INFLUENCE OF TRITON X-100 ON THE STRUCTURE AND FUNCTIONS OF PEA THYLAKOID MEMBRANES

Low temperature (77K) chlorophyll fluorescence measurements indicated the complex character of Triton X-100 - induced alteration of the exci tation energy distribution between chlorophyll-protein complexes of PS II and PSI in pea chloroplast membranes. At Triton X-100 concentration s around its CMC (0.58 mM) the value of the low temperature F737/F695 fluorescence ratio decreased to 1.14 compared with non-treated membran es (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 concentration s resulted in a sharp decline of the F735/F695 ratio. It was also obse rved that the hall-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. Follow ing 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 dynam ic properties of the thylakoid membranes as determined by measuring th e mobility of the spin probe SSL. As a result of the Triton X-100 trea tments an increase of the rotation correlation time (tau(c)) was found , the effect being concentration dependent. The chlorophyll fluorescen ce changes and the observed alterations in both PSII and PSI related p hotochemical activities are discussed in terms of Triton X-100 caused effects on the chloroplast structure and the corresponding diffusion c ontrolled rearrangements of the chlorophyll protein complexes of PSII and PSI.