EFFECT OF A GALACTOSE-SPECIFIC LECTIN ON STRUCTURE OF THE LIPID BILAYER AND ELECTRON-TRANSPORT IN CHLOROPLAST MEMBRANES

Preliminary incubation of isolated broad bean chloroplasts (Vicia faba L.) in the presence of a lectin from soybean seeds (Glycine max Merr.) induced subsequent suppression of phenazine methosulfate-catalyzed photophosphorylation. The effect of the lectin depended upon its concentration and the time of preincubation, and was completely prevented by galactose. Analogous action was exerted by lectins from kidney bean (Phaseolus vulgaris L.), peanut (Arachis hypogaea L.), and castor (Ricinus communis L.) seeds. Lectins from soybean seeds suppressed noncyclic electron transport (the Hill reaction with ferricyanide) and increased polarization of the fluorescence of diphenylhexatriene embedded in thylakoids. These effects were sharply amplified by light during preincubation with the lectin and were additionally amplified in the presence of ATP. Decay of low-temperature fluorescence in the 690-nm band (PSII) and increase in the 735-nm band (PSI) occurred under influence of the lectin. It is hypothesized that the increasing disbalance in distribution of excitation energy between the photosystems and increase in the density of lipid packing can serve as causes of electron transport inhibition under the influence of galactose-specific lectins.