Sugar exudation by roots of kallar grass [ Leptochloa fusca (L.) Kunth] is strongly affected by the nitrogen source

Abstract

Exudation of sugars (glucose, fructose and sucrose) and that of cations and anions from intact roots of kallar grass [Leptochloa fusca (L.) Kunth] grown hydroponically with ammonium or nitrate (3 mM) as N source was investigated. In different experiments, plants grown on ammonium had slightly higher sugar contents than nitrate-grown plants, but their total sugar exudation during a 2-h period was up to 79-fold higher than under nitrate nutrition. Relative root exudation of inorganic anions and cations and that of amino acids (as a percentage of the internal contents exuded per time) was either similar or slightly higher from ammonium-grown than from nitrate-grown plants. Analysis of root architectural parameters revealed that ammonium-grown plants had a higher number of root tips/side roots per gram root fresh weight than nitrate-grown plants, whereas other root parameters, viz. length, diameter, volume and surface area were similar under the two N sources. A majority of the fine roots having diameter up to 0.4 mm represented up to 86% of the total root length, 64% of the total root surface area, and 35% of the total root volume; the root length and surface area per root system of that major root population were similar in ammonium- and nitrate-grown plants. Apparently, root architecture was not responsible for the different exudation rates. Within 12-24 h after shifting ammonium-grown plants to nitrate nutrition, root sugar levels and visible root architecture remained unchanged, yet the sugar exudation rate was reduced 30-fold. Short-term uptake of [14C]glucose (10 microM) from the rooting medium was similar for ammonium- and nitrate-grown plants. Thus, the very different sugar exudation rates were neither related to internal root sugar concentration, nor to the different root architecture, nor to differential resorption of sugars by ammonium- versus nitrate-grown plants. Increased external Ca2+ did not alter sugar exudation, and decreased external pH (4.5) only slightly increased sugar exudation from roots of nitrate-grown plants kept at pH 6.5. It is suggested that the much higher sugar exudation in response to ammonium may facilitate the ecologically and economically important association of diazotrophs with kallar grass roots.

Wheat growth in a saline sandy loam soil as affected by N form and application rate

“…In contrast to the findings of Al-Mutawa and ElKatony (2001), Cox and Reisenauer (1973), Frechilla et al (2001), Inal and Tarakcioglu (2001), Lewis et al (1989) and Mahmood and Kaiser (2003) the results of this study indicated that, compared to NO 3 −N, NH 4 −N nutrition resulted in higher shoot and root dry weights at rates higher than N50. Increasing N addition may have resulted in increasing plant protein content and photosynthetic capacity (Cox and Reisenauer 1973), thus stimulating plant growth.…”

“…In studies conducted in hydroponics, NO 3 −N was taken up at higher rates by maize compared to NH 4 −N in saline solutions with EC 6-8 dS m −1 (Lewis et al 1989). Also, compared to NH 4 + , NO 3 − nutrition increased plant uptake of Ca 2+ , Mg 2+ , K + and N and plant biomass at EC 10 dS m −1 induced using NaCl (Mahmood and Kaiser 2003). Moreover, in a solution with EC 15 dS m −1 , NO 3 −N uptake by barley increased with increasing concentration of Ca 2+ salts (Ward et al 1986).…”

“…Under non-saline conditions, most plant species exhibit preference for NO 3 − compared to NH 4 + nutrition (Al-Mutawa and El-Katony 2001). Compared to NH 4 −N, NO 3 −N nutrition increased the uptake of cations such as Ca 2+ , Mg 2+ and K + (Cox and Reisenauer 1973;Mahmood and Kaiser 2003). Nitrate nutrition can cause an increase in the rhizosphere pH through OH − and HCO 3 − release which can enhance mobilization of soil P in acidic soils (Gahoonia et al 1992).…”

The influence of root assimilated inorganic carbon on nitrogen acquisition/assimilation and carbon partitioning

“…The fact that the organic acids accounted for a relatively small proportion of the exuded label probably reflects the fact that the plants were grown with adequate P nutrition (2 m). Phloem-derived sugars translocated through the root apoplast may 'leak' into the external solution (Jones & Darrah, 1993;Marschner, 1995), although this notion has been challenged by work on Leptochloa fusca, which may sustain diazotrophic bacteria with sugar exudates (Mahmood et al, 2002).…”

Variations in the growth, oil quantity and quality, and mineral nutrients of chamomile genotypes under salinity stress

“…It has been found that organic fertilization and mineral elements such as phosphorus and nitrogen can regulate plant drought stress responses by maintaining a higher relative water content, lower malondialdehyde, and promoting antioxidant enzyme activity such as superoxide dismutases and peroxidase (Li-Ping et al, 2006). N uptake and metabolism affect plant nutrient composition (Kováčik et al, 2012), contributing to nutrient balance and plant resistance to salt-stress (Mahmood and Kaiser 2003;Abdelgadir et al, 2005). Therefore, application of appropriate N fertilizer rate and source is a requirement of good agricultural practices in chamomile, which can affect not only quantitative traits but also its qualitative traits such as pharmaceutical properties and nutritional values (Andrzejewska and WoropajJanczak 2014).…”