Stomatal Aperture Width Research Articles

Simulated microgravity facilitates stomatal ingression by Salmonella in lettuce and suppresses a biocontrol agent

As human spaceflight increases in duration, cultivation of crops in spaceflight is crucial to protecting human health under microgravity and elevated oxidative stress. Foodborne pathogens (e.g., Salmonella enterica) carried by leafy green vegetables are a significant cause of human disease. Our previous work showed that Salmonella enterica serovar Typhimurium suppresses defensive closure of foliar stomata in lettuce (Lactuca sativa L.) to ingress interior tissues of leaves. While there are no reported occurrences of foodborne disease in spaceflight to date, known foodborne pathogens persist aboard the International Space Station and space-grown lettuce has been colonized by a diverse microbiome including bacterial genera known to contain human pathogens. Interactions between leafy green vegetables and human bacterial pathogens under microgravity conditions present in spaceflight are unknown. Additionally, stomatal dynamics under microgravity conditions need further elucidation. Here, we employ a slow-rotating 2-D clinostat to simulate microgravity upon in-vitro lettuce plants following a foliar inoculation with S. enterica Typhimurium and use confocal microscopy to measure stomatal width in fixed leaf tissue. Our results reveal significant differences in average stomatal aperture width between an unrotated vertical control, plants rotated at 2 revolutions per minute (2 RPM), and 4 RPM, with and without the presence of S. typhimurium. Interestingly, we found stomatal aperture width in the presence of S. typhimurium to be increased under rotation as compared to unrotated inoculated plants. Using confocal Z-stacking, we observed greater average depth of stomatal ingression by S. typhimurium in lettuce under rotation at 4 RPM compared to unrotated and inoculated plants, along with greater in planta populations of S. typhimurium in lettuce rotated at 4 RPM using serial dilution plating of homogenized surface sterilized leaves. Given these findings, we tested the ability of the plant growth-promoting rhizobacteria (PGPR) Bacillus subtilis strain UD1022 to transiently restrict stomatal apertures of lettuce both alone and co-inoculated with S. typhimurium under rotated and unrotated conditions as a means of potentially reducing stomatal ingression by S. typhimurium under simulated microgravity. Surprisingly, rotation at 4 RPM strongly inhibited the ability of UD1022 alone to restrict stomatal apertures and attenuated its efficacy as a biocontrol following co-inoculation with S. typhimurium. Our results highlight potential spaceflight food safety issues unique to production of crops in microgravity conditions and suggest microgravity may dramatically reduce the ability of PGPRs to restrict stomatal apertures.

Epibrassinolide application improves Brassica juncea L. performance by augmenting gas exchange markers, stomatal behavior, cellular viability, enzymatic activities and yield attributes

Epibrassinolide (EBL) is an emerging plant growth regulator of the brassinosteroids group that has the potential to modulate various morpho-physiological processes in plants. Therefore, due to its key role in boosting plant functioning mechanisms, it is widely used in agriculture to enhance crop growth and yield. The present research work was planned to investigate the role of exogenously applied EBL on the mustard crop by assessing morphological, physiochemical, and yield features. This randomized pot experiment contains three mustard cultivars i.e., Rohini (Roh), Chutki (Chk), and Nath Sona (Nas) and various graded levels of EBL, 0 (Control), 10−8 M, 10−7 M, 10−6 M, 10−5 M, and 10−4 M. EBL was applied twice by giving first spray at 50 days after sowing (DAS) and the second at 70 DAS. Evaluation of plants was done at 90 DAS to study phenological traits, gas exchange attributes, non-enzymatic antioxidant activities, and microscopical parameters. The yield and quality features were studied at 120 DAS. The results revealed that treatment of 10−6 M EBL proved effective and increased fresh weight by 17.76 %, 19.11 %, and 19.34 %, chlorophyll content by 26.50 %, 26.59 %, and 25.86 %, net photosynthetic rate by 45.67 %, 57.88 % and 49.76 %, protein content by 66.98 %, 68.62 % and 69.47 %, proline content by 25.70 %, 24.05 % and 21.87 %, ascorbate content by 94.91 %, 89.99 % and 87.43 %, carbonic anhydrase activity by 32.43 %, 30.84 % and 29.93 %, seed yield by 44.85 %, 51.36 %, and 57 % and oil yield by 68.75 %, 72.71 % and 74.34 % in cultivars Nas, Roh, and Chk respectively over the control plants. Moreover, 10−6 M EBL supplementation significantly improved stomatal aperture width and root cell longevity. Cultivar Nas, followed by cultivars Roh and Chk, showed better responses on nearly all characters studied. The effect of EBL treatment in terms of enhancing the performance of the crop being in the order of 10−6 M > 10−7 M > 10−8 M > 10−5 M > 10−4 M. It may be concluded that among sprayed EBL levels, two sprays of 10−6 M EBL proved efficacious in improving the phenotypic, physiochemical, and yield traits of mustard cultivars.

Increasing the growth and yield of shallot (Allium cepa L. Aggregatum group) by using Methyl Jasmonic Acid (MeJA) concentrations under drought condition

Drought is one of the limiting factors for plant production, and there is a continuous demand for drought tolerant plants. Shallots are considered a shallow-rooted crop and have been reported to have little tolerance to drought conditions. One of the efforts to increase plant tolerance to drought conditions is through the addition of Methyl Jasmonic Acid (MeJA). MeJA is involved in several physiological and biochemical procedures in plant growth and development. Application of MeJA can increase the plant tolerance to drought conditions through chlorophyll synthesis, stomatal conductivity, transpiration, net photosynthetic rate and biomass production. This research was conducted in a complete randomized block design with three replications to determine the response of shallot plants to the application of MeJA (0 µM, 25 µM, 50 µM and 100 µM) under drought conditions, which was simulated through the frequency of watering (once daily, every other day, once in three days). Soil water content calculated before the watering treatment was 24.45%, 20.34% and 18.45% for watering once daily, every other day, once in three days, respectively. The results showed that the addition of MeJA played a role in enhancing the growth and productivity of shallot plants under normal and drought conditions. Application of 50 µM of MeJA could increase the Water Use Efficiency, maintain the Relative Water Content, increase the width of stomatal aperture, and increase the leaf area and Leaf Area Index. This also led to increasing Net Assimilation Rate and Plant Growth Rate. Application of 50 µM of MeJA gave in increasing bulb productivity and reached 7.86 ton.ha-1, which was 58.2 % higher than that of in control (without MeJA application). Application of MeJA to shallot plants exhibited avoiding type of physiological tolerance.

Controlling stomatal aperture, a potential strategy for managing plant bacterial disease

Bacterial blight of crucifers caused by Pseudomonas cannabina pv. alisalensis (Pcal) inflicts great damage on crucifer production. To explore efficient and sustainable strategies for Pcal disease control, we here investigated and screened for amino acids with reduced disease development. We found that exogenous foliar application with multiple amino acids reduced disease symptoms and bacterial populations in cabbage after spray-inoculation, but not syringe-inoculation. These results indicate that these amino acids showed a protective effect before Pcal entered plants. Therefore, we observed stomatal responses, which is a main gateway for Pcal entry into the apoplast, after amino acid treatments. As a results, we found several amino acids induce stomatal closure. Moreover, our findings demonstrated that reducing stomatal aperture width can limit bacterial entry into plants, leading to reduced disease symptoms. Indeed, Cys, Glu, and Lys, which showed a protective effect on cabbage, reduced stomatal aperture width and bacterial entry. Therefore, managing stomatal aperture can be a powerful strategy for controlling bacterial disease.

ABA-mediated regulation of stomatal density is OST1-independent.

Stomata, small pores on the surfaces of leaves formed by a pair of guard cells, adapt rapidly to changes in the environment by adjusting the aperture width. As a long‐term response, the number of stomata is regulated during stomatal development. The hormone abscisic acid (ABA) regulates both processes. In ABA mediated guard cell signaling the protein kinase OPEN STOMATA1 (OST1) has a central role, as stomatal closure in the ost1 mutant is impaired in response to ABA and to different environmental stimuli. We aimed to dissect the contribution of different ABA‐related regulatory mechanisms in determining stomatal conductance, a combination of stomatal density and aperture width, and crossed the ost1 mutant with mutants that either decreased (aba3) or increased (cyp707a1/a3) the concentration of ABA in plants. The double mutant ost1 aba3 had higher stomatal conductance than either parent due to a combination of increased stomatal aperture width and higher stomatal density. In the triple mutant ost1 cyp707a1/a3, stomatal conductance was significantly lower compared to ost1‐3 due to lower stomatal density. Further characterization of the single, double and triple mutants showed that responses to treatments that lead to stomatal closure were impaired in ost1 as well as ost1 aba3 and ost1 cyp707a1/a3 mutants, supporting a critical role for OST1 in stomatal aperture regulation. On the basis of our results, we suggest that two signaling pathways regulate water flux from leaves, that is, stomatal conductance: an ABA‐dependent pathway that determines stomatal density independent of OST1; and an OST1‐dependent pathway that regulates rapid changes in stomatal aperture.

The Tolerance of Photosynthesis of Some Maize Cultivars (Zea mays L.) to Waterlogging at Different Stages of Growth

The tolerance of plants to waterlogging can be ascertained by identifying the characteristics of morphology, anatomy, and physiology of plants. As yet little is known about the photosynthetic characteristics of many cultivars of maize in Indonesia when waterlogged at various stages of growth. This research aimed to determine the photosynthesis tolerance of some maize cultivars to inundation that occurred at different stages of growth. The factorial completely randomized block design with two factors and three replications was used. The first factor consisted of nine maize cultivars, i.e. Bisi 2, Pioneer 21, Gumarang, Bisma, Sukmaraga, Srikandi Kuning 1, Bima 2, Bima 4, and Bima 5. The second was waterlogged conditions at different stages of growth i.e. the vegetative phase (leaved-four stage- – V4 stage), the early phase of reproduction (silk phase - R1 stage), and the middle phase of reproduction (milk stage - R3 stage), and no waterlogging as the control. During the period of waterlogging, the water level of 5 cm was maintained for 10 days. The results showed that no interaction effect between maize cultivars and waterlogging conditions to almost all photosynthesis variable except stomatal aperture. Ten days of waterlogging at different stages of growth affected photosynthesis by decreasing the chlorophyll content (a, b and total), photosynthetic rate, and the stomatal aperture width. The R1 stage was the stage of growth sensitive to photosynthesis when waterlogged. Bisma cultivar was the maize cultivar that was not tolerant to waterlogging stress at the V4 stage and Gumarang was not tolerant at the R3 stage. It showed a low rate of photosynthesis. At the R1 stage, Bima 5 and Bima 2 cultivars were the maize cultivars that were tolerant to waterlogging stress, while at the R3 stage all cultivars were tolerant except Gumarang was not. Therefore Bima 5 and Bima 2 cultivars can be recommended to be planted in the swampy areas.

Potential of Corn as Forage on Alfisol and Vertisol Soil in Agrosilvopastural System with Kayuputih (Melaleuca leucadendron Linn)

This research was aimed to know the morphologic and physiologic characteristics and corn plant production as forage on alfisol and vertisol soil at Kayuputih intercropping system. Supporting forage supply is one of goals in forest for food/feed program, and it significantly showed at Kayuputih (Melaleuca leucadendron Linn) intercropping system. Kayuputih intercropping system of corn was planted particularly at the 3rd rotation (May-July). The research performed by a strip plot design, soil type was the main plot, and the interface zone (IZ) was the secondary plot. Interface zone was 1 m (IZ-1), 2 m (IZ-2), and 3 m (IZ-3) distance from the Kayuputih plantation row. Growth and physiologic data was analyzed using Bartlette to obtain data homogenity, followed by analysis of variance and DMRT at 5% degree of confidence, data transformation was performed when needed. Contrast orthogonal (5%) test was used to do the grouping based on soil type. Biplot technique as a development from the multivariate technique was performed to determine the stability of IZ treatment toward result. Forage potency on alfisol was higher (5.04 ton/ha) than on vertisol (4.04 ton/ha). Interaction between the IZ and soil type was found at several variables: number of stomata, stomatal aperture width, proline content, plant growth rate on 3-6 wap, net assimilation rate on 3-6 wap, fresh root weight on 3 wap, root dry weight on 3 wap, fresh canopy weight on 6 wap and canopy dry weight on 6 wap. The highest level of corn forage production was IZ-3 on alfisol soil (1.26 ton/ha) and the lowest production was IZ-1 on vertisol soil (0.73 ton/ha).

Physiological Responses of Oil Palm Seedlings to the Drought Stress Using Boron and Silicon Applications

A B S T R A C T The objectives of the study were to determine (1) The level of physiological resistance of oil palm seedlings to drought stress by boron (B) and silicon (Si) application and (2) The mechanism of B and Si actions to induce physiological resistance of oil palm seedlings to drought stress. The B and Si were the elements capably inducing the internal resistance of plant tissues to drought stress, especially through physiological resistance mechanisms. Field trial was arranged in the factorial Randomized Complete Block Design (RCBD) using three blocks as replications. The first factor was six dose of B: 0.00, 0.17, 0.44, 0.87 and 1.31 g plantG 1 . The second factor was five dose of Si: 0.00, 1.15, 2.31, 3.46 and 4.69 g plantG 1 . Observations were done on the Nitrate Reductase Activity (NRA), the content of chlorophyll a, b and total, density, length and width of stomatal aperture, stomatal conductance and transpiration rate, photosynthetic rate and photosynthetic activity per plant, dry weight of plant parts and trunk height and diameter of the oil palm seedlings. The data were analyzed using ANOVA and the means were separated using Duncan's multiple range test at 5% level. Meanwhile, the optimum dose of B and Si were determined using regression analysis. The results showed that B and Si application could induce physiological resistance of oil palm seedlings to drought stress. Mechanism of action of B in inducing physiological resistance of oil palm seedlings to drought stress were by increasing of greenish leaves, width of stomatal aperture and photosynthetic activity per plant while Si application capable to increase of greenish leaves and to decrease the density of lower leaf surface stomatal. The optimal dose of B was 0.33-0.57 g/seedlings and the optimal dose of Si was 2.22 g/seedling in inducing physiological resistance of oil palm seedlings to drought stress.

Phenotypic plasticity of European beech (Fagus sylvatica L.) stomatal features under water deficit assessed in provenance trial

The results of research into leaf stomatal variability of five European beech provenances origi - nating from Austria, Bosnia and Hercegovina, Germany, Romania and Serbia are presented in this paper. Aim of the study was to investigate how stomatal traits of provenances originating from different environ- ments change in response to drought stress and to assess the phenotypic plasticity of the stomatal features investigated. The study was conducted during two different years, characterized by contrasting weather conditions (2010 and 2011). Two-way ANOVA revealed that provenances differ significantly in terms of stomatal density (SD), width of stomatal aperture (W b ), potential conductance index (PCI) and relative sto- matal pore surface (RSPS), during both seasons. In a dry year (2011) all provenances significantly increased stomatal density by between 16.1% (Hasbruch - DE) and 21.9% (Cer - SRB). Guard cell length (L A ) was not statistically different among provenances in either year (2010 and 2011), even though L A decreased in the dry year (2011) in all provenances. Reaction norms were steep in most of the parameters suggesting the possibility of a plastic response of provenances toward changes in soil water regime, influenced by the prevailing weather each year. Phenotypic plasticity indices were the highest in regards of SD, PCI and RSPS, indicating that these traits would be good candidates for improvement in breeding programs aimed at selection of drought resistant.

Effects of light irradiance on stomatal regulation and growth of tomato

Light is not only a primary energy source for photosynthesis but also a vital regulator of numerous processes in plants. However, high light intensity always poses a dilemma for plants: to grow or to suffer. Combining physiological techniques at plant, tissue, and cellular levels, we investigated the regulation of stomatal behaviour and cytosolic Ca2+ concentration ([Ca2+]cyt) on growth of tomato plants under different light irradiance. Overall, plants exhibited a distinct short-term (days) and a long-term (weeks) response to high light by significantly increasing shoot biomass, leaf number, leaf temperature, vapour pressure deficit, stomatal index, aperture length and guard cell length. However, most physiological parameters were significantly reduced upon high light treatment, indicating a strong negative impact of high light on photosynthesis and stomatal opening. For instance, Short- and long-term exposure to high light significantly reduced stomatal aperture width by 31.7% and 46.3%, respectively. Moreover, high light treatments significantly decreased [Ca2+]cyt from 252±39 to 52±16nM in stomatal guard cells. Aperture width, guard cell width and stomatal index were the parameters that highly significantly correlated to photosynthesis and growth of tomato plants (P<0.01) followed by aperture width/length, guard cell volume and stomatal density. These causal links revealed some insights into the fine-regulation of stomata on plant performance despite some non-stomatal factors. Therefore, stomatal parameters including aperture width/length, guard cell width, stomatal density and index and [Ca2+]cyt could be employed as physiological markers for fast and effective assessment of performance of tomato plants.

Effects of experimental warming on stomatal traits in leaves of maize (Zea may L.).

We examined the warming effects on the stomatal frequency, stomatal aperture size and shape, and their spatial distribution pattern of maize (Zea may L.) leaves using a light microscope, an electron scanning microscope, and geostatistic techniques. A field manipulative experiment was conducted to elevate canopy temperature by 2.08°C, on average. We found that experimental warming had little effect on stomatal density, but significantly increased stomatal index due to the reduction in the number of epidermal cells under the warming treatment. Warming also significantly decreased stomatal aperture length and increased stomatal aperture width. As a result, warming significantly increased the average stomatal aperture area and stomatal aperture circumference. In addition, warming dramatically changed the stomatal spatial distribution pattern with a substantial increase in the average nearest neighbor distance between stomata on both adaxial and abaxial surfaces. The spatial distribution pattern of stomata was scale dependent with regular patterns at small scales and random patterns at larger scales on both leaf surfaces. Warming caused the stomatal distribution to become more regular on both leaf surfaces with smaller L(t) values (Ripley's K-function, L(t) is an expectation of zero for any value of t) in the warming plots than the control plots.

Plant architectural traits and their role in defense mechanism against malformation in mango (Mangifera Indica L.)

Different physiological factors related to intensity of floral malformation in twelve mango cultivars differing in their degree of resistance to malformation were investigated. The results revealed that thickness of leaf blade had no significant correlation with intensity of floral malformation, but mango resistant cultivars Bhadauran and Elaichi showed thicker leaf blade when compared with highly susceptible cultivar like Eldon. Leaf wax content showed highly significant negative correlation with intensity of mango floral malformation (r=−0.88). Results revealed that highly susceptible cultivars have less wax thickness (315–375μg/cm2) when compared to resistant cultivars (484–522μg/cm2). The number of stomata per unit area (mm2) of leaf surface did not show significant correlation (r=−0.28) with intensity of malformation, but the total number of stomata per leaf showed significant positive correlation (r=0.53) with percent malformation intensity in mango cultivars. Maximum number of stomata per leaf surface area was found in highly susceptible cultivar Amrapali, followed by susceptible cultivar Chausa. Whereas minimum number of stomata per mango leaf surface was found in resistant variety Bhadauran. Stomata size (length and breadth) and width of stomatal aperture did not show significant correlation with intensity of floral malformation. Intensity of malformation had significant positive correlations to leaf length, width, weight and leaf area r=0.59, 0.53, 0.57 and 0.55 respectively.

Change in Levels of Starch and Sugars in Epidermis ofCommelina benghalensisduring Fusicoccin Stimulated Stomatal Opening

The concentrations of malate, starch and sugars were determined in presonicated epidermal strips of Commelina benghalensis. During opening, the starch content of epidermis decreased while the level of sugars or malate increased. Fusicoccin (FC) stimulated stomatal opening and elevated the levels of malate and sugars. However, the contribution from sugars was nearly 50% of the osmotic effect of malate and it increased to more than 60% in the presence of FC. We conclude that FC stimulates stomatal opening by enhancing not only potassium influx into guard cells but also hydrolysis of starch into sugars (and malate). Significant correlations were noticed between the width of stomatal aperture and epidermal starch (negative), malate and sugars (both positive). The negative relationship between starch and malate or sugars within epidermis indicated that starch hydrolysis lead to formation of sugars as well as malate. Starch-sugar interconversion can therefore play a significant role in modulating the solute potential of guard cells.

Mehler-type reagents in the enhancement of stomatal opening in epidermal strips

A substantial enhancement of the width of stomatal aperture was produced by methyl viologen (MV) a Mehler reagent, in isolated epidermal strips from the leaves ofCommelina benghalensis L., andPisum sativum L., other Mehler reagents, flavin mononucleotide and anthraquinone were also found to stimulate the opening process. Histochemical tests have revealed a much greater influx of K+ into the guard cells in presence of MV. Isolated mesophyll chloroplasts possessed appreciable activity of MV-supported photophosphorylation and of oxygen uptake through Mehler reaction.

Comparative Hydroecological Studies on Some Hydrophytes, Wet and Dry Halophytes and Xerophytes

Summary In Wadi EI-Natrun region, the wide variation in the topography and depth of water table provides a good chance for the occurrence of plants belonging to some ecological groups namely hydrophytes, halophytes (dry and wet) and xerophytes, within a limited area under almost similar climatic conditions. The main factors controlling root extensions in the studied habitats are the depth of water table and the soil moisture content. In the swampy habitat, the ground surface is continuously inundated with water and the roots are weekly developed with very limited extensions. In the salt marsh habitat the water table is shallow and accordingly the soil is wet with high salt content. In this habitat the roots are shallow with limited vertical penetration. In dry salty sites with deeper water table and relatively dry soil, the roots exhibit great vertical and horizontal extensions. In the desert habitat the extremely deep water table and the dry soil favour the great vertical and horizontal extensions of roots as well as the high ratio of root to shoot. The daily march of the stomatal opening runs parallel to that of the transpiration rate in nearly all the cases. The widest stomatal aperture and the highest transpiration rate were exhibited by hydrophytes. The width of stomatal aperture in dry halophytes was slightly greater than that of xerophytic species. In case of wet halophytes, the width of stomatal aperture and rate of transpiration were intermediate between those of hydrophytes and xerophytic species. The lowest osmotic pressure of plant sap (from 5.92 to 6.81 atm.) was shown by hydrophytic species and the highest (from 24.44 to 40.61 atm.) by dry halophytes. In wet halophytes the osmotic pressure of shoot sap was relatively high but generally less than that of dry halophytes and higher than that of xerophytes. The high osmotic pressure of dry and wet halophytes is mainly due to accumulation of salts since roots of these plants grow in saline soils containing a relatively high percentage of salts. In case of hydrophytes and xerophytic species, the odmotically active constituents of the cell sap are mainly nonelectrolytes.

The Effect of Epidermal Cell Water Potential on Stomatal Response to Illumination of Leaf Discs of Vicia faba

AbstractIlluminated leaf discs of Vicia faba were brought into equilibrium with a series of mannitol solutions. The width of stomatal aperture and the osmotic potential of guard cells and epidermal cells were determined. It was found that the maximal aperture was obtained when epidermal cells were at about incipient plasmolysis and that any increase in their turgor pressure brought about a decrease in stomatal aperture. These findings emphasize the importance of epidermal cells in determining the width of the stomatal pore.