Occurrence, structure, and evolution of nitric oxide synthase–like proteins in the plant kingdom

Gloss In animals, nitric oxide (NO) is mainly produced by NO synthases (NOSes), a family of enzymes partly conserved in bacteria. In contrast, how NO is produced in plants is poorly understood, and whether these organisms have proteins homologous to animal NOSes is unknown. In this Review, with three figures, two tables, and 60 references, we describe a search for the presence of NOSes in over 1300 species of land plants and algae, which showed that NOSes are present in a few algal species but appear to not be conserved in land plants. Thus, land plants seem to have evolved mechanisms for NO synthesis different from those present in animals. These mechanisms rely mainly on nitrite reduction.