Brassinolide ameliorates the detrimental effects of arsenic in tomato: Insights into iron and arsenic absorption, antioxidant capacity, nitrogen, and sulfur assimilation

The role of brassinosteroids (BRs) in enabling plants to respond effectively to adverse conditions is well known, though the precise mechanism of action that helps plants cope with arsenic (As) toxicity is still difficult to interpret. Therefore we tested the effect of brassinolide (BL) spray (0, 0.5, and 1 mg · L−1) on As (0, and 10 mg · L−1) stressed tomato defense responses As stress led to the induction of oxidative stress, impaired chlorophyll and nitrogen metabolism, and Fe uptake, in conjunction with a reduction in plant growth and biomass. BL spray, on the contrary, protected the photosynthetic system and helped plants grow better under As stress. This was achieved by controlling the metabolism of chlorophyll and proline and lowering the amounts of methylglyoxal and H2O2 through glyoxalase I and II and antioxidant enzymes. BL decreased arsenic accumulation by directing As sequestration towards vacuoles and increased Fe amount in the leaves and roots by regulating the expression of As (Lsi1 and Lsi2) and Fe (IRT1, IRT2, NRAMP1, and NRAMP3) transporters in As-stressed tomatoes. Furthermore, BL boosted adaptability against As phytotoxicity, while reducing the damaging impacts on photosynthesis, nitrogen metabolism, sulfur asimilation, and Fe absorption. These results offer a solid framework for the development of exogenous BRs-based breeding strategies for safer agricultural development. © 2024 Chinese Society for Horticultural Science (CSHS) and Institute of Vegetables and Flowers (IVF), Chinese Academy of Agricultural Sciences (CAAS).