Non-photochemical Energy Dissipation Determined by Chlorophyll Fluorescence Quenching: Characterization and Function

Chlorophyll (Chi) a fluorescence has become an important non-invasive tool to investigate the utilization and dissipation of absorbed light energy in photosynthesis. In particular, analysis of Chi fluorescence quenching serves as a convenient, widely applied method to obtain complex information on the response of the photosynthetic apparatus in green plants to environmental factors. Whereas ‘photochemical quenching,’ qP, reflects the operation of the linear electron transport pathway, ‘non-photochemical quenching,’ qN, indicates thermal dissipation of excitation energy. In this chapter, basic characteristics of fluorescence quenching are described. The mechanisms of the two major components of qN, ‘energy-dependent quenching,’ qE, related to the trans-thylakoid proton gradient, and ‘photoinhibitory quenching,’ ql, associated with photoinhibition of photosynthesis, are reviewed in detail, considering the evidence obtained from the study of mutants and transgenic plants. In addition, the functions of qE and ql in thermal energy dissipation and photoprotection under conditions of excessive light are discussed.