Ammonium nutrition modulates K⁺ and N uptake, transport and accumulation during salt stress acclimation of sorghum plants

ABSTRACT

NH₄⁺ nutrition has emerged as an effective approach to generate salt tolerance in sorghum plants. Our hypothesis was that salt-tolerance mechanisms in NH₄⁺-grown sorghum are related to rapid absorption and assimilation of NH₄⁺ as well as favorable K⁺ uptake. Sorghum plants were grown in nutrient solutions containing NO₃⁻ or NH₄⁺ and subjected to NaCl at 75 mM. Under control conditions, K⁺ uptake was more pronounced in NO₃⁻ than that of NH₄⁺-fed plants. Under salinity, NH₄⁺-grown plants showed lower Na⁺ and higher K⁺ contents than NO₃^–grown plants at 1 and 10 days after salt exposure, and thereby increased K⁺/Na⁺ ratio. The data indicate that NH₄⁺ does not increase K⁺ uptake under salt stress conditions, but decrease the K⁺ efflux and maintain an elevated K⁺/Na⁺ ratio in tissues. In parallel, sorghum plants displayed elevated NH₄⁺ uptake, evidenced by higher V_max for NH₄⁺, assimilating a higher amount of NH₄⁺ into amino acids in roots; whereas NO₃⁻-fed plants accumulated NH₄⁺ in the shoot. In conclusion, NH₄⁺-fed salt-stressed sorghum plants maintain favorable K⁺/Na⁺ homeostasis due to greater retention of K⁺ in tissues together with restricting control of Na⁺ accumulation and transport. S. bicolor face to NH₄⁺ toxicity by activating mechanisms for rapid inorganic N-assimilation.

KEYWORDS:

• Inorganic nitrogen
• ions uptake
• kinetic parameters
• salinity
• Sorghum bicolor

Acknowledgements

The Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Instituto Nacional de Ciência e Tecnologia em Salinidade (INCTSal) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for financial support.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

This work was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) [444807/2014-4]; Fundação Cearense de Apoio ao Desenvolvimento Científico e Tecnológico (FUNCAP) [5827691/2018].