Nitric Oxide Signaling in Aquatic Systems

Nitric oxide (NO) is a small, diffusible gasotransmitter produced by nitric oxide synthase (NOS) enzymes or via reduction of nitrite and nitrate under hypoxic or acidic conditions. In aquatic organisms, from microorganisms and invertebrates to fish and amphibians, NO modulates vascular tone, immune defences, osmotic balance and neural function. In marine and freshwater settings, planktonic microbes generate NO as part of nitrogen cycling, influencing biofilm formation and symbiotic interactions. In fish gills and kidneys, NO regulates ion transport and acid–base homeostasis in response to salinity changes. In corals and other symbiotic systems, NO mediates stress responses to temperature anomalies, affecting bleaching dynamics. The versatility of NO signalling underpins its role in adaptation to hypoxia, pathogen challenge and pollutant exposure. Recent advances have elucidated the interplay between enzymatic and non-enzymatic NO production, the spatial dynamics of NO diffusion in tissues, and the downstream activation of cyclic GMP-dependent pathways. Understanding NO signalling across diverse aquatic taxa is vital for predicting ecosystem resilience, optimising aquaculture health and harnessing microbial processes for biotechnological applications.

Research from Nature Portfolio

Recent studies have revealed a pivotal role for NO in coral–algal symbiosis under thermal stress. Under elevated temperatures, host tissues display upregulated NOS activity, leading to transient NO bursts that trigger antioxidant defences and modulate algal expulsion. This feedback loop appears to determine bleaching thresholds and may guide interventions to enhance coral resilience. In marine phytoplankton, nutrient deprivation has been shown to induce NO-mediated colony formation. Diatoms under nitrogen or phosphorus limitation produce NO via nitrate reductase pathways, which acts as a quorum-sensing signal to initiate protective chain structures. These findings uncover conserved NO signalling networks that link environmental cues to community-level responses in aquatic ecosystems.

Nitric Oxide Signaling in Aquatic Systems publication trend

The graph below shows the total number of articles in nitric oxide signaling in aquatic systems across all publications each year (not limited to Nature Index journals).

Technical terms

Nitric oxide (NO): A gaseous signalling molecule generated enzymatically by NOS or by reduction of nitrite/nitrate; regulates vascular, immune and neural processes.

Nitric oxide synthase (NOS): A family of enzymes (constitutive and inducible isoforms) that convert L-arginine to NO and citrulline in the presence of cofactors.

NADPH-diaphorase (NADPH-d): A histochemical marker for NOS activity in tissues, revealing NO-producing cells.

Osmoregulation: The physiological process by which aquatic organisms maintain fluid and electrolyte balance in varying salinity conditions.

Gasotransmitter: A small endogenous gaseous molecule (such as NO, carbon monoxide or hydrogen sulfide) that acts as a signalling agent.

References

1. Induction of Inducible Nitric Oxide Synthase by Lipopolysaccharide and the Influences of Cell Volume Changes, Stress Hormones and Oxidative Stress on Nitric Oxide Efflux from the Perfused Liver of Air-Breathing Catfish, Heteropneustes fossilis. PLOS ONE (2016).
2. Distribution of nitric oxide-producing cells along spinal cord in urodeles. Frontiers in Cellular Neuroscience (2014).