Effect of Phytoaccumulation of Arsenic and Chromium on Structural and Ultrastructural Changes of Brake Fern (Pteris vittata)

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.