Ammonium Toxicity Alleviation by Silicon is Dependent on Cytokinins in Tomato cv. Micro-Tom
2022
Barreto, Rafael Ferreira | de Mello Prado, Renato | Lúcio, José Clebson Barbosa | López-Díaz, Isabel | Carrera, Esther | Carvalho, Rogério Falleiros
The objectives were to verify the effects of the lack of cytokinins (CKs), comparing tomato cv. Micro-Tom (MT, wild type) to MT CKX2 (transgenic with less CKs) fed with nitrate (NO₃⁻) and ammonium (NH₄⁺), in the presence and absence of silicon (Si); verify if the attenuation of NH₄⁺ toxicity by Si depends on the increase of CKs in MT; and verify if 6-benzyladenine (6-BA) attenuates NH₄⁺ toxicity in MT. Three experiments were performed with treatments via nutrient solution. First, MT and MT CKX2 were grown with NO₃⁻ or NH₄⁺ (5.9 mmol L⁻ ¹), in the absence and presence of Si (1.28 mmol L⁻ ¹). Second, MT was grown with NO₃⁻ or NH₄⁺ (5.9 mmol L⁻ ¹), in the absence and presence of Si (1.28 mmol L⁻ ¹). Third, MT was grown with NO₃⁻ or NH₄⁺ (5.9 mmol L⁻ ¹) and 6-BA (from 1e⁻¹⁰ to 1e⁻⁶ mol L⁻¹) associated with NH₄⁺. The MT and MT CKX2 had a decrease of 18% and 48% in the shoot dry weight, respectively, when fed with NH₄⁺, compared to NO₃⁻. Si attenuated NH₄⁺ toxicity in MT, but not in MT CKX2. This attenuation in MT was accompanied by a decrease in trans-zeatin (tZ) content in the roots and increase in the shoots. 6-BA did not improve the shoot growth of MT fed with NH₄⁺. In conclusion, the alleviation of NH₄⁺ toxicity by Si was dependent on the increase in tZ content in shoots. In CK-deficient plants, Si did not alleviate NH₄⁺ toxicity, and 6-BA did not alleviate NH₄⁺ toxicity in MT shoots.
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