Regulation by ABA of osmotic-stress-induced changes in protein synthesis in tomato roots

Polypeptide synthesis and accumulation were examined in the roots of tomato seedlings exposed to a polyethylene glycol‐imposed water deficit stress. In these roots, the synthesis of a number of polypeptides was induced, while that of several others was enhanced or repressed. To examine the role played by abscisic acid (ABA) in co‐ordinating the accumulation of these proteins, water‐deficit‐stress‐responsive polypeptide synthesis was investigated in the roots of the ABA‐deficient mutant flacca. In the roots of this mutant, the ability to accumulate a complete set of water‐deficit‐stress‐responsive polypeptides was impaired, indicating that ABA is required for their synthesis. The role of ABA was further examined by exposing the roots of both genotypes to exogenous ABA, which, with one exception, elicited the accumulation of all water‐deficit‐stress‐responsive proteins. Polyethylene glycol‐induced polypeptide accumulation was accompanied by a 1·6‐fold increase in the level of endogenous ABA in the roots of wild‐type plants and a 5‐fold increase in the roots of flc. Thus, although the absolute level was lower than that of the wild‐type, flc has the capacity to accumulate ABA in its roots. When fluridone was used to prevent the biosynthesis of ABA, the accumulation of several water‐deficit‐stress‐responsive polypeptides was reduced further. The synthesis of polypeptides was also examined in the roots of salt‐treated seedlings. Salt altered the accumulation of several polypeptides, all of which were previously observed in water‐deficit‐stressed roots, indicating that their synthesis was the result of the osmotic component of the salt stress. However, the accumulation of these polypeptides was not impaired in flc roots, indicating that the role played by ABA in regulating their accumulation in salt‐and polyethylene glycol‐treated roots differs. As such, salt‐ and water‐deficit‐stress‐induced changes in gene expression may be effected by different mechanisms, at least at the level of polypeptide accumulation.     

Salt-induced protein synthesis in tomato roots: the role of ABA

The role played by abscisic acid (ABA) in regulating salt-induced protein synthesis was investigated in roots of tomato (Lycopersicon esculentum Mill. cv. Ailsa Craig). Roots of 9-d-old Ailsa Craig (AC) seedlings and the near-isogenic ABA-deficient mutant, flacca (flc), were exposed to salt which elicited the appearance of novel polypeptides and both repressed and enhanced the synthesis of others. The polypeptide profiles of salt-treated AC and flc roots were similar suggesting that the synthesis of most novel polypeptides in salt-treated roots is not dependent on an elevated level of endogenous ABA. Exogenous ABA and a combined ABA/salt treatment were applied to the roots of AC and flc. Exogenous ABA, in the absence of salt, induced the accumulation of several polypeptides that were unique to this treatment as well as a subset of those synthesized in salt-treated roots. Interestingly, in roots exposed to the combined ABA/salt treatment, only those polypeptides that accumulated in both ABA or salt-treated roots were synthesized. Endogenous ABA levels increased 2-fold in salt-treated AC roots and 14-fold in salt-treated flc roots. Although the absolute level of ABA was lower in salt-treated flc than in AC, this demonstrates that flc has the capacity to accumulate some ABA in its roots following a salt treatment. Since it is possible that this level of ABA was sufficient to induce the changes in polypeptide synthesis observed in salt-treated roots of flc, the salt-induced accumulation of endogenous ABA was prevented by treating AC roots with fluridone. In these roots, the set of salt-induced polypeptides was similar to that observed in salt-treated roots indicating that an elevated level of endogenous ABA may not play a major role in regulating the accumulation of most salt-induced proteins in tomato roots.Keywords: Salt stress, ABA, polypeptide synthesis, roots.      

Estimation of cadmium availability using transformed roots

We have explored cultures of roots transformed by Agrobacterium rhizogenes to test the availability of cadmium in sewage sludges. The toxic effects of Cd and the kinetics of Cd accumulation were examined for three species of transformed roots, grown for 2 weeks in nutrient media, containing Cd as a salt. Roots of sugar beet (Beta vulgaris L.) were highly sensitive, while those of tobacco (Nicotiana tobaccum L.) and morning glory (Calystegia sepium R. Br) were more tolerant. Cd accumulation was higher in sugar beet and morning glory than in tobacco. We developed a non-sterile, 5-day procedure for testing the accumulation (an indication of availability) of Cd from sludge suspensions, using transformed roots of morning glory and tobacco. Cd accumulation varied with plant species and source of sludge. Ranking of Cd availability using this biological assay for Cd accumulation was confirmed by chemical tests with NH₄ acetate and EDTA. Results from transformed roots were also compared with those from normal, excised, tobacco roots and normal and transformed tobacco plantlets. No major alteration in Cd uptake was associated with genetic transformation. We thus demonstrated the feasibility of using transformed roots to estimate the availability of Cd in metal-contaminated materials like sewage sludges.     

Effect of Water Velocity on Hydroponic Phytoremediation of Metals

The influence of flow velocity on the uptake of cadmium, copper, lead, and zinc by hydroponically grown soft stem bulrush (Scirpus validus) was investigated. The roots of the plants were exposed to a continually recycled, nutrient enriched, synthetic stormwater. Plants were divided into groups and the roots of each group exposed to different but constant water velocities. The metal concentrations in the roots and stems were compared after three weeks. Metal accumulation in roots was increased for water velocities between 1.3 and 4.0 cm s^?1. In a second experiment, the roots of all plants were exposed to a single velocity and the root and stem metal concentrations were determined as a function of time. Metal concentrations in the roots approached a constant value after three weeks. After this time, accumulation of metals depends upon root growth. The results suggest that long-term accumulation by the roots of hydroponic Scirpus validus can be increased by increasing water velocity, which implies that floating islands with movement will retain more metals from the water column.     

Resistance of pea roots to endomycorrhizal fungus or Rhizobium correlates with enhanced levels of endogenous salicylic acid

The analysis of SA accumulation in roots of plant symbiotic mutants revealed two independent phenomena associated with the inability of either the plant or the microsymbiont to form a compatible symbiosis. SA accumulation in roots of the wild type and symbiosis-resistant P2 (Nod^-, MYC^-) Pisum sativum genotypes was induced upon interaction with Glomus mosseae. The amplitude of this accumulation was higher in P2 plants and increased with time, an effect that was not observed in roots of the wild-type, an effect that was not observed in roots of the wild-type P. sativum genotype. Likewise, Rhizobium leguminosarum wild type or a mutant blocked in Nod factor biosynthesis induced SA accumulation in P2, whereas SA accumulation in roots of the wild-type plant was dependent on the inability of the bacterium to produce Nod factors. These results suggest that the sym30 gene, which is mutated in P2 plants, could be implicated in a common pathway that leads to the suppression of an SA-dependent defence mechanism in legume plants against Rhizobium and endomycorrhizal fungi, thus allowing establishment of symbiosis.     

In vitro root differentiation and essential-oil accumulation in Angelica archangelica

Summary We studied the relationship between root differentiation and the accumulation of essential oils in Angelica archangelica in in vitro cultures and in the intact plant. Root regeneration was obtained using stem and leaf explants subjected to treatment with the auxins indole-3-butyric acid, indole-3-acetic acid and α-naphthaleneacetic acid. In both stem and leaf explants, treatment with indole-3-butyric acid induced the highest rhizogenic response in terms of both percentage of explants with roots and number of roots per explant. Independently of hormonal treatment, stem explants produced a higher average number of roots per explant. Root meristemoids were already visible at day 7 of culture in the treatments with indole-3-butyric acid and indole-3-acetic acid; they were formed directly by cambial-cell division. In vitro-regenerated roots retained primary root structure and differentiated only two primary ephemeral ducts in the pericycle; no accumulation of essential oils was detected. Same-size roots taken from the intact plant showed secondary structure and essential-oil accumulation. The results of this study suggest that the synthesis and accumulation of essential oils in Angelica archangelica is closely linked to the differentiation of secondary secretory ducts.     

Mycorrhizal infection,phosphorus uptake,and phenology in Ranunculus adoneus: implications for the functioning of mycorrhizae in alpine systems

Phosphorus levels, phenology of roots and shoots, and development of vesicular arbuscular mycorrhizal (VAM) fungi were monitored for two years in natural populations of the perennial alpine herb, Ranunculus adoneus. The purpose of this study was to understand how phosphorus uptake relates to the phenology of R. adoneus and to ascertain whether arbusculus, fungal structures used for nutrient transfer, were present when maximum phosphorus accumulation was occurring. Arbuscules were only present for a few weeks during the growing season of R. adoneus and their presence corresponded with increased phosphorus accumulation in both the roots and shoots of R. adoneus. In addition, phosphorus accumulation and peaks in mycorrhizal development occurred well after plant reproduction and most plant growth had occurred. The late season accumulation of phosphorus by mycorrhizal roots of R. adoneus is stored for use during early season growth and flowering the following spring. In this way R. adoneus can flower before soils thaw and root or mycorrhizal nutrient uptake can occur.     

Uptake and Distribution of Mercury within Higher Plants

The uptake and distribution of inorganic mercury (HgCl₂) within higher plants (Pisum sativum and Mentha spicata) was examined using solution culture and radiotracer techniques. Plants were found to tolerate an external level of 1 mgHg/kg of solution but both physiological and biochemical processes were affected at 5 mgHg/kg and 10 mgHg/kg. The uptake of Hg into plants grown in hydroponic solution was a function of external concentration. Over the concentration range considered the accumulation of Hg in the roots was linear on a log-log basis although the uptake of the element into the shoots appeared to be two-phased. The distribution of Hg in plants was asymmetrical with much greater amounts of the element in the roots than the shoots. Although the level of Hg increased generally in plant tissues with increasing external levels, the proportion retained in the roots, relative to the shoots, was constant (approximately 95%). Two binding characteristics of the Hg within plant tissue were detected. A major proportion of Hg was tightly bound, being unaffected by treatment with ethanol and hydrochloric acid. The remaining Hg in the tissue was removed by either water or hydrochloric acid treatment. Cell fractionation indicated that the major binding component of Hg in plant tissues was the cell wall.     

Ni-induced Changes in Nitrate Assimilation and Antioxidant Metabolism of Verbascum olympicum Boiss.: Could the Plant be Useful for Phytoremediation or/and Restoration Purposes?

Verbascum olympicum Boiss. (Scrophulariaceae) were studied as a candidate plant for remediating the Ni polluted soils. The metabolic responses, such as nitrate assimilation (nitrate reductase and glutamine synthetase activity) and antioxidant system activity [superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activity], of this species exposed to nickel in Hoagland's nutrient medium were investigated as remediation performance parameters. The accumulation of nickel and the variations in the content of some elements (B, Cu, Fe, Mg, Mn, Mo and Zn) and some growth parameters, such as the water content, biomass production, and contents of chlorophyll and soluble protein, were also examined. The accumulation of Ni in both the roots and leaves varied depending on the exposure times and doses. Increased oxidative stress was suggested by the increases in the activities of SOD, CAT and APX. Although some element contents were inhibited by Ni treatments, these inhibitory effects was decreased depending on the time, and even these elements are accumulated in roots. These results are the novelties in the use of this species in biotechnology.     

Salinity-calcium interactions on growth and ionic concentration of Citrus plants

Two-year-old Navel orange scions (Citrus sinensis (L.) Osbeck) budded to either Cleopatra mandarin (C. reticulata) and Troyer citrange (C. sinensis × P. trifoliata) rootstocks were used in this experiment. Cleopatra manda in rootstock was considered more tolerant to salinity than Troyer citrange, and this property was attributed to a greater capacity to exclude chloride ions.Plants were grown under glasshouse conditions and supplied with nutrient solution containing either no or 45 mM NaCl. Calcium concentration was increased from 3 to 30 mM. Sodium, potassium, calcium and chloride concentrations in plant organs were analyzed after 90 days of treatment.Supplemental Ca was found to mitigate the adverse effects of salinity on plant growth, defoliation or leaf injury.Chemical analysis indicated that in plants grafted on Troyer citrange Ca restricted uptake and subsequent translocation of Na to the leaves and increased K concentration in both roots and leaves. However, in Cleopatra mandarin-grafted plants increasing Ca levels seemed to reduce transport of Na from roots to leaves, and Na accumulation in roots was associated with reduced concentration of K in this rootstock.Organ chloride analysis showed that Cl accumulation in leaves of plants grafted on both rootstocks was reduced when external Ca concentration increased, whereas Cl concentration in roots remained constant or increased. The data of distribution of Cl in plants showed that a high external Ca level increased Cl accumulation in the basal stem and roots, and reduced the transport of Cl from roots to leaves.     

茉莉酸甲酯对牛膝生长及主要药用成分积累的影响

不同浓度的外源茉莉酸甲酯(Me JA)对牛膝生长及其主要药用成分齐墩果酸和蜕皮甾酮均有不同的影响。该文采用不同浓度的Me JA分别浸种处理牛膝种子:0(对照)、0.1 mmol·L-1(T1)、0.15 mmol·L-1(T2)、0.2 mmol·L-1(T3)、0.25 mmol·L-1(T4),对照(CK)以同体积的蒸馏水浸泡。取浸种处理后生长培养60 d的牛膝植株,测定牛膝的株高、根长、地上及地下部分的生物量;取牛膝的叶及根,HPLC法测定其齐墩果酸和蜕皮甾酮的含量,研究Me JA对牛膝生长及主要药用成分齐墩果酸和蜕皮甾酮积累的影响。结果表明:0.15 mmol·L-1Me JA浸种处理,对牛膝生长及生物量的促进作用最佳,其株高、根长、地上部分鲜重及根鲜重分别比对照显著升高43.9%、38.7%、26.4%、64.0%(P0.05);0.15 mmol·L-1Me JA处理,对牛膝的根和叶中齐墩果酸的积累作用最佳,分别比对照组显著增加了114.3%和60%(P0.05);0.25 mmol·L-1Me JA处理,对牛膝根中蜕皮甾酮的积累最佳,比对照高出90.3%(P0.05),却不利于根和叶中齐墩果酸的积累,并可抑制叶中蜕皮甾酮的形成。说明0.15 mmol·L-1Me JA浸种处理对牛膝的生长及其根和叶中齐墩果酸的积累作用最佳,并能显著促进根中蜕皮甾酮的积累,有利于牛膝药材产量和品质的提高。     

金铁锁毛状根构型对其生长的影响

毛状根的构型是影响其生长速度和生物量积累的重要因素,为了规模化培养金铁锁毛状根,进一步解决金铁锁资源短缺问题,该研究以金铁锁毛状根为材料,通过改变培养基类型、碳源及碳源浓度,观察和分析了毛状根的生长状态,找出影响毛状根构型的因素。结果表明:最适合金铁锁毛状根生长的培养基为B5+蔗糖30 g·L~(-1),金铁锁毛状根主根长而粗壮,一级、二级侧根生长量大,根系表面积较大,生长效果最佳。经液体悬浮培养验证,测定毛状根的生长量,与在固体培养基培养的毛状根生长状态基本一致。通过该项研究,优化了培养基中营养成分的配比,实现了金铁锁毛状根的快速生长和生物量的积累。     

A differential response to chemical elicitors in Catharanthus roseus in vitro cultures

The effects of methyl jasmonate, salicylic acid and ethylene on alkaloid accumulation in in vitro cell suspension, hairy roots and rootless shoot cultures of Catharanthus roseus were analyzed. Ajmalicine, but not catharanthine, accumulation was promoted by jasmonate and ethylene treatments in cell suspensions. In hairy roots, jasmonate induced the accumulation of both alkaloids, whereas ethylene only induced catharanthine accumulation. In shoot cultures, positive effects of jasmonate and ethylene were recorded only in vindoline accumulation. Ethylene diminished catharanthine accumulation in these cultures. No effect of salicylic acid was observed in any of the studied in vitro culture systems. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Accumulation of reactive oxygen species in arbuscular mycorrhizal roots

We investigated the accumulation of reactive oxygen species (ROS) in arbuscular mycorrhizal (AM) roots from Medicago truncatula, Zea mays and Nicotiana tabacum using three independent staining techniques. Colonized root cortical cells and the symbiotic fungal partner were observed to be involved in the production of ROS. Extraradical hyphae and spores from Glomus intraradices accumulated small levels of ROS within their cell wall and produced ROS within the cytoplasm in response to stress. Within AM roots, we observed a certain correlation of arbuscular senescence and H₂O₂ accumulation after staining by diaminobenzidine (DAB) and a more general accumulation of ROS close to fungal structures when using dihydrorhodamine 123 (DHR 123) for staining. According to electron microscopical analysis of AM roots from Z. mays after staining by CeCl₃, intracellular accumulation of H₂O₂ was observed in the plant cytoplasm close to intact and collapsing fungal structures, whereas intercellular H₂O₂ was located on the surface of fungal hyphae. These characteristics of ROS accumulation in AM roots suggest similarities to ROS accumulation during the senescence of legume root nodules.     

NRT1.1B improves selenium concentrations in rice grains by facilitating selenomethinone translocation

Selenium (Se) is an essential trace element for humans and other animals, yet approximately one billion people worldwide suffer from Se deficiency. Rice is a staple food for over half of the world's population that is a major dietary source of Se. In paddy soils, rice roots mainly take up selenite. Se speciation analysis indicated that most of the selenite absorbed by rice is predominantly transformed into selenomethinone (SeMet) and retained in roots. However, the mechanism by which SeMet is transported in plants remains largely unknown. In this study, SeMet uptake was found to be an energy‐dependent symport process involving H⁺ transport, with neutral amino acids strongly inhibiting SeMet uptake. We further revealed that NRT1.1B, a member of rice peptide transporter (PTR) family which plays an important role in nitrate uptake and transport in rice, displays SeMet transport activity in yeast and Xenopus oocyte. The uptake rate of SeMet in the roots and its accumulation rate in the shoots of nrt1.1b mutant were significantly repressed. Conversely, the overexpression of NRT1.1B in rice significantly promoted SeMet translocation from roots to shoots, resulting in increased Se concentrations in shoots and rice grains. With vascular‐specific expression of NRT1.1B, the grain Se concentration was 1.83‐fold higher than that of wild type. These results strongly demonstrate that NRT1.1B holds great potential for the improvement of Se concentrations in grains by facilitating SeMet translocation, and the findings provide novel insight into breeding of Se‐enriched rice varieties.     

Salt affects plant Cd-stress responses by modulating growth and Cd accumulation

Cadmium contamination is a serious environmental problem for modern agriculture and human health. Salinity affects plant growth and development, and interactions between salt and cadmium have been reported. However, the molecular mechanisms of salinity–cadmium interactions are not fully understood. Here, we show that a low concentration of salt alleviates Cd-induced growth inhibition and increases Cd accumulation in Arabidopsis thaliana. Supplementation with low concentrations of salt reduced the reactive oxygen species level in Cd-stressed roots by increasing the contents of proline and glutathione and down-regulating the expression of RCD1, thereby protecting the plasma membrane integrity of roots under cadmium stress. Salt supplementation substantially reduces the Cd-induced elevation of IAA oxidase activity, thereby maintaining auxin levels in Cd-stressed plants, as indicated by DR5::GUS expression. Salt supply increased Cd absorption in roots and increased Cd accumulation in leaves, implying that salt enhances both Cd uptake in roots and the root-to-shoot translocation of Cd. The elevated Cd accumulation in plants in response to salt was found to be correlated with the elevated levels of phytochelatin the expression of heavy metal transporters AtHMA1-4, especially AtHMA4. Salt alleviated growth inhibition caused by Cd and increased Cd accumulation also was observed in Cd accumulator Solanum nigrum.     

Methyl jasmonate and salicylic acid elicitation induces ginsenosides accumulation, enzymatic and non-enzymatic antioxidant in suspension culture Panax ginseng roots in bioreactors

The effects of methyl jasmonate (MJ) and salicylic acid (SA) on changes of the activities of major antioxidant enzymes, superoxide anion accumulation (O₂ ⁻), ascorbate, total glutathione (TG), malondialdehyde (MDA) content and ginsenoside accumulation were investigated in ginseng roots (Panax ginseng L.) in 4 l (working volume) air lift bioreactors. Single treatment of 200 μM MJ and SA to P. ginseng roots enhanced ginsenoside accumulation compared to the control and harvested 3, 5, 7 and 9 days after treatment. MJ and SA treatment induced an oxidative stress in P. ginseng roots, as shown by an increase in lipid peroxidation due to rise in O₂ ⁻ accumulation. Activity of superoxide dismutase (SOD) was inhibited in MJ-treated roots, while the activities of monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), SOD, guaiacol peroxidase (G-POD), glutathione peroxidase (GPx) and glutathione reductase (GR) were induced in SA-treated roots. A strong decrease in the activity of catalase (CAT) was obtained in both MJ- and SA-treated roots. Activities of ascorbate peroxidase (APX) and glutathione S transferase (GST) were higher in MJ than SA while the contents of reduced ascorbate (ASC), redox state (ASC/(ASC+DHA)) and TG were higher in SA- than MJ-treated roots while oxidized ascorbate (DHA) decreased in both cases. The result of these analyses suggests that roots are better protected against the O₂ ⁻ stress, thus mitigating MJ and SA stress. The information obtained in this work is useful for efficient large-scale production of ginsenoside by plant-root cultures.     

Effect of Organic Ligands on Accumulation of Copper in Hyperaccumulator and Nonaccumulator Commelina communis

Better understanding of copper uptake and accumulation regulation in plants is critical to the phytoremediation of copper contaminated soil. This study employed a 30-day pot experiment to assess the relationship between organic ligands and copper accumulation in plants. Hyperaccumulator and nonaccumulator varieties of Commelina communis were used, different organic ligands were applied, and the data of copper accumulation in shoots were collected. The six organic ligands included ethylenediaminetetraacetic acid and organic acids (formic acid, citric acid, malic acid, tartaric acid, and succinic acid). The results showed that organic ligands added to culture increased the copper accumulation both varieties. The results of the copper accumulation in shoots agreed with the study of the root uptake kinetics of copper influx. The addition of organic acids could increase copper accumulation in shoots because the copper influx in roots was increased. The results also indicated that the copper influx of hyperaccumulator roots was higher than that of nonaccumulator roots. This is one of the mechanisms by which a hyperaccumulator could amass large amounts of copper in its shoots. In this accumulation process, little effect on the leaf relative water content was in the hyperaccumulator and nonaccumulator of leaves and normal physiological condition of plants.     

The Response of Lupinus albus Roots to the Signal from Phosphorus-Deficient Substrate1

The excretion of organic acids into the rhizosphere is induced by low phosphorus content in roots of white lupine (Lupinus albus L.). The aim of this study was to investigate how did the white lupine roots respond to the signals of P-deficiency in the substrate, by using the method of separating the root system into two parts, one part being placed into P-deficient solution and another part into P-sufficient solution. The results showed that the root tips (1-cm-long) accept the signal of P-deficiency in the substrate. This signal can be transmitted from one root tip to another, and can induce the accumulation and excretion of malic acid in the root tips and the development of proteoid roots. In order to investigate whether a phytohormone was involved in the response, the external hormones were used. Indole-3-butyric acid added to P-sufficient solution can induce the development of proteoid roots, but without any accumulation of citric acid in them. On the contrary, 6-benzyladenine (BA) added to the P-deficient solution can inhibit the development of proteoid roots and the accumulation of malic acid in the root tips. The inhibitory effect increases with increasing BA supply.     

丹参多酚氧化酶基因的克隆及表达分析

前期研究发现多酚氧化酶(PPO)能正向调控丹酚酸B合成,该研究运用RACE技术,从丹参毛状根中克隆到多酚氧化酶基因(SmPPO,GenBank登录号为KF712274)全长序列,其cDNA全长1 930bp,开放阅读框为1 770bp,编码589个氨基酸。将SmPPO与管状花目其它4个物种进行氨基酸序列比对,在N端类囊体转移结构域中发现都存在2个N-豆蔻酰化位点。在丹参毛状根培养液中加入不同诱导因子,利用实时荧光定量PCR检测,发现该基因在酵母提取物处理中表达量显著上调,但在银离子、抗坏血酸和L-半胱氨酸处理中表达受到明显抑制。运用HPLC技术同步检测毛状根中丹酚酸B含量,显示出与基因表达相同的变化趋势。研究表明,丹参中多酚氧化酶基因(SmPPO)对丹酚酸B的合成具有正向调控作用。