Can the stomatal changes caused by acute ozone exposure be predicted by changes occurring in the mesophyll? A simplification for models of vegetation response to the global increase in tropospheric elevated ozone episodes

2000 ◽  
Vol 27 (3) ◽  
pp. 211 ◽  
Author(s):  
Marion J. Martin ◽  
Peter K. Farage ◽  
Steve W. Humphries ◽  
Steve P. Long
Keyword(s):  
Stomatal Conductance ◽  
Model Simulation ◽  
Stomatal Closure ◽  
Photosynthetic Apparatus ◽  
Interactive Effects ◽  
Ozone Exposure ◽  
Leaf Photosynthesis ◽  
Ozone Dose ◽  
Ozone Episodes

The prediction of complex interactive effects of rising concentrations of ozone and CO2on vegetation will require robust models based on mechanistic understanding of how these two gases affect photosynthesis. This paper describes the development of a model of acute ozone exposure effects on wheat leaf photosynthesis, based on the mechanism of reactive oxygen scavenging processes. Based on experimental data, the dose of ozone to the leaf above a threshold flux, here termed the effective ozone dose, was found to be linearly related to the decline in the in vivo maximum rate of carboxylation. The proposed mechanism is that ozone damage to the photosynthetic ap paratus will only occur above a critical rate of ozone delivery. By combining the model of the response of ribulose-1,5-bisphosphate-saturated and limited photosynthesis to ozone exposure with both a mechanistic biochemical model of leaf photosynthesis and a phenomenological model of stomatal conductance, it was possible to investigate the degree of dependency of ozone-induced stomatal closure on changes in the mesophyll. The stomatal conductance of the model simulation compared well with the magnitude of measured stomatal closure. The results indicate that the stomatal changes caused by acute ozone exposure can be predicted from changes in the mesophyll rather than directly on the stomata. The findings that the effects of ozone on photosynthesis can be predicted by an effective ozone dose to the leaf, and that the resulting reduction in CO2 assimilation rate can, in turn, predict stomatal closure, greatly simplifies modelling the effects of elevated concentrations of ozone and CO2 on wheat photosynthesis. Future work should determine whether the model can be adapted to predict chronic ozone exposure effects on photosynthesis, and whether it can be applied to other species by adjusting the values of threshold flux, related to the maximum scavenging capacity within the leaf, and the ozone slope coefficient, representing the inherent sensitivity of the photosynthetic apparatus to ozone.

scholarly journals VOC reactivity and its effect on ozone production during the HaChi summer campaign

2011 ◽  
Vol 11 (3) ◽  
pp. 8595-8623 ◽  
Author(s):  
L. Ran ◽  
C. S. Zhao ◽  
W. Y. Xu ◽  
X. Q. Lu ◽  
M. Han ◽  
...  
Keyword(s):  
Model Simulation ◽  
Sensitivity Study ◽  
Ozone Exposure ◽  
Ozone Production ◽  
The North ◽  
Photochemical Production ◽  
Key Species ◽  
Volatile Organic ◽  
Exposure Risks ◽  
Ozone Episodes

Abstract. Measurements of ozone and its precursors conducted within the HaChi (Haze in China) project in summer 2009 were analyzed to characterize volatile organic compounds (VOCs) and their effects on ozone photochemical production at a suburban site in the North China Plain. Ozone episodes, during which running 8-h average ozone concentrations exceeding 80 ppbv lasted for more than 4 h, occurred on about two thirds of the observational days during the 5-week field campaign. This suggests continuous ozone exposure risks in this region during the summer. The average concentrations of nitrogen oxides (NOx) and VOCs are about 20 ppbv and 650 ppbC, respectively. Total VOC reactivity is dominated by anthropogenic VOCs, including aromatics, alkanes and most alkenes. The contribution of biogenic VOCs to total ozone-forming potential, however, is also considerable in the daytime. 2-butenes, isoprene, trimethylbenzenes, xylenes, 3-methylhexane, n-hexane and toluene are key species associated with ozone photochemical production. Formation of ozone is found to be NOx-limited as indicated by measured VOCs/NOx ratios and further confirmed by a sensitivity study using a photochemical box model NCAR_MM. The Model simulation suggests that ozone production is also sensitive to changes in VOC reactivity under the NOx-limited regime, although this sensitivity depends strongly on how much NOx is present.

scholarly journals VOC reactivity and its effect on ozone production during the HaChi summer campaign

2011 ◽  
Vol 11 (10) ◽  
pp. 4657-4667 ◽  
Author(s):  
L. Ran ◽  
C. S. Zhao ◽  
W. Y. Xu ◽  
X. Q. Lu ◽  
M. Han ◽  
...  
Keyword(s):  
Model Simulation ◽  
Sensitivity Study ◽  
Ozone Exposure ◽  
Ozone Production ◽  
The North ◽  
Photochemical Production ◽  
Key Species ◽  
Volatile Organic ◽  
Exposure Risks ◽  
Ozone Episodes

Abstract. Measurements of ozone and its precursors conducted within the HaChi (Haze in China) project in summer 2009 were analyzed to characterize volatile organic compounds (VOCs) and their effects on ozone photochemical production at a suburban site in the North China Plain (NCP). Ozone episodes, during which running 8-h average ozone concentrations exceeding 80 ppbv lasted for more than 4 h, occurred on about two thirds of the observational days during the 5-week field campaign. This suggests continuous ozone exposure risks in this region in the summer. Average concentrations of nitrogen oxides (NOx) and VOCs are about 20 ppbv and 650 ppbC, respectively. On average, total VOC reactivity is dominated by anthropogenic VOCs. The contribution of biogenic VOCs to total ozone-forming potential, however, is also considerable in the daytime. Key species associated with ozone photochemical production are 2-butenes (18 %), isoprene (15 %), trimethylbenzenes (11 %), xylenes (8.5 %), 3-methylhexane (6 %), n-hexane (5 %) and toluene (4.5 %). Formation of ozone is found to be NOx-limited as indicated by measured VOCs/NOx ratios and further confirmed by a sensitivity study using a photochemical box model NCAR_MM. The Model simulation suggests that ozone production is also sensitive to changes in VOC reactivity under the NOx-limited regime, although this sensitivity depends strongly on how much NOx is present.

Quantitative Ranking of Ligand Binding Kinetics with a Multiscale Milestoning Simulation Approach

2018 ◽  
Author(s):  
Benjamin R. Jagger ◽  
Christoper T. Lee ◽  
Rommie Amaro
Keyword(s):  
Molecular Dynamics ◽  
Drug Discovery ◽  
Small Molecule ◽  
Brownian Dynamics ◽  
Model Simulation ◽  
Computational Cost ◽  
Lead Selection ◽  
Delta G ◽  
Dynamics Simulations

<p>The ranking of small molecule binders by their kinetic (kon and koff) and thermodynamic (delta G) properties can be a valuable metric for lead selection and optimization in a drug discovery campaign, as these quantities are often indicators of in vivo efficacy. Efficient and accurate predictions of these quantities can aid the in drug discovery effort, acting as a screening step. We have previously described a hybrid molecular dynamics, Brownian dynamics, and milestoning model, Simulation Enabled Estimation of Kinetic Rates (SEEKR), that can predict kon’s, koff’s, and G’s. Here we demonstrate the effectiveness of this approach for ranking a series of seven small molecule compounds for the model system, -cyclodextrin, based on predicted kon’s and koff’s. We compare our results using SEEKR to experimentally determined rates as well as rates calculated using long-timescale molecular dynamics simulations and show that SEEKR can effectively rank the compounds by koff and G with reduced computational cost. We also provide a discussion of convergence properties and sensitivities of calculations with SEEKR to establish “best practices” for its future use.</p>

scholarly journals Overexpressing the HD-Zip class II transcription factor EcHB1 from Eucalyptus camaldulensis increased the leaf photosynthesis and drought tolerance of Eucalyptus

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Keisuke Sasaki ◽  
Yuuki Ida ◽  
Sakihito Kitajima ◽  
Tetsu Kawazu ◽  
Takashi Hibino ◽  
...  
Keyword(s):  
Transcription Factor ◽  
Leaf Area ◽  
Leucine Zipper ◽  
Eucalyptus Grandis ◽  
Eucalyptus Camaldulensis ◽  
Class Ii ◽  
Cell Multiplication ◽  
Leaf Photosynthesis ◽  
Unit Leaf

Abstract Alteration in the leaf mesophyll anatomy by genetic modification is potentially a promising tool for improving the physiological functions of trees by improving leaf photosynthesis. Homeodomain leucine zipper (HD-Zip) transcription factors are candidates for anatomical alterations of leaves through modification of cell multiplication, differentiation, and expansion. Full-length cDNA encoding a Eucalyptus camaldulensis HD-Zip class II transcription factor (EcHB1) was over-expressed in vivo in the hybrid Eucalyptus GUT5 generated from Eucalyptus grandis and Eucalyptus urophylla. Overexpression of EcHB1 induced significant modification in the mesophyll anatomy of Eucalyptus with enhancements in the number of cells and chloroplasts on a leaf-area basis. The leaf-area-based photosynthesis of Eucalyptus was improved in the EcHB1-overexpression lines, which was due to both enhanced CO2 diffusion into chloroplasts and increased photosynthetic biochemical functions through increased number of chloroplasts per unit leaf area. Additionally, overexpression of EcHB1 suppressed defoliation and thus improved the growth of Eucalyptus trees under drought stress, which was a result of reduced water loss from trees due to the reduction in leaf area with no changes in stomatal morphology. These results gave us new insights into the role of the HD-Zip II gene.

scholarly journals Interactions between leaf water potential, stomatal conductance and abscisic acid content of orange trees submitted to drought stress

2004 ◽  
Vol 16 (3) ◽  
pp. 155-161 ◽  
Author(s):  
Mara de Menezes de Assis Gomes ◽  
Ana Maria Magalhães Andrade Lagôa ◽  
Camilo Lázaro Medina ◽  
Eduardo Caruso Machado ◽  
Marcos Antônio Machado
Keyword(s):  
Abscisic Acid ◽  
Water Stress ◽  
Stomatal Conductance ◽  
Water Potential ◽  
Leaf Water Potential ◽  
Acid Content ◽  
Stomatal Closure ◽  
Leaf Water ◽  
Orange Trees ◽  
Abscisic Acid Content

Thirty-month-old 'Pêra' orange trees grafted on 'Rangpur' lemon trees grown in 100 L pots were submitted to water stress by the suspension of irrigation. CO2 assimilation (A), transpiration (E) and stomatal conductance (g s) values declined from the seventh day of stress, although the leaf water potential at 6:00 a.m. (psipd) and at 2:00 p.m. (psi2) began to decline from the fifth day of water deficiency. The CO2 intercellular concentration (Ci) of water-stressed plants increased from the seventh day, reaching a maximum concentration on the day of most severe stress. The carboxylation efficiency, as revealed by the ratio A/Ci was low on this day and did not show the same values of non-stressed plants even after ten days of rewatering. After five days of rewatering only psi pd and psi2 were similar to control plants while A, E and g s were still different. When psi2 decreases, there was a trend for increasing abscisic acid (ABA) concentration in the leaves. Similarly, stomatal conductance was found to decrease as a function of decreasing psi2. ABA accumulation and stomatal closure occurred when psi2 was lower than -1.0 MPa. Water stress in 'Pera´ orange trees increased abscisic acid content with consequent stomatal closure and decreased psi2 values.

Transgenic overexpression of β2-adrenergic receptors in airway epithelial cells decreases bronchoconstriction

2000 ◽  
Vol 279 (2) ◽  
pp. L379-L389 ◽  
Author(s):  
Dennis W. McGraw ◽  
Susan L. Forbes ◽  
Judith C. W. Mak ◽  
David P. Witte ◽  
Patricia E. Carrigan ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Airway Epithelium ◽  
Adrenergic Receptors ◽  
Airway Epithelial Cells ◽  
Airway Responsiveness ◽  
Ozone Exposure ◽  
Clara Cell ◽  
Whole Body ◽  
Airway Epithelial

Airway epithelial cells express β2-adrenergic receptors (β2-ARs), but their role in regulating airway responsiveness is unclear. With the Clara cell secretory protein (CCSP) promoter, we targeted expression of β2-ARs to airway epithelium of transgenic (CCSP-β2-AR) mice, thereby mimicking agonist activation of receptors only in these cells. In situ hybridization confirmed that transgene expression was confined to airway epithelium, and autoradiography showed that β2-AR density in CCSP-β2-AR mice was approximately twofold that of nontransgenic (NTG) mice. Airway responsiveness measured by whole body plethysmography showed that the methacholine dose required to increase enhanced pause to 200% of baseline (ED200) was greater for CCSP-β2-AR than for NTG mice (345 ± 34 vs. 157 ± 14 mg/ml; P < 0.01). CCSP-β2-AR mice were also less responsive to ozone (0.75 ppm for 4 h) because enhanced pause in NTG mice acutely increased to 77% over baseline ( P < 0.05) but remained unchanged in the CCSP-β2-AR mice. Although both groups were hyperreactive to methacholine 6 h after ozone exposure, the ED200for ozone-exposed CCSP-β2-AR mice was equivalent to that for unexposed NTG mice. These findings show that epithelial cell β2-ARs regulate airway responsiveness in vivo and that the bronchodilating effect of β-agonists results from activation of receptors on both epithelial and smooth muscle cells.

Interactive effects of cocaine and gender on thymocytes: a study of in vivo repeated cocaine exposure

1998 ◽  
Vol 20 (12) ◽  
pp. 737-749 ◽  
Author(s):  
W. Xu ◽  
T. Flick ◽  
J. Mitchell ◽  
C. Knowles ◽  
K. Ault
Keyword(s):  
Interactive Effects ◽  
Cocaine Exposure ◽  
And Gender

scholarly journals Quantifying seasonal and diurnal variation of stomatal behavior in a hydraulic-based stomatal optimization model

2018 ◽  
Vol 5 ◽  
pp. e001
Author(s):  
William R. L. Anderegg
Keyword(s):  
Stomatal Conductance ◽  
Shadow Price ◽  
Stomatal Closure ◽  
Predictive Ability ◽  
Plant Responses ◽  
Seasonal And Diurnal Variation ◽  
Angiosperm Species ◽  
Term Response ◽  
Single Set ◽  
Optimization Theories

Plant responses to drought occur across many time-scales, with stomatal closure typically considered to be a critical short-term response. Recent theories of optimal stomatal conductance linked to plant hydraulic transport have shown promise, but it is not known if stomata update their hydraulic “shadow price” of water use (marginal increase in carbon cost with a marginal drop in water potential) over days, seasons, or in response to recent drought. Here, I estimate the hydraulic shadow price in five species – two semi-arid gymnosperms, one temperate and two tropical angiosperms – at daily timescales and in wet and dry periods. I tested whether the shadow prices varies predictably as a function of current and/or lagged drought conditions. Diurnal estimates of the hydraulic shadow price estimated from observed stomatal conductance, while variable, did not vary predictably with environmental variables. Seasonal variation in shadow price was observed in the gymnosperm species, but not the angiosperm species, and did not meaningfully influence prediction accuracy of stomatal conductance. The lack of systematic variation in shadow price and high predictive ability of stomatal conductance when using a single set of parameters further emphasizes the potential of hydraulic-based stomatal optimization theories.

A model of stomatal closure driven by nonlinearities in soil-plant hydraulics

2021 ◽  
Author(s):  
Fabian Wankmüller ◽  
Mohsen Zarebanadkouki ◽  
Andrea Carminati
Keyword(s):  
Hydraulic Conductivity ◽  
Stomatal Conductance ◽  
Water Potential ◽  
Leaf Water Potential ◽  
Environmental Conditions ◽  
Plant Traits ◽  
Stomatal Closure ◽  
Leaf Water ◽  
Optimization Models ◽  
Soil Conditions

&lt;p&gt;Predicting plant responses to drought is a long-standing research goal. Since stomata regulate gas-exchange between plants and the atmosphere, understanding their response to drought is fundamental. Current predictions of stomatal behavior during drought mainly rely on empirical models. These models may suit well to a specific set of plant traits and environmental growth conditions, but their predictive value is doubtful when atmospheric and soil conditions change. Stomatal optimization offers an alternative framework to predict stomatal regulation in response to drought for varying environmental conditions and plant traits. Models which apply this optimization principle posit that stomata maximize the carbon gain in relation to a penalty caused by water loss, such as xylem cavitation. Optimization models have the advantage of requiring a limited number of parameters and have been successfully used to predict stomatal response to drought for varying environmental conditions and species. However, a mechanism that enables stomata to optimally close in response to water limitations, and more precisely to a drop in the ability of the soil-plant continuum to sustain the transpiration demand, is not known. Here, we propose a model of stomatal regulation that is linked to abscisic acid (ABA) dynamics (production, degradation and transport) and that allows plants to avoid excessive drops in leaf water potential during soil drying and increasing vapor pressure deficit (VPD). The model assumes that: 1) stomatal conductance (g&lt;sub&gt;s&lt;/sub&gt;) decreases when ABA concentration close to the guard cells (C&lt;sub&gt;ABA&lt;/sub&gt;) increases; 2) C&lt;sub&gt;ABA&lt;/sub&gt; increases with decreasing leaf water potential (due to higher production); and 3) C&lt;sub&gt;ABA&lt;/sub&gt; decreases with increasing photosynthesis (e.g. due to faster degradation or transport to the phloem). Our model includes simulations of leaf water potential based on transpiration rate, soil water potential and variable hydraulic conductances of key elements (rhizosphere, root and xylem), and a function linking stomatal conductance to assimilation. It was tested for different soil properties and VPD. The model predicts that stomata close when the relation between assimilation and leaf water potential becomes nonlinear. In wet soil conditions and low VPD, when there is no water limitation, this nonlinearity is controlled by the relation between stomatal conductance and assimilation. In dry soil conditions, when the soil hydraulic conductivity limits the water supply, nonlinearity is controlled by the excessive drop of leaf water potential for increasing transpiration rates. The model predicts different relations between stomatal conductance and leaf water potential for varying soil properties and VPD. For instance, the closure of stomata is more abrupt in sandy soil, reflecting the steep decrease in hydraulic conductivity of sandy soils. In summary, our model results in an optimal behavior, in which stomatal closure avoids excessive (nonlinear) decrease in leaf water potential, similar to other stomatal optimization models. As based on ABA concentration which increases with decreasing leaf water potential but declines with assimilation, this model is a preliminary attempt to link optimization models to a physiological mechanism.&lt;/p&gt;

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