Maria Grazia Corradi

Chromium toxicity in Salvia sclarea—I. Effects of hexavalent chromium on seed germination and seedling development

Abstract Seeds and seedlings of Salvia sclarea L. were treated with different concentrations of hexavalent chromium (as K2Cr2O7). In vitro seed germination was not affected, but when the emergent radicle came into contact with the Cr solution, its growth was inhibited although early shoots and cotyledons developed normally. If the seedlings were transferred to Eppendorf vials so that the roots were completely immersed in the Cr solution, not only root elongation, but also shoot and cotyledon development were inhibited. After 48 hr cotyledons appeared chlorotic, chlorophyll and carotenoid contents were reduced, but chloroplast ultrastructure was normal. The only ultrastructural alteration was a partial detachment of the plasma membrane from the cell wall.

Toxicity of copper and zinc to two strains of Scenedesmus acutus having different sensitivity to chromium

Abstract A Cr-tolerant strain of Scenedesmus acutus (Chlorophyceae) was cultured in the presence of different Cu 2+ or Zn 2+ concentrations to evaluate if it was also tolerant to these metals and consequently maintained unaltered its nutritional value for consumer organisms. The evaluation of tolerance was based on culture growth and recovery rates which were compared with those of the wild type. The evaluation of the nutritional value was based on quantitative determinations of dry mass and carbohydrate and protein content. In the presence of Cu concentrations that were toxic to the wild type, the Cr-tolerant strain grew better and, when transferred to metal-free culture medium, resumed growth more quickly. It also maintained fluorescence and unchanged protein levels. This suggests that the Cr-tolerant strain is also less sensitive to copper. However, no evidence of a lower sensitivity to zinc was found.

Responses of Xanthoria parietina thalli to environmentally relevant concentrations of hexavalent chromium

Thalli of the lichen Xanthoria parietina (L.) Th. Fr. were soaked for either 24 or 48 h in a buffered medium in the presence of environmentally relevant concentrations (4.8 and 9.6 μM) of hexavalent chromium [Cr(VI)]. Treatment effects on the antioxidant status, differential distribution and fate of Cr(VI) among the mycobiont and the photobiont cells, and potential damage to cell ultrastructure in the two bionts, were evaluated. The adopted conditions of low Cr(VI) stress caused: (i) an increase in the level of ascorbic acid and a decrease in that of reduced glutathione, as well as a moderate increase in guaiacol peroxidase activity, only observed after treatment with 9.6 μM Cr(VI); (ii) no changes in malondialdehyde content; (iii) a remarkable Cr accumulation in the mycobiont cytosol and compartmentalisation in the mycobiont vacuoles;(iv) a modest apoplastic Cr immobilisation by the outer part of the cell walls, of both the mycobiont and the photobiont. The response of X.parietina to low concentrations of Cr(VI) appears to be a complex phenomenon, which might reflect maintenance of cellular homeostatic equilibria, rather than specific response pathways.

Is Cr(VI) toxicity to Daphnia magna modified by food availability or algal exudates? The hypothesis of a specific chromium/algae/exudates interaction

The long-term effects of Cr(VI) on life history traits of Daphnia magna Straus were studied in relation to different feeding conditions or to the presence of Scenedesmus acutus exudates, which had proved to reduce chromium toxicity to the alga. In high feeding conditions the concentration of 14 microg Cr(VI)/L had negative effects on survival, growth and fecundity. In low feeding conditions the effects on growth were not evident, but daphnids changed the reproductive strategy normally adopted in case of food shortage and showed a daily rate of newborn production higher than control; however, newborn were of a smaller size and less resistant to starvation. The most relevant effect of Cr was a shortening of the daphnid life span, which was independent of the feeding conditions and occurred also when growth and daily rate of neonate production were not affected. The algal exudates resulted ineffective in reducing Cr toxicity to daphnids, but caused a strong decrease in daphnid fecundity. Further experiments on S. acutus demonstrated that the detoxifying effect observed in the algae might involve a specific Cr/algae/exudates interaction, which occurs only when the algae are previously subjected to a short-time stress by chromium.

The effect of Cr (VI) on different inbred lines ofZea mays

SummaryFour inbred lines ofZea mays (33.16, B 68, N 7B, B 77) were grown in nutrient solution to which K2Cr2O7 was added to give final concentration of 5 mg/l Cr (VI). The most evident differences in metal tolerance were observed between the B 68 and 33.16 line: in fact, even though the level of Cr (VI) was almost the same in the root tissues of both lines after 6 d of treatment, in the B 68 line, Cr induced marked alterations of nuclear structure and a progressive arrest of the cell cycle in G 1. In the 33.16 line, on the contrary, the integrity of the nuclei was well preserved and the progression of the cell cycle was only barely affected.

Identification of S2-T A63: a cDNA fragment corresponding to a gene differentially expressed in a Cr-tolerant strain of the unicellular green alga Scenedesmus acutus.

The gene expression of the wild type (S2-N) and a Cr-tolerant strain (S2-T) of the unicellular green alga Scenedesmus acutus has been compared in order to get more insight on their different chromium sensitivity. The RNA of the two strains was extracted after 4 days of culture in standard medium without chromium and analyzed by means of RNA differential display. The two strains showed differential gene transcription even in the absence of the heavy metal and six putatively differential amplicons were evidenced in the Cr-tolerant strain. Among the isolated amplicons, S2-T A63 was much more pronouncedly transcribed in the tolerant than in the wild type strain and was further characterized. S2-T A63 corresponding gene is present with the same copy number in the wild type and tolerant genomes and corresponds to an mRNA of about 2000 nt. The corresponding transcript is overexpressed in the Cr-tolerant strain after a 4-day culture and is not up-regulated by chromium exposure. The S2-T A63 sequence, obtained up to now, does not show significant homologies with any known gene. However, the analysis of the putative translation product reveals the presence of an interrupted fasciclin domain. This extracellular domain has been found in proteins from mammals, insects, echinoderms, plants, yeast and bacteria and is usually involved in cell adhesion. This finding suggests that the product for the S2-T A63 translation has an extracellular collocation, maybe as surface or secreted protein involved in external chromium detoxification.