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- Efeitos a posteriori dos défices hídricos sobre a actividade fotossintética: mecanismos de fotoprotecção e sistema enzimático antioxidantePublication . Barrote, IsabelA resposta dos mecanismos fotossintéticos à duração e intensidade do défice hídrico e posterior rehidratação foi investigada em plantas envasadas de Helianthus annuus L. e Lupinus albus L. A rega foi manipulada de modo a induzir diferentes intensidades de défice hídrico e posterior rehidratação. Nas plantas de H. annuus foram analisadas comparativamente folhas jovens e folhas maduras, tendo-se também avaliado nas folhas jovens o efeito da diminuição temporária da intensidade luminosa nas plantas em défice hídrico e rehidratação. Foram também avaliados comparativamente os efeitos dos défices hídricos e da rehidratação na actividade fotossintética e no sistema antioxidante em folhas de H. annuus e L. albus, espécies com estratégias diferentes perante o défice hídrico (H. annuus é tolerante ao défice hídrico e L. albus evita o défice hídrico). Os resultados obtidos indicam que, apesar de as taxas de fotossíntese terem diminuído em resposta ao défice hídrico, não ocorreu fotoinibição crónica nem foi induzida senescência foliar nas folhas de H. annuus amostradas. Nestas plantas, em situação de défice hídrico, ocorreram limitações metabólicas à actividade fotossintética, que nas folhas maduras podem ter incluído a activação da reacção de Mehler e da fotorrespiração. As folhas jovens revelaram possuir a capacidade de reforçar a sua protecção antioxidante em resposta ao défice hídrico, através do aumento do teor foliar em carotenóides. No entanto, as diferenças registadas entre as folhas jovens e as folhas maduras nas plantas em défice hídrico não se repercutiram na sua capacidade de recuperação da actividade fotossintética após rehidratação, que foi semelhante. Os dados obtidos mostraram que o aumento do ‘quenching’ não fotoquímico nem sempre está directamente relacionado com o aumento do índice de desepoxidação do ciclo das xantofilas e confirmaram a relação de dependência entre ambos os parâmetros e a densidade de fluxo quântico. Nas plantas em défice hídrico transferidas para intensidade luminosa baixa, a ausência de stresse oxidativo pode ter implicado falhas na sinalização interna das plantas, enquanto o estímulo aparente da exportação de fotoassimilados durante a rehidratação pode ter conduzido à inibição do crescimento, pelo que não se observaram vantagens na imposição do défice hídrico e da rehidratação a baixas densidades de fluxo quântico. A manutenção de altos teores foliares de sacarose nas plantas rehidratadas sob irradiância alta não evitou que estas não recuperassem completamente a actividade fotossintética. O défice hídrico induziu senescência foliar em L. albus. Esta pode ter resultado do stresse oxidativo induzido nas plantas em défice hídrico, aparentemente devido ao desequilíbrio entre as actividades da dismutase do superóxido e da peroxidase do ascorbato. Os resultados mostram que o défice hídrico pode, por si só, induzir respostas normalmente associadas à ocorrência conjunta de défice hídrico e intensidade luminosa alta, tais como o stresse oxidativo e o aumento no teor foliar em pigmentos antioxidantes.
- Effectiveness and consistency of a suite of descriptors to assess the ecological status of seagrass meadows (Posidonia oceanica L. Delile)Publication . Rotini, Alice; Belmonte, A.; Barrote, Isabel; Micheli, C.; Peirano, A.; Santos, Rui; Silva, JoãoThe increasing rate of human-induced environmental changes on coastal marine ecosystems has created a demand for effective descriptors, in particular for those suitable for monitoring the status of seagrass meadows. Growing evidence has supported the useful application of biochemical and genetic descriptors such as secondary metabolite synthesis, photosynthetic activity and genetic diversity. In the present study, we have investigated the effectiveness of different descriptors (traditional, biochemical and genetic) in monitoring seagrass meadow conservation status. The Posidonia oceanica meadow of Monterosso al Mare (Ligurian sea, NW Mediterranean) was subjected to the measurement of bed density, leaf biometry, total phenols, soluble protein and photosynthetic pigment content as well as to RAPD marker analysis. This suite of descriptors provided evidence of their effectiveness and convenient application as markers of the conservation status of P. oceanica and/or other seagrasses. Biochemical/genetic descriptors and those obtained by traditional methods depicted a well conserved meadow with seasonal variability and, particularly in summer, indicated a healthier condition in a portion of the bed (station C), which was in agreement with the physical and sedimentological features of the station. Our results support the usefulness of introducing biochemical and genetic approaches to seagrass monitoring programs since they are effective indicators of plant physiological stress and environmental disturbance.
- 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.
- Influence of nutrient availability on drought-induced changes in the activity of antioxidant enzymes in sunflower leavesPublication . David, Maria Manuela; Barrote, Isabel; Correia, Maria JoãoWe aimed to evaluate if plants with different nutrient availability evidenced a different capacity to overcome drought-induced oxidative stress. Membrane peroxidative damages as MDA concentration and the activity of several antioxidant enzymes were determined in leaves of well watered (WW) and water stressed (WS) H. annuus plants grown either with adequate (Adeq Nutr) or limited (Limit Nutr) nutrient regimes. Constitutive capacity to eliminate ROS was not overall changed by growing plants with different nutrient supply regimes, but a diverse enzyme-dependent response was observed. In response to drought SOD and DHAR activity increased only in plants with limited nutrient supply, while in plants with adequate nutrient supply the activity of these enzymes did not change and were constitutively higher, but the activity APX increased by 50%. The subtle observed changes in the activity of the antioxidant enzymes are discussed, given that no oxidative damage was observed.
- Heatwave effects on the photosynthesis and antioxidant activity of the seagrass Cymodocea nodosa under contrasting light regimesPublication . Costa, Monya; Silva, João; Barrote, Isabel; Santos, RuiGlobal climate change, specifically the intensification of marine heatwaves, affect seagrasses. In the Ria Formosa, saturating light intensities may aggravate heatwave effects on seagrasses, particularly during low spring tides. However, the photophysiological and antioxidant responses of seagrasses to such extreme events are poorly known. Here, we evaluated the responses of Cymodocea nodosa exposed at 20 °C and 40 °C and 150 and 450 μmol quanta m−2 s−1. After four-days, we analyzed (a) photosynthetic responses to irradiance, maximum photochemical efficiency (Fv/Fm), the effective quantum yield of photosystem II (ɸPSII); (b) soluble sugars and starch; (c) photosynthetic pigments; (d) antioxidant responses (ascorbate peroxidase, APX; oxygen radical absorbance capacity, ORAC, and antioxidant capacity, TEAC); (d) oxidative damage (malondialdehyde, MDA). After four days at 40 °C, C. nodosa showed relevant changes in photosynthetic pigments, independent of light intensity. Increased TEAC and APX indicated an “investment” in the control of reactive oxygen species levels. Dark respiration and starch concentration increased, but soluble sugar concentrations were not affected, suggesting higher CO2 assimilation. Our results show that C. nodosa adjusts its photophysiological processes to successfully handle thermal stress, even under saturating light, and draws a promising perspective for C. nodosa resilience under climate change scenarios.
- The effects of drought on net CO2 uptake, chlorophyll fluorescence and photosynthetic pigments in mature and young leaves of sunflowerPublication . Osório, Maria Leonor; Barrote, Isabel; Osório, Júlio; David, Maria Manuela; Correia, Maria JoãoPhotosynthesis, photosystem II activity and photosynthetic pigments were analysed in mature and Young leaves of sunflower (Helianthus annuus L.) during dehydration and rehydration, in order to determine the influence of leaf age on the sensitivity to drought. Dehydration caused a more pronounced inhibition in photosynthetic rates in mature leaves compared to younger leaves, but 24 h after rewatering the recovery was complete in spite of leaf age. After exposure to drought, mature leaves showed a larger reduction in the actual PSII photochemical efficiency and a higher increase in nonradiative energy dissipation than young leaves. In well-watered plants the de-epoxidation level represented by the ratio A+Z/V+A+Z was higher in young leaves. However drought had opposite effects on both type of leaves: in young leaves A+Z/V+A+Z decreased with water deficit, while in mature leaves increased with soil drying. The results obtained suggest that leaf age influence the “strategy” to avoid irreversible damage of PSII activity under drought and that older leaves are more drought-sensitive than younger leaves of sunflower.
- Effects of water deficit on the activity of nitrate reductase and content of sugars, nitrate and free amino acids in the leaves and roots of sunflower and white lupin plants growing under two nutrient supply regimesPublication . Correia, Maria João; Fonseca, Filomena; Azedo-Silva, João; Dias, Celeste; David, Maria Manuela; Barrote, Isabel; Osório, Maria Leonor; Osório, JúlioThe effects of a two weeks soil drying period on the activity of nitrate reductase (NR; EC 1.6.6.6) were studied on Helianthus annuus L. and non-nodulated Lupinus albus L. plants, growing under two nutrient supply regimes. NR activity was assessed in leaf and root extracts, by measuring the activity of the unphosphorylated active form (NRact), the maximal extractable activity (NRmax) and the activation state. To get insight into potential signalling compounds, nitrate, amino acids and soluble sugars concentrations were also quantified. On both species, foliar NRact and NRmax were negatively affected by soil drying and reduced supply of nutrients, the observed changes in NR activity being linearly-correlated with the depletion of nitrate. Similar results were obtained in the roots of sunflower. Conversely, in white lupin roots NRmax was found to be independent of tissue nitrate concentration. Regardless of the species and organ, the activation state of the enzyme was unaffected by the nutrient supply regime. In well-watered sunflower roots only about 50% of the existing NR was unphosphorylated, but the activation state increased significantly in response to drought. In contrast, lupin roots always exhibited NR activation state values close to 80% or even higher. At the leaf level, NR activation state was hardly changed in response to soil drying. The contribution of changes in the concentrations of soluble 5 sugars and amino acids to explain the observed variations in NR activity are discussed.
- Alterações sazonais da fotossíntese e do ciclo das xantófilas em alfarrobeira (Ceratonia siliqua L.)Publication . Barrote, Isabel; Correia, Maria João; David, Maria ManuelaThis study aimed to follow the seasonal changes in the photosynthetic performance of two Ceratonia siliqua cultivars – Mulata and Mulata do Espargal – growing in a non-irrigated orchard in Algarve (South Portugal). Measurements and sampling (leaf water potential, leaf gas exchange, pigments and dark-adapted chlorophyll fluorescence) were taken in days with similar photon flux density, during the dry season in June and July, and in November after the first autumnal rainfalls (»91 mm) when minimum temperatures droped below 10°C. Photosynthetic rates remained low for both cvs, and did not recover in November despite the observed increase in stomatal conductance and y. Fv/Fm slowly decreased from June to November, specially at midday. This changes in Fv/Fm were attributed mainly to increasing F0 which might reflect structural changes or damages at the chloroplast membranes level. Dry season conditions seemed to have triggered some thermal photoprotective mechanisms, as indicated through the increased ratio A+Z/VAZ. In November, however, the ratio A+Z/VAZ decreased. We suggest that the lack of recovery of A associated with higher F0 measured in both cvs, either at pre-dawn or midday, could be attributed to structural changes within the membranes mediated either by rehydration and/or by chilling temperatures.
- Citrus Pruning in the Mediterranean climate: a reviewPublication . Matias, Pedro; Barrote, Isabel; Azinheira, Gonçalo; Continella, Alberto; Duarte, AmilcarPruning is a common practice in citrus for various reasons. These include controlling and shaping the canopy; improving phytosanitary health, productivity, and fruit quality; and facilitating operations such as harvesting and phytosanitary treatments. Because pruning is an expensive operation, its need is sometimes questioned. However, it has been proven to be particularly important in Mediterranean citriculture, which is oriented towards producing fruits for a high-quality demanding fresh market. Herein, we summarize and explain the pruning techniques used in Mediterranean citriculture and refer to the main purposes of each pruning type, considering citrus morphology and physiology.
- High CO2 decreases the long-term resilience of the free-living coralline algae Phymatolithon lusitanicumPublication . SORDO, LAURA; Santos, Rui; Barrote, Isabel; Silva, JoãoMaerl/rhodolith beds are protected habitats that may be affected by ocean acidification (OA), but it is still unclear how the availability of CO2 will affect the metabolism of these organisms. Some of the inconsistencies found among OA experimental studies may be related to experimental exposure time and synergetic effects with other stressors. Here, we investigated the long-term (up to 20months) effects of OA on the production and calcification of the most common maerl species of southern Portugal, Phymatolithon lusitanicum. Both the photosynthetic and calcification rates increased with CO2 after the first 11months of the experiment, whereas respiration slightly decreased with CO2. After 20months, the pattern was reversed. Acidified algae showed lower photosynthetic and calcification rates, as well as lower accumulated growth than control algae, suggesting that a metabolic threshold was exceeded. Our results indicate that long-term exposure to high CO2 will decrease the resilience of Phymatolithon lusitanicum. Our results also show that shallow communities of these rhodoliths may be particularly at risk, while deeper rhodolith beds may become ocean acidification refuges for this biological community.