Nitrate alleviates ammonium toxicity in wheat (Triticum aestivumL.) by regulating tricarboxylic acid cycle and reducing rhizospheric acidification and oxidative damage

Abstract

Ammonium (NH 4 + ) is one of the most important nutrients required by plants. However, a high concentration of NH 4 + as the sole nitrogen source suppresses plant growth. Although nitrate (NO 3 − ) can alleviate NH 4 + toxicity, the mechanisms underlying this ability have not been fully elucidated. In this study, wheat plants were cultivated in hydroponic solution with 7.5 mM NO 3 − (control), 7.5 mM NH 4 + (sole ammonium, SA) or 7.5 mM NH 4 + plus 1.0 mM NO 3 − (ammonium and nitrate, AN). The results showed that compared with the control, the SA treatment significantly decreased root growth, protein content and the concentrations of most intermediates and the activity of enzymes from the tricarboxylic acid (TCA) cycle. Moreover, increased the activity of plasma membrane H + -ATPase and the rate of H + efflux along roots, caused solution acidification, and increased the activity of mitochondrial respiratory chain complexes I–IV and the contents of protein-bound carbonyls and malondialdehyde in roots. SA treatment induced ultrastructure disruption and reduced the viability of root cells. Compared with the SA treatment, the AN treatment increased root growth, protein content, the concentrations of most intermediates and the activity of enzymes from the TCA cycle. Furthermore, AN treatment decreased the rate of H + efflux, retarded medium acidification, decreased protein carbonylation and lipid peroxidation in roots and relieved ultrastructure disruption and increased the viability of root cells. Taken together, these results indicate that NO 3 – -dependent alleviation of NH 4 + toxicity in wheat seedlings is closely associated with physiological processes that mediate TCA cycle, relieve rhizospheric acidification and decrease the production of ROS and oxidative damage.

Nitrate transporter NRT1.1 and anion channel SLAH3 form a functional unit to regulate nitrate‐dependent alleviation of ammonium toxicity

“…The authors proposed that medium alkalization by nitrate absorption and assimilation may play a role in ammonium detoxification (Hachiya et al, 2012). This notion is supported by a recent study in wheat that NO 3 − supply can inhibit H + efflux mediated by NH 4 + uptake (Du et al, 2021). Previously, our studies indicated that a NO 3 − efflux channel SLAH3 is involved in nitrate-dependent alleviation of ammonium toxicity and, importantly, the medium alkalization greatly contributes to this process (Zheng et al, 2015;Sun et al, 2021).…”

Nitrate alleviates ammonium toxicity in Brassica napus by coordinating rhizosphere and cell pH and ammonium assimilation

“…In contrast to NRT‐mediated uptake, which is typically associated with H + influx, uptake via AMTs is driven by the electrical potential generated by PM H + ‐ATPase to maintain charge balance (Meier et al., 2020; Vidal et al., 2020; Xu et al., 2012). may assist in dissipate H + efflux caused by uptake, which can lead to rhizosphere alkalization and alleviate toxicity (Du et al., 2021; Xiao et al., 2022). In Arabidopsis , SLAH3, a permeable channel, facilitates efflux from the root and participates in ‐dependent mitigation of toxicity (Zheng et al., 2015).…”

The alleviation of ammonium toxicity in plants

“…A small amount of NO 3 − is able to effectively alleviate NH 4 + toxicity in many plant species such as maize, wheat, tomato, cucumber, and Arabidopsis , referred to as NO 3 − ‐dependent alleviation of NH 4 + toxicity (Roosta and Schjoerring, 2008; Garnica et al, 2010; Hachiya et al, 2012; Du et al, 2021). Although NO 3 − ‐based N fertilizers have been used to antagonize NH 4 + toxicity in agricultural practice for a long time, how NO 3 − detoxifies NH 4 + has been blurred until very recently (Hachiya et al, 2012).…”

“…Nitrate, however, was found to relieve NH 4 + toxicity without affecting NH 4 + accumulation, organic acids, and inorganic cations (Hachiya et al, 2012). Instead, several studies in wheat, cucumber, and Arabidopsis (Wang et al, 2004; Roosta and Schjoerring, 2007; Du et al, 2021) have shown that NO 3 − supply can accelerate NH 4 + assimilation, promote organic acid synthesis in the TCA cycle, and maintain inorganic cation levels. In addition, NO 3 − may function as a signaling molecule to modulate the signal pathways of hormones such as CK and IAA, as either low or high levels of NO 3 − are sufficient to alter hormone levels under high‐NH 4 + conditions (Garnica et al, 2010).…”

“…-dependent alleviation of NH 4 + toxicity (Roosta and Schjoerring, 2008;Garnica et al, 2010;Hachiya et al, 2012;Du et al, 2021).…”