Nitrate deficiency triggers a redox-auxin crosstalk that modulates root system plasticity in tomato

Nitrate (NO3−) availability is a primary determinant of root system architecture, with auxin serving as a pivotal mediator of N-responsive root development. Concurrently, hydrogen peroxide (H2O2) functions as a key signaling molecule that interacts with auxin to modulate root growth. Although the individual interactions of NO3−–auxin and auxin–H2O2 in controlling root plasticity have been extensively characterized, the coordinated interplay among N status, auxin dynamics, and H2O2 signaling in regulating root growth under NO3− deficiency remains to be elucidated. Therefore, this study aimed to verify whether auxins depend on H2O2 during the response of tomato roots to N deficiency. Micro-Tom (MT) plants were grown for 10 days in hydroponic systems under a sufficiency (1.0 mmol L−1) or deficiency (0.1 mmol L−1) of NO3− and both with and without the auxin transport inhibitor, 2,3,5-triiodo-benzoic acid (TIBA), and the inhibitor of H2O2 accumulation (catalase). The experiment was conducted in a completely randomized design in a 2x4 factorial scheme with three replicates. Shoot length and dry biomass as well as root dry biomass, length, area and volume were analyzed. In addition, the malondialdehyde (MDA) and H2O2 contents were also quantified. NO3− deficiency reduced shoot growth and promoted higher root growth. Furthermore, TIBA inhibited root growth under both NO3− conditions. Additionally, the presence of catalase during NO3− deficiency resulted in reduced root volume, area, and dry mass. These findings indicate that auxins could rely on H2O2 for tomato root responses to NO3− deficiency. Therefore, our study demonstrated a complex interaction between auxin, H2O2, and N-deficiency that modulates root development.