Induction of expression of a 14-3-3 gene in response to copper exposure in the marine alga, Fucus vesiculosus.

The macro-alga Fucus vesiculosus has a broad global and estuarine distribution and exhibits exceptional resistance to toxic metals, the molecular basis of which is poorly understood. To address this issue a cDNA library was constructed from an environmental isolate of F. vesiculosus growing in an area with chronic copper pollution. Characterisation of this library led to the identification of a cDNA encoding a protein known to be synthesised in response to toxicity, a full length 14-3-3 exhibiting a 71% identity to human/mouse epsilon isoform, 70-71% identity to yeast BMH1/2 and 95 and 71% identity to the Ectocarpus siliculosus 14-3-3 isoforms 1 and 2 respectively. Preliminary characterisation of the expression profile of the 14-3-3 indicated concentration- and time-dependent inductions on acute exposure of F. vesiculosus of copper (3-30 µg/l). Higher concentrations of copper (≥150 µg/l) did not elicit significant induction of the 14-3-3 gene compared with the control even though levels of both intracellular copper and the expression of a cytosolic metal chaperone, metallothionein, continued to rise. Analysis of gene expression within environmental isolates demonstrated up-regulation of the 14-3-3 gene associated with the known copper pollution gradient. Here we report for the first time, identification of a gene encoding a putative 14-3-3 protein in a multicellular alga and provide preliminary evidence to link the induction of this 14-3-3 gene to copper exposure in this alga. Interestingly, the threshold exposure profile may be associated with a decrease in the organism's ability to control copper influx so that it perceives copper as a toxic response.

Isomerization and Peroxidizing Phytotoxicity of Thiadiazolidine-thione Compounds.

Eight 5-arylimino-3,4-tetramethylene-1,3,4-thiadiazolidine-2-thiones and eight 4-aryl-1,2- tetramethylene-1,2,4-triazolidine-3,5-dithiones were synthesized and their phytotoxic activities were investigated using sawa millet (Echinochloa utilis), green microalgae (Scenedesmus acutus) and protoporphyrinogen-IX oxidase isolated from etiolated corn (Zea mays) seedlings. 5-Arylimino-3,4-tetramethylene-1,3,4-thiadiazolidine-2-thiones showed strong phytotoxic activities and the same herbicidal mode of action as known for peroxidizing herbicides. 5-Arylimino-3,4-tetramethylene-1,3,4-thiadiazolidine-2-thiones were not or very little converted into 4-aryl-1,2-tetram ethylene-1,2,4-triazolidine-3,5-dithiones either with E. utilis seedlings present for 7 days, with S. acutus cells, or using glutathione 5-transferase (GST) and glutathione (GSH). The phytotoxic activities of 4-aryl-1,2-tetram ethylene-1,2,4-triazolidine- 3,5-dithiones were stronger than those of 5-arylimino-3,4-tetram ethylene-1,3,4-thiadiazolidine- 2-thiones [cf. Sato, Y., et al., Z. Naturforsch. 49c, 49-56 (1994)].