Concepts of photochemical damage of Photosystem II and the role of excessive excitation

Photoinhibition is one of the most controversial topics in photophysiology. Well into the 21 st century, scientists have not agreed on the mechanism of action, primary site, and roles of excess energy absorbed by photosynthetic pigments. It is recognized that Photosystem II is the most fragile component during photoinhibition and that excess excitation absorbed by the photosynthetic pigments has a strong impact on it. Consensus is yet to come on terminology, guidelines to study photoinhibition, or boundaries of what can be considered photodamage. Some of these controversies are the result of how we understand the phenomenon of photoinhibition, as this is what determines a given experimental design. Thus, how we understand photodamage depends on the philosophical approach of each group. While some efforts have been made in the parametrization of Photosystem II photoinhibition, an updated review about the concepts of photoinhibition of Photosystem II and how to study it is still pending. In this work, a review of the concepts used in the field of photoinhibition is presented, accompanied by a synopsis on the history and mechanisms of action.