Cell Wall Elasticity Research Articles

Nitrate Starvation Induces Lateral Root Organogenesis in Triticum aestivum via Auxin Signaling.

The lateral root (LR) is an essential component of the plant root system, performing important functions for nutrient and water uptake in plants and playing a pivotal role in cereal crop productivity. Nitrate (NO3-) is an essential nutrient for plants. In this study, wheat plants were grown in 1/2 strength Hoagland's solution containing 5 mM NO3- (check; CK), 0.1 mM NO3- (low NO3-; LN), or 0.1 mM NO3- plus 60 mg/L 2,3,5-triiodobenzoic acid (TIBA) (LNT). The results showed that LN increased the LR number significantly at 48 h after treatment compared with CK, while not increasing the root biomass, and LNT significantly decreased the LR number and root biomass. The transcriptomic analysis showed that LN induced the expression of genes related to root IAA synthesis and transport and cell wall remodeling, and it was suppressed in the LNT conditions. A physiological assay revealed that the LN conditions increased the activity of IAA biosynthesis-related enzymes, the concentrations of tryptophan and IAA, and the activity of cell wall remodeling enzymes in the roots, whereas the content of polysaccharides in the LRP cell wall was significantly decreased compared with the control. Fourier-transform infrared spectroscopy and atomic microscopy revealed that the content of cell wall polysaccharides decreased and the cell wall elasticity of LR primordia (LRP) increased under the LN conditions. The effects of LN on IAA synthesis and polar transport, cell wall remodeling, and LR development were abolished when TIBA was applied. Our findings indicate that NO3- starvation may improve auxin homeostasis and the biological properties of the LRP cell wall and thus promote LR initiation, while TIBA addition dampens the effects of LN on auxin signaling, gene expression, physiological processes, and the root architecture.

Mechanical strategies supporting growth and size diversity in Filamentous Fungi.

The stereotypical tip growth of filamentous fungi supports their lifestyles and functions. It relies on the polarized remodeling and expansion of a protective elastic cell wall (CW) driven by large cytoplasmic turgor pressure. Remarkably, hyphal filament diameters and cell elongation rates can vary extensively among different fungi. To date, however, how fungal cell mechanics may be adapted to support these morphological diversities while ensuring surface integrity remains unknown. Here, we combined super-resolution imaging and deflation assays to measure local CW thickness, elasticity and turgor in a set of fungal species spread on the evolutionary tree that spans a large range in cell size and growth speeds. While CW elasticity exhibited dispersed values, presumably reflecting differences in CW composition, both thickness and turgor scaled in dose-dependence with cell diameter and growth speeds. Notably, larger cells exhibited thinner lateral CWs, and faster cells thinner apical CWs. Counterintuitively, turgor pressure was also inversely scaled with cell diameter and tip growth speed, challenging the idea that turgor is the primary factor dictating tip elongation rates. We propose that fast-growing cells with rapid CW turnover have evolved strategies based on a less turgid cytoplasm and thin walls to safeguard surface integrity and survival.

Assessing the hydromechanical control of plant growth.

Multicellular organisms grow and acquire their shapes through the differential expansion and deformation of their cells. Recent research has addressed the role of cell and tissue mechanical properties in these processes. In plants, it is believed that growth rate is a function of the mechanical stress exerted on the cell wall, the thin polymeric layer surrounding cells, involving an effective viscosity. Nevertheless, recent studies have questioned this view, suggesting that cell wall elasticity sets the growth rate or that uptake of water is limiting for plant growth. To assess these issues, we developed a microfluidic device to quantify the growth rates, elastic properties and hydraulic conductivity of individual Marchantia polymorpha plants in a controlled environment with a high throughput. We characterized the effect of osmotic treatment and abscisic acid on growth and hydromechanical properties. Overall, the instantaneous growth rate of individuals is correlated with both bulk elastic modulus and hydraulic conductivity. Our results are consistent with a framework in which the growth rate is determined primarily by the elasticity of the wall and its remodelling, and secondarily by hydraulic conductivity. Accordingly, the coupling between the chemistry of the cell wall and the hydromechanics of the cell appears as key to set growth patterns during morphogenesis.

Multi-scale investigation on mechanical properties of wood joints bonded with a polyurethane adhesive in successive cycles of accelerated aging treatments

To gain a deeper understanding of the bond durability in adhesively bonded wood products, a multiscale investigation of the mechanical properties of wood joints bonded with a one-component polyurethane (PU) adhesive in successive cycles of accelerated aging treatment was conducted by combining nanoindentation (NI) and conventional tensile-shear techniques. The delamination ratio, shear strength, and wood failure ratio of the wood joints, as well as the reduced elasticity modulus (Er) and hardness (H) of the PU resin, cell walls in the interphase region (CW–I), and control cell walls (CW) were evaluated. The correlations between the macro shear strength and micromechanical properties were further established. The results showed that the average delamination ratios of the wood joints were 10%–26 % after eight cycles of hydrothermal treatment. Macromechanical and most micromechanical properties substantially decreased with an increase in the number of treatment cycles, with maximum reductions of 37 %, 24 %, 60 %, 56 %, 48 %, and 57 % for the shear strength, wood failure ratio, Er of PU, H of PU, Er of CW-I, and Er of CW, respectively. The linear regression for the mechanical properties and the number of treatment cycles indicated that the Er of PU, CW-I, and CW, as well as the H of PU, showed linear downward trends (with R2 values of 0.765–0.921) during successive aging treatments. Significant and positive linear correlations were found between the shear strength and micromechanical properties of PU, with correlation coefficients of 0.970 (P < 0.01) and 0.941 (P < 0.05) for Er and H of PU, respectively. The wood failure ratio showed significant positive correlations with the Er values of CW-I (P < 0.01) and CW (P < 0.05), whereas the proportion of wood failure in the interphase was significantly (P < 0.05) negatively correlated with the Er value of CW. The shear strength was positively correlated with the Er of the cell walls, with correlation coefficients of 0.861 and 0.868 for CW-I and CW, respectively. In summary, both the micromechanical properties of the PU resin and the elasticity of the wood cell walls in the wood-adhesive interphase were demonstrated to be key factors affecting the bond durability of wood bond joints.

Dimensionally stable and durable wood by lignin impregnation

Cracking, warping, and decaying stemming from wood's poor dimensional stability and durability are the most annoying issues of natural wood. There is an urgent need to address these issues, of which, sustainable and green chemical treatments are favorably welcomed. Herein, we developed a facile method through the incorporation of environmentally friendly biopolymer lignin into wood cells for wood dimensional stability and durability enhancement. Enzymatic hydrolysis lignin (EHL) was dissolved into various solvents followed by impregnation and drying to incorporate lignin into wood cells. Impregnation treatment was developed to incorporate into wood to improve its dimensional stability, durability, and micromechanics. The anti-swelling efficiency reached up to 99.4 %, the moisture absorption decreased down to 0.55 %, the mass loss after brown rot decay decreased to 7.22 %, and the cell wall elasticity as well as hardness increased 8.7 % and 10.3 %, respectively. Analyses acquired from scanning electron microscopy, fluorescent microscopy, and Raman imaging revealed that the EHL was successfully colonized in cell lumen as well as in cell walls, thus improved wood dimensional stability and durability. Moreover, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirmed EHL interaction with the cell wall components, thus the wood mechanical property was not impaired significantly, whereas nanoindentation data indicated even slight mechanical enhancement on the cell walls. This facile approach can improve the wood properties in multiple aspects and remarkably enhance the outdoor performance of modified wood products. In addition, using lignin as a natural modifying agent to improve wood performance will have a great positive impact on the environment.

One‐Hour Ambient‐Pressure‐Dried, Scalable, Stretchable MXene/Polyurea Aerogel Enables Synergistic Defense Against High‐Frequency Mechanical Shock and Electromagnetic Waves

AbstractThe rapid, energy‐efficient, scalable preparation of high‐strength, flexible, multifunctional nanostructured aerogels is highly desired yet challenging. Here, an ambient‐pressure‐dried (APD) strategy is developed involving self‐foaming, dip‐coating, and graphene oxide (GO)‐assisted multiple cross‐linking treatments for the prompt, large‐area preparation of polyurea/transition metal carbides/nitrides (MXenes) aerogels. The APD MXene‐based aerogels showcase low density, remarkable mechanical strength, and ultraflexiblity involving stretchability, good conductivity, hydrophobicity, and high resistance to various solvents. Synergies of robust, elastic cell walls and porous structure contribute to high‐efficiency absorption of high‐frequency, high‐speed mechanical shock waves for the aerogels, significantly transcendinging the biomasses, plastics, elastomers, ceramics, and metals. In addition to the excellent microwave shielding performance of over 40 dB in ultrabroadband frequencies of 4–40 GHz, the oxidation stability is elevated for APD MXene aerogels, consequently yielding applicability in harsh conditions. Furthermore, the superior light absorption capability of aerogels leads to the efficient photothermal conversion, therapy, antibacterial, desalination, water purification, deicing, and thick oil absorption. This work provides a facile, time‐ and energy‐efficient, scalable APD methodology for manufacturing large‐area, high‐strength, ultraflexible, multifunctional MXene‐based aerogels, enlighting a novel synergistic defense against mechanical shock and electromagnetic waves, and promoting them as a prospective candidate in aerospace, device protection, and next‐generation electronics.

Salinity-driven changes in Salicornia cell wall nanomechanics and lignin composition

Widespread increases in soil salinization significantly reduce agricultural lands. Nevertheless, salt-tolerant plants, such as Salicornia europaea L., can play a crucial role in the reclamation of these lands. We selected S. europaea for this study due to its potential to mitigate soil salinization and its numerous applications, such as intercropping in agriculture, biocompounds production and bioenergy. This work was designed to determine whether different salinities induce significant biophysical, anatomical, lignin and gene transcript changes in S. europaea. Through atomic force microscopy (AFM), we revealed that salinity stimulated an increase in cell wall elasticity (CWE) as an important physiological mechanism of adaptation known as cell’s turgor conservation effect. Direct values of the cell wall stiffness subjected to salinity were obtained, with Young’s modulus (E) ranging from low and high salinity 0.52 to 0.03 MPa. The softening of the cell wall properly correlated with an increase in cell size, plant cells under strong salinity 1000 mM NaCl, swelled 5.4 times. The best salinity range found for its optimum growth was 200–400 mM NaCl. At higher salinities, we identified increases in the lignified xylem, large calcium oxalate crystals, and in transcript amounts of SeSOS1 and SeNHX1, which has a significant negative correlation with cell wall stiffness (−0.57 and −0.95, respectively). The high syringyl and guaiacyl ratio (S/G) in lignin for 0–400 mM NaCl may have influenced the rigidity and hydrophobicity of the cell walls. A positive S/G ratio and sugar yields are associated with higher bioethanol production, these values may also be useful for agriculture, biorefinery, biocompounds and plant-breeding applications. We conclude that salinity indeed influenced the cell wall traits of S. europaea. This halophyte is capable of markedly softening its cell wall as a way of adapting to the high level of salinity. Our presented insights and correlations not only provide a better understanding of cell wall remodelling but are also considered vital traits of adaptation strategies that this halophyte holds under salinity environment. These inputs can also be applied in future research aiming to produce biomass and biofuel or to improve the salinity tolerance during the cultivation of non-tolerant plants, crops and glycophytes, which is a significant challenge in agriculture, particularly in arid and coastal regions. The unique properties of the S. europaea cell walls could also inspire the development of materials with enhanced nanomechanical elasticity for resistance to osmotic stress.

Physiological mechanisms preventing plant wilting under heat stress: a case study on a wheat (Triticum durum Desf.) bound water-mutant

Wilting is the main symptom of plants suffering the dehydration stresses, but the mechanisms governing this phenomenon are yet to be completely understood. In this work, a holistic analysis of physiological traits potentially involved in leaf wilting was performed, comparing a wheat wild type (WT), Trinakria and its water-mutant (WM) with a “high affinity for bound water (BW)”. In addition to the tendency to wilt, significant differences between genotypes were observed for leaf temperature achieved under heat stress, leaf turgor loss with decreasing water potential, cuticular transpiration, and Q10 of leaf water uptake velocity. We hypothesize that mutant plants prevent the increase in leaf temperature thanks to the rapid and low energetic cost of water diffusion from the vessels to the outside, driven by the BW. Under strong thermal-induced dehydration stress, BW delays leaf wilting through its positive effects on cell wall elasticity and passive osmoregulation.

Root growth of monocotyledons and dicotyledons is limited by different tissues.

Plant growth and morphogenesis are determined by the mechanical properties of its cell walls. Using atomic force microscopy, we have characterized the dynamics of cell wall elasticity in different tissues in developing roots of several plant species. The elongation growth zone of roots of all species studied was distinguished by a reduced modulus of elasticity of most cell walls compared to the meristem or late elongation zone. Within the individual developmental zones of roots, there were also significant differences in the elasticity of the cell walls of the different tissues, thus identifying the tissues that limit root growth in the different species. In cereals, this is mainly the inner cortex, whereas in dicotyledons this function is performed by the outer tissues-rhizodermis and cortex. These differences result in a different behaviour of the roots of these species during longitudinal dissection. Modelling of longitudinal root dissection using measured properties confirmed the difference shown. Thus, the morphogenesis of monocotyledonous and dicotyledonous roots relies on different tissues as growth limiting, which should be taken into account when analyzing the localization of associated molecular events. At the same time, no matrix polysaccharide was found whose immunolabelling in type I or type II cell walls would predict their mechanical properties. However, assessment of the degree of anisotropy of cortical microtubules showed a striking correlation with the elasticity of the corresponding cell walls in all species studied.

Cell wall polysaccharide and glycoprotein content tracks growth-form diversity and an aridity gradient in the leaf-succulent genus Crassula.

Cell wall traits are believed to be a key component of the succulent syndrome, an adaptive syndrome to drought, yet the variability of such traits remains largely unknown. In this study, we surveyed the leaf polysaccharide and glycoprotein composition in a wide sampling of Crassula species that occur naturally along an aridity gradient in southern Africa, and we interpreted its adaptive significance in relation to growth form and arid adaptation. To study the glycomic diversity, we sampled leaf material from 56 Crassula taxa and performed comprehensive microarray polymer profiling to obtain the relative content of cell wall polysaccharides and glycoproteins. This analysis was complemented by the determination of monosaccharide composition and immunolocalization in leaf sections using glycan-targeting antibodies. We found that compact and non-compact Crassula species occupy distinct phenotypic spaces in terms of leaf glycomics, particularly in regard to rhamnogalacturonan I, its arabinan side chains, and arabinogalactan proteins (AGPs). Moreover, these cell wall components also correlated positively with increasing aridity, which suggests that they are likely advantageous in terms of arid adaptation. These differences point to compact Crassula species having more elastic cell walls with plasticizing properties, which can be interpreted as an adaptation toward increased drought resistance. Furthermore, we report an intracellular pool of AGPs associated with oil bodies and calcium oxalate crystals, which could be a peculiarity of Crassula and could be linked to increased drought resistance. Our results indicate that glycomics may be underlying arid adaptation and drought resistance in succulent plants.

Selected indigenous drought tolerant rhizobium strains as promising biostimulants for common bean in Northern Spain.

Drought is the most detrimental abiotic stress in agriculture, limiting crop growth and yield and, currently, its risk is increasing due to climate change. Thereby, ensuring food security will be one of the greatest challenges of the agriculture in the nearest future, accordingly it is essential to look for sustainable strategies to cope the negative impact of drought on crops. Inoculation of pulses with biostimulants such as rhizobium strains with high nitrogen fixation efficiency and drought-tolerance, has emerged as a promising and sustainable production strategy. However, some commercial inoculums are not effective under field conditions due to its lower effectiveness against indigenous rhizobium strains in the establishment of the symbiosis. Thus, in the present study, we evaluated the ability to improve drought tolerance in common bean plants of different indigenous rhizobia strains isolated from nearby crop fields in the Basque Country either affected by drought or salinity. The plants in this trial were grown in a climatic chamber under controlled conditions and exposed to values of 30% relative soil water content at the time of harvest, which is considered a severe drought. From the nine bacteria strains evaluated, three were found to be highly efficient under drought (namely 353, A12 and A13). These strains sustained high infectiveness (nodulation capacity) and effectiveness (shoot biomass production) under drought, even surpassing the plants inoculated with the CIAT899 reference strain, as well as the chemically N-fertilized plants. The tolerance mechanisms developed by plants inoculated with 353, A12 and A13 strains were a better adjustment of the cell wall elasticity that prevents mechanical damages in the plasma membrane, a higher WUE and an avoidance of the phenological delay caused by drought, developing a greater number of flowers. These results provide the basis for the development of efficient common bean inoculants able to increase the yield of this crop under drought conditions in the Northern Spain and, thus, to be used as biostimulants. In addition, the use of these efficient nitrogen fixation bacteria strains is a sustainable alternative to chemical fertilization, reducing cost and minimizing its negative impact on environment.

Are cell wall traits a component of the succulent syndrome?

Succulence is an adaptation to low water availability characterised by the presence of water-storage tissues that alleviate water stress under low water availability. The succulent syndrome has evolved convergently in over 80 plant families and is associated with anatomical, physiological and biochemical traits. Despite the alleged importance of cell wall traits in drought responses, their significance in the succulent syndrome has long been overlooked. Here, by analyzing published pressure-volume curves, we show that elastic adjustment, whereby plants change cell wall elasticity, is uniquely beneficial to succulents for avoiding turgor loss. In addition, we used comprehensive microarray polymer profiling (CoMPP) to assess the biochemical composition of cell walls in leaves. Across phylogenetically diverse species, we uncover several differences in cell wall biochemistry between succulent and non-succulent leaves, pointing to the existence of a 'succulent glycome'. We also highlight the glycomic diversity among succulent plants, with some glycomic features being restricted to certain succulent lineages. In conclusion, we suggest that cell wall biomechanics and biochemistry should be considered among the characteristic traits that make up the succulent syndrome.

Transcriptomic analysis of CO2-treated strawberries (Fragaria vesca) with enhanced resistance to softening and oxidative stress at consumption.

One of the greatest threats to wild strawberries (Fragaria vesca Mara des Bois) after harvest is the highly perishability at ambient temperature. Breeders have successfully met the quality demands of consumers, but the prevention of waste after harvest in fleshy fruits is still pending. Most of the waste is due to the accelerated progress of senescence-like process after harvest linked to a rapid loss of water and firmness at ambient temperature. The storage life of strawberries increases at low temperature, but their quality is limited by the loss of cell structure. The application of high CO2 concentrations increased firmness during cold storage. However, the key genes related to resistance to softening and cell wall disassembly following transference from cold storage at 20°C remain unclear. Therefore, we performed RNA-seq analysis, constructing a weighted gene co-expression network analysis (WGCNA) to identify which molecular determinants play a role in cell wall integrity, using strawberries with contrasting storage conditions, CO2-cold stored (CCS), air-cold stored (ACS), non-cold stored (NCS) kept at ambient temperature, and intact fruit at harvest (AH). The hub genes associated with the cell wall structural architecture of firmer CO2-treated strawberries revealed xyloglucans stabilization attributed mainly to a down-regulation of Csl E1, XTH 15, Exp-like B1 and the maintenance of expression levels of nucleotide sugars transferases such as GMP and FUT as well as improved lamella integrity linked to a down-regulation of RG-lyase, PL-like and PME. The preservation of cell wall elasticity together with the up-regulation of LEA, EXPA4, and MATE, required to maintain cell turgor, is the mechanisms controlled by high CO2. In stressed air-cold stored strawberries, in addition to an acute softening, there is a preferential transcript accumulation of genes involved in lignin and raffinose pathways. Non-cold stored strawberries kept at 20°C after harvest are characterized by an enrichment in genes mainly involved in oxidative stress and up-expression of genes involved in jasmonate biosynthesis. The present results on transcriptomic analysis of CO2-treated strawberries with enhanced resistance to softening and oxidative stress at consumption will help to improve breeding strategies of both wild and cultivated strawberries.

Prefermentative Grape Microwave Treatment as a Tool for Increasing Red Wine Phenolic Content and Reduce Maceration Time

Phenolic compounds are responsible for color and, with it, the quality of red wines. Its content will depend, among other factors, on the oenological techniques applied in the winery and, among them, the maceration time. Long maceration times can generate logistical problems at the moment of maximum grape entry into the winery. Applying techniques that accelerate the extraction of phenolic compounds from the grape solid parts to the must-wine would allow reducing the maceration time. Among the techniques of interest, microwaves use electromagnetic waves to produce dipole rotation and ion conduction, which can increase the elasticity of cell walls and cause the destruction of the cell membrane, facilitating the phenolic compound extraction. To study this effect, crushed grapes of the Cabernet Sauvignon variety were treated with this technology, macerated for 72 h and 7 days, and compared with respect to a control wine without any treatment. The results showed that the application of microwaves to the crushed grape favored a rapid extraction of the phenolic compounds, increasing the color of the wine and with only 72 h of maceration, the wines from treated grapes showed a similar phenolic content and chromatic characteristics to a control wine with 7 maceration days. The extraction of the less astringent skin tannins and the formation of stable pigments was also favored indicating that this technology may allow reducing the maceration time during the winemaking process without affecting the quality and stability of the wine.

Elastic shell theory for plant cell wall stiffness reveals contributions of cell wall elasticity and turgor pressure in AFM measurement

The stiffness of a plant cell in response to an applied force is determined not only by the elasticity of the cell wall but also by turgor pressure and cell geometry, which affect the tension of the cell wall. Although stiffness has been investigated using atomic force microscopy (AFM) and Young’s modulus of the cell wall has occasionally been estimated using the contact-stress theory (Hertz theory), the existence of tension has made the study of stiffness more complex. Elastic shell theory has been proposed as an alternative method; however, the estimation of elasticity remains ambiguous. Here, we used finite element method simulations to verify the formula of the elastic shell theory for onion (Allium cepa) cells. We applied the formula and simulations to successfully quantify the turgor pressure and elasticity of a cell in the plane direction using the cell curvature and apparent stiffness measured by AFM. We conclude that tension resulting from turgor pressure regulates cell stiffness, which can be modified by a slight adjustment of turgor pressure in the order of 0.1 MPa. This theoretical analysis reveals a path for understanding forces inherent in plant cells.

Physiological and Structural Responses to Prolonged Water Deficit in Young Trees of Two Olive Cultivars.

This study aimed to characterize the physiological and structural responses of potted one-year-old olive trees belonging to two olive cultivars—‘Nocellara del Belice’ and ‘Cerasuola’—exposed to prolonged drought under greenhouse conditions. Two irrigation treatments based on evapotranspiration (ET) were imposed for 69 days, i.e., well-watered (WW, 100% ET) and drought-stressed (DS, 10–30% ET). Leaf stomatal conductance (gs), stem water potential (Ψstem), transpiration (E), photosynthetic capacity (Amax), water use efficiency (WUE), stem (Kstem) and root (Kroot) hydraulic conductance, trunk diameter variations (TDV), and leaf patch attenuated pressure fluctuations (pp, a proxy of the inverse of leaf turgor pressure) were measured in WW and DS trees at different stages of the experiment. Leaf gs did not significantly differ between cultivars under DS, whereas differences in Ψstem only became significant at the end of prolonged drought, when ‘Nocellara del Belice’ experienced Ψstem < −4 MPa. ‘Cerasuola’ trees expressed the best WUE under drought, although they were more susceptible to photoinhibition under optimal plant water status. Both cultivars tended to increase their Kstem at the end of the drought period. A marked reduction in Kroot occurred in ‘Cerasuola’ plants after prolonged drought; however, a similar mechanism was not observed in ‘Nocellara del Belice’. The ratio between Kstem and Kroot exponentially increased towards the end of the prolonged drought period in both cultivars, but more markedly in ‘Cerasuola’. TDV and pp trends suggested that ‘Cerasuola’ plants keep better plant water status under severe drought compared to ‘Nocellara del Belice’ by maintaining high leaf turgor and reduced trunk diameter fluctuations. These responses may be related to reduced cell wall elasticity and xylem vessel size and/or wall thickness—drought avoidance mechanisms. The Kstem/Kroot ratio can serve as an indicator of drought stress avoidance mechanisms to compare genotype-specific responses to drought stress.

Boron-mediated lignin metabolism in response to aluminum toxicity in citrus (Poncirus trifoliata (L.) Raf.) root

Aluminum (Al) toxicity has conspicuous detrimental effects on citrus production whereas boron (B) has been shown to alleviate its toxicity. Lignin plays a critical role in the cell wall extensibility and root elongation under stressed conditions. Hence, the interaction between B and Al on cell wall structure and lignin-related metabolic pathway was investigated in root of trifoliate orange (Poncirus trifoliata (L.) Raf.) seedlings. The results showed B supply considerably decreased the Al content in root, particularly in cell wall, and reduced Al-induced damage on growth-related parameters and thickness of cell wall. Boron application decreased the hydrogen peroxide (H2O2), malondialdehyde (MDA), and lignin contents in the Al-treated root, which prevents the inhibitory effects of Al on the root length. Moreover, metabonomics results showed that B addition resulted in the reduction of metabolites involved in the lignin biosynthesis pathways (phenylpropanoid metabolic) i.e., shikimic acid, tyrosine, caffeic acid, chlorogenic acid, coniferyl alcohol, sinapinic acid, sinapaldehyde, and sinapyl alcohol, as well as distinctively restrain the activities of lignin biosynthesis-related enzymes (4-coumarate-CoA ligase (4CL), cinnamyl-alcohol dehydrogenase (CAD)) under Al toxicity. Collectively, our findings suggest that the positive effects of B on the resistance of Al toxicity may be it reduces Al accumulation in the cell wall, lignin biosynthesis, and cell wall thickness, thereby increasing the extensibility and elasticity of cell wall and thus promoting root elongation.

Characterizing Mechanical Properties of Primary Cell Wall in Living Plant Organs Using Atomic Force Microscopy

The mechanical properties of the primary cell walls determine the direction and rate of plant cell growth and, therefore, the future size and shape of the plant. Many sophisticated techniques have been developed to measure these properties; however, atomic force microscopy (AFM) remains the most convenient for studying cell wall elasticity at the cellular level. One of the most important limitations of this technique has been that only superficial or isolated living cells can be studied. Here, the use of atomic force microscopy to investigate the mechanical properties of primary cell walls belonging to the internal tissues of a plant body is presented. This protocol describes measurements of the apparent Young's modulus of cell walls in roots, but the method can also be applied to other plant organs. The measurements are performed on vibratome-derived sections of plant material in a liquid cell, which allows (i) avoiding the use of plasmolyzing solutions or sample impregnation with wax or resin, (ii) making the experiments fast, and (iii) preventing dehydration of the sample. Both anticlinal and periclinal cell walls can be studied, depending on how the specimen was sectioned. Differences in the mechanical properties of different tissues can be investigated in a single section. The protocol describes the principles of study planning, issues with specimen preparation and measurements, as well as the method of selecting force-deformation curves to avoid the influence of topography on the obtained values of elastic modulus. The method is not limited by sample size but is sensitive to cell size (i.e., cells with a large lumen are difficult to examine).

Drought acclimation of Quercus ilex leaves improves tolerance to moderate drought but not resistance to severe water stress.

Increasing temperature and drought can result in leaf dehydration and defoliation even in drought-adapted tree species such as the Mediterranean evergreen Quercus ilex L. The stomatal regulation of leaf water potential plays a central role in avoiding this phenomenon and is constrained by a suite of leaf traits including hydraulic conductance and vulnerability, hydraulic capacitance, minimum conductance to water vapour, osmotic potential and cell wall elasticity. We investigated whether the plasticity in these traits may improve leaf tolerance to drought in two long-term rainfall exclusion experiments in Mediterranean forests. Osmotic adjustment was observed to lower the water potential at turgor loss in the rainfall-exclusion treatments, thus suggesting a stomatal closure at more negative water potentials and a more anisohydric behaviour in drier conditions. Conversely, leaf hydraulic conductance and vulnerability did not exhibit any plasticity between treatments so the hydraulic safety margins were narrower in the rainfall-exclusion treatments. The sequence of leaf responses to seasonal drought and dehydration was conserved among treatments and sites but trees were more likely to suffer losses of turgor and hydraulic functioning in the rainfall-exclusion treatments. We conclude that leaf plasticity might help the trees to tolerate moderate drought but not to resist severe water stress.

Drought-related leaf functional traits control spatial and temporal dynamics of live fuel moisture content

Large forest fires generally occur when the moisture content of fuels is low. For live fuels, our understanding of the physiological basis of variation in moisture content has recently advanced. However, process-based models of live fuel moisture content (LFMC) remain elusive. Here, we aim to further our understanding of the role of physiological mechanisms and plant functional traits in driving spatiotemporal variations in LFMC. We examined whether temporal variation in LFMC could be predicted from pressure-volume curve data, which measures leaf water potential and water content on cut shoots dehydrating on a bench. We also examined whether leaf dry mass traits could predict spatial variation in maximum LFMC. We undertook our study in eucalypt forests and woodlands spanning a large climatic gradient in eastern Australia. We found that LFMC models developed from pressure-volume curves reliably predicted seasonal variation in LFMC across four co-occurring species. A two-phase LFMC model, which fit models above and below the turgor loss point (mean absolute error = 3.7-33.2%), performed similarly well to a simple linear model (mean absolute error = 3.4-35.3%). Across a large climatic gradient, the maximum LFMC of 16 species was correlated with specific leaf area (R2 = 0.54), with the exception of one species with terete terminal stems. Maximum LFMC was highly correlated with aridity (R2 = 0.82), with lower LFMC observed in more arid sites. Our study demonstrates that spatiotemporal dynamics of LFMC are governed by both leaf dry mass traits and the relationship between leaf water potential and water content, which in turn is determined by traits such as cell wall elasticity. Thus, incorporating these traits into models of LFMC, whether these models are based on drought indices, soil moisture, or remotely sensed imagery, is likely to improve overall model performance, and subsequently improve forecasts of wildfire danger.