Biostimulant activity of chitosan in horticulture

Chitosan is formed from chitin, a co-polymer of N-acetyl-D-glucosamine and D-glucosamine, when over 80% of the acetyl groups of the N-acetyl-D-glucosamine residues are removed. Chitosan-based materials exhibit various interesting properties, which make them applicable in many fields, including agriculture, where they are used as biostimulants. Chitosan induces several defensive genes in plants, such as pathogenesis-related genes, like glucanase and chitinase. It also induces many enzymes in the reactive oxygen species scavenging system, such as superoxide dismutase, catalase and peroxidase. The signal transduction pathway from chitosan that elicits its responses involves hydrogen peroxide and nitric oxide signals, and it may also directly control gene expression by interacting with chromatin. Chitosan has been used both as a biostimulant to stimulate plant growth, and abiotic stress tolerance, and as to induce pathogen resistance; however, these responses are complex and they depend on different chitosan-based structures and concentrations as well as the plant species and developmental stage. This review gathers information on chitosan provided by recent research, especially when it is used as plant biostimulant in horticulture. (C) 2015 Elsevier B.V. All rights reserved.