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- Field performance of seedlings and microproppagated plants of carob treePublication . Osório, Maria Leonor; Osório, Júlio; David, Maria Manuela; Romano, AnabelaMicropropagated plantlets of cv. Mulata and cv. Galhosa growing in pots, after acclimatization in the glasshouse and growth for several months under natural conditions, were transferred to a field trial. Carob seedlings of ‘Mulata’ were also transferred under the same conditions. The field trial has been established with 100% of success in micropropagated plants and 97% in seedlings. Three months after transfer to the field, plants showed good growth but micropropagated plants of ‘Mulata’ exhibited more vigour than ‘Galhosa’ and than seedlings, with the greatest number of branches and a larger length increase in the main stem. Before transference to the field, net photosynthetic rates (PN), water use efficiency (PN/gs) and quantum yield of PSII (fPSII) of the potted plants were higher in seedlings than in micropropagated plants. Three months after transplantation all gas exchange parameters were improved for all types of plants, particularly net photosynthetic rate, and no significant differences were observed between plants either micropropagated or seedlings. On the other hand, fPSII decreased significantly in seedlings. The results suggest that the pre-acclimation, in pots, to external environmental conditions might have improved field survival, plant vigour and enhanced the endurance to adverse conditions of micropropagated carob trees.
- Carbon metabolism of Carob young trees under low temperature: different responses among cultivarsPublication . Cavaco, A. M.; Ferreira, V. L.; Santos, A. M.; David, Maria ManuelaYoung trees of two carobs (Ceratonia siliqua L.) cultivars, Mulata and Galhosa, ,propagated in vitro and grown for 3-4 years in a greenhouse were moved into a growth chamber under environmental controlled conditions where they were exposed to 25/15º C (control), 10/5º C (chilling) and again to 25/15º C (recovery).
- 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.
- Responses of “Newhall" orange trees to iron deficiency in hydroponics: effects on leaf chlorophyll, photosynthetic efficiency, and root ferric chelate reductase activityPublication . Pestana, M.; David, Maria Manuela; de Varennes, A.; Abadía, Javier; Faria, E. A.Orange (Citrus sinensis L. Osb. cv. ‘Newhall’) plants grafted on Citrange troyer rootstock were grown in nutrient solution with 0, 5, 10 or 20 M Fe, with and without calcium carbonate. Calcium carbonate was added in order to mimic the natural conditions in calcareous soils. Leaf chlorophyll concentration was estimated every 3–4 days using the portable instrument SPAD-502 meter. Chlorophyll fluorescence parameters, photosynthetic capacity estimated from oxygen 2 evolution, leaf Fe concentrations, and root tip ferric chelate reductase activity were measured at the end of the experiment. Plants from the 0 and 5 μM Fe treatments showed leaf chlorosis and had decreased leaf chlorophyll concentrations. Leaves of plants grown in the absence of Fe in the solution had smaller rates of oxygen evolution both in the presence and absence of calcium carbonate, compared with plants grown in the presence of 10 M Fe. In the absence of calcium carbonate the photosystem II efficiency, estimated from fluorescence parameters, was similar in all treatments. A slight decrease in photosystem II efficiency was observed in plants grown without Fe and in the presence of calcium carbonate. A 2.5-fold increase in root tip ferric chelate reductase activity over the control values was found only when plants were grown with low levels of Fe and in the presence of calcium carbonate.
- 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.
- Efeitos do stress hídrico no metabolismo fotossintético de Lupinus albus L.Publication . David, Maria Manuela; Pereira, João SantosApresentam-se neste trabalho os resultados de um conjunto de estudos sobre os efeitos do stress hídrico nas trocas gasosas e no metabolismo fotossintético do carbono de plantas C3, em especial de Lupinus albus L.. Nos diferentes ensaios foi possível induzir défices hídricos moderados ou severos, obtidos rápida ou mais lentamente. As trocas gasosas foram claramente afectadas nas plantas stress, que apresentaram valores de condutância estomática muito inferiores aos das plantas regadas. As alterações na capacidade fotossintética (taxa de fotossíntese a concentrações de CCU e a irradiância saturantes) das plantas em stress e a recuperação depois de rehidratadas. e ainda os resultados da análise de parâmetros de fluorescência da clorofila a, sugerem que, no tremoceiro, a fotossíntese ao nível do mesófilo só é significativamente afectada em condições de défice hídrico severo (RWC < 65%) ou prolongado. Enquanto que para esta espécie a componente estomática parece revestir-se de maior importância na limitação da taxa fotossintética em condições de secura, estudos efectuados em condições idênticas com eucalipto e videira revelaram que a principal limitação à fotossíntese no eucalipto está também associada à componente estomática. enquanto que na videira estão evidenciadas alterações ao nível do funcionamento foto e bioquímico do mesófilo. No tremoceiro, os efeitos do stress hídrico na fotossíntese a CO2 ambiente foi mais acentuado nas folhas velhas do que nas novas. No entanto, após rehidratação, são as folhas mais novas as que apresentaram maiores atrasos na recuperação da condutância estomática. Pelo contrário as folhas velhas não recuperaram a capacidade fotossintética pré-stress. Os efeitos dos défices hídricos nas proteínas fotossintéticas foi estudado ao nível da quantidade e actividade da RuBisCO em folhas de diferentes idades. Durante o ciclo de stress a actividade inicial da RuBisCO decresceu independentemente da idade; a actividade total e a quantidade desta enzima diminuíram apenas nas folhas mais velhas. Após rehidratação a quantidade de RuBisCO decresceu mais acentuadamente, em paralelo com a quantidade de proteína solúvel, tanto nas folhas novas como nas velhas. Estes resultados aliados à observação da aceleração do padrão acrópeto de senescência foliar induzido pelo stress hídrico, mais conspícua após a rehidratação, são discutidos numa perspectiva da planta inteira. Os défices hídricos também induziram alterações ao nível da partição dos assimilados recentes. A síntese da sacarose e/ou a hidrólise do amido parecem ter sido estimuladas tanto em tecidos essencialmente consumidores (culturas em suspensão de células heterotróficas de Chenopodium ruhrum). como em tecidos essencialmente produtores (folhas de L. albus). O aumento resultante na razão entre os teores de açúcares não estruturais solúveis e insolúveis é discutido face ao papel desempenhado pela acumulação de solutos compatíveis na osmoregulação. Discute-se também os possíveis efeitos inibitórios da acumulação de açúcares solúveis na actividade fotossintética mediados por mecanismos de dowu regulation e/ou por modificações na expressão genética. Conclui-se que, para o tremoceiro. o decréscimo na actividade fotossintética em condições de stress hídrico moderado ou de pouca duração pode ser atribuído principalmente à limitação na difusão do COt imposta pelo encerramento dos estornas. Em condições de stress hídrico mais severo ou prolongado sobrepoem-se a esta limitação as que parecem resultar de um ajustamento coordenado do teor e actividade da RuBisCO. a par de alterações ao nível do metabolismo da sacarose e do amido, às condições de crescimento limitado pelos défices hídricos. Para algumas plantas, e.g. videira, a importância relativa da componente não-estomática é maior mesmo para défices hídricos muito moderados.
- Leaf age effects on photosynthetic activity and sugar accumulation in droughted and rewatered Lupinus albus L. plantsPublication . David, Maria Manuela; Coelho, Dulce; Barrote, Isabel; Correia, Maria JoãoChanges in the photosynthetic rate (A), stomatal conductance (g), water relations, photosynthetic pigments, Rubisco and soluble sugars accumulation were studied in different aged leaves of white lupin during soil drying and following rehydration. In water-stressed plants, A and g sharply declined and recovered only partially after rewatering. The way Ci and A/gchanged with drought was strongly dependent on leaf age; only in the young leaves did A/g increase and Ci decrease. Drought induced accumulation of soluble sugars was also age dependent, decreasing as leaves aged. In response to soil drying, the contents of photosynthetic pigments, total soluble protein and Rubisco protein increased in the young leaves and were either not affected or slightly decreased in the older ones. Rehydration accentuated the losses in pigments and Rubisco in the old leaves of water-stressed plants. These results suggest that the contribution of mesophyll limitations to explain drought inhibition of photosynthesis increases with leaf age, decreasing the ability to recover after rewatering. In young leaves the tolerance of the photosynthetic apparatus to dehydration and rehydration episodes is high and it is associated with high contents of Rubisco and in soluble sugars, particularly hexoses.
- Photosynthetic responses of Lupinus albus to soil water fluctuationsPublication . Barrote, Isabel; Osório, Maria Leonor; Osório, Júlio; David, Maria Manuela; Correia, Maria JoãoLupinus albus plants were grown in 3 dm3 pots in a semi-controled greenhouse. Two water regimes were imposed: water deficit (S, 47% of soil capacity), and control (T, 86% of soil capacity). Plants water status was monitored through foliar relative water content (TRA) and pre-dawn (ypd) and midday water potential (ymd). Gas exchanges, chlorophyll a fluorescence and photosynthetic capacity (Amax) were measured. Pigments and soluble protein were quantified and antioxidant system enzymes activity was determined. Plants under water deficit were rehydrated and the same measurements and sampling were done again after 48 h (R1) and 72 h (R2). Albeit water availability has diminished from 86% to 47% of soil capacity, there weren’t any remarkable changes on S plants. R1 plants which haven’t shown any alterations neither in Amax nor in stomatal conductance (gH2O), exhibited a significant decrease on net photosynthesis (A), reaching negative values, along with a raise in non-photochemical quenching (NPQ). Presumably this raise should be related with an increase in the xanthophyll cycle deepoxidation state. The significantly increase in Superoxide dismutase (SOD) specific activity in R1 and R2 plants might be related with the activation of Mehler-peroxidase reaction which provokes lumen DpH raising. This can provide photosynthesis protection through VAZ cycle and may justify the NPQ increase.