Chloroplast ultrastructure and chlorophyll performance in the leaves of heterophyllous Nuphar lutea (L.) Smith. plants

Nuphar lutea (L.) Smith. heterophyllous aquatic plants produce both submerged and floating leaves. After the water level of a river decreases, plants grow at the riverside, and leaves with the short petioles are in the air. In this work, we are the first to perform a comparative analysis of the chloroplast ultrastructure, chlorophyll fluorescence and pigment content in submerged, floating and aerial leaves. Significant differences were found in the chloroplast ultrastructure of near-bottom leaves in comparison with their floating and aerial counterparts. In addition, exposure of leaves to 30, 60, 100, 200, 500, and 1000 μmol photon m−2 s−1 showed that submerged leaves showed significant photosystem II (PSII) sensitivity to higher light intensities. The data obtained for the chloroplast ultrastructure, pigment content, and PSII working efficiency in N. lutea leaves suggest that floating and aerial leaves should be considered sun-adapted, while submerged near-bottom leaves should be considered shade-adapted. The high phenotypic plasticity of the photosynthetic apparatus observed in N. lutea heterophyllous plants ensures the effectiveness of the photosynthesis process in variable natural environments, particularly under different light intensities.