Fluorescence of Photosynthetic Pigments in Vitro and in Vivo

Oxygenic photosynthesis is the unique process (at least in the solar system) by which plants absorb fleeting sunlight photons and store their energy in three stable forms of chemical energy: (i) As non-autoxidizable reduced organic compounds (e.g., carbohydrates), (ii) as transmembrane electrochemical gradients (e.g., proton motive force difference), and (iii) as chemical bonds of high negative free energy of hydrolysis of ATP. Its origin can be traced perhaps to the late Archaean Era (3.85 billion years ago). Subsequently, along a highly eventful course of evolution oxygenic photosynthesis managed to oxygenate the atmosphere to a level of ap-prox. 20% v/v oxygen, to generate an ozone shield in the upper atmosphere against incoming ultraviolet light, to oxidize minerals on the Earth’s surface, and in general to produce the environment as we know it today. This introductory chapter provides capsule information on the essential molecular structures and supramolecular assemblies (chlorophylls, accessory pigments, light harvesting antennae, reaction centers, electron transporting redox couples and thylakoid membranes) and the partial photosynthetic processes which add up to the highly complex and highly efficient process of oxygenic photosynthesis. The chapter is intended as introduction to chapters that follow, which focus on the exploitation of the chlorophyll fluorescence signal as an investigative tool of various aspects of the photosynthetic process.