Nitric oxide functional relationships with nitrogen-containing stress metabolites: Role in plant adaptation to...

Polyamines, γ-aminobutyric acid (GABA), proline, and glycine betaine (GB) are important plant stress metabolites that are interconnected in common metabolic cycles. These compounds have a multifunctional protective effect on plant cells under stress conditions, acting as osmoregulators, antioxidants, chaperones, and intracellular pH stabilizers, among other roles. The key role of these compounds, however, lies in their involvement in the signaling network of plant cells. Stress metabolites, in particular, engage in a complex functional interaction with reactive oxygen species (ROS) and nitric oxide (NO). Nevertheless, information detailing the links between NO and major nitrogen-containing stress metabolites is fragmented. Consequently, a holistic understanding of these interactions, even at the theoretical model level, has yet to be presented in the literature. The review investigates the phenomenology and mechanisms of NO's involvement as a signaling mediator in the stress-protective function of polyamines and GABA in plants. It also analyses the effect of NO on the content of polyamines, GABA, proline, and GB under normal and stressful conditions. The latest data on the role of S-nitrosation processes of enzymes involved in the regulation of content of low-molecular nitrogen-containing compounds in plant adaptation, and on the effect of polyamines on S-nitrosation of the proteome are summarized. Particular attention is paid to the links between nitric oxide and other signaling mediators (primarily ROS and Ca²⁺) during its functional interaction with stress metabolites. Regulation of NO and stress metabolite levels is considered one of the promising tools for managing plant stress resistance.