Photosynthesis within the leaves of green plants is one of the best known and most researched of biological processes. In this series of chemical and physical reactions, light energy is used to convert atmospheric CO2 into sugars, producing oxygen as a by-product. Thus, photosynthesis is the ultimate source of essentially all organic matter and all oxygen in the biosphere. Each of the 78 discrete steps from light capture to carbohydrate synthesis is known in some detail and their kinetic properties described. For photosynthesis to occur, CO2 must enter the leaf through tiny pores called stomata, which are found on the surfaces of leaves. As CO2 diffuses into the leaf, water and O2 diffuse out, and stomatal aperture must vary dynamically throughout the day to admit sufficient CO2 for photosynthesis while preventing excessive water loss. Although less well understood than photosynthesis, many of the biochemical and biophysical steps controlling stomatal opening are now described, and there is new evidence that photosynthetic processes may underlie many stomatal responses. Computational power and numerical methods are now sufficient to allow the simulation of the complete process of leaf photosynthesis from carbon dioxide and oxygen exchange through the stomata to light energy transduction into carbohydrate in the underlying photosynthetic tissue. This work, for the first time, brings together the complete description of the photosynthetic process and hypothesized mechanisms of stomatal movements to produce a computer or in silico representation of the leaf. The product of this effort will be capable of mimicking the dynamic responses of leaves to changes in light, carbon dioxide and oxygen, and comparisons to real measurements of the dynamics of leaf photosynthesis will be used to test and improve the model. It will provide a workbench for investigating the dynamic linkages between stomatal movement and photosynthesis. More broadly it will provide a means for exploring the mathematical properties of a complex natural system that is unusually rich in measurable properties. The project will contribute to education by providing a portal to the in silico leaf, allowing classroom investigation of both dynamic environmental responses and genetic modification of individual steps in the photosynthetic process. Undergraduate Research Experiences linked to this project will aid this implementation of the portal.
