When adapted to high zinc concentrations the periphytic green alga Stigeoclonium tenue produces high amounts of novel phytochelatin-related peptides.
Two ecotypes of the green alga Stigeoclonium tenue Kütz. coming from polluted or unpolluted freshwaters and showing various Zn-tolerance were compared for their production of non-proteinaceous thiols in response to Zn. In short-term (17 h) exposures to 15 microM Zn they did not reveal any significant difference in levels of glutathione, phytochelatins and some unknown thiols. However, after prolonged metal exposure (48 h) the Zn-tolerant S. tenue (T) isolated from Zn-polluted mining water, produced at the expense of GSH besides phytochelatins (PC(2)-PC(4)) much higher amounts of novel, phytochelatin-related peptides. After a 6-week exposure to 30 microM Zn, phytochelatins (approximately 6 micromol SH per g D.W.) and the novel thiol peptides (approximately 31 micromol SH per g D.W.), only in the surviving Zn-tolerant alga, were produced. HPLC analysis suggested that the novel peptides (P1-P3) differ from each other by one gammaGlu-Cys unit. ESI/MS analysis of the purified, most abundant peptides P2 and P3, of m/z values 643 and 875, respectively, suggested that they contain one cysteine residue more than PC(2) and PC(3). A 22-fold higher concentration of these peptides in Zn-tolerant S. tenue (T) than in Zn-sensitive S. tenue (S) was also observed in response to Pb exposure. Biosynthesis of the large amounts of the novel thiol peptides, which contain more SH-groups than phytochelatins, detected in the Zn-tolerant organism after long Zn exposure, and lack of such a response in the Zn-sensitive ecotype S. tenue (S), isolated from unpolluted water, suggest that they are essential in the adaptation of S. tenue (T) to increased heavy metal concentrations.
Pawlik-Skowrońska
Barbara
B
Department of Ecotoxicology and Ecology of Microorganisms, Institute of Ecology Niecała 18/3, 20-080, Lublin, Poland. pawlik@golem.umcs.lulin.pl
D000222:Adaptation, Physiological; D000460:Chlorophyta / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid; D004781:Environmental Exposure; D005978:Glutathione; D008667:Metalloproteins / Q000819:agonists / Q000096:biosynthesis*; D008906:Mining; D010452:Peptide Biosynthesis; D054811:Phytochelatins; D014873:Water Pollutants / Q000009:adverse effects* / Q000494:pharmacology*; D015032:Zinc / Q000009:adverse effects* / Q000494:pharmacology*
D008667:Metalloproteins; D014873:Water Pollutants; D054811:Phytochelatins; D005978:Glutathione; D015032:Zinc