The regulatory role of nitric oxide and its significance for future postharvest applications

Nitric oxide (NO), a highly reactive small gaseous molecule, has received increasing attention over the past forty years. First studied and analysed as an air pollutant, it was later identified as an important signalling molecule in living organisms. While being a cardinal part of mammalian neurotransmission and respiratory energy production, much of the molecular mechanism underlying NO homeostasis in plants remains unclear. When considering the physiological function of NO during fruit ripening and postharvest storage, the signalling pathways and regulatory mechanisms are even more poorly understood. In this frontiers article, a comprehensive overview of NO synthesis and signalling is provided, introducing to the reader to the complex regulatory mechanisms NO influences. We continue to explore the diverse roles nitric oxide plays in mediating both plant biotic and abiotic stresses, including its intricate relationship with various plant hormones. Special attention goes to the significance of stress mediation by NO for the postharvest industry. Especially the recent implication of nitric oxide - ethylene crosstalk during hypoxia stress, is of particular relevance for controlled atmosphere storage of fresh produce. An overview of the current uses and applications of NO in a postharvest context is also provided, highlighting the difficulties surrounding commercial application of NO. This review is concluded by identifying the main critical questions and research gaps on NO in a postharvest context.