Short-Term Cadmium and Lead Exposure in Common Buckwheat: Metal Accumulation, Physiological Responses, and Compositional Changes

Cadmium (Cd) and lead (Pb) contamination may alter common buckwheat (Fagopyrum esculentum Moench cv. ‘Korona’) physiology and composition. The objective was to determine whether common buckwheat maintains physiological performance under controlled Cd and Pb exposure while assessing metal transfer to harvested achenes. A 12-day in vitro phytotoxicity assay based on seed germination and root elongation and a six-week pot experiment were conducted. Cd had a stronger impact on in vitro seed germination and root growth than Pb. Under the highest metal treatments, soil concentrations reached 14,733.98 µg g−1 DW for Cd and 5621.60 µg g−1 DW for Pb; concentrations in leaves and achenes were substantially lower, although Cd transfer to the achenes remained relevant to food safety. Adult plants showed no consistent treatment-related changes in leaf water content, photosynthetic pigments, or Fv/Fm. Biochemical analyses detected treatment effects in proline, H2O2, SOD, CAT, and total phenolics. The treatment with 1000 mg L−1 of Cd showed the highest leaf SOD activity and mature-achene total phenolic content. The largest observed compositional difference was the high lysine content under 5000 mg L−1 of Cd in leaves and mature achenes, but this coincided with substantial Cd contamination and therefore cannot be interpreted as biofortification or a nutritional benefit. Overall, responses were non-monotonic and organ-specific, indicating substantial physiological adjustment during short-term exposure while confirming Cd transfer to mature achenes as a food-safety concern.