Experimental evidence for negative turgor pressure in small leaf cells of Robinia pseudoacacia L versus large cells of Metasequoia glyptostroboides Hu et W.C.Cheng. 1. Evidence from pressure‐volume curve analysis of dead tissue.

This paper provides a mini‐review of evidence for negative turgor pressure in leaf cells starting with experimental evidence in the late 1950s and ending with biomechanical models published in 2014. In the present study, biomechanical models were used to predict how negative turgor pressure might be manifested in dead tissue, and experiments were conducted to test the predictions. The main findings were as follows: (i) Tissues killed by heating to 60 or 80 °C or by freezing in liquid nitrogen all became equally leaky to cell sap solutes and all seemed to pass freely through the cell walls. (ii) Once cell sap solutes could freely pass the cell walls, the shape of pressure‐volume curves was dramatically altered between living and dead cells. (iii) Pressure‐volume curves of dead tissue seem to measure negative turgor defined as negative when inside minus outside pressure is negative. (iv) Robinia pseudoacacia leaves with small palisade cells had more negative turgor than Metasequoia glyptostroboides with large cells. (v) The absolute difference in negative turgor between R. pseudoacacia and M. glyptostroboides approached as much as 1.0 MPa in some cases. The differences in the manifestation of negative turgor in living versus dead tissue are discussed.     

Refilling of Embolized Vessels in Young Stems of Laurel. Do We Need a New Paradigm?

Recovery of hydraulic conductivity after the induction of embolisms was studied in woody stems of laurel (Laurus nobilis). Previous experiments confirming the recovery of hydraulic conductivity when xylem pressure potential was less than −1 MPa were repeated, and new experiments were done to investigate the changes in solute composition in xylem vessels during refilling. Xylem sap collected by perfusion of excised stem segments showed elevated levels of several ions during refilling. Stem segments were frozen in liquid N₂ to view refilling vessels using cryoscanning electron microscopy. Vessels could be found in all three states of presumed refilling: (a) mostly water with a little air, (b) mostly air with a little water, or (c) water droplets extruding from vessel pits adjacent to living cells. Radiographic probe microanalysis of refilling vessels revealed nondetectable levels of dissolved solutes. Results are discussed in terms of proposed mechanisms of refilling in vessels while surrounding vessels were at a xylem pressure potential of less than −1 MPa. We have concluded that none of the existing paradigms explains the results.     

Whole Grain Intakes in the Diets Of Malaysian Children and Adolescents – Findings from the MyBreakfast Study

Background

Diets rich in whole grain are associated with several health benefits. Little is known however, about whole grain consumption patterns in Malaysia. The aim of this study was to assess whole grain intakes and dietary source in Malaysian children and adolescents.

Methods

This analysis is from the MyBreakfast study, a national cross sectional study investigating eating habits among primary and secondary school children throughout Malaysia, conducted in 2013. Children (n = 5,165) and adolescents (n = 2,947) who completed two days of dietary assessment using a food record or recall respectively were included. The whole grain content of foods was estimated mainly through the use of quantitative ingredient declarations on food labels. All wholegrain foods were considered irrespective of the amount of whole grain they contained.

Results

Overall, only 25% of children and 19% of adolescents were wholegrain consumers. Mean daily intakes in the total sample were 2.3g/d (SD 5.8g/d) in children and 1.7g/d (SD 4.7g/d) in adolescents and in the consumer’s only sample, mean intakes reached 9.1g/d (SD 8.6) and 9.2g/d (SD 7.1g/d) respectively. Wheat was the main grain source of whole grain while ready to eat breakfast cereals and hot cereals were the main food contributors. Less than 3% of the children and adolescents reached the US quantitative whole grain recommendation of 48g/day.

Conclusion

Whole grain is consumed by only a minority of Malaysian children and adolescents and even among consumers, intakes are well below recommendations. Efforts are needed to firstly understand the barriers to whole grain consumption among Malaysian children in order to design effective health promotion initiatives to promote an increase in whole grain consumption.     

Factors controlling plasticity of leaf morphology in Robinia pseudoacacia: III. biophysical constraints on leaf expansion under long-term water stress

In this article, we measured the relative growth rate (RGR) of leaves of Robinia pseudoacacia seedlings under well-watered and water-stressed conditions (mid-day Ψ(w) = leaf water potential estimated with a pressure bomb of -0.48 and -0.98 MPa, respectively). Pressure-volume (PV) curves were done on growing leaves at 25, 50 and 95% of the mature size (growth stage) in order to compute solute potential (Ψ) and turgor pressure (Ψ(P) ) as a function of Ψ(w) . The PV curves and diurnal measurements of Ψ(w) and RGR allowed us to evaluate the parameters (cell wall extensibility m and growth turgor threshold Y) of the Lockhart equation, RGR = m(Ψ(P)-Y), at each growth stage. Our data showed that m and Y did change with leaf age, but the changes were slow enough to evaluate m and Y on any given day. We believe this is the first study to provide evidence that the Lockhart equation adequately quantifies leaf growth of trees over a range of time domains. The value of m linearly declined and Y linearly increased with growth stage. Also, mild drought stress caused a decline in m and increase in Y relative to controls. Although water stress caused an osmotic adjustment which, in turn, increased Ψ(P) in stressed plants relative to controls, the RGR and final leaf sizes were reduced in water-stressed plants because of the impact of water stress on decreased m and increased Y.     

Cigarette smoke-induced accumulation of lung dendritic cells is interleukin-1α-dependent in mice

Background

Evidence suggests that dendritic cells accumulate in the lungs of COPD patients and correlate with disease severity. We investigated the importance of IL-1R1 and its ligands IL-1α and β to dendritic cell accumulation and maturation in response to cigarette smoke exposure.

Methods

Mice were exposed to cigarette smoke using a whole body smoke exposure system. IL-1R1-, TLR4-, and IL-1α-deficient mice, as well as anti-IL-1α and anti-IL-1β blocking antibodies were used to study the importance of IL-1R1 and TLR4 to dendritic cell accumulation and activation.

Results

Acute and chronic cigarette smoke exposure led to increased frequency of lung dendritic cells. Accumulation and activation of dendritic cells was IL-1R1/IL-1α dependent, but TLR4- and IL-1β-independent. Corroborating the cellular data, expression of CCL20, a potent dendritic cells chemoattractant, was IL-1R1/IL-1α-dependent. Studies using IL-1R1 bone marrow-chimeric mice revealed the importance of IL-1R1 signaling on lung structural cells for CCL20 expression. Consistent with the importance of dendritic cells in T cell activation, we observed decreased CD4⁺ and CD8⁺ T cell activation in cigarette smoke-exposed IL-1R1-deficient mice.

Conclusion

Our findings convey the importance of IL-1R1/IL-1α to the recruitment and activation of dendritic cells in response to cigarette smoke exposure.     

Impact of simulated herbivory on water relations of aspen (<Emphasis Type="Italic">Populus tremuloides</Emphasis>) seedlings: the role of new tissue in the hydraulic conductivity recovery cycle

Physiological mechanisms behind plant–herbivore interactions are commonly approached as input–output systems where the role of plant physiology is viewed as a black box. Studies evaluating impacts of defoliation on plant physiology have mostly focused on changes in photosynthesis while the overall impact on plant water relations is largely unknown. Stem hydraulic conductivity (k _h), stem specific conductivity (k _s), percent loss of hydraulic conductivity (PLC), CO₂ assimilation (A) and stomatal conductance (g _s) were measured on well-irrigated 1-month-old Populus tremuloides (Michx.) defoliated and control seedlings until complete refoliation. PLC values of defoliated seedlings gradually increased during the refoliation process despite them being kept well irrigated. k _s of defoliated seedlings gradually decreased during refoliation. PLC and k _s values of control seedlings remained constant during refoliation. k _s of new stems, leaf specific conductivity and A of leaves grown from new stems in defoliated and control seedlings were not significantly different, but g _s was higher in defoliated than in control seedlings. The gradual increase of PLC and decrease of k _s values in old stems after defoliation was unexpected under well-irrigated conditions, but appeared to have little impact on new stems formed after defoliation. The gradual loss of conductivity measured during the refoliation process under well-irrigated conditions suggests that young seedlings of P. tremuloides may be more susceptible to cavitation after herbivore damage under drought conditions.     

Cavitation fatigue in conifers: a study on eight European species

After drought-induced embolism and repair, tree xylem may be weakened against future drought events (cavitation fatigue). As there are few data on cavitation fatigue in conifers available, we quantified vulnerability curves (VCs) after embolism/repair cycles on eight European conifer species. We induced 50% and 100% loss of conductivity (LC) with a cavitron, and analyzed VCs. Embolism repair was obtained by vacuum infiltration. All species demonstrated complete embolism repair and a lack of any cavitation fatigue after 50% LC . After 100% LC, European larch (Larix decidua), stone pine (Pinus cembra), Norway spruce (Picea abies), and silver fir (Abies alba) remained unaffected, while mountain pine (Pinus mugo), yew (Taxus baccata), and common juniper (Juniperus communis) exhibited 0.4–0.9 MPa higher vulnerability to embolism. A small cavitation fatigue observed in Scots pine (Pinus sylvestris) was probably biased by incomplete embolism repair, as indicated by a correlation of vulnerability shifts and conductivity restoration. Our data demonstrate that cavitation fatigue in conifers is species-specific and depends on the intensity of preceding LC. The lack of fatigue effects after moderate LC, and relevant effects in only three species after high LC, indicate that conifers are relatively resistant against cavitation fatigue. This is remarkable considering the complex and delicate conifer pit architecture and may be important considering climate change projections.     

Ultrasonic Acoustic Emissions from the Sapwood of Thuja occidentalis Measured inside a Pressure Bomb

An improved method of counting acoustic emission (AE) events from water-stressed stems of cedar (Thuja occidentalis L.) is presented. Amplified AEs are analyzed on a real time basis by a microcomputer. The instrumentation counts AE events in a fashion nearly analogous to scintillation counting of radioactive materials.

The technique was applied to measuring ultrasonic AEs from the stems of cedar inside a pressure bomb. The shoots were originally fully hydrated. When the shoots are dehydrated in the bomb by application of an overpressure very few AEs were detected. When the bomb pressure is reduced after dehydration of the shoot, AE events could be detected. We conclude that ultrasonic AEs are caused by cavitation events (= structural breakdown of water columns in the tracheids of cedar) and not by the breaking of cellulose fibers in the wood.

     

A requirement for sucrose in xylem sap flow from dormant maple trees

The response of excised stem segments of several tree species to freezing and thawing cycles was studied. All species studied (Thuja occidentalis, Fagus grandifolia, and Betula papyrifera) except maple (Acer spp.) exuded sap while freezing and absorbed on thawing. Maple stems absorbed sap while freezing and exuded sap during the thaw only when sucrose was present in the vessel solution. Increased concentration of sucrose in the vessel sap led to increased exudation. In the absence of sucrose, maple stems absorbed sap on thawing. The presence of sucrose enhanced sap absorption during freezing cycles in maples. In general, large sugars, disaccharides and larger, could substitute for sucrose in the maple exudation response while sugar hexoses could not. The results are discussed in relation to the O'Malley-Milburn model (1983 Can J Bot 61: 3100-3106) of sap flow in maples.