Nitrate movement in xylem of lucerne plants

Nitrate content in lucerne stems and leaf blades immersed by cut ends in distilled water or in KNO₃ solution increased with the increase in KNO₃ concentration and with the duration of exposure under irradiance of 100 or 230 W m^?2 PAR. The nitrate content increased from basal stem parts to apical stem parts and leaves. Nitrate was transported mainly with transpiration stream. Some flow variations occurred in stems causing time changes in nitrate content in different parts of stems.     

Electrophysiological factors in the influence of nitrate and ammonium ions on calcium uptake and translocation in tomato plants

Abstract Tomato plants (Lycopersicon esculentum Mill. cv. San Marzano), grown in dilute nutrient solutions containing (in meq ˙ 1^-1) 0.5 NaNO₃, 0.5 NH₄NO₃ or 0.25 (NH₄)₂ SO₄ as the nitrogen source, were detopped for collection of xylem sap and measurement of trans-root electrical potentials. The plant parts and the xylem exudate were subsequently analysed for mineral content. The commonly observed effects of NH₄⁺ were noted, including reduction of calcium concentration in the xylem sap, and of calcium content in stems and leaves, compared with NO₃^-fed plants. This effect was attributed principally to the less negative trans-root electrical potential measured in NH₄⁺-fed plants, and the resultant reduction of inward driving force on passively moving divalent cations.     

Induction of a high-capacity nitrate-uptake mechanism in barley roots prompted by nitrate uptake through a constitutive low-capacity mechanism

Roots of nitrate-starved and nitrate-pretreated seedlings of Hordeum vulgare were used to investigate the induction of a high-capacity uptake mechanism for nitrate. When exposed to 0.2 mmol·l^-1KNO₃, nitrate-starved roots took up nitrate at a rate of approx. 1 mol·(g FW)^-1·h^-1; K⁺ was absorbed at a rate ten-times higher. Nitrate uptake accelerated after a lag of about 1 h, until it matched the rate of K⁺ uptake about 4 h later. p-Fluorophenylalanine (FPA), which prevents the synthesis of functioning proteins, suppressed the development of the high-capacity mechanism. Pretreatment of the roots with 0.2 mmol·l^-1 Ca(NO₃)₂ for 24 h established the high-capacity mechanism. Pretreated roots were able to absorb nitrate at high rates immediately upon exposure to 0.2 mmol·l^-1KNO₃, in the absence or presence of FPA. The high-capacity mechanism, once established, appeared to have a protein turnover as slow as that of the low-capacity mechanism or that of the mechanism involved in the uptake of K⁺. In contrast, the mechanisms for the transport of nitrate and K⁺ into the xylem vessels were completely blocked by FPA within 1 h of application, confirming earlier evidence for a rapid turnover of the transport proteins in the xylem parenchyma.Nitrate reduction proceeded at rates which were roughly one-tenth as large as the rates of the respective nitrate-uptake processes, indicating that nitrate-reductase activity was determined by the rate of nitrate uptake and not vice versa.We conclude that the formation of a high-capacity nitrate-uptake mechanism in barley roots occurs in response to nitrate uptake through a constitutive mechanism of low capacity which appears to function as a sensing mechanism for nitrate in the environment of the roots.Abbreviation FPA p-fluorophenylalanine     

Change in uptake, transport and accumulation of ions in Nerium oleander (rosebay) as affected by different nitrogen sources and salinity

Background and Aims

The source of nitrogen plays an important role in salt tolerance of plants. In this study, the effects of NaCl on net uptake, accumulation and transport of ions were investigated in Nerium oleander with ammonium or nitrate as the nitrogen source in order to analyse differences in uptake and cycling of ions within plants.

Methods

Plants were grown in a greenhouse in hydroponics under different salt treatments (control vs. 100 mm NaCl) with ammonium or nitrate as the nitrogen source, and changes in ion concentration in plants, xylem sap exuded from roots and stems, and phloem sap were determined.

Key Results

Plant weight, leaf area and photosynthetic rate showed a higher salt tolerance of nitrate-fed plants compared with that of ammonium-fed plants. The total amount of Na⁺ transported in the xylem in roots, accumulated in the shoot and retranslocated in the phloem of ammonium-fed plants under salt treatment was 1·8, 1·9 and 2·7 times more, respectively, than that of nitrate-treated plants. However, the amount of Na⁺ accumulated in roots in nitrate-fed plants was about 1·5 times higher than that in ammonium-fed plants. Similarly, Cl⁻ transport via the xylem to the shoot and its retranslocation via the phloem (Cl⁻ cycling) were far greater with ammonium treatment than with nitrate treatment under conditions of salinity. The uptake and accumulation of K⁺ in shoots decreased more due to salinity in ammonium-fed plants compared with nitrate-fed plants. In contrast, K⁺ cycling in shoots increased due to salinity, with higher rates in the ammonium-treated plants.

Conclusions

The faster growth of nitrate-fed plants under conditions of salinity was associated with a lower transport and accumulation of Na⁺ and Cl⁻ in the shoot, whereas in ammonium-fed plants accumulation and cycling of Na⁺ and Cl⁻ in shoots probably caused harmful effects and reduced growth of plants.Key words: Mineral cycling, Nerium oleander, nitrogen source, salinity, xylem and phloem transport     

Evaluation of the Relative Ureide Content of Xylem Sap as an Indicator of N(2) Fixation in Soybeans: GREENHOUSE STUDIES

The use of the relative ureide content of xylem sap [(ureide-N/total N) × 100] as an indicator of N₂ fixation in soybeans (Merr.) was examined under greenhouse conditions. Acetylene treatments to inhibit N₂ fixation were imposed upon the root systems of plants totally dependent upon N₂ fixation as their source of N and of plants dependent upon both N₂ fixation and uptake of exogenous nitrate. Significant decreases in the total N concentration of xylem sap from plants of the former type were observed, but no significant decrease was observed in the total N concentration of sap from the latter type of plants. In both types of plants, acetylene treatment caused significant decreases in the relative ureide content of xylem sap. The results provided further support for a link between the presence of ureides in the xylem and the occurrence of N₂ fixation in soybeans. The relative ureide content of xylem sap from plants totally dependent upon N₂ fixation was shown to be insensitive to changes in the exudation rate and total N concentration of xylem sap brought about by diurnal changes in environmental factors. There was little evidence of soybean cultivars or nodulating strains affecting the relative ureide content of xylem sap. `Ransom' soybeans nodulated with Rhizobium japonicum strain USDA 110 were grown under conditions to obtain plants exhibiting a wide range of dependency upon N₂ fixation. The relative ureide content of xylem sap was shown to indicate reliably the N₂ fixation of these plants during vegetative growth using a ¹⁵N method to measure N₂ fixation activity. The use of the relative ureide content of xylem sap for quantification of N₂ fixation in soybeans should be evaluated further.     

Microscopic investigation of changes in histology and digestibility in the rumen of a forage grass and a forage legume during the first growth stage.

An Italian "Dalita" ryegrass (Lolium italicum) and a European lucerne (Medicago sativa) were harvested at 5 different growth stages to determine the anatomical factors limiting their digestibility and in particular the effects of lignification of the tissues. In vitro digestibility, cell wall contents of the whole plant and stem of lucerne and of the whole plant, stem and leaf blade of ryegrass were determined. The rate and the extent of degradation in the rumen of the different tissues were observed by scanning electron microscopy. This degradation occurred very rapidly with the lucerne stems; the xylem of lucerne was the only undegradable tissue whatever the stage. The collenchyma was degraded in the rumen although with acid phloroglucinol it stained positive for the presence of phenolic compounds. Ryegrass stems were digested more slowly than lucerne stems, and the sclerenchyma and xylem of ryegrass were indigestible whatever the stage. The parenchyma located close to the sclerenchyma became indigestible as the cell walls lignified progressively from the third stage. These results contribute to the understanding of the decrease in digestibility over the first growth stage and the variation in rate of digestion of lucerne and ryegrass in the rumen.     

Seasonal Dynamics in Resource Partitioning to Growth and Storage in Response to Drought in a Perennial Rhizomatous Grass, <Emphasis Type="Italic">Leymus chinensis</Emphasis>

A natural grassland in northeastern China dominated by Leymus chinensis (Trin.) was subject to drought treatments to determine the seasonal dynamics in resource partitioning to shoot and storage organs in response to drought. The growing season was divided into six stages according to the phenology of L. chinensis. Plant samples of L. chinensis were collected at each stage to determine biomass, gross calorific value, relative water content, and key mineral contents of plant parts, including rhizomes, roots, leaves, and stems. Resource partitioning to shoot and storage organs as measured by biomass, gross calorific value, and N, K⁺, and Na⁺ contents varied significantly among phenologic stages. Drought treatment (natural precipitation, 50–60 % of field capacity) significantly reduced biomass, gross calorific value, relative water content of shoot, and N and K⁺ contents in both shoot and storage organs, but it enhanced rhizome : shoot ratio and Na⁺ content. A negative correlation in biomass, gross calorific value, and K⁺ and Na⁺ contents between shoot and storage organs was found throughout the growing season, which may have been accentuated by drought when soil moisture was limited. Our results indicate that resource partitioning to storage plays an important role in regulating plant growth of L. chinensis, especially under drought conditions.     

高盐生境中乌拉尔甘草盐离子分泌与积存格局的研究

采用植物水培方法,以乌拉尔甘草为研究材料,用不同浓度(0、80、160、320mmol·L~(-1))NaCl溶液胁迫处理乌拉尔甘草幼苗3周后,分析其叶片表面盐离子(K~+、Ca~(2+)、Na+)分泌速率的差异,并采集盐化低地草甸重盐土生境中2年生乌拉尔甘草植株,应用ICP-AES测定其不同部位(根、根状茎、茎、老叶和幼叶)中的盐离子(K~+、Na~+、Ga~(2+)、Mg~(2+))含量,探究盐离子在乌拉尔甘草叶片上的分泌格局以及盐离子在植株体内的积存格局,为完善甘草耐盐机理的研究提供依据。结果显示:(1)随着盐胁迫浓度的升高,乌拉尔甘草叶片上K~+、Ca~(2+)、Na+的分泌速率均呈增加趋势,且Na~+的分泌速率远远大于Ca~(2+)和K+的分泌速率。(2)在乌拉尔甘草各部位中,K+的积存量从大到小依次为:幼叶根根状茎茎老叶;Na~+在各个部位的积存量都十分有限,且无论地下部分还是地上部分,差异均不大;Ca~(2+)积存量由大到小依次为:老叶幼叶茎根状茎根,且老叶中Ca~(2+)的积存量显著高于其它部位。研究认为,在重盐碱地生境中,K+主要积存在幼叶中,Ga~(2+)主要积存在老叶中,植株体内各个部位Na~+的积存量很低,乌拉尔甘草表现出明显的拒Na现象;叶片分泌的主要盐离子为Na~+;乌拉尔甘草通过泌盐的方式将Na+排出体外,从而有效降低Na~+在体内的积存,这是其能够在重盐碱地生存生长的重要原因。     

Nitrate content and nitrate reductase activity in Rumex obtusifolius L.

Summary With Rumex obtusifolius L., the influence of some environmental conditions on nitrate uptake and reduction were investigated. Nitrate concentrations of plant material were determined by HPLC, the activity of nitrate reductase by an in vivo test. As optimal incubation medium, a buffer containing 0.04 M KNO₃; 0.25 M KH²PO₄; 1.5% propanol (v/v); pH 8.0 was found. Vacuum infiltration caused an increase of enzyme activity of up to 40%.High nitrate concentrations were found in roots and leaf petioles. Nitrate reductase activity of these organs, however, was low. On the other hand, the highest nitrate reductase activity was observed in leaf laminae, which contained lowest nitrate concentrations.In leaves, nitrate content and nitrate reductase activity exhibited inverse diurnal fluctuations. During darkness, decreasing activities of the enzyme were followed by increasing nitrate concentrations, while during light the contrary was true. In petioles diurnal fluctuations in nitrate content were observed, too. No significant correlations with illumination, however, could be found.Our results prove that Rumex obtusifolius is characterized by an intensive nitrate turnover. Theoretically, internal nitrate content of the plant would be exhausted within a few hours, if a supply via the roots would be excluded.     

New evidence for a role of vessel-associated cells and phloem in the rapid xylem refilling of cavitated stems of Laurus nobilis L.

Xylem recovery from embolism was studied in Laurus nobilis L. stems that were induced to cavitate by combining negative xylem pressure potentials (P_X = ?1.1 MPa) with positive air pressures (P_C) applied using a pressure collar. Xylem refilling was measured by recording the percentage loss of hydraulic conductance (PLC) with respect to the maximum 2 min, 20 min and 15 h after pressure release. Sodium orthovanadate (an inhibitor of many ATP‐ases) strongly inhibited xylem refilling while fusicoccin (a stimulator of the plasma membrane H⁺‐ATPase) promoted complete embolism reversal. So, the refilling process was interpreted to result from energy‐dependent mechanisms. Stem girdling induced progressively larger inhibition to refilling the nearer to the embolized stem segment phloem was removed. The starch content of wood parenchyma was estimated as percentages of ray and vasicentric cells with high starch content with respect to the total, before and after stem embolism was induced. A closely linear positive relationship was found to exist between recovery from PLC and starch hydrolysis. This, was especially evident in vasicentric cells. A mechanism for xylem refilling based upon starch to sugar conversion and transport into embolized conduits, assisted by phloem pressure‐driven radial mass flow is proposed.     

Influence of abscisic acid on unidirectional fluxes and intracellular compartmentation of K+ and Na+ in excised barley root segments

Using compartmental analysis, unidirectional fluxes of K⁺ and Na⁺ and their intracellular compartmentation in excised barley (Hordeum distichon L. cv. Kocher-perle) root segments have been measured during a steady state in the presence or absence of ABA. Almost all flux rates were altered in the presence of external ABA, in particular the xylem transport R’ and the plasmalemma influx Ø_oc (see below) were strongly inhibited in the steady state. At the same time the presence of ABA induced a strong increase in the vacuolar K⁺ and Na⁺ content Q_v and a decrease in the cytoplasmic one (Q_c). Since the fluxes of an ion and its vacuolar or, in particular, cytoplasmic concentrations are interrelated, the ratios of fluxes originating from the cytoplasm and the cytoplasmic ion content were taken into account. On this basis ABA had the following effects: a) the secretion of K⁺ or Na⁺ to the xylem vessels was drastically inhibited; b) the plasmalemma K⁺ or Na⁺ efflux Ø_co was moderately stimulated and c) the tonoplast influx Ø_cv of Na⁺ was stimulated, while the tonoplast influx of K⁺ appeared to be unchanged (the decrease in Ø_cv being due to the decreased cytoplasmic K⁺ content). By a similar argument, also the apparent inhibition of the plasmalemma influx Ø_oc of K⁺ and Na⁺ in the steady state merely is an indirect effect of ABA. It only reflects the strong ABA-induced decrease in the xylem transport, that governs the magnitude of Ø_oc in the steady state. The results are discussed with reference to possible regulatory functions of ABA. In this respect it is suggested that – in particular under conditions of stress – ABA might regulate cellular metabolic processes by changing the cytoplasmic K⁺ level.     

Water Transport in the Liana Bauhinia fassoglensis (Fabaceae)

To determine the efficiency of xylem conductance in the liana (woody vine) Bauhinia fassoglensis Kotschy ex Schweinf., we measured hydraulic conductance per unit stem length (measured K_h), leaf-specific conductivity (LSC = K_h/distal leaf area), transpiration rate (E), xylem water potential (ε), vessel number, and vessel diameter. The measured K_h was 49% (se = 7%) of the predicted K_h from Poiseuille's law. The mean LSC for unbranched stem segments was 1.10 × 10⁻⁸ square meters per megapascal per second (se = 0.07). LSCs were much lower (about 0.2) at branch junctions. At midday, with E at 7 × 10⁻⁸ meters per second, the measured drop in ε was about 0.08 megapascal per meter along the stems and branches and about 0.27 megapascal in going from stem to leaf. In addition, there was a drop of about 0.20 megapascal at branch junctions as predicted by E/LSC. In diurnal measurements leaf ε never dropped below about −1.2 megapascal. For long (e.g. 16 meters) stems, the predicted mid-day drop in ε through the xylem transport system might be great enough to have substantial physiological impact.     

Ionic Balance of Root-Shoot Nitrate Transfer in Dwarf Bean

The Dijkshoorn-Ben Zioni model about potassium recycling in higher plants proposes a stoichiometric coupling between the upward transport of nitrate and potassium, and therefore a 1:1 ratio of these ions in the xylem sap. Phaseolus vulgaris grown in media with different NO₃: K⁺ ratios, however, only rarely showed equimolar concentrations of the two ions in the bleeding sap. Ratios between 0.2 and 11 were observed and the ratios between concentrations of the ions in the exudate and in the external solution were positively correlated. An analysis of the major inorganic constituents of the exudate revealed an ionic balance that requires negligible amounts of charges from organic molecules.     

NaCl处理对西伯利亚白刺幼苗生长及离子平衡的影响

以1年生西伯利亚白刺水培幼苗为材料,研究了不同浓度NaCl(0、200、400mmol·L~(-1))处理对幼苗生长及不同器官(根、茎、叶)中Na~+、K~+、Ca~(2+)、Mg~(2+)的吸收、运输与分配的影响,探讨西伯利亚白刺的盐适应机制。结果表明:(1)200mmol·L~(-1) NaCl处理促进了西伯利亚白刺幼苗的生长及叶片肉质化程度,400mmol·L-1 NaCl处理显著抑制其生长。(2)随着NaCl处理浓度的升高,西伯利亚白刺幼苗根、茎、叶中Na~+含量显著增加,且叶中Na~+含量显著高于茎和根中;根系中K~+含量显著增加;根、茎、叶中Ca~(2+)、Mg~(2+)含量在200mmol·L~(-1) NaCl处理下保持平稳或上升,而在400mmol·L-1 NaCl处理下显著下降。(3)各器官中K~+/Na~+、Ca~(2+)/Na~+和Mg~(2+)/Na~+比值总体随NaCl处理浓度的升高呈下降趋势,且根部离子比值始终高于叶片和茎。(4)随着NaCl处理浓度的升高,西伯利亚白刺幼苗根-茎SK,Na显著下降,而根-茎SCa,Na、SMg,Na及茎-叶SK,Na、SCa,Na、SMg,Na逐渐提高。研究发现,西伯利亚白刺的盐适应机制主要是通过植株的补偿生长效应及叶片对Na~+的聚积作用实现的,同时也与根系对K~+的扣留及茎叶对K~+、Ca~(2+)、Mg~(2+)选择性运输能力增强有关。     

Organ-dependent responses of Periploca sepium to repeated dehydration and rehydration

Plant responses to water deficit occur in a complex framework of organ interactions, but few studies focus on the effect of drought stress on all organs in a whole-plant. The effects of repeated dehydration and rehydration (DH) on physiological and biochemical responses in various organs of Periploca sepium Bunge (P. sepium) were investigated. The leaf relative water content decreased significantly during drought, but recovered and showed an increase when compared to well-watered control plants. The malondialdehyde (MDA) content increased in mature and old leaves, but decreased in young leaves, new stems and fine roots during drought, indicating that the young and vigorous tissues of a whole-plant are protected preferentially from the oxidative stress. Among all organs, the fine roots showed the highest levels of proline, total free amino acids (TFAA) and Na⁺, while the leaves showed the highest levels of total soluble sugars (TSS), soluble proteins (SP), Ca²⁺ and Mg²⁺. The response to DH differed in different organs, both in magnitude and in the type of solutes involved. Drought stress increased the contents of proline, TFAA, TSS, SP and K⁺ in all organs of P. sepium plants, while the accumulation amounts were obviously different among the organs. The storage starch in stems and roots plays an important role in providing carbohydrates for growth. Changes in Na⁺, Ca²⁺ and Mg²⁺ under DH presented a high degree of organ specificity. Our data indicates that response strategies are different between different organs; therefore, evidence the needs to integrate all the information in order to better understand plant tolerance mechanisms.     

NaCl胁迫对圆柏幼苗生长和离子吸收及分配的影响

以当年生圆柏幼苗为实验材料,采用温室调控盆栽土培法研究了不同浓度NaCl(0、100、200、300mmol·L-1)胁迫21d对其生长情况及不同器官(根、茎、叶)中K~+、Na~+、Ca~(2+)和Mg~(2+)的吸收和分配的影响,以探讨圆柏幼苗对盐环境的生长适应性及耐盐机制。结果表明:(1)随着NaCl胁迫浓度的增加,圆柏幼苗生长,包括株高、地径、相对生长量以及生物量的积累均呈下降趋势,而其根冠比却增加。(2)在各浓度NaCl胁迫处理下,圆柏幼苗根、茎、叶中Na~+含量较对照均显著增加,而且叶中Na~+含量显著高于茎和根,叶中Na~+含量是根中的5倍。(3)随着NaCl胁迫浓度的升高,圆柏幼苗各器官中K~+、Ca~(2+)和Mg~(2+)含量以及K~+/Na~+、Ca~(2+)/Na~+及Mg~(2+)/Na~+比值均呈下降趋势。(4)在NaCl胁迫条件下,圆柏幼苗根系离子吸收选择性系数SK,Na、SCa,Na、SMg,Na显著提高,茎、叶离子转运选择性系数SCa,Na、SMg,Na则逐渐降低,叶中离子转运选择性系数SK,Na则随着NaCl胁迫浓度的升高显著降低,大量Na~+进入地上部,减缓了盐胁迫对根系的伤害。研究认为,圆柏幼苗的盐适应机制主要是通过根系的补偿生长效应及茎、叶对Na~+的聚积作用来实现的,同时也与根对K~+、Ca~(2+)、Mg~(2+)的选择性运输能力增强和茎、叶稳定的K~+、Ca~(2+)、Mg~(2+)的选择性运输能力有关。     

盐胁迫对3种平欧杂种榛幼苗叶片解剖结构及离子吸收、运输与分配的影响

研究盐胁迫下3个品种平欧杂种榛幼苗叶片解剖结构和离子代谢特征,以揭示盐胁迫响应与适应机制及不同品种的耐盐性差异。以‘达维’、‘辽榛7号’、‘玉坠’2年生压条苗为材料,在盆栽条件下经轻度、中度、重度(分别为50、100、200 mmol/L NaCl)盐胁迫处理,设对照为0,研究幼苗叶片显微解剖结构参数和Na~+、K~+、Cl~-、Ca²⁺含量的变化及其在根、茎、叶中的吸收、运输和分配特征。不同品种平欧杂种榛叶片厚度、上表皮厚度、下表皮厚度、栅栏组织和海绵组织厚度随着盐胁迫程度的增强呈现出先增加后降低的特点,轻度和中度胁迫下各参数显著高于对照。中度盐胁迫显著提高了各品种叶片结构紧密度。盐胁迫导致平欧杂种榛根、茎、叶Na~+和Cl~-含量明显高于对照。盐胁迫下,Na~+和Cl~-在叶中的绝对含量明显高于茎和根,但二者的增幅以根中最大,叶中最小,表明平欧杂种榛根系首先会吸收并截留一定数量的Na~+和Cl~-,然后将其运输至茎和叶中。与对照相比,轻度和中度盐胁迫下根、茎对K~+和Ca²⁺的吸收保持稳定或减少,叶对K~+和Ca²⁺...     

Partial nitrate nutrition amends photosynthetic characteristics in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L. var. <Emphasis Type="Italic">japonica</Emphasis>) differing in nitrogen use efficiency

Partial nitrate nutrition (PNN) was found to improve rice (Oryza sativa L. var. japonica) growth. However, how PNN is related to photosynthesis in rice cultivars with different nitrogen use efficiency (NUE) is still not clear. Two rice cultivars, Nanguang (high NUE) and Elio (low NUE), were grown under sole NH₄ ⁺ and PNN at a total nitrogen concentration of 2.86 mM. The dry weight, leaf area, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and gas exchange parameters were measured. Nitrogen and Rubisco contents in the newly expanded leaves of cv. Nanguang were similar to those of cv. Elio when only NH₄ ⁺ was supplemented in the nutrient solution. However, in cv. Nanguang, nitrogen and Rubisco contents increased under PNN than under sole NH₄ ⁺ nutrition. Higher nitrogen and Rubisco contents were recorded in cv. Nanguang than in cv. Elio under PNN. The ratio of carboxylation efficiency (CE) to Rubisco content in cv. Nanguang was 11 and 14% higher than that in cv. Elio under NH₄ ⁺ and PNN, respectively. CE was 14% higher in cv. Nanguang than that in cv. Elio. The results suggest that PNN causes an increase in photosynthesis in cv. Nanguang. It is concluded that differences in Rubisco activity, rather than stomatal limitation, are responsible for the differences in photosynthesis between the two cultivars. The presence of nitrate increases Rubisco content in rice with a high NUE, which leads to faster biomass accumulation at later growth stages.     

Changes in ion and water content of individual shoot organs in a salt-tolerant and a salt-sensitive clone of Agrostis stolonifera L. during and subsequent to treatment with sodium chloride

Abstract Individual leaves and stems were analysed for Na⁺, Cl^?, K⁺ and water content in two clones of Agrostis stolonifera differing in salt resistance, during 14 d of treatment with NaCl, 100 and 200 mol m^?3, and a further 7 d in a salt-free medium. Great differences in ion and water content were revealed between individual organs, and organ-by-organ analysis also emphasized the differences between the clones better than whole shoot analysis. In both clones, Na⁺ and Cl^? accumulated to the greatest degree in the older leaves, but for corresponding organs, the concentrations were lower in the more tolerant clone. In the sensitive clone, the lowest leaves dehydrated in 200 mol m^?3 NaCl and failed to recover, while the plants of the more resistant clone maintained viable water content in all organs. In the resistant clone, K⁺ concentration decreased less in response to salt treatment than in the more sensitive clone. For a full appreciation of the plants' reactions, it was found necessary to express the analytical data on several bases, namely, per unit dry-weight, unit water, and total ion-content.