How does glutamine synthetase activity determine plant tolerance to ammonium?

Abstract

The wide range of plant responses to ammonium nutrition can be used to study the way ammonium interferes with plant metabolism and to assess some characteristics related with ammonium tolerance by plants. In this work we investigated the hypothesis of plant tolerance to ammonium being related with the plants' capacity to maintain high levels of inorganic nitrogen assimilation in the roots. Plants of several species (Spinacia oleracea L., Lycopersicon esculentum L., Lactuca sativa L., Pisum sativum L. and Lupinus albus L.) were grown in the presence of distinct concentrations (0.5, 1.5, 3 and 6 mM) of nitrate and ammonium. The relative contributions of the activity of the key enzymes glutamine synthetase (GS; under light and dark conditions) and glutamate dehydrogenase (GDH) were determined. The main plant organs of nitrogen assimilation (root or shoot) to plant tolerance to ammonium were assessed. The results show that only plants that are able to maintain high levels of GS activity in the dark (either in leaves or in roots) and high root GDH activities accumulate equal amounts of biomass independently of the nitrogen source available to the root medium and thus are ammonium tolerant. Plant species with high GS activities in the dark coincide with those displaying a high capacity for nitrogen metabolism in the roots. Therefore, the main location of nitrogen metabolism (shoots or roots) and the levels of GS activity in the dark are an important strategy for plant ammonium tolerance. The relative contribution of each of these parameters to species tolerance to ammonium is assessed. The efficient sequestration of ammonium in roots, presumably in the vacuoles, is considered as an additional mechanism contributing to plant tolerance to ammonium nutrition.

Hydroponic culturing upregulates sucrose and glutamine metabolism by enhancing their utilization via intermediates of aerobic pathway in wheat

“…As NH 4 NO 3 increases the activity of nitrogen metabolizing and aminotransferases enzymes, we therefore speculate that high concentrations of ammonium nitrogen in nutrient solution may lead to accumulation of toxic amounts of ammonium ions in the plants (Britto and Kronzucker 2002;Lasa et al 2002). Similar to our observation, Lewis et al (1987), Britto and Kronzucker (2002) and Cruz et al (2006) proposed that, the presence of nitrate in the nutrient medium suppresses an over-rapid absorption of the ammonium ion and the consequent over-allocation of carbon to nitrogenous compounds, most of which are transported out of the root to the shoot.…”

The influence of organic manure formulated from goat manure on growth and yield of tomato (Lycopersicum esculentum)

“…Kawamura-Aoyama et al (2014) maintain that vegetative growth can be increased even in other crops such as lettuce when grown in organic nutrient solution degraded by microorganisms. This is because there are sufficient levels of nitrate in nutrient solutions formulated from organic sources such as animal manure, since most vegetable crops prefer nitrate (N) over ammonium (N) (Cruz et al, 2006). As is evident from the current study's levels of nitrate in the organic nutrient solution, it was sufficient to produce vegetative growth in tomato plants similar to when they were grown under conventional nutrient solution, and significantly more improved more than when plants were grown without the addition of either manure or fertilizer.…”

Tolerancia de lisianthus (Eustoma grandiflorum (Raf.) Shinn.) a elevadas concentraciones de amonio en la solución nutritiva

“…This concentration of NH 4 + is located above the level that most species of plants stand; Coraspe-León et al (2009) and Furlani et al (1999) en las concentraciones de aminoácidos en el citoplasma también pueden estar involucrados en la regulación del crecimiento y absorción de iones (Causin y Barneix, 1993) cuando la planta realizan un almacén eficiente de NH 4 + en las raíces, principalmente en la vacuola, lo cual se considera como un mecanismo adicional que contribuye la tolerancia al suministro de NH 4 + (Cruz et al, 2006).…”

“…Changes in amino acid concentrations in the cytoplasm may also be involved in growth regulation and absorption of ions (Causin and Barneix, 1993) when the plant efficiently stores NH 4 + in the roots, mainly in the vacuole, which is considered as an additional mechanism contributing to the tolerance of NH 4 + supply (Cruz et al, 2006). vegetal aéreo se obtuvo con el aumento de la proporción de NH 4 + en la SN, pero fue más marcada la extracción en plantas nutridas con la relación 50:50.…”