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Browsing FCT4-Vários by Author "Barrote, Isabel"
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- Compared photophysiology of native seagrasses with an invasive macroalga in Sydney Harbour, AustraliaPublication . Silva, João; Runcie, J. W.; Barrote, Isabel; Costa, Monya; Santos, RuiThe comparative photophysiology of the seagrasses Zostera capricorni and Halophila ovalis and the invasive macroalgae Caulerpa taxifolia was investigated in a shallow mixed meadow at Chowder Bay (Sydney, Australia), where the three species coexist. This study was developed under the auspices of the COST Action “Seagrasses: from genes to ecosystems”, targeting one of its objectives, the development of innovative devices for the continuous measurement of seagrass photosynthesis. Automated multi-channel chlorophyll fluorometers were deployed for 24-hour periods to examine and compare the changes in the photosynthetic efficiency and energy quenching mechanisms of the 3 species. Tissue samples were collected at predawn and noon, frozen and analysed by HPLC for detailed pigment analysis. The invasive C. taxifolia showed generally higher photosynthetic efficiency than both Z. capricorni and H. ovalis. Both seagrass species showed down-regulation of photosynthesis at noon, evidenced by the low quantum yield and the significant reduction of the antennae pigments between pre-dawn and noon. In contrast, C. taxifolia showed no reduction in antennae pigments or total photosynthetic pigments along the day. While both seagrasses showed 3- to 7-fold increases in the epoxidation state of xanthophyll cycle pigments between pre-dawn and noon, in C. taxifolia there was no significant change. Our results show that C. taxifolia is better adapted to high light conditions than Z. capricorni and H. ovalis, which means that, from the photophysiological point of view, this invasive macroalgae constitutes a serious competitor for seagrasses in shallow areas with high irradiance.
- Oxidative stress and quantum yield efficiency in the intertidal seagrass zostera noltiiPublication . Silva, João; Barrote, Isabel; Santos, RuiWe investigated the combined effects of several environmental stressors in the photosynthetic performance and in the activation of biochemical defense mechanisms in the intertidal seagrass Zostera noltii in Ria Formosa coastal lagoon (southern Portugal). The maximum (Fv/Fm) and the effective (F’v/F’m) quantum use efficiencies of PSII were sampled monthly in both neap and spring tides over one year. Other fluorescence parameters, such as the Stern-Volmer non-photochemical quenching (NPQ) and the novel parameter LNP (which expresses the general decrease in PSII photochemical activity in the light) were derived from quantum use efficiency measurements. Sampling for antioxidant enzymes activity, pigments, soluble protein and malondialdehyde (MDA) was conducted in parallel. Reactive oxygen species (ROS) are formed as a normal part of the metabolism. An increment on ROS formation is a common response to those stresses and can cause several types of damage, namely lipid peroxidation. MDA is a product of the peroxidation of membrane lipids and thus is commonly used as an indicator of oxidative stress. Carotenoids and antioxidant enzymes such as ascorbate peroxidase (APx) are part of the plants’ antioxidative system. Higher content of carotenoids indicate a higher photoprotection and increased activities of ROS scavenging enzymes such as APx are correlated with stress tolerance. The relationships among critical environmental parameters (irradiance, temperature, air exposure), oxidative stress, antioxidative responses and quantum use efficiency in Z. noltii were explored through multifactorial analysis.
- Physiological stress indicators in seagrassesPublication . Barrote, Isabel; Santos, Rui; Silva, JoãoWe investigated the combined effects of several environmental stressors in the biochemical defence mechanisms of the intertidal seagrass Zostera noltii and the subtidal seagrasses Zostera marina and Cymodocea nodosa in Ria Formosa coastal lagoon (southern Portugal). During one year Z. noltii was sampled for antioxidant enzymes activity, pigments, soluble protein and malondialdehyde (MDA) in both neap and spring tides. Intertidal seagrasses are periodically exposed to potentially stressful conditions such as desiccation, osmotic stress, high light and very high or freezing temperatures, depending on the season, latitude and tidal amplitude. In Ria Formosa Z. marina and C. nodosa appear frequently in the same meadow and compete for space, light and nutrients. These species are also exposed to stressful environmental conditions such as light or temperature stress and their survival depends on their relative ability to cope with all these stressors. In order to study the effects of low light in Z. marina and C. nodosa, four different levels of shading were imposed on field plots of both species during three weeks. P-I relationships were determined and samples were collected to determine photosynthetic pigments, non-structural carbohydrates, soluble protein, phenols and malondialdehyde concentration. Reactive oxygen species (ROS) are formed as a normal part of the plants metabolism. An increment on ROS formation is a common response to stress and can induce several types of damage, namely lipid peroxidation. MDA is a product of the peroxidation of membrane lipids and thus is commonly used as an indicator of oxidative stress, as is the concentration of phenolic compounds. Carotenoids and antioxidant enzymes are part of the plants’ antioxidative system. Higher content of carotenoids, besides amplifying the photosynthetic useful wavelengths, indicate higher photoprotection. Increased activities of ROS scavenging enzymes are correlated with stress tolerance. The relationships among experimental and environmental data will be discussed.
- Posidonia oceanica photosynthesis along a depth gradientPublication . Costa, Monya; Silva, João; Olivé, Irene; Barrote, Isabel; Santos, RuiSeagrass photosynthetic rates depend largely on light availability, along with other environmental factors and the physiological condition of the plants. Along a vertical gradient, seagrasses are permanently exposed to distinct light environments, to which the photosynthetic apparatus must adapt. In this study, the response of Posidonia oceanica photosynthesis to light was investigated in plants collected at three different depths (3, 20 and 30m) in the Bay of Revellata, Corsica, France, in the the marine research station Stareso (42º34’4’’N, 8º43’2’’E) in October, 2011. Photosynthesis-irradiance curves (P-I) were measured in an oxygen electrode system (DW3/CB1, Hansatech). Photosynthetic rates were determined over an increasing range of irradiance values, from darkness to 850 µmol quanta m-2 s-1. The Jassby and Platt hyperbolic model (1957) equation was fitted to the obtained data, to calculate the relevant photosynthetic parameters. For each depth, maximum photosynthetic rate (Pmax), inicial slope (), light saturation point (Ik), light compensation point (Ic) and dark respiration (Rd) were determined. Photosynthetic parameters showed significant variations with depth, particularly between the shallowest plants (3m) and the two other depths. As expected, P. oceanica from 3m depth revealed a “sun-adapted” photosynthetic behavior in contrast with plants from deeper waters.
- Quantum yield by the intertidal seagrass Zostera noltiiPublication . Silva, João; Barrote, Isabel; Santos, Rui; Carlo, G. Di; Calladine, A.; Zuljevic, A.The maximum (Fv/FM) and the effective (F'v/F'm) quantum ise efficinecies of PSII were investigated in the intertidal seagrass Zostera noltii from Ria Formosa coastal lagoon (southern Portugal). Modulated chlorophyll fluorescence measurements were conducted monthly in both neap and spring tides over a yearly cycle. Other fluorescence parameters such as the Stern-Volmer non-photochemical quenching (NPQ) and the novel parameter LNP (which expresses the general decrease in PSII photochemical activity in the light) were derived from quantum use efficiency measurements. In all the samplings Fv/Fm presented a typical midday depression, which amplitude was higher during neap tides, when low tide occurs at noon and the plants are air-exposed. Annual patterns also emerged , revealing higher maximum quantum use efficiencies in winter and early spring, under mild temperatures and moderate irradiances. During summer months the maximum quantum use efficiency was at its lowest, most likely due to increased stress levels imposed by the combination of high temperature and strong irradiances. Relationships between quantum use efficiency (as revealed by chlorophyll fluorescence data) and critical environmental parameters (irradiance, temperature, air exposure) were explored through multifactorial analysis.