Studies on cadmium localization in the water fern Azolla

Uptake of cadmium by the water fern Azolla filiculoides (Lamarck) was characterized, and the localization of the metal in the roots and shoots as well as its effects on some essential elements were studied. Cadmium was accumulated at a rapid rate in Azolla plants within 1 h and then more gradually up to 77 h. Cadmium content was increased in the inner epidermis, cortex and bundle cell walls of the root between 33 and 77 h. This accumulation was characterized by the appearance of small dark grains with high content of cadmium, phosphate and calcium along the epidermal cells. The shoots of Azolla plants grown in the presence of cadmium showed high content of cadmium only in the ventral lobe submerged in the growth medium, suggesting that cadmium was absorbed directly from the medium. The effect of cadmium on essential elements in Azolla was characterized by simultaneous increases in calcium and cadmium content in the root and shoot and by decreases in magnesium content in the root and potassium content in the shoot.