Nitrogen Assimilation in Barley (Hordeum vulgare L. cv. Mazurka) in Response to Nitrate and Ammonium Nutrition

Humic substances stimulate maize nitrogen assimilation and amino acid metabolism at physiological and molecular level

“…The nitrate reductase (NR EC 1.7.1.1) activity was assayed according to Lewis and collaborators [49] and expressed as unit per milligramme protein. One unit corresponds to the production of 1 μmol of NO 2 − per minute at 25°C.…”

Futile transmembrane NH 4 + cycling: A cellular hypothesis to explain ammonium toxicity in plants

“…However, in many cases, toxicity is equally observed in pH-buffered media (13), and a recent study on pea (Pisum sativum), known to be ammonium sensitive, has discounted the occurrence of ammonium-induced cytosolic pH disturbance (12). Others have suggested that carbohydrate limitation may contribute to the toxicity syndrome, based on the finding that NH 4 ϩ per se is not translocated to the shoot in most plants (14), and, thus, all C skeletons for N assimilation must be provided in roots, causing local C deprivation (15). In some cases, external provision of ␣-ketoglutarate, a key carbon source for N assimilation, alleviated toxicity symptoms (4), but in other cases it failed to enhance NH 4 ϩ metabolism (16), suggesting that other factors may limit NH 4 ϩ assimilation.…”

Plant N Fluxes and Modulation by Nitrogen, Heat and Water Stresses: A Review Based on Comparison of Legumes and Non Legume Plants

“…In non legume plants such as maize supplied with nitrate, the xylem sap has higher glutamine concentration while maize fed with ammonium has higher asparagine concentration in xylem (Murphy & Lewis, 1987). Glutamine and asparagine are also the predominant amino compounds in oilseed rape (Balint & Rengel, 2011) or barley (Lewis et al, 1982). Phloem sap has an alkaline pH (7 to 8.5) and transports mostly sucrose, in some species fructanes, raffinose-family oligosaccharides (raffinose, stachyose, verbascose), and a tiny amount of hexoses (glucose and fructose) except in wounded tissues, alcohol sugars and amino acids.…”