Structure of Chlorenchyma and the Profile of Membrane Lipids in Leaves of Halophytic Chenopodiaceae Species with Different Types of Photosynthesis

The mesophyll structure and the lipid profile of membranes were examined in leaves of four Chenopodiaceae halophytes with different types of photosynthesis. The analyzed plants represented the annual species with photosynthesis of C₃ type (Salicornia perennans),C₃–C₄intermediate type (Sedobassia sedoides), and C₄-NAD type (Climacoptera crassa) as well as a perennial half-shrub Kochia prostrate with photosynthesis of C₄-NADP type; the chosen species inhabited biotopes with various salinity and soil moisture content. The annual species with succulent leaves accumulated 7–15 times larger amounts of Na⁺ than the perennial half-shrub. A strong positive correlation was found between the leaf thickness and leaf water content (r = 0.98, P = 0.04) and the total amount of elements accumulated in leaves (r = 0.96, P = 0.04). Mesophyll cells of the C₃ species S. perennans were substantially larger than the mesophyll and bundle sheath cells of the C₄ species; the number of chloroplasts per cell in the C₃ species was 1.5–3.5 times higher than in the C₄ species. The species with Kranz anatomy differed between one another in terms of the size and the relative number of bundle sheath and mesophyll cells. The total surface area of chloroplasts per unit leaf area in plants with Kranz anatomy was higher in mesophyll cells than in the bundle sheath cells. The assimilating surface areas of mesophyll and chloroplasts in plants with the C₃ and C₃–C₄ types of photosynthesis were similar, as was that in species with C₄-NAD and C₄-NADP types of photosynthesis. The total number of cells and the number of chloroplasts in mesophyll cells correlated positively with the content of total lipids per unit leaf area (r = 0.95, P = 0.04). The content of 18:2(n-6) fatty acid decreased, while the content of 18:1(n-9) increased in the series C₃ → C₃–C₄ → C₄-NAD → C₄-NADP species. It is concluded that differences among the examined species in terms of the volume and surface area of cells and chloroplasts in mesophyll and bundle sheath tissues become larger, while the content of membrane lipids in cells, chloroplasts, and mitochondria per unit leaf area decreases along with the extent to which the C₄ syndrome is pronounced. The composition of lipids and fatty acids is suited to support the metabolic activity of chloroplasts and mitochondria according to the type of photosynthesis.