Temperature dependence of the light-induced spectral shift of carotenolds in Cyanidium caldarium and higher plant leaves. Evidence for an effect of the physical phase of chloroplast membrane lipids on the permeability of the membrane to ions

Abstract

1. 1. Kinetics of the light-induced spectral shift of carotenoids were studied by changing temperature of cells of the thermophilic alga Cyanidium caldarium. Below the temperature of phase transition of thylakoid membrane lipids at 9 °C, the dark recovery of the carotenoid shift after several seconds of illumination was composed of a fast and a slow decay component. Above the phase transition temperature only the slow decay component was seen. 2. 2. In chloroplasts of a desert plant, Tidestromia oblongifolia, the fluorescence versus temperature curve indicated that the phase transition of the thylakoid membrane lipids occurred at about 5 °C. Below the phase transition temperature the kinetics of dark decay of the spectral shift of carotenoids at 520 nm in leaves was composed of a fast and a slow component. Above the phase transition temperature only the slow decay component was present. 3. 3. The light-induced spectral shift of carotenoids was measured at 520 nm in leaves of the chilling-sensitive plants, tomato and bean. The Arrhenius plots of dark recovery of the light-induced changes showed characteristic breaks at 10 and 12 °C in tomato leaves grown at 15 and 25 °C, respectively, and at 15 °C in a bean leaf. In leaves of the chilling-resistant plants lettuce and spinach, on the other hand, the dark recovery of the carotenoid shift showed no breaks in the Arrhenius plots. 4. 4. If the light-induced spectral shift of carotenoids in the photosynthetic membrane is caused by a production of a transmembrane electric field, then the dark recovery of this shift is an indicator of the disappearance of this accumulated electric charge. It is concluded that the diffusion of ions through thylakoid membranes is greatly affected by the physical phase of membrane lipids and that the membrane becomes leaky to the ions when the lipids are in the phase separation state.