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João Pereira - One of the best experts on this subject based on the ideXlab platform.
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ABA xylem concentrations determine maximum daily Leaf Conductance of field‐grown Vitis vinifera L. plants
Plant Cell and Environment, 1995Co-Authors: Maria João Correia, João Pereira, M. M. Chaves, Maria Luísa Rodrigues, C. PachecoAbstract:Differences in maximum Leaf Conductance in grapevine plants growing in soils with contrasting water availabilities during mid-summer in Portugal could be accounted for by differences in the concentration of ABA in xylem sap. This conclusion is reinforced by the observation that the relationship between Leaf Conductance and endogenous ABA concentration can be mimicked by the application of exogenous ABA to leaves detached from irrigated plants. During the day, Leaf Conductance decreased after a morning peak, even when the leaves remained in a constant environment at a moderate temperature and Leaf-to-air vapour pressure difference. This decline in Leaf Conductance was not a consequence of an increase in the xylem ABA concentration or the rate of delivery of this compound by the transpiratory stream. The afternoon depression in Leaf Conductance was associated with an apparent limitation in stomatal opening potential, which persisted even when detached leaves were fed with water and rehydrated. The reason for this inhibition has still to be identified.
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The control of Leaf Conductance of white lupin by xylem ABA concentration decreases with the severity of water deficits
Journal of Experimental Botany, 1995Co-Authors: Maria João Correia, João PereiraAbstract:We studied the effects of drought on Leaf Conductance (g), Leaf water relations and on the concentration of abscisic acid (ABA) in the xylem sap of lupinus albus L. plants. Drought was imposed by withholding watering until predawn Leaf water potential (ψ pd ) decreased below − 0.7 MPa. The abaxial stomata of waterstressed plants closed to a greater extent than the adaxial stomata and the same trend was evident after feeding exogenous ABA. Under moderate water deficits (ψ pd = − 0.32 ± 0.05 MPa) xylem ABA concentration was significantly higher in water-stressed plants (0.1 mmol m −3 ) than in the controls, and the observed depression in g could be mimicked when excised leaves of wellwatered plants were fed with exogenous ABA at the same concentration found in the xylem sap of moderately stressed plants. As soil drying progressed xylem ABA concentration increased further, reaching 0.8-0.9 mmol m −3 after 17 d without watering. However, feeding a similar concentration of exogenous ABA to leaves of well-watered plants failed to reproduce the depression in g observed in severely stressed plants. After rewatering, full recovery of g was not achieved immediately, in spite of xylem ABA concentration and ψ pd returning to pre-stress levels. Our results indicate that the increase in xylem ABA concentration is quantitatively sufficient to account for the depression in Leaf Conductance observed in white lupin plants subjected to moderate water deficits, but the role of xylem ABA in controlling g apparently decreases when soil drying and plant water stress becomes severe
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Abscisic acid in apoplastic sap can account for the restriction in Leaf Conductance of white lupins during moderate soil drying and after rewatering
Plant Cell and Environment, 1994Co-Authors: M. J. Correia, João PereiraAbstract:We studied the effects of drought on Leaf Conductance (g) and on the concentration of abscisic acid (ABA) in the apoplastic sap of Lupinus albus L. leaves. Withholding watering for 5d resulted in complete stomatal closure and in severe Leaf water deficit. Leaf water potential fully recovered immediately after rewatering, but the aftereffect of drought on stomata persisted for 2d. ABA and sucrose were quantified in pressurized Leaf xylem extrudates. We assumed that the xylem sucrose concentration is negligible and hence that the presence of sucrose in Leaf extrudates indicated that they were contaminated by phloem. To eliminate this interference, the concentration of ABA in Leaf apoplast was estimated by extrapolation to zero sucrose concentration, using the regression between ABA and sucrose concentrations. The estimated apoplastic ABA concentration increased by 100-fold with soil drying and did not return to pre-stress values immediately following rewatering. g was closely related to the concentration of ABA in Leaf apoplast. Furthermore, the feeding of exogenous ABA to leaves detached from well-watered plants brought about the same degree of depression in g as resulted from the drought-induced increase in ABA concentration. We therefore conclude that the observed changes in the concentration of ABA in Leaf apoplast were quantitatively adequate to explain drought-induced stomatal closure and the delay in stomatal reopening following rewatering.
Priit Kupper - One of the best experts on this subject based on the ideXlab platform.
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Predawn Leaf Conductance depends on previous day irradiance but is not related to growth in aspen saplings grown under artificially manipulated air humidity.
Functional plant biology : FPB, 2021Co-Authors: Priit Kupper, Ants Kaasik, Mai Kukumägi, Gristin Rohula-okunev, Linda Rusalepp, Anu SõberAbstract:Recent studies have suggested that predawn stomatal opening may enhance early-morning photosynthesis (A) and improve the relative growth rate of trees. However, the causality between night-time stomatal Conductance, A, and tree growth is disputable because stomatal opening in darkness can be mediated by previous day photosynthate loads and might be a consequence of growth-related processes like dark respiration (R). To identify linkages between night-time Leaf Conductance (gl_night), A, R, and tree growth, we conducted an experiment in hybrid aspen saplings grown under different air relative humidity (RH) conditions and previous day irradiance level (IR_pday). Predawn Leaf Conductance (gl_predawn) depended on RH, IR_pday and R (P < 0.05), whereas early-morning gross A (Agross_PAR500) depended on IR_pday and gl_predawn (P < 0.001). Daytime net A was positively related to Agross_PAR500 and Leaf [N] (P < 0.05). Tree diameter and height increment correlated positively with gl at the beginning and middle of the night (P < 0.05) but not before dawn. Although our results demonstrate that gl_night was related to tree growth, the relationship was not determined by R. The linkage between gl_predawn and Agross_PAR500 was modified by IR_pday, indicating that daily CO2 assimilation probably provides feedback for stomatal opening before dawn.
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Variation in Leaf Conductance of silver birch: effects of irradiance, vapour pressure deficit, Leaf water status and position within a crown
Forest Ecology and Management, 2004Co-Authors: Arne Sellin, Priit KupperAbstract:Abstract Responses of Leaf Conductance (gL) to variation in photosynthetic photon flux density (QP), Leaf-to-air vapour pressure difference (VPD), bulk Leaf water potential (Ψx) and soil to Leaf hydraulic Conductance (GT) were studied in silver birch (Betula pendula Roth) foliage with respect to Leaf position within the canopy. The upper canopy leaves demonstrated 2.0–2.4 times higher (P Leaf Conductance decreased if Ψx fell below certain values after the noon, while the sun foliage experienced greater negative water potentials than the shade foliage. In a diurnal scale the influence of bulk Leaf water potential on gL altogether was rather weak. The lower-canopy foliage exhibited more conservative water-use behaviour, having lower maximum stomatal Conductance and greater sensitivity to Ψx bringing about a smaller responsiveness to VPD than the upper canopy foliage. The mean GT was 1.7–1.8 times bigger (P
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Within-crown variation in Leaf Conductance of Norway spruce: effects of irradiance, vapour pressure deficit, Leaf water status and plant hydraulic constraints
Annals of Forest Science, 2004Co-Authors: Arne Sellin, Priit KupperAbstract:Responses of Leaf Conductance (gL) to variation in photosynthetic photon flux density, Leaf-to-air vapour pressure difference, shoot water potential and soil-to-Leaf hydraulic Conductance (GT) were studied in Picea abies (L.) Karst. foliage with respect to shoot age and position within the canopy. The upper canopy shoots demonstrated on average 1.6 times higher daily maximum gL as compared to the lower canopy shoots growing in the shadow of upper branches. Functional acclimation of the shade foliage occurred in the form of both a steeper initial slope of the light-response curve and a lower light-saturation point of gL. The mean GT was 1.6-1.8 times bigger for the upper canopy compared to the lower canopy. We set up an hypothesis that stomatal Conductance at the base of the live crown is constrained not only by low light availability but also by plant's inner hydraulic limitations.
Maria João Correia - One of the best experts on this subject based on the ideXlab platform.
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ABA xylem concentrations determine maximum daily Leaf Conductance of field‐grown Vitis vinifera L. plants
Plant Cell and Environment, 1995Co-Authors: Maria João Correia, João Pereira, M. M. Chaves, Maria Luísa Rodrigues, C. PachecoAbstract:Differences in maximum Leaf Conductance in grapevine plants growing in soils with contrasting water availabilities during mid-summer in Portugal could be accounted for by differences in the concentration of ABA in xylem sap. This conclusion is reinforced by the observation that the relationship between Leaf Conductance and endogenous ABA concentration can be mimicked by the application of exogenous ABA to leaves detached from irrigated plants. During the day, Leaf Conductance decreased after a morning peak, even when the leaves remained in a constant environment at a moderate temperature and Leaf-to-air vapour pressure difference. This decline in Leaf Conductance was not a consequence of an increase in the xylem ABA concentration or the rate of delivery of this compound by the transpiratory stream. The afternoon depression in Leaf Conductance was associated with an apparent limitation in stomatal opening potential, which persisted even when detached leaves were fed with water and rehydrated. The reason for this inhibition has still to be identified.
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The control of Leaf Conductance of white lupin by xylem ABA concentration decreases with the severity of water deficits
Journal of Experimental Botany, 1995Co-Authors: Maria João Correia, João PereiraAbstract:We studied the effects of drought on Leaf Conductance (g), Leaf water relations and on the concentration of abscisic acid (ABA) in the xylem sap of lupinus albus L. plants. Drought was imposed by withholding watering until predawn Leaf water potential (ψ pd ) decreased below − 0.7 MPa. The abaxial stomata of waterstressed plants closed to a greater extent than the adaxial stomata and the same trend was evident after feeding exogenous ABA. Under moderate water deficits (ψ pd = − 0.32 ± 0.05 MPa) xylem ABA concentration was significantly higher in water-stressed plants (0.1 mmol m −3 ) than in the controls, and the observed depression in g could be mimicked when excised leaves of wellwatered plants were fed with exogenous ABA at the same concentration found in the xylem sap of moderately stressed plants. As soil drying progressed xylem ABA concentration increased further, reaching 0.8-0.9 mmol m −3 after 17 d without watering. However, feeding a similar concentration of exogenous ABA to leaves of well-watered plants failed to reproduce the depression in g observed in severely stressed plants. After rewatering, full recovery of g was not achieved immediately, in spite of xylem ABA concentration and ψ pd returning to pre-stress levels. Our results indicate that the increase in xylem ABA concentration is quantitatively sufficient to account for the depression in Leaf Conductance observed in white lupin plants subjected to moderate water deficits, but the role of xylem ABA in controlling g apparently decreases when soil drying and plant water stress becomes severe
Arne Sellin - One of the best experts on this subject based on the ideXlab platform.
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Variation in Leaf Conductance of silver birch: effects of irradiance, vapour pressure deficit, Leaf water status and position within a crown
Forest Ecology and Management, 2004Co-Authors: Arne Sellin, Priit KupperAbstract:Abstract Responses of Leaf Conductance (gL) to variation in photosynthetic photon flux density (QP), Leaf-to-air vapour pressure difference (VPD), bulk Leaf water potential (Ψx) and soil to Leaf hydraulic Conductance (GT) were studied in silver birch (Betula pendula Roth) foliage with respect to Leaf position within the canopy. The upper canopy leaves demonstrated 2.0–2.4 times higher (P Leaf Conductance decreased if Ψx fell below certain values after the noon, while the sun foliage experienced greater negative water potentials than the shade foliage. In a diurnal scale the influence of bulk Leaf water potential on gL altogether was rather weak. The lower-canopy foliage exhibited more conservative water-use behaviour, having lower maximum stomatal Conductance and greater sensitivity to Ψx bringing about a smaller responsiveness to VPD than the upper canopy foliage. The mean GT was 1.7–1.8 times bigger (P
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Within-crown variation in Leaf Conductance of Norway spruce: effects of irradiance, vapour pressure deficit, Leaf water status and plant hydraulic constraints
Annals of Forest Science, 2004Co-Authors: Arne Sellin, Priit KupperAbstract:Responses of Leaf Conductance (gL) to variation in photosynthetic photon flux density, Leaf-to-air vapour pressure difference, shoot water potential and soil-to-Leaf hydraulic Conductance (GT) were studied in Picea abies (L.) Karst. foliage with respect to shoot age and position within the canopy. The upper canopy shoots demonstrated on average 1.6 times higher daily maximum gL as compared to the lower canopy shoots growing in the shadow of upper branches. Functional acclimation of the shade foliage occurred in the form of both a steeper initial slope of the light-response curve and a lower light-saturation point of gL. The mean GT was 1.6-1.8 times bigger for the upper canopy compared to the lower canopy. We set up an hypothesis that stomatal Conductance at the base of the live crown is constrained not only by low light availability but also by plant's inner hydraulic limitations.
Jaleh Ghashghaie - One of the best experts on this subject based on the ideXlab platform.
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Relationships between Leaf Conductance to CO2 diffusion and photosynthesis in micropropagated grapevine plants, before and after ex vitro acclimatization
Journal of experimental botany, 2006Co-Authors: Gianni Fila, Franz-w. Badeck, Sylvie Meyer, Zoran G. Cerovic, Jaleh GhashghaieAbstract:In vitro-cultured plants typically show a low photosynthetic activity, which is considered detrimental to subsequent ex vitro acclimatization. Studies conducted so far have approached this problem by analysing the biochemical and photochemical aspects of photosynthesis, while very little attention has been paid to the role of Leaf Conductance to CO2 diffusion, which often represents an important constraint to CO2 assimilation in naturally grown plants. Mesophyll Conductance, in particular, has never been determined in in vitro plants, and no information exists as to whether it represents a limitation to carbon assimilation during in vitro growth and subsequent ex vitro acclimatization. In this study, by means of simultaneous gas exchange and chlorophyll fluorescence measurements, the stomatal and mesophyll Conductance to CO2 diffusion were assessed in in vitro-cultured plants of the grapevine rootstock ‘41B’ (Vitis vinifera ‘Chasselas’3Vitis berlandieri), prior to and after ex vitro acclimatization. Their impact on electron transport rate partitioning and on limitation of potential net assimilation rate was analysed. In vitro plants had a high stomatal Conductance, 155 versus 50 mmol m 22 s 21 in acclimatized plants, which ensured a higher CO2 concentration in the chloroplasts, and a 7% higher electron flow to the carbon reduction pathway. The high stomatal Conductance was counterbalanced by a low mesophyll Conductance, 43 versus 285 mmol m 22 s 21 , which accounted for a 14.5% estimated relative limitation to photosynthesis against 2.1% estimated in acclimatized plants. It was concluded that mesophyll Conductance represents an important limitation for in vitro plant photosynthesis, and that in acclimatization studies the correct comparison of photosynthetic activity between in vitro and acclimatized plants must take into account the contribution of both stomatal and mesophyll Conductance.
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Photosynthesis, Leaf Conductance and water relations of in vitro cultured grapevine rootstock in relation to acclimatisation
Physiologia Plantarum, 1998Co-Authors: Gianni Fila, Jaleh Ghashghaie, Jackson Hoarau, Gabriel CornicAbstract:Leaf net CO 2 uptake and Leaf photosynthetic capacity were investigated in micro-propagated 41B grapevine rootstock (Vitis vinifera 'Chasselas' x Vitis berlandieri, Mill. De Gr.) plants grown in the presence of four sucrose concentrations (6.25, 12.5, 25.0 or 37.5 g l -1 ). Sucrose concentration in the medium during growth in vitro did not affect the Leaf photosynthetic performance of plants neither before nor after transplantation. The maximun photosynthetic rate, measured as CO,-dependent O 2 evolution, was 7.3 μmol m -2 s -1 before transplanting and 15.4 μmol m -2 s -1 one month after transplantation. The maximum quantum yield of O 2 evolution (on the basis of incident light) was about 0.07 for all sucrose treatments both before and after transplantation. Dry biomass before transplanting was highest in plants grown with 25.0 or 37.5 g l -1 sucrose in the medium. One month after transplantation the highest dry biomass was also observed for the same treatments. Survival of plants was 100% for all treatments. Leaf Conductance to water vapour was always higher in plants before than after transplantation. Both before and after transplanting it increased with increasing light intensity and decreased slightly with increasing CO 2 molar ratio in in vitro plants. Stomata of plants before transplantation were unresponsive to vapour pressure deficit. In vitro plants experience an acute water stress when they are maintained with the whole root system in water and exposed to ambient controlled conditions in a growth chamber. However, there was no wilting of the leaves when similar plants with roots cut off were left in the same conditions. Hydraulic conductivity was low at both root and shoot-root connection levels. It is likely that water supply could be limiting during tansplantation because of the low, root and root-stem connection conductivity. Water uptake by roots rather than water loss from the shoots would be of primary importance for the maintenance of water balance during acclimatisation.