Nitrate Addition Alleviates Ammonium Toxicity Without Lessening Ammonium Accumulation, Organic Acid Depletion and Inorganic Cation Depletion in Arabidopsis thaliana Shoots

Abstract

When ammonium is the sole nitrogen (N) source, plant growth is suppressed compared with the situation where nitrate is the N source. This is commonly referred to as ammonium toxicity. It is widely known that a combination of nitrate and ammonium as N source alleviates this ammonium toxicity (nitrate-dependent alleviation of ammonium toxicity), but the underlying mechanisms are still not completely understood. In plants, ammonium toxicity is often accompanied by a depletion of organic acids and inorganic cations, and by an accumulation of ammonium. All these factors have been considered as possible causes for ammonium toxicity. Thus, we hypothesized that nitrate could alleviate ammonium toxicity by lessening these symptoms. We analyzed growth, inorganic N and cation content and various primary metabolites in shoots of Arabidopsis thaliana seedlings grown on media containing various concentrations of nitrate and/or ammonium. Nitrate-dependent alleviation of ammonium toxicity was not accompanied by less depletion of organic acids and inorganic cations, and showed no reduction in ammonium accumulation. On the other hand, shoot growth was significantly correlated with the nitrate concentration in the shoots. This suggests that nitrate-dependent alleviation of ammonium toxicity is related to physiological processes that are closely linked to nitrate signaling, uptake and reduction. Based on transcript analyses of various genes related to nitrate signaling, uptake and reduction, possible underlying mechanisms for the nitrate-dependent alleviation are discussed.

Photosynthetic and Antioxidant Performance Are Differentially Affected by Short-Term Nitrogen Supply in Highbush Blueberry Cultivars at the Short-Term

“…Excess nitrogen is frequently associated with ammonium (NH 4 + ) toxicity in vascular plants (Hachiya et al, 2012). The negative impacts of a high NH 4 + accumulation in plant tissues might be a consequence of Discussion Nitrogen (N) is an essential nutrient for photosynthesis, plant growth and development.…”

Allosteric Regulation of Transport Activity by Heterotrimerization of Arabidopsis Ammonium Transporter Complexes in Vivo

“…However, supply of ammonium as the sole N form has a negative impact on root growth: The elongation of the primary and lateral roots is severely repressed, resulting in a stunted root phenotype while lateral root branching is stimulated (Lima et al, 2010;Rogato et al, 2010). In addition, excess ammonium intake unbalances cellular pH homeostasis and primary metabolism (Hachiya et al, 2012). Therefore, plant roots repress ammonium uptake at elevated ammonium supplies (Wang et al, 1993;Rawat et al, 1999;Lanquar et al, 2009), which implies the existence of ammonium sensing mechanisms and feedback regulation of ammonium uptake.…”

Response of radish seedlings ( Raphanus sativus L.) to different concentrations of ammoniacal nitrogen in absence and presence of silicon

“…In this way, it exerts influence on the growth of plant species and on the production of reserve substances and maturation. Ammoniacal nitrogen can bring some benefits to plants, because it acts as an important intermediary in many metabolic reactions (Britto and Kronzucker, 2002), has lower energy expenditure for its metabolism, and dispenses the reduction phases, which are required to the absorption of NO 3 - (Hachiya et al, 2012). However, elevated concentrations of NH 4 + lead to several issues: induces toxicity in plants, may lead to chlorosis in leaves, reduction of photosynthesis, lower plant performance, lower nutrient level, cation and metabolites mismatches, as well as a decrease of amino acids and organic acids (Britto and Kronzucker, 2002).…”