Biologia
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- A new northern limit for the distribution range of Lipophrys canevae (Pisces: Blenniidae) in the Atlantic OceanPublication . Almada, Vítor Carvalho; Oliveira, Rui Filipe; Gonçalves, Emanuel João; Almeida, Armando J.; Barata, Eduardo NunoIn this note, the occurence of Lipophris canevae at Arrábida (Portugal) is reported, which extends 160 Km north the known range ot this species in the Atlantic coast of the Iberian Peninsula. This species has been consistently found at Arrábida since 1987. The presence of a crest on the head of the males, which is considered a rare secondary sexual character in the Mediterranean populations, is very common in the specimens known from portuguese waters, even in the females, where it is vestigial. The meristic and morphometric data from specimens known from portuguese waters are summarized. At Arrábida, the nests occur in the midlittoral zone, often in the transition to the sublittoral, and remain out of water for several hours during low tide. Breeding takes place during Spring and Summer. ------ SUMÁRIO ----- Na presente nota, descreve-se a ocorrência Lipophris canevae na costa da Arrábida (Portugal), o que estende 160 Km para norte e distribuição conhecida para esta espécie na costa atlântica da Península Ibérica. A ocorrência desta espécie na Arrábida tem sido registada regularmente desde 1987. A presença de uma crista na cabeça dos machos, que para as populações mediterrânicas é considerada um carácter sexual secundário raro, ocorre com grande frequência nos espéciemens conhecudis das águas portuguesas, inclusive nas fêmeas embora nestas seja vestigial. Resumem-se os dados merísticos e morfométricos para os exemplares até agora capturados na costa portuguesa. Na Arrábida, os ninhos ocorrem no médio-litoral, por vezes na transição para o infra-litoral, e permanecem emersos durante várias horas na baixa-mar. A reprodução tem lugar na Primavera e Verão.
- Oxygen sensitivity of C4 photosynthesis: Evidence from gas exchange and chlorophyll fluorescence analyses with different C4 subtypesPublication . Maroco, João; Ku, Maurice S. B.; Edwards, Gerald E.Because photosynthetic rates in C4 plants are the same at normal levels of O2 (c. 20 kPa) and at c. 2 kPa O2 (a conventional test for evaluating photorespiration in C3 plants) it has been thought that C4 photosynthesis is O2 insensitive. However, we have found a dual effect of O2 on the net rate of CO2 assimilation among species representing all three C4 subtypes from both monocots and dicots. The optimum O2 partial pressure for C4 photosynthesis at 30 °C, atmospheric CO2 level, and half full sunlight (1000 μmol quanta m-2 s-1) was about 5-10 kPa. Photosynthesis was inhibited by O2 below or above the optimum partial pressure. Decreasing CO2 levels from ambient levels (32.6 Pa) to 9.3 Pa caused a substantial increase in the degree of inhibition of photosynthesis by supra-optimum levels of O2 and a large decrease in the ratio of quantum yield of CO2 fixation/quantum yield of photosystem II (PSII) measured by chlorophyll α fluorescence. Photosystem II activity, measured from chlorophyll α fluorescence analysis, was not inhibited at levels of O2 that were above the optimum for CO2 assimilation, which is consistent with a compensating, alternative electron flow as net CO2 assimilation is inhibited. At suboptimurn levels of O2, however, the inhibition of photosynthesis was paralleled by an inhibition of PSII quantum yield, increased state of reduction of quinone A, and decreased efficiency of open PSII centres. These results with different C4 types suggest that inhibition of net CO2assimilation with increasing O2 partial pressure above the optimum is associated with photorespiration, and that inhibition below the optimum O2 may be caused by a reduced supply of ATP to the C4 cylcle as a result of inhibition of its production photochemically.
- Oxygen requirement and inhibition of C4 photosynthesisPublication . Maroco, João; Ku, Maurice S. B.; Lea, Peter J.; Dever, Louisa V.; Leegood, Richard C.; Furbank, Robert T.; Edwards, Gerald E.The basis for O2 sensitivity of C4 photosynthesis was evaluated using a C4-cycle-limited mutant of Amaranthus edulis (a phosphoenolpyruvate carboxylase-deficient mutant), and a C3-cyclelimited transformant of Flaveria bidentis (an antisense ribulose-1,5- bisphosphate carboxylase/oxygenase [Rubisco] small subunit transformant). Data obtained with the C4-cycle-limited mutant showed that atmospheric levels of O2 (20 kPa) caused increased inhibition of photosynthesis as a result of higher levels of photorespiration. The optimal O2 partial pressure for photosynthesis was reduced from approximately 5 kPa O2 to 1 to 2 kPa O2, becoming similar to that of C3 plants. Therefore, the higher O2 requirement for optimal C4 photosynthesis is specifically associated with the C4 function. With the Rubisco-limited F. bidentis, there was less inhibition of photosynthesis by supraoptimal levels of O2 than in the wild type. When CO2 fixation by Rubisco is limited, an increase in the CO2 concentration in bundle-sheath cells via the C4 cycle may further reduce the oxygenase activity of Rubisco and decrease the inhibition of photosynthesis by high partial pressures of O2 while increasing CO2 leakage and overcycling of the C4 pathway. These results indicate that in C4 plants the investment in the C3 and C4 cycles must be balanced for maximum efficiency.
- Utilization of O2 in the metabolic optimization of C4 photosynthesisPublication . Maroco, João; Ku, Maurice S. B.; Edwards, Gerald E.The combined effects of O2 on net rates of photosynthesis, photosystem II activity, steady-state pool size of key metabolites of photosynthetic metabolism in the C4 pathway, C3 pathway and C2 photorespiratory cycle and on growth were evaluated in the C4 species Amaranthus edulis and the C3 species Flaveria pringlei. Increasing O2 reduced net CO2 assimilation in F. pringlei due to an increased flux of C through the photorespiratory pathway. However, in A. edulis increasing O2 up to 5–10% stimulated photosynthesis. Analysis of the pool size of key metabolites in A. edulis suggests that while there is some O2 dependent photorespiration, O2 is required for maximizing C4 cycle activity to concentrate CO2 in bundle sheath cells. Therefore, the response of net photosynthesis to O2 in C4 plants may result from the balance of these two opposing effects. Under 21 versus 5% O2, growth of A. edulis was stimulated about 30% whereas that of F. pringlei was inhibited about 40%.
- First census of the green turtle at Poilão, Bijagós Archipelago, Guinea-Bissau: the most important nesting colony on the Atlantic coast of AfricaPublication . Catry, Paulo; Barbosa, Castro; Indjai, Bucar; Almeida, Amadeu; Godley, Brendan J.; Vié, Jean-ChristopheThe island of Poilão in the Bijagós Archipelago, Guinea-Bissau, is known to be an important nesting site for the green turtle Chelonia mydas, but until recently there were no quantitative estimates of the number of clutches deposited annually. In 2000 a survey was carried out to assess the magnitude of nesting, and an estimated 7,400 green turtle clutches were deposited. Four nesting hawksbill turtles Eretmochelys imbricata were also encountered. This study confirmed that Poilão is one of the most important nesting sites for green turtles in the Atlantic, and the largest known nesting colony on the west coast of Africa. Traditionally Poilão has been regarded as a sacred site by the Bijagós people, and this has contributed to the conservation of these turtles. However, the development of fisheries in this region is an emerging threat. To conserve this site a National Marine Park was designated in August 2000.
- How plants cope with water stress in the field? Photosynthesis and growthPublication . Chaves, Maria Manuela; Pereira, João Santos; Maroco, João; Rodrigues, M. Lucília; Ricardo, Cândido Pereira Pinto; Osório, M. L.; Carvalho, Isabel Saraiva de; Faria, T.; Pinheiro, C.Plants are often subjected to periods of soil and atmospheric water deficit during their life cycle. The frequency of such phenomena is likely to increase in the future even outside today’s arid/semi‐arid regions. Plant responses to water scarcity are complex, involving deleterious and/or adaptive changes, and under field conditions these responses can be synergistically or antagonistically modified by the superimposition of other stresses. This complexity is illustrated using examples of woody and herbaceous species mostly from Mediterranean‐type ecosystems, with strategies ranging from drought‐avoidance, as in winter/spring annuals or in deep‐rooted perennials, to the stress resistance of sclerophylls. Differences among species that can be traced to different capacities for water acquisition, rather than to differences in metabolism at a given water status, are described. Changes in the root : shoot ratio or the temporary accumulation of reserves in the stem are accompanied by alterations in nitrogen and carbon metabolism, the fine regulation of which is still largely unknown. At the leaf level, the dissipation of excitation energy through processes other than photosynthetic C‐metabolism is an important defence mechanism under conditions of water stress and is accompanied by down‐regulation of photochemistry and, in the longer term, of carbon metabolism.
- Limitations to leaf photosynthesis in field-grown grapevine under drought - metabolic and modelling approachesPublication . Maroco, João; Rodrigues, M. Lucília; Lopes, Carlos Manuel Antunes; Chaves, Maria ManuelaThe effects of a slowly-imposed drought stress on gas-exchange, chlorophyll a fluorescence, biochemical and physiological parameters of Vitis vinifera L. leaves (cv. Aragonez, syn. Tempranillo) growing in a commercial vineyard (South Portugal) were evaluated. Relative to well-watered plants (predawn water potential, ΨPD = –0.13 ± 0.01 MPa), drought-stressed plants (ΨPD = –0.97 ± 0.01 MPa) had lower photosynthetic rates (ca 70%), stomatal conductance, and PSII activity (associated with a higher reduction of the quinone A pool and lower efficiency of PSII open centres). Stomatal limitation to photosynthesis was increased in drought-stressed plants relative to well-watered plants by ca 44%. Modelled responses of net photosynthesis to internal CO2 indicated that drought-stressed plants had significant reductions in maximum Rubisco carboxylation activity (ca 32%), ribulose-1,5-bisphosphate regeneration (ca 27%), and triose phosphate (triose-P) utilization rates (ca 37%) relative to well-watered plants. There was good agreement between the effects of drought on modelled biochemical parameters, and in vitro activities of key enzymes of carbon metabolism, namely Rubisco, glyceraldehyde-3-phosphate dehydrogenase, ribulose-5-phosphate kinase and fructose-1,6-bisphosphate phosphatase. Quantum yields measured under both ambient (35 Pa) and saturating CO2 (100 Pa) for drought-stressed plants were decreased relative to well-watered plants, as well as maximum photosynthetic rates measured at light and CO2 saturating conditions (three times ambient CO2 levels). Although stomatal closure was a strong limitation to CO2 assimilation under drought, comparable reductions in electron transport, CO2 carboxylation, and utilization of triose-P capacities were also adaptations of the photosynthetic machinery to dehydration that slowly developed under field conditions. Results presented in this study confirm that modelling photosynthetic responses based on gas-exchange data can be successfully used to predict metabolic limitations to photosynthesis.
- Effects of long-term exposure to elevated CO2 and N fertilization on the development of photosynthetic capacity and biomass accumulation in Quercus suber L.Publication . Maroco, João; Breia, Elsa; Faria, T.; Pereira, João Santos; Chaves, Maria ManuelaThe effects of long-term (4 year) CO2 enrichment (70Pa versus 35 Pa) and nitrogen nutrition (8mM versus 1mM NO3–) on biomass accumulation and the development of photosynthetic capacity in leaves of cork oak (Quercus suber L., a Mediterranean evergreen tree) were studied. The evolution of photosynthetic parameters with leaf development was estimated by fitting the biochemical model of Farquhar et al. (Planta 149, 78–90, 1980) with modifications by Sharkey (Botanical Review 78, 71–75, 1985) to A–Ci response curves. CO2 enrichment had a small reduction effect on the development of the maximum CO2 fixation capacity by Rubisco (VCmax), and no effect over maximum electron transport capacity (Jmax), day-time respiration(Rd) and Triose-P utilization (TPU). However, there was a statistically significant effect of N fertilization and the interaction CO2×N over the evolution of VCmax, Jmax and TPU. Relative stomatal limitation (estimated from A–Ci curves) was higher (+20%) for plants grown under ambient CO2 than for plants grown under elevated CO2. There was a significant effect of CO2 and N fertilization over total biomass accumulation as well as leaf area. Plants grown at elevated CO2 had 27% more biomass than plants grown at ambient CO2 when given high N. However, for plants grown under low N there was no significant effect of CO2 enrichment on biomass accumulation. Plants grown under low N also had significantly higher root: shoot ratios whereas there were no differences between CO2 treatments. The larger biomass accumulation of Q. suber under elevated CO2 is attributable to a higher availability of CO2 coupled to a larger leaf area, with no significant decrease in photosynthetic capacity under CO2 enrichment and elevated N fertilization. For low N fertilization, the effects of CO2 enrichment over leaf area and biomass accumulation are lost, suggesting that in native ecosystems with low N availability, the effects of CO2 enrichment may be insignificant.
- A revision of the status of Lepadogaster lepadogaster (Teleostei: Gobiesocidae): sympatric subspecies or a long misunderstood blend of species?Publication . Henriques, Miguel; Lourenço, Rita; Almada, Frederico José Oliveira de; Calado, Gonçalo; Gonçalves, David; Guillemaud, Thomas; Cancela, M. Leonor; Almada, Victor CarvalhoMolecular (partial mitochondrial 12S ribosomal DNA sequences), morphological and meristic analysis of Lepadogaster lepadogaster lepadogaster, L. l. purpurea and L. zebrina were performed to investigate the relationships between these taxa. On the western shore of mainland Portugal, where the two subspecies of L. lepadogaster occur sympatrically, they differ in microhabitat preferences and their breeding seasons are largely out of phase. This information, combined with data on distribution patterns, led to the following conclusions: Lepadogaster l. purpurea is considered to be a valid species, L. purpurea (Bonnaterre, 1788), different from L. l. lepadogaster, now designated L. lepadogaster (Bonnaterre, 1788). L. zebrina was found to be a synonym of L. lepadogaster. The two newly defined species were found to be in sympatry at Madeira and the Canary islands, the Atlantic coast of the Iberian Peninsula, and the Mediterranean at least as far as Genoa (Italy). Diagnostic characters and a list of synonyms are provided. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 76, 327–338.
- Understanding plant responses to drought - from genes to thePublication . Chaves, Maria Manuela; Maroco, João; Pereira, João SantosIn the last decade, our understanding of the processes underlying plant response to drought, at the molecular and whole-plant levels, has rapidly progressed. Here, we review that progress. We draw attention to the perception and signalling processes (chemical and hydraulic) of water deficits. Knowledge of these processes is essential for a holistic understanding of plant resistance to stress, which is needed to improve crop management and breeding techniques. Hundreds of genes that are induced under drought have been identified. A range of tools, from gene expression patterns to the use of transgenic plants, is being used to study the specific function of these genes and their role in plant acclimation or adaptation to water deficit. However, because plant responses to stress are complex, the functions of many of the genes are still unknown. Many of the traits that explain plant adaptation to drought — such as phenology, root size and depth, hydraulic conductivity and the storage of reserves — are those associated with plant development and structure, and are constitutive rather than stress induced. But a large part of plant resistance to drought is the ability to get rid of excess radiation, a concomitant stress under natural conditions. The nature of the mechanisms responsible for leaf photoprotection, especially those related to thermal dissipation, and oxidative stress are being actively researched. The new tools that operate at molecular, plant and ecosystem levels are revolutionising our understanding of plant response to drought, and our ability to monitor it. Techniques such as genome-wide tools, proteomics, stable isotopes and thermal or fluorescence imaging may allow the genotype–phenotype gap to be bridged, which is essential for faster progress in stress biology research.