Carotenoids and their role in the non-photochemical quenching of higher plants

Abstract

Photosynthesis drives the majority of life on earth. It involves the conversion of light energy into stable chemical energy which can be used to fuel metabolic processes. The bioenergetics of light capture have been well characterised but this neglects the essential regulatory processes which deal with excesses in absorbed energy. Central to these is non-photochemical quenching which is the dissipation of excited state energy as heat. There have been many proposed models for how this occurs and how it balances with e cient photosynthetic turnover, most of which are contradictory and involve essentially the same experimental observations. The photosynthetic membrane must be able to quench energy when rate of absorption exceeds turnover rate at the reaction centre but reduce this mechanism when light is in lower supply. The main points of contention are the site of quenching within the photosynthetic membrane, the nature of the quencher and the switch mechanism. In this thesis I have formulated a simple model to explain this mechanism. I show how slow energy transfer to the naturally dissipative Cars, present throughout the membrane, is su cient for deep quenching. I also propose, with some theoretical evidence, that small changes in the mutual orientation of pigments can have signi cant e ects of the energetic pathways. These are potentially responsible for the switch between light-harvesting and dissipative states.