Nitrate and ammonium nutrition of plants: Effects on acid/base balance and adaptation of root cell plasmalemma H⁺ATPase

Abstract

The increase of rhizosphere pH in the course of nitrate nutrition results from H+ consumption in the external medium during uptake of NO3− in a H+ co‐transport and from internal OH− production during nitrate reduction. Synthesis of organic acids for NH4+ assimilation as well as strong partial depolarization of membrane potential with NH4+ uptake are the important reasons for rhizosphere acidification during ammonium nutrition. Despite differences in proton balance depending on N form, cytoplasmic pH changes are small due to physico‐chemical buffering, biochemical pH regulation, H+ inclusion in vacuoles, and H+ release into the rhizosphere. Because of the large capacity for proton excretion the plasmalemma H+ ATPase of root cells plays an essential role during ammonium nutrition. An increase of the kinetic parameter Vmax after ammonium nutrition relative to nitrate nutrition suggests that the capacity of H+ release may be adjusted to the particular requirements of ammonium nutrition. Moreover, H+ ATPase is adjusted not only quantitatively but also qualitatively. The increase of the kinetic parameter km as well as the capability of the plasmalemma vesicles in vitro to establish a steeper pH gradient favours the supposition that H+ ATPase isoforms are formed which allow H+ release into the rhizosphere under conditions of low pH or poor H+ buffering of the soil. In this respect species differences exist, e.g. between maize (efficient adaptation) and faba bean (poor adaptation).

Differential effects of nitrogen forms on cell wall phosphorus remobilization in rice (Oryza sativa) are mediated by nitric oxide, pectin content and the expression of the phosphate transporter OsPT2

“…When plants absorb NH 4 + , their roots secrete protons, thereby acidifying their rhizosphere and causing a release of P from the soil. However, in this study, we buffered the nutrient solution with 5 mM MES at pH 5.5, and at a stable pH, the hydrolytic activity or pumping activity of the H + -ATPase should be the same under both NH 4 + and NO 3 2 treatment (Schubert and Yan, 1997;Zhu et al, 2009). Furthermore, because of the absence of both soluble and insoluble P in the 2P hydroponic solution, the involvement of the pH is excluded.…”

“…NH 4 + and NO 3 2 are the two major N sources that are taken up by plant roots (Marschner, 1995;Falkengren-Grerup et al, 2000). In general, with the absorption of NH 4 + by plants, the related proton release decreases the pH of the rhizosphere (Wang et al, 1993;Mistrik and Ullrich, 1996;Schubert and Yan, 1997;Zhao et al, 2009), which leads to increased solubility and uptake of P by the plants (Sarkar and Jones, 1982;Hoffmann et al, 1994). The opposite appears to be true with the uptake of N in the form of NO 3 2 (Smiley, 1974;Marschner and Römheld, 1983;Moorby et al, 1985;Watanabe et al, 1998).…”

Proton toxicity interferes with the screening of common bean (Phaseolus vulgaris L.) genotypes for aluminium resistance in nutrient solution

“…Because of the high proton sensitivity of common bean, Massot et al (1990) classified six genotypes for Al resistance using a solution pH of 4.8, but without control of pH and also without monitoring Al activity in solution. The high proton sensitivity of common bean may be related to a low efficiency of the plasma-membrane proton ATPase (Yan et al, 1992(Yan et al, , 1998, and thus the inability to maintain the cytosolic pH leading to cell injury (Schubert and Yan, 1997).…”

Adaptation of H+-Pumping and Plasma Membrane H+ ATPase Activity in Proteoid Roots of White Lupin under Phosphate Deficiency

“…If this holds true, an adaptation of plasma membrane H ϩ ATPase in active proteoid roots can be expected. In fact, it has been demonstrated that plasma membrane H ϩ ATPase responds to a number of environmental factors, such as saline stress (Niu et al, 1993), low solution pH (Yan et al, 1998), nutrient supply (Schubert and Yan, 1997), and Fe deficiency (Delló rto et al, 2000). It is feasible to hypothesize that plasma membrane H ϩ ATPase of proteoid root cells may be involved in the release of citric acid and possibly plays a central role in the adaptation of white lupin to P deficiency.…”