MULTIPLE EFFECTS OF SODIUM DODECYL-SULFATE TREATMENT ON THE CHLOROPLAST ULTRASTRUCTURE AND MEMBRANE-PROPERTIES OF PEA THYLAKOIDS

Multi-stage sodium dodecylsulfate (SDS)-induced solubilization pattern s of pea (Pisum sativum L.) chloroplasts were monitored as an initial decrease in the light scattering intensity of the chloroplast suspensi on at subsolubilizing detergent concentrations and a consequent increa se at concentrations higher than 1.6 mM. Electron microscopic measurem ents revealed that SDS treatment altered the chloroplast structure res ulting in disruption of grana stacks at low detergent concentrations a nd formation of concentric multilamellar structures at SDS concentrati ons higher than 1.6 mM. The estimated net negative surface charge dens ity was -0.067 C m(-2) and -0.036 C m(-2) at 1.6 mM SDS and 8.1 mM SDS respectively, as compared to non-treated membranes (-0.046 C m(-2)). Kinetic analysis of the salt-induced increase of chlorophyll fluoresce nce indicated that the rate of increase of the distance between PSII a nd PSI complexes is markedly reduced in SDS treated thylakoids than in control. These changes were accompanied by remarkable alterations in the dynamic properties of the SDS-treated thylakoid membranes as deter mined by measuring the mobility of the spin probe SSL (spin labelled s tearic acid). The results are discussed in terms of a specific concent ration dependent SDS-induced effects on the physical properties of thy lakoid membranes and their influence on the chloroplast structural org anisation.