Root-secreted nicotinic acid ameliorates Mn toxicity in sugarcane

Nicotinic acid (NIA) is known to function in heavy metal detoxification; however, the regulation and physiological significance of its endogenous secretion in metal tolerance remain unclear. In this study, NIA was identified as a predominant component of Mn-induced root exudates in sugarcane by combining high performance liquid chromatography and ultra-high-performance liquid chromatography-tandem mass spectrometry. Low-Mn-accumulating cultivars (ZZ1 and GT44) exhibited 1.59 3.08-fold higher NIA secretion rates than in high-Mn-accumulating cultivars (F175 and GT55) under Mn stress. NIA secretion rates increased significantly with increasing duration of Mn exposure (6–24 h) in ZZ1. High–resolution mass spectrometry analysis revealed the formation of NIA–Mn complex in NIA/MnCl 2 solution. Exogenous NIA significantly mitigated Mn toxicity, reducing plant Mn uptake and tissue Mn content by more than 50 %. It concurrently restored root elongation by 50 %, and reversed Mn-induced leaf chlorosis, elevating leaf SPAD values by 72.9 %. Furthermore, NIA fully reversed Mn-induced malondialdehyde and Evans blue accumulation in roots. Fluorescence microanalysis demonstrated that NIA completely abolished the Mn-induced red fluorescence in propidium iodide-stained root tips. However, NIA did not alter the Mn distribution ratio between roots and shoots or between young leaves and shoots. These findings demonstrate that the Mn-induced secretion of NIA from roots facilitates Mn resistance in sugarcane by excluding Mn uptake through Mn chelation. • Nicotinic acid (NIA) is secreted in Mn-induced root exudates in sugarcane. • Low-Mn-accumulating cultivars secrete 1.59 3.08-fold more NIA than high-Mn-accumulating ones under Mn stress. • Formation of a NIA–Mn complex indicates detoxification via chelation. • NIA treatment reduces Mn uptake, reverses chlorosis and oxidative damage.