Stomatal Responses to Two Herbicidal Auxins

The effects of 1-naphthylacetic acid (NAA) and 2-naphthoxyaceticacid (NOXA) on stomatal opening on illumination of excised,turgid leaves of Stachytarpheta indica were investigated bymicroscopic examination of abaxial epidermises fixed in absoluteethanol. Both chemicals were effective in restricting, but notcompletely preventing, stomatal opening and suppressing starchhydrolysis and potassium accumulation in the guard cells. Therepressive effects were only partly reversed by CO₂-free air.It is concluded that NAA and NOXA do not greatly affect passiveopening mediated by changes in the leaf water balance, but partlysupress photoactive opening by arresting starch hydrolysis andpotassium accumulation in the guard cells and partly by disturbingthe intercellular CO₂ concentration. A possible link betweenstarch hydrolysis and potassium accumulation in the guard cellsis briefly mentioned.     

Stomatal Responses to High Temperature in Darkness

The effect of a temperature increase from 25 to 35°C onstomatal opening in darkness (‘night opening’) onexcised, turgid leaves of Stachytarpheta indica was investigatedby microscopic examination of a baxial epidermis fixed in absoluteethanol. An appreciable degree of opening occurred towards theend of a 14-h night at 25°C, and this was substantiallyenhanced by the temperature increase to 35°C in the dark,which also promoted a marked increase in starch hydrolysis andaccumulation of potassium in the guard cells. The degree oftemperature-induced night opening was somewhat smaller thanthat of light-induced opening, and was higher in CO₂-free airthan in normal air. 2,4-dinitrophenol (DNP) was effective inarresting stomatal opening and suppressing starch hydrolysisand increase in stomatal potassium. The temperature-inducednight opening is related, to a great extent, to the enhancementby high temperature of starch hydrolysis and potassium accumulationin the guard cells, and the inhibitory effect of DNP on stomatalopening is attributed largely to its suppression of these twometabolic processes. The importance of oxidative phosphorylationas a possible source of energy for stomatal opening is brieflydiscussed.     

Stomatal Responses and the Senescence of Leaves

Guard cell responses were examined in green and senescing leavesof Victa faba using detached epidermal strips to eliminate influencesfrom the mesophyll. Stomatal opening was greater in epidermalstrips from mature leaves than from senescing leaves althoughthe latter still retained the ability to respond to CO₂ andto kinetin. It was concluded that the decline in stomatal activityduring senescence is an independent but parallel process tochanges occurring in the mesophyll. Vicia faba, leaf senescence, stomata, kinetin     

Stomatal Responses to Sulphur Dioxide and Vapour Pressure Deficit

Stomatal conductances (g_s) of plants of Vicia faba, Raphanussativus, Phaseolus vulgaris, Heilanthus annuus, and Nicotianatabacum were measured in chambers containing either clean airor air containing between 18 and 1000 parts 10^–9 SO₂ atwater vapour pressure deficits (vpd) ranging from 1·0to 1·8 kPa. When vpd was low (<1·3 kPa at 22 °C) and stomatawere open, exposure to SO₂ induced rapid and irreversible increasesin g_s in V. faba. This response persisted throughout the exposure(3 d). The increase in g_s, 20–30% compared with cleanair, was independent of SO₂ concentration up to 350 parts 10^–9Stomatal conductances of polluted plants at night were greaterthan controls. When stomata were closed before exposure to SO₂,there was no effect on g_s. When vpd was varied, g_s of unpolluted plants of P. vulgarisshowed no response, but that of R. sativus increased slightlywith increasing vpd. In both species exposure to SO₂ causedan increase in g_s at all vpd values. g_s of unpolluted plantsof V. faba, H. annuus, and N. tabacum decreased with increasingvpd. At low vpd values exposure to SO₂ in these species causedan increase in g_s, but, above a certain value of vpd, dependingon species, g_s decreased with exposure to SO₂. It is postulated that SO₂, once in the substomatal cavity, entersthe stomatal complex via adjacent epidermal cells and at lowconcentrations leads to a reduction in turgor in these cellsand consequently to stomatal opening. In vpd-sensitive species,increased transpiration from guard cells or epidermal cellsadjacent to the stomata induced by SO₂ may lead to stomatalclosure at large vpd levels. Stomatal sensitivity to vpd insuch cases may be enhanced because adjacent epidermal cell turgoris lowered by SO₂. At high SO₂ concentrations direct disruptionof guard cell structure may lead to a loss of turgor and stomatalclosure.     

一个气孔对环境因子响应的机理性教学模型

本文在已知的气孔运动机理的基础上,对现有的教学模型加以改进,建立了除ＶＰＤ、ＣＯ２和土壤水势的影响外,还能模拟光照和温度等因子对气孔影响的数学模型。在不同组合的环境因子下模拟得到的结果与公认的实验观测结果基本一致。它可以作为研究气孔整体行为的理论框架,也可用于检验多种关于气孔运动的假设。     

The Responses of Stomatal Density to CO2 Partial Pressure

Experiments on a range of species of tree, shrub and herb haveshown that stomatal density and stomatal index increase as thepartial pressure of CO₂ decreases over the range from the currentlevel of 34 Pa to 22.5 Pa. Stomatal density responds to thereduced partial pressure of CO₂ in a simulation of high altitude(3000 m), when the CO₂ mole fraction is unchanged. When the partial pressure of CO₂ is increased from 35 to 70Pa stomatal density decreases slightly, with a response to unitchange in CO₂ which is about 10% of that below 34 Pa. Measurements of gas exchange on leaves which had developed indifferent CO₂ partial pressures, but at low saturation vapourpressure deficits in the range of 0.7 to 0.9 kPa, indicatedlower photosynthetic rates but higher stomatal conductancesat reduced CO₂ partial pressures. Experiments on populations of Nardus stricta originating fromaltitudes of 366 m and 810 m in Scotland, indicated geneticdifferences in the responses of stomatal density to CO₂ in pressuressimulating altitudes of sea level and 2 000 m. Plants from thehigher altitude showed greater declines in stomatal densitywhen the CO₂ partial pressure was increased. Key words: Stomata, CO₂, gas exchange, altitude, atmospheric pressure     

Acute Effects of Pathogenic Simian-Human Immunodeficiency Virus Challenge on Vaccine-Induced Cellular and Humoral Immune Responses to Gag in Rhesus Macaques

Simian-human immunodeficiency virus (SHIV) infection in macaques provides a convenient model for testing vaccine efficacy and for understanding viral pathogenesis in AIDS. We immunized macaques with recombinant, Salmonella typhimurium (expressing Gag) or soluble Gag in adjuvant to generate T-cell-dependent lymphoproliferative or serum antibody responses. Immunized animals were challenged by intrarectal inoculation with SHIV89.6PD. Virus infection was accompanied by rapid losses of lymphoproliferative responses to Gag or phytohemagglutinin. By 8 weeks, mitogen responses recovered to near normal levels but antigen-specific immunity remained at low or undetectable levels. Serum antibody levels were elevated initially by virus exposure but soon dropped well below levels achieved by immunization. Our studies show a rapid depletion of preexisting Gag-specific CD4⁺ T cells that prevent or limit subsequent antiviral cellular and humoral immune responses during acute SHIV infection.     

Stomatal Responses to Humidity and the Water Potentials of Epidermal and Mesophyll Tissue

Effects of ambient humidity on relative water contents (RWC)and water potentials were measured separately for epidermaland mesophyll tissues in leaves of two species. Water potentialsdid not always change in the same direction as RWC within thesame tissue and rarely were the changes in water potential andRWC of one tissue correlated with those of the other. The natureof the humidity responses of stomata in certain species is discussedin relation to these results and to the anatomical propertiesof epidermal tissues.     

The Measurement of Stomatal Responses to Stimuli in Leaves and Leaf Discs

A comparison has been made of stomatal responses in intact leaves,leaf discs supplied with water via their cut edges and leafdiscs floating on water. Xanthium pennsylvanicum leaf discswatered via their cut edges appeared to be more turgid thanintact leaves; this considerably slowed down the rate of stomatalopening but it slightly increased the final steady-state stomatalopening. When the water potential of such leaf discs was loweredby pre-treatment with mannitol solutions rates of stomatal openingincreased whereas maximum steady-state openings decreased. In tobacco leaf discs floating on water the stomata in contactwith water were wider open than those in contact with normalair and they did not respond to treatment with carbon dioxide-freeair. The rate of photosynthesis was severely reduced in tobaccoleaf discs floating with the lower epidermis on water, mostprobably owing to the slow rate of diffusion of carbon dioxidein water. By floating such discs on osmotica the degree of stomatalopening was increased, however, a response to treatment withcarbon dioxide-free air was still not measurable. It is postulatedthat, on account of the relative unavailability of carbon dioxidefrom the water, the carbon dioxide concentration in the substomatalcavities of the lower surface is abnormally low, irrespectiveof whether ordinary air or carbon dioxide-free air is availableto the upper surface. A comparison between porometer readings and measurements ofsiliconerubber impressions of stomatal pores taken from insidethe porometer cup confirmed that the silicone-rubber impressionmethod of assessing stomatal responses to stimuli has severelimitations, especially at small stomatal apertures.     

Natural Variation in Stomatal Responses to Environmental Changes among Arabidopsis thaliana Ecotypes

Stomata are small pores surrounded by guard cells that regulate gas exchange between plants and the atmosphere. Guard cells integrate multiple environmental signals and control the aperture width to ensure appropriate stomatal function for plant survival. Leaf temperature can be used as an indirect indicator of stomatal conductance to environmental signals. In this study, leaf thermal imaging of 374 Arabidopsis ecotypes was performed to assess their stomatal responses to changes in environmental CO2 concentrations. We identified three ecotypes, Köln (Kl-4), Gabelstein (Ga-0), and Chisdra (Chi-1), that have particularly low responsiveness to changes in CO2 concentrations. We next investigated stomatal responses to other environmental signals in these selected ecotypes, with Col-0 as the reference. The stomatal responses to light were also reduced in the three selected ecotypes when compared with Col-0. In contrast, their stomatal responses to changes in humidity were similar to those of Col-0. Of note, the responses to abscisic acid, a plant hormone involved in the adaptation of plants to reduced water availability, were not entirely consistent with the responses to humidity. This study demonstrates that the stomatal responses to CO2 and light share closely associated signaling mechanisms that are not generally correlated with humidity signaling pathways in these ecotypes. The results might reflect differences between ecotypes in intrinsic response mechanisms to environmental signals.     

Stomatal Responses of Woody Seedlings to Flooding in Relation to Nutrient Status in Leaves

Ten-week-old woody seedlings of Gmelina arborea Roxb., Tectonagrandis L. (De Wild. & Th. Dur.) Merrill, and Nauclea diderrichiif., were subjected to 10 weeks flooding and a 5-week-long post-floodingperiod. Flooding induced the development of hypertrophied lenticels,adventitious roots, and root aerenchyma in Gmelina and Tectona,while it did not in Nauclea. All three species responded toflooding by first closing their stomata and reopening at differenttimes during the flooding period. The time and extent of reopeningwere earliest and greatest in Gmelina, followed by Tectona,and latest and smallest in Nauclea. Differences in stomatalconductance at the end of the flooding period paralleled theconcentrations of ethanol in roots and inorganic nutrients inleaves. After flooding was discontinued, stomatal conductanceincreased in Gmelina, but did not in the other species. Leafwater potentials and transpiration rates of flooded Gmelinaand Tectona plants were higher at week 8 than at week 2 whilethe reverse was the case in Nauclea. It is argued that whilepersistently small stomatal apertures during the post-floodingperiod in Nauclea may be a strategy to slow down the movementof accumulated toxic substances from the soil, the higher leafwater potential and transpiration in Gmelina and Tectona atweek 8 than at week 2 may represent recovery of shoot waterrelations resulting from adventitious roots development. Key words: Flooding, stomatal conductance, transpiration, adventitious roots, ethanol     

Short- and Long-term Stomatal Responses to Fluctuations in Environment in Southern European Greenhouses

Stomatal behaviour in cucumber (Cucumis sativus L.) was analysed and modelled as a function of different greenhouse environmental parameters, under variable summer conditions. Solar radiation was the main regulating factor. During the day, large atmospheric vapour pressure deficit increased transpiration which was followed by a reduction in stomatal aperture, suggesting the presence of a feedback response to water stress. However, stomatal behaviour was more sensitive to high atmospheric vapour pressure deficit when this was accompanied by a rapid decrease of solar radiation. The response to the difference between leaf and air temperature was also influenced by air vapour pressure deficit and duration of plant exposure to high evaporative demand. Calculation of the crop water stress index showed that the air vapour pressure deficit of 1 kPa used in the control treatment probably caused water stress and induced some hardening, a necessary condition for adaptation to summer climate in southern Europe. The importance of the interaction between climatic parameters and plant response in greenhouse environmental management is analysed. Classical models of stomatal resistance are also discussed.     

Stomatal Responses to CO(2) in Paphiopedilum and Phragmipedium: Role of the Guard Cell Chloroplast

A role of the guard cell chloroplasts in the CO₂ response of stomata was investigated through a comparison of the leaf gas exchange characteristics of two closely related orchids: Paphiopedilum harrisianum, which lacks guard cell chloroplasts and Phragmipedium longifolium, which has chlorophyllous guard cells. Leaves of both species had an apparent quantum yield for assimilation of about 0.05, with photosynthesis saturating at 0.300 to 0.400 millimoles per square meter per second. CO₂ curves were obtained by measuring steady-state assimilation and stomatal conductance under 0.180 or 0.053 millimoles per square meter per second white light, or darkness, at 0 to 400 microliters per liter ambient CO₂. The response of assimilation to changes in CO₂ was similar in the two species, but the response of conductance was consistently weaker in Paphiopedilum than in Phragmipedium. The data suggest involvement of guard cell chloroplasts in the stomatal response to CO₂ and in the coupling of assimilation and conductance in the intact leaf.     

Stomatal Responses to Light and Drought Stress in Variegated Leaves of Hedera helix

Direct and indirect mechanisms underlying the light response of stomata were studied in variegated leaves of the juvenile phase of Hedera helix L. Dose response curves of leaf conductance were measured with blue and red light in leaves kept in normal or in an inverted position. In the green portions of the leaves, the sensitivity to blue light was nearly 100 times higher than that to red light. No response to red light was observed in the white portions of the leaves up to 90 micromoles per square meter per second. Red light indirectly affected leaf conductance while blue light had a direct effect. Leaf conductance was found to be more sensitive to drought stress and showed a more persistent aftereffect in the white portions of the leaves. A differential effect of drought stress on the responses to blue and red light was also observed.     

Stomatal Responses of Phaseolus vulgaris L. Seedlings to Potassium Chloride in the Nutrient Solution

Alteration in KNO₃ and KCl levels of culture solutions resultedin the production of a series of Phaseolus vulgaris seedlingscontaining a range of chloride levels in the primary leaves;such treatments did not affect leaf potassium content. Irrespectiveof the leaf chloride content the stomata responded to increasedlight intensity by a decrease in stomatal resistance. The stomataof seedlings grown in culture solutions containing KCI offeredhigher diffusive resistances than those of seedlings not receivingthis treatment. This increase in stomatal resistance was foundover the whole range of elevated leaf chloride contents produced.Presence of chloride in the leaf tissue did not, however, affectstomatal responses to fluctuations in atmospheric CO₂ concentration.     

Allergic Non-Asthmatic Adults Have Regional Pulmonary Responses to Segmental Allergen Challenge

Background

Allergic non-asthmatic (ANA) adults experience upper airway symptoms of allergic disease such as rhinorrhea, congestion and sneezing without symptoms of asthma. The aim of this study was to utilize PET-CT functional imaging to determine whether allergen challenge elicits a pulmonary response in ANA subjects or whether their allergic disease is truly isolated to the upper airways.

Methods

In 6 ANA subjects, bronchoalveolar lavages (BAL) were performed at baseline and 24h after instillation of an allergen and a diluent in separate lung lobes. After instillation (10h), functional imaging was performed to quantify and compare regional perfusion, ventilation, fractional gas content (Fgas), and glucose uptake rate (Ki) between the baseline, diluent and allergen lobes. BAL cell counts were also compared.

Results

In ANA subjects, compared to the baseline and diluent lobes, perfusion and ventilation were significantly lower in the allergen lobe (median [inter-quartile range], baseline vs. diluent vs. allergen: Mean-normalized perfusion; 0.87 [0.85–0.97] vs. 0.90 [0.86–0.98] vs. 0.59 [0.55–0.67]; p<0.05. Mean-normalized ventilation 0.89 [0.88–0.98] vs. 0.95 [0.89–1.02] vs. 0.63 [0.52–0.67], p<0.05). In contrast, no significant differences were found in Fgas between baseline, diluent and allergen lobes or in Ki. Total cell counts, eosinophil and neutrophil cell counts (cells/ml BAL) were significantly greater in the allergen lobe compared to the baseline lobe (all P<0.05).

Conclusions

Despite having no clinical symptoms of a lower airway allergic response (cough and wheeze) allergic non-asthmatic subjects have a pulmonary response to allergen exposure which manifests as reduced ventilation and perfusion.     

Photosynthetic and Stomatal Responses of the Grey Mangrove, Avicennia marina, to Transient Salinity Conditions

Measurements of gas exchange characteristics were made on intact, attached leaves of hydroponically grown seedlings of Avicennia marina (Forstk.) Vierh. var australasica (Walp.) Moldenke as the NaCl concentration of the culture solution was varied by step changes of 50 millimolar NaCl every 2nd day from 50 to 500 to 50 millimolar NaCl. The CO₂ assimilation rate, stomatal conductance, intercellular CO₂ concentration, and evaporation rate decreased at salinities above 250 millimolar NaCl and recovered substantially upon return to the original salinity.

The assimilation rate was measured as a function of the intercellular CO₂ concentration [A(c_i) curve]. The lower linear portion of this curve was insensitive to variation in salinity, whereas the upper nonlinear portion declined with increasing salinity, indicating a reduction in the capacity for CO₂ assimilation which recovered upon return to the original salinity. Stomatal conductance changed such that the intercellular CO₂ concentration measured under normal atmospheric conditions occurred in the transition between the lower, linear and upper nonlinear portions of the A(c_i) curve. Thus, stomatal conductance and photosynthetic capacity together co-limited the assimilation rate. The changes in gas exchange characteristics were such that water loss was minimal relative to carbon gain.

     

Stomatal Responses of Tradescantia albiflora to Changing Air Humidity in Light and in Darkness

Tradescantia albiflora has green variegated and white leaves.Its stomatal apparatus consists of the guard cells and two pairsof subsidiary cells. Investigations were carried out by observingthe stomata microscopically by means of a video system in situin a CO₂ exchange chamber and by simultaneously measuring thegas exchange of the leaves. In response to air humidity changes,stomatal movements in T. albiflora begin, owing to turgor changes,in the polar and lateral subsidiary cells. The stomatal responseof green leaves to changes of air humidity showed typical transientand oscillatory phases prior to steady-state reactions. In darkness,stomata closed when air humidity decreased; however, they didnot reopen when air humidity was raised again. Stomata of illuminatedwhite leaves responded like those of green leaves in darkness.With increasing soil water stress stomata responded to changingair humidity with reductions of the transient phases and a decreasingtendency to reopen when air humidity became high again. CO₂deficiency of the air caused the stomata to open in the dark,and interacted with the air humidity effect in such a way thatstomata of green leaves responded to air humidity changes indarkness in a similar way as they did in light. Key words: Stomata, humidity response, green and white leaf areas, CO₂ deficient air