Regulation of Ammonium Cellular Levels is An Important Adaptive Trait for the Euhalophytic Behavior of Salicornia europaea.

Salinization of agricultural land is a devastating phenomenon which will affect future food security. Understanding how plants survive and thrive in response to salinity is therefore critical to potentiate tolerance traits in crop species. The halophyte has been used as model system for this purpose. High salinity causes NH accumulation in plant tissues and consequent toxicity symptoms that may further exacerbate those caused by NaCl. In this experiment we exposed Salicornia plants to five concentrations of NaCl (0, 1, 10, 50 and 200 mM) in combination with two concentrations of NHCl (1 and 50 mM). We confirmed the euhalophytic behavior of Salicornia that grew better at 200 vs. 0 mM NaCl in terms of both fresh (+34%) and dry (+46%) weights. Addition of 50 mM NHCl to the growth medium caused a general growth reduction, which was likely caused by NH accumulation and toxicity in roots and shoots. When plants were exposed to high NHCl, high salinity reduced roots NH concentration (-50%) compared to 0 mM NaCl. This correlates with the activation of the NH assimilation enzymes, glutamine synthetase and glutamate dehydrogenase, and the growth inhibition was partially recovered. We argue that NH detoxification is an important trait under high salinity that may differentiate halophytes from glycophytes and we present a possible model for NH detoxification in response to salinity.