Many abiotic and biotic factors can influence the partitioning equilibrium of heavy metals, thus influencing metal impact on aquatic environments. Unicellular algal species release soluble organic substances able to complex metals. In our laboratory a Cr-tolerant strain was selected and isolated from a wild type strain of Scenedesmus acutus. The exudates released by the two strains counteracted the growth inhibition caused by Cr(VI) and the exudates of the Cr-tolerant strain were more effective. On the contrary, the exudates did not reduce chromium toxicity to the cladoceran Daphnia magna. The reduction of chromium effect on algae seems the consequence of an algae-specific interaction among Cr(VI), exudates and algal cells. Chromium uptake resulted to be energy-dependent since bioaccumulation rate in subdued light condition was lower than at high light intensity. The effect of Cr(VI) on algae changed depending on metabolism of the cells and in particular it seemed to be related to the bioaccumulation rate. Tolerance in the selected strain could not be ascribed to a lower uptake of chromium. The difference in sensitivity to chromium between the two strains was exploited to evaluate if tolerance acquired by algae could have consequences for Daphnia. After treatment with Cr(VI), the two strains of S. acutus were used as food source for D. magna. The results indicate that chromium is accumulated by algae in a form not available for daphnids and that Cr tolerance acquired by the algae can be of some advantage to the consumer organism.
Abstract Regenerated plants of Lycopersicon esculentum var. Alice were obtained from in vitro culture of cotyledons. Some of them showed different grades of leaf variegation, but a few plants were completely white. Here the chloroplasts of the mesophyll cells had completely failed to differentiate and contained no thylakoids. On the contrary those of the epidermal and stomata guard cells were normally developed. This suggests that in the albino plants a mutation had occurred in the submarginal initial cell responsible for mesophyll formation.
AbstractIn order to conserve and multiply the aquatic fern Marsilea quadrifolia L., in a long-term in vitro procedure, the effects of different cytokinins, i.e., 6-benzylaminopurine, zeatine riboside, and N6-(2-isopentenyl)adenine, were investigated, varying their concentration and period of supplementation. No clear stimulatory effect on the de novo nodes produced per explant was detected when compared with hormone-free (HF) condition. On the contrary, the rhizome explant micropropagation was inhibited, the inhibition decreasing with the decreasing strength of cytokinins, though without reaching any significant enhancement. Since, as a consequence of the tissue culture procedure, the occurrence of somaclonal variation may introduce genomic alterations, genetic stability was assessed by random amplified polymorphic DNA (RAPD) analysis by comparing eight randomly selected micropropagated plants derived from repeated subcultures, with donor plant. Eighteen different primers generated 189 bands ranging from 100 to 3250 bp, and the same banding profiles were exhibited. No genomic alterations were evidenced in any of the micropropagated plants. Well-developed micropropagated plants were also successfully acclimatized under greenhouse condition. These positive results suggest that the in vitro HF micropropagation could be useful in the development of ex situ conservation programs of M. quadrifolia, even in order to possibly reintroduce the plants in their natural environment.Keywords:: Conservationcytokininsgenetic stabilityin vitro micropropagationnodal explants AcknowledgementsThe authors are grateful to Dr Sira Pizzoni and Dr Francesca Sandrini for their contribution to the experimental procedures. The authors thank Mrs Simona Lari for the English revision of the manuscript.
