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At least 109 records · Page 6Linked to original sources
PubMed2003

High-resolution spatial analysis of stomatal ozone uptake in arable crops and pastures.

Ozone effects on plants depend on atmospheric transport and stomatal uptake. Thus, ozone-risk assessments should use measured ozone concentrations and account for the influence of atmospheric conditions and soil moisture on stomatal and nonstomatal ozone deposition. This requires disaggregated data for the physical input parameters and species-specific data for specific stomatal conductance (g(s)). In this study, an approach was developed based on a resistance analogue transport model. This model requires interpolated routine-measuring data for ozone concentration at 3-5 m height, wind speed, precipitation, and soil moisture content as inputs to estimate the amount of ozone taken up by wheat (Triticum aestivum) and grass/clover pastures with a 1x1-km resolution. The model was applied to the area under agricultural production in Switzerland. Using data for June 1994, the calculations revealed that the median of the distribution of stomatal ozone uptake was 88% higher in wheat compared to grassland. This was mainly due to the higher maximum stomatal conductance in wheat. Because ozone flux to soil and to external plant surfaces was comparable in both vegetation types, the difference in the stomatal fluxes was mainly responsible for distinct differences in flux partitioning. In both cases, only about 11% of the total cumulative flux was absorbed by external plant surfaces, whereas the soil was a strong sink responsible for as much as 50% of the total flux into grasslands. The higher-ozone flux to wheat resulted in clearly lower-ozone concentrations at canopy height, but no significant correlation between cumulative canopy-level ozone exposure, expressed as accumulated exposure above 40 ppb (AOT40), and stomatal uptake was found. Thus, to estimate the ozone risk for crops using a flux-based approach may lead to results that differ substantially from those obtained with a concentration-based approach.

Ecosystem↗
PubMed2001

Effects of leaf wetting and high humidity on stomatal function in leafy cuttings and intact plants of Corylus maxima.

When rooted cuttings of Corylus maxima Mill. cv. Purpurea are moved from the wet and humid conditions of the rooting environment, the leaves frequently shrivel and die. Since the newly formed adventitious root system has been shown to be functional in supplying water to the shoot, stomatal behaviour in C. maxima was investigated in relation to the failure to prevent desiccation. Stomatal conductance (gs) in expanding leaves (L3) of cuttings increased almost 10-fold over the first 14 days in the rooting environment (fog), from 70 to 650 mmol m-2 s-1. In contrast, gs of expanded leaves (L1) changed little and was in the region of 300 mmol m-2 s-1. Midday leaf water potential was much higher in cuttings than in leaves on the mother stock-plant (-0.5 versus -1.2 MPa) even before any roots were visible. Despite this, leaf expansion of L3 was inhibited by >50% in cuttings and stomata showed a gradual reduction in their ability to close in response to abscisic acid (ABA). To determine whether the loss of stomatal function in cuttings was due to severance or to unnaturally low vapour pressure deficit and wetting in fog, intact plants were placed alongside cuttings in the rooting environment. The intact plants displayed reductions in leaf expansion and in the ability of stomata to close in response to dark, desiccation and ABA. However, in cuttings, the additional effect of severance resulted in smaller leaves than in intact plants and more severe reduction in stomatal closure, which was associated with a 2.5-fold increase in stomatal density and distinctively rounded stomatal pores. The similarities between stomatal dysfunction in C. maxima and that observed in many species propagated in vitro are discussed, as is the possible mechanism of dysfunction.

Journal Article↗
PubMed2003

Visualization of abscisic acid-perception sites on the plasma membrane of stomatal guard cells.

Abscisic acid (ABA) is a phytohormone that plays a key role as a stress signal, regulating water relations during drought conditions, by inducing stomatal closure. However, to date, no putative ABA receptor(s) has been reported at the protein sequence, gene family, or cellular localization levels. We used biotinylated ABA (bioABA) to characterize the ABA-perception sites in the stomatal guard cells of Vicia faba. Treatment with bioABA induced stomatal closure and shrinkage of guard cell protoplasts (GCPs). The ABA-perception sites were visualized by fluorescence microscopy and confocal laser scanning microscopy (CLSM), using bioABA and fluorescence-labeled avidin. Fluorescent particles were observed in patches on the surface of the GCPs. Fluorescence intensity was quantified by flow cytometry (FCM) as well as by CLSM. Binding of bioABA was inhibited by ABA in a dose-dependent manner. Pre-treatment of GCPs with proteinase K also blocked the binding of bioABA. Binding of bioABA was inhibited by RCA-7a, an ABA analog that induces stomatal closure, but not by RCA-16, which has no effect on stomatal aperture. Another ABA analog, PBI-51, inhibited ABA-induced stomatal closure. This ABA antagonist also inhibited binding of bioABA to the GCPs. These results suggest that ABA is perceived on the plasma membrane of stomatal guard cells, and that the present experimental methods constitute valuable tools for characterizing the nature of the ABA receptor(s) that perceives physiological ABA signals. These imaging studies allow us to demonstrate the spatial distribution of the ABA-perception sites. Visualization of the ABA-perception sites provides new insights into the nature of membrane-associated ABA receptor(s).

Abscisic Acid↗
PubMed2001

Quantification of stomatal uptake of ionic solutes using a new model system.

Evidence for stomatal uptake of solutes by leaves without the application of surfactants or pressure has recently been provided (Eichert et al., 1998). In the present study, experimental conditions were refined in that the water potential was held at <0 on the physiologically inner side of the epidermal strips (ES) by use of a ceramic plate or the proper mesophyll of the plant. The penetrated substances were immobilized on the inner side by ion exchange membranes. The influence of humidity, light, stomatal density, and re-wetting on the uptake of anions (fluorescein) and cations (Fe(3+)) was investigated, using leaves of Allium porrum, Commelina communis and Sedum telephium. Uptake increased with humidity, stomatal aperture and stomatal density. It was restricted to stomatal areas, and was especially high below the rims of drying droplets. Again, penetration of stomatal pores was observed. Uptake was strongly correlated with the number of penetrated stomata, although usually less than 10% of the stomata contributed to uptake. The number of stomata that had been penetrated was highly variable, increasing extremely significantly with the number of repeated drying/ wetting cycles. These results indicate that stomatal uptake can be a major pathway for the foliar uptake of ionic solutes. It is a dynamic process, depending on environmental conditions and history of the residues on the leaf, aspects that had been neglected in previous concepts.

Allium↗
PubMed2006

Species-dependent changes in stomatal sensitivity to abscisic acid mediated by external pH.

The direct effects of pH changes and/or abscisic acid (ABA) on stomatal aperture were examined in epidermal strips of Commelina communis L. and Arabidopsis thaliana. Stomata were initially opened at pH 7 or pH 5. The stomatal closure induced by changes in external pH and/or ABA (10 microM or 10 nM) was monitored using video microscopy and quantified in terms of changes in stomatal area using image analysis software. Measurements of aperture area enabled stomatal responses and, in particular, small changes in stomatal area to be quantified reliably. Both plant species exhibited a biphasic closure response to ABA: an initial phase of rapid stomatal closure, followed by a second, more prolonged, phase during which stomata closure proceeded at a slower rate. Changes in stomatal sensitivity to ABA were also observed. Comparison of these effects between C. communis and A. thaliana demonstrate that this differential sensitivity of stomata to ABA is species-dependent, as well as being dependent on the pH of the extracellular environment.

Abscisic Acid↗
PubMed2003

Simultaneous measurement of stomatal conductance, non-photochemical quenching, and photochemical yield of photosystem II in intact leaves by thermal and chlorophyll fluorescence imaging.

A new imaging system capable of simultaneously measuring stomatal conductance and fluorescence parameters, non-photochemical quenching (NPQ) and photochemical yield of photosystem II (Phi(PSII)), in intact leaves under aerobic conditions by both thermal imaging and chlorophyll fluorescence imaging was developed. Changes in distributions of stomatal conductance and fluorescence parameters across Phaseolus vulgaris L. leaves induced by abscisic acid treatment were analyzed. A decrease in stomatal conductance expanded in all directions from the treatment site, then mainly spread along the lateral vein toward the leaf edge, depending on the ABA concentration gradient and the transpiration stream. The relationships between stomatal conductance and fluorescence parameters depended on the actinic light intensity, i.e. NPQ was greater and Phi(PSII) was lower at high light intensity. The fluorescence parameters did not change, regardless of stomatal closure levels at a photosynthetically active photon flux (PPF) of 270 micro mol m(-2) s(-1); however, they drastically changed at PPF values of 350 and 700 micro mol m(-2) s(-1), when the total stomatal conductance decreased to less than 80 and 200 mmol m(-2) s(-1), respectively. This study has, for the first time, quantitatively analyzed relationships between spatiotemporal variations in stomatal conductance and fluorescence parameters in intact leaves under aerobic conditions.

Abscisic Acid↗
PubMed1985

Stomatal Limitation to Carbon Gain in Paphiopedilum sp. (Orchidaceae) and Its Reversal by Blue Light.

Leaves from Paphiopedilum sp. (Orchidaceae) having achlorophyllous stomata, show reduced levels of stomatal conductance when irradiated with red light, as compared with either the related, chlorophyllous genus Phragmipedium or with their response to blue light. These reduced levels of stomatal conductance, and the failure of isolated Paphiopedilum stomata to open under red irradiation indicates that the small stomatal response measured in the intact leaf under red light is indirect.The overall low levels of stomatal conductance observed in Paphiopedilum leaves under most growing conditions and their capacity to increase stomatal conductance in response to blue light suggested that growth and carbon gain in Paphiopedilum could be enhanced in a blue light-enriched environment. To test that hypothesis, plants of Paphiopedilum acmodontum were grown in controlled growth chambers under daylight fluorescent light, with or without blue light supplementation. Total photosynthetic photon flux density was kept constant in both conditions. Blue light enrichment resulted in significantly higher growth rates-of up to 77%-over a 3 to 4 week growing period, with all evidence indicating that the blue light effect was a stomatal response. Manipulations of stomatal properties aimed at long-term carbon gains could have agronomic applications.

Journal Article↗
PubMed1985

Direct Observation of Reversible and Irreversible Stomatal Responses of Attached Sunflower Leaves to SO(2).

The effects of SO(2) on stomatal aperture of attached sunflower leaves were observed with a remote-control light microscope system that permitted continuous observation of stomatal responses over periods of several hours. The relationship between actual stomatal aperture and stomatal conductance, measured with a porometer, also was examined on leaves before and after exposure to SO(2).A distinction between uninjured and injured regions was clearly visible on leaves after exposure to 1.5 microliters per liter SO(2) for less than an hour. During the exposure, the mean value of apertures for many stomata, which indicates stomatal conductance and transpiration rate, tended to decrease simultaneously in the uninjured and injured regions. However, the rate of decrease in the injured region was slower than that in the uninjured region because of a transient opening induced by water-soaking in the injured region. The transient opening was less common in stomata near veins and veinlets.There was a good correlation between pore width and stomatal conductance measured with a porometer before exposure to SO(2). This correlation continued in leaves exposed to SO(2) until visible, irreversible injury occurred, but then it disappeared.The results of these experiments indicate the necessity of continuous observation of individual stomata under the microscope to understand the effects of air pollutants such as SO(2) on stomatal behavior.

Journal Article↗
PubMed1986

Stomatal responses to light and leaf-air water vapor pressure difference show similar kinetics in sugarcane and soybean.

Stomatal responses to light and humidity (vapor pressure difference, VPD) are important determinants of stomatal conductance. Stomatal movements induced by light are the result of a transduction of the light stimulus into modulated ion fluxes in guard cells and concomitant osmotic adjustments and turgor changes. It is generally assumed that this transduction process is a general stomatal property, with different environmental stimuli integrated into guard cell metabolism through their modulation of ion fluxes. In contrast with this notion, the VPD response, which is unique because both its triggering signal and the turgor changes required for aperture modulations involve water molecules, has been considered to be hydropassive and thus independent of guard cell metabolism. We used a kinetic approach to compare the light and VPD responses in order to test the hypothesis that hydropassive changes in guard cell turgor could be faster than the metabolism-dependent light responses. Changes in stomatal conductance in intact leaves of sugarcane and soybean were measured after application of step changes in VPD and in light. In spite of a 5-fold difference in overall rates between the two species, the response rates following light or VPD steps were similar. Although a coincidental kinetic similarity between two mechanistically different responses cannot be ruled out, the data suggest a common mechanism controlling stomatal movements, with the VPD stimulus inducing metabolic modulations of ion fluxes analogous to other stomatal responses.

Journal Article↗
PubMed1990

Effects of cycloheximide on abscisic Acid biosynthesis and stomatal aperture in bean leaves.

Cycloheximide was shown to block abscisic acid (ABA) biosynthesis in nonstressed as well as in stressed Phaseolus vulgaris leaves. Leaf wilting caused by cycloheximide resulted from increased stomatal opening as judged by a decreased stomatal diffusion resistance. The inhibition of ABA biosynthesis by cycloheximide was at least partially responsible for the increase in stomatal opening as suggested by the cooccurrence of inhibition of ABA biosynthesis and increased stomatal opening, and the partial reversal of stomatal opening in cycloheximide-treated leaves by exogenous ABA. Dark treatment failed to close stomatal in cycloheximide-treated leaves, suggesting that stomatal closure in response to darkness may normally be mediated by ABA.

Journal Article↗
PubMed2004

B1-type cyclin-dependent kinases are essential for the formation of stomatal complexes in Arabidopsis thaliana.

Cyclin-dependent kinases (CDKs) are key regulators of the cell cycle. In yeasts, only one CDK is sufficient to drive cells through the cell cycle, whereas higher eukaryotes developed a family of related CDKs. Curiously, plants contain a unique class of CDKs (B-type CDKs), whose function is still unclear. We show that the CDKB1;1 gene of Arabidopsis (Arabidopsis thaliana) is highly expressed in guard cells and stomatal precursor cells of cotyledons, suggesting a prominent role for B-type CDKs in stomatal development. In accordance, transgenic Arabidopsis plants with reduced B-type CDK activity had a decreased stomatal index because of an early block of meristemoid division and inhibition of satellite meristemoid formation. Many aberrant stomatal cells were observed, all of them blocked in the G2 phase of the cell cycle. Although division of stomatal precursors was inhibited, cells still acquired stomatal identity, illustrating that stomatal cell differentiation is independent of cellular and nuclear division.

Arabidopsis↗
PubMed2004

Depolymerization of actin cytoskeleton is involved in stomatal closure-induced by extracellular calmodulin in Arabidopsis.

Extracellular calmodulin (CaM) plays significant roles in many physiological processes, but little is known about its mechanism of regulating stomatal movements. In this paper, whether CaM exists in the guard cell walls of Arabidopsis and whether depolymerization of actin cytoskeleton is involved in extracellular CaM-induced stomatal closing are investigated. It is found that CaM exists in guard cell walls of Arabidopsis, and its molecular weight is about 17 kD. Bioassay using CaM antagonists W7-agarose and anti-CaM serum shows that the endogenous extracellular CaM promotes stomatal closure and delays stomatal opening. The long radial actin filaments in guard cells undergo disruption in a time-dependent manner during exogenous CaM-induced stomatal closing. Pharmacological experiments show that depolymerization of actin cytoskeleton enhances the effect of exogenous CaM-induced stomatal closing and polymerization reduces the effect. We also find that exogenous CaM triggers an increase in [Ca2+]cyt of guard cells. If [Ca2+]cyt increase is blocked with EGTA, exogenous CaM-induced stomatal closure is inhibited. These results indicate that extracellular CaM causes elevation of [Ca2+]cyt in guard cells, subsequently resulting in disruption of actin filaments and finally leading to guard cells closure.

Actins↗
PubMed2001

Assessing the potential for the stomatal characters of extant and fossil Ginkgo leaves to signal atmospheric CO2 change.

The stomatal density and index of fossil Ginkgo leaves (Early Jurassic to Early Cretaceous) have been investigated to test whether these plant fossils provide evidence for CO(2)-rich atmosphere in the Mesozoic. We first assessed five sources of natural variation in the stomatal density and index of extant Gingko biloba leaves: (1) timing of leaf maturation, (2) young vs. fully developed leaves, (3) short shoots vs. long shoots, (4) position in the canopy, and (5) male vs. female trees. Our analysis indicated that some significant differences in leaf stomatal density and index were evident arising from these considerations. However, this variability was considerably less than the difference in leaf stomatal density and index between modern and fossil samples, with the stomatal index of four species of Mesozoic Ginkgo (G. coriacea, G. huttoni, G. yimaensis, and G. obrutschewii) 60-40% lower than the modern values recorded in this study for extant G. biloba. Calculated as stomatal ratios (the stomatal index of the fossil leaves relative to the modern value), the values generally tracked the CO(2) variations predicted by a long-term carbon cycle model confirming the utility of this plant group to provide a reasonable measure of ancient atmospheric CO(2) change.

Journal Article↗
PubMed2001

[Characteristics and quantitative simulation of stomatal conductance of Aneurolepidium chinense].

Based on field measurements of stomatal conductance and photosynthesis of Aneurolepidium chinense, the dynamic characteristics and the relationship between stomatal conductance and environmental conditions were examined to develop a leaf stomatal conductance model for A. chinense. The results showed that the variation of stomatal conductance of A. chinense was closely correlated with environmental factors, such as physiologically active radiation (PAR), vapor pressure deficit (VPD) and air temperature (Ta). The daily variation of A. chinense stomatal conductance could be described as M-type curve at fair-weather, but [symbol: see text]-type curve at cloudy weather. The value of stomatal conductance increased with the increase of PAR or Ta, but decreased with the increase of VPD. The relationship between stomatal conductance(gs) and environmental factors could be expressed as: gs = PAR(2.01 Ta2 + 147.74 Ta2321.11)/((444.62 + PAR)(-538.04 + VPD)). This model would be helpful to simulate the dynamical photosynthesis of leaf and canopy and to further simulate the NPP of ecosystems and the exchange of water and heat among the soil-plant-atmosphere continuum.

Computer Simulation↗
PubMed2002

Stomatal control in tomato with ABA-deficient roots: response of grafted plants to soil drying.

The hypothesis that ABA produced by roots in drying soil is responsible for stomatal closure was tested with grafted plants constructed from the ABA-deficient tomato mutants, sitiens and flacca and their near-isogenic wild-type parent. Three types of experiments were conducted. In the first type, reciprocal grafts were made between the wild type and sitiens or flacca. Stomatal conductance accorded with the genotype of the shoot, not the root. Stomates closed in all of the grafted plants in response to soil drying, regardless of the root genotype, i.e. regardless of the ability of the roots to produce ABA. In the second type of experiment, wild-type shoots were grafted onto a split-root system consisting of one wild-type root grafted to one mutant (flacca or sitiens) root. Water was withheld from one root system, while the other was watered well so that the shoots did not experience any decline in water potential or loss of turgor. Stomates closed to a similar extent when water was withheld from the mutant roots or the wild-type roots. In the third type of experiment, grafted plants with wild-type shoots and either wild-type or sitiens roots were established in pots that could be placed inside a pressure chamber, and the pressure increased as the soil dried so that the shoots remained fully turgid throughout. Stomates closed as the soil dried, regardless of whether the roots were wild type or sitiens. These experiments demonstrate that stomatal closure in response to soil drying can occur in the absence of leaf water deficit, and does not require ABA production by roots. A chemical signal from roots leading to a change in apoplastic ABA levels in leaves may be responsible for the stomatal closure.

Abscisic Acid↗
PubMed2004

[Nitric oxide, a signaling component of ABA-induced stomatal closure].

The present study provided the evidence that exogenous NO and ABA regulated the stomatal movement in poplar leaves. It showed that different levels of SNP and ABA induced the stomatal closure in detached leaves. NO enhanced stomatal closure that induced by ABA. The effect of NO and ABA on stomatal closure was suppressed by c-PTIO, a specific NO scavenger. It was confirmed that NO involved in ABA-mediated stomatal movement. The activities of POD were dramatically inhibited, but those of SOD hardly decreased in different levels of SNP and ABA treatment. However, in vitro experiments indicated that the activities of POD were dramatically inhibited by NO, but not ABA. The results demonstrated that NO mediated ABA-induced stomatal closure of trees, and was a signaling component of ABA-induced stomatal closure.

Abscisic Acid↗
PubMed1999

Identification of connexins in human oral mucosa and therapeutic effect of irsogladine maleate on aphthous stomatitis.

We identified connexins 26 and 32 in human oral mucosa. The presence of the connexins indicates the presence of gap junctions in this tissue. However, immunofluorescence study found no significant differences in the expression of the connexins between patients with aphthons stomatitis and controls. Irsogladine maleate, which reinforces gap junctional intercellular communication in vitro, was effective for the treatment of transient and relapsing aphthous stomatitis, as well as symptomatic and drug-induced aphthous stomatitis. It was also useful for prevention of episodes of relapsing aphthous stomatitis, with daily administration preverting recurrence of stomatitis for more than 4 years one patient. These findings suggest that irsogladine maleate accelerates the wound healing process in oral mucosa by reinforcing gap junctional intercellular communication among oral mucosal cells; and that it is useful for the treatment and prevention of aphthous stomatitis.

Adult↗
PubMed1996

Denture stomatitis: quantification of interleukin-2 production by mononuclear blood cells cultured with Candida albicans.

Denture stomatitis is usually associated with the presence of yeast, particularly Candida albicans, and several bacteria. In this study mononuclear blood cells were grown in the presence of Candida albicans from a single colony, and interleukin-2 production induced in T lymphocytes was measured. Blood cells were from a population of patients with denture stomatitis and a control group of denture wearers without stomatitis. Induction of interleukin-2 production was correlated with factors that condition denture stomatitis, namely, isolation of Candida albicans in selective medium, age of the denture, and diabetes. Concentrations of interleukin-2 in supernatant and serum were also compared. Significant differences in interleukin-2 production were found between patients with denture stomatitis and controls. Statistical analysis demonstrated a significant association between isolation of Candida albicans and elevated interleukin-2 production in cultures from patients with and without denture stomatitis.

Adult↗