Respostas fisiológicas de macroalgas continentais à radiação ultravioleta
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Data
2017-06-23
Autores
Saraiva, Anna Isabel Nassar Bautista [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Nos últimos séculos a história do ser humano no planeta Terra tem sido marcada por intensos impactos ambientais antropogênicos negativos, dentre os quais destaca-se a maior exposição da radiação ultravioleta (UV) na superfície terrestre devido à destruição da Camada de Ozônio ocasionada pela liberação de substâncias tais como os CFCs (clorofluorcarbonetos). A radiação UV tem sido considerada com um dos principais fatores que afetam a distribuição dos organismos fotossintetizantes em ambientes aquáticos, tendo efeitos biológicos diversos como danos no DNA e em moléculas proteicas, alteração dos pigmentos fotossintéticos, modificações nos parâmetros fotossintéticos e crescimento desses organismos. Torna-se evidente, portanto, que as mudanças da incidência de radiação UV na superfície terrestre podem levar a alterações ecofisiológicas nas comunidades algais. Nesse contexto, este trabalho teve como objetivo central analisar as respostas fisiológicas (parâmetros fotossintéticos, concentração de pigmentos fotossintéticos e de substâncias fotoprotetoras) à radiação ultravioleta (UVA e UVAB) em macroalgas continentais (ambientes lóticos e aerofíticos). A idéia geral foi avaliar o nível de resposta (tendência de aumento ou diminuição em maior ou menor grau) na performance em função da exposição à radiação ultravioleta. Duas hipóteses gerais foram formuladas: 1) as respostas das macroalgas consistirão essencialmente de tendência de diminuição de sua performance fisiológica (parâmetros fotossintéticos e concentração de pigmentos) e aumento de substâncias fotoprotetoras sob exposição à radiação UV; 2) o nível de resposta será diferente entre os grupos de algas, sendo que para as algas verdes (tipicamente algas de sol) espera-se que sejam mais tolerantes à radiação UV, enquanto que as rodófitas (tipicamente algas de sombra) tenderão a ser mais sensíveis e as cianobactérias deverão apresentar respostas intermediárias. Hipóteses mais específicas foram formuladas para cada parte do trabalho (capítulos). Experimentos foram realizados em três condições: PAR apenas (400-700nm); PAR + UVA (320-700nm), UVA; PAR + UVA + UVB (280-700nm), UVAB. A tese foi dividida em três capítulos com seus respectivos objetivos e hipóteses: 1) “Respostas fotossintéticas dos estágios gametofítico e esporofítico da macroalga vermelha continental Kumanoa ambigua (Rhodophyta, Batrachospermales) sob radiação UV”. O objetivo foi analisar o desempenho fotossintético dos estágios (gametófito e esporófito, 'Chantransia') de K. ambigua em cultura sob radiação UV. Hipotetizou-se que os estágios do histórico de vida de K. ambigua exibiriam respostas fotossintéticas diferentes à exposição à UV. 2) “Efeitos da radiação UV na fotossíntese e fotoproteção em duas espécies de Cyanobacteria”. O objetivo foi analisar o desempenho fotossintético (parâmetros derivados da fluorescência da clorofila), as concentrações de pigmentos (clorofila a e carotenóides) e a presença de compostos absorventes de UV (aminoácidos tipo-micosporinas - MAAs e scitoneminas) em duas cianobactérias aerofíticas, Leptolyngbya cf. henningsii e Scytonema sp. em resposta à exposição à radiação UV em condições de cultura. Hipotetizou-se que ambas espécies teriam desempenho fotossintético semelhantes em resposta à exposição de radiação UV, mas elas difeririam em termos de concentrações de pigmento e formação de compostos absorvedores de UV. 3) Efeitos da radiação UV na fotossíntese de três espécies de macroalgas lóticas tropicais. O objetivo foi analisar o desempenho fotossintético (parâmetros derivados da fluorescência da clorofila), as concentrações de clorofila a e a presença de compostos absorventes de UV (MAAs) em Cladophora glomerata (Chlorophyta), Spirogyra sp. (Streptophyta) e Sirodotia delicatula (Rhodophyta) coletadas em condições naturais em resposta à exposição de radiação UV em condições laboratoriais. Hipotetizou-se que Spirogyra sp. and C. glomerata, típicas algas adaptadas ao sol, apresentariam performances fotossintéticas semelhantes, com uma leve resposta à exposição à radiação UV e que S. delicatula, caracterizada por ser uma alga adaptada à sombra, exibiria uma resposta distinta com uma maior sensibilidade à exposição à UV. Os principais resultados e conclusões encontrados foram: i) este é o primeiro trabalho que reportou não somente os efeitos da radiação UV sobre o desempenho fotossintético de macroalgas tropicais, bem como descreveu a presença de MAAs em duas espécies de algas vermelhas de água doce; ii) O gametófito de K. ambigua respondeu com um aumento da sua performance fotossintética, além da presença de shinorina (MAA) sob UVA, sugerindo que é menos sensível à radiação UV, particularmente UVA, em comparação com o esporófito em condições de cultura, além de indicar que a radiação UVA, quando moderada, tem efeitos benéficos em alguns organismos aquáticos, tais como o gametófito de K. ambigua; iii) Espécimes coletados em condições naturais de S. delicatula apresentaram dois tipos de MAAs (shinorina e palatina) e foram praticamente insensíveis aos tratamentos com radiação UV, sugerindo que não somente a presença de MAAs é um importante escudo de proteção contra radiação UV, mas também demonstra que apesar de ser uma rodófita tipicamente adaptada à sombra, pode tolerar altas irradiâncias, incluindo-se a radiação UV; iv) C. glomerata apresentou uma diminuição mais acentuada da fotossíntese em UVA em relação a UVAB, apesar de menor teor de clorofila a ter sido observado em UVAB; v) Spirogyra sp. apresentou uma diminuição da performance fotossintética em PAR, sugerindo que a radiação UVAB deve ser importante na indução de fotoreparo e/ou uma fonte energia para fotossíntese; vi) Apesar de serem algas verdes adaptadas ao sol, C. glomerata e Spirogyra sp., apresentaram respostas distintas no desempenho fotossintético e concentrações de clorofila a sob exposição da radiação UV, indicando que elas utilizam estratégias diferentes para lidar com a radiação UV; vii) A ausência de MAAs e de scitoneminas e a pouca variação do desempenho fotossintético indicam que L. cf. henningsii foi insensível à exposição a UV nas condições testadas, e que o aumento do conteúdo de carotenóides sob UVA e UVAB sugerem que estes pigmentos atuaram como escudo eficaz para a radiação UV; viii) Scytonema sp. apresentou um aumento da atividade fotossintética em UVA, sinalizando que também é capaz de usar UVA como fonte de energia para a fotossíntese, e/ou em mecanismos de reparo relacionados ao DNA. Em contrapartida, observou-se uma diminuição do desempenho fotossintético em UVAB, acompanhada de maiores concentrações de MAAs, sugerindo que estes pigmentos não foram suficientemente eficazes para evitar os efeitos negativos da radiação UV. Em síntese, as duas hipóteses iniciais foram refutadas: a primeira, pois nem sempre as algas responderam com tendência à diminuição de sua performance fotossintética ou de produção de substâncias fotoprotetoras à radiação ultravioleta. A segunda, pois as duas espécies de algas verdes, C. glomerata e Spirogyra sp., típicas algas adaptadas ao sol, não mostraram ser mais tolerantes à radiação UV em relação às algas vermelhas, consideradas adaptadas à sombra. Além disso, as respostas foram espécie-específicas, como exemplificado pelas duas espécies de cianobactérias (Leptolyngbya cf. henningsii e Scytonema sp.) e entre os dois estágios de vida de K. ambigua. Estes resultados são muito relevantes por representarem a primeira abordagem para compreensão da adaptação e aclimatação fisiológica de macroalgas tropicais às mudanças globais do clima, notadamente radiação UV.
The history of human on planet Earth has been marked by intense negative anthropogenic environmental impacts, which enhanced the exposure to ultraviolet (UV) radiation the Earth's surface due to depletion of the ozone layer caused by the release of substances, such as, CFCs (chlorofluorocarbons). UV radiation has been considered as one of the main factors that affect the distribution of photosynthetic organisms in aquatic environments, with varied biological effects, such as, damage to DNA and protein molecules, alteration of photosynthetic pigments, changes in photosynthetic parameters and growth of these organisms. Changes in the incidence of UV radiation on the Earth's surface can lead to ecophysiological alterations in algal communities. In this context, the objective of this investigation was to analyze the physiological responses (photosynthetic parameters, concentration of photosynthetic pigments and photoprotective substances) to ultraviolet radiation (UVA and UVAB) in inland macroalgae (lotic and aerophytic habitats). The general idea was to evaluate the level of response (trend of increase or decrease to greater or lesser degree) in photosynthetic performance to ultraviolet exposure. Two general hypotheses were formulated: 1) the responses of macroalgae will essentially consist of a trend to decrease in their physiological performance (photosynthetic parameters and pigment concentration) and increase photoprotective substances under UV exposure; 2) the response level will be different among algal groups, with green algae (typically sun-adapted algae) expected to be more tolerant to UV radiation, whereas red algae (typically shaded-adapted algae) to be more sensitive and the cyanobacteria having intermediate responses. Specific hypotheses were formulated for each part of the work (chapters). Experiments were performed under three conditions: PAR only (400-700nm); PAR + UVA (320-700nm), UVA; PAR + UVA + UVB (280-700nm), UVAB. The thesis was divided into three chapters with their respective objectives and hypotheses: 1) “UV-radiation effects on photosynthesis and photoprotection in gametophytic and sporophytic stages of the freshwater red alga Kumanoa ambigua (Rhodophyta, Batrachospermales)”. The aim was to analyze the photosynthetic performance of gametophytic and sporophytic (‘Chantransia’) stages of Kumanoa ambigua in culture under UV radiation. We hypothesized that the life history stages of K. ambigua would exhibit different photosynthetic responses to UV exposure; 2) “UV-radiation effects on photosynthesis and photoprotection of two species of Cyanobacteria”. The aim was to analyze the photosynthetic performance (parameters derived of chlorophyll fluorescence), pigment concentrations (chlorophyll a and carotenoids) and the presence of UV-absorbing compounds (mycosporine-like aminoacids - MAAs and scytonemin) in two terrestrial cyanobacteria, Leptolyngbya cf. henningsii and Scytonema sp. in response to UV radiation exposure under culture conditions. It was hypothesized that the responses to UV exposure would be similar in both species for photosynthetic performance but they would differ in terms of pigment concentrations and UV-absorbing compounds; 3) “UV-radiation effects on photosynthesis in three species of tropical lotic macroalgae”. The aim was to analyze the photosynthetic performance (parameters derived of chlorophyll fluorescence), chlorophyll a concentrations and the presence of UV-absorbing compounds (mycosporine-like aminoacids - MAAs) in three tropical lotic macroalgae, Cladophora glomerata (Chlorophyta), Spirogyra sp. (Streptophyta) and Sirodotia delicatula (Rhodophyta) collected in natural conditions in response to UV radiation exposure under laboratory conditions. We hypothesized that Spirogyra sp. and C. glomerata, typical sun-adapted algae, would present similar photosynthetic performance with slight responses to UV exposure, while S. delicatula, a typical shaded-adapted alga, would exhibit a distinct strategy with higher sensitivity to UV exposure. The main results and conclusions were: i) this is the first work that reported not only the effects of UV radiation on the photosynthetic performance of tropical macroalgae, but also described the presence of MAAs in two species of freshwater red algae; ii) the increase of photosynthetic performance and the presence of shinorine (MAA) under UVA, suggests that gametophyte of K. ambigua is less sensitive to UV radiation, particularly UV in comparison to the sporophyte under culture conditions. In addition, UVA radiation, in moderate levels, could have beneficial effects in some aquatic organisms, such as the gametophyte of K. ambigua; iii) specimens collected under natural conditions of S. delicatula had two types of MAAs (shinorine and palythine) and were practically insensitive to treatments with UV radiation. These results suggest that not only the presence of MAAs is an important protection shield against UV radiation, but also demonstrates that some Rhodophyta, typically shaded-adapted algae, can tolerate high irradiances, including UV radiation; iv) C. glomerata presented a more pronounced decrease of photosynthesis under UVA in relation to UVAB, although a lower chlorophyll a content has been observed in UVAB; v) Spirogyra sp. had a decrease in photosynthetic performance in PAR, suggesting that UVAB radiation should be important in the induction of photorepair and/or as energy source to photosynthesis; vi) C. glomerata and Spirogyra sp., although considered typical sun-adapted algae, presented distinct responses on photosynthetic performance and chlorophyll concentrations under UV exposure, indicating that they use different strategies to deal with UV radiation; vii) the lack of MAAs and scitonemins and the weak responses of photosynthetic performances indicate that L. cf. henningsii was insensitive to UV exposure under the conditions tested. In addition, the increased carotenoid content under UVA and UVAB suggests that these pigments act as effective shield for UV radiation; viii) Scytonema sp. showed an increase in photosynthetic activity under UVA, signaling that it is also capable to use UVA as a source of energy for photosynthesis, and/or in repair mechanisms of DNA. In contrast, a decrease in the photosynthetic performance in UVAB was observed, although associated to higher concentrations of MAAs, suggested that these pigments were not effective enough to avoid the negative effects of UV radiation. In summary, the two initial hypotheses were rejected: the first, because the algal species not always responded with a trend to decrease of their physiological performances or to produce photoprotective substances under UV radiation. The second, because the two green algae, C. glomerata and Spirogyra sp., typical sun-adapted, were not shown to be more tolerant to UV radiation in comparison to the red algae, considered as shade-adapted. In addition, the responses were species-specific as clearly demonstrated by the two cyanobacterial species (Leptolyngbya cf. henningsii e Scytonema sp.) and between the two stages of K. ambigua. These results are relevant to be a first approach to a understanding of the adaptation and physiological acclimation of tropical macroalgae to global climate changes, notably UV radiation.
The history of human on planet Earth has been marked by intense negative anthropogenic environmental impacts, which enhanced the exposure to ultraviolet (UV) radiation the Earth's surface due to depletion of the ozone layer caused by the release of substances, such as, CFCs (chlorofluorocarbons). UV radiation has been considered as one of the main factors that affect the distribution of photosynthetic organisms in aquatic environments, with varied biological effects, such as, damage to DNA and protein molecules, alteration of photosynthetic pigments, changes in photosynthetic parameters and growth of these organisms. Changes in the incidence of UV radiation on the Earth's surface can lead to ecophysiological alterations in algal communities. In this context, the objective of this investigation was to analyze the physiological responses (photosynthetic parameters, concentration of photosynthetic pigments and photoprotective substances) to ultraviolet radiation (UVA and UVAB) in inland macroalgae (lotic and aerophytic habitats). The general idea was to evaluate the level of response (trend of increase or decrease to greater or lesser degree) in photosynthetic performance to ultraviolet exposure. Two general hypotheses were formulated: 1) the responses of macroalgae will essentially consist of a trend to decrease in their physiological performance (photosynthetic parameters and pigment concentration) and increase photoprotective substances under UV exposure; 2) the response level will be different among algal groups, with green algae (typically sun-adapted algae) expected to be more tolerant to UV radiation, whereas red algae (typically shaded-adapted algae) to be more sensitive and the cyanobacteria having intermediate responses. Specific hypotheses were formulated for each part of the work (chapters). Experiments were performed under three conditions: PAR only (400-700nm); PAR + UVA (320-700nm), UVA; PAR + UVA + UVB (280-700nm), UVAB. The thesis was divided into three chapters with their respective objectives and hypotheses: 1) “UV-radiation effects on photosynthesis and photoprotection in gametophytic and sporophytic stages of the freshwater red alga Kumanoa ambigua (Rhodophyta, Batrachospermales)”. The aim was to analyze the photosynthetic performance of gametophytic and sporophytic (‘Chantransia’) stages of Kumanoa ambigua in culture under UV radiation. We hypothesized that the life history stages of K. ambigua would exhibit different photosynthetic responses to UV exposure; 2) “UV-radiation effects on photosynthesis and photoprotection of two species of Cyanobacteria”. The aim was to analyze the photosynthetic performance (parameters derived of chlorophyll fluorescence), pigment concentrations (chlorophyll a and carotenoids) and the presence of UV-absorbing compounds (mycosporine-like aminoacids - MAAs and scytonemin) in two terrestrial cyanobacteria, Leptolyngbya cf. henningsii and Scytonema sp. in response to UV radiation exposure under culture conditions. It was hypothesized that the responses to UV exposure would be similar in both species for photosynthetic performance but they would differ in terms of pigment concentrations and UV-absorbing compounds; 3) “UV-radiation effects on photosynthesis in three species of tropical lotic macroalgae”. The aim was to analyze the photosynthetic performance (parameters derived of chlorophyll fluorescence), chlorophyll a concentrations and the presence of UV-absorbing compounds (mycosporine-like aminoacids - MAAs) in three tropical lotic macroalgae, Cladophora glomerata (Chlorophyta), Spirogyra sp. (Streptophyta) and Sirodotia delicatula (Rhodophyta) collected in natural conditions in response to UV radiation exposure under laboratory conditions. We hypothesized that Spirogyra sp. and C. glomerata, typical sun-adapted algae, would present similar photosynthetic performance with slight responses to UV exposure, while S. delicatula, a typical shaded-adapted alga, would exhibit a distinct strategy with higher sensitivity to UV exposure. The main results and conclusions were: i) this is the first work that reported not only the effects of UV radiation on the photosynthetic performance of tropical macroalgae, but also described the presence of MAAs in two species of freshwater red algae; ii) the increase of photosynthetic performance and the presence of shinorine (MAA) under UVA, suggests that gametophyte of K. ambigua is less sensitive to UV radiation, particularly UV in comparison to the sporophyte under culture conditions. In addition, UVA radiation, in moderate levels, could have beneficial effects in some aquatic organisms, such as the gametophyte of K. ambigua; iii) specimens collected under natural conditions of S. delicatula had two types of MAAs (shinorine and palythine) and were practically insensitive to treatments with UV radiation. These results suggest that not only the presence of MAAs is an important protection shield against UV radiation, but also demonstrates that some Rhodophyta, typically shaded-adapted algae, can tolerate high irradiances, including UV radiation; iv) C. glomerata presented a more pronounced decrease of photosynthesis under UVA in relation to UVAB, although a lower chlorophyll a content has been observed in UVAB; v) Spirogyra sp. had a decrease in photosynthetic performance in PAR, suggesting that UVAB radiation should be important in the induction of photorepair and/or as energy source to photosynthesis; vi) C. glomerata and Spirogyra sp., although considered typical sun-adapted algae, presented distinct responses on photosynthetic performance and chlorophyll concentrations under UV exposure, indicating that they use different strategies to deal with UV radiation; vii) the lack of MAAs and scitonemins and the weak responses of photosynthetic performances indicate that L. cf. henningsii was insensitive to UV exposure under the conditions tested. In addition, the increased carotenoid content under UVA and UVAB suggests that these pigments act as effective shield for UV radiation; viii) Scytonema sp. showed an increase in photosynthetic activity under UVA, signaling that it is also capable to use UVA as a source of energy for photosynthesis, and/or in repair mechanisms of DNA. In contrast, a decrease in the photosynthetic performance in UVAB was observed, although associated to higher concentrations of MAAs, suggested that these pigments were not effective enough to avoid the negative effects of UV radiation. In summary, the two initial hypotheses were rejected: the first, because the algal species not always responded with a trend to decrease of their physiological performances or to produce photoprotective substances under UV radiation. The second, because the two green algae, C. glomerata and Spirogyra sp., typical sun-adapted, were not shown to be more tolerant to UV radiation in comparison to the red algae, considered as shade-adapted. In addition, the responses were species-specific as clearly demonstrated by the two cyanobacterial species (Leptolyngbya cf. henningsii e Scytonema sp.) and between the two stages of K. ambigua. These results are relevant to be a first approach to a understanding of the adaptation and physiological acclimation of tropical macroalgae to global climate changes, notably UV radiation.
Descrição
Palavras-chave
Chlorophyta, Cyanobacteria, Fluorescência da clorofila, Fotossíntese, Macroalgas tropicais, Micosporinas, Radiação UV, Rhodophyta, Substâncias fotoprotetoras, UVA, UVB, Chlorophyll fluorescence, Mycosporine-like amino, Acids, Photosynthesis, Screening substances, Tropical macroalgae, UV radiation