Photosynthetic performance,oxidative damage and antioxidants in <Emphasis Type="Italic">Cylindrotheca closterium</Emphasis> in response to high irradiance,UVB radiation and salinity |
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Authors: | F Roncarati J W Rijstenbil R Pistocchi |
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Institution: | (1) Centro Interdipartimentale per la Ricerca sulle Scienze Ambientali, Alma Mater Studiorum Università di Bologna, Via S. Alberto 163, 48100 Ravenna, Italy;(2) Centre for Estuarine and Marine Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Korringaweg 7, 4401 NT Yerseke, The Netherlands;(3) Present address: AE3 Consultancy, Fuchsialaan 8, 4401 HV Yerseke, The Netherlands |
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Abstract: | Cylindrotheca closterium is a common marine diatom living in intertidal environments where it can be present both in the water column and on sediments,
depending on the tidal regime. In the present work this diatom was employed to investigate the responses to desiccation and
to increase in PAR and UVB intensity, as occurs during emersion. Under these circumstances, the production of active oxygen
species (AOS) may be enhanced resulting in an oxidative stress. Stress responses in this species were measured by exposing
it to normal (30) and double salinity (60), supplying light of low or high intensity for 12 h, in the latter case either without
or with moderate dose rates of UVB. Pulse amplitude modulated fluorometry was used to measure Chl a autofluorescence (F
0), an index of photosynthetic efficiency of PSII (F
v/F
m) and the relative electron transfer rate (rETR). The oxidative stress was evaluated by analysing GSH pools and SOD activity.
It was observed that at double salinity and under low light, intracellular pools of reduced glutathione (GSH) were higher
than under the two conditions of high light without and with UVB at both salinities. The antioxidative defence activity of
superoxide dismutase (SOD) was far higher under hypersaline conditions. The oxidative damage was evaluated as protein and
lipid damage. The results showed that it expressed itself mainly through protein peroxidation: at normal salinity relative
protein carbonyl content was (a) twice as high as in cells grown at double salinity, and (b) three times as high under UVB.
Total unsaturated lipid contents doubled under hypersalinity conditions. The lipid peroxidation marker malondialdehyde showed
the strongest response to low light and UVB at salinity value of 60. Lipid peroxide content was significantly higher at salinity
of 60 compared to normal salinity and was the highest under low light and high light with UVB. The simulated emersion condition
of the diatom seems to lead to the establishment of a balance between damage and repair, expressed mainly as (a) oxidative
protein damage at normal salinity, in particular due to UV radiation, (b) sufficient protection by SOD activity mainly under
hypersaline conditions. |
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