γ-Aminobutyric Acid Alleviates Cadmium Toxicity and Is Associated with Increased Ascorbate and Glutathione Levels in Brassica Species.

γ-Aminobutyric acid (GABA) is a signaling metabolite involved in plant stress responses; its role in cadmium (Cd) stress adaptation in oilseed crops remains poorly understood. Here, we investigated the effects of exogenous GABA on Cd stress responses in two Brassica species, oilseed rape (Brassica napus, Bn) and Indian mustard (Brassica juncea, Bj). GABA alleviated Cd toxicity, as indicated by improved chlorophyll retention and reduced Cd accumulation by 22-29% across the two species. Moreover, GABA altered Cd subcellular partitioning and was accompanied by elevations in ascorbate (ASA) and glutathione (GSH) contents, respectively, together with reduced superoxide anion radical (O2-) and hydrogen peroxide (H2O2) accumulation. GABA also altered fatty acid compositions, suggesting changes in membrane lipid metabolism under Cd stress. Transcriptome analysis identified 2502 and 352 upregulated genes under GABA + Cd treatment (relative to the control) in Bn and Bj, respectively, of which 2245 and 219 were uniquely detected in the GABA + Cd treatment groups. Moreover, GABA supplementation was associated with transcriptional changes in genes related to redox metabolism and ABC transporter-associated processes. Collectively, these findings suggest that GABA supplementation was associated with improved Cd tolerance in Brassica species, accompanied by changes in Cd subcellular partitioning, non-enzymatic antioxidant metabolism, fatty acid profiles, and stress-responsive transcriptome reprogramming.