Lemon juice solution (LJS) contains several bioactive substances, which could make it a novel phyto-catalyst for stressed crops. It may act as an anti-heavy metal agent, effectively ameliorating damage to plants under cadmium (Cd) stress. Therefore, this investigation was undertaken to investigate the potential reinforcing influences of priming Phaseolus vulgaris seeds in 0.8 mM citric acid (CiA) or 5% LJS on germination, growth, physio-biochemical attributes, antioxidant capacity, and antioxidant gene expressions under watering with 1.0 mM Cd-contaminated water (Cd-CW). Watering the P. vulgaris with Cd-CW reduced seed germination and root activity while increasing Cd translocation factor (Cd-TF) and Cd level of root and shoot systems. Furthermore, Cd-CW elevated the levels of O2•−, H2O2, malondialdehyde (MDA), and electrolyte leakage (EL) while reducing membrane stability (MSI), total chlorophyll and carotenoids, and efficiency of the photosystem II (Fv/Fm) due to the reduced relative water content (RWC), thereby decreasing seedling biomass. However, seed priming in LJS or CiA attenuated the Cd stress damage of P. vulgaris seedlings. LJS or CiA elevated seed germination (by 56.9 or 31.4%), root activity (by 51.9 or 29.6%), RWC (by 80.6 or 75.1%), MSI (by 59.4 or 29.8%), total chlorophyll content (by 107.0 or 47.4%), carotenoids content (by 77.1 or 37.1%), and Fv/Fm (by 94.9 or 48.7%) with reduced Cd-TF (by 26.5 or 11.8%), Cd content in roots (by 25.2 or 15.7%) and shoots (by 44.6 or 23.7%). These positive outcomes from LJS or CiA were associated with reductions in the levels of O2•−, H2O2, MDA, and EL due to the increased levels of osmo-regulators (ORs) (soluble sugars and proline), various antioxidants (enzymatic and non-enzymatic) activities, and enzyme-related genes expression. Our findings support the use of LJS as a novel phyto-catalyst, which yielded better results, markedly superior to CiA under Cd stress.
