Regulation Of Water Loss Research Articles

Study of surfactant–skin interactions by skin impedance measurements

The stratum corneum (SC) plays a very critical physiological role as skin barrier in regulating water loss through the skin and protects the body from a wide range of physical and chemical exogenous insults. Surfactant-containing formulations can induce skin damage and irritation owing to surfactant absorption and penetration. It is generally accepted that reduction in skin barrier properties occurs only after surfactants have penetrated/permeated into the skin barrier. To mitigate the harshness of surfactant-based cleansing products, penetration/permeation of surfactants should be reduced. Skin impedance measurements have been taken in vitro on porcine skin using vertical Franz diffusion cells to investigate the impact of surfactants, temperature and pH on skin barrier integrity. These skin impedance results demonstrate excellent correlation with other published methods for assessing skin damage and irritation from different surfactant chemistry, concentration, pH, time of exposure and temperature. This study demonstrates that skin impedance can be utilized as a routine approach to screen surfactant-containing formulations for their propensity to compromise the skin barrier and hence likely lead to skin irritation.

Water loss regulation in mature Hevea brasiliensis: effects of intermittent drought in the rainy season and hydraulic regulation

Effects of soil and atmospheric drought on whole-tree transpiration (E(T)), leaf water potential (Ψ(L)) and whole-tree hydraulic conductance (K(T)) were investigated in mature rubber trees (Hevea brasiliensis, clone RRIM 600) during the full canopy stage in the rainy season in a drought-prone area of northeast Thailand. Under well-watered soil conditions, transpiration was tightly regulated in response to high evaporative demand, i.e., above reference evapotranspiration (ET(0)) ~2.2 mm day(-1) or maximum vapor pressure deficit ~1.8 kPa. When the trees experienced intermittent soil drought E(T) decreased sharply when relative extractable water in the top soil was < 0.4. The midday leaf water potential (Ψ(md)) on sunny days did not change as a function of soil drought and remained stable at approximately - 1.95 MPa, i.e., displaying isohydric behavior. The decrease in E(T) was mainly due to the change in K(T). K(T) remained constant over a wide range of environmental conditions and decreased sharply at low soil water availability. A simple hydraulic model incorporating critical minimum water potential and the response of whole-tree hydraulic conductance to relative extractable water correctly simulated patterns of transpiration over 6 months. We conclude that an explicit and simplified framework of hydraulic limitation hypothesis was sufficient to describe water use regulation of a mature rubber tree stand in water-limited conditions. Given the complexity of constraints in the soil-plant-atmosphere pathway, our results confirm the relevance of this approach to synthesize the overall behavior of trees under drought.

Predicting Transpiration Response to Climate Change: Insights on Physiological and Morphological Interactions that Modulate Water Exchange from Leaves to Canopies

Leaves are key factors in the global water exchange cycle. As the primary control interface involved in regulating water loss, understanding the relative influence of leaf morphological and physiological transpiration factors is critical to accurate evapotranspiration predictions. We parameterized a three-dimensional array model, MAESTRA, to establish a link from the leaf to canopy scale and attempted to isolate and understand the interplay among variation in morphological and physiological variables affecting transpiration. When physiological differences were accounted for, differences in leaf width (Lw) among Acer rubrum L. genotypes significantly affected leaf temperature and transpiration under slow to moderate wind velocities. In instances, Lw variation among genotypes resulted in a 25% difference in transpiration. This study demonstrates how simple morphological traits like Lw can provide useful selection criteria for plant breeders to consider in a changing climate.

Adjustment of metabolite composition in the haemolymph to seasonal variations in the land snail Helix pomatia

In temperate regions, land snails are subjected to subzero temperatures in winter and hot temperatures often associated to drought in summer. The response to these environmental factors is usually a state of inactivity, hibernation and aestivation, respectively, in a temperature and humidity buffered refuge, accompanied by physiological adjustments to resist cold or heat stress. We investigated how environmental factors in the microhabitat and body condition influence the metabolite composition of haemolymph of the endangered species Helix pomatia. We used UPLC and GC-MS techniques and analyzed annual biochemical variations in a multivariate model. Hibernation and activity months differed in metabolite composition. Snails used photoperiod as cue for seasonal climatic variations to initiate a physiological state and were also highly sensitive to temperature variations, therefore constantly adjusting their physiological processes. Galactose levels gave evidence for the persistence of metabolic activity with energy expenditure during hibernation and for high reproductive activity in June. Triglycerides accumulated prior to hibernation might act as cryoprotectants or energy reserves. During the last month of hibernation snails activated physiological processes related to arousal. During activity, protein metabolism was reflected by high amino acid level. An exceptional aestivation period was observed in April giving evidence for heat stress responses, like the protection of cells from dehydration by polyols and saccharides, the membrane stabilization by cholesterol and enhanced metabolism using the anaerobic succinic acid pathway to sustain costly stress responses. In conclusion, physiological adjustments to environmental variations in Helix pomatia involve water loss regulation, cryoprotectant or heatprotectant accumulation.

Winter desiccation and rapid changes in the live fuel moisture content of Calluna vulgaris

Background: Dramatic reductions in early-spring Calluna vulgaris moisture content have been linked to extreme fire hazard and plant die-back. Aims: To investigate spatial and temporal variation in the fuel moisture content of Calluna vulgaris. Methods: Calluna vulgaris plants were sampled in different sites and seasons to examine vertical profiles in moisture content. Live moisture content was monitored throughout autumn 2003 and spring 2004. Changes were compared to trends in temperature, soil resistance and rainfall. The effect of exposure was examined by comparing shoot moisture content in sheltered and exposed locations. Results: Significant spatial and temporal variation in moisture content was observed. In spring rapid fluctuations in moisture coincided with periods of dry weather, low temperatures and frozen ground. Shoots from exposed locations had significantly lower moisture content when the ground was frozen. Conclusions: Significant declines in the live fuel moisture content of Calluna vulgaris are associated with physiological drought caused by cold, clear conditions and frozen ground. Over-winter damage to leaf cuticles reduces the ability of the plant to regulate water loss. Changes in moisture content can be rapid, and managers should be aware of the potential for extreme fire behaviour.

Expression of StMYB1R-1, a Novel Potato Single MYB-Like Domain Transcription Factor, Increases Drought Tolerance

Potato (Solanum tuberosum) is relatively vulnerable to abiotic stress conditions such as drought, but the tolerance mechanisms for such stresses in potato are largely unknown. To identify stress-related factors in potato, we previously carried out a genetic screen of potato plants exposed to abiotic environmental stress conditions using reverse northern-blot analysis. A cDNA encoding a putative R1-type MYB-like transcription factor (StMYB1R-1) was identified as a putative stress-response gene. Here, the transcript levels of StMYB1R-1 were enhanced in response to several environmental stresses in addition to drought but were unaffected by biotic stresses. The results of intracellular targeting and quadruple 9-mer protein-binding microarray analysis indicated that StMYB1R-1 localizes to the nucleus and binds to the DNA sequence (G)/(A)GATAA. Overexpression of a StMYB1R-1 transgene in potato plants improved plant tolerance to drought stress while having no significant effects on other agricultural traits. Transgenic plants exhibited reduced rates of water loss and more rapid stomatal closing than wild-type plants under drought stress conditions. In addition, overexpression of StMYB1R-1 enhanced the expression of drought-regulated genes such as AtHB-7, RD28, ALDH22a1, and ERD1-like. Thus, the expression of StMYB1R-1 in potato enhanced drought tolerance via regulation of water loss. These results indicated that StMYB1R-1 functions as a transcription factor involved in the activation of drought-related genes.

Ecophysiological responses of salt cedar (Tamarix spp. L.) to the northern tamarisk beetle (Diorhabda carinulata Desbrochers) in a controlled environment

The northern tamarisk beetle (Diorhabda carinulata Desbrochers) was released in several western states as a biocontrol agent to suppress Tamarix spp. L. which has invaded riparian ecosystems; however, effects of beetle herbivory on Tamarix physiology are largely undocumented and may have ecosystem ramifications. Herbivory by this insect produces discoloration of leaves and premature leaf drop in these ecosystems, yet the cause of premature leaf drop and the effects of this leaf drop are still unknown. Insect herbivory may change leaf photosynthesis and respiration and may affect a plant’s ability to regulate water loss and increase water stress. Premature leaf drop may affect plant tissue chemistry and belowground carbon allocation. We conducted a greenhouse experiment to understand how Tamarix responds physiologically to adult beetle and larvae herbivory and to determine the proximate cause of premature leaf drop. We hypothesized that plants experiencing beetle herbivory would have greater leaf and root respiration rates, greater photosynthesis, increased water stress, inefficient leaf nitrogen retranslocation, lower root biomass and lower total non-structural carbohydrates in roots. Insect herbivory reduced photosynthesis rates, minimally affected respiration rates, but significantly increased water loss during daytime and nighttime hours and this produced increased water stress. The proximate cause for premature leaf drop appears to be desiccation. Plants exposed to herbivory were inefficient in their retranslocation of nitrogen before premature leaf drop. Root biomass showed a decreasing trend in plants subjected to herbivory. Stress induced by herbivory may render these trees less competitive in future growing seasons.

Natural ventilation effectively reduces hyperhydricity in shoot cultures of Aloe polyphylla Schönland ex Pillans

An investigation into the role of ventilation to reduce hyperhydricity in tissue cultures of Aloe polyphylla Schonland ex Pillans revealed that gaseous exchange between the in-vitro atmosphere and the outside environment is an essential prerequisite for controlling this disorder. In closed culture vessels, hyperhydricity affected as much as 84% of the newly-formed shoots on media gelled with gelrite. The leaves of hyperhydric shoots had a bright green colour, smooth epidermis and large, open stomata. Gaseous exchange was promoted by using modified lids with a hole covered with polyester or cotton mesh. In ventilated cultures, hyperhydricity was completely eliminated irrespective of the type of gelling agent used. Natural ventilation was further advantageous for the microplants in terms of leaf chlorophyll content as well as the deposition of epicuticular wax, indicating the onset of mechanisms that regulate water loss from the explants. Although culture ventilation was negatively correlated to the regeneration rate and shoot growth, it has the potential to control the appearance of abnormal phenotypes and can be easily adopted for routine A. polyphylla propagation in vitro.

Ecological responses to soil water content in four hybrid Populus clones.

Aims Pot experiments were conducted to investigate effects of water deficit and duration of the deficit (0,15,36 and 14 days recovery) on four hybrid Populus: 15-29 (P. trichocarpa×P. deltoids), DN-2 (P.deltoids×P.nigra), DN-14274 (P. deltoids× P.nigra) and R-270 (P.deltoids×P. nigra). Our objective was to examine the responses of Populus plants to soil water deficit by analyzing eco-physiological, morphological, and growth characteristics, as well as several parameters of plant performance. Methods Seedlings were exposed to four treatments: 100%,70%,50% and 30% of soil field water capacity (treatments T1-T4, respectively). Important findings The four hybrids were sensitive to water deficit. All developed physiological adaptive mechanisms as well as configurational strategies to cope with water shortages to different degrees by closing stomata and reducing leaf number and leaf area to regulate water loss, by depressing net photosynthetic rate (Pn), transpiration rate (Tr) and leaf water potential (ψ) to enhance water use efficiency (WUE), or by changing allocation of biomass productivity (Bp). Under water stress, R-270 only decreased its leaf dry weight but the other three hybrids decreased their dry weight of leaf, stem and root. With declining soil moisture, root/shoot of 15-29 and R-270 increased, implying the roots obtained more carbohydrates, which favors water absorption. Carbon isotope composition (δ13) of DN-2 was significantly positively correlated to WUE, but δ13 of R-270 was significantly negatively correlated to WUE. Pn, stomatal conductance (Gs), Tr,ψ, biomass and canopy areas of the seedlings in T1 and T2 are higher than those in T3 and T4, suggesting that the four hybrids can obtain high production in arid areas under sufficient-moderate irrigation. Lower Pn, Gs, Tr,ψ, biomass, canopy areas and higher WUE of the seedling in T3 and T4 indicate that the four hybrids can develop survival strategies under water stress, but biomass production was negatively affected. Clone 15-29 and R-270 showed a stronger adaptive response than DN-2 and DN-14274 under water stress, implying they have greater drought-resistance ability.

PHOTOSYNTHETIC RESOURCE-USE EFFICIENCY AND DEMOGRAPHIC VARIABILITY IN DESERT WINTER ANNUAL PLANTS

We studied a guild of desert winter annual plants that differ in long-term variation in per capita reproductive success (lb, the product of per capita survival from germination to reproduction, l, times per capita reproduction of survivors, b) to relate individual function to population and community dynamics. We hypothesized that variation in lb should be related to species' positions along a trade-off between relative growth rate (RGR) and photosynthetic water-use efficiency (WUE) because lb is a species-specific function of growing-season precipitation. We found that demographically variable species have greater RGR and greater leaf carbon isotope discrimination (Delta, a proxy inversely related to WUE). We examined leaf nitrogen and photosynthetic characteristics and found that, in this system, variation in Delta is a function of photosynthetic demand rather than stomatal regulation of water loss. The physiological characteristics that result in low Delta in some species may confer greater photosynthetic performance during the reliably moist but low temperature periods that immediately follow winter rainfall in the Sonoran Desert or alternatively during cool periods of the day or early growing season. Conversely, while species with high Delta and high RGR exhibit low leaf N, they have high biomass allocation to canopy leaf area display. Such trait associations may allow for greater performance during the infrequent conditions where high soil moisture persists into warmer conditions, resulting in high demographic variance. Alternatively, high variance could arise from specialization to warm periods of the day or season. Population dynamic buffering via stress tolerance (low RGR and Delta) correlates negatively with buffering via seed banks, as predicted by bet-hedging theory. By merging analyses of population dynamics with functional trait relationships, we develop a deeper understanding of the physiological, ecological, and evolutionary mechanisms involved in population and community dynamics.

The Clickable Guard Cell, Version II: Interactive Model of Guard Cell Signal Transduction Mechanisms and Pathways.

Guard cells are located in the leaf epidermis and pairs of guard cells surround and form stomatal pores, which regulate CO(2) influx from the atmosphere into leaves for photosynthetic carbon fixation. Stomatal guard cells also regulate water loss of plants via transpiration to the atmosphere. Signal transduction mechanisms in guard cells integrate a multitude of different stimuli to modulate stomatal apertures. Stomata open in response to light. Stomata close in response to drought stress, elevated CO(2), ozone and low humidity. In response to drought, plants synthesize the hormone abscisic acid (ABA) that triggers closing of stomatal pores. Guard cells have become a highly developed model system for dissecting signal transduction mechanisms in plants and for elucidating how individual signaling mechanisms can interact within a network in a single cell. Many new findings have been made in the last few years. This chapter is an update of an electronic interactive chapter in the previous edition of The Arabidopsis Book (Mäser et al. 2003). Here we focus on mechanisms for which genes and mutations have been characterized, including signaling components for which there is substantial signaling, biochemical and genetic evidence. Ion channels have been shown to represent targets of early signal transduction mechanisms and provide functional signaling and quantitative analysis points to determine where and how mutations affect branches within the guard cell signaling network. Although a substantial number of genes and proteins that function in guard cell signaling have been identified in recent years, there are many more left to be identified and the protein-protein interactions within this network will be an important subject of future research. A fully interactive clickable electronic version of this publication can be accessed at the following web site: http://www-biology.ucsd.edu/labs/schroeder/clickablegc2/. The interactive clickable version includes the following features: Figure 1. Model for the roles of ion channels in ABA signaling.Figure 2. Blue light signaling pathways in guard cells.Figure 3. ABA signaling pathways in guard cells.Figure 1 is linked to explanations that appear upon mouse-over. Figure 2 and Figure 3 are clickable and linked to info boxes, which in turn are linked to TAIR, to relevant abstracts in PubMed, and to updated background explanations from Schroeder et al (2001), used with permission of Annual Reviews of Plant Biology.

Regulation of transpirational water loss in Quercus suber trees in a Mediterranean-type ecosystem

Sap flux density in branches, leaf transpiration, stomatal conductance and leaf water potentials were measured in 16-year-old Quercus suber L. trees growing in a plantation in southern Portugal to understand how evergreen Mediterranean trees regulate water loss during summer drought. Leaf specific hydraulic conductance and leaf gas exchange were monitored during the progressive summer drought to establish how changes along the hydraulic pathway influence shoot responses. As soil water became limiting, leaf water potential, stomatal conductance and leaf transpiration declined significantly. Predawn leaf water potential reflected soil water potential measured at 1-m depth in the rhizospheres of most trees. The lowest predawn leaf water potential recorded during this period was -1.8 MPa. Mean maximum stomatal conductance declined from 300 to 50 mmol m(-2) s(-1), reducing transpiration from 6 to 2 mmol m(-2) s(-1). Changes in leaf gas exchange were attributed to reduced soil water availability, increased resistances along the hydraulic pathway and, hence, reduced leaf water supply. There was a strong coupling between changes in soil water content and stomatal conductance as well as between stomatal conductance and leaf specific hydraulic conductance. Despite significant seasonal differences among trees in predawn leaf water potential, stomatal conductance, leaf transpiration and leaf specific hydraulic conductance, there were no differences in midday leaf water potentials. The strong regulation of changes in leaf water potential in Q. suber both diurnally and seasonally is achieved through stomatal closure, which is sensitive to changes in both liquid and vapor phase conductance. This sensitivity allows for optimization of carbon and water resource use without compromising the root-shoot hydraulic link.

Sapwood moisture in Douglas-fir boles and seasonal changes in soil water

Large conifers, such as Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco var. menziesii), purportedly draw on water stored in their boles during periods of summer drought. The relation of seasonal changes in soil moisture to sapwood water content was evaluated in four forest stands dominated by mature Douglas-fir along a transect from the Pacific Coast to 1200 m in the western Cascade Mountains of Oregon, USA. The sites varied in stand age, elevation, topography, and soil characteristics, including available soil water capacity. At two sites, gravimetric measures of sapwood relative water content (SRWC) were taken approximately every 4 weeks from May 2002 through July 2004; two additional sites were similarly measured from February 2003 through July 2004. Automated meteorological stations located on the sites and in adjacent open areas continuously monitored weather and soil moisture. Plant-available soil water (ASW) in the upper 0.6 m of soil reached minimum values during the summer drought and rewetted during fall and winter. Large seasonal changes in ASW did not result in corresponding changes in SRWC. Minimum SRWC was lower at sites with higher ASW. At all sites, Douglas-fir trees apparently regulate water loss to maintain consistent (±10%) bole water content throughout the year despite large changes in soil moisture.

Fungal endophytes nearly double minimum leaf conductance in seedlings of a neotropical tree species

Drought strongly influences plant phenology, growth and mortality in tropical forests, thereby shaping plant performance, population dynamics and community structure (Bunker &amp; Carson 2005, Condit et al. 1995). Microbial symbionts of plants profoundly influence host water relations (Lösch &amp; Gansert 2002), but are rarely considered in studies of tropical plant physiology. In particular, plant–fungus associations, which are ubiquitous in plant communities and especially common in tropical forests, play important and varied roles in plant water status. Fungal pathogens associated with roots, vascular tissue and foliage may interfere with water uptake and transport, increase rates of foliar transpiration, and induce xylem embolism and tissue death (Agrios 1997). In contrast, rhizosphere mutualists such as ecto- and arbuscular mycorrhizal fungi may benefit hosts by increasing surface area for water uptake, enhancing stomatal regulation of water loss, and increasing root hydraulic conductivity (Auge 2001, Lösch &amp; Gansert 2002).

Habitat requirements of the seabird tick, Ixodes uriae (Acari: Ixodidae), from the Antarctic Peninsula in relation to water balance characteristics of eggs, nonfed and engorged stages

The seabird tick Ixodes uriae is exposed to extreme environmental conditions during the off-host phase of its life cycle on the Antarctic Peninsula. To investigate how this tick resists desiccation, water requirements of each developmental stage were determined. Features of I. uriae water balance include a high percentage body water content, low dehydration tolerance limit, and a high water loss rate, which are characteristics that classify this tick as hydrophilic. Like other ticks, I. uriae relies on water vapor uptake as an unfed larva and enhanced water retention in the adult, while nymphs are intermediate and exploit both strategies. Stages that do not absorb water vapor, eggs, fed larvae and fed nymphs, rely on water conservation. Other noteworthy features include heat sensitivity that promotes water loss in eggs and unfed larvae, an inability to drink free water from droplets, and behavioral regulation of water loss by formation of clusters. We conclude that I. uriae is adapted for life in a moisture-rich environment, and this requirement is met by clustering in moist, hydrating, microhabitats under rocks and debris that contain moisture levels that are higher than the tick's critical equilibrium activity.

δD values of individual n-alkanes from terrestrial plants along a climatic gradient – Implications for the sedimentary biomarker record

The compound-specific hydrogen isotope composition ( δD) of sedimentary n-alkanes is increasingly used as a palaeoclimate proxy. To explore the origin of the hydrogen isotope signal of n-alkanes from higher terrestrial plant biomass in sedimentary organic matter of small lakes we have analysed the n-alkane composition and δD values of 31 plant biomass samples (Birch ( Betula), Beech ( Fagus), Oak ( Quercus), Alder ( Alnus), Hornbeam ( Carpinus) and Myrtle ( Myrtus) as well as non-stomata containing Sphagnum, Cladonia and moss) from 14 sites along a climatic gradient from Northern Finland to Southern Italy. Eleven of the sites were previously investigated for the n-alkane δD values in adjacent lake sediments and are compared to the leaf wax n-alkane δD values. The distribution of terrestrial n-alkanes in lake sediments was not found to be characteristic of the dominant vegetation around the lake. Evidently, n-alkane distributions within the same species at different sites were found to be variable. These findings complicate the use of certain n-alkane distributions in sediments as a palaeoenvironmental indicator. δD values of plant biomass n-alkanes show a significant positive correlation with the precipitation δD values. Biomass n-alkane δD values are in general less negative than the associated sedimentary n-alkanes of terrestrial origin, possibly due to the stronger evapotranspiration during the summer, when sampling took place. This suggests, that n-alkanes in leaves show seasonal variations and the sedimentary organic matter receives the lighter isotope signal of the autumn, when most leaves are incorporated into the sediment. The variability of the δD values from non-stomata containing plants is much higher than for broadleaf trees, since stomata can regulate water loss through evapotranspiration. The average chain length (ACL) of n-alkanes from deciduous tree leaves increases from North to South. With increasing ACL the hydrogen isotopic fractionation ( ε) between source water and n-alkanes also increases. Our results prove that terrestrial n-alkane δD values record the δD value of precipitation, modified by the amount of isotope enrichment in the leaf water due to plant anatomy (stomata vs. no stomata) and site specific meteorological conditions, such as evapotranspiration, relative humidity and soil moisture. Therefore, terrestrial n-alkanes in lake sediments can deliver information on changes in these parameters over geological timescales. In lake sediments where aquatic n-alkanes, such as n-C 17 record the lake water δD value, the isotopic difference between terrestrial and aquatic n-alkanes could therefore be used to reconstruct changes in evapotranspiration.

The control of stomata by water balance

It is clear that stomata play a critical role in regulating water loss from terrestrial vegetation. What is not clear is how this regulation is achieved. Stomata appear to respond to perturbations of many aspects of the soil-plant-atmosphere hydraulic continuum, but there is little agreement regarding the mechanism (or mechanisms) by which stomata sense such perturbations. This review discusses feedback and feedforward mechanisms by which hydraulic perturbations are putatively transduced into stomatal movements, in relation to generic empirical features of those responses. It is argued that a metabolically mediated feedback response of stomatal guard cells to the water status in their immediate vicinity ('hydro-active local feedback') remains the best explanation for many well-known features of hydraulically related stomatal behaviour, such as transient 'wrong-way' responses and the equivalence of hydraulic supply and demand as stomatal effectors. Furthermore, many curious phenomena that appear inconsistent with feedback, such as 'apparent feedforward' humidity responses and 'isohydric' behaviour (water potential homeostasis), are in fact expected to emerge from the juxtaposition of hydro-active local feedback and the well-known hysteretic and threshold-like effect of water potential on xylem hydraulic resistance.

Vulnerability to embolism differs in roots and shoots and among three Mediterranean conifers: consequences for stomatal regulation of water loss?

We investigated the potential links between stomatal control of transpiration and the risk of embolism in root and shoot xylem of seedlings of three Mediterranean conifers (Cupressus sempervirens, Pinus halepensis and P. nigra) grown in a greenhouse under semi-controlled conditions. We measured the intrinsic vulnerability to embolism in roots and current year shoots by the air injection method. Root and shoot segments were subjected to increasing pressures, and the induced loss of hydraulic conductivity recorded. The three species displayed very different vulnerabilities in shoots, with P. nigra being much more vulnerable than P. halepensis and C. sempervirens. Roots were distinctly more vulnerable than shoots in C. sempervirens and P. halepensis (50% loss of conductivity induced at 3.0 MPa and 1.7 MPa higher xylem water potential in roots vs shoots). In P. nigra, no significant difference of vulnerability between shoots and roots was found. Seedlings were subjected to soil drought, and stomatal conductance, twig hydraulic conductivity and needle water potential were measured. The water potential resulting in almost complete stomatal closure (90%) was very close to the threshold water potential inducing loss of conductivity (10%) in twigs in P nigra, resulting in a very narrow safety margin between stomatal closure and embolism induction. The safety margin was larger in P. halepensis and greatest in C. sempervirens. Unexpectedly, this water potential threshold produced a 30–50% loss of conductivity in 3–5 mm diameter roots, depending on the species. The implications of this finding are discussed.

Effect of Tape Stripping on Percutaneous Penetration and Topical Vaccination

The stratum corneum provides the first barrier to the percutaneous absorption of drugs as well as regulating water loss. This barrier limits the topical/transdermal delivery of drugs and biological macromolecules. Chemical and physical approaches have been examined to decrease these properties. Tape stripping is commonly used to disrupt the epidermal barrier, to enhance the delivery of drugs and to obtain information about stratum corneum function. Tape stripping results in the production and release of cytokines and co-stimulatory molecules and increases the humoral and cellular immune responses against peptide, protein and DNA antigens by a topical vaccination in vivo. This paper reviews the stripping method, experimental factors and its applications for penetration and topical vaccination.

Influence of decreasing soil moisture on stem water potential, transpiration rate and carbon exchange rate of the lowbush blueberry (Vaccinium angustifolium Ait.) in a controlled environment

SummaryA controlled environment study was performed to examine the direct short-term effects of decreasing soil moisture in the lowbush blueberry. Four computer controlled growth chambers were used and stem water potential (SWP), transpiration rate and net carbon exchange rate (NCER) were measured. The experiment was arranged as a randomized complete block design including a control and drought stressed treatment replicated six times using individual growth chambers as the blocking factor. At the conclusion of the experiment, the control treatment displayed a soil moisture value of 75% while the drought treatment had decreased to 50%. After 116 h of nonreplenished moisture loss, the drought stressed plants showed greater variability and a decrease of at least 60% in stem water potential. Decreasing water availability resulted in lowered transpiration and photosynthetic rates (Pn), with a slight decrease in nighttime respiration rates in the drought stressed plants compared with the control plants. Like most drought tolerant plants, the adaptive mechanism of the lowbush blueberry appears to regulate water loss via stomatal and mesophyll conductance.