Hydrogen cyanide acts as a regulator of reactive oxygen species metabolism.

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conclusionHydrogen cyanide (HCN) is a ubiquitous gasotransmitter essential for regulating ROS metabolism and cellular redox balance. This modulation plays a crucial role in metabolic processes in higher plants and animals, highlighting HCN's importance in cellular signalling and stress response. Hydrogen cyanide (HCN) is synthesised in plants and animals and present ubiquitously in the environment. It is considered to be a gasotransmitter and is proposed to play a fundamental role in the origin of life. At concentrations higher than 100 µM, HCN is highly toxic to most aerobes, but at lower concentrations (below 100 µM) it serves as a signalling molecule in plants. The importance of this molecule in plant metabolism is highlighted by the fact that all higher plants produce HCN via various pathways. Given its toxicity, plants frequently store HCN as conjugates with sugars or lipids in vacuoles. HCN modulates the metabolism of reactive oxygen species (ROS), and this is also linked to the disruption of electron flow in the mitochondrial respiration chain. ROS are signalling compounds acting together with hormones in regulation of many physiological processes and typically modify the activity of enzymatic antioxidants by altering ROS levels, thereby impacting cellular redox potential. The aim of this review, therefore, is to describe the relationship between HCN activity and ROS metabolism, with a focus on higher plant systems in particular.