Influence of Triton X-100 on the Structure and Functions of Pea Thylakoid Membranes

Abstract

Low temperature (77K) chlorophyll fluorescence measurements indicated the complex character of Triton X-100 - induced alteration of the excitation energy distribution between chlorophyll-protein complexes of PSII and PSI in pea chloroplast membranes. At Triton X-100 concentrations around its CMC (0.58 mM) the value of the low temperature F737/F695 fluorescence ratio decreased to 1.14 compared with non-treated membranes (1.37). Above the CMC, the F735/F695 ratio increased up to 1.67 at 4.0 mM Triton X-100. A further increase of the detergent concentrations resulted in a sharp decline of the F735/F695 ratio. It was also observed that the half-time (t 1/2) of the Mg2+-induced rise of the room temperature chlorophyll fluorescence increased from 17.5 s in control membranes to 24.5 s in 0.57 mM Triton X-100 treated thylakoids. Following the kinetic analysis of the salt-induced fluorescence increase it was found that the rate of increase of the distance between PSII and PSI complexes is markedly reduced below and around the detergent CMC. These changes were accompanied by significant alterations of the dynamic properties of the thylakoid membranes as determined by measuring the mobility of the spin probe SSL. As a result of the Triton X-100 treatments an increase of the rotation correlation time (τc) was found, the effect being concentration dependent. The chlorophyll fluorescence changes and the observed alterations in both PSII and PSI related photochemical activities are discussed in terms of Triton X-100 caused effects on the chloroplast structure and the corresponding diffusion controlled rearrangements of the chlorophyll protein complexes of PSII and PSI.