Локализация и синтез липид-траспортирующих белков у растений гороха, обработанных штаммом рост стимулирующих бактерий, и их роль в формировании поясков Каспари и регуляции гидравлической проводимости

Lack of O2 and high concentrations of iron (Fe) are common in flooded soils where Rice (Oryza sativa L.) is cultivated. We tested the hypothesis that growing in stagnant or high Fe conditions might induce the formation of apoplastic barriers in roots with different properties and chemical compositions. We measured radial O2 loss (ROL) from intact roots, the chemical composition of roots and the formation of root iron plaques in Fe-sensitive and Fe-tolerant rice genotypes grown in aerated, deoxygenated stagnant solutions or in aerated solutions containing high concentrations of Fe. Roots of plants grown in stagnant conditions developed tight barriers to ROL, while those grown in high Fe conditions developed only partial barriers. Chemical analysis of enzymatically isolated sclerenchyma/exodermal root cells indicated that roots grown in stagnant conditions showed increased amounts of suberin and glycerol esters. In contrast, roots in high Fe conditions showed an increase in suberization along with formation of iron plaques covering the roots. In high Fe conditions, exodermal suberization and the formation of partial ROL barriers were not influenced by the genotype's tolerance to Fe. The amount of O2 diffused from roots is influenced by the various layers that impede O2 diffusion. Specifically, increased amounts of glycerol esters in the suberized exodermis provide the greater resistance to ROL.

Inoculation with plant growth-promoting rhizobacteria can increase plant salt resistance. We aimed to reveal bacterial effects on the formation of apoplastic barriers and hormone concentration in relation to maintaining ion homeostasis and growth of salt-stressed plants. The rhizosphere of a durum wheat variety was inoculated with cytokinin-producing Bacillus subtilis and auxin-producing Pseudomonas mandelii strains. Plant growth, deposition of lignin and suberin and concentrations of sodium, potassium, phosphorus and hormones were studied in the plants exposed to salinity. Accumulation of sodium inhibited plant growth accompanied by a decline in potassium in roots and phosphorus in shoots of the salt-stressed plants. Inoculation with both bacterial strains resulted in faster appearance of Casparian bands in root endodermis and an increased growth of salt-stressed plants. B. subtilis prevented the decline in both potassium and phosphorus concentrations and increased concentration of cytokinins in salt-stressed plants. P. mandelii decreased the level of sodium accumulation and increased the concentration of auxin. Growth promotion was greater in plants inoculated with B. subtilis. Increased ion homeostasis may be related to the capacity of bacteria to accelerate the formation of Casparian bands preventing uncontrolled diffusion of solutes through the apoplast. We discuss the relative impacts of the decline in Na accumulation and maintenance of K and P content for growth improvement of salt-stressed plants and their possible relation to the changes in hormone concentration in plants.

The changes in hydraulic conductivity and clay dispersivity of a Fallbrook soil (fine‐loamy, mixed, thermic Typic Haploxeralfs) as a function of concentration (⩽ 3 meq/liter) and Na adsorption ratio (⩽ 30) of the percolating solutions were measured. Both phenomena were very sensitive to the level of exchangeable Na and to salt concentration of the soil solution. When the salt concentration is 3.0 meq/liter, the hydraulic conductivity and clay dispersion decrease if the exchangeable sodium percentage (ESP) values exceed 12. Conversely, in distilled water, clay dispersion and hydraulic conductivity decrease at ESP values as low as 1 to 2%. We hypothesize that mineral soils, which readily release salt during leaching with distilled water, will not be susceptible to exchangeable Na < 10%. Conversely, mineral soils with low rates of mineral dissolution, like the Fallbrook soil, should be susceptible even at lower ESP values. Also, surface soils, when leached with rainwater, will be especially susceptible at such low levels of exchangeable Na.

The root endodermis is the primary boundary between the inner vascular tissue and the outer cortex, operating as an apoplasmic barrier for selective nutrient uptake and defence. How is the production of endodermal barriers regulated during development? New research in The Plant Journal (Cohen et al., 2020) describes a transcription factor that controls the establishment of the endodermal suberin lamellae. The discovery is an important milestone in understanding the formation of this hydrophobic barrier and its role in maintaining plant fitness. The root endodermal barrier requires the coordinated action of two hydrophobic polymers, lignin and suberin. Lignin is a building block for the Casparian strip, a ring-like structure that surrounds the walls of mature, fully elongated endodermal cells. The suberin lamellae appears later in development, at first as a ‘patchy’ zone, where endodermal cells are suberized intermittently, and later as a ‘continuous’ zone, when cells are fully differentiated (Barberon, 2017). Whereas the Casparian strip serves as an apoplastic barrier, the suberin lamellae limits solute transports intracellularly. Despite the important role that suberization plays at the root endodermis, the regulation of this process is not well understood. In a previous study, Asaph Aharoni and his team discovered two Arabidopsis transcription factors (MYB107 and MYB9) that play a role in suberin monomer biosynthesis and transport, as well as in their subsequent polymerization in the seed outer integument layer (Lashbrooke et al., 2016). In this follow-up study, the team discovered and characterized a related MYB-type transcription factor, MYB39, that regulates root endodermis suberization. The transcription factor, aptly named SUBERMAN, was able to activate the entire suberin metabolism machinery when expressed heterologously in Nicotiana tabacum (tobacco), even in leaves, which naturally do not deposit suberin lamellae in cell walls. Altering the expression of SUBERMAN resulted not only in changes in the deposition patterns of suberin, but also affected the nutrient uptake capacity of the root. The work comes from Aharoni’s lab at the Weizmann Institute (Rehovot, Israel), in collaboration with scientists at the Horticultural Plant Biology and Metabolomics Center in Fujian Agriculture and Forestry University, China. Aharoni’s team has long focused on diverse aspects of plant metabolism, including the production, regulation, and role of secondary metabolites in plant development and stress responses. Hagai Cohen, first author of the paper, was a postdoctoral fellow in Aharoni’s group, and now directs his own lab at the Agricultural Research Organization (ARO, Volcani Center, Israel). Cohen’s group investigates plant lipophilic barriers and their role in pathogen response. Cohen et al. (2020) demonstrates that SUBERMAN triggers the expression of not only suberin biosynthesis genes, but also of genes required to assemble and deposit these unique structures at their correct subcellular sites (see Figure). The authors point out that SUBERMAN probably cooperates with other still-unknown transcription factors to execute the necessary steps for establishing the suberin lamellae. Their current work on root transcriptomics and other approaches has highlighted additional candidate genes with potential roles in suberin metabolism, which the team plans to investigate further to determine their role in suberin deposition in different plant tissues and cell types. The results from Cohen et al. (2020) open the way for dissecting the molecular mechanisms involved in establishing a major root barrier. According to Cohen and Aharoni, in the future, their discoveries could be used to implement metabolic engineering strategies aimed at designing novel barriers in roots or other plant parts. These barriers could make plants more resistant to diverse stress conditions, such as mineral deficiency or pathogen invasion. Other research groups are also likely to recruit SUBERMAN to the rescue. For example, one group is trying to engineer plants to overproduce suberin to sequester carbon from the atmosphere and thereby slow down climate change.

The majority of test data indicate that the hydraulic conductivity of soil-sodium bentonite mixtures increases several folds with many of the chemicals found at waste disposal sites. This investigation is on mixtures consisting of calcium bentonites from four different sources, cement, slag, and fly ash using flexible wall permeameter. The mix with calcium bentonite from Greece yielded hydraulic conductivity values which were equal to or lower than 10-7 cm/s. With water and organic chemicals (aniline 5,000 ppm, phenol 5,000 ppm, toluene 500 ppm) the soil mix showed a decrease in hydraulic conductivity. Over a 40 day period the hydraulic conductivity decreased from about 10-7 cm/s to 10-9 cm/s. The rate of decrease in hydraulic conductivity with phenol was somewhat slower. The hydraulic conductivity did not increase with time with any of the chemicals.

Hydraulic conductivity is an important parameter for predicting groundwater inrush in coal mining worksites. Hydraulic conductivity varies with deformation and failure of rocks induced by mining. Understanding the evolution pattern of hydraulic conductivity during mining is important for accurately predicting groundwater inrush. In this study, variations of hydraulic conductivity of rock samples during rock deformation and failure were measured using the triaxial servo rock mechanic test in a laboratory. The exponential formula of hydraulic conductivity-volume strain was proposed based on the experimental data. The finite-difference numerical model FLAC3D was modified by replacing constant hydraulic conductivity with the strain-dependent hydraulic conductivity. The coupled water flow and rock deformation and failure were simulated using the modified model. The results indicate that in the early time, the rocks undergo elastic compression with increasing rock strain, resulting in a decrease in hydraulic conductivity; then, the microcracks and fissures appear in the rock after it yields results in a sudden jump in hydraulic conductivity; in the later time, the hydraulic conductivity decreases gradually again owing to the microcracks and fissures that were compacted. The conductivity exponentially decreases with the volumetric strain during the periods of both elastic compression and postyielding. The simulated stress-strain curves using the modified model agree with the triaxial tests. The modified model was applied to the groundwater inrush of a coal mining worksite in China. The simulated water inflow agrees well with the observed data. The original model significantly underestimates the water inflow owing to it to neglect the variations of the hydraulic conductivity induced by mining.

Although it is implied that suberized apoplastic barriers of roots negatively correlate with water and solute permeabilities, direct transport measurements across roots with altered amounts and compositions of aliphatic suberin are scarce. In the present study, hydroponically grown Arabidopsis wild types (Col8 and Col0) and different suberin mutants with altered amounts and/or compositions (horst, esb1-1, and esb1-2) were used to test this hypothesis. Detailed histochemical studies revealed late development of Casparian bands and suberin lamellae in the horst mutant compared with wild types and esb mutants. Suberin analysis with gas chromatography and mass spectrometry (GC-MS) showed that the horst mutant had ∼33% lower amounts of aliphatic monomers than Col8 and Col0. In contrast, enhanced suberin mutants (esb1-1 and esb1-2) had twice the amount of suberin as the wild types. Correlative permeability measurements, which were carried out for the first time with a root pressure probe for Arabidopsis, revealed that the hydraulic conductivity (Lpr) and NaCl permeability (Psr) of the whole root system of the horst mutant were markedly greater than in the respective wild types. This was reflected by the total amounts of aliphatic suberin determined in the roots. However, increased levels of aliphatic suberin in esb mutants failed to reduce either water or NaCl permeabilities below those of the wild types. It was concluded that the simple view and the conventional assumption that the amount of root suberin negatively correlates with permeability may not always be true. The aliphatic monomer arrangement in the suberin biopolymer and its microstructure also play a role in apoplastic barrier formation.

Liquid-soil compatibility of soil hydraulic conductivity is reviewed with respect to the materials and methods used in evaluating waste-soil interactions, factors influencing interpretation of test results, and the interactions that are thought to alter significantly the hydraulic conductivity of clay soils. Significant increases in hydraulic conductivity may result from flocculation of clay particles due to interactions with electrolyte solutions, shrinkage of the soil matrix in the presence of concentrated organic solvents, and acid-base dissolution of the soil. Observed effects typically are greater in rigid-wall permeameters than flexible-wall permeameters. Considerable evidence supports the use of the Gouy-Chapman theory for describing the influence of aqueous solutions on the fabric and, therefore, the hydraulic conductivity of clay soils. However, swelling test results suggest that the Gouy-Chapman theory does not account properly for shrinkage effects which have been observed to result in large increases in hydraulic conductivity upon permeation with concentrated organic solvents. Three mechanisms may contribute to an increase in the hydraulic conductivity of clay soils upon permeation with acid permeants: (1) flocculation of the clay, (2) dissolution of the clay minerals (aluminosilicates), and (3) dissolution of other minerals (e.g., CaCO3) in the clay soil. Dissolution and piping of clay minerals leads to increases in hydraulic conductivity. Dissolution of carbonates initially leads to buffering, re-precipitation, pore clogging, and a decrease in hydraulic conductivity. Depletion of the buffering capacity leads to a decrease in pH, dissolution of constituents, and a possible increase in hydraulic conductivity. The measured hydraulic conductivity of a compacted sand-bentonite mixture is shown to be significantly affected by the sequence of permeation to a saturated calcium solution. The effect, termed “first exposure”, has important implications with respect to the application of laboratory test results for evaluation of the suitability of a material for a waste containment barrier.

The hydraulic conductivity is a key parameter in geotechnical engineering. It is closely associated to soil microstructure. In practice, consolidation stress, dry density, and natural structure of soil can affect pore diameter and distribution of soil. Thus, to investigate soil hydraulic conductivity, their effects on microstructure and the corresponding hydraulic conductivity were analyzed. The undisturbed soil and the remolded soil with different dry densities were studied by the oedometer tests, hydraulic conductivity tests, and field emission scanning electron microscope (FESEM) tests. The results indicate that the natural structure inside the undisturbed soil is the intrinsic reason that affects hydraulic conductivity. The increase of consolidation stress mainly reduces the number and size of interaggregate pores in terms of provoking aggregation of soil particles. The increase in dry density will fill the interaggregate pores and weaken their connectivity. The area percentage of macropores can be used to reflect the change of soil microstructure. The consolidation stress is the main factor dominating the area percentage of macropores under a high-stress level. A stable intrinsic structure will be developed to inhibit the soil deformation when dry density is 1.4 g/cm3 or above, which helps to restrain the reduction of area percentage and slow down the decrease of hydraulic conductivity. Finally, a brief statistical regression analysis indicates that the area percentage of pores whose diameter larger than 0.4 μm is significantly related to the hydraulic conductivity, which are responsible for seepage in soft clay.

We report the first data on how effective pressure and deformation influence the hydraulic conductivity of glacial sediments. Fifty eight static hydraulic conductivity tests, 28 triaxial deformation tests and 25 dynamic hydraulic conductivity tests (in which hydraulic conductivity is measured simultaneously with deformation) have been undertaken on seven samples of glacial sediments recovered from the margins of Haut Glacier d’Arolla, Switzerland, and from Traeth y Mwnt, mid Wales. Testing reveals that hydraulic conductivity is inversely related to effective pressure, particularly at effective pressures below c. 100 kPa. Over the full range of effective pressures used (50–900 kPa), this relationship is best described by a negative power law above a base hydraulic conductivity value, termed K 0 . The value of K 0 varies between samples by over three orders of magnitude, from 10 −8 m s −1 to 10 −11 m s −1 . These values vary directly, but weakly, with the square of the effective grain-size of the samples tested. Dynamic testing revealed a commonly repeated pattern of sample failure: axial stress approached a maximum value after which the sample deformed in a ductile manner from its initially cylindrical shape to a barrel shape. Most commonly, sample deformation and failure were accompanied by a decrease in hydraulic conductivity, although increases were also recorded. Dynamic testing also resulted in strongly linear relationships between effective pressure and the yield stress at failure. Such relationships are broadly consistent with a Mohr-Coulomb type model, revealing significant inter-sample variability in frictional resistance, and a cohesive term that is statistically indistinguishable from zero.

Stomatal regulation is crucial for forest species performance and survival on drought-prone sites. We investigated the regulation of root and shoot hydraulics in three Pinus radiata clones exposed to drought stress and its coordination with stomatal conductance (gs ) and leaf water potential (Ψleaf ). All clones experienced a substantial decrease in root-specific root hydraulic conductance (Kroot-r ) in response to the water stress, but leaf-specific shoot hydraulic conductance (Kshoot-l ) did not change in any of the clones. The reduction in Kroot-r caused a decrease in leaf-specific whole-plant hydraulic conductance (Kplant-l ). Among clones, the larger the decrease in Kplant-l , the more stomata closed in response to drought. Rewatering resulted in a quick recovery of Kroot-r and gs . Our results demonstrated that the reduction in Kplant-l , attributed to a down regulation of aquaporin activity in roots, was linked to the isohydric stomatal behaviour, resulting in a nearly constant Ψleaf as water stress started. We concluded that higher Kplant-l is associated with water stress resistance by sustaining a less negative Ψleaf and delaying stomatal closure.

Hydraulic conductivity behaviour of soil blended with geofiber inclusions

This study evaluates the influence of nanomaterials (nano-copper and nano-alumina) on the suction and hydraulic conductivity of compacted soil-bentonite mixture with different plasticity indexes. The soil suction and hydraulic conductivity of the compacted soil-bentonite mixtures were measured before and after the addition of nanomaterials. Soil-water characteristic curves were then developed for compacted soil samples (with and without nanomaterial) using a pressure membrane apparatus. It was found that saturated water content was lower in the soil samples mixed with nanomaterials. The soil hydraulic conductivity also decreased with increasing nanomaterial content, except for S3 soil sample with nano-copper content. The decrease of hydraulic conductivity was possibly caused by the reduction of the effective porosity due to pore clogging. The results from testing samples after one to four drying times show that the largest rise in soil hydraulic conductivity occurred at first or second drying. Adding nanomaterials can reduce the soil hydraulic conductivity by as much as seven times for soil samples with high clay (bentonite) content.

Pseudomonas mandelii strain IB-Ki14 has recently been shown to strengthen the apoplastic barriers of salt-stressed plants, which prevents the entry of toxic sodium. It was of interest to find out whether the same effect manifests itself in the absence of salinity and how this affects the hydraulic conductivity of barley plants. Berberine staining confirmed that the bacterial treatment enhanced the deposition of lignin and suberin and formation of Casparian bands in the roots of barley plants. The calculation of hydraulic conductance by relating transpiration to leaf water potential showed that it did not decrease in bacteria-treated plants. We hypothesized that reduced apoplastic conductivity could be compensated by the higher conductivity of the water pathway across the membranes. This assumption was confirmed by the results of the immunolocalization of HvPIP2;5 aquaporins with specific antibodies, showing their increased abundance around the areas of the endodermis and exodermis of bacteria-treated plants. The immunolocalization with antibodies against auxins and abscisic acid revealed elevated levels of these hormones in the roots of plants treated with bacteria. This root accumulation of hormones is likely to be associated with the ability of Pseudomonas mandelii IB-Ki14 to synthesize these hormones. The involvement of abscisic acid in the control of aquaporin abundance and auxins—in the regulation of and formation of apoplast barriers—is discussed.

ABSTRACTApoplastic barriers in the endodermis, such as Casparian strips and suberin lamellae, control the passage of water and minerals into the stele. Apoplastic barriers are thus thought to contribute to salt exclusion in salt-excluding plants such as sweet sorghum (Sorghum bicolor). However, little is known about the genes involved in the development of the apoplastic barrier. Here, we identified candidate genes involved in Casparian strip and suberin lamella development in the roots of a sweet sorghum line (M-81E). Three distinct developmental regions (no differentiation, developing, and mature) were identified based on Casparian strip and suberin lamella staining in root cross sections. Sequencing of RNA extracted from these distinct sections identified key genes participating in the differentiation of the apoplastic barrier. The different sections were structurally distinct, presumably due to differences in gene expression. Genes controlling the phenylpropanoid pathway, fatty acid elongation, and fatty acid ω-hydroxylation appeared to be directly responsible for the formation of the apoplastic barrier. Our dataset elucidates the molecular processes underpinning apoplastic barrier development and provides a basis for future research on molecular mechanisms of apoplastic barrier formation and salt exclusion.Abbreviations: SHR, SHORTROOT; MYB, MYB DOMAIN PROTEIN; CIFs, Casparian strip integrity factors; CASP, Casparian strip domain proteins; PER, peroxidase; ESB1, ENHANCED SUBERIN1; CS, Casparian strip; RPKM, reads per kilobase per million reads; DEGs, differentially expressed genes; FDR, false discovery rate; GO, Gene Ontology; KEGG, Kyoto Encyclopedia of Genes and Genomes; RNA-seq, RNA sequencing; PAL, phenylalanine ammonia-lyase; CYP, cytochrome P450 monooxygenases; 4CL, 4-coumarate-CoA ligase; AAE5, ACYL-ACTIVATING ENZYME5; CCR, cinnamoyl CoA reductase; TKPR, TETRAKETIDE ALPHA-PYRONE REDUCTASE1; CAD, cinnamyl alcohol dehydrogenase; HST, shikimate O-hydroxycinnamoyltransferase; PMAT2, PHENOLIC GLUCOSIDE MALONYLTRANSFERASE2; CCOAOMT, caffeoyl-CoA O-methyltransferase; KCS, β-ketoacyl-CoA synthase; CUT1, CUTICULAR PROTEIN1; DET2, 5-alpha-reductase; TAX, 3ʹ-N-debenzoyl-2ʹ-deoxytaxol N-benzoyltransferase; CER1, ECERIFERUM1; FAR, fatty acyl reductase; AF-CoA, alcohol-forming fatty acyl-CoA reductase; ABCG, ATP-binding cassette, subfamily G; ERF, ethylene-responsive transcription factor; HSF, heat stress transcription factor; NTF, NUCLEAR TRANSCRIPTION FACTOR Y SUBUNIT B-5; GPAT, glycerol 3-phosphate acyltransferase.