Regulation of nitrogen acquisition (NO3-, NH4+ et N2) by nitrogen status
ABSTRACT: affy_nitrogen_medicago - affy_nitrogen_medicago - Experiment has been designed to characterize the molecular expression patterns associated to a contrasted modification of the nitrogen status of the whole plant. The systemic effects of nitrogen status modifications are investigated and compared on non nodulated plant supplied with NO3, NH4 or nodulated plants (Sinorhizobium meliloti 2011) supplied with air. The root systems were separated in two compartments of unequal sizes (split root system). Two treatments were applied on the larger compartment in order to modulate the nitrogen status of the plant: for the S treatment, roots are supplied with nutrient solution containing 10 mM NH4NO3,, whereas for the C treatment, roots are supplied with nitrogen free medium. In the case of N2 fixing plants, N limitation was obtained by replacing air by a mixture of Ar and O2 80 per cent and 20 per cent. The effects of these treatments were investigated on roots of the minor compartment supplied continuously with either NO3 1 mM, NH4 1 mM or air (N2) and on the shoots. We were also interested in the molecular expression patterns associated to the roots deprived of N.-The root system of non-nodulated (NO3- and NH4+) or nodulated (N2) plants is split into two unequal parts and each one is installed in a separate compartment. For the S treatement, the major root part is supplied with NH4NO3 10 mM whereas the minor part is supplied with either NO3- 1mM, NH4+ 1mM or N2. For the C treatement, the major root part is supplied with nitrogen-free nutrient solution whereas the minor part is supplied with either NO3- 1mM, NH4plus 1mM or N2. Each treatement is four days long. Samples of roots of six biological types (NO3S, NO3C, NH4S, NH4C, N2S and N2C) were collected. Two biological repeats per biological types have been analyzed. The effect of the S and C treatments were investigated for each N sources by comparing Affymetrix transcriptomes (NO3C vs NO3S, NH4C vs NH4S, N2C vs N2S). Keywords: treatement (nitrogen-sufficient) vs treatement (nitrogen-limited) Overall design: 26 arrays - medicago
Project description:affy_nitrogen_medicago - affy_nitrogen_medicago - Experiment has been designed to characterize the molecular expression patterns associated to a contrasted modification of the nitrogen status of the whole plant. The systemic effects of nitrogen status modifications are investigated and compared on non nodulated plant supplied with NO3, NH4 or nodulated plants (Sinorhizobium meliloti 2011) supplied with air. The root systems were separated in two compartments of unequal sizes (split root system). Two treatments were applied on the larger compartment in order to modulate the nitrogen status of the plant: for the S treatment, roots are supplied with nutrient solution containing 10 mM NH4NO3,, whereas for the C treatment, roots are supplied with nitrogen free medium. In the case of N2 fixing plants, N limitation was obtained by replacing air by a mixture of Ar and O2 80 per cent and 20 per cent. The effects of these treatments were investigated on roots of the minor compartment supplied continuously with either NO3 1 mM, NH4 1 mM or air (N2) and on the shoots. We were also interested in the molecular expression patterns associated to the roots deprived of N.-The root system of non-nodulated (NO3- and NH4+) or nodulated (N2) plants is split into two unequal parts and each one is installed in a separate compartment. For the S treatement, the major root part is supplied with NH4NO3 10 mM whereas the minor part is supplied with either NO3- 1mM, NH4+ 1mM or N2. For the C treatement, the major root part is supplied with nitrogen-free nutrient solution whereas the minor part is supplied with either NO3- 1mM, NH4plus 1mM or N2. Each treatement is four days long. Samples of roots of six biological types (NO3S, NO3C, NH4S, NH4C, N2S and N2C) were collected. Two biological repeats per biological types have been analyzed. The effect of the S and C treatments were investigated for each N sources by comparing Affymetrix transcriptomes (NO3C vs NO3S, NH4C vs NH4S, N2C vs N2S). Experiment Overall Design: 26 arrays - medicago
Project description:BACKGROUND AND AIMS: Tea (Camellia sinensis) is considered to be acid tolerant and prefers ammonium nutrition, but the interaction between root zone acidity and N form is not properly understood. The present study was performed to characterize their interaction with respect to growth and mineral nutrition. METHODS: Tea plants were hydroponically cultured with NH4+, NO3- and NH(4+) + NO3-, at pH 4.0, 5.0 and 6.0, which were maintained by pH stat systems. KEY RESULTS: Plants supplied with NO3- showed yellowish leaves resembling nitrogen deficiency and grew much slower than those receiving NH4+ or NH(4+) + NO3- irrespective of root-zone pH. Absorption of NH4+ was 2- to 3.4-fold faster than NO3- when supplied separately, and 6- to 16-fold faster when supplied simultaneously. Nitrate-grown plants had significantly reduced glutamine synthetase activity, and lower concentrations of total N, free amino acids and glucose in the roots, but higher concentrations of cations and carboxylates (mainly oxalate) than those grown with NH4+ or NH(4+) + NO3-. Biomass production was largest at pH 5.0 regardless of N form, and was drastically reduced by a combination of high root-zone pH and NO3-. Low root-zone pH reduced root growth only in NO(3-)-fed plants. Absorption of N followed a similar pattern as root-zone pH changed, showing highest uptake rates at pH 5.0. The concentrations of total N, free amino acids, sugars and the activity of GS were generally not influenced by pH, whereas the concentrations of cations and carboxylates were generally increased with increasing root-zone pH. CONCLUSIONS: Tea plants are well-adapted to NH(4+)-rich environments by exhibiting a high capacity for NH4+ assimilation in their roots, reflected in strongly increased key enzyme activities and improved carbohydrate status. The poor plant growth with NO3- was largely associated with inefficient absorption of this N source. Decreased growth caused by inappropriate external pH corresponded well with the declining absorption of nitrogen.
Project description:Background and Aims:Soil waterlogging adversely impacts most plants. Melilotus siculus is a waterlogging-tolerant annual forage legume, but data were lacking for the effects of root-zone hypoxia on nodulated plants reliant on N2 fixation. The aim was to compare the waterlogging tolerance and physiology of M. siculus reliant on N2 fixation or with access to NO3-. Methods:A factorial experiment imposed treatments of water level (drained or waterlogged), rhizobia (nil or inoculated) and mineral N supply (nil or 11 mm NO3-) for 21 d on plants in pots of vermiculite in a glasshouse. Nodulation, shoot and root growth and tissue N were determined. Porosity (gas volume per unit tissue volume) and respiration rates of root tissues and nodules, and O2 microelectrode profiling across nodules, were measured in a second experiment. Key Results:Plants inoculated with the appropriate rhizobia, Ensifer (syn. Sinorhizobium) medicae, formed nodules. Nodulated plants grew as well as plants fed NO3-, both in drained and waterlogged conditions. The growth and total N content of nodulated plants (without any NO3- supplied) indicated N2 fixation. Respiration rates (mass basis) were highest in nodules and root tips and lowest in basal root tissues. Secondary aerenchyma (phellem) formed along basal root parts and a thin layer of this porous tissue also covered nodules, which together enhanced gas-phase diffusion of O2 to the nodules; O2 was below detection within the infected zone of the nodule interior. Conclusions:Melilotus siculus reliant on N2 fixation grew well both in drained and waterlogged conditions, and had similar tissue N concentrations. In waterlogged conditions the relatively high respiration rates of nodules must rely on O2 movement via the aerenchymatous phellem in hypocotyl, roots and the outer tissue layers of nodules.
Project description:Nitrogen nutrition can influence cluster root formation in many wild species, but the effect of N form on cluster root formation and root exudation by white lupin is not known. In a solution culture study, we examined the effect of N nutrition (ammonium, nitrate, both or N2 fixation) on cluster root formation and H+ extrusion by white lupin plants under deficient and adequate P supply. The number of cluster roots increased greatly when plants were supplied with I microM P compared with 50 microM P, the increase being 7.8-fold for plants treated with (NH4)2SO4, 3-fold for plants treated with KNO3 and NH4NO3, and 2-4-fold for N2-fixing plants. Under P deficiency. NH4+-N supply resulted in production of a greater number and biomass of cluster roots than other N sources. Dry weight of cluster roots was 30 % higher than that of non-cluster roots in P-deficient plants treated with (NH4)2SO4 and NH4NO3. In plants treated with sufficient P (50 microM), the weight of non-cluster roots was approx. 90 % greater than that of cluster roots. Both total (micromol per plant h(-1)) and specific (micromol g(-1) root d. wt h(-1)) H+ extrusions were greatest from roots of plants supplied with (NH4)2SO4, followed by those supplied with NH4NO3 and N2 fixation, whereas plants receiving KNO3 had negative net H+ extrusion between the third and fifth week of growth (indicating uptake of protons or release of OH- ions). The rate of proton extrusion by NH4+-N-fed plants was similar under P-deficient and P-sufficient conditions. In contrast, proton exudation by N2-fixing plants and KNO3-treated plants was ten-fold greater under P deficiency than under P sufficiency. In comparison with P deficiency, plants treated with 50 microM P had a significantly higher concentration of P in roots, shoots and youngest expanded leaves (YEL). Compared with the N2 fixation and KNO3 treatments, total N concentration was highest in roots, shoots and YEL of plants supplied with (NH4)2SO4 and NH4NO3, regardless of P supply. Under P deficiency, K concentrations in roots decreased at all N supplies, especially in plants treated with (NH4)2SO4 and NH4NO3, which coincided with the greatest H+ extrusion at these P and N supplies. In conclusion, NH4-N nutrition stimulated cluster root formation and H+ extrusion by roots of P-deficient white lupin.
Project description:BACKGROUND:Nutrition with ammonium (NH4+) can enhance the drought tolerance of rice seedlings in comparison to nutrition with nitrate (NO3-). However, there are still no detailed studies investigating the response of nitric oxide (NO) to the different nitrogen nutrition and water regimes. To study the intrinsic mechanism underpinning this relationship, the time-dependent production of NO and its protective role in the antioxidant defense system of NH4+- or NO3--supplied rice seedlings were studied under water stress. RESULTS:An early NO burst was induced by 3 h of water stress in the roots of seedlings subjected to NH4+ treatment, but this phenomenon was not observed under NO3- treatment. Root oxidative damage induced by water stress was significantly higher for treatment with NO3- than with NH4+ due to reactive oxygen species (ROS) accumulation in the former. Inducing NO production by applying the NO donor 3 h after NO3- treatment alleviated the oxidative damage, while inhibiting the early NO burst by applying the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO) increased root oxidative damage in NH4+ treatment. Application of the nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine methyl ester(L-NAME) completely suppressed NO synthesis in roots 3 h after NH4+ treatment and aggravated water stress-induced oxidative damage. Therefore, the aggravation of oxidative damage by L-NAME might have resulted from changes in the NOS-mediated early NO burst. Water stress also increased the activity of root antioxidant enzymes (catalase, superoxide dismutase, and ascorbate peroxidase). These were further induced by the NO donor but repressed by the NO scavenger and NOS inhibitor in NH4+-treated roots. CONCLUSION:These findings demonstrate that the NOS-mediated early NO burst plays an important role in alleviating oxidative damage induced by water stress by enhancing the antioxidant defenses in roots supplemented with NH4+.
Project description:Nitrogen (N) is a major essential nutrient for plant growth, and rice is an important food crop globally. Although ammonium (NH4+) is the main N source for rice, nitrate (NO3-) is also absorbed and utilized. Rice responds to NO3- supply by changing root morphology. However, the mechanisms of rice root growth and formation under NO3- supply are unclear. Nitric oxide (NO) and auxin are important regulators of root growth and development under NO3- supply. How the interactions between NO and auxin in regulating root growth in response to NO3- are unknown. In this study, the levels of indole-3-acetic acid (IAA) and NO in roots, and the responses of lateral roots (LRs) and seminal roots (SRs) to NH4+ and NO3-, were investigated using wild-type (WT) rice, as well as osnia2 and ospin1b mutants. NO3- supply promoted LR formation and SR elongation. The effects of NO donor and NO inhibitor/scavenger supply on NO levels and the root morphology of WT and nia2 mutants under NH4+ or NO3- suggest that NO3--induced NO is generated by the nitrate reductase (NR) pathway rather than the NO synthase (NOS)-like pathway. IAA levels, [3H] IAA transport, and PIN gene expression in roots were enhanced under NO3- relative to NH4+ supply. These results suggest that NO3- regulates auxin transport in roots. Application of SNP under NH4+ supply, or of cPTIO under NO3- supply, resulted in auxin levels in roots similar to those under NO3- and NH4+ supply, respectively. Compared to WT, the roots of the ospin1b mutant had lower auxin levels, fewer LRs, and shorter SRs. Thus, NO affects root growth by regulating auxin transport in response to NO3-. Overall, our findings suggest that NO3- influences LR formation and SR elongation by regulating auxin transport via a mechanism involving NO.
Project description:Trichoderma spp., are saprophytic fungi that can improve plant growth through increased nutrient acquisition and change in the root architecture. In the present study, we demonstrate that Trichoderma asperellum T42 mediate enhancement in host biomass, total nitrogen content, nitric oxide (NO) production and cytosolic Ca2+ accumulation in tobacco. T42 inoculation enhanced lateral root, root hair length, root hair density and root/shoot dry mass in tobacco under deprived nutrients condition. Interestingly, these growth attributes were further elevated in presence of T42 and supplementation of NO3- and NH4+ nutrients to tobacco at 40 and 70 days, particularly in NO3- supplementation, whereas no significant increment was observed in nia30 mutant. In addition, NO production was more in tobacco roots in T42 inoculated plants fed with NO3- nutrient confirming NO generation was dependent on NR pathway. NO3- dependent NO production contributed to increase in lateral root initiation, Ca2+ accumulation and activities of nitrate transporters (NRTs) in tobacco. Higher activities of several NRT genes in response to T42 and N nutrients and suppression of ammonium transporter (AMT1) suggested that induction of high affinity NRTs help NO3- acquisition through roots of tobacco. Among the NRTs NRT2.1 and NRT2.2 were more up-regulated compared to the other NRTs. Addition of sodium nitroprusside (SNP), relative to those supplied with NO3-/NH4+ nutrition and T42 treated plants singly, and with application of NO inhibitor, cPTIO, confirmed the altered NO fluorescence intensity in tobacco roots. Our findings suggest that T42 promoted plant growth significantly ant N content in the tobacco plants grown under N nutrients, notably higher in NO3-, providing insight of the strategy for not only tobacco but probably for other crops as well to adapt to fluctuating nitrate availability in soil.
Project description:It has been hypothesized that faunal activity in the rhizosphere influences root growth via an auxin-dependent pathway. In this study, two methods were used to adjust nematode and bacterial populations within experimental soils. One is "exclusion", where soil mixed with pig manure was placed in two bags with different mesh sizes (1mm and 5?m diameter), and then surrounded by an outer layer of unamended soil resulting in soil with a greater populations of bacterial-feeding nematodes (1mm) and a control treatment (5?m). The second method is "inoculation", whereby autoclaved soil was inoculated with bacteria (E. coli and Pseudomonas) and Nematodes (Cephalobus and C. elegans). In order to detect the changes in the rice's perception of auxin under different nutrient and auxin conditions in the presence of soil bacterial-feeding nematodes, responses of soil chemistry (NH4+, NO3- and indole acetic acid (IAA)), rice root growth and the expression of an auxin responsive gene GH3-2 were measured. Results showed that, under low soil nutrient conditions (exclusion), low NO3- correlated with increased root branching and IAA correlated with increased root elongation and GH3-2 expression. However, under high soil nutrient conditions (inoculation), a high NH4+ to NO3- ratio promoted an increase in root surface area and there was an additional influence of NH4+ and NO3- on GH3-2 expression. Thus it was concluded that soil bacterial-feeding nematodes influenced soil nutritional status and soil IAA content, promoting root growth via an auxin dependent pathway that was offset by soil nitrogen status.
Project description:A potted experiment with Populus × euramericana 'Neva' was carried out to assess whether there are positive effects of magnetic treatment of saline water (MTSW) on nitrogen metabolism under controlled conditions in a greenhouse. Growth properties, nitrogen contents, enzyme activities and metabolite concentrations were determined based on field experiments and laboratory analysis after a 30-day treatment. The results were as follows: (1) Biomass accumulation, root morphological properties and total nitrogen content were improved by MTSW. (2) Magnetization led to a greater increase in nitrate-nitrogen (NO3--N) content in roots than in leaves, accompanied by greater NO3- efflux and activated nitrate reductase. (3) MTSW led to a higher ammonium-nitrogen (NH4+-N) content and greater uptake of net NH4+ in the leaves than that in the roots. (4) Magnetization stimulated glutamine synthase, glutamate dehydrogenase and glutamate synthase activities, whereas the concentrations of glutathione and oxidized glutathione were increased in leaves but decreased in roots, and the total glutathione content was increased. Overall, these results indicated some beneficial impacts of MTSW on nitrogen translocation under field conditions, especially for equilibrating the distribution of NO3--N and NH4+-N. Moreover, these findings confirmed the potential of using low-quality water for agriculture.
Project description:BACKGROUND AND AIMS: Although ammonium (NH4(+)) is the preferred form of nitrogen over nitrate (NO3(-)) for rice (Oryza sativa), lateral root (LR) growth in roots is enhanced by partial NO3(-) nutrition (PNN). The roles of auxin distribution and polar transport in LR formation in response to localized NO3(-) availability are not known. METHODS: Time-course studies in a split-root experimental system were used to investigate LR development patterns, auxin distribution, polar auxin transport and expression of auxin transporter genes in LR zones in response to localized PNN in 'Nanguang' and 'Elio' rice cultivars, which show high and low responsiveness to NO3(-), respectively. Patterns of auxin distribution and the effects of polar auxin transport inhibitors were also examined in DR5::GUS transgenic plants. KEY RESULTS: Initiation of LRs was enhanced by PNN after 7 d cultivation in 'Nanguang' but not in 'Elio'. Auxin concentration in the roots of 'Nanguang' increased by approx. 24 % after 5 d cultivation with PNN compared with NH4(+) as the sole nitrogen source, but no difference was observed in 'Elio'. More auxin flux into the LR zone in 'Nanguang' roots was observed in response to NO3(-) compared with NH4(+) treatment. A greater number of auxin influx and efflux transporter genes showed increased expression in the LR zone in response to PNN in 'Nanguang' than in 'Elio'. CONCLUSIONS: The results indicate that higher NO3(-) responsiveness is associated with greater auxin accumulation in the LR zone and is strongly related to a higher rate of LR initiation in the cultivar 'Nanguang'.