Effects of lead on Cladophora rupestris: localization, subcellular distribution, and cell ultrastructure

This study investigated the effects of various Pb concentrations and different exposure times on the Cladophora rupestris, the subcellular distributions, and ultrastructures were investigated using air acetylene flame atomic absorption spectrometry, transmission electron microscopy (TEM), and energy dispersive X-ray (EDX). Results showed that Pb was mainly distributed in the cell wall, followed by organelle fractions under low concentration of Pb (<= 5.0 mg/L), whereas its relative content in soluble fraction was higher than that in organelle when its concentration exceeded 5.0 mg/L. With the increase in exposure time, the proportion of Pb in the cell wall decreased by 13.14%, and the organelle and soluble fractions increased significantly. TEM and EDX revealed that C. rupestris could accumulate Pb intracellularly and extracellularly. The ultrastructure of C. rupestris changed markedly under 7.5 mg/L of Pb stress, the cells underwent plasmolysis, and some chloroplasts were swollen into a sphere containing starch granules or destroyed into fragmented structure. This study provided an evidence that C. rupestris uses cell wall sequestration and vacuolar compartmentalization to reduce the migration of Pb.