Arsenic is toxic to most forms of life, and occurs naturally in soil and ground water in many regions of the world. Chronic exposure to arsenic has been linked to lung, bladder and kidney cancer, and thus there are strict limits on allowable levels or arsenic in drinking water. Chemically similar to phosphorus, arsenic forms arsenate (AsO43-), which closely resembles phosphate (PO43-). Arsenate interferes with many phosphate-requiring metabolic reactions, including synthesis of adenosine triphosphate (ATP), a ubiquitous and essential source of cellular energy. Thus, exposure to even low levels of arsenic can be extremely toxic.
In well-aerated soils, arsenic exists mainly as arsenate, which is taken up by plant roots using a phosphate transporter protein. Plant tissues rapidly reduce arsenate to arsenite (AsO33-), which is transported to the aerial portions of the plant. In aquatic environments or water-logged soils, arsenic exists primarily as arsenite. Whereas rice grains can accumulate up to 60 μg/g arsenic, the fern Pteris vittata (see figure) can hyperaccumulate arsenic to levels 1000-fold greater than this. A team of researchers led by David Salt and Jo Ann Banks of Purdue University have recently isolated a gene encoding an arsenite transporter protein. This transporter allows these ferns to sequester arsenic in the vacuole, a cellular storage compartment isolated from the cytoplasm by the vacuolar membrane.
In research published this week in The Plant Cell and performed primarily by graduate student Emily Indriolo (now a researcher at the University of Toronto), these scientists describe how they used an arsenic-sensitive strain of yeast to isolate and characterize a gene encoding the P. vittata arsenite transporter. Yeast cells are arsenic-resistant because their plasma membrane contains an arsenite effluxer protein that is encoded by the <
|Contact: Gregory Bertoni|
American Society of Plant Biologists