Single cell C4 photosynthesis in aquatic and terrestrial plants: A gas exchange perspective

Another "green revolution" is needed for crop yields to meet the demands for food and this has provided a new focus on photosynthesis research. Many important crops have the C3 photosynthetic pathway and a range of options for enhancing leaf photosynthesis in C3 species are being tested. George Bowes' pioneering research elucidated the inducible single cell C4 photosynthetic mechanism of aquatic plants such as Hydrilla verticillata. Here we review the efficacy of single cell C4 photosynthesis by comparing the physiology of terrestrial Kranz C4 photosynthesis with that of terrestrial and aquatic single cell C4 photosynthesis. The comparison shows that the terrestrial single cell system which involves spatially separated cytoplasmic domains and dimorphic chloroplasts equals Kranz C4 photosynthesis in efficiency; whereas, the simpler aquatic single cell system employed by H. verticillata which operates the C4 pathway between cytoplasmic space and chloroplasts is less efficient due to diffusive constraints. Nevertheless, understanding this readily inducible C4 pathway may provide valuable lessons for improving C3 photosynthesis by enhancing chloroplast CO2 concentrations.