Sugar exudation by roots of kallar grass [<Emphasis Type="Italic">Leptochloa fusca</Emphasis> (L.) Kunth] is strongly affected by the nitrogen source

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.     

Ion Relations of Symplastic and Apoplastic Space in Leaves from Spinacia oleracea L. and Pisum sativum L. under Salinity

Salt tolerant spinach (Spinacia oleracea) and salt sensitive pea (Pisum sativum) plants were exposed to mild salinity under identical growth conditions. In order to compare the ability of the two species for extra- and intracellular solute compartmentation in leaves, various solutes were determined in intercellular washing fluids and in aqueously isolated intact chloroplasts. In pea plants exposed to 100 millimolar NaCl for 14 days, apoplastic salt concentrations in leaflets increased continuously with time up to 204 (Cl⁻) and 87 millimolar (Na⁺), whereas the two ions reached a steady concentration of only 13 and 7 millimolar, respectively, in spinach leaves. In isolated intact chloroplasts from both species, sodium concentrations were not much different, but chloride concentrations were significantly higher in pea than in spinach. Together with data from whole leaf extracts, these measurements permitted an estimation of apoplastic, cytoplasmic, and vacuolar solute concentrations. Sodium and chloride concentration gradients across the tonoplast were rather similar in both species, but spinach was able to maintain much steeper sodium gradients across the plasmamembrane compared with peas. Between day 12 and day 17, concentrations of other inorganic ions in the pea leaf apoplast increased abruptly, indicating the onset of cell disintegration. It is concluded that the differential salt sensitivity of pea and spinach cannot be traced back to a single plant performance. Major differences appear to be the inability of pea to control salt accumulation in the shoot, to maintain steep ion gradients across the leaf cell plasmalemma, and to synthesize compatible solutes. Perhaps less important is a lower selectivity of pea for K⁺/Na⁺ and NO₃⁻/Cl⁻ uptake by roots.     

Difference in zeaxanthin formation in nitrate- and ammonium-grown Phaseolus vulgaris

Absorption at 505 nm and high-performance liquid chromatography showed that light-induced conversion of violaxanthin to antheraxanthin and zeaxanthin was much stronger in leaves of nitrate- than in leaves of ammonium-grown Phaseolus vulgaris . Feeding ascorbate via the petiole increased zeaxanthin formation in ammonium-grown plants. However, there was no difference in energy quenching, qE, or photoinhibition (measured as FV/FM), as determined by chlorophyll fluorescence in nitrate- and ammonium-grown plants. Dithiothreitol decreased the light-induced stimulation of zeaxanthin formation and increased photoinhibition in nitrate-grown plants, suggesting that these plants utilize zeaxanthin for the protection of photosystem II (PSII). Ammonium-grown plants seem to have established an alternative way to protect PSII.     

Inorganic nitrogen assimilation in the non-N2-fixing cyanobacterium Phormidium laminosum. I. Cellular levels of glutamine synthetase and NADPH-dependent glutamate dehydrogenase

Cell-free extracts of nitrate-grown as well as of ammonium-grown cells of the filamentous non-nitrogen-fixing cyanobacterium Phormidium laminosum (strain OH-1-p.Cl₁) showed detectable levels of both glutamine synthetase (GS, EC 6.3.1.2) and NADPH-dependent glutamate dehydrogenase (GDH, EC 1.4.1.4) activities. The GS level of nitrate-grown cells was higher than that of ammonium-grown cells, whereas the GDH level was higher in ammonium-grown cells and depended on the external ammonium concentration. When nitrate-grown cells were transferred to an ammonium-containing medium, a decrease of GS and an increase of GDH specific activities occurred, even in the presence of nitrate. Conversely, when ammonia-grown cells were transferred to a nitrate-containing medium, an increase of GS and a decrease of GDH-specific activities took place. Both these effects were inhibited by chloramphenicol and were probably mediated by de novo protein synthesis. When either cell type was transferred to a medium without nitrogen source, the specific activities of both enzymes increased. When nitrate-grown cells were transferred to nitrate medium with L-methionine-DL-sulphoximine (MSX) added, the specific activity of GDH also increased. Here we present some evidence that, under certain conditions of nitrogen availability, GDH would play a minor role in ammonium assimilation.     

Changes in fatty acids,amino acids and carbon/nitrogen biomass during nitrogen starvation of ammonium- and nitrate-grownIsochrysis galbana

Growth of cells ofIsochrysis galbana with either nitrate or ammonium as the N-source, and the effects of subsequent N-starvation of these cells, were compared. During exponential N-sufficient growth nitrate-grown cells had double the fatty acid content of the ammonium-grown cells but lower concentrations of a few amino acids. Following resuspension in N-free medium the fatty acid content of the ammonium-grown cells increased to that of the nitrate-grown cells, but there was no further increase in fatty acid content on a C-biomass or cellular basis during the following 4 days for either culture. Fatty acid synthesis was continuous during N-starvation, while it occurred during the light-phase only in exponential growth. The proportion of 18:1n9 fatty acid increased from 10 to 25% total fatty acids during N-starvation. Intracellular free amino acid content decreased in a similar manner in both cultures on N-starvation, the ratio of intracellular free amino-N/cell-C falling more rapidly than overall cellular N/C. It was concluded that optimal amino acid and fatty acid content would be attained by growth in the presence of excess nitrate. Measurements of chlorophyll and carotenoid content and ofin vivo fluorescence indicated that these parameters had potential for monitoring the C and N biomass in cultures grown under relatively constant (not necessarily continuous) illumination.     

Carbohydrate metabolism and phosphorus/salinity interactions in wheat (Triticum aestivum L.)

Foliar inorganic ion and carbohydrate concentrations were determined in wheat plants treated with factorial combinations of phosphorus fertilizer and NaCl in a glasshouse experiment. Growth reductions and visual symptoms of salt toxicity were minimized when phosphorus nutrition was adequate, and were intensified by phosphorus deficiency. Foliar sodium and chloride accumulated up to 4.0–5.5% d.w. with salinity treatment. However, ionic concentrations within corresponding leaves or distributions between leaves of plants with different phosphorus treatments were not influenced by phosphorus treatment and had no relationship to the severity of salt toxicity symptoms. This suggests that phosphorus deficiency reduced the cellular tolerance for ion accumulation. A combination of phosphorus deficiency and salinity induced an accumulation of foliar starch and sucrose despite substantial reductions in net CO₂ assimilation rates. This accumulation did not occur if phosphorus nutrition was adequate, which is consistent with the roles of phosphorus in carbohydrate metabolism. It is proposed that adequate phosphorus nutrition is essential for effective ion compartmentation by contributing to efficient carbohydrate utilization in salt-stressed wheat.     

Ion Homeostasis in Chloroplasts under Salinity and Mineral Deficiency : I. Solute Concentrations in Leaves and Chloroplasts from Spinach Plants under NaCl or NaNO(3) Salinity

Spinach (Spinacia oleracea var “Yates”) plants in hydroponic culture were exposed to stepwise increased concentrations of NaCl or NaNO₃ up to a final concentration of 300 millimoles per liter, at constant Ca²⁺-concentration. Leaf cell sap and extracts from aqueously isolated spinach chloroplasts were analyzed for mineral cations, anions, amino acids, sugars, and quarternary ammonium compounds. Total osmolality of leaf sap and photosynthetic capacity of leaves were also measured. For comparison, leaf sap from salt-treated pea plants was also analyzed. Spinach plants under NaCl or NaNO₃ salinity took up large amounts of sodium (up to 400 millimoles per liter); nitrate as the accompanying anion was taken up less (up to 90 millimoles per liter) than chloride (up to 450 millimoles per liter). Under chloride salinity, nitrate content in leaves decreased drastically, but total amino acid concentrations remained constant. This response was much more pronounced (and occurred at lower salt concentrations) in leaves from the glycophyte (pea, Pisum sativum var “Kleine Rheinländerin”) than from moderately salt-tolerant spinach. In spinach, sodium chloride or nitrate taken up into leaves was largely sequestered in the vacuoles; both salts induced synthesis of quarternary ammonium compounds, which were accumulated mainly in chloroplasts (and cytosol). This prevented impairment of metabolism, as indicated by an unchanged photosynthetic capacity of leaves.     

Ammonia emission from young barley plants: influence of N source, light/dark cycles and inhibition of glutamine synthetase

Barley (Hordeum vulgare L. cv. Golf) plants were grown at twodifferent relative addition rates; 0.1 and 0.2 d^–1 ofnitrate. Three to five days before measurements started theplants were transferred to a nutrient solution with 2 mM nitrateor ammonium. The ammonium-grown plants showed increased ammoniumlevels in both shoots and roots and also increased ammoniumconcentrations in xylem sap. Ammonia emission measured in cuvettes connected to an automaticNH₃ monitor was close to zero for nitrate-grown plants but increasedto 0.59 and 0.88 nmol NH₃ m^–2 S^–1 for plants transferredto ammonium after growing at RA=0.2 and 0.1 d^–1, respectively.In darkness, NH₃ emission decreased together with photosynthesisand transpiration, but increased rapidly when the light wasturned on again. Addition of 0.5 mM methionine sulphoximine (MSO) to the plantscaused an almost complete inhibition of both root and shootglutamine synthetase (GS) activity after 24 h. Ammonia emissionincreased dramatically and photosynthesis and transpirationdecreased in both nitrate- and ammonium-grown plants as a resultof the GS inhibition. At the same time plant tissue and xylemsap ammonium concentrations increased, indicating the importanceof GS in controlling plant ammonium levels and thereby NH₃ emissionfrom the leaves. Key words: Hordeum vulgare, ammonia emission, ammonium, glutamine synthetase, nitrogen nutrition, photosynthesis, transpiration     

GROWTH OF HETEROSIGMA CARTERAE (RAPHIDOPHYCEAE) ON NITRATE AND AMMONIUM AT THREE PHOTON FLUX DENSITIES: EVIDENCE FOR N STRESS IN NITRATE-GROWING CELLS

The marine alga Heterosigma carterae Hulburt (Raphidophyta) was grown in N-limiting batch cultures using either nitrate or ammonium as the N source, at photon flux densities (PFDs) of 50, 200, and 350 μmol·m^-2·s^-1 in a 12:12 h LD cycle. Carbon content could be estimated from biovolume (μg C = 0.278 × nL; R = 0.98) but not reliably from pigment content. During exponential growth, ammonium-grown cells (in comparison with nitrate-grown cells at the same PFD) attained higher growth rates by at least 20%, contained more N, and had a lower C:N ratio, higher concentrations of intracellular free amino acids, and higher ratios of glutamine: glutamate (Gln: Glu) and asparagine: aspartate (Asn:Asp). Growth was nearly light-saturated on ammonium at 200 μmol·m^-2·s^-1 (cell-specific growth rate of 1.2 d^-1) but probably not saturated in nitrate-grown cells at 350 μmol·m^-2·s^-1. PFD did not affect Gln: Glu or Asn: Asp for a given N source. These results indicate that the nitrate-growing cells were more N-stressed than those using ammonium (which in contrast were relatively C-stressed) and that this organism would show an enhanced competitive advantage against other species when supplied with a transient supply of ammonium rather than nitrate .     

盐生植物星星草叶表皮具有泌盐功能的蜡质层

利用扫描电镜和 X射线电子探针研究了星星草 (Puccinellia tenuiflora)的叶表皮及其与生境高盐的关系。结果表明 ,叶表皮由表皮细胞和气孔器组成 ,下表皮气孔器多于上表皮 ,且常下陷 ,表皮具表皮毛。表皮细胞外存在丰富的蜡质纹饰和蜡质颗粒 ,这些蜡质包含盐离子 ,具有泌盐的功能。这些特征表明星星草受外界生态因素的影响 ,而演化出具有泌盐功能的蜡质层来适应所生长的高盐生境     

NITROGEN METABOLISM AND AMINO ACID NUTRITION IN THE SOIL ALGA STICHOCOCCUS BACILLARIS (CHLOROPHYCEAE)1

Nitrate-grown cells of Stichococcus bacillaris Naeg. (UTEX 314) contained much higher activities of glutamine synthetase (GS) and NADPH-glutamate dehydrogenase (GDH) than ammonium-grown cells. Methylamine, a non-metabolizable ammonium analog, caused a decrease in GS activity in nitrate-grown cells suggesting that GS is regulated by the size of the endogenous ammonium pool. The decrease in GS observed in methylammonium-loaded nitrate-grown cells was accompanied by an increase in NADPH-GDH activity. Stichococcus bacillaris can be grown in the presence of methionine sulfoximine (MSX), a potent inhibitor of GS. However, only a fraction of a control cell population showed a requirement for glutamine or arginine for growth following MSX addition. Fully adapted MSX-grown cells were indistinguishable from control cells in their ability to photosynthesize and utilize amino acids as nitrogen sources. Alanine, arginine, asparagine, glutamine, glycine and proline were good nitrogen sources, and maximum capacity for amino acid transport was developed in cells grown on these amino acids. Compared to nitrate-grown cells the activity of GS in ammo acid-grown cells was low, whereas NADPH-GDH was very active. The activity of NADH-GDH in amino acid-grown cells was highest under heterotrophic conditions.     

A Nitrate-Inducible Plasma Membrane Protein of a Marine Alga, Heterosigma akashiwo

The rate of nitrate uptake by Heterosigma akashiwo cells thathad been cultured in medium with nitrate or ammonium ions asthe source of nitrogen was measured using¹⁵NO_3– The ratioof ¹⁵N/¹⁴N increased dramatically in nitrate-grown cells. Inammonium-grown cells, the ratio of ¹⁵N/¹⁴N did not increasefor 3 h but then it began to increase. Even when nitrate reductaseactivity was inhibited by tungstate, nitrate-grown cells couldtake up nitrate. Plasma membranes from nitrate-grown and ammonium-grown cellswere purified by the silica-microbead method, and polypeptidesassociated with the membranes were analyzed by SDS-PAGE andimmunostaining. A major polypeptide with a molecular mass of26 kDa appeared 3 h after the transfer of ammonium-grown cellsto nitrate-containing medium, and it disappeared 2 d after thetransfer of nitrate-grown cells to ammonium-containing medium.The 26 kDa polypeptide also appeared when cell growth shiftedfrom the logarithmic phase to the stationary phase and the ammoniumcontent of the medium decreased, even when the cells were culturedin ammonium-containing medium. (Received April 10, 1992; Accepted July 30, 1992)     

Involvement of nitrite in the nitrate-mediated modulation of fermentative metabolism and nitric oxide production of soybean roots during hypoxia

It is widely accepted that nitrate but not ammonium improves tolerance of plants to hypoxic stress, although the mechanisms related to this beneficial effect are not well understood. Recently, nitrite derived from nitrate reduction has emerged as the major substrate for the synthesis of nitric oxide (NO), an important signaling molecule in plants. Here, we analyzed the effect of different nitrogen sources (nitrate, nitrite and ammonium) on the metabolic response and NO production of soybean roots under hypoxia. Organic acid analysis showed that root segments isolated from nitrate-cultivated plants presented a lower accumulation of lactate and succinate in response to oxygen deficiency in relation to those from ammonium-cultivated plants. The more pronounced lactate accumulation by root segments of ammonium-grown plants was followed by a higher ethanol release in the medium, evidencing a more intense fermentation under oxygen deficiency than those from nitrate-grown plants. As expected, root segments from nitrate-cultivated plants produced higher amounts of nitrite and NO during hypoxia compared to ammonium cultivation. Exogenous nitrite supplied during hypoxia reduced both ethanol and lactate production and stimulated cyanide-sensitive NO emission by root segments from ammonium-cultivated plants, independent of nitrate. On the other hand, treatments with a NO donor or a NO scavenger did not affect the intensity of fermentation of soybean roots. Overall, these results indicate that nitrite participates in the nitrate-mediated modulation of the fermentative metabolism of soybean roots during oxygen deficiency. The involvement of mitochondrial reduction of nitrite to NO in this mechanism is discussed.     

Some mechanisms of salt tolerance in crop plants

Summary In the first part of this review the main features of salt tolerance in higher plants are discussed. The hypothesis of intracellular compartmentation of solutes is used as a basis for models of tolerance mechanisms operating in roots and in leaves. Consideration is given to the implications of the various mechanisms for the yield potential of salt-tolerant crop plants.Some work on the more salt-tolerant members of the Triticeae is then described. The perennial speciesElytrigia juncea andLeymus sabulosus survive prolonged exposure to 250 mol m^–3 NaCl, whereas the annual Triticum species are severely affected at only 100 mol m^–3 NaCl. In the perennial species the tissue ion levels are controlled within narrow limits. In contrast, the more susceptible wheats accumulate far more sodium and chloride than is needed for osmotic adjustment, and the effects of salt stress increase with time of exposure.Two different types of salt tolerance are exhibited in plants capable of growing at high salinities. In succulent Chenopodiaceae, for example, osmotic adjustment is achieved mainly by accumulation of high levels of sodium and chloride in the shoots, accompanied by synthesis of substantial amounts of the compatible solute glycinebetaine. This combination of mechanisms allows high growth rates, in terms of both fresh and dry weight. At the opposite end of the spectrum of salt tolerance responses are the halophytic grasses, which strictly limit the influx of salts into the shoots, but suffer from very much reduced growth rates under saline conditions. Another variation is shown in those species that possess salt glands. The development and exploitation of crop plants for use on saline soils is discussed in relation to the implications of these various mechanisms.     

Plasticity of the mitoproteome to nitrogen sources (nitrate and ammonium) in Chlamydomonas reinhardtii: The logic of Aox1 gene localization

Nitrate and ammonium constitute primary inorganic nitrogen sources that can be incorporated into carbon skeletons in photosynthetic eukaryotes. In Chlamydomonas, previous studies and the present one showed that the mitochondrial AOX is up-regulated in nitrate-grown cells in comparison with ammonium-grown cells. In this work, we have performed a comparative proteomic analysis of the soluble mitochondrial proteome of Chlamydomonas cells growth either on nitrate or ammonium. Our results highlight important proteomics modifications mostly related to primary metabolism in cells grown on nitrate. We could note an up-regulation of some TCA cycle enzymes and a down-regulation of cytochrome c₁ together with an up-regulation of l-arginine and purine catabolism enzymes and of ROS scavenging systems. Hence, in nitrate-grown cells, AOX may play a dual role: (1) lowering the ubiquinone pool reduction level and (2) permitting the export of mitochondrial reducing power under the form of malate for nitrate and nitrite reduction. This role of AOX in the mitochondrial plasticity makes logical the localization of Aox1 in a nitrate assimilation gene cluster.     

Triadimenol Increases Nitrate Levels and Nitrate Reductase Activity in Canola Leaves

Nitrate reductase activity in the first true leaves of canola(Brassica napus L.) seedlings grown in one-quarter strengthHoagland's solution from seeds pretreated with triadimenol (0.3or 30 g (a.i.) kg^–1 of seed) was higher than controlsduring the growth period of 15 to 25 d after planting. Triadimenolalso increased chlorophyll levels, the increase being more pronouncedat its lower concentration. The treatment also increased theweight and nitrate content of the leaves. When seedlings weregrown in nutrient solution containing 1 to 20 mM nitrate, theincrease in nitrate reductase activity by triadimenol was higherat lower rather than at higher nitrate concentrations. The nitratelevels and Kjeldahl nitrogen in the triadimenol-treated leaveswas higher than the controls at concentrations of added nitrateabove 2 mM. Addition of nitrate to plants grown in ammonium,increased nitrate reductase activity more in plants grown fromtriadimenol-treated seeds than controls. However, addition of10µM triadimenol for 24 h to ammonium-grown plants hadlittle effect on enzyme activity, both in the absence as wellas the presence of nitrate. This study demonstrates that triadimenolincreases nitrate reductase activity and nitrate accumulationin the leaves and at least part of the increased enzyme activityis independent of nitrate accumulation. Key words: Triazoles, nitrate content, nitrate reductase activity     

Foliar application of nitrate or ammonium as sole nitrogen supply in Ricinus communis. II. The flows of cations, chloride and abscisic acid

Following a precultivation with pedospheric nitrogen nutrition, Ricinus plants were supplied with nitrogen solely by spraying nitrate or ammonium solution onto the leaves during the experimental period. The chemical composition of tissues, xylem and phloem exudates was determined and on the basis of the previously determined nitrogen flows (Peuke et al., New Phytologist (1998), 138 , 657–687) the flows of potassium, sodium, magnesium, calcium, chloride and ABA were modelled. These data, which permit quantification of net-uptake, transport in xylem and phloem, and utilization in shoot and root, were compared with results obtained in plants with pedospherically-supplied nitrate or ammonium and data in the literature. Although the overall effects on the chemical composition of supplying ammonium to the leaves were not as pronounced as in pedospherically supplied plants, there were some typical responses of plants fed with ammonium (ammonium syndrome). In particular, in ammonium-sprayed plants uptake and transport of magnesium decreased and chloride uptake was increased compared with nitrate-sprayed plants. Furthermore, acropetal ABA transport in the xylem in ammonium-sprayed Ricinus was threefold higher than in nitrate-sprayed plants. Additionally, concentrations of anions were more or less increased in tissues, particularly in the roots, and transport fluids. The overall signal from ammonium-sprayed leaves without a direct effect of ammonium ions on uptake and transport systems in the root is discussed.     

Regulation of Chloroplast Development by Nitrogen Source and Growth Conditions in a Chlorella protothecoides Strain

Chlorella strain (UTEX 27) maintains optimal photosynthetic capacity when growing photoautotrophically in the presence of ammonium. Nitrate-grown photoautotrophic cells, however, show a drastic loss of chlorophyll content and ribulose-1,6-bisphosphate carboxylase/oxygenase activity, resulting in a greater than 10-fold decrease in photosynthetic capacity and growth rate. Nitrate-grown cells are not deficient in protein content, and under mixotrophic and heterotrophic conditions, the alga can utilize nitrate as well as it does ammonium. The alga metabolizes both glucose and acetate in the dark with a doubling time of 5 to 6 hours. However, its growth on acetate is inhibited by light. Ribulose-1,6-biphosphate carboxylase/oxygenase activity correlates well with photosynthetic capacity, and glucose 6-phosphate dehydrogenase and hexokinase activities are altered in a manner consistent with the availability of glucose in growing cells. The alga appears to assimilate ammonium under photoautotrophic conditions primarily via the glutamine synthetase pathway, and shows an induction of both NADH and NADPH dependent glutamate dehydrogenase pathways under mixotrophic and heterotrophic conditions. Multiple isoforms are present only for hexokinase and glucose 6-phosphate dehydrogenase. Etiolated nitrate-grown cells resume greening and increase their photosynthetic capacity after about 6 hours of incubation in the presence of ammonium under photoautotrophic conditions. Similarly, the loss of photosynthetic capacity in ammonium-grown photoautotrophic cells commence about 9 hours after their transfer to heterotrophic nitrate containing media.     

Sodium transport and salt tolerance in plants

The ability of plant cells to maintain low cytosolic sodium concentrations is an essential process associated with the ability of plants to grow in high salt concentrations. Recent results have identified pathways for Na(+) entry, and the cloning of vacuolar Na(+)/H(+) antiporters has demonstrated the role of intracellular Na(+) compartmentation in plant salt tolerance.     

Physiological studies in salinity tolerance ofSesbania aculeata POIR

A pot culture experiment was performed to evaluate salt tolerance potential ofSesbania aculeata Poir. The plant can tolerate salinity levels up to electrical conductivity (ECe), 10 mS cm^?1 and at 15 mS cm^?1 thero is about 40% reduction in dry matter production. The analysis of inorganic constituents in different plant parts revealed that the plant has the capacity to regulate sodium uptake under saline conditions and chloride uptake always exceeded that of sodium. The potassium: sodium ratio is also maintained at a fairly constant level in leaflets while it is reduced in leaf rachis, stem and roots. Salt stress caused accumulation of calcium and magnesium in all plant parts. A considerable decline in phosphorus uptake was observed due to salinity. Iron was found to be accumulated more in salt stressed roots only. Nitrogen accumulated in both roots and leaves while considerable proline accumulation was observed in leaves of salt stressed plants. The amount of soluble sugars was increased in roots and leaves due to salt stress, while starch content of roots decreased. Those changes induced by salinity are discussed in relation to salt tolerance capacity of the plant.