Morphological, photosynthetic, and CAM physiological responses of the submerged macrophyte Ottelia alismoides to light quality

Light quality strongly affect a great many physiological processes in terrestrial plants. Whatever, few studies have investigated how the submerged macrophytes response to different light quality. The present research aimed to understand how light quality affect morphogenesis, photosynthesis, as well as crassulacean acid metabolism (CAM) operation during the growth of Ottelia alismoides, a freshwater facultative CAM macrophyte. The plants were grown under three light qualities of white (W), red (R) and blue (B) lights with same light intensity of 100 μmol m−2 s−1. Leaf development, leaf anatomic characteristics, photosynthetic traits, as well as CAM metabolism were determined on the newly produced leaves during light treatment. Monochromatic R stimulated leaf blade and petiole elongation, leaf area and dry weight, but reduced leaf thickness, negatively influenced chlorophyll content and Fv/Fm. On the contrary, B- grown plants were dwarf and with compact size as well as lower leaf dry weight. The content of photosynthetic product starch under B was significantly lower as compared with R, moreover, combined with the analysis of ultrastructural characteristics of epidermal and mesophyll chloroplasts, it showed that B inhibited starch to be translocated out of epidermal chloroplasts. Furthermore, both R- and B- grown plants exhibited obvious diurnal acidity fluctuation comparable to W- grown plants, and had high activity of enzymes including ribulose-bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEPC) and pyruvate phosphate dikinase (PPDK) that required for CAM cycle, indicating that CAM was present in both R- and B- grown plants and monochromatic R and B did not affect CAM activity. In conclusion, monochromatic red and blue light differentially played their special roles in regulating leaf growth and morphogenesis, as well as photosynthetic metabolism in O. alismoides.