Acute toxicity tests were conducted to establish the response of Selenastrum capricornutum Printz to sublethal concentrations of As, Cr, Cu, Ni and Zn at a broad range ofpH levels. Cultures were incubated for a period of seven days at pH 4 in standard algal assay media containing sublethal concentrations of metals. At this low pH, growth was depressed for all metals tested. The adjustment of pH to higher levels resulted in increased growth when cultures were treated with As, Cu, or Ni and incubated for an additional 7 days. Toxicity was least at the optimum pH range for growth of the alga.The observation that the toxicity of As, Cu, and Ni to S. capricornutum decreases markedly at pH values above 4.0 may be of ecological importance in the control of acid mine pollution. Ifa high percentage of algae show a similar response to decreasing toxicity with increasing pH, it clearly would be of value to adopt measures which control pH as well as the levels of metals present. It was suggested that algae with a broad pH growth range, such as S. capricornutum, could benefit from the addition of highly alkaline materials to waters where certain metals are present.

No abstract

The effectiveness of the inhibitor, canavanine, was evaluated by examining its action in Canavalia ensiformis and Glycine max. Isolated roots were grown in culture tubes containing White's medium plus canavanine or arginine. A differential effect of canavanine on the incorporation of precursors of DNA, RNA, and protein was found, which is assumed to be related to the ability of the plant to utilize canavanine in reactions typically involving arginine. Canavanine was not found to affect DNA, RNA, or protein synthesis in Canavalia ensiformis, a plant in which this amino acid is synthesized naturally. In the canavanine sensitive species, Glycine max, of the same subfamily Papilionoideae, canavanine was observed to inhibit strongly DNA, RNA, and protein synthesis. A primary inhibition of the RNA synthesizing system is suggested. The data indicate the canavanine inhibitions are more complex than a simple competition with arginine in protein synthesis.

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No abstract