Magnesium: An overlooked signalling ion in plant physiology and circadian regulation

Magnesium (Mg²⁺) is essential for plant growth and metabolism, acting as a cofactor in numerous enzymatic and structural processes. This review outlines the main physiological and biochemical functions of Mg²⁺ and summarizes current knowledge on its transport and homeostatic regulation. We examine how Mg²⁺ homeostasis intersects with broader signalling networks and metabolic pathways, including its crosstalk with other mineral nutrients, where antagonistic and synergistic interactions influence nutrient acquisition, allocation and stress responses. Emerging evidence further suggests that, beyond its classical roles, Mg²⁺ may function as a regulatory ion with signalling properties reminiscent of secondary messengers in animal systems. Finally, we highlight recent findings linking Mg²⁺ dynamics to circadian regulation, suggesting reciprocal interactions between temporal control mechanisms and nutrient fluxes. These insights underscore the central importance of Mg²⁺ in plant biology and identify key gaps in understanding its regulatory and integrative roles.