Correction to: Imaging plant responses to water deficit using electrical resistivity tomography

Plant and Soil - The original version of this article unfortunately contained a mistake. The authors would like to add Andreas Kemna as the fifth author of this paper. The updated list of authors...     

Correction to: Imaging plant responses to water deficit using electrical resistivity tomography

Plant and Soil - Soil microorganisms play an important role in biogeochemical cycles in terrestrial ecosystems. Increasing nitrogen (N) and phosphorus (P) deposition are likely to regulate...     

Plant cellular responses to water deficit

Water availability and drought limit crop yields worldwide. The responses of plants to drought vary greatly depending on species and stress severity. These responses include changes in plant growth, accumulation of solutes, changes in carbon and nitrogen metabolism, and alterations in gene expression. In this article, we review cellular and molecular responses to water deficit, and their influence on plant dehydration tolerance.     

电阻率成像法在树干水分吸收过程研究中的应用

将地球物理学中广泛运用的电阻率成像法成功地运用于树干内部截面电阻率分布特性的监测,利用电阻率平面分布图来分析树干内水分的空间分布和动态变化特征。结果表明：截面内树干水分的含量具有从核心部沿径向向外逐渐递增的趋势;位置较高的截面比较低的截面具有更多的水分含量,但充足的水分补给能打破这种水分分布的规律性,靠近补给源的截面含水率上升幅度最高;即使是在水分补给充足的情况下,树干内水分的吸收并不是面状饱和推进的过程,而是存在着优先纵向流动的生理机制;利用电阻率的变化,可以实现水分在截面上的优势流的定位。     

Modeling of plant adaptation to climatic drought induced water deficit

Soil moisture flux to root surface is considered the main determining factor of the transpiration intensity of plants. This assumption is valid not only in optimal plant physiological conditions without any physical barrier for the evaporation from the leaves, but in climatic drought as well, when high usable soil water amount cannot supply the evapo-transpiration intensity of plant. A new algorithm we built up describing the plant adaptation in climatic drought when stoma’s closure and reduction of plant’s potential evapo-transpiration (PET) starts. The adaptation algorithm of Doorenbos et al. (1978) is developed further defining that soil moisture content initiating the stomata’s closure. The critical soil moisture content is varying according to the PET, and drought tolerance of plant. If soil moisture content is less than the critical one, the plant evapo-transpiration (ET) can be highly different in the drought tolerance plant groups. The new drought tolerance algorithm is applied to maize field plots on chernozem soil of the experimental station of the Debrecen University, in East Hungary. Simulated soil water storages are compared to measured ones of a field plot treatment in five consecutive years. The soil moisture content profiles are measured with a BR-150 capacitance probe (Andrén et al. 1991). Differences between measured and simulated soil water storages are not significant in 2003. Simulations indicate low soil water storages in autumn of 2006, and in the first half of 2007 predicting the low maize production realized in 2007. The new plant adaptation algorithm can be used for a climate and soil moisture content sensitive irrigation control as well. The maize production is an illustrative biohydrological example of water flow through the soil-plant-atmosphere continuum.     

Tolerance and physiological responses of Phragmites australis to water deficit

The water stress tolerance of Phragmites australis (Cav.) Trin ex. Steud. grown in the laboratory were investigated by examining effects of different levels of imposed water deficits on growth, photosynthesis and various physiological traits related to water stress. Individual plants were grown under conditions of unrestricted water supply and compared with groups of plants receiving 60, 30, 15 or 5% of previous daily water requirements, respectively.Water deficit was found to reduce the leaf area and the leaf biomass per plant due to decreased production of new leaves, increased leaf shedding and reduced average leaf size. Leaf production and leaf expansion growth were very sensitive to water availability and were reduced when plants were subjected to fairly mild water deficit. Osmolality in sap expressed from leaves and the concentration of proline in leaves were only significantly increased in severely stressed plants, indicating that osmotic adjustment was of minor importance until a critical stress level was reached. Photosynthetic parameters were rather unaffected until the water availability was very low and led to the assertion that reduced CO₂ assimilation was mainly due to stomatal closure and not biochemical changes. Water stress had no effect on the activity of Rubisco. The CO₂ assimilation rate and stomatal conductance decreased in such a way that the intrinsic water use efficiency (A/g_s) increased, indicating efficient CO₂ utilization in water stressed plants. The apparent quantum yield (φ_i) was reduced in leaves of the most stressed plants, probably due to a decrease in the CO₂ molar fraction in the chloroplasts following stomatal closure.The initial response of P. australis to water deficit is a reduction in leaf area, the remaining leaves staying physiological rather well functioning until they are severely stressed. A high intrinsic water use efficiency and the ability to maintain some capacity for photosynthesis under severe water stress can undoubtedly contribute to the survival of P. australis under dry conditions. Taken together with its well-developed adaptations to flooding, P. australis seems very well adapted to grow in wetland areas with a widely fluctuating hydroperiod. P. australis grows very well in rather deep water, but can also tolerate extensive periods of drought with reduced availability of water.     

Contrasting physiological responses of six eucalyptus species to water deficit

BACKGROUND AND AIMS: The genus Eucalyptus occupies a broad ecological range, forming the dominant canopy in many Australian ecosystems. Many Eucalyptus species are renowned for tolerance to aridity, yet inter-specific variation in physiological traits, particularly water relations parameters, contributing to this tolerance is weakly characterized only in a limited taxonomic range. The study tests the hypothesis that differences in the distribution of Eucalyptus species is related to cellular water relations. METHODS: Six eucalypt species originating from (1) contrasting environments for aridity and (2) diverse taxonomic groups were grown in pots and subjected to the effects of water deficit over a 10-week period. Water potential, relative water content and osmotic parameters were analysed by using pressure-volume curves and related to gas exchange, photosynthesis and biomass. KEY RESULTS: The six eucalypt species differed in response to water deficit. Most significantly, species from high rainfall environments (E. obliqua, E. rubida) and the phreatophyte (E. camaldulensis) had lower osmotic potential under water deficit via accumulation of cellular osmotica (osmotic adjustment). In contrast, species from low rainfall environments (E. cladocalyx, E. polyanthemos and E. tricarpa) had lower osmotic potential through a combination of both constitutive solutes and osmotic adjustment, combined with reductions in leaf water content. CONCLUSIONS: It is demonstrated that osmotic adjustment is a common response to water deficit in six eucalypt species. In addition, significant inter-specific variation in osmotic potential correlates with species distribution in environments where water is scarce. This provides a physiological explanation for aridity tolerance and emphasizes the need to identify osmolytes that accumulate under stress in the genus Eucalyptus.     

Assessing the performance of a cold region evapotranspiration landfill cover using lysimetry and electrical resistivity tomography

In order to test the efficacy ofa cold-region evapotranspiration (ET) landfill cover against a conventional compacted clay (CCL) landfill cover, two pilot scale covers were constructed in side-by-side basin lysimeters (20m x 10m x 2m) at a site in Anchorage, Alaska. The primary basis of comparison between the two lysimeters was the percolation of moisture from the bottom of each lysimeter. Between 30 April 2005 and 16 May 2006, 51.5 mm of water percolated from the ET lysimeter, compared to 50.6 mm for the the CCL lysimeter. This difference was not found to be significant at the 95% confidence level. As part of the project, electrical resistivity tomography (ERT) was utilized to measure and map soil moisture in ET lysimeter cross sections. The ERT-generated cross sections were found to accurately predict the onset and duration of lysimeter percolation. Moreover, ERT-generated soil moisture values demonstrated a strong linear relationship to lysimeter percolation rates (R-Squared = 0.92). Consequently, ERT is proposed as a reliable tool for assessing the function of field scale ET covers in the absence of drainage measurement devices.     

PHENOPSIS, an automated platform for reproducible phenotyping of plant responses to soil water deficit in Arabidopsis thaliana permitted the identification of an accession with low sensitivity to soil water deficit

The high-throughput phenotypic analysis of Arabidopsis thaliana collections requires methodological progress and automation. Methods to impose stable and reproducible soil water deficits are presented and were used to analyse plant responses to water stress. Several potential complications and methodological difficulties were identified, including the spatial and temporal variability of micrometeorological conditions within a growth chamber, the difference in soil water depletion rates between accessions and the differences in developmental stage of accessions the same time after sowing. Solutions were found. Nine accessions were grown in four experiments in a rigorously controlled growth-chamber equipped with an automated system to control soil water content and take pictures of individual plants. One accession, An1, was unaffected by water deficit in terms of leaf number, leaf area, root growth and transpiration rate per unit leaf area. Methods developed here will help identify quantitative trait loci and genes involved in plant tolerance to water deficit.     

Deciphering genetic variations of proteome responses to water deficit in maize leaves

The proteome of the basal part of growing Zea mays leaves was analyzed from 4 to 14 d after stopping watering and in well watered controls. The relative quantity of 46 proteins was found to increase in leaves of plants submitted to water deficit. Different types of responses were observed, some proteins showing a constant increase during water deficit, while others showed stabilization after a first increase or a transient increase. Isoforms encoded by the same gene showed different responses. The response to water deficit showed genetic variation. Some increased proteins were induced specifically in one of the two studied genotypes (e.g. ASR1) while others were significantly induced in both genotypes but to a different level or with different kinetics. Analyses of relations between protein quantities, relative water content (RWC) and abscisic acid (ABA) concentration allowed us to show that the quantitative variation of some proteins (e.g. ABA45 and OSR40 proteins) was linked to differences in ABA accumulation between the genotypes. Other proteins showed genetic variations that were not related to differences in water status or ABA concentration (e.g. a cystatin). Data obtained from these experiments, together with data from other experiments, contribute to the characterization of maize proteome response to drought in different conditions and in different genotypes. This characterization allows the search for candidate proteins, i.e. for protein whose genetic variation of expression could be partly responsible for the variability of plant responses to drought.     

植物响应水分胁迫的主要功能蛋白

植物对水分胁迫的响应蛋白根据其在抗逆机制中的作用不同分为调节蛋白和功能蛋白,本文就植物抵抗和适应水分胁迫的活性氧清除机制、渗透调节机制及膜修饰机制相关的主要功能蛋白作一综述。     

Morpho-physiological and biochemical responses of muskmelon genotypes to different degree of water deficit

Morpho-physiological and biochemical analyses were carried out in eight diverse indigenous muskmelon (Cucumis melo L.) genotypes exposed to different degrees of water deficit (WD). The ability of genotypes MM-7, and especially MM-6, to counteract better the negative effect of WD was associated with maintaining higher relative water content (RWC), photosynthetic rate, efficiency of PSII, and photosynthetic pigments compare to other genotypes. Furthermore, MM-6 showed a better ability to maintain cellular homeostasis than the others. It was indicated by a stimulated antioxidative defense system, i.e., higher activities of antioxidant enzymes, accumulation of nonenzymatic antioxidants together with lower concentration of reactive oxygen species and malondialdehyde. However, the genotypes MM-2 and MM-5 suffered greatly due to WD and showed reduced RWC, photosynthetic rates, pigment content, and exhibited higher oxidative stress observed as lower antioxidant enzyme activities.     

Stomatal response to vapour pressure deficit and the effect of plant water stress

Abstract The dynamic response of stomata to changes in atmospheric humidity was investigated in Fragaria × ananassa Duch., Picea engelmannii Parry, and Pseudotsuga menziesii (Mirb.) Franco; and the effect of water stress on this response was determined in Pseudotsuga menziesii. The plants were rotated through three regimes of ambient temperature and vapour pressure deficit: 35°C–3. 5kPa, 35°C–0. 5 kPa, and 20°C–1. 5kPa. Branch and leaflet conductance were measured with a steady-state porometer, first at ambient vapour pressure deficit and then at one of four treatment conditions achieved by increasing or decreasing vapour pressure within the porometer cuvette. All three species showed similar stomatal response: enhanced conductance at low vapour pressure deficit and depressed conductance at high vapour pressure deficit. Engelmann spruce was more sensitive than Douglas fir and strawberry. Plant water status significantly altered stomatal response to vapour pressure deficit. The relationship of conductance of xylem water potential was linear under ambient conditions but became curvilinear when conductance was measured above and below ambient vapour pressure deficit. Between ?0. 5 MPa and ?2. 0 MPa xylem water potential, the stomata were sensitive to vapour pressure deficit, but below ? 2. 0 MPa, the sensitivity decreased.     

Estimation of the spatial variability of root water uptake of maize and sorghum at the field scale by electrical resistivity tomography

Saving water for crop production is an old, but ongoing, challenge which requires a better understanding of the in situ functioning of root systems. In particular, this requires a better quantification and understanding of the spatial and temporal variability of the root water uptake at the field scale. Electrical Resistivity Tomography (ERT) is a non-destructive soil imaging technique, related to water content, which could help in spatializing active zones of water uptake. In this article, we evaluate ERT as an alternative method for quantifying and spatializing root water uptake at the field scale. To this aim, an experimental field study with maize and sorghum submitted to different water supply levels (Fully, Moderately or Poorly Irrigated treatments—FI, MI, PI zones) was conducted for 3 months with concomitant conventional, local, water balance measurements and 2D ERT imaging. ERT images showed an heterogeneous depletion of soil water by the crops, particularly, in the MI and PI zones with patches of high/low electrical resistivity (and thus water content) variations. This heterogeneity was greatest in the MI zone and points to spatial variations in rooting pattern and/or root efficiency. The 5-days difference in electrical resistivity could be quantitatively related to root uptake in the surface layer (down to 60 cm) but the relationship depends on the mean soil water content. At greater soil depth, in the water stressed zones, the water extraction front progressing downwards could not be assessed with the ERT surface setting used in this study. As a conclusion, ERT can be a useful, unique, technique for monitoring and estimating field water uptake by plant roots and its variability if combined water content measurements are available for in situ calibration and if the sensitivity/resolution of the technique is improved for estimation over the whole root zone.     

Polyamines induce adaptive responses in water deficit stressed cucumber roots

The aim of this study was to investigate the effect of exogenous polyamines (PAs) on the membrane status and proline level in roots of water stressed cucumber (Cucumis sativus cv. Dar) seedlings. It was found that water shortage resulted in an increase of membrane injury, lipoxygenase (LOX) activity, lipid peroxidation and proline concentration in cucumber roots during progressive dehydration. PA pretreatment resulted in a distinct reduction of the injury index, and this effect was reflected by a lower stress-evoked LOX activity increase and lipid peroxide levels at the end of the stress period. In contrast, PA-supplied stressed roots displayed a higher proline accumulation. The presented results suggest that exogenous PAs are able to alleviate water deficit-induced membrane permeability and diminish LOX activity. Observed changes were accompanied by an accumulation of proline, suggesting that the accumulation of this osmolyte might be another possible mode of action for PAs to attain higher membrane stability, and in this way mitigate water deficit effects in roots of cucumber seedlings.     

Breast imaging using 3D electrical impedence tomography

Aim: To determine the diagnostic efficiency of 3D Eletrical Impedance Tomography (EIT) compared to Mammography (MG) and Ultrasonography (USG) in imaging the breast. Materials and Methods: A group of 88 patients presenting with various breast complaints was examined using combined Mammography and Ultrasonography (MG & USG) or either of these modalities alone. The same patients were then examined using the 3D EIT imaging system "MEIK". The findings were then compared. The sensitivity of these modalities for this group of patients were later determined and statistically analysed. Results: Of the total of 88 patients, 59 findings were "suspicious" by any of the 3 modalities alone or by their combination. EIT had a sensitivity of 77.8 % compared to MG with a sensitivity of 83.3 % and USG with a sensitivity of 94.4 % regarding cases of fibrocystic mastitis. For cases involving cysts, EIT had 100 % sensitivity which was the same as that for USG compared to MG with a sensitivity of only 81 %. Among cases of fibroadenoma, EIT had a sensitivity of just 68.8 % compared to MG with a sensitivity of 87.5 % and USG with a sensitivity of 75 %. Finally among cases of carcinoma, EIT had a sensitivity of 75 % compared to the sensitivity of 100 % of MG and USG in our group of patients. The study revealed that there was no overall significant difference in sensitivity between MG-USG (p = 0.219) and MG-EIT (p = 0.779) and USG-EIT (p = 0.169). However, in regard to identifying cysts there was significant difference in the sensitivity of MG compared to USG & EIT suggesting that EIT has a role in these cases. Conclusion: Electrical impedance could be used as an adjunct to Mammography and Ultrasonography for breast cancer detection. However, the differentiation of malignant from benign lesions based on impedance measurements needs further investigation. Multifrequency electrical impedance imaging appears the most promising for detecting breast malignancies but methodological improvements need to be made to realise its potential.     

Osmoregulation and membrane-mediated responses to altered water potential in plant cells

Plant cells respond to short-term stress dehydration by modification of internal Ψ_π such that an inward gradient of Ψ_ω is maintained. In response to lowered Ψ_ω, increases in internal Ψ_π are created by alteration of cell inorganic ions and small organic solute content. Passive movement of water follows, changing cell hydration and forcing the plasma membrane against the elastic cell wall. The stretched cell wall presses against the cell contents, creating a hydrostatic pressure, Ψ_π, which tends to force water out of the cell. The resulting hydrostatic pressure eventually comes into equilibrium with forces bringing water into the cell, largely Ψ_π, and the net flow of water ceases.The mechanism for sensing cell Ψ_ω changes is unknown but the initial event must be physical, not biochemical. The method of translation of such physical events into biochemical actions is also unknown but the Zimmermann model provides a means of signal transduction and amplification, through the alteration of membrane parameters, which could account for the observed changes. As for animal cells, cell levels of Ca²⁺ are important for their regulation of membrane P_j in these responses but unlike osmoregulation in higher animals, the involvement of plant hormones in these responses have not been clearly established. However, the important role of plant cell limiting membranes in plant cell osmoregulation responses seems obvious.     

The photosynthetic response of tobacco plants overexpressing ice plant aquaporin McMIPB to a soil water deficit and high vapor pressure deficit

We investigated the photosynthetic capacity and plant growth of tobacco plants overexpressing ice plant (Mesembryanthemum crystallinum L.) aquaporin McMIPB under (1) a well-watered growth condition, (2) a well-watered and temporal higher vapor pressure deficit (VPD) condition, and (3) a soil water deficit growth condition to investigate the effect of McMIPB on photosynthetic responses under moderate soil and atmospheric humidity and water deficit conditions. Transgenic plants showed a significantly higher photosynthesis rate (by 48 %), higher mesophyll conductance (by 52 %), and enhanced growth under the well-watered growth condition than those of control plants. Decreases in the photosynthesis rate and stomatal conductance from ambient to higher VPD were slightly higher in transgenic plants than those in control plants. When plants were grown under the soil water deficit condition, decreases in the photosynthesis rate and stomatal conductance were less significant in transgenic plants than those in control plants. McMIPB is likely to work as a CO₂ transporter, as well as control the regulation of stomata to water deficits.     

Leaf water relations during summer water deficit: differential responses in turgor maintenance and variation in leaf structure among different plant communities in south-western Australia

We measured leaf water relations and leaf structural traits of 20 species from three communities growing along a topographical gradient. Our aim was to assess variation in seasonal responses in leaf water status and leaf tissue physiology between sites and among species in response to summer water deficit. Species from a ridge-top heath community showed the greatest reductions in pre-dawn leaf water potentials (Psi(leaf)) and stomatal conductance during summer; species from a valley-floor woodland and a midslope mallee community showed less reductions in these parameters. Heath species also displayed greater seasonal reduction in turgor-loss point (Psi(TLP)) than species from woodland or mallee communities. In general, species that had larger reductions in Psi(leaf) during summer showed significant shifts in either their osmotic potential at full turgor (Psi(pi 100); osmotic adjustment) or in tissue elasticity (epsilon(max)). Psi(pi 100) and epsilon(max) were negatively correlated, during both spring and summer, suggesting a trade-off between these different mechanisms to cope with water stress. Specific leaf area varied greatly among species, and was significantly correlated with seasonal changes in Psi(TLP) and pre-dawn Psi(leaf). These correlations suggest that leaf structure is a prerequisite for cellular mechanisms to be effective in adjusting to water deficit.