Plant Translocation Research Articles

Osmotic and saline effect on growth, water relations, and ion uptake and translocation in Phlomis purpurea plants

The effect of different levels of water deficit and saline stress on physiological and morphological parameters in Phlomis purpurea plants was studied to evaluate their adaptability to such conditions. P. purpurea plants, grown under greenhouse conditions, were subjected to four irrigation treatments lasting 26 weeks: control (C, 1dSm−1, 100% water holding capacity), moderate water deficit (MWD, 1dSm−1, 60% of the control level of irrigation water), severe water deficit (SWD, 1dSm−1, 40% of the control level of irrigation water) and saline (S, 4dSm−1, nutrient solution containing 44mM NaCl). Aerial dry weight decreased in all three treatments, although this response was more marked in the water deficit treatments, especially SWD. Stem diameter, leaf number and leaf area were similarly reduced in both water deficit treatments, while only leaf area decreased in saline treated plants. Throughout the experiment, plant height remained similar in both control and saline treated plants but was inhibited 10 weeks after the beginning of the deficit irrigation. At the end of the experiment there were significant differences in plant height between the control and saline treatment. The control treatment produced a higher number of plants with flowers. Plants irrigated with saline water had higher Na+ concentrations in their leaves than in their roots and shoots, while the increase in the Cl− concentrations were similar in leaves and roots, suggesting some resistance to the movement of the latter ions from root to shoots. There was a negative relationship between leaf growth and Na+ concentration in the saline treated plants, in which the accumulation of salt in leaves was associated with osmotic adjustment, which was responsible for maintaining predawn and midday leaf turgor. However, no osmotic adjustment was observed in plants submitted to water stress. Root hydraulic resistance increased in SWD plants, in which the lowest leaf water potential values were recorded. In water stressed plants, in general the decrease of photosynthesis rate was mainly related with stomata factors, although the reductions observed in saline-stressed plants suggest that non-stomatal limitations to photosynthesis could also have been operating.

Pb-induced ultrastructural alterations and subcellular localization of Pb in two species of Lespedeza by TEM-coupled electron energy loss spectroscopy

Transmission electron microscopy (TEM) coupled electron energy loss spectroscopy (EELS) was conducted in the present study, in order to explore mechanisms involved in Pb tolerance and detoxification in two species of Lespedeza (Fabaceae). Both Lespedeza chinensis and Lespedeza davidii have been recently shown to be suitable for chelate-assisted Pb phytoremediation. Ultrastructural alterations, Pb localization and speciation in leaf and root cells of both species were investigated after Pb exposure. Additionally, the influence of EDTA which facilitates Pb translocation in plants was investigated. In general, deleterious effects were more pronounced in root cells of both species than in leaf cells. Similar ultrastructural alterations such as vacuolization and dilation of the nuclear envelopes were induced in leaf and root cells of both species by Pb treatment. The effects were intensified with the addition of EDTA. Autophagy occurred only in leaf cells of L. davidii after Pb and Pb plus EDTA treatment, and in root cells of both species after Pb treatment. Moreover, electron-dense deposits with variable shapes such as acicular, granulated, punctuated and amorphous, were present in cell walls, intercellular spaces, cytoplasm and vacuoles of root cells of both species after Pb and Pb plus EDTA treatment. These deposits contained Pb as identified via the Pb-M 4,5 edge by EELS in a 120 kV TEM. As phosphorus was always measured at the sites of Pb deposition, it is likely that Pb in Lespedeza is stored as lead phosphate particularly in cell walls and vacuoles. The occasional presence of S and Ca in Pb depositions may point to additional other Pb compounds. Our studies suggest that Pb is transported both in apoplastic and symplastic pathways, independent of the presence or absence of EDTA. Different possible detoxification strategies such as sequestration in cell walls or compartmentalization in vacuoles exist both in L. chinensis and L. davidii. Only minor differences in ultrastructural alterations and Pb localization were observed between two species.

Characterization of the Nuclear- and Plastid-EncodedsecA-Homologous Genes in the Unicellular Red AlgaCyanidioschyzon merolae

SecA is an ATP-driven motor for protein translocation in bacteria and plants. Mycobacteria and listeria were recently found to possess two functionally distinct secA genes. In this study, we found that Cyanidioschyzon merolae, a unicellular red alga, possessed two distinct secA-homologous genes; one encoded in the cell nucleus and the other in the plastid genome. We found that the plastid-encoded SecA homolog showed significant ATPase activity at low temperature, and that the ATPase activity of the nuclear-encoded SecA homolog showed significant activity at high temperature. We propose that the two SecA homologs play different roles in protein translocation.

A Review on Mechanisms of Plant Tolerance and Role of Transgenic Plants in Environmental Clean-up

This article deals with the advances and implication of phytoremediation technologies with emphasis on remediation of toxic heavy metals from contaminated soil. Most of the conventional remedial technologies are expensive and inhibit the soil fertility and cause negative impacts on various ecosystem services. However, phytoremediation is a cost effective and ecofriendly approach, which does not adversely affect soil properties and ecosystem services. In recent years, major progresses have been made in understanding the physiological mechanisms of metal uptake and transport in hyper accumulators. However, the molecular mechanisms of metal uptake, translocation, accumulation and detoxification in plants and their further implication in transgenic development for efficient phytoremediation are not well understood. In view of above, present review article brings together existing bits of information to create a new direction for future research, critical gap in knowledge and a new perspective on remediation of toxic pollutants.

Fe isotope fractionation caused by translocation of iron during growth of bean and oat as models of strategy I and II plants

The determination of the plant-induced Fe-isotopic fractionation is a promising tool to better quantify their role in the geochemical Fe cycle and possibly to identify the physiological mechanisms of Fe uptake and translocation in plants. Here we explore the isotope fractionation caused by translocation of Fe during growth of bean and oat as representatives of strategy I and II plants. Plants were grown on a nutrient solution supplemented with Fe(III)-EDTA and harvested at three different ages. We used the technique of multi-collector ICP-MS to resolve the small differences in the stable iron isotope compositions of plants. Total bean plants, regardless of their age, were found to be enriched in the light iron isotopes by −1.2‰ relative to the growth solution throughout. During growth plants internally redistributed isotopes where young leaves increasingly accumulated the lighter isotopes whereas older leaves and the total roots were simultaneously depleted in light iron isotopes. Oat plants were also enriched in the light iron isotopes but during growth the initial isotope ratio maintained in all organs at all growth stages. We conclude that isotope fractionation in bean as a representative of strategy I plants is a result of translocation or re-translocation processes. Furthermore we assume that both uptake and translocation of Fe in oat maintains the irons’ ferric state, or that Fe is always bound to high-mass ligands, so that isotope fractionation is virtually absent in these plants. However, in contrast to our previous study in which strategy II plants were grown on soil substrate, oat plants grown on Fe(III)-EDTA contain iron that enriches 54Fe by 0.5 permil over 56Fe. A possible explanation for the enrichment is the prevalence of a constitutive reductive uptake mechanism of iron in the nutrient solution used which is non-deficient in iron.

The origin of lead in the organic horizon of tundra soils: Atmospheric deposition, plant translocation from the mineral soil or soil mineral mixing?

Knowledge of the anthropogenic contribution to lead (Pb) concentrations in surface soils in high latitude ecosystems is central to our understanding of the extent of atmospheric Pb contamination. In this study, we reconstructed fallout of Pb at a remote sub-arctic region by using two ombrotrophic peat cores and assessed the extent to which this airborne Pb is able to explain the isotopic composition ( 206Pb/ 207Pb ratio) in the O-horizon of tundra soils. In the peat cores, long-range atmospheric fallout appeared to be the main source of Pb as indicated by temporal trends that followed the known European pollution history, i.e. accelerated fallout at the onset of industrialization and peak fallout around the 1960s–70s. The Pb isotopic composition of the O-horizon of podzolic tundra soil ( 206Pb/ 207Pb = 1.170 ± 0.002; mean ± SD) overlapped with that of the peat ( 206Pb/ 207Pb = 1.16 ± 0.01) representing a proxy for atmospheric aerosols, but was clearly different from that of the parent soil material ( 206Pb/ 207Pb = 1.22–1.30). This finding indicated that long-range fallout of atmospheric Pb is the main driver of Pb accumulation in podzolic tundra soil. In O-horizons of tundra soil weakly affected by cryoturbation (cryosols) however, the input of Pb from the underlying mineral soil increased as indicated by 206Pb/ 207Pb ratios of up to 1.20, a value closer to that of local soil minerals. Nevertheless, atmospheric Pb appeared to be the dominant source in this soil compartment. We conclude that Pb concentrations in the O-horizon of studied tundra soils – despite being much lower than in boreal soils and representative for one of the least exposed sites to atmospheric Pb contaminants in Europe – are mainly controlled by atmospheric inputs from distant anthropogenic sources.

Alleviation of Chromium Toxicity by Silicon Addition in Rice Plants

The alleviatory effect of silicon (Si) on chromium (Cr) toxicity to rice plants was investigated using a hydroponic experiment with two Cr levels (0 and 100 μmol L −1), three Si levels (0, 1.25, and 2.5 mmol L −1) and two rice genotypes, differing in grain Cr accumulation (Dan K5, high accumulation and Xiushui 113, low accumulation). The results showed that 100 μmol L −1 Cr treatment caused a marked reduction of seedling height, dry biomass, soluble protein content, and root antioxidant enzyme activity, whereas significantly increased Cr concentration and TBARS (thiobarbituric acid reactive substances) content. However, the reductions of seedling height, dry biomass, and soluble content were greatly alleviated due to Si addition to the culture solution. Compared with the plants treated with Cr alone, Si addition markedly reduced Cr uptake and translocation in rice plants. No significant differences were observed between the two Si treatments (1.25 and 2.5 mmol L −1) in shoot Cr concentration and Cr translocation factor. Under the treatment of 100 μmol L −1 Cr+2.5 mmol L −1 Si, higher root Cr concentration but lower shoot Cr concentration and Cr translocation factor were observed in Dan K5 than those in Xiushui 113, indicating that the beneficial effect of Si on inhibiting Cr translocation was more pronounced in Dan K5 than in Xiushui 113. Si addition also alleviated the reduction of antioxidative enzymes (superoxide dismutase (SOD) and ascorbate peroxidase (APX) in leaves; catalase (CAT) and APX in roots) and the increase of TBARS content in the Cr-stressed plants. Furthermore, the beneficial effects of Si on activities of antioxidative enzymes under Cr stress were genotype-dependent. The highest activities of SOD, POD (guaiacol peroxidase), CAT, and APX in leaves occurred in the treatment of 100 μmol L −1 Cr+2.5 mmol L −1 Si for Xiushui 113 and in the treatment of 100 μmol L −1 Cr+1.25 mmol L −1 Si for Dan K5. The beneficial effect of Si on alleviating oxidative stress was much more pronounced in Dan K5 than in Xiushui 113. It may be concluded that Si alleviates Cr toxicity mainly through inhibiting the uptake and translocation of Cr and enhancing the capacity of defense against oxidative stress induced by Cr toxicity.

Zn Uptake and Translocation in Rice Plants

Zinc (Zn) is an essential micronutrient with numerous cellular functions in plants, and its deficiency represents one of the most serious problems in human nutrition worldwide. Zn deficiency causes a decrease in plant growth and yield. On the other hand, Zn could be toxic if excess amounts are accumulated. Therefore, the uptake and transport of Zn must be strictly regulated. In this review, the dominant fluxes of Zn in soil–root–shoot translocation in rice plants (Oryza sativa) are described, including Zn uptake from soils in the form of Zn2+ and Zn-DMA at the root surface, and Zn translocation to shoots. Knowledge of these fluxes could be helpful to formulate genetic and physiologic strategies to address the widespread problem of Zn-limited crop growth.

Biogenic volatile organic compound and respiratory CO2 emissions after 13C-labeling: online tracing of C translocation dynamics in poplar plants.

BackgroundGlobally plants are the primary sink of atmospheric CO2, but are also the major contributor of a large spectrum of atmospheric reactive hydrocarbons such as terpenes (e.g. isoprene) and other biogenic volatile organic compounds (BVOC). The prediction of plant carbon (C) uptake and atmospheric oxidation capacity are crucial to define the trajectory and consequences of global environmental changes. To achieve this, the biosynthesis of BVOC and the dynamics of C allocation and translocation in both plants and ecosystems are important.MethodologyWe combined tunable diode laser absorption spectrometry (TDLAS) and proton transfer reaction mass spectrometry (PTR-MS) for studying isoprene biosynthesis and following C fluxes within grey poplar (Populus x canescens) saplings. This was achieved by feeding either 13CO2 to leaves or 13C-glucose to shoots via xylem uptake. The translocation of 13CO2 from the source to other plant parts could be traced by 13C-labeled isoprene and respiratory 13CO2 emission.Principal FindingIn intact plants, assimilated 13CO2 was rapidly translocated via the phloem to the roots within 1 hour, with an average phloem transport velocity of 20.3±2.5 cm h−1. 13C label was stored in the roots and partially reallocated to the plants' apical part one day after labeling, particularly in the absence of photosynthesis. The daily C loss as BVOC ranged between 1.6% in mature leaves and 7.0% in young leaves. Non-isoprene BVOC accounted under light conditions for half of the BVOC C loss in young leaves and one-third in mature leaves. The C loss as isoprene originated mainly (76–78%) from recently fixed CO2, to a minor extent from xylem-transported sugars (7–11%) and from photosynthetic intermediates with slower turnover rates (8–11%).ConclusionWe quantified the plants' C loss as respiratory CO2 and BVOC emissions, allowing in tandem with metabolic analysis to deepen our understanding of ecosystem C flux.

Seedling growth and metal accumulation of selected woody species in copper and lead/zinc mine tailings

A greenhouse pot experiment was conducted to evaluate the potential of selected woody plants for revegetation in copper (Cu) and lead/zinc (Pb/Zn) mine tailing areas. Five woody species ( Amorpha fruticosa Linn, Vitex trifolia Linn. var. simplicifolia Cham, Glochidion puberum (Linn.) Hutch, Broussonetia papyrifera, and Styrax tonkinensis) and one herbaceous species ( Sesbania cannabina Pers) were planted in Cu and Pb/Zn tailings to assess their growth, root morphology, nutrition uptake, metal accumulation, and translocation in plants. Amorpha fruticosa maintained normal growth, while the other species demonstrated stress related growth and root development. Sesbania cannabina showed the highest biomass among the plants, although it decreased by 30% in Cu tailings and 40% in Pb/Zn tailings. Calculated tolerance index (TI) values suggested that A. fruticosa, an N-fixing shrub, was the most tolerant species to both tailings (TI values 0.92-1.01), while S. cannabina had a moderate TI of 0.65-0.81 and B. papyrifera was the most sensitive species, especially to Pb/Zn tailings (TI values 0.15-0.19). Despite the high concentrations of heavy metals in the mine tailings and plants roots, only a small transfer of these elements to the aboveground parts of the woody plants was evident from the low translocation factor (TF) values. Among the woody plants, V. trifolia var . simplicifolia had the highest TF values for Zn (1.32), Cu (0.78), and Pb/Zn (0.78). The results suggested that A. fruticosa and S. cannabina, which have the highest tolerance and biomass production, respectively, demonstrated the potential for tailings revegetation in southern China.

Optimality of the Münch mechanism for translocation of sugars in plants.

Plants require effective vascular systems for the transport of water and dissolved molecules between distal regions. Their survival depends on the ability to transport sugars from the leaves where they are produced to sites of active growth; a flow driven, according to the Münch hypothesis, by osmotic gradients generated by differences in sugar concentration. The length scales over which sugars are produced (Lleaf) and over which they are transported (L(stem)), as well as the radius r of the cylindrical phloem cells through which the transport takes place, vary among species over several orders of magnitude; a major unsettled question is whether the Münch transport mechanism is effective over this wide range of sizes. Optimization of translocation speed predicts a scaling relation between radius r and the characteristic lengths as r∼(Lleaf Lstem)1/3. Direct measurements using novel in vivo techniques and biomimicking microfluidic devices support this scaling relation and provide the first quantitative support for a unified mechanism of sugar translocation in plants spanning several orders of magnitude in size. The existence of a general scaling law for phloem dimensions provides a new framework for investigating the physical principles governing the morphological diversity of plants.

Influence of Methylobacterium on iron translocation in plants

Iron metabolism in plants is essential to maintain optimal growth and iron nutrition is dependent on uptake of iron from the environment and movement of iron in the plant tissues. We have examined the translocation of iron in plant leaves following foliar application of FeEDTA to Vicia faba and Zea mays. Using radiolabeled iron, we observed that iron translocation is stimulated by products of Methylobacterium mesophylicum and by the cytokinin, kinetin. When cytokinins were applied to leaves along with (55)FeEDTA, the rate of iron translocation was greater than in controls without cytokinin addition. Since recent studies indicate that M. mesophylicum is widely distributed in the environment as a pyllospheric bacterium, this organism may have an important role in enhancing translocation of nutrients in plant leaves.

Analysis on the Tolerance of Four Ecotype Plants Against Copper Stress in Soil

To screen copper tolerant species, Four ecotype plants, Catalpabungei C. A. Mey, Catalpa ovata G. Don, tall fescue (Festuca arundinacea), and Sedum lineare Thunb, were planted in soil contaminated by Cu in greenhouse to reveal their characteristics of survival, growth and morphology, as well as copper uptake, accumulation and translocation in plants. The survival rate(S) of Catalpabungei C. A. Mey under Cu stress was high, while that of Catalpa ovata G. Don was just the opposite. With the increasing of Cu concentrations in soil, tree height(H) increment percents of both Catalpabungei C. A. Mey and Catalpa ovata G. Don declined significantly(significant level, α=0.05), but for stem bases(D) there were not obvious differences. The translocation factors (TF) and bioconcentration factors(BCF) of Catalpabungei C. A. Mey and Catalpa ovata G. Don were both lower than 0.5. The Cu content in roots of Catalpabungei C. A. Mey was significantly positively correlated with that in soil(r = 0.98; P < 0.05). Tolerance index (TI) of tall fescue and Sedum lineare Thunb were low. The concentrations of Cu in tall fescue and Sedum lineare Thunb both had significantly positive correlation with those in soils. The results suggested that Catalpabungei C. A. Mey, tall fescue, and Sedum lineare Thunb were tolerant to Cu stress in soil to some extent, and were of application potential as pioneer species for ecological restoration in areas suffering Cu pollution.

Allelopathic effect of Cylindrospermopsis raciborskii extracts on the germination and growth of several plant species

Cylindrospermopsis raciborskii is an invasive cyanobacterium and a potential producer of the alkaloid toxin cylindrospermopsin (CYN). Extracts of two strains of C. raciborskii were tested for their effects on the germination and growth of Lactuca sativa, Phaseolus vulgaris, Pisum sativum and Solanum lycopersicum. Germination was not significantly inhibited for any of the plant species tested, but growth was affected, depending on the species. Root and stem growth in L. sativa was generally stimulated by both strains. Ph. vulgaris root growth was stimulated by both strains but no effect was visible in stem growth. S. lycopersicum root growth was inhibited by both strains and stem growth was inhibited only by the CYN strain. P. sativum root growth was also inhibited by both strains but stem growth was stimulated. CYN accumulation was also differential with toxin transfer to the stem. Ph. vulgaris accumulated the highest CYN concentration. This study suggests that plants behave differently in their response to this toxin and that roots and stems also show different abilities to react and accumulate the toxin. Knowledge of the impact of CYN- and non-CYN-producing cyanobacteria in different plant species and translocation of the toxin to different plant parts is essential for the avoidance of human as well as environmental health hazards.

Potassium channel α-subunit AtKC1 negatively regulates AKT1-mediated K+ uptake in Arabidopsis roots under low-K+ stress

Potassium transporters play crucial roles in K(+) uptake and translocation in plants. However, so far little is known about the regulatory mechanism of potassium transporters. Here, we show that a Shaker-like potassium channel AtKC1, encoded by the AtLKT1 gene cloned from the Arabidopsis thaliana low-K(+) (LK)-tolerant mutant Atlkt1, significantly regulates AKT1-mediated K(+) uptake under LK conditions. Under LK conditions, the Atkc1 mutants maintained their root growth, whereas wild-type plants stopped their root growth. Lesion of AtKC1 significantly enhanced the tolerance of the Atkc1 mutants to LK stress and markedly increased K(+) uptake and K(+) accumulation in the Atkc1-mutant roots under LK conditions. Electrophysiological results showed that AtKC1 inhibited the AKT1-mediated inward K(+) currents and negatively shifted the voltage dependence of AKT1 channels. These results demonstrate that the 'silent' K(+) channel alpha-subunit AtKC1 negatively regulates the AKT1-mediated K(+) uptake in Arabidopsis roots and consequently alters the ratio of root-to-shoot under LK stress conditions.

Plant structure. A colour guide, 2nd edn

I regularly – and (I hope) rightly – bemoan the lack of plant anatomical knowledge of modern-day biology graduates, so it's always good to see books that try to remedy that deficiency! Expectations were accordingly high when I received Plant structure by Bowes and Mauseth (hereafter referred to as B&M2e) to review. Although BM there is a standard set of topics that are fundamental to plant anatomy that all books that aspire to deliver on the subject ought to contain. Each chapter begins with a short introductory text that summarizes the main features of the chapter's subject. And this is done with admirable succinctness. Briefly, the contents are: Chapter 1, Introduction, which sets the theme for the atlas and covers such topics as the variety of land plants, transpiration and translocation in vascular plants, general morphology of angiosperms (the book is largely concerned with flowering plant anatomy), floral and reproductive features. Chapter 2, The Plant Cell, is an introduction to plant cell ultrastructure. Chapter 3, Plant Histology, considers cells and tissues of the primary and secondary plant body (this and all subsequent chapters contain images almost solely at the light-microscope, LM, level, the primary level of inquiry of the book). After Chapter 4, Apical Meristems, there follow chapters dedicated to the major organs of the vegetative plant body: 5, The Green Leaf; 6, The Stem; and 7, The Root. The anatomical survey is concluded with Chapter 8 on Plant Reproduction. A selected bibliography, glossary and index complete the book. Perhaps the most telling comparison of BM Chapter 8 is termed Plant Reproduction in B&M2e – rather than Sexual Reproduction – because it has been expanded to include asexual propagation methods. Whilst the text in both editions is largely the same, it has been considerably supplemented in many places in B&M2e, e.g. approx. 2·5 pages on leaf modifications in Chapter 6 (although this may not sound much, since the text of a chapter in B&M2e is only approx. 6·25 pages this represents a substantial increase). And there are also new sections dealing with mangroves, succulent roots, parasitic plants and ant-plants in Chapter 7. As one might expect from Mauseth's involvement, there are a lot of cactus images in B&M2e (and yes! anatomy of cactus spines is one of the new items on leaf modification in Chapter 5). The bibliography, glossary and index are also all larger in B&M2e. Inevitably in such a volume, attention focuses on the images. And here is where I have a big problem with B&M2e. Notwithstanding how stunning and beautiful the images are (which they are and for which full credit is rightly and richly deserved), they suffer from a massive fundamental flaw: nowhere are scale bars provided for any image, nor even an indication of the magnification (which latter basic information was provided in 1e). Why is this essential information not provided? Not only is its omission baffling and bizarre, it seriously undermines any value the text has as an aid to teaching plant anatomy! BM although both of these have accompanying CDs with digital versions of the book's images – which addition would have made BM although their images may not be as impressive as B&M2e's, they do at least give details of the magnification. Without doubt Bowes & Mauseth's Plant structure is a stunning collection of anatomical images at the light-microscope level with informative accompanying text. And at approx. £0·05 per image it represents excellent value. It is therefore such a shame that its educational worth is considerably devalued by images devoid of any indication of magnification or scale.

OsSPX1 suppresses the function of OsPHR2 in the regulation of expression of OsPT2 and phosphate homeostasis in shoots of rice

Phosphate (Pi) homeostasis in plants is required for plant growth and development, and is achieved by the coordination of Pi acquisition, translocation from roots to shoots, and remobilization within plants. Previous reports have demonstrated that over-expression of OsPHR2 (the homolog of AtPHR1) and knockdown of OsSPX1 result in accumulation of excessive shoot Pi in rice. Here we report that OsPHR2 positively regulates the low-affinity Pi transporter gene OsPT2 by physical interaction and upstream regulation of OsPHO2 in roots. OsPT2 is responsible for most of the OsPHR2-mediated accumulation of excess shoot Pi. OsSPX1 suppresses the regulation on expression of OsPT2 by OsPHR2 and the accumulation of excess shoot Pi, but it does not suppress induction of OsPT2 or the accumulation of excessive shoot Pi in the Ospho2 mutant. Our data also show that OsSPX1 is a negative regulator of OsPHR2 and is involved in the feedback of Pi-signaling network in roots that is defined by OsPHR2 and OsPHO2. This finding provides new insight into the regulatory mechanism of Pi uptake, translocation, allocation and homeostasis in plants.

EFFECTS OF PHOSPHORUS FERTILIZATION ON ARSENIC UPTAKE BY WHEAT GROWN IN POLLUTED SOILS

In this study we have examinated the results of two experiments on the uptake and distribution of arsenic (As) in roots, shoots, and grain of wheat grown in As-polluted soils and in an unpolluted soil irrigated with As-contaminated water in absence or presence of phosphorus (P) fertilization. Arsenic concentrations in wheat samples of the two experiments are higher than those in the plants grown on uncontaminated soil. In the experiments showed in this work, it is highlighted the role of P fertilization in preventing As uptake and translocation in wheat plants. These findings could have important implications to reduce the potential risk posed to human health by As entering the food-chain.

Dieldrin uptake and translocation in plants growing in hydroponic medium

It has been known that the Cucurbitaceae family takes up a large amount of persistent organic pollutants from soils and that the translocation of those compounds in cucurbits is higher than those in non-cucurbits. To understand the persistent organic pollutant uptake mechanisms of plant species, we compared the dieldrin absorption and transportation potentials of several plants in hydroponic medium. Sorghum (Sorghum vulgare Moench), sunflower (Helianthus annuus L.), soybean (Glycine max), komatsuna (Brassica rapa var. peruviridis), white-flowered gourd (Lagenaria siceraria var. hispida), cucumber (Cucumis sativus L.), and zucchini (Cucurbita pepo L.) were grown in a dieldrin-added hydroponic medium for 10 d, and then the amount of dieldrin in their shoots and roots was measured. All of the roots contained dieldrin, whereas only the cucurbits (white-flowered gourd, cucumber, and zucchini) contained considerable amounts of dieldrin in their shoots. The dieldrin uptake to the roots depended on the concentration of the n-hexane soluble components in the roots, regardless of whether the dieldrin in the roots was translocated to shoots or not. The dieldrin uptake from the solution to the roots was thought to be due to a passive response, such as adsorption on the roots. The translocation of dieldrin from the roots to the shoots was probably through the xylems. The amounts of dieldrin in the shoots per transpiration rates were higher for cucurbits than for non-cucurbits. It seems likely that cucurbits have uptake mechanisms for hydrophobic organic chemicals.

Behavior of Decabromodiphenyl Ether (BDE-209) in the Soil−Plant System: Uptake, Translocation, and Metabolism in Plants and Dissipation in Soil

Deca-bromodiphenyl ether (BDE-209) is the major component of the commercial deca-BDE flame retardant. There is increasing concern over BDE-209 due to its increasing occurrence in the environment and in humans. In this study the behavior of BDE-209 in the soil-plant system was investigated. Accumulation of BDE-209 was observed in the roots and shoots of all the six plant species examined, namely ryegrass, alfalfa, pumpkin, summer squash, maize, and radish. Root uptake of BDE-209 was positively correlated with root lipid content (P < 0.001, R(2) = 0.81). The translocation factor (TF, C(shoot)/C(root)) of BDE-209 was inversely related to its concentration in roots. Nineteen lower brominated (di- to nona-) PBDEs were detected in the soil and plant samples and five hydroxylated congeners were detected in the plant samples, indicating debromination and hydroxylation of BDE-209 in the soil-plant system. Evidence of a relatively higher proportion of penta- through di-BDE congeners in plant tissues than in the soil indicates that there is further debromination of PBDEs within plants or low brominated PBDEs are more readily taken up by plants. A significant negative correlation between the residual BDE-209 concentration in soil and the soil microbial biomass measured as the total phospholipid fatty acids (PLFAs) (P < 0.05, R(2) = 0.74) suggests that microbial metabolism and degradation contribute to BDE-209 dissipation in soil. These results provide important information about the behavior of BDE-209 in the soil-plant system.