Ammonium enhances resistance to salinity stress in citrus plants.

In this work, we demonstrate that NH₄⁺ nutrition in citrange Carrizo plants acts as an inducer of resistance against salinity conditions. We investigated its mode of action and provide evidence that NH₄⁺ confers resistance by priming abscisic acid and polyamines, and enhances H₂O₂ and proline basal content. Moreover, we observed reduced Cl⁻ uptake as well as enhanced PHGPx expression after salt stress. Control and N-NH₄⁺ plants showed optimal growth. However, N-NH₄⁺ plants displayed greater dry weight and total lateral roots than control plants, but these differences were not observed for primary root length. Our results revealed that N-NH₄⁺ treatment induces a similar phenotypical response to the recent stress-induced morphogenetic response (SIMRs). The hypothesis is that N-NH₄⁺ treatment triggers mild chronic stress in citrange Carrizo plants, which might explain the SIMR observed. Moreover, we observed modulators of stress signaling, such as H₂O₂ in N-NH₄⁺ plants, which could acts as an intermediary between stress and the development of the SIMR phenotype. This observation suggests that NH₄⁺ treatments induce a mild stress condition that primes the citrange Carrizo defense response by stress imprinting and confers protection against subsequent salt stress.