Localization of selenium deposits in meristematic cells of Allium sativum L. roots treated with selenium salts.

Ultrastructural analysis of garlic roots treated for 24 h with sodium selenate or sodium selenite at the concentrations 80, 160, 320 microM revealed the presence of selenium deposits in meristematic cells. They appeared as small and large granules or aggregates of electron-dense material. Many small granules were localised in plastids but some in mitochondria, endoplasmic reticulum as well as in Golgi apparatus, nucleus and cytoplasm. Sometimes the large granules were seen in cytoplasm but aggregates of electron-dense material only in vacuoles. It seems possible that these deposits represent a non-dissolved form of selenium, i.e. elemental selenium or its complexes with other ions.

The effect of calcium on DNA synthesis in pea (Pisus sativus L.) roots after treatment with heavy metals.

Cortex cells of the meristematic (1 mm) and differentiated (7 mm) zones of Pisus sativus L. roots after 144 h culture in distilled water (control), Ca2+ (10(-3) M) and/or Cd2+, Cr3+, Pb2+ solutions (10(-4) M, each) were subject of the present studies. Reductions in the number of nuclei incorporating 3H thymidine was observed in meristem in the presence of Cd2+ and in differentiated zone in Pb2+ treated roots. Intensity of DNA synthesis diminished after Pb2+ treatment but mostly in Cd2+ treated roots, mainly in meristem. Addition of calcium to the metal solutions caused an increase in the number of nuclei witch uptook the radioactive material in both studied root zones. Positive effect of calcium alone was visible also in the differentiated zone. Presence of calcium in the metal solutions caused a marked increase in 3H thymidine incorporation into nuclear DNA in meristem, although neutralizing calcium effect in this root zone was visible only in roots treated with Cr2+ and Pb2+. In the differentiated zone of roots growing in Cd2+ solution, calcium addition stimulated DNA synthesis but the intensity of this process was lower than in control (water).

Calcium influence on the dry mass content and surface area of nuclei and cytoplasm during differentiation of cortex cells in pea (Pisum sativum L.) roots treated with heavy metals.

The effect of Ca addition to Cd, Cr and Pb solutions on the nuclear and cytoplasmic dry mass content and its concentration as well as on these organelles dimensions were studied in cortex cells of pea roots. Ca alone, at the concentration 10(-8)M brought about a decrease (in comparison to water) in the dry mass content of nuclei and its concentration, but the increment was almost twice in the dry mass content of cytoplasm; however, it has no significant effect on its concentration. Ca ions addition does not change the surface area of nuclei except the 1st and 5th mm segments but causes a doubling of the area occupied by cytoplasm. In response to Ca addition to Cd or Cr solutions a further diminution of nuclear dry mass content takes place. Only in the case of Pb nuclear dry mass increases in the 7th mm or is similar in remaining root segments. The diminution of nuclear dry mass content due to Ca presence in metal solutions is accompanied by a lowering in its concentration, although in the presence of Cd and Pb the diminution is not significant. Ca ions addition results in an increase in cytoplasmic dry mass content. No such regularities were observed in the 1st (Cd, Pb) and 3rd (Cr) root segments. In response to Ca ions the concentration of cytoplasmic dry mass content increased insignificantly in differentiation zone and underwent reducation in the meristematic zone--in the 1st mm (Cr) and 3rd (Cd). After Ca addition to studied metal solutions the decrease in nuclear dimensions was visible only in Cd or Pb treated cells in the 3rd and 7th or in the 1st mm, respectively. An increase in nuclear size occurred only in Cr treated cells in the 7th mm. Enrichment of heavy metals with Ca caused the marked enlargement in cytoplasmic area in differentiation zone but the increment in it in meristematic zone was observed only in Cd (1st, 3rd) and Cr (1st) treated cells.

Heavy metal action on the dry mass content and surface area of nuclei and cytoplasm during differentiation of cortex cells in pea (Pisum sativum L.) roots.

The cortex cells of pea roots (Pisum sativum L.) grown for 144 h in the presence of cadmium, chromium and lead at the concentration 10(-4) M were the object of the present studies. Applied metals reduced dry mass content and concentration of nuclei in meristematic and differentiation zones. Chromium only enhanced nuclear mass concentration in the differentiation zone. The metals also made dry mass content and concentration of cytoplasm reduce, but they diminished mostly the concentration of cytoplasm in the meristematic zone and its dry mass in differentiation zone. Stimulation of cytoplasmic dry mass concentration was visible in the 1st mm (Cr) and 7th mm (Cd). Moreover, chromium caused a marked increase of cytoplasmic dry mass content in the 3rd mm of root. The studied metals reduced nuclear size, calculated as surface area, in the meristematic and differentiation zones. The increment of nuclear dimensions was observed only in the 1-3rd mm (Pb), 3rd (Cr) and 7th mm (Cd). In the presence of the applied metals the surface area of cytoplasm increased only in the 3rd mm and in 5th mm (chromium only). The present observations have shown that the toxicity of studied metals is as follows; Cd greater than Pb greater than Cr (nucleus - dry mass content and concentration, cytoplasmic area), Pb greater than Cd greater than Cr (cytoplasmic dry mass content and concentration and Cd greater than Cr greater than Pb (nuclear dimensions).