Worldwide, crop productivity is highly influenced by heavy metal toxicity. Lead (Pb) the is second-most toxic heavy metal that has high persistence in soil. Lead is translocated in plants from rhizosphere soil and enters the food chain, where it poses a significant hazard to the health of humans. In the present investigation, seed priming with triacontanol (Tria) was used to mitigate Pb phytotoxicity in Phaseolus vulgaris L. (common bean). Seeds were primed with different concentrations of Tria (control, 10 µmol L-1, 20 µmol L-1, 30 µmol L-1) solutions. The pot experiment was carried out by sowing Tria-primed seeds in contaminated soil with 400 mg kg-1 Pb. Lead alone induced a decrease in the rate of germination and a significant reduction in biomass and growth of P. vulgaris as compared to the control. All these negative effects were reversed by Tria-primed seeds. Proliferation of photosynthetic pigments was observed 1.8-fold by Tria under Pb stress. Primed seeds with 20 µmol L-1 Tria enhanced stomatal conductance (gs), photosynthetic rate (A), transpiration rate (Ei), and uptake of mineral contents (Mg+2, Zn+2, Na+, and K+) and reduced Pb accumulation in seedlings. Tria caused a 1.3-fold increase in osmotic regulator proline synthesis to alleviate Pb stress. Phenolics, soluble protein, and DPPH free radical scavenging activity were enhanced by Tria application, suggesting that exogenous Tria could be employed to improve plant tolerance to Pb stress.
Keywords: Phaseolus vulgaris L.; growth; lead stress; seed priming; triacontanol.