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

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 NO(3)(-)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.