Cotton root and shoot response to localized supply of nitrate,phosphate and potassium: Split-pot studies with nutrient solution and vermiculitic soil

Vertical stratification of plant-available K in vermiculitic soil profiles contributes to a late-season K deficiency that limits cotton (Gossypium hirsutum L.) yields on affected soils. Split-root solution culture and split-pot soil experiments were conducted to determine whether root distribution and cultivar differences in root extension in these stratified profiles result from a compensatory response to localized enrichment with NO₃-N, PO₄-P, and/or K in the root zone. Compensatory root growth was greatest in response to localized NO₃-N enrichment. For two cultivars examined in solution culture, 74% of new root development occurred in the half-pot providing 90% of the total NO₃-N supply. Only 60% of cultivar root development occurred in the half-pot providing 90% of the PO₄-P. No compensatory root growth was observed in response to localized K enrichment. In the split-pot system, the proportion of total root surface area developing in a half-pot was highly correlated with localized soil NO₃-N levels (r²=0.81), while increased K availability in one half of the root zone did not affect root distribution. Mean soil NO₃-N supply to the whole root system determined shoot N accumulation (r²=0.97). Shoot K accumulation was not related to soil K availability but was strongly correlated with mean root surface area density (r²=0.86). Cultivar Acala GC510, known to be less sensitive to K deficiency than Acala SJ-2, had significantly larger root diameter in all nutrient-supply environments. Under conditions of K stress, Acala GC510 had increased root branching and allocated greater dry matter to roots relative to shoots than Acala SJ-2. The results demonstrate that K acquisition by cotton is strongly influenced by the quantity and distribution of NO₃-N in the root zone through its effects on root proliferation, and that distinct cultivar differences associated with crop performance on low K soils can be detected in short-term, solution culture growth systems.     

Root growth and nitrate utilization of maize cultivars under field conditions

In a 2-year field study conducted on a high fertilized Gleyic Luvisol in Stuttgart-Hohenheim significant differences among 10 maize cultivars were observed in soil nitrate depletion. The different capability of the cultivars to utilize nitrate particularly from the subsoil was positively correlated with (a) shoot N uptake at maturity, and (b) root length density (L_v) in the subsoil layers at silking. Critical root length densities for nitrate uptake were estimated by (a) calculating uptake rates per unit root length (U), (b) subsequent calculation of needed nitrate concentration in soil solution (C₁) to sustain calculated U according to the Baldwin formula, and (c) reducing measured L_v and proportionate increase of U until needed concentration equaled measured concentration. Uptake rate generally increased with soil depth. Critical root length densities for cultivar Brummi (high measured root length densities and soil nitrate depletion) at 60–90 cm depth ranged from 7 % (generative growth) to 28 % (vegetative growth) of measured L_v Measured root length density of each other cultivar was higher than critical root length density for Brummi indicating that the root system of each cultivar examined would have been able to ensure N uptake of Brummi. Positive relationships between root length density and nitrate utilization as indicated by correlation analysis therefore could not be explained by model calculations. This might be due to simplifying assumptions made in the model, which are in contrast to non-ideal uptake conditions in the field, namely irregular distribution of roots and nitrate in the soil, limited root/soil contact, and differences between root zones in uptake activity. It is concluded from the field experiment that growing of cultivars selected for high N uptake-capacity of the shoots combined with high root length densities in the subsoil may improve the utilization of a high soil nitrate supply.     

Al avoidance and Al tolerance ofMucuna pruriens var.utilis: Effects of a heterogeneous root environment and the nitrogen form in the root environment

InMucuna pruriens var.utilis, grown with nitrate-N in a hydroponic split-root system, an Al avoidance reaction of root growth was observed, which was ascribed to local P stress in the Al containing compartment. The Al avoidance reaction was similar to the avoidance ofMucuna roots of acid subsoil in the field where roots grew preferentially in the topsoil. In the present paper the effect of different N forms (NO₃ ^– and NH₄ ⁺) on the reactions ofMucuna to Al were studied, since in acid soils N is present as a mixture of NO₃ ^– and NH₄ ⁺. No interaction between the N form and Al toxicity was found. A hydroponic split-root experiment with NH₄NO₃ nutrition, which is comparable to the situation in the field, showed that under these conditions Al avoidance did not occur. It is concluded that a relation between the Al avoidance reaction ofMucuna and P stress is still likely.Abbreviations D_r root diameter - L_pr total root length per plant - L_rw specific root length - NRA nitrate reductase activity - S/R shoot: root ratio     

Influence of NO3 - and NH4 + nutrition on fermentation,nitrate reductase activity and adenylate energy charge of roots of Carex pseudocyperus L. and Carex sylvatica Huds. exposed to anaerobic nutrient solutions

The adenylate energy charge, production of ethanol and lactate, and nitrate reductase activity were determined in order to study the influence of different nitrogen sources on the metabolic responses of roots of Carex pseudocyperus L. and Carex sylvatica HUDS. exposed to anaerobic nutrient solutions. Determination of adenylates was carried out by means of a modified HPLC technique. Total quantity of adenylates was higher in Carex pseudocyperus than in Carex sylvatica under all conditions. In contrast, the adenylate energy charge was only slightly different between the species and decreased more or less in relation to the applied nitrogen source under oxygen deficiency. The adenylate energy charge in roots of plants under nitrate nutrition showed a smaller decrease under anaerobic environmental conditions than plants grown with ammonium or nitrate/ammonium. Roots of nitrate-fed plants showed a lower ethanol and lactate production than ammonium/nitrate- and ammonium-fed plants. Ethanol production was higher in C. pseudocyperus, formation of lactate was lower compared to that in Carex sylvatica. The activity of enzymes involved in fermentation processes (ADH, LDH and PDC) was enhanced significantly after 24 hours of exposure to anaerobic nutrient solutions in roots of both species. The induction of these enzymes was only slightly influenced by different nitrogen supply. In vivo nitrate reductase activity increased almost 3-fold compared to the aerobic treatment in both species and overcompensated loss of NADH reoxidation capacity caused by decrease of ethanol and lactate development. Induction of in vitro nitrate reductase activity was enhanced 313% in C. pseudocyperus and 349% in C. sylvatica under anaerobic environmental conditions and nitrate supply. These results indicate that nitrate may serve as an alternative electron acceptor in anaerobic plant root metabolism and that the nitrate-supported energy charge may be due to an accelerated glycolytic flux resulting from a more effective NADH reoxidation capacity by nitrate reduction plus fermentation than by fermentation alone.Abbreviations ADH alcohol dehydrogenase - AEC adenylate energy charge - DMSO dimethyl sulfoxide - EDTA ethylen diamine tetraacetic acid - HPLC high performance liquid chromatography - LDH lactate dehydrogenase - NRA nitrate reductase activity - PCA perchloric acid - PDC pyruvate decarboxylase - PVP polyvinylpyrrolidone - PVPP polyvinylpolypyrrolidone - TCA trichloroacetic acid, Tris-tris(hydroxymethyl)aminomethane     

Aluminum accumulation and associated effects on 15NO3 − influx in roots of two soybean genotypes differing in Al tolerance

A study was conducted to examine aluminum (Al) exclusion by roots of two differentially tolerant soybean (Glycine max L. Merr.) lines, Pl-416937 (Al-tolerant) and Essex (Al-sensitive). Following exposure to 80μM Al for up to 2 h, roots were rinsed with a 10 mM potassium citrate solution and rapidly dissected to allow estimation of intracellular Al accumulation in morphologically distinct root regions. Using 10 min exposures to 300μM ¹⁵NO₃ ⁻ and dissection, accompanying effects on NO₃ ⁻ uptake were measured. With Al exposures of 20 min or 2 h, there was greater Al accumulation in all root regions of Essex than in those of Pl-416937. The genotypic difference in Al accumulation was particularly apparent at the root apex, both in the tip and in the adjacent root cap and mucilage. Exposure of roots to Al inhibited the uptake of ¹⁵NO₃ ⁻ to a similar extent in all root regions. The results are consistent with Al exclusion from cells in the root apical region being an important mechanism of Al tolerance.     

植物吸收转运无机氮的生理及分子机制

氮是植物生长必需的营养元素。植物从土壤中吸收的氮素主要是NO3-和NH4 等无机氮源。植物吸收NO3-和NH4 的系统均有高亲和转运系统(high-affinity transport system,HATS)和低亲和转运系统(low-affinity transport system,LATS)之分。近10多年的研究已对这些转运系统的分子基础有了较好的理解,本文着重对近年来植物吸收无机氮分子机制的研究进展进行了综述。     

AgNO3 dependant modulation of glucose mediated respiration kinetics in Escherichia coli at different pH and temperature

The inhibitory role of AgNO₃ on glucose‐mediated respiration in Escherichia coli has been investigated as a function of pH and temperature using Clark‐type electrode, environmental scanning electron microscopy, and computational tools. In the given concentration of bacterial suspension (1 × 10⁸ CFU/ml), E. coli showed an increasing nonlinear trend of tetra‐phasic respiration between 1–133 μM glucose concentration within 20 min. The glucose concentrations above 133 μM did not result any linear increment in respiration but rather showed a partial inhibition at higher glucose concentrations (266–1066 μM). In the presence of glucose, AgNO₃ caused a concentration‐dependent (47–1960 μM) inhibition of the respiration rate within 4 min of its addition. The respiration rate was the highest at pH 7–8 and then was decreased on either side of this pH range. The inhibitory action of AgNO₃ upon bacterial respiration was the highest at 37 °C. The observations of the respiration data were well supported by the altered bacterial morphology as observed in electron microscopic study. Docking study indicated the AgNO₃ binding to different amino acids of all respiratory complex enzymes in E. coli and thereby explaining its interference with the respiratory chain. Copyright © 2016 John Wiley & Sons, Ltd.     

Aspergillus oryzae nrtA affects kojic acid production

We analyzed the role of the nitrate transporter-encoding gene (nrtA) of Aspergillus oryzae by gene disruption. Southern hybridization analysis indicated that homologous recombination occurred at the resident nrtA locus. Real-time PCR showed that the nrtA gene was strongly inducible by NaNO₃. The nrtA disruptant did not exhibit normal growth when nitrate was available as the sole nitrogen source. These results indicate that NrtA is essential for nitrate uptake in A. oryzae. Kojic acid (KA) production was inhibited by the addition of a small amount of sodium nitrate. The nrtA-disrupted strain was deficient in the uptake of nitrate. As a result, KA production in this strain was not considerably affected by the presence of nitrate.     

Nitrogen fixation by the diazotroph Cylindrospermopsis raciborskii (Cyanophyceae)

Nitrogen fixation has been proposed as a mechanism that allows the diazotrophic cyanobacterium, Cylindrospermopsis raciborskii, to bloom in nitrogen‐limited freshwater systems. However, it is unclear whether dinitrogen fixation (N₂ fixation) can supplement available dissolved inorganic nitrogen (DIN) for growth, or only provides minimum nitrogen (N) for cell maintenance under DIN deplete conditions. Additionally, the rate at which cells can switch between DIN use and N₂ fixation is unknown. This study investigated N₂ fixation under a range of nitrate concentrations. Cultures were grown with pretreatments of nitrate replete (single dose 941 μmol  · L^?1) and N‐free conditions and then either received a single dose of 941 μmol  · L^?1 (N941), 118 μmol  · L^?1 (N118) or 0 N. Heterocysts appeared from days 3 to 5 when treatments of high were transferred to N free media (N941:N0), and from day 5 in N941 transferred to N118 treatments. Conversely, transferring cells from N0 to N941 resulted in heterocysts being discarded from day 3 and day 5 for N0:N118. Heterocyst appearance correlated with a detectable rate of N₂ fixation and up‐regulation of nifH gene expression, the discard of heterocysts occurred after sequential reduction of nifH expression and N₂ fixation. Nitrate uptake rates were not affected by pretreatment, suggesting no regulation or saturation of this uptake pathway. These data demonstrate that for C. raciborskii, N₂ fixation is regulated by the production or discard of heterocysts. In conclusion, this study has shown that N₂ fixation only provides enough N to support relatively low growth under N‐limited conditions, and does not supplement available nitrate to increase growth rates.