Effects of Cadmium–Selenium Interaction on Glyoxalase and Antioxidant Systems of Pisum sativum Germinating Seeds

Anthropogenic activities lead to plant exposure to increasing concentrations of heavy metals, including cadmium (Cd). In this regard, alleviation of Cd stress by selenium (Se) addition to pea seeds germination medium was assessed. Different concentrations of Se (0, 5, and 15 µM) were combined with CdCl₂ (0 or 300 µM). The addition of Se reversed the detrimental effects of Cd on seedling growth in terms of biomass production. Seedling exposure to Cd stress induced the loss of membrane integrity, as manifested by the increased lipoperoxidation byproduct (malondialdehyde) content and the lipoxygenase activity. The enrichment of germination medium with Se reduced Cd accumulation in the plant tissues (more than 40% in radicles and epicotyls) and counteracted the Cd effects on membrane integrity traits. The Se protective effects on cell membrane were associated with proline over-accumulation in Cd-exposed radicles and epicotyls (32% and 28% increase, respectively). The Se-induced proline accumulation could be a consequence of its increased biosynthesis via Δ¹-pyrroline-5-carboxylate synthetase upregulation, concomitantly with a decrease of its oxidation by the proline dehydrogenase enzyme. Besides, when supplied in combination with Cd, the highest Se concentration abolished the Cd-triggered decrease of glyoxalase I and glyoxalase II activities, leading to the reduction of methylglyoxal levels. The amelioration of the cellular redox state under the combination of Cd with Se was reflected by the reduction of hydrogen peroxide accumulation. This positive impact was mediated by the stimulation of the Cd-downregulated superoxide dismutase and ascorbate peroxidase activities and the reduction of the Cd-stimulated catalase. Overall, the current findings suggest that the enrichment of the seeds germination medium with Se appeared as a suitable option to ameliorate pea seedling tolerance to Cd stress. The present study could be extended to crops grown on the soil to confirm the protecting role of Se against heavy metal pollution.