engleski

Cyclobutane pyrimidine dimers in marine phytoplankton DNA as a consequence of ultraviolet irradiation

Increased level of UV was evidenced recently. Because of its natural exposure to sunlight phytoplankton has become an important object for determination of UV effects on living species. The aim of our study was to investigate the effect of UV irradiation on cell genome and DNA in marine phytoplankton I. galbana . Phytoplankton monocultures were irradiated under laboratory conditions or were exposed to sunlight. The effect of UV was measured by determination of cyclobutane pyrimidine dimers(CPDs) that represent an exclusive and specific DNA damage induced by UV. CPDs are formed in DNA by covalent interaction of two adjacent pyrimidines in the same polynucleotide chain resulting in lesion that can interfere transcription and DNA replication and could finally endanger cells life cycle. For specific detection of CPDs the method of alkaline filter elution was adapted using T4 endonuclease V tratment of DNA. This enzyme introduces single strand breaks in the DNA at the CPD sites. The UV dose response was detected in two different cultures growing under 24/0 and 16/8 light/dark regime. Both cultures were exposed to several doses of artificial UV light, however, culture with 16/8 light regime showed higher sensitivity. Smaller amounts of UV absorbing and photosynthetic pigments were measured in respect to the 24/0 culture. Thus,pigments act as cell protecting elements and as UV target as well. For the same UV doses, removal of CPDs ( up to 24 hours of repair) was investigated. Depending on the dose , in one day 80-90% of CPD was repaired, but during the repair time phytoplankton cells did not duplicate and the normal cell dividing and culture growth was altered. Phytoplankton cultures were exposed to the sunlight in Rovinj at noon in midsummer for 3 hours. The amount of CPDs decreased between 1 hour and 3 hours suggesting that sunlight exposure induces not only DNA damage but also repair; both DNA damaging and repair are simultaneous. At present knowledge the potential damage of UV to phytoplankton populations can only be roughly estimated but our results showed that the consequences of increasing UV irradiation through weakening phytoplankton population could affect food chains in marine community.

pyrimidine dimers; DNA damage; UV irradiation

nije evidentirano