SummaryAtomic force microscopy (AFM) in aqueous solution was used to investigate native nacre of the marine snail Haliotis laevigata on the microscopic scale and the interaction of purified nacre proteins with calcium carbonate crystals on the nanoscopic scale. These investigations were controlled by scanning electron microscopy (SEM), light microscopy (LM) and biochemical methods. For investigations with AFM and SEM, nacre was cleaved parallel to the aragonite tablets in this biogenic polymer/mineral composite. Multilamellar organic sheets consisting of a core of chitin with layers of proteins attached on both sides lay between the aragonite layers consisting of confluent aragonite tablets. Cleavage appeared to occur between the aragonite tablet layer and the protein layer. AFM images revealed a honeycomb-like structure to the organic material with a diameter of the 'honeycombs' equalling that of the aragonite tablets. The walls of the structures consisted of filaments, which were suggested to be collagen. The flat regions of the honeycomb-like structures exhibited a hole with a diameter of more than 100 nm. When incubated in saturated calcium carbonate solution, aragonite needles with perfect vertical orientation grew on the proteinacous surface. After treatment with proteinase K, no growth of orientated aragonite needles was detected. Direct AFM measurements on dissolving and growing calcite crystals revealed a surface structure with straight steps the number of which decreased with crystal growth. When the purified nacre protein perlucin was added to the growth solution (a super-saturated calcium carbonate solution) new layers were nucleated and the number of steps increased. Anion exchange chromatography of the water-soluble proteins revealed a mixture of about 10 different proteins. When this mixture was dialysed against saturated calcium carbonate solution and sodium chloride, calcium carbonate crystals precipitated together with perlucin leaving the other proteins in the supernatant. Thus perlucin was shown to be a protein able to nucleate calcium carbonate layers on calcite surfaces, and in the presence of sodium chloride, is incorporated as an intracrystalline protein into calcium carbonate crystals.

Introduction Historical Outline Proteins Involved in Biomineralization Biosilicates Calcium Carbonate Biomineralization in Invertebrates The Avian Eggshell Patents Outlooks and Perspectives Acknowledgments

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Background: The phosphorous as one of the agricultural, industrial, and urban pollutants has an important role in the eutrophication phenomenon of the surface waters. Objectives: In this research, the effect of three species of aquatic plants, including Salicornia (Persica), Typha, and Juncus, were investigated and compared with the potential of phosphate uptake. Methods: After preparing the condition and cultivation of plants, they were irrigated by synthetic wastewaters with various phosphate concentrations (7, 18, and 28 mg. L-1) for 28 days. In this test, the adsorbed phosphate was calculated based on mg. g-1 of the plant dry tissues weight using two methods: mass balance and wet digestion methods. Results: The results showed that increase in the pollutants concentration and passing time had a significant effect on the accumulative increase in phosphate uptake in all three plants at 5% level. Thus, the maximum adsorption capacity was obtained on the 28th day in high concentration of pollutant which was measured for Salicornia, Juncus, and Typha as 9.68, 6.37, and 7.68 mg. g-1 of plant dry tissues weight, respectively. Also based on the reported regression coefficients values and the obtained equations, it can be concluded that the variable 'time' was more effective than the 'concentration' variable in terms of adsorbed phosphate by the studied plants. The results of the measurement of phosphate uptake in the terrestrial and aerial parts showed that the maximum uptake was measured as 6.35 and 10.33 mg. g-1 of terrestrial and aerial parts dry weight in Salicornia plant, respectively. Moreover, the results showed that the translocation factor in Salicornia, Juncus, and Typha plants were 1.54, 1.12, and 1.46, respectively, as Salicoenia was maximum and Juncus was minimum. Conclusions: Finally, according to the obtained results from research, all three plants can be known as the hyper-accumulate plants, and they can be used for phytoremediation of phosphate from the agricultural soils according to the high capacity of these plants and prevent these pollutants from entering to the surface waters.

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