Modeling the protection of photosynthesis

It is hard to overstate the importance of photosynthesis for mankind and the biosphere. It produces the oxygen we breathe and the food we eat, and images of Earth from space show the green of terrestrial vegetation and swirls of marine phytoplankton. To meet our increasing demand for food and energy, it seems inevitable that we will need to increase the efficiency of photosynthesis in plants and algae. There is therefore some urgency in our drive to better understand the operation, regulation, and limitations of photosynthesis. This ambition is made particularly challenging because of the complexity of photosynthesis; it comprises many significant subprocesses that range in scale from quantum mechanics to ecosystems. Given the complexity of photosynthesis, mathematical models have proven to be a vital tool with which to encapsulate knowledge and to describe, analyze, and simulate the operation of photosynthesis in vivo (1). In PNAS, Zaks et al. (2) describe a comprehensive mathematical model for qE, a mechanism with a somewhat odd name that is essential for protecting a component of photosynthesis, photosystem II (PSII), from photodamage. In vivo, qE is a dynamic, actively controlled process whose regulation depends on the combined effects of photosynthetic electron and proton transport, and photosynthetic metabolism. To model qE, therefore, Zaks et al. needed to produce an impressive toolkit of models that will be useful for modeling much more than just qE. Photosynthesis uses the energy of absorbed photons to drive the otherwise endothermic reduction of CO2, and the importance of qE arises because leaves are often unable to use for CO2 fixation all the light absorbed by their photosynthetic pigments. Ideally, the light absorbed by the leaf would be used to fix carbon dioxide with a constant quantum efficiency across all natural light intensities, with the efficiency being determined