Hydraulic Signals Research Articles

Research on Hydraulic Pressure Detection System for Mine

According to mine hydraulic testing requirement, the article puts forward an online hydraulic testing method, which is used in mine hydraulic cylinder,three-way valve and so on. It makes real-time, multi-channel hydraulic pressure signal gathering and processing procedure come true, thus completes the online assessment for mine hydraulic testing. The method uses a multi-thread, multi-channel, multi-buffer synchronous detection mode by combining soft and hardware hydraulic test features and establishes data collecting and interactive model as well as data display and storage model, which owns a powerful interactive interface. It can display real-time multi-channel pressure histogram and waveform graph, which also has function of personalized settings, real-time detection, permanent preservation, history record inquiry and report print. Furthermore, this mechod reflects the real-timing and reliability of system in practical application.

Innovation: The Intelligence Behind Intelligent Completions

President's column There are many definitions of intelligent completions, but the one I find most apt is a well completion that enables remote monitoring and control of the well inflow without physical intervention to optimize production and reservoir management. Before the late 1980s, when intelligent completions were introduced into our industry, data collection or well intervention had to be carried out by introducing tools from the surface using wireline or coiled tubing. However, a number of factors drove us to seek more cost-effective ways of obtaining well data and downhole intervention without shutting down production. As we developed the capacity to drill in increasingly deep water, opening up new reserves, we had to find more innovative, cost-effective means of well intervention. The high upfront costs and the loss of revenue resulting from shutting these wells in just to obtain well data had a huge impact on the revenue stream of companies. Another factor that encouraged application of intelligent completions is that, during penetration of many stacked reservoirs, operators saw that it was cost-effective to complete as many of the horizons as possible in one go but to retain the flexibility to manage which zones could be brought into production without incurring the expense of a rig or rigless intervention. In addition, many authorities were becoming more flexible in allowing commingling of production from different reservoirs. The opportunities encouraged many service companies to develop new types of completions, either alone or in collaboration with other companies. The equipment already existed, but needed to be repackaged for the new application that was required (Docherty 2001). In designing intelligent completions, oilfield operators specified a number of requirements relating to reliability, ability to segregate inflow, minimal impact on existing well equipment, and the ability to integrate with current technology. Over the years, new technologies have enabled real-time surveillance of wells and real-time control of inflow of reservoir fluids or the injection into reservoirs for pressure maintenance. Surveillance is achieved using modern electronic devices, while control is managed by the installation of innovative downhole equipment (a valve or sleeve) that is controlled using electric, hydraulic, or electrohydraulic signals. Operators all over the world have applied the technology to provide services ranging from the control of gas breakthrough to selecting which part of long horizontal completions can be brought into production, to managing water injection for pressure maintenance. The use of intelligent completions has even been extended to shallow-well operations, where economics is the driver. Similar to deep-well operations, the cost of well intervention and the attendant loss of production have encouraged operators to install intelligent completions when such wells are initially completed. The use of intelligent completions also obviates the need for direct human intervention with possible attendant safety risks.

Spatio-temporal decoupling of stomatal and mesophyll conductance induced by vein cutting in leaves of Helianthus annuus.

Reduction of hydraulic conductance to the canopy has been shown to result in stomatal responses to limit transpiration. To test for similar responses to perturbations of the hydraulic network in leaves, we simultaneously measured leaf gas exchange with spatially explicit chlorophyll-a fluorescence and leaf temperature to examine the effects of cutting a primary leaf vein in Helianthus annuus. We repeated the leaf treatment at each of three different vapor pressure deficits and monitored the short-term dynamics of gas exchange following the treatment. Immediately after treatment, photosynthesis and stomatal conductance (gs) showed a transient “wrong way” response in which photosynthesis declined despite increased gs. Comparisons of fluorescence and temperature across the leaf showed that both photosynthesis and gs were transiently patchy across the measured leaf area, but that the patchiness of the two processes did not correspond in space or time. This suggests that photosynthesis and gs respond to vein cutting-induced cavitation via different mechanisms. Because the stomatal response varied by vapor pressure difference condition but photosynthesis did not, it is likely that gs, but not photosynthesis, responded to a hydraulic signal. In contrast, we hypothesize that photosynthesis declined due to a wound-induced electrical signal that has recently been shown to transiently decrease mesophyll conductance to CO2. The interaction of epidermal hydraulics and the electrical signal across the leaf likely created a patchy pattern of chlorophyll fluorescence and leaf temperature that cannot be explained through the action of a single signal.

The mechanism of propagation of variation potentials in wheat leaves

Here we examined the mechanism of propagation of variation potential (VP) induced by burning in wheat leaves. Participation of hydraulic and chemical mechanisms in VP transmission was analyzed by optical coherent tomography and a radioactive tracer method, respectively. The speed of the hydraulic signal considerably exceeded the VP velocity. Investigation of a chemical substance spreading from the zone of local wounding was based on experimental data for radioactive marker transmission derived with a one-dimensional diffusion equation. The speed of the marker transmission was in accordance with VP velocity. The elimination of the potential transmission of a chemical signal by a timed severing of the leaf between the burn site and the recorded site blocked VP propagation. We suggest that a VP is formed by the transmission of a wound substance, the velocity of which is likely increased by hydraulic wave propagation.

Processing of Hydraulic Pressure Sensor Signal Based on Wavelet Analysis

Hydraulic pressure sensor in the automobile is vulnerable to be polluted by the environment of vehicle, the excitation of road and other factors. In this paper, a method based on wavelet analysis is proposed to solve the interference of hydraulic sensor signal. With the wavelet time-frequency analysis, the development trend of the effective signal is identified by wavelet decomposition. Then on the basis of the estimation method, which estimates the noise variance by correlation coefficients, the sensor signal is treated by use of wavelet threshold de-noising. Finally, the available sample value of the signal is constructed by mean filter. In addition, it has been proved by the experiment that the approach, put forward in this paper, is an effective way on the analysis of hydraulic signal and noise elimination.

Bundle‐sheath cell regulation of xylem‐mesophyll water transport via aquaporins under drought stress: a target of xylem‐borne ABA?

The hydraulic conductivity of the leaf vascular system (K(leaf) ) is dynamic and decreases rapidly under drought stress, possibly in response to the stress phytohormone ABA, which increases sharply in the xylem sap (ABA(xyl) ) during periods of drought. Vascular bundle-sheath cells (BSCs; a layer of parenchymatous cells tightly enwrapping the entire leaf vasculature) have been hypothesized to control K(leaf) via the specific activity of BSC aquaporins (AQPs). We examined this hypothesis and provide evidence for drought-induced ABA(xyl) diminishing BSC osmotic water permeability (P(f) ) via downregulated activity of their AQPs. ABA fed to the leaf via the xylem (petiole) both decreased K(leaf) and led to stomatal closure, replicating the effect of drought. In contrast, smearing ABA on the leaf blade, while also closing stomata, did not decrease K(leaf) within 2-3 h of application, demonstrating that K(leaf) does not depend entirely on stomatal closure. GFP-labeled BSCs showed decreased P(f) in response to 'drought' and ABA treatment, and a reversible decrease with HgCl(2) (an AQP blocker). These P(f) responses, absent in mesophyll cells, suggest stress-regulated AQP activity specific to BSCs, and imply a role for these cells in decreasing K(leaf) via a reduction in P(f) . Our results support the above hypothesis and highlight the BSCs as hitherto overlooked vasculature sensor compartments, extending throughout the leaf and functioning as 'stress-regulated valves' converting vasculature chemical signals (possibly ABA(xyl) ) into leaf hydraulic signals.

Monitoring of Deep Processing of Oil De-Noising Technique

Oil for deep processing of the signal contains a lot of pulse interference monitoring and random non-stationary noise characteristics; this paper presents a wavelet-based moving average against impulse noise filter. First on the hydraulic signal wavelet de-noising, wavelet processing and then the results after anti-pulse moving average processing. The simulation signals and hydraulic monitoring signal de-noising experiments show that: the use of wavelet technology and anti-pulse interference filter combination of moving average method has good oil pressure monitoring signal filtering, to achieve deep process debris blocking fault laid the foundation for monitoring.

The effect of competition from neighbours on stomatal conductance in lettuce and tomato plants.

Competition decreased transpiration from young lettuce plants after 2 days, before any reductions in leaf area became apparent, and stomatal conductance (g(s) ) of lettuce and tomato plants was also reduced. Stomatal closure was not due to hydraulic signals or competition for nutrients, as soil water content, leaf water status and leaf nitrate concentrations were unaffected by neighbours. Competition-induced stomatal closure was absent in an abscisic acid (ABA)-deficient tomato mutant, flacca, indicating a fundamental involvement of ABA. Although tomato xylem sap ABA concentrations were unaffected by the presence of neighbours, ABA/pH-based stomatal modulation is still likely to underlie the response to competition, as soil and xylem sap alkalization was observed in competing plants. Competition also modulated leaf ethylene production, and treatment of lettuce plants with an ethylene perception inhibitor (1-methylcyclopropene) diminished the difference in g(s) between single and competing plants grown in a controlled environment room, but increased it in plants grown in the greenhouse: ethylene altered the extent of the stomatal response to competition. Effects of competition on g(s) are discussed in terms of the detection of the absence of neighbours: increases in g(s) and carbon fixation may allow faster initial space occupancy within an emerging community/crop.

Method Based on Knowledge Modules of Hydraulic Fault and it’s Application

According to various problems by using traditional redundant fault-tolerance technology and information fault-tolerant technology, a novel method of knowledge modules of hydraulic fault (KMHF) was proposed in this paper. The principle of the method was that new type of fluid information expression units were designed to perceive and process the fault information of the system, then the information was expressed as mechanical signal, hydraulic signal or electrical signal, which could be used to implement fault tolerance at power stage. The engineering application of the method of KMHF can solve the problems of the whole fault tolerance in the hydraulic system, moreover, with it the structure of hydraulic system can be greatly simplified.

Changes in the water status and rheological characteristics of pea seedling axillary buds during their transitions growth-dormancy-growth in apical dominance

The technique of isopiestic thermocouple psychrometry was used for the analysis of bud transition from dormancy to growth and back in 8-18-day-old pea (Pisum sativum L.) seedlings. We monitored changes in the water (ψw) and osmotic (ψs + m) potentials and also turgor pressure (ψp) in dormant buds and threshold turgor (Y) in growing buds, the latter being one of the cell-wall rheological characteristics. Seedling decapitation resulted in a decrease of Y in the bud, which coincided with the start of its outgrowth. The replacement of terminal shoot with exogenous auxin (IAA or NAA) retarded bud outgrowth and maintained the high level of Y, which argues for the auxin control of this parameter. When growth of the first axillary bud was inhibited by the second one, positioned higher and remained on the plant, the beginning of Y increase preceded visible correlative growth suppression; this makes this rheological index an early marker of bud transition from growth to dormancy. The effects of the terminal shoot part and auxin application on the bud osmotic status differed substantially. In fact, bud transition to dormancy in the presence of the terminal shoot, the main or developing from the second axillary bud, was accompanied by the rise in ψs + m, whereas, in the case of the replacement of the second bud with exogenous auxin, the first bud growth suppression occurred with the decrease in ψs + m. The low value of the bud ψs + m is a factor for creating a considerable gradient of the water potential between the stem and bud supporting water transport to the bud, which was much more active than in plants with a terminal shoot. It seems likely that this is the reason for the absence of complete growth suppression observed by us and other researchers even after application of high auxin concentrations. Immediately after seedling decapitation, ψs + m in the buds reduced; however, this was not the result of trophic metabolite redistribution due to the loss of their active sink because ψs + m reduced also in experiments with complete isolation of the bud releasing from dormancy in the chamber at 100% humidity. Auxin application to the cut surface of decapitated seedlings did not affect the ψs + m decrease. Like decapitation, cotyledon removal resulted in the increase in the bud turgor pressure. However, in this case, water stress did not change the bud osmotic status. Thus, the induction of osmotica accumulation in the bud after the removal of the terminal shoot is evidently related to neither trophic, nor auxin, nor hydraulic signal. The data obtained allowed us to conclude that both components of the bud water potential—ψs + m and Y—play an important role in the control of bud growth at apical dominance. Auxin produced in the shoot apex is involved in the control of Y, whereas the nature of the signal controlling the ψs + m level is unclear.

Variable conductivity and embolism in roots and branches of four contrasting tree species and their impacts on whole-plant hydraulic performance under future atmospheric CO2 concentration

Anatomical and physiological acclimation to water stress of the tree hydraulic system involves trade-offs between maintenance of stomatal conductance and loss of hydraulic conductivity, with short-term impacts on photosynthesis and long-term consequences to survival and growth. Here, we study the role of variations in root and branch maximum hydraulic specific conductivity (k(s-max)) under high and low soil moisture in determining whole-tree hydraulic conductance (K(tree)) and in mediating stomatal control of gas exchange in four contrasting tree species growing under ambient and elevated CO₂ (CO₂(a) and CO₂(e)). We hypothesized that K(tree) would adjust to CO₂(e) through an increase in root and branch k(s-max) in response to anatomical adjustments. However, physiological changes observed under CO₂(e) were not clearly related to structural change in the xylem of any of the species. The only large effect of CO₂(e) occurred in branches of Liquidambar styraciflua L. and Cornus florida L. where an increase in k(s-max) and a decrease in xylem resistance to embolism (-P₅₀) were measured. Across species, embolism in roots explained the loss of K(tree) and therefore indirectly constituted a hydraulic signal involved in stomatal regulation and in the reduction of G(s-ref), the sap-flux-scaled mean canopy stomatal conductance at a reference vapour pressure deficit of 1 kPa. Across roots and branches, the increase in k(s-max) was associated with a decrease in -P₅₀, a consequence of structural acclimation such as larger conduits, lower pit resistance and lower wood density. Across species, treatment-induced changes in K(tree) translated to similar variation in G(s-ref). However, the relationship between G(s-ref) and K(tree) under CO₂(a) was steeper than under CO₂(e), indicating that CO₂(e) trees have lower G(s-ref) at a given K(tree) than CO₂(a) trees. Under high soil moisture, CO₂(e) greatly reduced G(s-ref). Under low soil moisture, CO₂(e) reduced G(s-ref) of only L. styraciflua and Ulmus alata. In some species, higher xylem dysfunction under CO₂(e) might impact tree performance in a future climate when increased evaporative demand could cause a greater loss of hydraulic function. The results contributed to our knowledge of the physiological and anatomical mechanisms underpinning the responses of tree species to drought and more generally to global change.

Development of synchronized, autonomous, and self-regulated oscillations in transpiration rate of a whole tomato plant under water stress

Plants respond to many environmental changes by rapidly adjusting their hydraulic conductivity and transpiration rate, thereby optimizing water-use efficiency and preventing damage due to low water potential. A multiple-load-cell apparatus, time-series analysis of the measured data, and residual low-pass filtering methods were used to monitor continuously and analyse transpiration of potted tomato plants (Solanum lycopersicum cv. Ailsa Craig) grown in a temperature-controlled greenhouse during well-irrigated and drought periods. A time derivative of the filtered residual time series yielded oscillatory behaviour of the whole plant's transpiration (WPT) rate. A subsequent cross-correlation analysis between the WPT oscillatory pattern and wet-wick evaporation rates (vertical cotton fabric, 0.14 m2 partly submerged in water in a container placed on an adjacent load cell) revealed that autonomous oscillations in WPT rate develop under a continuous increase in water stress, whereas these oscillations correspond with the fluctuations in evaporation rate when water is fully available. The relative amplitude of these autonomous oscillations increased with water stress as transpiration rate decreased. These results support the recent finding that an increase in xylem tension triggers hydraulic signals that spread instantaneously via the plant vascular system and control leaf conductance. The regulatory role of synchronized oscillations in WPT rate in eliminating critical xylem tension points and preventing embolism is discussed.

Grapevine under deficit irrigation: hints from physiological and molecular data.

A large proportion of vineyards are located in regions with seasonal drought (e.g. Mediterranean-type climates) where soil and atmospheric water deficits, together with high temperatures, exert large constraints on yield and quality. The increasing demand for vineyard irrigation requires an improvement in the efficiency of water use. Deficit irrigation has emerged as a potential strategy to allow crops to withstand mild water stress with little or no decreases of yield, and potentially a positive impact on fruit quality. Understanding the physiological and molecular bases of grapevine responses to mild to moderate water deficits is fundamental to optimize deficit irrigation management and identify the most suitable varieties to those conditions. How the whole plant acclimatizes to water scarcity and how short- and long-distance chemical and hydraulic signals intervene are reviewed. Chemical compounds synthesized in drying roots are shown to act as long-distance signals inducing leaf stomatal closure and/or restricting leaf growth. This explains why some plants endure soil drying without significant changes in shoot water status. The control of plant water potential by stomatal aperture via feed-forward mechanisms is associated with 'isohydric' behaviour in contrast to 'anysohydric' behaviour in which lower plant water potentials are attained. This review discusses differences in this respect between grapevines varieties and experimental conditions. Mild water deficits also exert direct and/or indirect (via the light environment around grape clusters) effects on berry development and composition; a higher content of skin-based constituents (e.g. tannins and anthocyanins) has generally being reported. Regulation under water deficit of genes and proteins of the various metabolic pathways responsible for berry composition and therefore wine quality are reviewed.

Terminal drought-tolerant pearl millet [Pennisetum glaucum (L.) R. Br.] have high leaf ABA and limit transpiration at high vapour pressure deficit.

It was previously shown that pearl millet genotypes carrying a terminal drought tolerance quantitative trait locus (QTL) had a lower transpiration rate (Tr; g cm−2 d−1) under well-watered conditions than sensitive lines. Here experiments were carried out to test whether this relates to leaf abscisic acid (ABA) and Tr concentration at high vapour pressure deficit (VPD), and whether that leads to transpiration efficiency (TE) differences. These traits were measured in tolerant/sensitive pearl millet genotypes, including near-isogenic lines introgressed with a terminal drought tolerance QTL (NIL-QTLs). Most genotypic differences were found under well-watered conditions. ABA levels under well-watered conditions were higher in tolerant genotypes, including NIL-QTLs, than in sensitive genotypes, and ABA did not increase under water stress. Well-watered Tr was lower in tolerant than in sensitive genotypes at all VPD levels. Except for one line, Tr slowed down in tolerant lines above a breakpoint at 1.40–1.90 kPa, with the slope decreasing >50%, whereas sensitive lines showed no change in that Tr response across the whole VPD range. It is concluded that two water-saving (avoidance) mechanisms may operate under well-watered conditions in tolerant pearl millet: (i) a low Tr even at low VPD conditions, which may relate to leaf ABA; and (ii) a sensitivity to higher VPD that further restricts Tr, which suggests the involvement of hydraulic signals. Both traits, which did not lead to TE differences, could contribute to absolute water saving seen in part due to dry weight increase differences. This water saved would become critical for grain filling and deserves consideration in the breeding of terminal drought-tolerant lines.

Partial rootzone drying and deficit irrigation increase stomatal sensitivity to vapour pressure deficit in anisohydric grapevines

The aim of this study was to investigate how alternative irrigation strategies affected grapevine (Vitis vinifera L.) stomatal response to atmospheric vapour pressure deficit (VPD). In two sites, application of partial rootzone drying (PRD) at 90–100% of crop evapotranspiration (ETc) increased stomatal sensitivity of Shiraz (Syrah) grapevines to high VPD compared with control vines irrigated with the same amount of water but applied on both sides of the vine. PRD significantly reduced vine water use (ESF) measured as sap flow and in dry conditions increased the depth of water uptake from the soil profile. In both experiments, PRD reduced vine water use by up to 50% at moderate VPD (~3 kPa) compared with control vines irrigated at the same level. In the same vines, the response to PRD applied at 100% ETc and deficit irrigation applied at 65% ETc was the same, increasing stomatal sensitivity to VPD and decreasing sap flow. Hydraulic signalling apparently did not play a role in changing stomatal sensitivity as there was no difference in stem water potentials between any of the treatment (PRD and DI) and control vines. This suggests that a long distance root-based chemical signal such as ABA may be responsible for the changes in stomatal behaviour. Shiraz grapevines have previously been classified as anisohydric-like, but application of PRD and DI increased stomatal closure in response to conditions of high evaporative demand making the vines behave in a more isohydric-like manner.

EFFECTS OF DRIP IRRIGATION MODE AND NaCl CONCENTRATION ON GROWTH AND HYDRAULIC CONDUCTANCE OF APPLE SEEDLINGS

Aims Hydraulic conductance, which is characterized by root water uptake and xylem water transport efficiency, is a physiological response of plants to different environmental factors, such as salt-stress and water deficit. However, there is little research on relationships between different drip irrigation modes and hydraulic conductance. Our objectives were to determine 1) the impact on growth and hydraulic conductance of different drip irrigation modes and salinity treatments and 2) the relationship between apple (Malus pumila) seedling growth and hydraulic conductance. Methods The experiment used a NaCl concentration gradient of 0 (CK), 0.2% (S1), 0.3% (S2) and 0.4% (S3) and three drip irrigation modes: alternate partial root zone drip irrigation (ADI, alternate watering on both sides of the root zone), fixed partial root zone drip irrigation (FDI, fixed watering on one side of the root zone) and conventional drip irrigation (CDI, simultaneous watering on both sides of the root-zone). Important findings Drip irrigation modes and NaCl concentration significantly affect apple seedling growth and hydraulic conductance. Dry matter, leaf area, net growth and hydraulic conductance of apple seedlings were significantly inversely related to NaCl concentration under the same drip irrigation treatment. Root hydraulic conductance (Kr) was significantly linearly correlated with total root dry weight, shoot hydraulic conductance (Ksh) and shoot dry weight. Under the same NaCl concentration treatment and compared with CDI, ADI had a water savings of up to 50%, but average root dry weight,shoot dry weight, total dry weight, leaf area, plant net growth and root hydraulic conductance of ADI only decreased by 8.7%, 19.24%, 13.47%, 11.87%, 32.96% and 10.72%, respectively, showing that ADI has an obvious promoting effect on apple seedling growth and hydraulic conductance. Compared with CDI, high NaCl concentrations S2 and S3 led to decreases in Kl+p of ADI of 33.56% and 44.26%, respectively, while the Kr of ADI treatment increased by 1.13% and 10.91%, respectively, indicating that the root hydraulic signal transmission efficiency of ADI treated seedlings, the ability of seedlings to regulate water balance and resistance stability to salt-stress could be enhanced. The growth and hydraulic conductance of ADI were all higher than FDI. Use of ADI not only improved water-saving regulation ability, but also strengthened resistance stability to salt-stress.

Does root-sourced ABA play a role for regulation of stomata under drought in quinoa ( Chenopodium quinoa Willd.)

The Andean seed crop quinoa ( Chenopodium quinoa Willd.) is traditionally grown under drought and other adverse conditions that constrain crop production in the Andes, and it is regarded as having considerable tolerance to soil drying. The objective of this research was to study how chemical and hydraulic signalling from the root system controlled gas exchange in a drying soil in quinoa. It was observed that during soil drying, relative g s and photosynthesis A max (drought stressed/fully watered plants) equalled 1, until the fraction of transpirable soil water (FTSW) decreased to 0.82 ± 0.152 and 0.33 ± 0.061, respectively, at bud formation, indicating that photosynthesis was maintained after stomata closure. The relationship between relative g s and relative A max at bud formation was represented by a logarithmic function ( r 2 = 0.79), which resulted in a photosynthetic water use efficiency WU E A max / g s of 1 when FTSW > 0.8, and increased by 50% with soil drying to FTSW 0.7–0.4. Mild soil drying slightly increased ABA in the xylem. It is concluded that during soil drying, quinoa plants have a sensitive stomatal closure, by which the plants are able to maintain leaf water potential ( ψ l) and A max, resulting in an increase of WUE. Root originated ABA plays a role in stomata performance during soil drying. ABA regulation seems to be one of the mechanisms utilised by quinoa when facing drought inducing decrease of turgor of stomata guard cells.

A quantitative approach to developing more mechanistic gas exchange models for field grown potato: A new insight into chemical and hydraulic signalling

In this study we introduce new gas exchange models that are developed under natural conditions of field grown potato. The new models could explain about 85% of the stomatal conductance variations, which was much higher than the well-known gas exchange models such as the Ball-Berry model [Ball, Woodrow, Berry, 1987. In: Nijhoff, M. (Eds.), Progress in Photosynthesis Research, vol. 4. Dordrecht, The Netherlands, pp. 5.221–5.224]. To overcome the limitations of previous models in simulating stomatal conductance when plants are exposed to drought stress, we proposed a down-regulating factor of chemical and hydraulic signalling on stomatal conductance as exp(− β[ABA])exp(− δ| ψ|) in which [ABA] and | ψ| are xylem ABA concentration and absolute value of leaf or stem water potential. In this study we found that stem water potential could be a very reliable indicator of how plant water status affects the stomatal conductance regulation. While previous models considered the same weighting for relative humidity and photosynthesis rate, we found that relative humidity has a more pronounced regulating effect on stomatal conductance than photosynthesis rate and the weightings for relative humidity and photosynthesis rate, respectively, were significantly higher and lower than unity.

Nitric oxide, actin reorganization and vacuoles change are involved in PEG 6000‐induced stomatal closure inVicia faba

Water deficit and the resulting osmotic stress affect stomatal movement. There are two types of signals, hydraulic and chemical signals, involving in the regulation of stomatal behavior responses to osmotic stress. Compared with the chemical signals, little has been known about the hydraulic signals and the corresponding signal transduction network and regulatory mechanisms. Here, using an epidermal-strip bioassay and laser-scanning confocal microscopy, we provide evidence that nitric oxide (NO) generation in Vicia faba guard cells can be induced by hydraulic signals. We used polyethylene glycol (PEG) 600 to simulate hypertonic conditions. This hydraulic signal led to stomatal closure and rapid promotion of NO production in guard cells. The effects were decreased by NO scavenger 2-(4-carboxyphenyl)-4,4,5, 5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO) and NO synthase (Enzyme Commission 1.14.13.39) inhibitor N(G)-nitro-L-Arg-methyl ester (L-NAME). These results indicate that PEG 6000 induces stomatal closure by promoting NO production. Cytochalasin B (CB) inhibited stomatal closure induced by PEG 6000 but did not prevent the increase of endogenous NO levels, indicating that microfilaments polymerization participate in stomatal closure induced by PEG 6000, and may act downstream of NO signaling. In addition, big vacuoles split into many small vacuoles were observed in response to PEG 6000 and sodium nitroprusside (SNP) treatment, and CB inhibited these changes of vacuoles, the stomatal closure was also been inhibited. Collectively, these results suggest that the stomatal closure induced by PEG 6000 may be intimately associated with NO levels, reorganization of actin filaments and the changes of vacuoles, showing a crude outline of guard-cells signaling process in response to hydraulic signals.

Electrical signalling and cytokinins mediate effects of light and root cutting on ion uptake in intact plants

Nutrient acquisition in the mature root zone is under systemic control by the shoot and the root tip. In maize, exposure of the shoot to light induces short-term (within 1-2 min) effects on net K+ and H+ transport at the root surface. H+ efflux decreased (from -18 to -12 nmol m(-2) s(-1)) and K+ uptake (approximately 2 nmol m(-2) s(-1)) reverted to efflux (approximately -3 nmol m(-2) s(-1)). Xylem probing revealed that the trans-root (electrical) potential drop between xylem vessels and an external electrode responded within seconds to a stepwise increase in light intensity; xylem pressure started to decrease after a approximately 3 min delay, favouring electrical as opposed to hydraulic signalling. Cutting of maize and barley roots at the base reduced H+ efflux and stopped K+ influx in low-salt medium; xylem pressure rapidly increased to atmospheric levels. With 100 mm NaCl added to the bath, the pressure jump upon cutting was more dramatic, but fluxes remained unaffected, providing further evidence against hydraulic regulation of ion uptake. Following excision of the apical part of barley roots, influx changed to large efflux (-50 nmol m(-2) s(-1)). Kinetin (2-4 microM), a synthetic cytokinin, reversed this effect. Regulation of ion transport by root-tip-synthesized cytokinins is discussed.