Sulfur Mitigates Cadmium Toxicity in Lettuce via Phytochelatins and the AsA–GSH Cycle

Cadmium (Cd), a toxic heavy metal, accumulates in crops and poses health risks. Sulfur (S) enhances plant metabolism and tolerance to heavy metal stress. In this hydroponic study, we investigated the effects of S on lettuce growth, sulfur-containing compounds, and Cd uptake under Cd stress. S promoted growth, reduced Cd accumulation, and increased phytochelatins (PCs) and PCs-Cd complexes, limiting Cd translocation. Subcellular analysis suggested decreased Cd in organelles and enhanced sequestration in vacuoles and the cell wall, while S alleviated oxidative damage via the AsA-GSH cycle. These findings, obtained under hydroponic conditions, may differ from those of field environments and require further validation. This study is novel in directly quantifying PCs-Cd complexes and analyzing subcellular Cd distribution, providing environmentally relevant insights for strategies to reduce Cd accumulation in crops and improve food safety.