluorescence yields of chlorophyll a and phycobilins extracted from Anacystis increased monotonously with decreasing temperature.