Response of cultured tomato cells subjected to excess zinc: role of cell wall in zinc compartmentation

The aim of this preliminary study was to evaluate the role of the cell wall in Zn accumulation and tolerance by tomato suspension-cultured cells. Growth parameters, Zn distribution and accumulation by tomato cells were determined in function of zinc concentration. A particular attention was paid to the variations of the total cell wall material (cell wall carbohydrates, proteins, and exopolymers) in relation to extracellular levels of Zn. Cells treated with 0.5-5 mM Zn showed typical symptoms of heavy metal toxicity as testified by various growth parameters. Fresh and dry weights as well as total cell volume per vial decreased with increasing Zn concentration in the culture medium. Concurrently, the cell wall biomass increased, as well as the Zn amount retained by cell wall polymers. Cell wall appeared to assume important roles in Zn fixation and could therefore limit Zn influx into the cell. Our results also suggested that zinc fixation by cell wall was not only due to an increase in cell wall biomass but also to an improvement of its binding capacity.