Physiological and cytological responses of Ocimum sanctum L. and Festuca rubra L.cv. Merlin seedlings to cadmium, lead and zinc

Increasing concentration of the metals reduced the shoot biomass in both species but the reduction was proportionally greater in Ocimum. The three metals markedly reduced root growth of Ocimum and Festuca in the order PbCdZn and CdPbZn, respectively. This metal-induced inhibition of root growth was accompanied by a parallel reduction in the length of the meristem and in increase in meristem width and volume. Increasing metal concentrations caused precocious differentiation of xylem element and root hair in both plants. Cd at 2.5 uM remarkably increased formation of lateral root primordia in Festuca but not in Ocimum, while Zn stimulated their formation in both species. The mitotic index in general was reduced by the metals in both species. In addition, nuclear, cell, and cytoplasmic areas of Festuca at 0 uM were three times larger than that of Ocimum. These characters was less affected by increasing metal concentrations in Festuca. On the other hand, the mean DNA density of Festuca interphase cells in the control treatment was 2.5 fold greater than that of Ocimum. All metals drastically reduced this character in Ocimum but only slightly in Festuca. The effect of Cd, Pb, and Zn in protein density was somewhat varied. In Festuca this character was significantly increased by 10 uM Cd, the same metal that increased the cytoplasmic area in this species. In Ocimum, protein density was markedly reduced by the metals. The roots of Festuca accumulated higher metal concentration than its shoots, while an opposite pattern was observed in Ocimum. The electron probe X-ray microanalysis revealed compartmentalization in Zn in the cytoplasm of Festuca cells. In contrast, Pb was detectable only in the cell walls of Festuca and Ocimum. On the other hand, Cd-containing globules were localized in both regions of the cell. Ocimum was found to be metal-sensitive based on the effects of Dc, Pb and Zn on root growth and various cytological characters. Cellular characters, particularly DNA and protein content, appear to be more sensitive to the metals, and thus can be used as indices of metal tolerance together with root elongation