Evidence of vacuolar compartmentalization of arsenic in the hyperaccumulator Pteris vittata

Pteris vittata can hyperaccumulate arsenic (As) to >1% of its dry weight without showing any signs of toxicity, indicating the existence of effective plant-internal detoxification mechanisms. Although vacuolar compartmentalization is known to play an important role in heavy metal detoxification and tolerance, direct evidence of arsenic compartmentalization in this hyperaccumulator was lacking. Here we report the subcellular localization of As in the callus of P vittata. The callus induced from gametophytes of P vittata exposed to 0.2 mmol/L arsenate for 20 days were examined by directly isolating cell walls, protoplasts and vacuoles, and determining arsenic concentrations. Of the total As in the callus, about 94% was in the protoplast, and of that, 91% was present in the vacuoles, indicating that vacuoles are a major storage site for As in P vittata. In addition, the changes in the chemical components of vacuoles were analyzed by Fourier transform infrared spectroscopy (FTIR).