Zinc is an essential microelement involved in many aspects of plant growth and development. Abnormal zinc amounts, mostly due to human activities, can be toxic to flora, fauna, and humans. In plants, excess zinc causes morphological, biochemical, and physiological disorders. Some plants have the ability to resist and even accumulate zinc in their tissues. To date, 28 plant species have been described as zinc hyperaccumulators. These plants display several morphological, physiological, and biochemical adaptations resulting from the activation of molecular Zn hyperaccumulation mechanisms. These adaptations can be varied between species and within populations. In this review, we describe the physiological and biochemical as well as molecular mechanisms involved in zinc hyperaccumulation in plants.

Screening of native plant species from mining sites can lead to identify suitable plants for phytoremediation approaches. In this study, we assayed heavy metals tolerance and accumulation in native and dominant plants growing on abandoned Pb/Zn mining site in eastern Morocco. Soil samples and native plants were collected and analyzed for As, Cd, Cu, Ni, Sb, Pb, and Zn concentrations. Bioconcentration factor (BCF), translocation factor (TF), and biological accumulation coefficient (BAC) were determined for each element. Our results showed that soils present low organic matter content combined with high levels of heavy metals especially Pb and Zn due to past extraction activities. Native and dominant plants sampled in these areas were classified into 14 species and eight families. Principal components analysis separated Artemisia herba-alba with high concentrations of As, Cd, Cu, Ni, and Pb in shoots from other species. Four plant species, namely, Reseda alba, Cistus libanotis, Stipa tenacissima, and Artemisia herba-alba showed strong capacity to tolerate and hyperaccumulate heavy metals, especially Pb, in their tissues. According to BCF, TF, and BAC, these plant species could be used as effective plants for Pb phytoextraction. Stipa tenacissima and Artemisia herba-alba are better suited for phytostabilization of Cd/Cu and Cu/Zn, respectively. Our study shows that several spontaneous and native plants growing on Pb/Zn contaminated sites have a good potential for developing heavy metals phytoremediation strategies.

Fruits, vol. 64 (4) 261Protoplast isolation and culture for banana regeneration via somatic embryogenesis.Abstract --Introduction. This protocol describes a method for obtaining protoplasts from banana leaves, calli and cell suspensions, and their sustainable development via somatic embryogenesis from embryogenic cell suspensions. The principle, key advantages, starting plant material, time required and expected results are presented. Materials and methods. This part describes the required laboratory materials, and media preparation for protoplast production and culture. Results. The first protoplasts may be seen after 30 min of incubation in enzyme maceration. With protoplasts from embryogenic cell suspension, complete development into a whole plant, through somatic embryogenesis, is observed in 12 weeks. The first cell divisions occur on feeder layers 3-8 days after protoplast plating. Proembryo formation is observed 14-21 days after initiation of protoplast culture. The transfer of derived embryo plantlets, at 8-10 weeks after protoplast plating, onto growth regulator-free medium, leads to plant rooting and elongation. Résumé --Introduction. Le protocole décrit une méthode qui permet d'obtenir des protoplastes à partir de feuilles, de cals et de suspensions cellulaires de bananiers, ainsi que le développement, par embryogenèse somatique, des protoplastes issus de suspensions cellulaires embryogènes. Le principe, les principaux avantages de la méthode, le matériel végétal de départ, le temps nécessaire et les résultats attendus sont présentés. Matériel et méthodes. Cette partie décrit le matériel de laboratoire nécessaire, la préparation des milieux pour l'obtention de protoplastes, ainsi que leur culture. Résultats. Dès la première demi-heure d'incubation dans la solution enzymatique, les premiers protoplastes sont libérés. En 12 semaines, les protoplastes, issus de suspensions cellulaires embryogènes, se développent en plantes entières via l'embryogenèse somatique. Sur les couches nourricières, les protoplastes reconstituent leur paroi ; les premières divisions cellulaires s'observent (3 à 8) jours après l'étalement des protoplastes. La formation des proembryons se déroule entre (14 et 21) jours après le début des cultures de protoplastes. Puis, (8 à 10) semaines après l'étalement des protoplastes, leur évolution embryogène conduit à des plantules qui s'enracinent et s'allongent après transfert sur un milieu dépourvu de facteurs de croissance.France / Musa sp. / méthode / milieu de culture / technique de culture / protoplaste / embryogenèse somatique / régénération in vitro

Heavy metal contamination is of particular concern for human health and the environment. Phytoremediation is an emerging cost‐effective strategy to remediate heavy metal contaminated soil. However, this technique is limited by the small number of plants that are tolerant to heavy metals and are also accumulators. This study assayed zinc, lead, and cadmium tolerance and accumulation in Cistus libanotis, Cistus albidus, and Cistus salviifolius. The plants were cultivated in hydroponic conditions and exposed to different concentrations of Pb(NO3)2 (100 and 200 µM), ZnSO4 (100 and 200 µM), or CdCl2 (10 and 20 µM) for 3 weeks. Plant biomass and metal accumulation in roots and aboveground parts varied greatly among the species. All three species appeared to be sensitive to Zn. However, C. albidus displayed strong tolerance to Pb and accumulated large quantities of Pb and Cd in its roots. C. libanotis accumulated large quantities of Pb and Cd in its aboveground parts. C. libanotis can thus be classified as a Pb and Cd accumulator species. The study results show that C. albidus is suitable for phytostabilization of Pb‐contaminated soils, while C. libanotis can be used for phytoextraction of both Pb and Cd.

Lateral buds of six cultivars of sweet potato were induced to form embryogenic callus in a culture medium solidified with two types of gelling agents, Agar or Gelrite, and supplemented with various concentrations of auxins, 2,4-D, 2,4,5-T and Picloram. Of the six cultivars screened, only three gave an embryogenic response. Best results with an average of 3.53% embryogenic response were obtained with the medium solidified with Agar, while in Gelrite only 0.45% of lateral buds gave rise to embryogenic callus. The interaction between the genotype and auxins was highly significant; particularly the optimal response was obtained with cv. Zho and 865 yielding 10.7 and 14.7% somatic embryogenesis, respectively, in the medium containing 2,4,5-T or Picloram. The plant conversion was dramatically improved by subculture of the embryogenic callus on the medium with the combination of 1 µM 2,4-D and 1 µM Kinetin or 5 µM ABA alone before transfer of mature embryos onto hormone-free medium. The embryogenic callus of sweet potato and its sustained ability to further regenerate plants have regularly been maintained for several years by frequent subculture in 5 µM 2,4,5-T or the combination of 10 µM 2,4-D and 1 µM BAP or kinetin. The embryo-derived plants seemed apparently genetically stable and similar to the hexaploid parental plants, based on morphological analysis and their ploidy level determined by using flow cytometry. To cite this article: Z.