Comparative study of defense strategies against UV-induced damage in an Antarctic diatom (Thalassiosira sp.) and a Sub-Antarctic phytoflagellate (Asteromonas sp.)

HERNANDO, M., G. MALANGA, S. PUNTARULO AND G.A. FERREYRA

Reports on Polar and Marine Research

Año: 2008 vol. 571 p. 243 - 253

During the past decades, spring-time stratospheric ozone depletion over the Antarctic and the Southern Ocean has resulted in enhanced levels of ultraviolet- B (UVB, 280-315 nm) radiation reaching the earth´s surface. One of the main difficulties to evaluate the potential ecological impact on natural phytoplankton of increased in UVB is that UV sensitivity is species specific (Hernando & San Román 1999; Hernando 2006). UVR induced effects on phytoplankton include the reduction of growth and photosynthetic rates (Villafañe et al., 2003). Some studies have demonstrated that the of ultraviolet-A (UVA, 315 – 400 nm) were generally higher than that of UVB (Villafañe et al., 2003). This is generally attributed to the fact that the amount of UVA energy that reaches the Earth’s surface is much higher than that in the UVBR region (Villafañe et al., 1999). Several biological effects of UVB involve endogenous photosensitization and formation of reactive oxygen species (Martin & Burch 1990). There are a variety of sensitizers within cells which absorb UVB. Interaction between excited sensitizers and triplet oxygen produces active oxygen intermediates consisting of singlet oxygen (1O2), superoxide radical (O2 -), hydroxyl radical (.OH) and hydrogen peroxide (H2O2) (Ichiki et al. 1994). One of the possible mechanisms that could counteract the damage generated by UVB radiation induced oxidative stress is the synthesis of both enzymatic and non-enzymatic antioxidants (Davidson 1998; Niyogi 1999). Moreover UVB can destroy the natural lipid soluble antioxidants and promote the formation of lipid peroxidation products (Estévez et al. 2001). The non-enzymatic antioxidants are generally small molecules, such as ascorbate and glutathione acting in the aqueous phase, whereas the lipophilic antioxidants (such as ��-tocopherol and ��-carotene) are active in the membrane environment. Especially ��-tocopherol is known for its protective effect against lipid peroxidation of biological membranes via peroxyl and alcoxyl radicals scavenging. In contrast, the main function of ��-carotene is photoreceptive, because it acts as a pigment antenna in the photosynthesis process. Another strategy to minimize the effects of UVR (ultraviolet radiation) is through the presence of UV screening compounds. The most studied compounds are those collectively named mycosporine like amino acids (MAAs), which are found in many marine and freshwater algae (Karentz et al. 1991; Banaszak 2003). MAAs have been proved to be an effective protection mechanism (Neale et al. 1998). The synthesis of MAAs was found in some natural populations and cultures of phytoplankton (Hernando et al. 2002; Zudaire & Roy 2001). How ever, the synthesis of MAA´s is not a general response, and several species do not show an increase of MAAs content even after several weeks of exposure to UVR (Villafañe et al. 2000). The aim of this work was to study immediate effects on growth rate and photoprotection parameters in response to UVB and UVA on a Sub-Antarctic phytoflagellate (Asteromonas sp.) and an Antarctic diatom (Thalassiosira sp.) under culture conditions. ever, the synthesis of MAA´s is not a general response, and several species do not show an increase of MAAs content even after several weeks of exposure to UVR (Villafañe et al. 2000). The aim of this work was to study immediate effects on growth rate and photoprotection parameters in response to UVB and UVA on a Sub-Antarctic phytoflagellate (Asteromonas sp.) and an Antarctic diatom (Thalassiosira sp.) under culture conditions. culture conditions.1O2), superoxide radical (O2 -), hydroxyl radical (.OH) and hydrogen peroxide (H2O2) (Ichiki et al. 1994). One of the possible mechanisms that could counteract the damage generated by UVB radiation induced oxidative stress is the synthesis of both enzymatic and non-enzymatic antioxidants (Davidson 1998; Niyogi 1999). Moreover UVB can destroy the natural lipid soluble antioxidants and promote the formation of lipid peroxidation products (Estévez et al. 2001). The non-enzymatic antioxidants are generally small molecules, such as ascorbate and glutathione acting in the aqueous phase, whereas the lipophilic antioxidants (such as ��-tocopherol and ��-carotene) are active in the membrane environment. Especially ��-tocopherol is known for its protective effect against lipid peroxidation of biological membranes via peroxyl and alcoxyl radicals scavenging. In contrast, the main function of ��-carotene is photoreceptive, because it acts as a pigment antenna in the photosynthesis process. Another strategy to minimize the effects of UVR (ultraviolet radiation) is through the presence of UV screening compounds. The most studied compounds are those collectively named mycosporine like amino acids (MAAs), which are found in many marine and freshwater algae (Karentz et al. 1991; Banaszak 2003). MAAs have been proved to be an effective protection mechanism (Neale et al. 1998). The synthesis of MAAs was found in some natural populations and cultures of phytoplankton (Hernando et al. 2002; Zudaire & Roy 2001). How ever, the synthesis of MAA´s is not a general response, and several species do not show an increase of MAAs content even after several weeks of exposure to UVR (Villafañe et al. 2000). The aim of this work was to study immediate effects on growth rate and photoprotection parameters in response to UVB and UVA on a Sub-Antarctic phytoflagellate (Asteromonas sp.) and an Antarctic diatom (Thalassiosira sp.) under culture conditions. ever, the synthesis of MAA´s is not a general response, and several species do not show an increase of MAAs content even after several weeks of exposure to UVR (Villafañe et al. 2000). The aim of this work was to study immediate effects on growth rate and photoprotection parameters in response to UVB and UVA on a Sub-Antarctic phytoflagellate (Asteromonas sp.) and an Antarctic diatom (Thalassiosira sp.) under culture conditions. culture conditions.), hydroxyl radical (.OH) and hydrogen peroxide (H2O2) (Ichiki et al. 1994). One of the possible mechanisms that could counteract the damage generated by UVB radiation induced oxidative stress is the synthesis of both enzymatic and non-enzymatic antioxidants (Davidson 1998; Niyogi 1999). Moreover UVB can destroy the natural lipid soluble antioxidants and promote the formation of lipid peroxidation products (Estévez et al. 2001). The non-enzymatic antioxidants are generally small molecules, such as ascorbate and glutathione acting in the aqueous phase, whereas the lipophilic antioxidants (such as ��-tocopherol and ��-carotene) are active in the membrane environment. Especially ��-tocopherol is known for its protective effect against lipid peroxidation of biological membranes via peroxyl and alcoxyl radicals scavenging. In contrast, the main function of ��-carotene is photoreceptive, because it acts as a pigment antenna in the photosynthesis process. Another strategy to minimize the effects of UVR (ultraviolet radiation) is through the presence of UV screening compounds. The most studied compounds are those collectively named mycosporine like amino acids (MAAs), which are found in many marine and freshwater algae (Karentz et al. 1991; Banaszak 2003). MAAs have been proved to be an effective protection mechanism (Neale et al. 1998). The synthesis of MAAs was found in some natural populations and cultures of phytoplankton (Hernando et al. 2002; Zudaire & Roy 2001). How ever, the synthesis of MAA´s is not a general response, and several species do not show an increase of MAAs content even after several weeks of exposure to UVR (Villafañe et al. 2000). The aim of this work was to study immediate effects on growth rate and photoprotection parameters in response to UVB and UVA on a Sub-Antarctic phytoflagellate (Asteromonas sp.) and an Antarctic diatom (Thalassiosira sp.) under culture conditions. ever, the synthesis of MAA´s is not a general response, and several species do not show an increase of MAAs content even after several weeks of exposure to UVR (Villafañe et al. 2000). The aim of this work was to study immediate effects on growth rate and photoprotection parameters in response to UVB and UVA on a Sub-Antarctic phytoflagellate (Asteromonas sp.) and an Antarctic diatom (Thalassiosira sp.) under culture conditions. culture conditions.2O2) (Ichiki et al. 1994). One of the possible mechanisms that could counteract the damage generated by UVB radiation induced oxidative stress is the synthesis of both enzymatic and non-enzymatic antioxidants (Davidson 1998; Niyogi 1999). Moreover UVB can destroy the natural lipid soluble antioxidants and promote the formation of lipid peroxidation products (Estévez et al. 2001). The non-enzymatic antioxidants are generally small molecules, such as ascorbate and glutathione acting in the aqueous phase, whereas the lipophilic antioxidants (such as ��-tocopherol and ��-carotene) are active in the membrane environment. Especially ��-tocopherol is known for its protective effect against lipid peroxidation of biological membranes via peroxyl and alcoxyl radicals scavenging. In contrast, the main function of ��-carotene is photoreceptive, because it acts as a pigment antenna in the photosynthesis process. Another strategy to minimize the effects of UVR (ultraviolet radiation) is through the presence of UV screening compounds. The most studied compounds are those collectively named mycosporine like amino acids (MAAs), which are found in many marine and freshwater algae (Karentz et al. 1991; Banaszak 2003). MAAs have been proved to be an effective protection mechanism (Neale et al. 1998). The synthesis of MAAs was found in some natural populations and cultures of phytoplankton (Hernando et al. 2002; Zudaire & Roy 2001). How ever, the synthesis of MAA´s is not a general response, and several species do not show an increase of MAAs content even after several weeks of exposure to UVR (Villafañe et al. 2000). The aim of this work was to study immediate effects on growth rate and photoprotection parameters in response to UVB and UVA on a Sub-Antarctic phytoflagellate (Asteromonas sp.) and an Antarctic diatom (Thalassiosira sp.) under culture conditions. ever, the synthesis of MAA´s is not a general response, and several species do not show an increase of MAAs content even after several weeks of exposure to UVR (Villafañe et al. 2000). The aim of this work was to study immediate effects on growth rate and photoprotection parameters in response to UVB and UVA on a Sub-Antarctic phytoflagellate (Asteromonas sp.) and an Antarctic diatom (Thalassiosira sp.) under culture conditions. culture conditions.��-tocopherol and ��-carotene) are active in the membrane environment. Especially ��-tocopherol is known for its protective effect against lipid peroxidation of biological membranes via peroxyl and alcoxyl radicals scavenging. In contrast, the main function of ��-carotene is photoreceptive, because it acts as a pigment antenna in the photosynthesis process. Another strategy to minimize the effects of UVR (ultraviolet radiation) is through the presence of UV screening compounds. The most studied compounds are those collectively named mycosporine like amino acids (MAAs), which are found in many marine and freshwater algae (Karentz et al. 1991; Banaszak 2003). MAAs have been proved to be an effective protection mechanism (Neale et al. 1998). The synthesis of MAAs was found in some natural populations and cultures of phytoplankton (Hernando et al. 2002; Zudaire & Roy 2001). How ever, the synthesis of MAA´s is not a general response, and several species do not show an increase of MAAs content even after several weeks of exposure to UVR (Villafañe et al. 2000). The aim of this work was to study immediate effects on growth rate and photoprotection parameters in response to UVB and UVA on a Sub-Antarctic phytoflagellate (Asteromonas sp.) and an Antarctic diatom (Thalassiosira sp.) under culture conditions. ever, the synthesis of MAA´s is not a general response, and several species do not show an increase of MAAs content even after several weeks of exposure to UVR (Villafañe et al. 2000). The aim of this work was to study immediate effects on growth rate and photoprotection parameters in response to UVB and UVA on a Sub-Antarctic phytoflagellate (Asteromonas sp.) and an Antarctic diatom (Thalassiosira sp.) under culture conditions. culture conditions.��-tocopherol is known for its protective effect against lipid peroxidation of biological membranes via peroxyl and alcoxyl radicals scavenging. In contrast, the main function of ��-carotene is photoreceptive, because it acts as a pigment antenna in the photosynthesis process. Another strategy to minimize the effects of UVR (ultraviolet radiation) is through the presence of UV screening compounds. The most studied compounds are those collectively named mycosporine like amino acids (MAAs), which are found in many marine and freshwater algae (Karentz et al. 1991; Banaszak 2003). MAAs have been proved to be an effective protection mechanism (Neale et al. 1998). The synthesis of MAAs was found in some natural populations and cultures of phytoplankton (Hernando et al. 2002; Zudaire & Roy 2001). How ever, the synthesis of MAA´s is not a general response, and several species do not show an increase of MAAs content even after several weeks of exposure to UVR (Villafañe et al. 2000). The aim of this work was to study immediate effects on growth rate and photoprotection parameters in response to UVB and UVA on a Sub-Antarctic phytoflagellate (Asteromonas sp.) and an Antarctic diatom (Thalassiosira sp.) under culture conditions. ever, the synthesis of MAA´s is not a general response, and several species do not show an increase of MAAs content even after several weeks of exposure to UVR (Villafañe et al. 2000). The aim of this work was to study immediate effects on growth rate and photoprotection parameters in response to UVB and UVA on a Sub-Antarctic phytoflagellate (Asteromonas sp.) and an Antarctic diatom (Thalassiosira sp.) under culture conditions. culture conditions.��-carotene is photoreceptive, because it acts as a pigment antenna in the photosynthesis process. Another strategy to minimize the effects of UVR (ultraviolet radiation) is through the presence of UV screening compounds. The most studied compounds are those collectively named mycosporine like amino acids (MAAs), which are found in many marine and freshwater algae (Karentz et al. 1991; Banaszak 2003). MAAs have been proved to be an effective protection mechanism (Neale et al. 1998). The synthesis of MAAs was found in some natural populations and cultures of phytoplankton (Hernando et al. 2002; Zudaire & Roy 2001). How ever, the synthesis of MAA´s is not a general response, and several species do not show an increase of MAAs content even after several weeks of exposure to UVR (Villafañe et al. 2000). The aim of this work was to study immediate effects on growth rate and photoprotection parameters in response to UVB and UVA on a Sub-Antarctic phytoflagellate (Asteromonas sp.) and an Antarctic diatom (Thalassiosira sp.) under culture conditions. ever, the synthesis of MAA´s is not a general response, and several species do not show an increase of MAAs content even after several weeks of exposure to UVR (Villafañe et al. 2000). The aim of this work was to study immediate effects on growth rate and photoprotection parameters in response to UVB and UVA on a Sub-Antarctic phytoflagellate (Asteromonas sp.) and an Antarctic diatom (Thalassiosira sp.) under culture conditions. culture conditions.