Chlorophyll fluorescence as a tool for describing the operation and regulation of photosynthesis in vivo

In very broad terms, photosynthesis begins with the absorption of light (the photosynthetically active kind) and ends with assimilation—the fixation of CO2—a process that is fundamental to trophic networks in the biosphere. In between the absorption of light and the act of assimilation, there are the intermediate processes of photosynthesis: photochemistry, electron transport and energy transduction, metabolism, and gaseous diffusion processes. The rate of assimilation will ultimately be determined by the limiting activity of these processes. There are also complex regulatory networks that coordinate the activities of the many subprocesses of photosynthesis whose combined activity is necessary for assimilation. To understand the relationship between light absorption and assimilation, it is necessary to understand operation of the intermediate processes, how they interact with each other, and how they individually or collectively limit the overall efficiency of assimilation. In this chapter, we will describe the principles and use of a major, widely used nondestructive method for measuring the operation and regulation of PSII not only in leaves and similar photosynthetic plant tissues but also in in vitro samples: steady-state chlorophyll fluorescence.