Calcium Oxalate Deposits in Leaves of Corchorus olitorius as Related to Accumulation of Toxic Metals1

This study was to report and describe the formation of Ca oxalate crystals and to explore whether there is any correlation between their abundant formation and the ability of plant to uptake and accumulate high levels of toxic metals. Soil-grown Corchorus olitorius L. (Tiliaceae) seedlings were further grown in water culture in the presence of Cd, Pb, Cu, or Al (0–10 g/ml) for 20 days. Light and electron microscopic examinations revealed a large number of intracellular prismatic-shaped Ca oxalate crystals in both leaf and callus cells. Crystals were formed in the vacuole, a single large crystal being formed per cell. The crystal-containing cells differed in size and shape from crystal-free cells, they were rich in organelles, membranes, and vesicles and have dense cytoplasm, enlarged nucleus and modified starch-lacking plastids with few grana. These cells look highly active. Corchorus plants treated with Cd, Pb, Cu, and Al accumulated these metals to the levels several times higher than untreated plants. The contents of Pb, Cd, Al, and Cu in leaf tissues of plants grown in the presence of 5 g/ml of these metals were 10, 20, 25, and 40 times higher, respectively, than those in plants grown on media devoid of them. X-ray microanalysis of Ca oxalate crystals in leaves from plants exposed to 5 g/ml Cd, Pb, Al, or Cu indicated the incorporation only of Al into these crystals. Results of this paper suggest a possible contribution for Ca oxalate-crystal formation in sequestering and tolerance of at least some toxic metals.