Ecophysiology of the Xanthophyll Cycle

Abstract

This chapter seeks to illustrate the impressive range of environmental modulation of the xanthophyll cycle in terrestrial plants in their natural habitats, where the demand for thermal energy dissipation can change within seconds or between seasons and vary from a moderate to a very large fraction of the absorbed light. Plants from habitats with concomitant xanthophyll cycle conversions and changes in energy dissipation activity are included as well as examples from habitats in which zeaxanthin and antheraxanthin (Z+A) persist and energy dissipation is modulated largely via their rapid engagement and disengagement. The well-characterized, rapidly inducible and reversible form of xanthophyll cycle-dependent energy dissipation is contrasted with the sustained maintenance of higher levels of (Z+A)-dependent thermal dissipation under various environmental stresses with an emphasis on seasonally low temperatures. Furthermore, the association of Z+A retention with the phenomenon of photoinhibition of Photosystem II (and alterations in the stoichiometry of proteins associated with PS II) is discussed as well as a possible involvement of thylakoid protein phosphorylation in sustained (Z+A)-dependent energy dissipation. An integrative understanding is sought by comparing acclimation patterns of thermal energy dissipation as well as overall foliar antioxidant capacity with those of photosynthetic and respiratory metabolism of whole plants. It is proposed that acclimation of all of these processes responds to whole plant source-sink relationships.