pH-adjustment alleviates NH₄⁺-induced toxicity in Arabidopsis thaliana

Abstract

This work was conducted to evaluate the effect of N source (NH₄⁺/NO₃^-) and the implication of NH4+-induced acidification on plant development in Arabidopsis thaliana. seedlings were hydroponically cultivated during 21 days under three ratios of NO₃⁻/NH₄⁺ (mM); 2.5/0.0; 1.25/1.25, and 0.0/2.5. For each ratio, plants were cultivated under not controlled pH and adjusted pH at 6.2. Ammonium-fed plants (0.0/2.5) showed chlorosis if cultivated under uncontrolled pH. This symptom was associated with suppressions in plant growth, chlorophyll and iron contents as well as shoots hydration and nutrient concentration. Growth was limited with increasing NH₄⁺ medium-concentration. At pH 6.2, plants receiving only NH₄⁺ produced the same biomass as NO₃-fed ones. The mineral disturbances in plants grown on strictly NH₄⁺-medium (0.0/2.5) were alleviated under controlled pH. The activities of nitrate reductase (NR) and nitrite reductase (NIR) were lower in plants amended only with NH₄⁺ under uncontrolled pH. At adjusted pH, the NR activity was ameliorated but that of NIR was not ameliorated, suggesting hence that NR activity depended on medium pH but that of NIR was related only to the pool of NO₂^-. In conclusion, this work demonstrated that the adjustment of pH at 6.2 mitigated significantly the toxic effects of ammonium to A. thaliana.

Keywords:

• Arabidopsis thaliana
• N-source, pH
• biomass
• N-assimilation

Acknowledgments

This work was conducted in the Laboratoire de productivité végétale et contraintes environnementales (PVCE) Faculté des Sciences de Tunis and financially supported by the Tunisian ministry of High Education and Scientific research.

Authors’ contributions

Sabah M’rah and Tahar Ghnaya conducted the experiment and wrote the MS. Abdellah Chalh helped in statistical analysis and the correction of the MS. Nada Bensalem and Saoussen Ben Abdallah helped in the experiment design and Zeineb Ouerghi is the head of the laboratory and providing necessary help.

Disclosure statement

No potential conflict of interest was reported by the author(s).