Morphophysiological, proteomic and metabolomic analyses reveal cadmium tolerance mechanism in common wheat (Triticum aestivum L.)

Soil cadmium (Cd) contamination can reduce wheat yield and quality, thus threatening food security and human health. Herein, morphological physiology, Cd accumulation and distribution, proteomic and metabolomic analyses were performed (using wheat cultivars 'Luomai23' (LM, Cd-sensitive) and 'Zhongyu10' (ZY, Cd-tolerant) at the seedling stage with sand culture) to reveal Cd tolerance mechanism. Cd inhibited wheat growth, caused oxidative stress, hindered carbon and nitrogen metabolism, and altered the quantity and composition of root exudates. The root Cd concentration was lower in ZY than in LM by about 35% under 15 μM Cd treatments. ZY reduced Cd uptake through root exudation of amino acids and alkaloids. ZY also reduced Cd accumulation through specific up-regulation (twice) of major facilitator superfamily (MFS) proteins. Furthermore, ZY enhanced Cd cell wall fixation and vacuolar compartmentalization by increasing pectin contents, hemicellulose1 contents, and adenosine triphosphate binding cassette subfamily C member 1 (ABCC1) transporter expression, thus reducing the Cd organelle fraction of ZY by about 12% and 44% in root and shoot, respectively, compared with LM. Additionally, ZY had enhanced resilience to Cd due to increased antioxidant capacity, plasma membrane stability, nitrogen metabolism, and endoplasmic reticulum homeostasis, indicating that the increased Cd tolerance could be because of multi-level coordination. These findings provide a reference for exploring the molecular mechanism of Cd tolerance and accumulation, providing a basis for safe utilization of Cd-contaminated soil by breeding Cd-tolerant and low Cd-accumulating wheat varieties.