Changes in k, rb, and na transport to shoots after anoxia

The effect of anoxia on subsequent uptake and transport of K, Rb, and Na was examined with seedlings of barley (Hordeum vulgare L.), corn (Zea mays L.), and tall fescue (Lolium × Festuca hybrid derivative) to further our understanding of xylem loading. Roots were incubated in solutions depleted of O₂ by flushing with N₂ gas. After 1 hour exposure, plants were returned to aerated solutions for 16 hours prior to measuring uptake and transport. For each species, anoxia pretreatment significantly enhanced Na transport to the shoot. The rate of Na accumulation into roots, however, was not affected. There was no enhancement of either K or Rb accumulation in shoots, indicating specificity for Na transport. A minimum exposure to anoxia of 30 minutes and a minimum of 12 hours elapsed time was necessary to achieve the maximum rate of Na transport to the shoot in barley seedlings. Accumulation of Na in the shoot of both the control and anoxia pretreated barley plants was inhibited by anoxia and by addition of the proline analog, l-azetidine-2-carboxylic acid, during the uptake period. Enhancement of Na transport was associated with a proportional increase in the rate of synthesis of a membrane bound protein with a molecular weight of 78,000 daltons.     

转HAL1基因番茄的耐盐性

利用农杆菌介导的叶盘法,把HAL1 基因转入番茄,Southern杂交检测得到转基因植株.耐盐实验表明, T1代转基因番茄在150 mmol/L的NaCl胁迫下仍有43%的发芽率,200 mmol/L的NaCl胁迫下发芽率为6%,而对照种子在100和150 mmol/L的NaCl胁迫下发芽率分别为11.0%和0.转基因番茄的电解质相对外渗率小于对照,而根冠比和叶绿素含量大于对照,转HAL1基因显著提高了番茄的耐盐性.盐胁迫下Na 、K 的累积状况表明,转基因番茄根、茎、叶的K /Na 均有所提高,根系的SK/Na增大,茎、叶的RSK/Na和RLK/Na减小,说明根系对K /Na 离子的选择吸收和运输能力加强.不但选择吸收K /Na ,而且表现出整株水平上的有利于耐盐的K /Na 区域化分配.     

Salt tolerance in Aster tripolium L. II. Ionic regulation

Abstract Measurements of tissue ion contents (Na, K and Cl) were carried out at frequent intervals on plants of Aster tripolium L. grown at a range of salinities for 36 d. Aster tripolium behaved as a typical halophyte showing high levels of inorganic ion accumulation even at low salinities. As salinity increased Na replaced K to a large extent in the shoot but root K was unaffected up to 500 mol m^?3 external NaCl. Shoot (Na + K) concentration on a tissue water basis was maintained constant in all treatments throughout the experiment, whereas shoot (Na + K) on a dry weight basis showed marked fluctuations in some treatments. An increase in (Na + K) per gram dry weight was, however, accompanied by a parallel increase in fresh weight: dry weight (FW : DW) ratio. Transport of (Na + K) to the shoot per unit root weight changed during the experiment in the manner expected, given the observed changes in shoot relative growth rate and FW : DW to result in a constant shoot (Na + K) concentration on a water basis. Chloride was the major balancing anion in the shoot at high salinity, but never accounted for more than 38% of the (Na + K) found in the root tissue. At all salinities (Na + K) salts accounted for the majority of the measured shoot sap osmotic potential. The interactions between salinity, growth, ion transport and osmotic adjustment are discussed.     

Adaptation of potassium translocation into the shoot of maize (Zea mays) to shoot demand: Evidence for xylem loading as a regulating step

In order to manipulate the shoot demand for mineral nutrients per unit root weight, maize ( Zea mays L.) seedlings were grown in nutrient solution with different temperatures in the root zone and at the shoot base. The aerial temperature was kept uniform at 24/20°C day/night. At a root zone temperature (RZT) of 24°C, shoot growth was reduced by decreasing the shoot base temperature (SBT) to 12°C; at a RZT of 12°C, shoot growth was increased by raising the SBT to 24°C. At both RZT root growth was not affected by the SBT. Thus, the shoot demand for nutrients per unit root was either increased by raising, or decreased by lowering the SBT. The net uptake rate of potassium (K), as determined from accumulation rates between sequential harvests, was not affected within the first 3 days after lowering the SBT, whereas net translocation rates of K into the shoot and translocation rates in the xylem exudate of decapitated plants were markedly reduced. Obviously, translocation of K into the shoot seems to be regulated independently from K uptake into the root cells. Translocation rates of K in the xylem exudate of decapitated plants were markedly reduced when the nutrient solution was replaced by CaCl₂ solution during exudation. But, depending on the SBT before decapitation, significant differences remained in the translocation rates of K even when K uptake from the nutrient solution was prevented.
From the results it is suggested that xylem loading of K is regulated separately from K uptake from the external solution and that the adaptation of K translocation to shoot demand is coupled with an altered capacity of the root for xylem loading.     

Root-shoot interactions in mineral nutrition

In this paper four classes of co-operative root-shoot interations are addressed. (I) Nitrogen concentrations in the xylem sap originating from the root and in the phloem sap as exported from source leaves are much lower than those required for growth by apices and developing organs. Enrichment of xylem sap N is achieved by xylem to xylem (X-X) transfer, by which reduced N, but not nitrate, is abstracted from the xylem of leaf traces and loaded into xylem vessels serving the shoot apex. Nitrogen enrichment of phloem sap from source leaves is enacted by transfer of reduced N from xylem to phloem (X-P transfer). Quantitative data for the extent of the contribution of X-X and X-P transfer to the nutrition of young organs of Ricinus communis L. and for their change with time are presented. (II) Shoot and root cooperate in nitrate reduction and assimilation. The partitioning of this process between shoot and root is shifted towards the root under conditions of nitrate- and K-deficiency and under salt stress, while P deficiency shifts nitrate reduction almost totally to the shoot. All four changes in partitioning can be attributed to the need for cation-anion balance during xylem transport and the change in electrical charge occurring with nitrate reduction. (III) Even maintenance of the specificity of ion uptake by the root may – in addition to its need for energy – require a shoot-root interaction. This is shown to be needed in the case of the maintenance of K/Na selectivity under the highly adverse condition of salt stress and absence of K supply from the soil. (IV) Hormonal root to shoot interactions are required in the whole plant for sensing mineral imbalances in the soil. This is shown and addressed for conditions of salt stress and of P deficiency, both of which lead to a strong ABA signalling from root to shoot but result in different patterns of response in the shoot.     

Salinity tolerance of japonica and indica rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) at the seedling stage

In order to identify the degree of salinity tolerance of the indica and japonica rice groups, 10 varieties were tested under saline and non-saline conditions. Twelve-day-old seedlings were grown in normal culture solution, then initially salinized at an electrical conductivity (EC) of 6 dS/m for 4 days, and finally salinized at an EC of 12 dS/m for the next 14 days. The growth parameters, and Na and K absorption in the shoot were measured to characterize the tolerance level of the two rice groups. Reduction in all growth parameters of tolerant varieties was significantly lower in indica varieties than in japonica varieties. Tolerant indica varieties were good Na excluders, absorbed high amounts of K, and maintained a low Na/K ratio in the shoot. Tolerant japonica varieties also absorbed less Na but were not as good excluders as indica varieties. Shoot K concentration alone did not show any relationship to salinity tolerance. These results indicate that, for all parameters measured, the tolerance level of indica was higher than that of japonica.     

Alkali grass resists salt stress through high [K+] and an endodermis barrier to Na+

In order to understand the salt-tolerance mechanism of alkali grass (Puccinellia tenuiflora) compared with wheat (Triticum aestivum L.), [K(+)] and [Na(+)] in roots and shoots in response to salt treatments were examined with ion element analysis and X-ray microanalysis. Both the rapid K(+) and Na(+) influx in response to different NaCl and KCl treatments, and the accumulation of K(+) and Na(+) as the plants acclimated to long-term stress were studied in culture- solution experiments. A higher K(+) uptake under normal and saline conditions was evident in alkali grass compared with that in wheat, and electrophysiological analyses indicated that the different uptake probably resulted from the higher K(+)/Na(+) selectivity of the plasma membrane. When external [K(+)] was high, K(+) uptake and transport from roots to shoots were inhibited by exogenous Cs(+), while TEA (tetraethylammonium) only inhibited K(+) transport from the root to the shoot. K(+) uptake was not influenced by Cs(+) when plants were K(+) starved. It was shown by X-ray microanalysis that high [K(+)] and low [Na(+)] existed in the endodermal cells of alkali grass roots, suggesting this to be the tissue where Cs(+) inhibition occurs. These results suggest that the K(+)/Na(+) selectivity of potassium channels and the existence of an apoplastic barrier, the Casparian bands of the endodermis, lead to the lateral gradient of K(+) and Na(+) across root tissue, resulting not only in high levels of [K(+)] in the shoot but also a large [Na(+)] gradient between the root and the shoot.     

Absorption and lymphatic transport of cholesterol and sitosterol in the rat

An attempt was made to determine the mechanism for the greater absorbability of cholesterol as compared to sitosterol. Sitosterol-22,23-(3)H in different combinations with cholesterol-4-(14)C, dissolved in 0.8 ml of triolein, was fed to rats with lymph fistulae. Feeding 1.5, 50, or 100 micro moles of sitosterol resulted in a transfer to the lymph in 24 hr of 3-6% of the sitosterol, largely independent of the dose fed. The total amount of sitosterol transferred to the lymph was therefore almost linearly related to the dose fed. 30% of a tracer dose of cholesterol-4-(14)C fed together with the sitosterol was transferred to the lymph in 24 hr. When a total of 50 micro moles of sterol, containing cholesterol-(14)C and sitosterol-(3)H in the proportions 1:3, 1:1, and 3:1, was similarly fed, we found that sitosterol had no significant effect on the lymphatic transport of the simultaneously fed cholesterol. The ratio of (3)H to (14)C in the lymph was between 0.1 and 0.2 (the ratio in each fed mixture being taken as 1.0). The ratio was constant during the absorption period and independent of the ratio of sterols in the fed sterol mixture. Thus the same percentage of each sterol was always absorbed, and the sterols exerted no mutual interference in each others' absorption. We conclude that the mechanism for specificity in sterol absorption must be located early in the transport of the sterols within the intestinal mucosa cell.     

Effect of Root Zone Temperature and Shoot Demand on Uptake and Xylem Transport of Macronutrients in Maize (Zea mays L.)

The effect of shoot demand for nutrients on nutrient uptakeand translocation in the xylem exudate was studied in maizegrowing in nutrient solution at uniform shoot zone (24/2C,day/night), but different root zone temperatures (RZT: 12C,18C, 24C). The shoot base (apical shoot meristem and zoneof leaf extension) was either kept within or lifted above thecooling zone. In plants with their shoot base above the coolingzone (RZT: 12C and 18C) shoot growth was significantly increasedbut not root growth. Therefore, at suboptimal RZT shoot freshweight increment d^–1 g^–1 root fresh weight, whichwas taken as a parameter for the shoot demand for nutrientsper unit root, varied strongly depending on the temperatureof the shoot base (shoot base temperature, SBT). In short-term studies (2 h and 1 d after onset of temperaturetreatment) rates of nutrient (nitrogen, N; potassium, K; phosphorus,P; calcium, Ca) uptake or translocation in the xylem exudatewere markedly decreased at suboptimal RZT (12C, 18C), irrespectiveof the SBT. In long-term studies (3, 5, and 10 d after onsetof temperature treatment) uptake and translocation of K, N,and Ca, but not P, increased in plants at suboptimal RZT whenthe shoot demand was high (shoot base above the cooling zone)but decreased when the shoot demand was low (shoot base withinthe cooling zone). These results suggest, that the increase of translocation ratesof N, K, and Ca after long-term exposure to suboptimal RZT wasa consequence of a higher shoot demand per unit root fresh weightand not due to a direct temperature effect on the nutrient uptakesystem. Key words: Xylem exudate, nutrient translocation, root zone temperature, shoot demand, nutrient circulation     

A net gain of sodium ions and a net loss of potassium ions accompanying the uptake of glycine by mouse ascites-tumour cells in the presence of sodium cyanide

1. The tumour cells were starved in a solution lacking Na(+) and then transferred to a Ringer solution containing 2mm-sodium cyanide, 150m-equiv. of Na(+)/l. and 10m-equiv. of K(+)/l. Such cells were depleted of ATP and contained an endogenous pool of various amino acids equivalent to a 26mm solution. 2. At 4min. after the transfer the cellular Na(+) content had increased by about 100% and roughly an equivalent amount of K(+) had left the cells. 3. Under these conditions [(14)C]glycine was absorbed from an 11mm solution and reached the same cellular concentration by about 4min. The pool size increased by approximately the same amount (DeltaGly), so glycine did not simply exchange with the endogenous components. 4. After 4min. with glycine, the cells contained about 20% more Na(+) (DeltaNa(+)) than the control and about 10% less K(+) (DeltaK(+)). The mean values of DeltaNa(+)/DeltaGly and DeltaK(+)/DeltaGly from five experiments were respectively 0.90+/-0.11 and 0.62+/-0.11equiv./mole. 5. A further indication that these two ratios were not equal was that the cells absorbed more water than the movement of glycine itself required. The excess of water was osmotically equivalent to 0.95+/-0.16equiv. of solute/mole of glycine absorbed. 6. The variation of DeltaNa(+)/DeltaGly with the duration of the incubation was consistent with the stimulated uptake of Na(+) being linked to the actual transport of glycine. The same may apply to the movement of K(+), though the time-dependence was not examined in that case. 7. The observations were analysed in terms of a model in which both K(+) and Na(+) moved with a glycine-carrier system without ATP being involved. The analysis supported the idea that the spontaneous movements of the ions through the system might concentrate glycine in the cells significantly by purely physical means (Christensen's hypothesis).     

Effect of the arbuscular mycorrhizal symbiosis upon uptake of cesium and other cations by plants

Pot experiments were set up to determine the species-specific uptake of cesium (Cs) by mycorrhizal (AM) and non-mycorrhizal (non-AM) plants. Using stable Cs and K application, side-effects of mineral fertilization (K) on AM development and uptake of Cs and the other cations Na, Ca and Mg were investigated. AM colonization by the fungus Glomus mosseae led to a significant decrease in shoot Cs content of Agrostis tenuis from the first (4 weeks) to the third harvest (8 weeks). With regard to the root system, statistically significant differences were observed from the first (4 weeks) to the second harvest (6 weeks). Supply of additional K produced a significant decrease in Cs uptake by both AM and non-AM plants over a 10-week period. In the case of AM plant shoots, K fertilization did not very effectively reduce Cs uptake by A. tenuis. Cs contents of fertilized AM roots were similar to non-AM controls. Potassium application resulted in an increase in K content and a slight reduction in Na and Mg contents of shoots and roots. Without K fertilization, the Na content of non-AM controls was significantly enhanced over AM shoots. Shoot and root Ca contents were generally higher without than with K addition. Negative side-effects of K fertilization as a countermeasure to Cs uptake were not observed in relation to AM development. The intensity of colonization by G. mosseae was not significantly depressed by K treatment. AM development in plants appeared to decrease Cs uptake, at least at moderate nutrient levels. It is possible that Cs is sequestered by AM extraradical fungal hyphae and consequently not transferred to the plant to the extent found in non-AM roots. Accepted: 6 November 2000     

Effects of PGE1 alone and on sympathetically mediated Na, K transport in the perfused main submandibular duct of rat

PGE1 was administered in 5 micrograms/kg doses every 5 min over a period of 70 min and Na and K transport in the perfused main duct of rat submandibular gland was examined during a period without stimulation of the sympathetic nerve as well as during stimulation of the sympathetic nerve. A 25% decrease in the amount of Na absorbed and a 42% decrease in the amount of K secreted occurred when PGE1 alone was administered; the same change occurred when the sympathetic nerve was stimulated in the presence of PGE1. These data show, for the first time, an effect of PGE1 alone on electrolyte transport, and suggest that specific PGE1 receptors are activated.     

Osmoregulatory action of 17beta-estradiol in the gilthead sea bream Sparus auratus

The osmoregulatory action of 17beta-estradiol (E2) was examined in the euryhaline teleost Sparus auratas. In a first set of experiments, fish were injected once with vegetable oil containing E2 (1, 2 and 5 microg/g body weight), transferred 12h after injection from sea water (SW, 38 ppt salinity) to hypersaline water (HSW, 55 ppt) or to brackish water (BW, 5 ppt salinity) and sampled 12h later (i.e. 24 h post-injection). In a second experiment, fish were injected intraperitoneally with coconut oil alone or containing E2 (10 microg/g body weight) and sampled after 5 days. In the same experiment, after 5 days of treatment, fish of each group were transferred to HSW, BW and SW and sampled 4 days later (9 days post-implant). Gill Na+,K+ -ATPase activity, plasma E2 levels, plasma osmolality, and plasma levels of ions (sodium and calcium), glucose, lactate, protein, triglyceride, and hepatosomatic index were examined. Transfer from SW to HSW produced no significant effects on any parameters assessed. E2 treatment did not affect any parameter. Transfer from SW to BW resulted in a significant decrease in plasma osmolality and plasma sodium but did not affect gill Na+,K+ -ATPase activity. A single dose of E2 attenuated the decrease in these parameters after transfer from SW to BW, but was without effect on gill Na+,K+ -ATPase activity. An implant of E2 (10 microg/g body weight) for 5 days significantly increased plasma calcium, hepatosomatic index, plasma metabolic parameters, and gill Na+,K+ -ATPase activity. In coconut oil-implanted (sham) fish, transfer from SW to HSW or BW during 4 days significantly elevated gill Na+,K+ -ATPase. Gill Na+,K+ -ATPase activity remained unaltered after transfer of E2-treated fish to HSW or BW. However, in E2-treated fish transferred from SW to SW (9 days in SW after E2-implant), gill Na+,K+ -ATPase activity decreased with respect to HSW- or BW-transferred fish. Shams transferred to HSW showed increased levels of lactate, protein, and trygliceride in plasma, while those transferred to BW only displayed increased trygliceride levels. E2-treated fish transferred to HSW showed higher protein levels without any change in other plasmatic parameters, while those transferred to BW displayed elevated plasma glucose levels but decreased osmolality and protein levels. These results substantiate a chronic stimulatory action of E2 on gill Na+,K+ -ATPase activity in the euryhaline teleost Sparus auratas.     

Effect of sub-optimal root zone temperatures at varied nutrient supply and shoot meristem temperature on growth and nutrient concentrations in maize seedlings (Zea mays L.)

Maize seedlings were grown for 10 to 20 days in either nutrient solution or in soils with or without fertilizer supply. Air temperature was kept uniform for all treatments, while root zone temperature (RZT) was varied between 12 and 24°C. In some treatments the basal part of the shoot (with apical shoot meristem and zone of leaf elongation) was lifted up to separate the indirect effects of root zone temperature on shoot growth from the direct effects of temperature on the shoot meristem.Shoot and root growth were decreased by low RZT to a similar extent irrespective of the growth medium (i.e. nutrient solution, fertilized or unfertilized soil). In all culture media Ca concentration was similar or even higher in plants grown at 12 as compared to 24°. At lower RZT concentrations of N, P and K in the shoot dry matter decreased in unfertilized soil, whereas in nutrient solution and fertilized soil only the K concentration decreased.When direct temperature effects on the shoot meristem were reduced by lifting the basal part of the shoot above the temperature-controlled root zone, shoot growth at low RZT was significantly increased in nutrient solution and fertilized soil, but not in unfertilized soil. In fertilized soil and nutrient solution at low RZT the uptake of K increased to a similar extent as plant growth, and thus shoot K concentration was not reduced by increasing shoot growth rates. In contrast, uptake of N and P was not increased, resulting in significantly decreased shoot concentrations.It is concluded that shoot growth at suboptimal RZT was limited both by a direct temperature effect on shoot activity and by a reduced nutrient supply through the roots. Nutrient concentrations in the shoot tissue at low RZT were not only influenced by availability in the substrate and dilution by growth, but also by the internal demand for growth.     

Effect of calcium on transport of cations to the xylem exudate of tobacco

Summary Roots of detopped tobacco plants (Nicotiana tabacum var. Virginia Gold) were exposed to Na, K, and Ca salts or to water, and cation transfer to xylem vessels was measured. In some cases plants had been exposed to Na in addition to regular nutrient solutions before detopping. Calcium in the external medium greatly depressed the transport of Na from the external medium to the xylem vessels and it often stimulated the transfer of K from the external medium to the xylem vessels. The K/Na ratio in the exudate thus was dependent upon the Ca content of the external medium under these conditions. In contrast, externally applied Ca or Ca deficiency had very little effect on the transfer of preaccumulated K and Na from compartments within roots to the xylem vessels. The K/Na ratio in the exudate under these conditions was not related to Ca levels nor to mild Ca deficiency. The ratios decreased with time after detopping regardless of Ca level. Intact plants accumulated more Na than did root systems of detopped plants in a 6-day period.Riverside University of CaliforniaSoil Science and Agricultural Engineering     

Dormancy in Seeds of Charlock (Sinapis arvensis L.): Early Effects of Gibberellic Acid on the Synthesis of Amino Acids and Proteins

Charlock (Sinapis arvensis L.) seeds were imbibed with 10 mm GA(3) for 24 hours at 0 C. After equilibration at 25 C, a 5-fold increase in radioactivity in the amino acids labeled from 2-(14)C-acetate was observed within 2 hours. The total amount of amino acids was reduced to half, and the specific radioactivity increased approximately 10-fold, indicating a diversion of metabolites for amino acid and protein synthesis in GA(3)-treated seeds. The rate of incorporation of l-(14) C-leucine into protein was doubled. Autoradiographs showed that enhancement of protein synthesis was localized in the shoot and root meristems, the developing vascular tissues, and in the endosperm cells inside the testa.     

NaCl胁迫对杂交狗牙根品种‘苏植2号’和‘Tifgreen’生长及Na＋和K＋积累的影响

对0（对照）和20g·L-1NaCl胁迫条件下杂交狗牙根（Cynodondactylon×C.transvaalensis）品种‘苏植2号’（‘SuzhiNo.2’）和‘Tifgreen’不同部位的生长状况以及Na＋和K＋积累的差异进行了研究,并分析了2个品种间Na＋、K＋转运调控机制的差异。结果显示：在NaCl胁迫条件下,2个品种的叶片相对枯黄率、地下茎和根系的相对干质量、叶片和根系的Na＋含量和Na＋/K＋比以及钠钾选择性转运系数增加;修剪茎叶及冠层和地上部的相对干质量、植株相对总干质量以及叶片和根系的K＋含量均降低,但茎叶含水量无显著变化。NaCl胁迫条件下,不同土层中2个品种的根系相对干质量均不同程度增加,且20-40和40-60cm土层中根系干质量的增幅大于0-20cm土层;在0-20cm土层中2个品种根系的分配比例均有所降低,而在20-40和40-60cm土层中则不同程度提高。与‘Tifgreen’相比,NaCl胁迫条件下‘苏植2号’叶片相对枯黄率、Na＋含量和Na＋/K＋比更低,修剪茎叶及冠层和地上部的相对干质量、植株相对总干质量、叶片K＋含量和钠钾选择性转运系数更高;在20-40和40-60cm土层中‘苏植2号’根系相对干质量显著高于‘Tifgreen’,根系分配比例总体也高于‘Tifgreen’。综合比较结果表明：‘苏植2号’的抗盐性强于‘Tifgreen’,可能与其深层根系分配量更高和钠钾选择性转运能力较强有关。     

盐胁迫下盐角草 Na ＋／H ＋转运基因表达分析

Na＋/H＋逆向转运蛋白具有调节细胞内离子浓度及维持pH值稳定的作用,是植物抵御盐胁迫的重要因子。从盐角草RNA-Seq数据中筛选Na＋/H＋逆向转运蛋白序列,利用生物信息学手段,拼接得到5条Na＋/H＋逆向转运蛋白完整cDNA序列,通过与NCBI已有序列比对分析,将其命名为SeNHX1、SeNHX3、SeNHX4、SeNHX5和SeN-haD。考察盐角草Na＋/H＋逆向转运蛋白在两种盐分变化情况下的表达变化：1）从无盐处理转移到200 mM NaCl处理;2）从200 mM NaCl培养基转移到无盐培养基。结果表明：SeNHX4的表达量非常低,在地下部几乎检测不到;SeNhaD在地上部的表达量是地下部的2倍左右,说明NhaD主要在盐角草地上部发挥作用;SeNHX1、SeNHX3和SeNHX5的表达量明显高于其他两个基因,对盐角草的耐盐机制起到更大的作用,并且SeNHX1和SeNHX5受盐分诱导表达,表达量与盐浓度呈正相关,可能在盐角草耐盐调控网络中发挥重要作用。综上,NHX基因家族和NhaD的表达量受到基质中盐分的调控作用,其表达在盐分处理或者盐分去除1～3d后发生变化。研究结果有助于阐明盐角草NHX基因家族和NhaD对盐分的响应特点。     

Effect of replacing nutrient potassium by sodium on uptake and distribution of sodium in tomato plants

Summary Tomato plants (Lycopersicon esculentum cv. Amberley Cross) were grown in a series of nutrient solutions in which 0, 60, 90, 95, 98 and 99 per cent of the K was replaced by Na. The plants selectively absorbed K relative to Na from the nutrient solutions and transported K to the shoots in preference to Na. In the nutrient solution having the highest K/Na ration most of the Na taken up by the plants accumulated in the roots, but as the K was progressively replaced by Na an increasing proportion of the total Na absorbed was transported to the leaves. Sodium was present at up to 2.4 per cent of the dry wt of whole, fully-expanded leaves without there being any apparent visual signs of damage or reduction in the rate of growth of the plants. On closer examination it was found that most of the Na transported to the leaves was excluded from the laminar tissue and accumulated in the adjacent petioles. The ability of the roots and petioles to retain large amounts of Na depended on an adequate supply of K to the plants.