Trolox-Mediated Protection of Secondary Metabolite Profiles in Cadmium-Stressed Vitis vinifera L. cv. Öküzgözü

Understanding the biochemical defense mechanisms of grapevines against heavy metal contamination is essential for developing sustainable viticulture practices in polluted environments. However, comprehensive knowledge about how antioxidant supplementation modulates secondary metabolite profiles under cadmium stress remains limited. We investigated phenolic compound accumulation, anthocyanin biosynthesis, and amino acid dynamics in three-year-old Vitis vinifera L. cv. Öküzgözü plants subjected to graduated cadmium concentrations (0, 5, 10, 20 ppm) with and without Trolox treatment (50 μM), followed by detailed metabolomic profiling. Both cadmium concentration and Trolox application significantly affected all metabolite classes (p < 0.001), with strong interaction effects for trans-p-coumaric acid, epicatechin, and quercetin among phenolics, and for delphinidin-3-glucoside, cyanidin-3-glucoside, and petunidin-3-glucoside among anthocyanins. Phenolic acid levels generally declined with increasing cadmium concentrations, while Trolox treatment partially restored gallic acid (4.12 vs. 0.96 μg g^-1 FW) and caffeic acid contents. Anthocyanin accumulation showed a similar trend, with pronounced reductions under cadmium stress but substantial recovery following Trolox supplementation, particularly for malvidin-3-glucoside (11.84 vs. 3.41 μg g^-1 FW). Amino acid metabolism exhibited a divergent pattern compared to secondary metabolites: total amino acid contents increased with higher cadmium levels, reflecting stress-induced nitrogen mobilization, whereas Trolox application moderated these elevations and maintained more balanced profiles. Distinct clustering of treatments was evident in the metabolic data, with Trolox-supplemented plants forming groups characterized by elevated phenolic and anthocyanin levels, and cadmium-stressed plants separated by enhanced amino acid accumulation. Principal component analysis explained 86.96% of the total variance (PC1 = 79.23%, PC2 = 7.73%), clearly distinguishing treatment effects. We conclude that Trolox application significantly enhances grapevine resilience to cadmium toxicity through comprehensive protection of secondary metabolite pathways. The differential metabolic responses between treated and untreated plants provide insights for antioxidant-based mitigation strategies, while the quantitative metabolite profiles identified offer valuable parameters for assessing vine health and fruit quality potential under heavy metal contamination scenarios.