Fotossíntese e acumulação de ácido abcísico em Lupinus albus sujeito a stress hídrico

The objective of the present work was to assess whether the depression of photosynthetic activity in droughted Lupinus albus L. plants was more closely associated with carbohydrate build-up or ABA accumulation. With that purpose we have measured the concomitant drought-induced changes in photosynthetic capacity and the concentrations of Rubisco, chlorophylls, non-structural carbohydrates and ABA in young and old leaves of white lupin plants. Although Rubisco and chlorophylls contents did not decrease with water stress, the photosynthetic capacity was decreased by soil drying, the decline in photosynthesis being more tighly related with ABA accumulation than with sugar content. In contrast to droughted plants, ABA feeding to intact plants resulted in a significant decrease in Rubisco and chlorophyll content. However, no increase in shoot ABA content was detected in ABA-fed plants. Therefore this work is not conclusive as to the correlation between photosynthetic capacity and ABA accumulation in droughted white lupin plants being causal or not

Influence of nutrient availability on drought-induced changes in the activity of antioxidant enzymes in sunflower leaves

We 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

Response to seasonal drought in three cultivars of Ceratonia siliqua: leaf growth and water relations

The responses of leaf growth and leaf water relations to seasonal drought were monitored, during two successive years, in three cultivars of Ceratonia siliqua L. growing in the field, in the South of Portugal. In leaves from the current year growth bulk leaf water relations parameters were characterised using pressure-volume analysis, and morphometric measurements of xylem in petioles were undertaken. The three cultivars under study (Galhosa, Espargal and Mulata) differed as to the seasonal pattern of leaf initiation: in Galhosa a sharp peak of leaf initiation occurred in June, soon before the period in which the highest leaf expansion rates were determined; on the other two cultivars (Espargal and Mulata), not only the onset of leaf growth occurred earlier, but they continued producing new leaves throughout the summer period. The diurnal pattern of water relations determined in recently-expanded leaves indicated that Galhosa was the only cultivar in which, during midsummer, leaf water potential was not decreased below the turgor loss point and leaf relative water content remained above 90%. Although no conclusive evidence was found for the occurrence of osmotic adjustment in recently-expanded leaves, during the dry season following leaf formation a seasonal decrease in osmotic potential sufficient to maintain turgor was detected in the leaves of Galhosa but not for the other cultivars. As to the anatomy of the xylem at the petioles, the widest xylem conduits were recorded in Galhosa. This might contribute to explain why in this cultivar midday leaf water potential never decreased below –2.0 MPa even at the end of summer drought season

Alterações sazonais da fotossíntese e do ciclo das xantófilas em alfarrobeira (Ceratonia siliqua L.)

This 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

Field performance of seedlings and microproppagated plants of carob tree

Micropropagated 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

Efeitos do stress hídrico no metabolismo fotossintético de Lupinus albus L.

Tese de Doutoramento, Ciências Biológicas, Unidade de Ciências e Tecnologias Agrárias, Universidade do Algarve, 1995Apresentam-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.The effects of imposed soil dehydration on gas exchange and photosynthetic carbon metabolism was studied in potted plants of Lupinus albus. Photosynthesis in air and leaf conductance were strongly reduced in stressed (non-watered) plants. Photosynthetic capacity (in saturating CCh and irradiance) and chlorophyll a fluorescence parameters, together with the recovery capacity on rehydration, revealed that stomatal components were the most important limiting factor of photosynthesis in lupin plants submitted to moderate or rapidly induced water deficits. Photosynthetic capacity decreased only significantly when leaf RWC < 65 % or after prolonged water stress (over two weeks). Measurements carried out in Eucalypíus glohulus and Vitis vinifera showed that the inhibition of photosynthesis under soil drought conditions was due in E. glohulus mainly to closure of stomata; in V. vinifera modifications of the photo and biochemical functioning of the mesophyll were also important. In lupins water stress effects on photosynthesis were most severe in old leaves. Although young leaves showed a longer delay in stomatal reopening after rehydration, old leaves did not fully recover their photosynthetic capacity. RuBisCO inicial activity decresed in ali leaves. RuBisCO total activity and amount were only significantly reduced in old leaves. After rehydration both young and old leaves showed a further decrease in the amount of RuBisCO in parallel with soluble protein. The acceleration of the acropetal pattern of senescence induced by water deficits and subsequent rehydration is discussed in a whole plant approach. Al the partition levei ofthe recent assimilated carbon, water stress seemed to induce alterations both on sink (Chenopodium rubrum suspension cell cultures) and source {Lupinus albus leaves) tissues. Starch was depleted and cells acumulated or maintained high leveis of soluble sugars. The resulting higher ratios, solubles/insolubles, are discussed in terms of osmotic regulation and in terms of down regulation of the photosynthetic activity mediated by mechanism involving genetic expression. The main conclusions of this study are that in lupins, the reduced photosynthetic activity under short or moderate water stress is atributed to CO2 diffusion limitations imposed by stomatal closure; under more severe or longer water deficit conditions other limitations are superimposed, namely those resulting from a coordinated adjustment of the levei and activity of RuBisCO, together with changes in the sucrose and starch metabolism, to the stress limited conditions of growth; for some plants, e.g. grapevine, non stomatal components are evoked early during the development ofwater stress

Seasonal changes in CO2 assimilation in leaves of seedlings and micropropagated plants of Carob tree established in the field

In this communication we evaluate the field performance of two micropropagated Portuguese carob cultivars (Galhosa and Mulata) throughout the season, particularly at extreme conditions of light and temperature. Two irrigated plots were established in the field: 1) micropropagated plants, vs 2) seedlings. During the first year following transplantation to the field, we followed net photosynthetic rate, stomatal conductance, transpiration rate, chlorophyll a fluorescence and leaf contents in chlorophyll, carotenoids and protein. No significant differences were detected between seedlings and micropropagated plants along the year. However, at the end of summer, despite irrigation, the photosynthetic rate (NP), the quantum yield of PSII (fPSII) and the intrinsic efficiency of open PSII reaction centers (F’v/F’m) declined, concomitantly with the increase of the thermal energy dissipation at the PSII (NPQ). As the maximal photochemical efficiency of PSII (Fv/Fm) was maintained high (0.82), these results indicate that regulated thermal dissipation in light harvesting complexes was promoted in order to avoid photoinhibition. After the first growth period in the field, data from micropropagated plants did not differ from seedlings, and those plants showed the characteristic behaviour of plants well adapted to Mediterranean climates. So, in vitro propagation could be use as a promising alternative to traditional propagation and establishment of carob orchards

Photosynthetic responses of Lupinus albus to soil water fluctuations

Lupinus 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

Interaction between water and nutrient deficiencies in helianthus annuus

The physiological response of plants to water deficits are known to vary according to the conditions of application of drought stress and the rate of development of leaf water deficits. At the whole plant level the effect of the water shess is usually perceived as a decrease in photosynthesis and growth, and is associated with alterations in C and N metabolism (McDonald and Davies, 1996). The decrease in water potential affects transpiration and hence xylem transport of nitrate or reduced N into growing regions. The response of the photo-synthetic apparatus either to water stress or rehydration seems to be dependent "on leaf age (O'Neill, 1983; Wolfe et al., 1988). Degradation of both thylakoid and stromal N-containing compounds can occur in response to water stress, recovery from which may pequire more than a week (Chaves, 1991)

Responses of “Newhall" orange trees to iron deficiency in hydroponics: effects on leaf chlorophyll, photosynthetic efficiency, and root ferric chelate reductase activity

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