Chemometric insights into Lactiplantibacillus plantarum effects on onion (Allium cepa L.) metabolism and antidiabetic activity under cadmium stress

Abstract

Cadmium (Cd) is a toxic heavy metal that causes severe physiological damage in plants, inhibiting growth and ultimately reducing crop yield. Lactic acid bacteria regulate Cd availability through bioaccumulation and biosorption. This study evaluated the Cd tolerance of Lactiplantibacillus plantarum 10CH by determining its survival capacity under Cd stress and its potential to mitigate Cd-induced stress in onion (Allium cepa L.). The bacterial strain tolerated Cd concentrations up to 100 µM, and whole-genome sequencing identified genes involved in Cd biosorption, accumulation, and efflux. Exposure of onion to increasing CdCl2 concentrations significantly reduced root and shoot biomass. Inoculation with Lb. plantarum 10CH alleviated Cd stress at 100 µM, enhancing root and shoot biomass, reducing Cd accumulation, lowering oxidative damage markers, and stimulating antioxidant enzyme activities. Metabolic profiling revealed that Cd stress significantly reduced primary metabolites and amino acids, particularly at 100 µM, while bacterial inoculation restored key amino acids and peptides, including arginine, tyrosine, and glutamic acid. Chemometric analysis using unsupervised (PCA) and supervised (OPLS-DA) models revealed clear metabolite variation among untreated, Cd-stressed, and bacterial inoculated Cd-stressed onion leaves. Furthermore, leaf extracts exhibited α-glucosidase inhibitory activity, with the highest activity in control plants (IC50 = 425.2 ± 0.5 µg/mL). Cd-stressed plants showed moderate antidiabetic activity, which was significantly reduced by bacterial inoculation. Overall, these findings demonstrate that Lb. plantarum 10CH can survive under Cd stress and alleviates Cd-induced stress in onion, highlighting its potential as a bioinoculant to mitigate heavy metal stress.