Effect of Thioligands on Plant-Hg Accumulation and Volatilisation from Mercury-contaminated Mine Tailings

This study investigated the effect of thioligands on mercury (Hg) volatilisation and plant accumulation for Brassica junceaplants grown in mine tailings collected from artisanal gold mines in Brazil (the Serra Pelada mine) and China (the Gold Mountain mine). Plants were treated with either (NH₄)₂S₂O₃or NH₄SCN and enclosed in gas-tight volatilisation chambers. Elemental Hg released from substrates was captured in a two-trap system containing 5 KMnO₄dissolved in 2N H₂SO₄. Mercury accumulation was enhanced in the presence of (NH₄)₂S₂O₃ for plants grown in GM tailings. There was no significant increase in the plant-Hg accumulation after application of NH₄SCN to the SP tailings. Volatilisation from planted substrates was not affected by the application of thioligands to either GM or SP mine tailings. Mercury volatilisation from planted substrates was significantly higher than from control substrates. Abiotic (photoreduction) and biotic (microbial interactions) factors might be linked to the enhanced plant effect on Hg volatilisation. There was no significant correlation for the Hg mass released from substrates and the amount of Hg uptake by roots and translocated to shoots. Our results indicate that volatilisation and plant-Hg accumulation are two independent processes. Thiosulphate-induced plant-Hg accumulation may be a potential tool for the phytoextraction of Hg contaminated soils but there are risks of groundwater contamination by Hg-containing leachates.     

Arsenic tolerance in mesquite (Prosopis sp.): Low molecular weight thiols synthesis and glutathione activity in response to arsenic

The effects of arsenic stress on the production of low molecular weight thiols (LMWT), glutathione S-transferase activity (GST) and sulfur metabolism of mesquite plant (Prosopis sp.) were examined in hydroponic culture at different arsenic [As(III) and (V)] concentrations. The production of LMWT was dependent on As speciation and concentration in the growth medium. The roots of As(III) treated plants produced significantly higher LMWT levels than As(V) treated roots at the same concentration of As applied. In leaves, the thiols content increased with increasing As(III) and (V) concentrations in the medium. Hypersensitivity of the plant to high As concentrations was observed by a significant decrease of LMWT produced in the roots at 50 mg/L treatment in both As(III) and (V) treatments. Sulfur was translocated from roots and accumulated mainly in the shoots. In response to As-induced phytotoxicity, the plants slightly increased the sulfur content in the roots at the highest As treatment. Compared with As(V)-treated plants, As(III)-treated roots and leaves showed significantly higher GST activity. The roots of both As(III) and (V) treated plants showed an initial increase in GST at low As concentration (5 mg/L), followed by significant inhibition up to 50 mg/L. The leaves had the highest GST activity, an indication of the ability of the plant to detoxify As in the leaves than in the roots. The correlation between LMWT content, S content and GST activity may be an indication these parameters may be used as biomarkers of As stress in mesquite.     

Behavior of mercury in a soil–plant system as affected by inoculation with the arbuscular mycorrhizal fungus Glomus mosseae

Effects of inoculation with the arbuscular mycorrhizal (AM) fungus Glomus mosseae on the behavior of Hg in soil–plant system were investigated using an artificially contaminated soil at the concentrations of 0, 1.0, 2.0, and 4.0 mg Hg kg⁻¹. Mercury accumulation was lower in mycorrhizal roots than in nonmycorrhizal roots when Hg was added at the rates of 2.0 and 4.0 mg kg⁻¹, while no obvious difference in shoot Hg concentration was found between mycorrhizal and nonmycorrhizal treatments. Mycorrhizal inoculation significantly decreased the total and extractable Hg concentrations in soil as well as the ratio of extractable to total Hg in soil. Equilibration sorption of Hg by soil was investigated, and the results indicated that mycorrhizal treatment enhanced Hg sorption on soil. The uptake of Hg was lower by mycorrhizal roots than by nonmycorrhizal roots. These experiments provide further evidence for the role of mycorrhizal inoculation in increasing immobilization of Hg in soil and reducing the uptake of Hg by roots. Calculation on mass balance of Hg in soil suggests the presence of Hg loss from soil presumably through evaporation, and AM inoculation enhanced Hg evaporation. This was evidenced by a chamber study to detect the Hg evaporated from soil.     

Effect of endophytic fungi on cadmium tolerance and bioaccumulation by Festuca arundinacea and Festuca pratensis

Endophytic fungi are a group of fungi that live asymptomatically inside plant tissue. These fungi may increase host plant tolerance to biotic and abiotic stresses. The effect of Neotyphodium endophytes in two grass species (Festuca arundinacea and Festuca pratensis) on cadmium (Cd) tolerance, accumulation and translocation has been our main objective. The plants were grown in a hydroponic system under different Cd concentrations (0, 5, 10, and 20 mg L(-1)) for 6 weeks. They were also grown in soil spiked with different concentrations of Cd (0, 10, 20, and 40 mg kg(-1)) for 2 months. The results from all Cd treatments showed higher biomass production (12-24%) and higher potential to accumulate Cd in roots (6-16%) and shoots (6-20%) of endophyte-infected plants than endophyte-free plants. Cadmium accumulation by plants indicated that the grasses were capable of Cd hyperaccumulation, a property that was augmented after endophyte infection. Maximum photochemical efficiency of photosystem II (Fv/Fm) revealed that Cd stress was significantly reduced in endophyte-infected plants compared to non-infected ones.     

Ascorbate promotes emission of mercury vapour from plants

Mercury vapour (Hg°) emission from plants contributes to the atmospheric mercury cycle. Although a part of this Hg° emission originates from Hg(II) uptake by the roots, the question how terrestrial plants reduce Hg(II) has not been addressed so far. Young barley plants grown on a hydroponic cultivation containing Hg(II) increased the Hg° emission significantly. Homogenates of barley leaves added to dissolved Hg(II) induced a powerful volatilization at alkaline but not at acidic pH. The same pH dependence and emission kinetic together with the highest reduction capacity was observed for ascorbic acid as compared to other phytoreductants. The electrochemical potentials of the reactions involved suggest an electron transfer from NADPH via GSH and ascorbate to Hg(II). The results support the assumption of a novel mechanism how plants transfer reduction equivalents from the antioxidative defense system via ascorbate to reduce Hg(II) ions, thus counteracting mercury toxicity by volatilizing the metal. This effect appears to be assisted by other light-dependent processes such as transpiration and ascorbate synthesis.     

Mercury uptake and phytotoxicity in terrestrial plants grown naturally in the Gumuskoy (Kutahya) mining area,Turkey

This study investigated mercury (Hg) uptake and transport from the soil to different plant parts by documenting the distribution and accumulation of Hg in the roots and shoots of 12 terrestrial plant species, all of which grow naturally in surface soils of the Gumuskoy Pb-Ag mining area. Plant samples and their associated soils were collected and analyzed for Hg content by ICP-MS. Mean Hg values in the soils, roots, and shoots of all plants were 6.914, 460, and 206 µg kg^?1, respectively and lower than 1. The mean enrichment factors for the roots (ECR) and shoots (ECS) of these plants were 0.06 and 0.09, respectively and lower than 1. These results show that the roots of the studied plants prevented Hg from reaching the aerial parts of the plants. The mean translocation factor (TLF) was 1.29 and higher than 1. The mean TLF values indicated that all 12 plant species had the ability to transfer Hg from the roots to the shoots but that transfer was more efficient in plants with higher ECR and ECS. Therefore, these plants could be useful for the biomonitoring of environmental pollution and for rehabilitating areas contaminated by Hg.     

Rhizosphere bacteria enhance the accumulation of selenium and mercury in wetland plants

The role of rhizosphere bacteria in facilitating Se and Hg accumulation in two wetland plants, saltmarsh bulrush (Scirpus robustus Pursh) and rabbitfoot grass (Polypogon monspeliensis (L.) Desf.), was studied. Ampicillin-amended plants (i.e., with inhibited rhizosphere bacteria) supplied with Na₂SeO₄ or HgCl₂ had significantly lower concentrations of Se and Hg, respectively, in roots than plants without ampicillin. These results were confirmed by inoculating axenic saltmarsh bulrush plants with bacteria isolated from the rhizosphere of plants collected from the field; these plants accumulated significantly more Se and Hg compared to axenic controls. Therefore, rhizosphere bacteria can increase the efficiency of Se and Hg phytoremediation by promoting the accumulation of Se and Hg in tissues of wetland plants. Received: 9 April 1999 / Accepted: 11 May 1999     

Pyruvate accumulation during phosphate deficiency stress of bean roots

Culture of bean plants (Phaseolus vulgaris L. cv., Złota Saxa) for 16 d on phosphate-deficient nutrient medium resulted in an over twofold increase of pyruvate concentration in the root tissues. In a variety of plant tissues, the marked decline in cellular concentrations of adenylates and inorganic phosphate (Pi) influences the activity of pyruvate producing enzymes, which are dependent on the availability of ADP. In bean roots after 16 d of phosphate starvation pyruvate producing enzymes: phosphoenolpyruvate phosphatase (EC 3.1.3.2) and phosphoenolpyruvate carboxylase (EC 4.1.1.31) had higher activities compared to those of control plants. The observed decrease of alanine and ethanol concentration and also alcohol dehydrogenase (EC 1.1.1.1) activity in phosphate-deficient roots may be the effect of the restrictions in pyruvate utilizing pathways. The increased activity of mitochondrial NAD-malic enzyme (EC 1.1.1.40) as well as the lower consumption of pyruvate during respiration of phosphate-deficient roots indicate that pyruvate concentration in mitochondria may be elevated. It is proposed that pyruvate accumulation in phosphate-deficient roots and alternative oxidase participation in respiration are important aspects of plant metabolic adaptations to Pi limitation, and may play a role in reducing oxidative stress induced by phosphate deficiency.     

Delivery rates of abscisic acid in xylem sap of Ricinus communis L. plants subjected to part-drying of the soil

Abscisic acid (ABA) moving from roots to shoots in the transpirationstream is a potential hormonal message integrating perceptionof a root stress with adaptive changes in the shoot. A twinroot system was used to study ways of estimating effects ofdroughting the upper roots of Ricinus communis L. on abscisicacid (ABA) transport to the shoot in the transpiration stream.Droughted plants transpired more slowly than controls. Droughtingalso increased concentrations of ABA up to I I-fold in sap inducedto flow from the roots of freshly decapitated plants at ratesof whole plant transpiration. However, because of dilution effectsarising from the different sap flows in control and droughtedplants, these changes in ABA concentration in the xylem sapdid not accurately reflect amounts of ABA transported. To overcomethis problem, delivery rates were calculated by multiplyingconcentration with sap flow rate to generate ABA delivery interms of µmol s–1 per plant. Droughting for 24 hor more increased ABA delivery from roots to shoots by 5-fold.Since droughting can alter the relative sizes of the roots andshoots and also the root:shoot ratio these delivery rates wererefined in several ways to reflect both the amount of root generatingthe ABA message and the size of the recipient shoot system. Key words: Abscisic acid, Ricinus communis L., soil drying, xylem sap     

Elemental sulfur improves growth and phytoremediative ability of wheat grown in lead-contaminated calcareous soil

Little is known about the effect of elemental sulfur on lead uptake and its toxicity in wheat. A pot experiment was conducted with the purpose to examine the impact of sulfur on improving Pb solubility in soil, and uptake and accumulation in wheat plants. The effect of three levels of lead (0, 50, and 100 mg/kg soil) and sulfur (0, 150, and 300 mmol/kg soil) was tested in all possible combinations. Root dry matter, straw, and grain yields, and the photosynthetic and transpiration rates decreased significantly with increase in the concentration of Pb in the soil. However, sulfur fertilization in the presence of Pb improved the photosynthetic and transpiration rates and consequently increased the straw and grain yields of wheat. It also enhanced Pb accumulation in roots, its translocation from roots to shoot, and accumulation in grain. S and Zn contents of different plant parts were also enhanced. Thus, by mitigating the toxic effect of Pb and improving wheat growth, sulfur enhances Pb accumulation by the aboveground plant parts and hence the phytoextraction capacity of wheat. However, total accumulation of Pb shows that wheat plant cannot be considered as a suitable candidate for phytoremediation.     

Effects of pH on NaCl tolerance of American elm (<Emphasis Type="Italic">Ulmus americana</Emphasis>) seedlings inoculated with <Emphasis Type="Italic">Hebeloma crustuliniforme</Emphasis> and <Emphasis Type="Italic">Laccaria bicolor</Emphasis>

In the present study, we investigated the effects of pH treatments on NaCl tolerance in mycorrhizal and non-mycorrhizal American elm. American elm (Ulmus americana) seedlings were inoculated with Hebeloma crustuliniforme, Laccaria bicolor or with both mycorrhizal fungi and subsequently subjected to different pH solutions (pH 3, 6 and 9) containing 0 mM (control) and 60 mM NaCl for 4 weeks. Inoculation with the mycorrhizal fungi did not have a large effect on seedling dry weights when the pH and NaCl treatments were considered independently. However, when the inoculated seedlings were treated with 60 mM NaCl at pH 3 or 6, shoot to root ratios and root hydraulic conductivity were higher compared with non-inoculated plants, likely reflecting changes in seedling water flow properties. At pH 6, transpiration rates were about twofold lower in non-inoculated plants treated with NaCl compared with non-treated controls. For NaCl-treated H. crustuliniforme- and L. bicolor-inoculated plants, the greatest reduction of transpiration rates was at pH 9. Treatment with 60 mM NaCl reduced leaf chlorophyll concentrations more in non-inoculated compared with inoculated plants, with the greatest, twofold, decrease occurring at pH 6. At pH 3, root Na concentrations were higher in inoculated than non-inoculated seedlings; however, there was no effect of inoculation on root Na concentrations at pH 6 and 9. Contrary to the roots, the leaves of inoculated plants had lower Na concentrations at pH 6 and 9, but not at pH 3. The results point to an interaction between ECM fungi and root zone pH for salt tolerance of American elm.     

Phytofiltration of Arsenic and Cadmium From the Water Environment Using Micranthemum Umbrosum (J.F. Gmel) S.F. Blake As A Hyperaccumulator

Arsenic (As) and cadmium (Cd) pollution in water is an important global issue. Phytofiltration is an eco-friendly technology that helps clean up pollutants using ornamental plants, such as Micranthemum umbrosum (J.F. Gmel) S.F. Blake. After a seven-day hydroponic experiment, M. umbrosum removed 79.3–89.5% As and 60–73.1% Cd from 0 to 1.0 μg As mL^–1 and 0.3 to 30.0 μg Cd mL^–1 solutions, respectively. For As treatment, root to stem and stem to leaf translocation factors greater than 1.0 indicated that accumulation of As in leaves was large compared to that in stem and roots. However, the accumulation of Cd in roots was higher than that in the leaves and stem. In addition, M. umbrosum completely removed Cd within three days from 0.38 to around 0 μg mL^–1Cd in the solution when the plant was exchanged daily. Bio-concentration factors (2350 for As and 3027 for Cd) for M. umbrosum were higher than for other As and Cd phytoremediators. The results show that M. umbrosum can be an effective accumulator of Cd and a hyper-accumulator of As, as it can lower As toxicity to a level close to the limit recommended by the World Health Organization (0.01 μg As mL^–1).     

Salicylic acid alleviates mercury toxicity by preventing oxidative stress in roots of Medicago sativa

Salicylic acid (SA) as a signal molecule mediates many biotic and environmental stress-induced physiological responses in plants. In this study, we investigated the role of SA in regulating Hg-induced oxidative stress in the roots of alfalfa (Medicago sativa). Plants pretreated with 0.2 mM SA for 12 h and subsequently exposed to 10 μM Hg²⁺ for 24 h displayed attenuated toxicity to the root. The SA-promoted root growth was correlated with decreased lipid peroxidation in root cells. The ameliorating effect of SA was confirmed by the histochemical staining for the detection of loss of membrane integrity in Hg-treated roots. We show that treatment with 0.2 mM SA increased the activity of NADH oxidase, ascorbate peroxidase (APX) and peroxidase (POD) in the roots exposed Hg. However, a slightly decreased superoxide dismutase (SOD) activity was observed in SA + Hg-treated roots when compared to those of Hg treatment alone. We also measured accumulation of ascorbate (ASC), glutathione (GSH) and proline in the roots of alfalfa and found that roots treated with SA in the presence of Hg accumulated more ASC, GSH and proline than those treated with Hg only. These results suggest that exogenous SA may improve the tolerance of the plant to the Hg toxicity.     

INSECTICIDAL-ACTION STUDIES WITH BISDIMETHYL-AMINO FLUOROPHOSPHINE OXIDE CONTAINING 32PHOSPHORUS

The absorption of the systemic insecticide bisdimethylamino fluorophosphine oxide containing ³²P by plants has been studied, and where possible comparisons have been made with bisdimethylaminophosphonous anhydride.
The radio-oxide is absorbed by the roots of a broad-bean plant from culture solutions. The level of radioactivity in the plant increases as the solution is absorbed and is higher in the washed roots than in the rest of the plant. The radioactivity of the remaining culture solution decreases as more of it is taken up by the plants showing that the roots selectively absorb the oxide from solution. In this latter respect it differs from the anhydride which is selectively rejected at similar rates of transpiration. The material is absorbed more slowly by plants growing in soil than in sand.
An appreciable part of the oxide absorbed by the roots is given off as vapour by the leaves. The transpired material can be collected and shown to be radioactive and systemically insecticidal. Aphids feeding on treated plants contain radioactive material.
The oxide is less lipoid soluble than the anhydride and does not penetrate as readily into the leaves of the broad bean. Since it is also lost by vaporization from the plants only small amounts are translocated following leaf applications to beans, cabbages and hops.     

Cd accumulation in roots and shoots of durum wheat: the roles of transpiration rate and apoplastic bypass

Cadmium is readily taken up from soils by plants, depending on soil chemistry, and variably among species and cultivars; altered transpiration and xylem transport and/or translocation in the phloem could cause this variation in Cd accumulation, some degree of which is heritable. Using Triticum turgidum var. durum cvs Kyle and Arcola (high and low grain Cd accumulating, respectively), the objectives of this study were to determine if low-concentration Cd exposure alters transpiration, to relate transpiration to accumulation of Cd in roots and shoots at several life stages, and to evaluate the role of apoplastic bypass in the accumulation of Cd in shoots. The low abundance isotope (106)Cd was used to probe Cd translocation in plants which had been exposed to elemental Cd or were Cd-na?ve; apoplastic bypass was monitored using the fluorescent dye PTS (8-hydroxy-1,3,6-pyrenetrisulphonate). Differential accumulation of Cd by 'Kyle' and 'Arcola' could be partially attributed to the effect of Cd on transpiration, as exposure to low concentrations of Cd increased mass flow and concomitant Cd accumulation in 'Kyle'. Distinct from this, exposure of 'Arcola' to low concentrations of Cd reduced translocation of Cd from roots to shoots relative to root accumulation of Cd. It is possible, but not tested here, that sequestration mechanisms (such as phytochelatin production, as demonstrated by others) are the genetically controlled difference between these two cultivars that results in differential Cd accumulation. These results also suggest that apoplastic bypass was not a major pathway of Cd transport from the root to the shoot in these plants, and that most of the shoot Cd resulted from uptake into the stele of the root via the symplastic pathway.     

Concentrations of abscisic acid and other solutes in xylem sap from root systems of tomato and castor-oil plants are distorted by wounding and variable sap flow rates

We investigated if concentrations of abscisic acid (ABA) andother solutes measured in the first few droplets of xylem sapfrom detopped root systems, are good estimates of those in thetranspiration stream as it enters the shoot-base of whole plants.Xylem sap from root systems of pot-grown tomato plants (Lycopersiconesculentum Mill., cv. Ailsa Craig), at the seven-leaf stage,was obtained by placing root systems in chambers pressurizedto 0.3 MPa with air. The first sample was taken from the cut-surfaceof the hypo-cotyl stump within 30 s of removing the shoot. ABA,sucrose and other osmolytes were more concentrated in the initial100–200 mm³ of xylem sap than in subsequent samples. Thissuggested the sap was contaminated and not unchanged transpirationfluid. The effect was reproduced on the same plant, severaltimes, by recutting the hypocotyl prior to reassembling thesap collecting set-up and repressurizing. Similar results werefound with castor-oil plants (Ricinus communis L., cv. Gibsonii).However, neither release of ABA from the cut surface of thehypocotyl stump, nor the effects of pressure to the roots causedthe contamination. Instead, small radial pressures exerted bya rubber sleeve attached to the hypocotyl stump, for collectingthe sap, were responsible. The effect was reproduced by lightlysqueezing the hypocotyl by hand. The possibility was examined that reliable estimates of ABAconcentrations in transpiration stream fluid may be obtainedfrom sap samples taken immediately after rejecting the initial,contaminated 200 mm³. However, ABA concentrations in these latersamples were also unsatisfactory since they changed with rateof sap flow. The problem may be overcome by analysing sap inducedto flow through detached root systems at rates close to thoseof whole-plant transpiration. Key words: Tomato, Lycopersicon esculentum Mill., Castor-oil plant, Ricinus communis L., roots, root to shoot communication, xylem sap, abscisic acid, sucrose, transpiration stream     

Improved tolerance of maize plants to salt stress by arbuscular mycorrhiza is related to higher accumulation of soluble sugars in roots

The effect of colonization with the arbuscular mycorrhizal (AM) fungus Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe on the growth and physiology of NaCl-stressed maize plants ( Zea mays L. cv. Yedan 13) was examined in the greenhouse. Maize plants were grown in sand with 0 or 100 mM NaCl and at two phosphorus (P) (0.05 and 0.1 mM) levels for 34 days, following 34 days of non-saline pre-treatment. Mycorrhizal plants maintained higher root and shoot dry weights. Concentrations of chlorophyll, P and soluble sugars were higher than in non-mycorrhizal plants under given NaCl and P levels. Sodium concentration in roots or shoots was similar in mycorrhizal and non-mycorrhizal plants. Mycorrhizal plants had higher electrolyte concentrations in roots and lower electrolyte leakage from roots than non-mycorrhizal plants under given NaCl and P levels. Although plants in the low P plus AM fungus treatment and those with high P minus AM fungus had similar P concentrations, the mycorrhizal plants still had higher dry weights, soluble sugars and electrolyte concentrations in roots. Similar relationships were observed regardless of the presence or absence of salt stress. Higher soluble sugars and electrolyte concentrations in mycorrhizal plants suggested a higher osmoregulating capacity of these plants. Alleviation of salt stress of a host plant by AM colonization appears not to be a specific effect. Furthermore, higher requirement for carbohydrates by AM fungi induces higher soluble sugar accumulation in host root tissues, which is independent of improvement in plant P status and enhances resistance to salt-induced osmotic stress in the mycorrhizal plant.     

Detection and quantification of unbound phytochelatin 2 in plant extracts of Brassica napus grown with different levels of mercury

The mercury (Hg) accumulation mechanism was studied in rape (Brassica napus) plants grown under a Hg concentration gradient (0 microm-1,000 microm). Hg mainly accumulated in roots. Therefore, the presence of phytochelatins (PCs) was studied in the roots of the plants. The high stability of the PC-Hg multicomplexes (mPC-nHg) seems to be the main reason for the lack of previous Hg-PC characterization studies. We propose a modification of the method to detect and quantify unbound PC of Hg in plant extracts via high-performance liquid chromatography coupled to electrospray tandem mass spectrometry and inductively coupled plasma mass spectrometry in parallel. We separated the PC from the Hg by adding the chelating agent sodium 2,3-dimercaptopropanesulfonate monohydrate. We only detected the presence of PC after the addition of the chelating agent. Some multicomplexes mPC-nHg could be formed but, due to their large sizes, could not be detected. In this study, only PC(2) was observed in plant samples. Hg accumulation was correlated with PC(2) concentration (r(2) = 0.98).     

Bioaccumulation of mercury,arsenic, cadmium,and lead in plants grown on coal mine soil

Mercury (Hg), arsenic (As), cadmium (Cd), and lead (Pb) are the major toxic metals released by coal mining activities in the surrounding environment. These metals get accumulated in the soils. The plants grown on the contaminated soil uptake these toxic metals in their roots and aerial parts. This study monitored the bioaccumulation of Hg and other three toxic metals in coal mine soil. The pot study of Hg accumulation in Brassica juncea showed that the extent of Hg uptake by roots and shoots of the plants grown on was high in the mature plant and Hg content in root was higher than the shoot. In the soil of unreclaimed overburden (OB) dump, the toxic metal content was higher than that of reclaimed OB dump which posed high ecological risk in the soil of unreclaimed OB dump. Bioaccumulation coefficient (BAC) value showed that Hg was not accumulated in the leaves of Dalbergia sissoo L., Gmelina arborea, Peltaphorum inerme L., Cassia seamea L, and Acacia mangium L grown on coal mine soil.     

Dependence of cytokinin distribution in plants on their physical and chemical properties and transpiration rate

The effect of transpiration on cytokinin accumulation and distribution in 7-day-old wheat (Triticum durum Desf.) seedlings grown on nutrient medium supplemented with zeatin or its riboside was studied. The content of cytokinins in plants and nutrient medium was measured by the immunoenzyme analysis; cytokinin distribution between root cells was assessed immunohistochemically using antibodies against zeatin derivatives. The rate of transpiration was reduced 20-fold by plant placing in humid chamber. At normal transpiration, after 6 h of plant incubation on the solution of zeatin, the level of cytokinins in plant tissues increased stronger than after incubation on the solution of zeatin riboside (by 7.3 and 3.5 times, respectively, as compared with control), although the rates of both cytokinin uptake were equal. Most portions of cytokinins were retained in the roots, which was stronger expressed in the case of free zeatin uptake. A decrease in the rate of transpiration did not affect substantially the zeatin absorption from nutrient medium and the total level of cytokinin accumulation in plants, but these indices were sharply decreased in the case of zeatin riboside. In the zone of absorption of both control roots and roots treated with cytokinins, more intense cytokinin immunostaining was observed in the cells of the central cylinder. The interrelation between cytokinin distribution between the cells and apoplast, their inactivation, and transport over the plant and their form (zeatin or zeatin riboside) used for treatment is discussed.