Physiological and Phytochemical Responses to Cadmium Stress in Three Wheat Cultivars

Wheat cultivars differ markedly in their responses to cadmium (Cd), but it remains unclear how these differences are reflected across physiological and biochemical levels. This study investigated the physiological, enzymatic, and phenolic responses of three Slovak wheat cultivars representing different genomic backgrounds (tetraploid emmer wheat Zirnitra and hexaploid bread wheat Sunanka, and Ilona) exposed to 50 mg L−1 Cd2+ (as CdCl2) for 10 days, integrating growth and pigment responses with Cd accumulation, subcellular partitioning, pathogenesis-related (PR) enzyme activities, and targeted profiling of phenolic metabolites. Cd similarly reduced shoot fresh weight in all cultivars, while chlorophyll content declined significantly in Sunanka and Ilona but remained stable in Zirnitra. All cultivars strongly restricted root-to-shoot Cd translocation, with Cd predominantly recovered in the combined cytosolic/vacuolar fraction. The integrated analysis revealed particularly pronounced cultivar-specific differences in phenolic profiles. Sunanka shoots showed a reciprocal rutin (RUT)–quercetin (QUER) response, with RUT becoming undetectable and QUER strongly accumulating, whereas Ilona roots showed depletion of trans-ferulic acid and chlorogenic acid accompanied by marked protocatechuic acid accumulation. In Zirnitra roots, RUT increased markedly, and root RUT was positively associated with Cd accumulation after FDR correction. PR-enzyme activities also responded in a cultivar-, tissue-, and activity-band-specific manner. Overall, the findings demonstrate that similar growth inhibition and restricted Cd translocation can coexist with distinct biochemical responses in wheat cultivars of different genomic backgrounds, highlighting root rutin accumulation as a candidate for further investigation in relation to Cd exposure.