• Stomatal conductance, usually measured in mmol m−2 s−1 by a porometer, estimates the rate of gas exchange (i.e., carbon dioxide uptake) and transpiration (i.e., water loss as water vapor) through the leaf stomata as determined by the degree of stomatal aperture (and therefore the physical resistances to the movement of gases between the air and the interior of the leaf). (wikipedia.org)
  • The stomatal conductance, or its inverse, stomatal resistance, is under the direct biological control of the leaf through its guard cells, which surround the stomatal pore. (wikipedia.org)
  • The turgor pressure and osmotic potential of guard cells are directly related to the stomatal conductance. (wikipedia.org)
  • Stomatal conductance is a function of stomatal density, stomatal aperture, and stomatal size. (wikipedia.org)
  • Stomatal conductance is integral to leaf level calculations of transpiration. (wikipedia.org)
  • Multiple studies have shown a direct correlation between the use of herbicides and changes in physiological and biochemical growth processes in plants, particularly non-target plants, resulting in a reduction in stomatal conductance and turgor pressure in leaves. (wikipedia.org)
  • Therefore, stomatal opening and closing has a direct relationship to stomatal conductance. (wikipedia.org)
  • Light is a major stimulus involved in stomatal conductance, and has two key elements that are involved in the process: 1) the stomatal response to blue light, and 2) photosynthesis in the chloroplast of the guard cell. (wikipedia.org)
  • For more details about CAM plant stomatal conductance, see: CAM Plants Stomatal opening occurs as a response to blue light. (wikipedia.org)
  • Recent studies have looked at the stomatal conductance of fast growing tree species to identify the water use of various species. (wikipedia.org)
  • For example, canopy stomatal conductance had a higher water potential in July than in October. (wikipedia.org)
  • The studies conducted for this experiment determined that the stomatal conductance allowed for a constant water use per unit leaf area. (wikipedia.org)
  • It was thus hypothesized that if guard cell chloroplasts are responsible for stomatal opening, it would be expected that light applied to the lower leaf surface would be much more effective at increasing stomatal conductance than light applied to the upper surface. (wikipedia.org)
  • Stomatal CO 2 responsiveness was not significantly related to any of the other functional traits investigated, while a parameter describing the relationship between photosynthesis and stomatal conductance in combined leaf gas exchange models ( g 1 ) was related to leaf area-specific plant hydraulic conductance. (springer.com)
  • Within-leaf N allocation and water use were strongly co-ordinated ( r 2 = 0.67), such that species with high fractional N investments into compounds maximizing photosynthetic capacity also had high stomatal conductance. (springer.com)
  • We overexpressed the rice EPIDERMAL PATTERNING FACTOR1 (OsEPF1) to produce rice plants with reduced stomatal densities, resulting in lowered leaf stomatal conductance and enhanced water use efficiency. (whiterose.ac.uk)
  • We conclude that RCA development and stomatal development are linked by two possible mechanisms: first that reduced stomatal conductance inhibits the diffusion of oxygen to the root, creating an oxygen deficit and stimulating the formation of RCA, second that an unknown EPF signalling pathway may be involved. (whiterose.ac.uk)
  • The stomatal conductance was restricted earlier in the younger leaf (4th) (on Day 3) than in the older leaf (3rd). (lancs.ac.uk)
  • Robust models of stomatal conductance are greatly needed to predict plant-atmosphere interactions in a changing climate, and to integrate new knowledge in physiology and ecological theory. (plantae.org)
  • Stomatal conductance (g s) is a key land-surface attribute as it links transpiration, the dominant component of global land evapotranspiration, and photosynthesis, the driving force of the global carbon cycle. (edu.au)
  • Factors affecting stomatal conductance (g1) of pearl millet (Pennisetum americanum [L.] Leeke), cultivar BJ 104, were examined in the field in India during the dry season. (icrisat.org)
  • The stomatal kinetics, analyzed by gas exchange, revealed BLINK1 accelerates changes in conductance, reducing the stomatal opening and closing halftimes. (plantae.org)
  • Coupled photosynthesis-stomatal conductance (A-gs) models are commonly used in ecosystem models to represent the exchange rate of CO2 and H2O between vegetation and the atmosphere. (reading.ac.uk)
  • This study provides insight into the impact of contrasting model configurations of water stress on the simulated leaf-level values of net photosynthesis (A), stomatal conductance (gs), the functional relationship among them and their ratio, the intrinsic water use efficiency (A/gs), as soil dries. (reading.ac.uk)
  • The loss-of-function pro mutant exhibited increased stomatal conductance and rapid wilting under water deficit stress. (iucc.ac.il)
  • Stomatal conductance, closely related to water flow in the soil-plant-atmosphere continuum, is an important parameter in the Penman-Monteith (P-M) model for estimating evapotranspiration (ET). (agri.gov.il)
  • In this study, a novel soil water stress index ω , considering intrinsic soil-plant water relations, was introduced into the Jarvis empirical estimation model of stomatal conductance to improve the representation of the effect of soil water stress on stomatal conductance. (agri.gov.il)
  • Combined plant and soil-based measurements from a greenhouse experiment provided the basis for investigating the relationship between leaf stomatal conductance g s and root zone soil water stress represented by ω . (agri.gov.il)
  • The reliability of ω was tested by coupling it into the Jarvis model to estimate leaf ( g s ) and canopy ( g c ) stomatal conductance, and thereupon into the P-M model to estimate cumulative ET (CET) in the greenhouse experiment and two field experiments. (agri.gov.il)
  • With this experiment she and her research team demonstrated that g s (stomatal conductance to water vapour) acclimation is influenced by pattern and intensity of light, modifying the stomatal kinetics at different times of the day and resulting in differences in the rapidity and magnitude of the g s response. (bristol.ac.uk)
  • The investigation of the stomatal regulation in combined heat and drought stress aimed to link effects of exogenous melatonin on stomatal conductance (g s ) and its mechanistic interactions with ABA or ROS signaling. (au.dk)
  • Nighttime stomatal conductance differs with nutrient availability in two temperate floodplain tree species. (uni-hamburg.de)
  • In our method, the stomatal movement is inferred by simple monitoring of the fluorescence intensity in the nucleus of the stomata. (nature.com)
  • Our method enables objective assessment of stomatal dynamics by simple monitoring of the fluorescence intensity of HoeAc 2 Fl in the nucleus of the stomata. (nature.com)
  • The exact correlation between fluorescence intensity and stomatal aperture showed that the visible fluorescence was only observed from stomata with an aperture of less than about 2.5-3 µm (Fig. 2c , three representative images of closed or open stomata are shown in Fig. S1 , and fluorescence images of various stomata having different apertures are shown in Fig. S2 ). (nature.com)
  • In the context of a changing climate, the dynamic nature of stomatal traits make stomata attractive targets in plant breeding. (edu.au)
  • Until recently, research on stomatal traits was limited by researchers' ability to measure stomata, as current methods used for stomata phenotyping are tedious. (edu.au)
  • We found that stomatal closure responses to increased CO 2 were stronger in angiosperms than in gymnosperms, and in monocots compared to dicots. (springer.com)
  • Tree species that exhibit a pronounced direct stomatal closure response to a short-term increase in [CO 2 ] are thus also likely to develop a long-term g s reduction in the field. (springer.com)
  • For some southern regions of Europe, where temperatures are close to or above optimum for stomatal opening, an increase in temperature of 2 °C could limit stomatal ozone uptake by enhancing stomatal closure during the summer months, whereas during the spring, when many plants are actively growing, a small increase in temperature would increase stomatal ozone uptake. (nerc.ac.uk)
  • The magnitude of water stress-induced stomatal closure increased down the plant, and was more marked in retarded than in flowering plants. (icrisat.org)
  • Plants employ stomatal closure and reduced growth to avoid water deficiency damage. (iucc.ac.il)
  • Here, we show that the tomato (Solanum lycopersicum) DELLA protein PROCERA (PRO), a negative regulator of GA signaling, acts in guard cells to promote stomatal closure and reduce water loss in response to water deficiency by increasing abscisic acid (ABA) sensitivity. (iucc.ac.il)
  • This result indicates that DELLA promotes stomatal closure independently of its effect on growth. (iucc.ac.il)
  • The responses of fls2 plants were similar to those of the Arabidopsis G-protein alpha subunit1-3 mutant, which is defective in abscisic acid-regulated stomatal closure, but were distinct from those of the Arabidopsis non-expressor of PR genes1 mutant, which is defective in salicylic acid-dependent stomatal closure and apoplast defense. (duke.edu)
  • Epistasis analyses show that salicylic acid signaling acts upstream of abscisic acid signaling in bacterium-triggered stomatal closure. (duke.edu)
  • 17. Phosphorylation of the plasma membrane H+-ATPase AHA2 by BAK1 is required for ABA-induced stomatal closure in Arabidopsis. (nih.gov)
  • Adding stomatal closure to the model, as a key ABA- and clock-regulated downstream process allowed to describe TOC1 effects on the rhythmic gating of stomatal closure. (nih.gov)
  • However, to speed the development of molecules capable of affecting stomatal movements, simple and high-throughput methods for chemical screening are urgently needed. (nature.com)
  • The larger the value of this parameter, the more sluggish the modelled stomatal response. (copernicus.org)
  • To explore if these traits are linked to taxonomic group identity and/or to other plant functional traits, we investigated the short-term stomatal CO 2 responses and the maximum rates of photosynthetic carboxylation ( V cmax ) and electron transport ( J max ) in an evolutionary broad range of tropical woody plant species. (springer.com)
  • However, the direct stomatal responses to a short-term increase in [CO 2 ] vary greatly among species and experiments, from no change to 75% reduction in g s at doubled compared to ambient [CO 2 ] (Morison 1998 ). (springer.com)
  • Therefore, a better understanding of the factors that control the large natural variation in short-term stomatal CO 2 responses would provide indication of which plant species and groups that are likely to experience large increases in water-use efficiency in future higher [CO 2 ] scenarios. (springer.com)
  • Stomatal and growth responses to hydraulic and chemical changes induced by progressive soil drying. (lancs.ac.uk)
  • This work identified critical timing of hydraulic and chemical changes at the onset of soil drying, which can be important in initiating early stomatal and growth responses to drought. (lancs.ac.uk)
  • Stomatal responses: the key to adaptation in newly planted jack pine and black spruce. (gc.ca)
  • CONCLUSIONS: The integrated model of the circadian clock circuit and ABA-regulated environmental sensing allowed us to explain multiple experimental observations on the timing and stomatal responses to genetic and environmental perturbations. (nih.gov)
  • At the sites from central and northern regions of Europe, including the UK and Sweden, climatic conditions were highly conducive to stomatal ozone uptake by vegetation during the summer months and therefore an increase in daily mean ozone concentration of 3-16% during this time of year (from increased background concentrations, reduced peaks) would have a large impact on stomatal ozone uptake. (nerc.ac.uk)
  • While these findings demonstrate that climate has a direct impact on stomatal morphology, the extent to which these patterns will persist in the future remains unknown. (botanyconference.org)
  • Herein, we report a simple and convenient method for the assessment of stomatal closing/opening in Arabidopsis thaliana based on fluorescent live imaging by Hoechst-tagged acetylfluorescein (HoeAc 2 Fl, Fig. 1a ). (nature.com)
  • Overexpression of the PM H + -ATPase in guard cells significantly enhances stomatal opening, photosynthesis and, subsequently, growth in Arabidopsis thaliana , a model plant 11 . (nature.com)
  • Scholars@Duke publication: A prominent role of the flagellin receptor FLAGELLIN-SENSING2 in mediating stomatal response to Pseudomonas syringae pv tomato DC3000 in Arabidopsis. (duke.edu)
  • 6. Arabidopsis phot1 and phot2 phosphorylate BLUS1 kinase with different efficiencies in stomatal opening. (nih.gov)
  • 8. Brassinosteroid Involvement in Arabidopsis thaliana Stomatal Opening. (nih.gov)
  • 15. CIPK23 regulates blue light-dependent stomatal opening in Arabidopsis thaliana. (nih.gov)
  • Stomatal guard cells surround pores in the epidermis of plant leaves, controlling the aperture of the pore to balance CO2 entry into the leaf for photosynthesis with water loss via transpiration. (gla.ac.uk)
  • The transpiration rate is influenced by the stomatal number and size. (easychair.org)
  • In plants, stomatal aperture mediates both CO 2 uptake for photosynthesis and water loss by transpiration. (plantae.org)
  • The effects of S-della on stomatal aperture and water loss were strongly suppressed in the ABA-deficient mutant sitiens, indicating that these effects of S-della are ABA dependent. (iucc.ac.il)
  • We find that stomatal behaviour differs among PFTs according to their marginal carbon cost of water use, as predicted by the theory underpinning the optimal stomatal model and the leaf and wood economics spectrum. (edu.au)
  • What are optimal stomatal patterning for efficient use of water in dry environments? (edu.au)
  • Although small increases in ozone concentration during these seasons could cause a modest increase in ozone uptake, for those species that are active at low temperatures, a 2 °C increase in temperature would increase stomatal ozone uptake even in the absence of further increases in ozone concentration. (nerc.ac.uk)
  • Expressing S-della under the control of a guard-cell-specific promoter was sufficient to increase stomatal sensitivity to ABA and to reduce water loss under water deficit stress but had no effect on leaf size. (iucc.ac.il)
  • Despite the pivotal role of g s in predictions of global water and carbon cycle changes, a global-scale database and an associated globally applicable model of g s that allow predictions of stomatal behaviour are lacking. (edu.au)
  • This Monday, Professor Tracy Lawson from the School of Biological Sciences of the University of Essex talked to students and academic staff of the LSB in Bristol about her last findings in the survey of stomatal behaviour as a response to different environmental stimuli. (bristol.ac.uk)
  • During the first part of her talk, Professor Lawson talked about how different plants have different patterns of stomatal behaviour and how these respond differently according to plant phenotype and environmental conditions. (bristol.ac.uk)
  • The following part of her talk was about the impact of dynamic growth light on stomatal acclimation and behaviour. (bristol.ac.uk)
  • Chloroplast density in pairs of stomatal guard cells of the accessions was also determined. (mrcalonline.com)
  • A Comparison of Different Stomatal Density Phenotypes of Hordeum vulgare under Varied Watering Regimes Reveals Superior Genotypes with Enhanced Drought Tolerance. (bvsalud.org)
  • Reduced stomatal density is linked to enhanced WUE, leading to improved drought resistance across plant genera. (bvsalud.org)
  • In this study, 10 barley varieties exhibiting a range of stomatal density phenotypes were grown under differing soil water contents to determine whether stomatal density influences the capacity of genotypes to resist low water availability. (bvsalud.org)
  • The low-stomatal-density genotype Hindmarsh showed the least impact on biomass production during early development, with a 37.13% decrease in dry biomass during drought treatment . (bvsalud.org)
  • Low-stomatal-density genotypes additionally outcompeted high-stomatal-density genotypes under water -deprivation conditions during the reproductive phase of development, exhibiting 19.35% greater wilting resistance and generating 54.62% more heads relative to high-stomatal-density genotypes (p (bvsalud.org)
  • Finally, a correlation analysis revealed a strong negative linear relationship between stomatal density and the traits of head number (r = -0.71) and the number of days until wilting symptoms (r = -0.67) (p (bvsalud.org)
  • The combined results indicate that low-stomatal-density genotypes show promising attributes for high WUE, revealing novel barley varieties that may be useful to future breed improvement for drought tolerance . (bvsalud.org)
  • Then, when blue light was added, stomatal opening increased even further, showing that a different photoreceptor system, stimulated by blue light, mediates the additional increases in opening. (wikipedia.org)
  • 4. A Raf-like protein kinase BHP mediates blue light-dependent stomatal opening. (nih.gov)
  • Stomatal pores, each surrounded by a pair of guard cells, regulate CO 2 uptake and water loss from leaves. (elsevierpure.com)
  • A changing ozone profile with small increases in background ozone concentrations over the course of a growing season could have significant impacts on the annual accumulated stomatal ozone uptake, even if peak concentrations of ozone are reduced. (nerc.ac.uk)
  • Predicted increases in stomatal ozone uptake showed a strong relationship with latitude and were larger at sites from northern and mid-Europe than those from southern Europe. (nerc.ac.uk)
  • To date most models representing ozone damage use either O 3 concentration or, more recently, flux-uptake-related reduction of stomatal opening, estimating suppressed land-atmosphere water and CO 2 fluxes. (copernicus.org)
  • In this study, we examined the involvement of PM H + -ATPase in NH 4 + uptake by rice roots and stomatal opening for CO 2 uptake and photosynthesis in rice leaves, with the aim of developing a new strategy to improve rice yield and N use efficiency (NUE) via the overexpression of a single gene, Oryza sativa PM H + -ATPase 1 ( OSA1 ). (nature.com)
  • This recognition is rooted in half a century of research into ion transport across the plasma and vacuolar membranes of guard cells that drive stomatal movements and the signaling mechanisms that regulate them. (gla.ac.uk)
  • and simple methods to assess stomatal dynamics are needed for physiological studies. (nature.com)
  • Stomatal CO 2 responsiveness and photosynthetic capacity vary greatly among plant species, but the factors controlling these physiological leaf traits are often poorly understood. (springer.com)
  • Therefore, ω should be feasible and reliable to delineate the response of stomatal physiological reaction to water stress, and hence helpful for accurate estimation of ET using Jarvis-based P-M models. (agri.gov.il)
  • Here, we survey a range of alternative hypotheses for drivers of water use and stomatal regulation. (nih.gov)
  • The understanding of stomatal regulation in climate stress is essential for ensuring resilient crops. (au.dk)
  • 19. New insights into the regulation of stomatal opening by blue light and plasma membrane H(+)-ATPase. (nih.gov)
  • We conclude that while stomatal CO 2 responsiveness of tropical woody species seems poorly related to other plant functional traits, photosynthetic capacity is linked to fractional within-leaf N allocation rather than total leaf N content and is closely co-ordinated with leaf water use. (springer.com)
  • Which non-stomatal factors influence water-use efficiency? (edu.au)
  • Accounting for water stress in coupled A-gs models by imposing either stomatal or biochemical limitations of A, as commonly practiced in most ecosystem models, failed to reproduce the observed functional relationship between key leaf gas exchange attributes. (reading.ac.uk)
  • The index ω accounted not only for current water availability by combing the effects of relative distribution of soil water to roots and nonlinear stomatal response, but also for the hysteresis effect of water stress by means of the inclusion of a recovery coefficient. (agri.gov.il)
  • This study aimed to measure the stomatal number and size of monocotyledon plants. (easychair.org)
  • She worked on the synthesis of small molecules capable of increasing stomatal numbers in plants. (nih.gov)
  • The second key element involved in light-dependent stomatal opening is photosynthesis in the chloroplast of the guard cell. (wikipedia.org)
  • PHOTOTROPISM , light-induced stomatal opening, and CHLOROPLAST movements in response to changes in light intensity. (nih.gov)
  • identified several small molecules that affect stomatal movements from a chemical library 9 . (nature.com)
  • We recently developed a rapid non-destructive method1 that allows high-throughput screening of stomatal traits in large experiment. (edu.au)
  • Which stomatal traits did breeders select for in recent varieties? (edu.au)
  • In particular, he investigates optimum stomatal traits for plant adaptation to drought. (edu.au)
  • In this study, we used eight sites from across Europe to investigate the implications of a future climate (2 °C warmer and 20% drier) and a changing ozone profile (increased background concentrations and reduced peaks) on stomatal ozone fluxes of three widely occurring plant species. (nerc.ac.uk)
  • Stomatal size in Populus trichocarpa is related to climate and exhibits plasticity across growing environments. (botanyconference.org)
  • The purpose of this experiment was to evaluate the associations between stomatal pore length and precipitation and humidity, two climate characteristics that are rapidly changing. (botanyconference.org)
  • By comparing the UWEC and NDSU data, we conclude that mean annual precipitation and relative humidity of the climate of origin have a significant association with stomatal pore length, and that pore length also demonstrates plasticity between gardens. (botanyconference.org)
  • Future research is needed to investigate how stomatal morphology will adapt to the changing climate. (botanyconference.org)
  • and stomatal movement takes place in response to several environmental stimuli, such as blue light, red light, low CO 2 , and chemicals. (nature.com)
  • Understanding this variation is important, since the short-term stomatal CO 2 response appears to be an important determinant for the long-term effect of growth in elevated [CO 2 ] on g s under field conditions. (springer.com)
  • However there is evidence that, for some species, O 3 damage can also cause an inertial "sluggishness" of stomatal response to changing surface meteorological conditions. (copernicus.org)
  • The en- hancement of Typha by elevated nutrients and increased flooding is associated with a syndrome of life history characteristics that includes rapid growth rates, high tissue con- centrations of P, tall leaves, and a greater response to contrasting environmental conditions. (researchgate.net)
  • 5. A BLUS1 kinase signal and a decrease in intercellular CO2 concentration are necessary for stomatal opening in response to blue light. (nih.gov)
  • 13. The Plasma Membrane H+-ATPase AHA1 Plays a Major Role in Stomatal Opening in Response to Blue Light. (nih.gov)
  • The contributors review recent advances in our understanding of plant plasticity, circadian rhythms, stomatal development, inflorescence architecture, symbiotic phosphate acquisition, and specialized plant metabolism and discuss how this knowledge might be used to boost yields, improve tolerance to pathogens and environmental stress, and enhance nutritional content. (cshlpress.com)
  • 7. Overexpression of plasma membrane H+-ATPase in guard cells promotes light-induced stomatal opening and enhances plant growth. (nih.gov)
  • Therefore, we proposed that HoeAc 2 Fl could constitute a useful chemical tool for the assessment of stomatal dynamics by simple monitoring of the intensity of the fluorescence of the nuclei of the guard cells. (nature.com)
  • Stomatal guard cells are widely recognized as the premier plant cell model for membrane transport, signaling, and homeostasis. (gla.ac.uk)
  • Stomatal opening is driven by the accumulation of K + salts and sugars in guard cells, which is mediated by electrogenic proton pumps in the plasma membrane and/or metabolic activity. (elsevierpure.com)
  • 9. Immunohistochemical detection of blue light-induced phosphorylation of the plasma membrane H+-ATPase in stomatal guard cells. (nih.gov)
  • Light-dependent stomatal opening occurs in many species and under many different conditions. (wikipedia.org)
  • Plant species, plant parts, and the combination between the two significantly influenced on stomatal number and size. (easychair.org)
  • The stomatal number correlated inversely with stomatal size both in plant species and plant parts. (easychair.org)
  • 16. Reactive Carbonyl Species Inhibit Blue-Light-Dependent Activation of the Plasma Membrane H+-ATPase and Stomatal Opening. (nih.gov)
  • Elevated levels of tropospheric ozone, O 3 , cause damage to terrestrial vegetation, affecting leaf stomatal functioning and reducing photosynthesis. (copernicus.org)
  • In so called free-air CO 2 enrichment (FACE) experiments with trees, the interspecific variation in long-term (years) effects of growth under elevated [CO 2 ] on g s was significantly and positively related to the variation in short-term stomatal CO 2 responsiveness, measured as the effect of short (hours) interruptions in CO 2 enrichment on sap flow (Cech et al. (springer.com)
  • However, Rhoeo discolor had the largest stomatal size (2285,7 μm) significantly compared to others while Cordyline fruticosa had the smallest (114,1 μm). (easychair.org)
  • Top plant parts had the highest stomatal number (172) significantly compared to the middle (141) and bottom parts (138). (easychair.org)
  • The sensitivity analyses emphasized the necessity to combine both stomatal and non-stomatal limitations of A in coupled A-gs models to accurately capture the observed functional relationships A vs. gs and A/gsvs. (reading.ac.uk)
  • Pathogen resistance was mediated in Atg3bp1 mutants by altered stomatal and apoplastic immunity. (edu.sa)
  • Herein, we report a fluorescence-imaging-based method using fluorescein diacetate tagged with Hoechst 33342, a nuclear staining chemical probe (HoeAc 2 Fl) for the qualitative assessment of stomatal dynamics. (nature.com)
  • 18. Identification and improvement of isothiocyanate-based inhibitors on stomatal opening to act as drought tolerance-conferring agrochemicals. (nih.gov)
  • In one study, the experiment began once stomatal opening had reached its saturation in red-light. (wikipedia.org)
  • Explain how light influences stomatal opening in a plant that has been previously in the dark. (digitalteachers.co.ug)
  • In the present study, we find that overexpression of a single rice gene, Oryza sativa plasma membrane (PM) H + -ATPase 1 ( OSA1 ), facilitates ammonium absorption and assimilation in roots and enhanced light-induced stomatal opening with higher photosynthesis rate in leaves. (nature.com)
  • In this review, we focus on recent progress in blue- and red-light-dependent stomatal opening. (elsevierpure.com)
  • Effects of light on morphologic and stomatal characteristics of Turkish fir needles (Abies nordmanniana subsp. (omu.edu.tr)