The reactive diatomic gas nitric oxide (NO) has been the subject of extensive investigations in plants. These studies revealed that NO is a signaling compound involved in numerous biological processes. Its main physiological functions, as well as its mode of action at the cellular and molecular levels, have been addressed in the 77th Volume of Advances in Botanical Research entitled “Nitric Oxide and Signaling in Plants”. More recently, the discovery and first functional analyses of nitric oxide synthases (NOSs) and NO-forming nitrite reductase in algae allowed a better understanding of NO biosynthesis in photosynthetic organisms. This review updates the NO production mechanisms in algae with a particular focus of NOSs.
