Stomatal Aperture Size Research Articles

Acquired changes in stomatal characteristics in response to ozone during plant growth and leaf development of bush beans ( Phaseolus vulgaris L.) indicate phenotypic plasticity

Bush bean ( Phaseolus vulgaris L.) lines ‘ S156’ (O 3-sensitive)/‘ R123’ (O 3-tolerant) and cultivars ‘ BBL 290’ (O 3-sensitive)/‘ BBL 274’ (O 3-tolerant) were used to study the effects of O 3 on stomatal conductance ( g s), density, and aperture size on leaf and pod surfaces with the objective of establishing links between the degree of plant sensitivity to O 3 and plasticity of stomatal properties in response to O 3. Studies in open-top chambers (OTCs) and in continuously stirred tank reactors (CSTRs) established a clear relationship between plant developmental stages, degrees of O 3 sensitivity and g s: while ‘ S156’ had higher g s rates than ‘ R123’ earlier in development, similar differences between ‘ BBL 290’ and ‘ BBL 274’ were observed at later stages. G s rates on the abaxial leaf surfaces of ‘ S156’ and ‘ BBL 290’, accompanied by low leaf temperatures, were significantly higher than their O 3-tolerant counterparts. Exposure to O 3 in CSTRs had greater and more consistent impacts on both stomatal densities and aperture sizes of O 3-sensitive cultivars. Stomatal densities were highest on the abaxial leaf surfaces of ‘ S156’ and ‘ BBL 290’ at higher O 3 concentrations (60 ppb), but the largest aperture sizes were recorded on the adaxial leaf surfaces at moderate O 3 concentrations (30 ppb). Exposure to O 3 eliminated aperture size differences on the adaxial leaf surfaces between sensitive and tolerant cultivars. Regardless of sensitivity to O 3 and treatment regimes, the smallest aperture sizes and highest stomatal densities were found on the abaxial leaf surface. Our studies showed that O 3 has the potential to affect stomatal plasticity and confirmed the presence of different control mechanisms for stomatal development on each leaf surface. This appeared to be more evident in O 3-sensitive cultivars.

Transpiration rate. An important factor controlling the sucrose content of the guard cell apoplast of broad bean.

Evaporation of water from the guard cell wall concentrates apoplastic solutes. We hypothesize that this phenomenon provides two mechanisms for responding to high transpiration rates. First, apoplastic abscisic acid is concentrated in the guard cell wall. Second, by accumulating in the guard cell wall, apoplastic sucrose (Suc) provides a direct osmotic feedback to guard cells. As a means of testing this second hypothesized mechanism, the guard cell Suc contents at a higher transpiration rate (60% relative humidity [RH]) were compared with those at a lower transpiration rate (90% RH) in broad bean (Vicia faba), an apoplastic phloem loader. In control plants (constant 60% RH), the guard cell apoplast Suc content increased from 97 +/- 81 femtomol (fmol) guard cell pair(-1) to 701 +/- 142 fmol guard cell pair(-1) between daybreak and midday. This increase is equivalent to approximately 150 mM external, which is sufficient to decrease stomatal aperture size. In plants that were shifted to 90% RH before daybreak, the guard cell apoplast Suc content did not increase during the day. In accordance, in plants that were shifted to 90% RH at midday, the guard cell apoplast Suc content declined to the daybreak value. Under all conditions, the guard cell symplast Suc content increased during the photoperiod, but the guard cell symplast Suc content was higher (836 +/- 33 fmol guard cell pair(-1)) in plants that were shifted to 90% RH. These results indicate that a high transpiration rate may result in a high guard cell apoplast Suc concentration, which diminishes stomatal aperture size.

Cadmium-Induced Changes in Leaf Epidermes, Photosynthetic Rate and Pigment Concentrations in Cajanus Cajan

Application of different concentrations of cadmium [5, 10, 15, 25 and 50 μg(CdCl2) g−1(soil d.m.)] markedly affected leaves of Cajanus cajan (Linn.) Huth. Due to increased Cd content in leaves, stomatal density and size on abaxial epidermis, and the size of stomatal aperture and length and density of trichomes on both leaf epidermes decreased significantly in the treated plants. Net photosynthetic rate and stomatal conductance were reduced significantly at each concentration of cadmium, whereas reduction in intercellular carbon dioxide concentration was significant at 10 μg Cd onwards. The contents of chlorophyll a, chlorophyll b and carotenoids were relatively low during early stages of plant development under the effect of Cd. Nitrate content, nitrate reductase activity and protein content were also lower in treated plants, compared with control.

The guard‐cell apoplast as a site of abscisic acid accumulation in Vicia faba L.

ABSTRACTAbscisic acid (ABA) integrates the water status of a plant and causes stomatal closure. Physiological mechanisms remain poorly understood, however, because guard cells flanking stomata are small and contain only attomol quantities of ABA. Here, pooled extracts of dissected guard cells of Vicia faba L. were immunoassayed for ABA at sub‐fmol sensitivity. A pulse of water stress was imposed by submerging the roots in a solution of PEG. The water potentials of root and leaf declined during 20 min of water stress but recovered after stress relief. During stress, the ABA concentration in the root apoplast increased, but that in the leaf apoplast remained low. The ABA concentration in the guard‐cell apoplast increased during stress, providing evidence for intra‐leaf ABA redistribution and leaf apoplastic heterogeneity. Subsequently, the ABA concentration of the leaf apoplast increased, consistent with ABA import via the xylem. Throughout, the ABA contents of the guard‐cell apoplast, but not the guard‐cell symplast, were convincingly correlated with stomatal aperture size, identifying an external locus for ABA perception under these conditions. Apparently, ABA accumulates in the guard‐cell apoplast by evaporation from the guard‐cell wall, so the ABA signal in the xylem is amplified maximally at high transpiration rates. Thus, stomata will display apparently higher sensitivity to leaf apoplastic ABA if stomata are widely open in a relatively dry atmosphere.

Accumulation of an apoplastic solute in the guard‐cell wall is sufficient to exert a significant effect on transpiration in Vicia faba leaflets

ABSTRACTAccumulation of recently photosynthesized sucrose in the guard‐cell wall is the empirical foundation for a hypothesis that links the rates of photosynthesis, translocation, and transpiration (Plant Physiology 114, 109–118). Critical assumptions of this hypothesis were tested by use of Vicia faba, an apoplastic phloem loader. Following measurements of the leaflet‐apoplastic‐water volume (by P–V isotherm analysis) and the guard‐cell wall volume (by 3‐D analysis), intact leaflets were fed dilute solutions of mannitol, an impermeant non‐toxic osmolyte. Even at bulk‐leaflet mannitol concentrations that would have only a negligible osmotic effect on stomata, transpiration at constant temperature, water‐vapour pressure, air movement and irradiance was diminished up to 25%, compared with controls. This effect on transpiration, a manifestation of smaller stomatal aperture size, was explained by accumulation of mannitol, up to 350 mol m−3, in the estimated aqueous volume of the guard‐cell wall. The conclusion is that mannitol, a xenobiotic with structural similarity to sucrose, can move throughout the apoplast of a transpiring leaflet and accumulate in an osmotically significant concentration in the guard‐cell wall. These data therefore provide support for a new role for sucrose as a signal metabolite that integrates essential functions of the whole leaf. In addition, the results raise questions about the physiological or experimental accumulation of other guard‐cell‐targeted apoplastic solutes such as plant growth regulators, particularly abscisic acid, and ions.

Dynamic organization of microtubules in guard cells of Vicia faba L. with diurnal cycle.

Stomatal movement is regulated by changes in the volume of guard cells, thought to be mainly controlled by an osmo-regulatory system. In the present study, we examined the additional involvement of cytoskeletal events in the regulation of stomatal movement. Microtubules (MTs) in guard cells of Vicia faba L., grown under sunlight, were observed during the day and night by immunofluorescence microscopy. Cortical MTs began to be organized in a radial array at dawn and increased in numbers in the morning following the increase in the stomatal aperture size. Thereafter, MTs became localized near the nucleus and began to be destroyed from the evening to midnight, following the decrease in stomatal aperture size. These diurnal changes in MT organization were observed even two days after transfer from natural light condition to total darkness, and were accompanied by corresponding changes in stomatal aperture. The increase in stomatal aperture size in the early morning was inhibited by 50 microM propyzamide, which destroys cortical MTs in guard cells, whereas the decrease in aperture size in the evening was suppressed by 10 microM taxol, which stabilizes cortical MTs. These results suggest that radially-organized cortical MTs of guard cells may control diurnal stomatal movement.

A New Mechanism for the Regulation of Stomatal Aperture Size in Intact Leaves (Accumulation of Mesophyll-Derived Sucrose in the Guard-Cell Wall of Vicia faba).

At various times after pulse-labeling broad bean (Vicia faba L.) leaflets with 14CO2, whole-leaf pieces and rinsed epidermal peels were harvested and subsequently processed for histochemical analysis. Cells dissected from whole leaf retained apoplastic contents, whereas those from rinsed peels contained only symplastic contents. Sucrose (Suc)-specific radioactivity peaked (111 GBq mol-1) in palisade cells at 20 min. In contrast, the 14C content and Sucspecific radioactivity were very low in guard cells for 20 min, implying little CO2 incorporation; both then peaked at 40 min. The guard-cell apoplast had a high maximum Suc-specific radioactivity (204 GBq mol-1) and a high Suc influx rate (0.05 pmol stoma-1 min-1). These and other comparisons implied the presence of (a) multiple Suc pools in mesophyll cells, (b) a localized mesophyll-apoplast region that exchanges with phloem and stomata, and (c) mesophyll-derived Suc in guard-cell walls sufficient to diminish stomatal opening by approximately 3 [mu]m. Factors expected to enhance Suc accumulation in guard-cell walls are (a) high transpiration rate, which closes stomata, and (b) high apoplastic Suc concentration, which is elevated when mesophyll Suc efflux exceeds translocation. Therefore, multiple physiological factors are integrated in the attenuation of stomatal aperture size by this previously unrecognized mechanism.

Experimental and numerical analysis of stomatal absorption of sulphur dioxide and transpiration by pine needles

We present the experimental results of flow chamber measurements on SO 2 dry deposition, and of separate field measurements on transpiration of Scots pine ( Pinus sylvestris L) twigs under typical northerly summertime conditions. These results are interpreted by a numerical model, which solves the steady-state diffusion equation for a single stoma approximated to have cylindrical symmetry. An analytical method to estimate the maximal effect of interference (merging concentration fields of adjacent stomata) between stomatal pores is introduced. As a result, a functional pore radius is found to be of order of 2–3 μm, which is significantly smaller than the maximal anatomical size of stomatal aperture. This indicates that stomata are capable to transfer vapours to different degrees. If the obtained estimates for needle resistances are divided by a factor of 4, the leaf area index of local pine canopy, the bulk stomatal resistance for SO 2 is of the order of 200–300 s m −1.

Elevated Levels of Both Sucrose-Phosphate Synthase and Sucrose Synthase in Vicia Guard Cells Indicate Cell-Specific Carbohydrate Interconversions.

A long series of reports correlate larger stomatal aperture size with elevated concentration of sucrose (Suc) in guard cells. To assess the role and autonomy of guard cells with respect to these changes, we have determined quantitatively the cellular distribution of the synthetic enzyme, Suc-phosphate synthase (SPS) and the degradative enzyme Suc synthase (SS) in Vicia leaflet. As expected for Suc-exporting cells, the photosynthetic parenchyma had a high SPS:SS ratio of approximately 45. Also as expected, in epidermal cells, which had only few and rudimentary plastids, the SPS:SS ratio was low (0.4). Of all cells and tissues measured, those that had the highest specific activity of SPS (about 4.8 [mu]mol mg-1 of protein h-1) were guard cells. Guard cells also had a very high relative specific activity of SS.

Grass leaf stomata preparation techniques for scanning electron microscopy

Studies on gramineous stomatal characteristics, such as stomatal density and aperture size, relate these traits to ecological concerns, e.g. drought tolerance and production. Techniques for studying stomata have been utilized in the past using light microscopy. In a comparative study of stomatal apertures, it is imperative that guard cell closure not occur and die cells retain as closely as possible their natural state at the time of collection. Two species utilized in seeding roadsides and pastures, Dactylis glomerata L. and Elymus canadensis L., were processed with four different techniques for the scanning electron microscope. Abaxial and adaxial surfaces, respectively, were examined.Leaf tissue was harvested from clonal greenhouse-grown plants and separated into four groups. One was air dried under ambient conditions. The second group was placed into a standard fixative. Following fixation, the samples were dehydrated through a standard series of ethanol and critical point dried. The third group was prepared the same as group 2, except the leaves were transferred to tetramethylsilane for two ten minute exchanges following ethanol dehydration.

Potassium involvement not demonstrated in stomatal movements of Paphiopedilum. Qualified confirmation of the Nelson–Mayo report

Guard cells of Paphiopedilum leaves lack chlorophyll, a unique condition. Whether potassium fluxes are involved in stomatal movements is controversial. In attempting to resolve this controversy, we have dissected individual guard cell pairs from frozen-dried epidermal peels of three species. These samples were assayed for potassium using quantitative histochemical methodology. We were unable to detect a correlation between guard cell potassium content and stomatal aperture size. With certain reservations, these results indicate potassium is not the major osmoticum causing stomata of these species to open.

Localization of photosynthetic products in potato leaves infected by Phytophthora infestans

Potato leaflets infected with Phytophthora infestans (Mont.) de Bary were fed with 14C-labelled carbon dioxide, and the distribution of radioactive products of photosynthesis was examined. The products accumulated in relatively high concentration in the colonized tissue surrounding the necrotic regions. This accumulation resulted from the retention of assimilates at the infection site; in uninfected regions carbohydrates continued to be translocated to other parts of the plant. The rate of photosynthesis in infected tissue was generally higher than in uninfected parts of the same leaflets. It is suggested that photosynthesis in uninfected regions was limited by the size of stomatal apertures, whereas the permanently wide open stomata at the infection sites allowed photosynthesis to proceed at a higher rate. Movement of assimilate towards the infection site, as is known to occur in rust-infected leaves, appeared not to be a major factor in the accumulation process. It is concluded that translocatory “sinks”, comparable to those in rust-infected leaves, are not established as a result of infection by Phytopthora infestans. In making this comparison attention is drawn to the transient nature of a potato blight infection which contrasts with the relatively localized and long-lived infections caused by rust pathogens.

Stomatal Closure in Conifer Seedlings in Response to Leaf Moisture Stress

The water content of foliage and moisture stress of twigs associated with stomatal closure were determined for 3-year-old seedlings of ponderosa pine, lodgepole pine, grand fir, Douglas-fir, and Engelmann spruce. Stomatal behavior during increasing soil drought was interpreted from transpiration trends of potted seedlings kept under controlled conditions, and relative degree of stomatal opening was determined with a pressure infiltration technique. In grand fir and Douglas-fir, a decline in transpiration rate in response to drought was associated with a relatively small reduction in size of stomatal aperture as compared with the pines and spruce, indicating that mesophyll resistance may have been a significant factor limiting transpiration in the firs. At stomatal closure, or end of the transpiration decline, needle water contents ranged from 122.5% to 162.5% and were lowest in Engelmann spruce and Douglas-fir, intermediate in the pines, and highest in grand fir. Needle relative turgidities ranged from 81...

Plant injury by air pollutants: influence of humidity on stomatal apertures and plant response to ozone.

Ozone injury to Bel W3 tobacco and pinto bean plants increases with increasing humidity. The degree of plant injury sustained correlates well with porometer measurements; this indicates that the size of stomatal apertures increases with increasing humidity. Humidity may therefore influence plant response to all pollutants and may account in part for the greater sensitivity of plants to ozone-type injury in the eastern United States compared with the same species of plants grown in the Southwest. with those grown in the Southwest.

Hydrogen Cyanide Fumigation

1. Different concentrations of hydrocyanic acid gas gave effects ranging from stimulative to depressive. The maximum of beneficial results was secured from concentrations deadly to insect life, but just a little below the point of first injury to the plant. 2. External factors having important action on the resistance are as follows: (a) wetting the leaves had a beneficial effect on the tomato; (b) reduced temperature and low light intensity during the day preceding fumigation increased resistance. 3. Injury closely paralleled the stomatal movement, increasing as the size of stomatal aperture increased. 4. A higher or lower water supply in the soil affected resistance, through hastening or retarding the growth rate. Rapid growing plants were susceptible to injury, while slow growing plants were more resistant. 5. High reducing sugar content seemed to be correlated with maximum resistance.