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Both natural and polluting metal ions are taken up by marine organisms. For many metal, and metal-containing ions, mechanisms exist which allow these organisms to discriminate between essential and non-essential ions, and reject the latter. In this article we examine the accumulation mechanisms and effects of metal and metal-containing ions on bivalve molluscs and tunicates (sea squirts). Special emphasis is put on the internal or physiological environment of metal ions in marine organisms. A molecular mechanism based on experimental studies is presented to explain the extraordinary accumulation of vanadium in tunicate blood cells called vanadocytes. Vanadium in the form of vanadate anion is transported into the blood cells by passage through anionic channels. Inside the cell it is reduced to cationic V (III) and V (IV) ions which are trapped inside.

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The preceding paper (2) has described some of the changes that occur in the photosynthetic activity of the mutant strain y-2 of the unicellular green alga Chlamydomonas reinhardi accompanying changes in chlorophyll content. These results indicated that photosynthetic activity might be regulated by a mechanism which is related to either a critical chlorophyll content or structural configuration within the chloroplast. In this paper, the postulated regulatory mechanism will be given further consideration by studying the effects of chloramphenicol on chlorophyll synthesis, protein synthesis, and photosynthetic 02 evolution. Electron micrographs of cells of regreening cultures were prepared to determine the relationship between the rate of photosynthesis and the structural configuration of the chloroplast. Materials and MethodsOrganismn and Growth Conditions. Cultures of the y-2 mutant strain of C. reinhardi were grown in the dark as described by Hudock and Levine (2). After 96 hours of growth in the dark, the cells were harvested by centrifugation (2 minutes at 4,080 X g, 00), washed in 0.068 Ai K phosphate buffer at pH 6.8, and resuspended in fresh high salt medium (4) supplemented with 0.20 % sodium acetate (Ac medium) and permitted to regreen. (2). The rate of protein synthesis was measured by a study of the kinetics of incorporation of C14-phenylalanine into trichloroacetic acid (10 % at 90°) insoluble material. Cultures of y-2 were grown in the dark and returned to the light in fresh Ac medium supplemented with C14-phenylalanine. Aliquots were taken at zero time and at hourly intervals during regreening. The cells were collected on mlillipore filters in a Tracerlab Precipitation Apparatus and were washed once with phosphate buffer and, theni, twice with trichloracetic acid. The filter discs wxere pasted to planchets and the incorporated radioactivity 'was determined with a gas flow counter.Photosynthetic 02 evolution was imieasured polarographically using a Clark electrode (3).Enhancement of photosynthesis was calculated as the ratio of the rate of oxygen evolution detected when a culture of y-2 was simultaneously illuminated with lights of equal energies at 650 andl 690 m,u ( Lights of equal energies at 650 and 690 m,u were obtained with Bausch and Lomb interference filters, half-band width of 5 to 7 m,, backed by Corning glass cut off filters.