Reversible uncoupling of energy transfer between phycobilins and chlorophyll in Anacystis nidulans: light stimulation of cold-induced phycobilisome detachment.

Phycobilin fluorescence of Anacystis nidulans grown at 28 degrees C increases substantially upon cooling below 10 degrees C. A maximal increase is found around -5 degrees C and amounts to 300%, with almost complete reversibility upon re-warming. Illumination with actinic light leads to considerable stimulation of the cold-induced phycobilin fluorescence increase. Analysis of the light stimulation phenomenon reveals: (1) Actinic illumination shifts the fluorescence-temperature characteristic by about 3 degrees C upwards on the T-axis. At temperatures below 5 degrees C the light stimulating effect becomes smaller again and fluorescence-temperature characteristics measured at high and low light intensity converge around -5 degrees C. (2) In the 13-8 degrees C region a large (up to 100%) light-induced phycobilin fluorescence increase is observed, while only negligible changes occur in the dark. (3) 3-(3,4-Dichlorophenyl)-1,1-dimethyl urea (DCMU) as well as uncouplers inhibit the light stimulation, which hence depends on coupled electron transport. In agreement with previous work (Schreiber, U. (1979) FEBS Lett. 107, 4-9) it is concluded that illumination enhances cold-induced phycobilisome detachment by increasing the net negative charge at the outer surface of the thylakoid membrane. The possible role of a fluid leads to ordered transition of membrane lipids (Murata, N. and Fork, D.C. (1975) Plant Physiol. 56, 791-796) is discussed.