Response of chloroplasts of tolerant and sensitive wheat genotypes to manganese excess: structural and biochemical properties

Effects related to the adaptation of wheat to Mn excess were determined by structural and biochemical characterization of chloroplasts obtained from three-leaf seedlings of Mn-treated wheat. Chloroplasts were isolated from two wheat genotypes: sensitive (Raweta) and tolerant (Parabola) cultivated in hydroponic conditions in Hoagland nutrient supplemented with 0 (control), 5, 10, and 20 mmol dm−3 MnSO4. Microscopic observations of the chloroplast structure revealed differences in the size and starch presence between both objects. Changes indicating the stresogenic influence of Mn on Raweta seedlings appeared already at the Mn dose of 10 mmol dm−3, whereas on Parabola, only at 20 mmol dm−3. Biochemical analysis indicated the differences in starch content. Results of measurements of lipid peroxidation, polarity, and electrokinetic potential of chloroplasts point to Mn-stimulated modifications of chloroplast membranes which occurred to be larger for Raweta. The activation of antioxidative enzymes (SOD and POX) shows that ROS are generated under Mn-excess conditions. The content of Mn and Cu, Fe, Mo, and Zn (microelements) as well as Ca, Mg, K, P, and S (macroelements) in chloroplasts was determined by mass (ICP MS) and plasma optic emission (ICP OES) spectrometry. Raweta accumulated greater amount of Mn in comparison with Parabola at all Mn doses in media. Increased concentration of Mn was accompanied with a decrease of uptake other investigated elements (except for K).