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Plants are able to extract metal(loid) contaminants from the soil or water through their roots and translocate them to harvestable aerial shoots. Of late, this plant potential has been used as a phytotechnology, termed as phytoextraction, for cleaning contaminated sites, and this process has successfully removed elements like As, Cd, Cu, Ni, and Pb, among others. Exploring plants with high metal-accumulation capacity, as well as engineering new hyperaccumulators, is a need of the hour. It is assumed that hyperaccumulators have a >1 shoot:root metal-accumulation ratio, which they achieve by way of (i) overexpression of transport systems for improved sequestration, (ii) tissue-specific protein expression, and (iii) high concentration of metal chelators. Unlike nonhyperaccumulators, the hyperaccumulating species normally bind metal ions to weak oxygen ligands and use strong ligands only for transient binding during transport to storage sites. Adequate understanding of genetics, biochemistry, and molecular biology of metal accumulation is a prelude to developing transgenics with improved phytoremediation capacity. Current research in plant breeding, genomics, and proteomics suggest promising leads to the creation of 'remediation' cultivars. Several transporter genes associated with metal uptake, transport, and accumulation have been identified. Efforts are underway to enhance the phytoextraction capacity of relevant species, not only by using chelating agents but also by attempting hybridization, protoplast fusion, as well as genetic engineering through novel gene transfer, overexpression of genes, and (or) reverse gene insertion, to enhance (i) transpiration rate; (ii) uptake, translocation, and metabolism of metals; (iii) activity of enzymes related to rate-limiting steps; and (iv) transformation of accumulated metal to volatile forms, and (or) silencing gene(s) that encode proteases. Genome evolution in hyperaccumulators needs to be understood through a systematic study of ecological and molecular genomics. Sequencing of a complete genome of hyperaccumulators can help in identifying the promising functional noncoding regions in the genome, thus making the experimental analysis more accurate. In addition to the constitutive overexpression of a single gene, simultaneous expression of several genes in specific cellular components has to be focused. Other areas that require expert attention include identification of metal-transporter proteins and the introduction of genes encoding the metal transporters, overexpression of metallothioneins and phytochelatin synthase, and overproduction of nicotianamine and histidine in plants. A comprehensive study of transgenic gene frequency, covering several plant generations growing on polluted as well as nonpolluted soils, may assess the possibility of gene escape into the environment and its transfer to the microorganisms present in the surroundings. This review attempts not only to collect and collate information available on mechanisms of metal accumulation and detoxification in plants and on the factors affecting the tolerance and phytoextraction capacity of plants but also the strategies that have been or can be devised for raising novel plant genotypes with elevated capacity of metal accumulation and toxicity tolerance. Key words: genetic engineering, hyperaccumulators, metal toxicity, phytoremediation, transgenics. Les plantes ont la capacite d'extraire par leurs racines, des contaminants metalliques et metalloides a partir du sol et de l'eau et de les transporter vers les tiges aeriennes recoltables. On a exploite cette capacite des plantes comme phytotechnologie, appelee phytoextraction, pour nettoyer les sites contamines en permettant d'extraire avec succes des elements comme les As, Cd, Cu, Ni et Pb, entre autres. On doit rapidement conduire l'exploration de plantes ayant une forte capacite a accumuler les metaux et developper de nouvelles hyperaccumulatrices. On assume que les hyperaccumulatrices possedent un ratio a >1 tige/ racine d'accumulation des metaux, qu'ils realisent au moyen d' (i) une surexpression des systemes de transport pour une meilleure sequestration, (ii) une expression de proteines specifiques aux tissus, et (iii) une forte teneur en chelateurs de metaux. Contrairement aux non-hyperaccumulatrices, les especes hyperaccumulatrices attachent normalement les ions metalliques a de faibles ligands oxygenes et utilisent des ligands forts seulement transitoirement au cours du transport vers les sites d'accumulation. Une comprehension de la genetique, de la biochimie et de la biologie moleculaire de l'accumulation des metaux constitue un prelude au developpement de plantes transgeniques douees de capacites de phytoremediation ameliorees. Les recherches courantes en amelioration genetique, genomique et proteomique suggerent des avancees prometteuses vers la creation de << cultivars de remediation >>. On a identifie plusieurs genes de transport associes a l'absorption des metaux. Des efforts sont en marche pour augmenter la capacite de phytoextraction d'especes appropriees, non seulement en utilisant des agents chelateurs, mais aussi en tentant des hybridations, des fusions protoplasmiques ainsi qu'en genie genetique, par de nouveaux transferts de genes, de la surexpression de genes et/ou l'insertion inverse afin d'augmenter (i) le taux de transpiration (ii) l'absorption, la translocation et le metabolisme des metaux (iii) l'activite d'enzymes reliees aux etapes limitatives (iv) la transformation de metaux accumules sous formes volatiles et le silencage de genes codants pour les proteases. L'evolution du genome chez les hyperaccumultrices doit etre comprise dans le cadre d'une etude systematique de la genomique ecologique et moleculaire. Le sequencage du genome complet d'hyperaccumulatricess pourrait aider a identifier les regions non codantes du genome, rendant ainsi l'analyse experimentale plus precise. En plus de la surexpression constitutive d'un gene unique, on doit cibler l'expression simultanee de plusieurs genes dans des constituants cellulaires specifiques. Voici d'autres activites requerant l'attention des experts incluant l'identification des proteines non transporteuses de metaux et l'introduction de genes codant pour le transport des metaux, ce sont la surexpression des metallothionines et la phytochelatine synthetase ainsi que la surproduction de nicotinamide et d'histidine dans les plantes. Une etude integrative de la frequence des genes transgeniques sur plusieurs generations de plantes croissant sur des sols pollues aussi bien que non pollues pourrait permettre d'evaluer la possibilite d'echappement d'un gene dans l'environnement et son transfert aux microorganismes presents dans les environs. Cette revue tente non seulement de recolter et colliger l'information disponible sur les mecanismes de l'accumulation des metaux et la detoxification par les plantes et des facteurs affectant la tolerance et la capacite de phytoextraction par les plantes, mais egalement d'examiner les strategies qui ont ete ou peuvent etre developpees pour obtenir de nouveaux genotypes de plantes possedant une forte capacite a tolerer et a accumuler les metaux. [Traduit par la Redaction] Mots-cles : genie genetique, hypercaccumulrices, toxicite des metaux, phytoremediation, transgenique., 1. Introduction The present-day spread of industrial activities is posing an unprecedented threat to the chemical balance of our biosphere (Iqbal et al. 2000; Harrison 2001; Hill 2010). The soil [...]

This study compares the yield and growth patterns of a high zinc-accumulating genotype (HZnG) and a low zincaccumulating genotype (LZnG) of chickpea (Cicer arietinum L.) grown for 120 days in earthen pots filled with soil at four zinc regimes (0, 2.5, 5 and 10 mg ZnSO4 kg-1) under naturally illuminated field conditions. Growth parameters were monitored at pre-flowering, flowering and post-flowering stages of the crop. Plants grown in Zn-deficient soil showed suppressed growth, as compared with those grown in soil with Zn (2.5, 5 or 10 mg kg-1 soil) supplied as zinc sulphate. Increase in Zn supply enhanced the growth parameters significantly; however, highest dose was inhibitive in both the genotypes. All growth parameters evinced improvement from pre-flowering stage to post-flowering stage, except for leaf area index, which declined at the post-flowering stage. There were significant genotypic differences for yield parameters; HZnG performed better than LZnG at deficient levels of zinc supply. The 5 mg Zn kg-1 supply was most effective in causing significant differences for the parameters studied. Cultivation of hyperaccumulating chickpea genotypes seems to be a sustainable and cost-effective approach to combat the increasing menace of Zn-deficiency in chickpea production. [ABSTRACT FROM AUTHOR]

The present study evaluated for the first time, some strength properties and the chemical compositions of seven hardwood species grown in Northeast Egypt, namely, Acacia saligna, Delonix regia, Erythrina humeana, Ficus elastica, Leucaena leucocephala, Melia azedarach, and Meryta sinclairii. The analysis of variance (ANOVA) results indicated that the effect of wood species on the mechanical properties and chemical compositions was significant (P<0.01). The parameters used to describe the mechanical properties and chemical compositions of the wood of the seven species differed from one species to another. The cellulose contents of the studied species, except for L. leucocephala (43.2%), M. azedarach (44.1%), and M. sinclairii (44.0%), were found to be lower than those of common hardwood species. The variations in MOR, MOE, Cmax, and tensile strength among the seven species were expected given the differences in wood density and chemical compositions. Except for E. humeana, the other hardwood species studied could be considered to have moderate hardness and are suitable for making floor parquets. Overall, based on the studied mechanical properties, the wood of M. azedarach and M. sinclairii showed good MOR, MOE, and Cmax values, whereas E. humeana wood had the lowest such values. In terms of mechanical properties, the seven hardwood species studied in the present investigation can thus be concluded to have the following order: M. azedarach > M. sinclairii > L. leucocephala > D. regia > F. elastica > A. saligna > E. humeana. [ABSTRACT FROM AUTHOR]

An efficient micropropagation protocol was developed for E. cotinifolia by utilizing mature nodal segments for axillary shoot proliferation. The nodal explants from a 2-year-old plant were cultured on Murashige and Skoog (MS) medium supplemented with different concentrations (0.5, 2.5, 5.0, 7.5 and 10.0 μM) of 6-benzyladenine (BA), Kinetin and 2-isopentenyl adenine singly as well as in combination with α-naphthalene acetic acid (NAA) or Indole-3-butyric acid (IBA) (0.1, 0.5 and 1.0 μM). The highest regeneration frequency (92 %) with multiple shoots (13.0 ± 1.15) and shoot length (4.23 ± 0.14 cm) was achieved on MS medium supplemented with 5.0 μM BA and 0.1 μM NAA after 8 weeks of culture. Further experiments were performed to test the effects of medium type, medium strength, pH and subculture passages on shoot induction and proliferation. An enhancement in average number of shoots (16.6 ± 0.45) per explant was obtained after four subculture passages. Micro shoots exhibited in vitro rooting on half strength MS medium containing 2.5 μM Indole-3-butyric acid (IBA) after 4 weeks of culture. The in vitro raised healthy plantlets with well-developed roots and shoots were successfully acclimatized in plastic cups containing sterile soilrite for 8 weeks under culture room conditions (150 PPFD) prior to field transfer. Through the acclimatization period (0–56 days), photosynthetic pigments (Chlorophyll a, b and Carotenoid content) decreased during the initial 2 weeks followed by significant increase during the successive period (21–56 days) of acclimatization. At the same time, all the tested antioxidant enzymes (SOD, CAT, APX and GR) exhibited an increasing trend throughout the acclimatization period. The culture room acclimatized plantlets were successfully established in earthen pots containing garden soil in greenhouse with 70 % survival rate. [ABSTRACT FROM AUTHOR]

Maize (Zea mays L.) is a multipurpose crop, which is immensely used worldwide for its nutritional as well as medicinal properties. This study evaluates the effect of varying concentrations of nitrogen (N) on accumulation of phenolic acids and antioxidant activity in different maize cultivars, including inbreds, hybrids and a composite, which were grown in natural light under controlled temperature (30°C/20°C D/N) and humidity (80%), with sufficient (4.5mM) and low (0.05mM) nitrogen supply. Seeds of different cultivars were powdered and extracted in a methanol:water (80:20) mixture through reflux at 60-75°C, and the extracts obtained were subjected to high performance thin layer chromatography (HPTLC), using ethyl acetate: acetic acid: formic acid: water (109:16:12:31) solvent system for the separation of phenolic acids. Antioxidant activity of the extracts was determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and H2O2-scavenging activity assays. At sufficient nitrogen condition, the contents of different phenolic acids were higher in the composite cultivar (8.7 mg g-1 d.wt. in gallic acid to 39.3 mg g-1 d.wt. in cinnamic and salicylic acids) than in inbreds and hybrids. Under low nitrogen condition, the phenolic acids contents declined significantly in inbreds and hybrids, but remained almost unaffected in the composite. The antioxidant activity was also the maximum in the composite, and declined similarly as phenolic acids under low nitrogen supply, showing a significant reduction in inbreds and hybrids only. Therefore, the maize composite has a potential for being used as a nutraceutical in human-health sector.

This study aimed at elucidating the process of cambial activity and wood formation in Acacia ehrenbergiana Hayne growing in the Al-Baha region of Saudi Arabia, has revealed that the vascular cambium was active for almost the whole year, producing phloem in two flushes (February-March and August-October), and xylem for about 11 months, with varying pace of cell division and differentiation. A close relationship existed between emergence of new leaves and initiation/acceleration of cambial activity and tissue differentiation. Monthly average of the maximum and mean daily temperature showed negative correlation with cambial-zone width. Relative humidity showed positive relationship with xylem differentiation. Leaf water deficit had an adverse effect on the cambial activity (r = -0.94, p < 0.01), xylem production (r = -0.93, p < 0.01) and phloem production (r = -0.97, p < 0.01). On the whole, moderate temperature, low water deficit and high relative humidity and rainfall favored cambial activity and vascular tissue formation. Annual production of xylem was about five times that of phloem. A. ehrenbergiana appears to be a drought-tolerant species by having narrow, dense and thick-walled vessels, thick-walled fibers, high wood density (0.9273 g cm(-3)), low vulnerability factor (4.20) and the capacity of thriving well at 35 to 47% water-saturation deficit.

A comparative performance of two explants types (CN and Nodal) for their efficiency to induce multiple shoot regeneration in Clitoria ternatea has been carried out. Thidiazuron (TDZ) in different concentrations (0.05-2.5 μM) was used as a supplement to the Murashige and Skoog's (MS) basal media. Explant type apart, two factors viz. concentration and exposure duration to TDZ played an important role in affecting multiple shoot regeneration. Cotyledonary node explants produced the best results at 0.1 μM TDZ, while in nodal explants the highest rate of shoot formation was achieved on MS medium supplemented with 1.0 μM TDZ. In both the explants, shoot multiplication increased when the regenerated shoots were subcultured on hormone free MS medium after 4 weeks of exposure to TDZ. Among the two, cotyledonary node explants produced considerably higher number of shoots at a comparatively lower concentration of TDZ than nodal explants. The regenerated shoots rooted best on MS medium containing 1.0 μM indole-3-butyric acid (IBA) and were successfully established in pots containing garden soil with 88 % survival rate. All the regenerated plants showed normal morphology and growth characteristics.

Plant biomass, antioxidant enzymes activity, ions accumulation and proline level in four soybean cultivars were investigated atdifferent NaCl concentrations (20, 40, 60, 80 and 100 mM) applied to plants 15 days after sowing. There was a significant decrease in plant biomass and soluble protein content with each NaCl treatment. Accumulation of Na+ and Cl- was maximum in roots, followed by the stem and leaves in all the treated cultivars; Pusa 9712 being the top accumulator. On the contrary, K+ and Ca2+ ion concentrations were inhibited in all the treated cultivars. Activities of antioxidant enzymes (superoxide dismutase, ascorbate peroxidase and glutathione reductase) and proline content increased significantly in all the cultivars with each NaCl treatment. The maximum increase was found in Pusa 9712. However, catalase activity decreased in all the cultivars except in Pusa 9712. On the whole, Pusa 9712 was most efficient in managing protection against salinity stress.

This study assesses the effect of NaCl (80 and 160 mM) and CaCl2 (10 mM) solutions, alone and in combination, to 30-day-old seedlings of Cichorium intybus L. Observations were made at 30 day intervals from the time of treatment till harvest (180 days after sowing). Application of NaCI resulted in significant decreases in lengths of root and stem, in dry weights of root, stem and leaves and in the leaf area, as compared with control. The reduction was less with the combined application of NaCI and CaCI2 than with the NaCI treatment alone. On the contrary treatment of CaCl2, alone promoted the above variables. Proline content in the leaves was enhanced with NaCl and CaCI, alone as well as with the NaCI + CaCI2 treatments; the maximum (six-fold) enhancement was observed with the combined treatments, compared with NaCl (four-fold increase) and CaCl2 (two-fold increase) alone. The sodium (Na+) and Chloride (CI) contents in different plant parts increased both with NaCI and with NaCI+ CaCI2 treatments. The maximum accumulation was observed in leaves, followed by that in stem and root. The potassium (K+) and calcium (Ca2+) contents decreased under NaCl stress, but increased with CaCI2 treatment. Thus, calcium ameliorated the deleterious effects of NaCI stress and stimulated the plant metabolism and growth.