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. (C) 2012 Elsevier GmbH. All rights reserved.