Cadmium-induced changes in the composition and structure of the light-harvesting chlorophyll a/b protein complex II in radish cotyledons

Five-day-old etiolated radish ( Raphanux salivux L. cv. Saxa) seedlings exposed to white continuous light in the presence of Cd²⁺ (0.2 mM) showed characteristic changes in their light-harvesting chlorophyll a/b protein complex II after 48 h of greening. The content of its oligomeric supramolecular form was greatly diminished with a concomitant increase in the level of the monomer. The isolation of highly purified light-harvesting chlorophyll a/b protein complex II from control and Cd²⁺ treated radish cotyledons and a detailed analysis of its structure and composition revealed that first of all, Cd²⁺ altered the content of the specific phosphatidylglycerol fatty acid - trans -Δ³-hexadecenoic acid, widely accepted as a component responsible for the oligomerization of this chlorophyll-protein complex. This fatty acid in the thylakoid membrane phosphatidylglycerol pool seems to be very sensitive to different environmental stresses lowering its content, which indicates the vital significance of this component for the supramolecular organization and proper functioning of the light-harvesting chlorophyll a/b protein complex II.