Regulation of electron transport in microalgae

Unicellular algae are characterized by an extreme flexibility with respect to their responses to environmental constraints. This flexibility probably explains why microalgae show a very high biomass yield, constitute one of the major contributors to primary productivity in the oceans and are considered a promising choice for biotechnological applications. Flexibility results from a combination of several factors including fast changes in the light-harvesting apparatus and a strong interaction between different metabolic processes (e.g. respiration and photosynthesis), which all take place within the same cell. Microalgae are also capable of modifying their photosynthetic electron flow capacity, by changing its maximum rate and/or by diverting photogenerated electrons towards different sinks depending on their growth status. In this review, we will focus on the occurrence and regulation of alternative electron flows in unicellular algae and compare data obtained in these systems with those available in vascular plants. This article is part of a Special Issue entitled: Regulation of Electron Transport in Chloroplasts.

Research Highlights
► The light-induced electron flow aliment both ATP and NADPH production in the chloroplast.
► In most cases, ATP and ADPH are produced in a ratio that is not sufficient for CO2 assimilation.
► Alternative electron flow processes may adjust the ATP and reducing power stoichiometries.
► These processes must be tightly regulated to avoid an excessive reduction of the quantum yield of photosynthesis.