Structural and ultrastructural changes caused by bioaccumulation of As and Cr in brake fern (Pteris vittata), a known arsenic hyperaccumulator, were investigated. Potted plants of brake fern were exposed to metal treatments of As and Cr for three weeks. Leaf, stem and root samples were collected periodically and fixed for LM (Light Microscopy), SEM (Scanning Electron Microscopy) and TEM (Transmission Electron Microscopy) to evaluate anatomical changes. The fresh weights, dry weights, RWC (Relative Water Content) and plant heights were obtained before the brake fern plants were harvested for metal accumulation analysis. The As accumulated mainly in the shoots while Cr accumulated mainly in the roots of the metal-treated plants. Significant changes in the ferns physical characters, including fresh weight, dry weight, RWC, and plant height were observed for only Cr-treated plants but not for As-treated plants. Microscopic studies reveal the Cr accumulation resulted in dehydration and collapse of internal structure of leaves and cellular breakdown of roots. The As-treated plants showed no significant structural changes in leaves, stems and roots compared to control plants. Clotted depositions were observed in roots and stems of plant groups treated with highest concentration of Cr and As when compared to control (T0) group. Our study indicates that Cr has a profound impact on physiology and structure of fern plants. The accumulation of Cr resulted in decrease in growth rate, total biomass and RWC. We believe that brake fern plants can uptake, translocate and sequester As because it caused no significant structural changes in leaves, stems and roots of the plants.

Os objetivos deste estudo foram identificar as mudanças estruturais causadas pelo acúmulo de Zn e Cd na parte aérea e nas raízes de plantas de cevada (Hordeum vulgare), como também correlacionar o acúmulo desses metais com alterações anatômicas, fisiológicas e morfológicas. Plantas cultivadas em vasos foram expostas a tratamentos com Zn e Cd por 19 e 16 d, respectivamente. Folhas, caules e raízes foram coletados para identificarem-se alterações estruturais e o acúmulo desses metais. As plantas efetivamente acumularam Zn (até 11283 mg kg-1) e Cd (até 584 mg kg-1) na parte aérea. Houve alterações estruturais microscópicas em folhas, caules e raízes de plantas tratadas com alta concentração de Zn, tais como decréscimo nos espaços intercelulares, comprometimento dos feixes vasculares e encolhimento das células epidérmicas e do parênquima paliçádico. Acumulação de Zn também resultou em decréscimos significativos no conteúdo de água, na massa fresca, na massa seca e na altura das plantas. Apenas em altas concentrações de Cd observaram-se mudanças estruturais nas raízes. Plantas de cevada acumularam quantidades significativas de Zn e de Cd sem exibir sintomas de fitotoxidade quando a concentração dos metais testados foi relativamente baixa.

The objectives of this study were to identify the structural changes caused by Zn and Cd accumulation in shoots and roots of barley (Hordeum vulgare) plants; and to correlate metal accumulation with anatomical, physiological and morphological changes. Potted plants were exposed to metal treatments of Zn and Cd for 19 and 16 d respectively. Leaves, stems and roots were harvested to identify structural changes and analyze metal accumulation. Barley effectively accumulated Zn (up to 11283 mg kg-1) and Cd (up to 584 mg kg-1) in the shoots. Microscopic structural changes, such as a decrease in intercellular spaces, breakdown of vascular bundles, and shrinkage of palisade and epidermal cells, occurred in leaves, stems and roots of plants treated with high concentrations of Zn. Zinc accumulation also resulted in a significant decrease in water content, fresh weight, dry weight and plant height. Cadmium only caused structural changes in roots at the higher concentrations. Barley plants were able to accumulate significant amounts of Zn and Cd without exhibiting symptoms of phytotoxicity when the metal concentrations were relatively low.