Thidiazuron-induced growth and developmental changes reshape metabolic, photosynthetic and transcriptomic signatures in Arabidopsis thaliana seedlings.

Thidiazuron (TDZ) is a synthetic growth regulator with cytokinin-like activity, widely used in biotechnology, but its physiological effects during the early stages of plant development are not yet fully understood. In this study, the impact of increasing concentrations of TDZ on the germination and early development of Arabidopsis thaliana was evaluated, with particular attention to physiological responses and their dose-dependent patterns. Seeds of the Col-0 ecotype were germinated in the presence of TDZ and analyzed using integrated approaches including morphological observations, photosynthetic efficiency measurements, and metabolic and hormonal profile analysis. The results show that low concentrations of TDZ do not significantly alter the main physiological parameters, while higher doses induce progressive alterations in cotyledon vascular pattern, hormonal imbalances, and a reduction in photosynthetic efficiency, indicating a functional impairment. Transcriptomic analysis revealed coordinated modulation of genes involved in hormonal regulation, energy metabolism, and stress responses, consistent with the observed phenotypes. Overall, the study demonstrates that TDZ exerts distinct and highly dose-dependent physiological effects, delineating a continuum ranging from responses compatible with normal development to those indicative of impaired development to conditions of physiological stress, and providing useful insights for a critical assessment of the benefits and risks associated with the use of this compound.