Do root hydraulic properties change during the early vegetative stage of plant development in barley (Hordeum vulgare)?

Background and Aims

As annual crops develop, transpirational water loss increases substantially. This increase has to be matched by an increase in water uptake through the root system. The aim of this study was to assess the contributions of changes in intrinsic root hydraulic conductivity (Lp, water uptake per unit root surface area, driving force and time), driving force and root surface area to developmental increases in root water uptake.

Methods

Hydroponically grown barley plants were analysed during four windows of their vegetative stage of development, when they were 9–13, 14–18, 19–23 and 24–28 d old. Hydraulic conductivity was determined for individual roots (Lp) and for entire root systems (Lp_r). Osmotic Lp of individual seminal and adventitious roots and osmotic Lp_r of the root system were determined in exudation experiments. Hydrostatic Lp of individual roots was determined by root pressure probe analyses, and hydrostatic Lp_r of the root system was derived from analyses of transpiring plants.

Key Results

Although osmotic and hydrostatic Lp and Lp_r values increased initially during development and were correlated positively with plant transpiration rate, their overall developmental increases (about 2-fold) were small compared with increases in transpirational water loss and root surface area (about 10- to 40-fold). The water potential gradient driving water uptake in transpiring plants more than doubled during development, and potentially contributed to the increases in plant water flow. Osmotic Lp_r of entire root systems and hydrostatic Lp_r of transpiring plants were similar, suggesting that the main radial transport path in roots was the cell-to-cell path at all developmental stages.

Conclusions

Increase in the surface area of root system, and not changes in intrinsic root hydraulic properties, is the main means through which barley plants grown hydroponically sustain an increase in transpirational water loss during their vegetative development.     

Exogenous spermidine enhances Epichloë endophyte-induced tolerance to NaCl stress in wild barley (Hordeum brevisubulatum)

Plant and Soil - We investigated morphological variations in podzols caused by changes in soil porosity and permeability upon the growth of large tree-roots in a tropical barrier island (Ilha...     

Hormonal regulation of gene expression in the “slender” mutant of barley (Hordeum vulgare L.)

The slender mutant of barley resembles a normal barley plant treated with high doses of gibberellic acid (GA₃). Expression of GA₃-regulated and abscisic acid (ABA)-regulated mRNAs was studied in the endosperm and roots of mutant and wild-type (WT) plants.Production of -amylase (EC 3.2.1.1) by WT embryoless half-grains was dependent on the presence of GA₃, and was prevented by ABA. In contrast, -amylase was produced by half-grains of the slender mutant in the absence of added GA₃, although it was still reduced by ABA. The spectrum of -amylase mRNAs in slender embryoless half-grains incubated in the absence of added GA₃ was the same as in WT endosperm half-grains incubated in the presence of GA₃. These results indicate that the endosperm of the slender mutant exhibits similar properties to WT endosperm treated with GA₃.In roots the expression of an ABA-inducible mRNA was similar in slender and WT seedlings either treated with exogenous ABA or exposed to dehydration. This result, and the effect of ABA on -amylase production by the endosperm, indicate that the slender plants retain sensitivity to ABA.Abbreviations ABA abscisic acid - AMV avian myeloblastosis virus - GA gibberellin - GA₁ gibberellin A₁ - GA₃ gibberellic acid - WT wild-type     

Effect of the fungal endophyte Epichloë bromicola on polyamines in wild barley (Hordeum brevisubulatum) under salt stress

Plant and Soil - The endophytic fungus Epichloë bromicola forms mutualistic symbiotic associations with wild barley (Hordeum brevisubulatum) in the saline-alkali areas of northwestern China....     

Seven members of the (1→3)-β-glucanase gene family in barley (Hordeum vulgare) are clustered on the long arm of chromosome 3 (3HL)

Members of the (13)--glucan glucanohydrolase (EC 3.2.1.39) gene family have been mapped on the barley genome using three doubled haploid populations and seven wheat-barley addition lines. Specific probes or polymerase chain reaction (PCR) primers were generated for the seven barley (13)--glucanase genes for which cDNA or genomic clones are currently available. The seven genes are all located on the long arm of chromosome 3 (3HL), and genes encoding isoenzymes GI, GII, GIII, GIV, GV and GVII (ABG2) are clustered in a region less than 20 cM in length. The region is flanked by the RFLP marker MWG2099 on the proximal side and the Barley Yellow Mosaic Virus (BYMV) resistance gene ym4 at the distal end. The gene encoding isoenzyme GVI lies approximately 50 cM outside this cluster, towards the centromere. With the exception of the gene encoding isoenzyme GIV, all of the (13)--glucanase genes are represented by single copies on the barley genome. The probe for the isoenzyme GIV gene hybridized with four DNA bands during Southern blot analysis, only one of which could be incorporated into the consensus linkage map.     

Characterization of cDNA clones of the family of trypsin/α-amylase inhibitors (CM-proteins) in barley (Hordeum vulgare L.)

Summary Recombinants encoding members of the trypsin/-amylase inhibitors family (also designated CM-proteins) were selected from a cDNA library prepared from developing barley endosperm. Inserts in two of the clones, pUP-13 and pUP-38, were sequenced and found to encode proteins which clearly belong to this family, as judged from the extensive homology of the deduced sequences with that of the barley trypsin inhibitor CMe, the only member of the group for which a complete amino acid sequence has been obtained by direct protein sequencing. These results, together with previously obtained N-terminal sequences of purified CM-proteins, imply that there are at least six different members of this dispersed gene family in barley. The relationship of this protein family to the B-3 hordein and to reserve prolamins from related species is discussed in terms of their genome structure and evolution.     

Haplotype diversity in the endosperm specific β-amylase gene Bmy1 of cultivated barley (Hordeum vulgare L.)

Five single nucleotide polymorphism (SNP) sites corresponding to substitutions in the protein sequence of the β-amylase gene Bmy1 at amino acid (AA) positions 115, 165, 233, 347 and 430 were genotyped in 493 cultivated barley accessions by Pyrosequencing and a CAPS assay. A total of 6 different haplotypes for the Bmy1 gene were discovered of which 4 haplotypes were identified as previously described alleles Bmy1-Sd1, Bmy1-Sd2L, Bmy1-Sd2H and Bmy1-Sd3, while 2 haplotypes were new. A broad spectrum of haplotypes was found in spring barleys, while the winter barleys were dominated by the newly described haplotype Bmy1-Sd4. Individual haplotype frequencies varied between the geographic regions.Three pairs of SNP loci within the gene showed highly significant (P<0.0001) elevated values of linkage disequilibrium (LD) with r ² > 0.6. In the European and Asian subpopulations different loci were in linkage disequilibrium due to the differences in haplotype frequency distributions. By applying LD data to select haplotype tagging SNPs, three SNP sites corresponding to AA positions 115, 233 and 347 were identified that allowed to discriminate 4 haplotypes and to capture 91.6% of the available diversity by distinguishing 452 out of 493 accessions. In a subset of 2-rowed German spring barley varieties 4 SNPs and 2 haplotypes had a significant association with the malting quality parameter final attenuation limit which is related to the total amylolytic enzymatic activity.     

Fungal endophyte Epichloë bromicola infection regulates anatomical changes to account for salt stress tolerance in wild barley (Hordeum brevisubulatum)

Plant and Soil - Plants can minimize the adverse effects of salinity by modifying morphological and anatomical features. Previous studies showed that endophytic Epichloë bromicola play an...     

Malting quality quantitative trait loci on a high-density map of Mikamo golden?×?Harrington cross in barley (Hordeum vulgare L.)

A high-density map consisting of 550 markers was constructed based on the segregation data of 95 doubled-haploid lines (DHLs) derived from the cross between a Japanese barley cultivar, Mikamo Golden and a North American barley cultivar, Harrington (MH-DHLs). Quality traits of malt extract (EX), total nitrogen (TN), soluble nitrogen (SN), Kolbach index (KI), diastatic power (DP), wort beta-glucan (WG) and viscosity (VS) were determined in three site/year crops. Quantitative trait loci (QTL) analyses were performed with these quality data sets, using the linkage map. Major QTL controlling EX, SN and KI were mapped on terminal region of 5H with Harrington as effective allele. Another QTL controlling EX was mapped on 2H with Mikamo Golden as effective allele. QTL controlling TN, DP, WG and VS were detected variably in terms of flanking markers and chromosomes depending on site/year. Cleaved amplified polymorphic sequences (CAPS) markers for EX based on the QTL detected on 2H and 5H were developed. Analysis of EX and genotypes of 33 malting barley cultivars from around the world as well as MH-DHLs revealed that the two CAPS marker on 2H and 5H affect EX by a significant difference, suggesting that the two CAPS markers were valuable for marker-assisted selection in malting barley breeding.     

Effect of soil compaction on barley (Hordeum vulgare L.) growth: II Are increased xylem sap ABA concentrations involved in maintaining leaf expansion in compacted soils?

The abscisic acid (ABA)-deficient mutant of barley, Az34, exhibiteda much reduced rate of leaf expansion at a bulk density of 1.6g cm^–3 as compared to the isogenic wild-type variety,Steptoe. Az34 had a consistently lower xylem sap ABA concentrationat 7 d and 14 d after emergence (DAE). The xylem sap data suggestthat ABA present at Steptoe concentrations may have a directrole in maintaining leaf expansion at the sub-critical bulkdensity (1.6 g cm^–3 To test this hypothesis, additionof synthetic ABA either to the rooting environment (100 nM)or directly to the xylem sap (5 pg µl^–1 to reproducethe xylem sap ABA concentrations found in Steptoe, increasedleaf expansion in Az34 to the wild-type level. Furthermore,feeding Steptoe xylem sap to Az34 produced similar effects.These experiments provide direct evidence of a positive rolefor ABA as a root-to-shoot signal which assists in maintainingleaf growth in plants experiencing subcritical levels of compactionstress. Key words: ABA-deficient mutant, leaf expansion, xylem sap, ABA     

The relationship between proline content, the expression level of P5CS (Δ1-pyrroline-5-carboxylate synthetase), and drought tolerance in Tibetan hulless barley (Hordeum vulgare var. nudum)

Many plants accumulate proline (Pro) when suffered from drought; thus, the relationship between Pro accumulation and plant drought tolerance becomes an increasing concern. Pro is synthesized from either glutamine or ornithine, and the former pathway dominates under osmotic stress conditions. In this study, the dynamic accumulation of free Pro under drought stress in 10 genotypes of Tibetan hulless barley (Hordeum vulgare var. nudum) with water lose rate (WLR) of 0.3304 to 0.5839 g/(h g dry wt) was investigated. However, no correlation between Pro accumulation and drought tolerance was found. Furthermore, the barley stripe mosaic virus establisheding virus-induced gene silencing was employed to suppress the expression of the encoding gene Δ¹-Pyrroline-5-Carboxylate Synthetase (P5CS), which catalyzes the ratelimiting step of Glu pathway in Pro biosynthesis. By the quantitative real-time polymerase chain reaction, the decrease of the P5CS expression was found, and a consequent Pro degradation was also detected in P5CS-silenced plants. However, neither increased WLR of detached leaves nor decreased survival rate under drought stress was found compared with control plants. These results suggested that the repressed expression of P5CS and decreased content of free Pro may not interfere with the drought tolerance of Tibetan hulless barley.     

Developmental regulation of K accumulation in pollen, anthers, and papillae: are anther dehiscence, papillae hydration, and pollen swelling leading to pollination and fertilization in barley (Hordeum vulgare L.) regulated by changes in K concentration?

The presence of potassium (K) in pollen, anthers and papillaefrom barley (Hordeum vulgare L.) flowers with different levelsof developmental stages starting from boot stage to fully matureflower, was studied by using the K-sensitive fluorescent dyePBFI (potassium-binding benzofuran isophthalate) and confocallaser scanning microscopy. The presence of heavy K fluorescencewas detected only at the aperture area of the mature pollen.Similarly, the presence of K increased with the progressionfrom immature to mature anther and papillae. In addition, ahigher concentration of K was observed only at the stomium area(the place of anther dehiscence) of mature anthers. Keepingin view the role of K as an active osmoticum and the consistentand synchronized appearance of K in mature pollen, anthers,and papillae, it was concluded that K may regulate anther dehiscence,pollen imbibition, and papillae hydration leading to pollinationand fertilization. Key words: Anther, confocal microscopy, papillae, PBFI, pollen, potassium     

What drives variation in the corticosterone stress response between subspecies? A common garden experiment of swamp sparrows (Melospiza georgiana)

Although differences in the corticosterone stress response have frequently been reported between populations or closely related subspecies, their origin remains unclear. These differences may appear because individuals adjust their corticosterone stress response to the environmental conditions they are experiencing. However, they may also result from selection that has favoured individuals with specific corticosterone stress response or from environmental factors that have affected the development of the corticosterone stress response during early life. We investigated these hypotheses by studying the corticosterone stress response of two closely related subspecies of swamp sparrows (Melospiza sp.). We showed for the first time that two closely related subspecies can differ in their corticosterone stress response when raised at the laboratory and held in similar conditions for a year. Thus, we demonstrated that selection, developmental processes or a conjunction of both of these processes can account for variation in the stress response between closely related subspecies.     

Is the variation of floral elaiophore size in two species of Stigmaphyllon (Malpighiaceae) dependent on interaction with pollinators?

Background: Intraspecific variations in floral traits of species over its geographic range can be associated with differences in pollinator assemblages and/or with environmental conditions.

Aims: We evaluated the area of elaiophores in different populations of Stigmaphyllon bonariense (n = 9) and S. jatrophifolium (n = 6), and we hypothesised a marked reduction in their size towards their southern limits of distribution, associated with different oil-collecting bee assemblages.

Methods: Area of elaiophores was calculated and we carried out linear correlations with floral size, pollinators, visitation rate and pollinator size along the latitudinal gradient of the plants’ distributions. Moreover, we examined the relative size relationships using allometric analyses, to verify this reduction.

Results: Floral elaiophore area decreased with latitude. However, for S. bonariense we observed an allometric reduction in elaiophore area with respect to floral size, while for S. jatrophifolium an isometric reduction was found. In both species, pollinator richness and visitation rate did not diminish with latitude, but pollinator size for S. bonariense varied.

Conclusions: Our results show a reduction in the size of elaiophores in both species along their distribution range, with dissimilar tendencies, suggesting that these species may have different selection pressures that cause variation of their phenotypic traits.     

What factors are responsible for the greater yield of ATP per carbon atom when fatty acids are completely oxidised to CO2 and water compared with glucose?

Some current textbooks of biochemistry present calculations which indicate that when palmitic or stearic acid is completely oxidised to CO₂ and water, more molecules of ATP are produced per carbon atom than when glucose is similarly oxidised. This greater yield of ATP is not due to ATP produced as a result of the β-oxidative process, but rather due to the increased yield of acetyl-CoA molecules produced from fatty acids (3 acetyl-CoA molecules per 6 carbon atoms) compared with that produced from glucose (2 acetyl-CoA molecules per 6 carbon atoms).     

The effect of phosphorus binding clay (Phoslock®) in mitigating cyanobacterial nuisance: a laboratory study on the effects on water quality variables and plankton

This laboratory study examined the lanthanum modified clay Phoslock^® for its effectiveness to bind soluble reactive phosphorus (SRP), release of nutrients from this modified clay, its influence on water quality variables (pH, oxygen saturation %, conductivity and turbidity), effects on phytoplankton growth (green alga Scenedesmus obliquus, cyanobacteria Microcystis aeruginosa and Anabaena sp.), and, lastly, its effect on the population growth of the rotifer Brachionus calyciflorus. A clear dose–response for SRP binding by the modified clay was observed. A small amount of ammonium is released from Phoslock^®. We found no effect of Phoslock^® on pH or oxygen saturation. Conductivity increased with the increasing concentration of Phoslock^®. An application of Phoslock^® caused a transient increase of turbidity up to 211 NTU. However, due to rapid settlement, turbidity fell below 13 NTU (~1 m Secchi depth), after 6 h. Phoslock^® addition caused a reduction in growth of all phytoplankton species tested that we attribute to the combined effects of light limitation, flocculation with the bentonite and binding of SRP to Phoslock^®. We estimated the EC₅₀ of Phoslock^® on the population growth of rotifer B. calyciflorus to be 0.15 g Phoslock^® l^?1. Overall, the results of our study indicate Phoslock^® seems to be suitable for field applications.     

Do pH changes in the leaf apoplast contribute to rapid inhibition of leaf elongation rate by water stress? Comparison of stress responses induced by polyethylene glycol and down‐regulation of root hydraulic conductivity

We have dissected the influences of apoplastic pH and cell turgor on short-term responses of leaf growth to plant water status, by using a combination of a double-barrelled pH-selective microelectrodes and a cell pressure probe. These techniques were used, together with continuous measurements of leaf elongation rate (LER), in the (hidden) elongating zone of the leaves of intact maize plants while exposing roots to various treatments. Polyethylene glycol (PEG) reduced water availability to roots, while acid load and anoxia decreased root hydraulic conductivity. During the first 30 min, acid load and anoxia induced moderate reductions in leaf growth and turgor, with no effect on leaf apoplastic pH. PEG stopped leaf growth, while turgor was only partially reduced. Rapid alkalinization of the apoplast, from pH 4.9 ± 0.3 to pH 5.8 ± 0.2 within 30 min, may have participated to this rapid growth reduction. After 60 min, leaf growth inhibition correlated well with turgor reduction across all treatments, supporting a growth limitation by hydraulics. We conclude that apoplastic alkalinization may transiently impair the control of leaf growth by cell turgor upon abrupt water stress, whereas direct hydraulic control of growth predominates under moderate conditions and after a 30-60 min delay following imposition of water stress.     

Effect of complex formation by taxifolin and naringenin with Cu(i) ions on the distribution of the components of complexes in the octanol–water system

The interaction of two structurally close flavanones: taxifolin and naringenin with copper(I) ions and its effect on the distribution of flavonoids and the corresponding ions in a biphasic system octanol–water have been studied. It has been shown that these polyphenols form complexes with copper ions of different stoichiometric ratio depending on the pH of medium (5.4, 7.4, and 9.0). The interaction of the flavonoids with copper ions leads to an increase in the fraction of polyphenols in the water phase at all pH values examined. The fraction of metal ions in octanol in the presence of both taxifolin and naringenin is maximal in the range of neutral pH values. The parameters obtained in the study, such as the partition coefficient and the coefficient of distribution in a biphasic system octanol–water (logP and logD) form the physicochemical basis necessary for the estimation of the bioavailability of flavonoids and the corresponding metal ions upon their combined consumption.