Electronic carotenoid-chlorophyll interactions regulating photosynthetic llght harvesting of higher plants and green algae.

Electronic interactions between chlorophylls (Chl) and carotenoids (Car) play a major role in the regulation of photosynthetic light harvesting of higher plants and green algae. In this contribution, we discuss different electronic regulation models that are based on various Chl-Car interactions, leading to switching between efficient light harvesting and thermal dissipation of excess energy. Most regulation models are based on three types of electronic Chl-Car interactions: direct Chl -> Car S-1 energy transfer, quenching by Car radical cations and bidirectional quenching processes. We will give an overview of the observations that have been made in our as well as other laboratories supporting one or the other model and discuss possible scenarios that may provide a unified picture considering all three types of regulation models