Arsenic distribution and speciation in the fronds of the hyperaccumulator Pteris vittata

Pteris vittata is the first plant reported to be a hyperaccumulator of arsenic (As), and little is known about the mechanisms of As hyperaccumulation in this plant. Arsenic distribution at the whole plant (fronds) and cellular level was investigated using chemical analyses and energy dispersive X-ray microanalyses (EDXA). Speciation of As in the fronds was determined using X-ray absorption near edge spectroscopy (XANES) analyses. The majority of As was found in the pinnae (96% of total As). The concentration of As in pinnae decreased from the base to the apex of the fronds. Arsenic concentrations in spores and midribs were much lower than in the pinnae. EDXA analyses revealed that As was compartmentalized mainly in the upper and lower epidermal cells, probably in the vacuoles. The distribution pattern of potassium was similar to As, whereas other elements (Ca, Cl, K, Mg, P and S) were distributed differently. XANES analyses showed that approximately 75% of the As in fronds was present in the As(III) oxidation state and the remaining as As(V)

Further Aspects of the Tris Effect In Beetroot Tissue During Its Lag Phase

The stimulation of K+ and Na+ uptake by tris(hydroxymethyl)arninomethane (Tris) in freshly cut beetroot tissue slices was inhibited by D.glucosamine. This effect could be fully reversed by further addition of D�glucose, and the reversal was specific for D.glucose. Tris caused a marked increase in glucose uptake from a dilute glucose solution (5 X 10-'M). The stimulation of glucose uptake was further enhanced by the presence of N a +.</jats:p

Respiratory Activity And Morphology of Mitochondria Isolated from Whole and Sliced Storage Tissue

Mitochondria isolated from whole tisSue and from freshly sliced and aged disks of beetroot and swedes were tested for their oxidative capacity and their morphology was compared by electron microscopy.</jats:p