Haustorium Formation and Cell Wall Appositions in Susceptible and Partially Resistant Wheat and Barley Seedlings Infected with Wheat Leaf Rust

Phase contrast light microscopy observations of wheat and barley seedlings infected with wheat leaf rust spores suggested that cell wall appositions are structural barriers against haustorium formation leading to abortion of infection structures. Nearly equal numbers of cell wall appositions per infection structure were detected in seedlings of susceptible and partially resistant wheat genotypes. Differences between susceptible and partially resistant genotypes became evident after the first haustorium had been formed. This again indicates the presence of a post-haustorial effect of partial resistance. Some factors influencing nutrient uptake are discussed. Wheat leaf rust colonies hardly formed haustoria in barley seedlings, the few not aborted infection structures were accompanied by cell collapse. The mechanisms of partial resistance in wheat and barley to their respective leaf rust fungi seem different, but their non-host reactions appear similar.     

The Effect of Polymetallic Pollution on Ion-Exchange Properties of Barley Root and Shoot Cell Walls

Doklady Biochemistry and Biophysics - For the first time we determined the ion-exchange properties of the cell walls (CWs) isolated from roots and shoots of barley plants grown in the conditions of...     

Isolation and Characterization of a Thionin Proprotein-processing Enzyme from Barley

Thionins are plant-specific antimicrobial peptides that have been isolated from the endosperm and leaves of cereals, from the leaves of mistletoes, and from several other plant species. They are generally basic peptides with three or four disulfide bridges and a molecular mass of ∼5 kDa. Thionins are produced as preproproteins consisting of a signal peptide, the thionin domain, and an acidic domain. Previously, only mature thionin peptides have been isolated from plants, and in addition to removal of the signal peptide, at least one cleavage processing step between the thionin and the acidic domain is necessary to release the mature thionin. In this work, we identified a thionin proprotein-processing enzyme (TPPE) from barley. Purification of the enzyme was guided by an assay that used a quenched fluorogenic peptide comprising the amino acid sequence between the thionin and the acidic domain of barley leaf-specific thionin. The barley TPPE was identified as a serine protease ({"type":"entrez-protein","attrs":{"text":"BAJ93208","term_id":"326526063","term_text":"BAJ93208"}}BAJ93208) and expressed in Escherichia coli as a strep tag-labeled protein. The barley BTH6 thionin proprotein was produced in E. coli using the vector pETtrx1a and used as a substrate. We isolated and sequenced the BTH6 thionin from barley to confirm the N and C terminus of the peptide in planta. Using an in vitro enzymatic assay, the recombinant TPPE was able to process the quenched fluorogenic peptide and to cleave the acidic domain at least at six sites releasing the mature thionin from the proprotein. Moreover, it was found that the intrinsic three-dimensional structure of the BTH6 thionin domain prevents cleavage of the mature BTH6 thionin by the TPPE.     

Effect of Ethylene on the Release of alpha-Amylase through Cell Walls of Barley Aleurone Layers

A large portion of the gibberellic acid (GA₃)-induced α-amylase in isolated aleurone layers is transported into the incubation medium. In the presence of GA₃ and ethylene, an even larger portion of the enzyme is found in the medium. Employing an acid washing technique developed by Varner and Mense (Plant Physiol 1972 49:187-189), it was observed that ethylene significantly reduces the amount of α-amylase trapped by the thick cell walls of aleurone layers. However, the amount of enzyme remaining in the cell (within the boundary of plasma membrane) is not affected by ethylene. Ethylene has no observable effect on membrane formation as measured by the incorporation of [³²P]orthophosphate into phospholipids. Because of these observations it is suggested that ethylene enhances the release of α-amylase, i.e. transport of α-amylase across cell walls, but not the secretion of α-amylase, i.e. transport of α-amylase past the barrier of plasma membrane. The possible mechanism of this ethylene effect is discussed.     

Identification and Severity Determination of Wheat Stripe Rust and Wheat Leaf Rust Based on Hyperspectral Data Acquired Using a Black-Paper-Based Measuring Method

It is important to implement detection and assessment of plant diseases based on remotely sensed data for disease monitoring and control. Hyperspectral data of healthy leaves, leaves in incubation period and leaves in diseased period of wheat stripe rust and wheat leaf rust were collected under in-field conditions using a black-paper-based measuring method developed in this study. After data preprocessing, the models to identify the diseases were built using distinguished partial least squares (DPLS) and support vector machine (SVM), and the disease severity inversion models of stripe rust and the disease severity inversion models of leaf rust were built using quantitative partial least squares (QPLS) and support vector regression (SVR). All the models were validated by using leave-one-out cross validation and external validation. The diseases could be discriminated using both distinguished partial least squares and support vector machine with the accuracies of more than 99%. For each wheat rust, disease severity levels were accurately retrieved using both the optimal QPLS models and the optimal SVR models with the coefficients of determination (R²) of more than 0.90 and the root mean square errors (RMSE) of less than 0.15. The results demonstrated that identification and severity evaluation of stripe rust and leaf rust at the leaf level could be implemented based on the hyperspectral data acquired using the developed method. A scientific basis was provided for implementing disease monitoring by using aerial and space remote sensing technologies.     

Effects of Infection Density on the Size of Barley and Wheat Leaf Rust Colonies before and on the Size of Uredia after the Start of Sporulation

Three barley genotypes were exposed to four different inoculum densities of barley leaf rust, Puccinia hordei. Colony area well before first sporulation and uredia size well after the start of sporulation were measured. In a second series two barley and two wheat cultivars were exposed to four different inoculum densities of barley and wheat leaf rust (P. recondita f. sp. tritici), respectively. Before the sporulation is initiated the colony size was independent of the uredia density. This was valid for densities ranging from approximately 7 to over 200 uredia per cm² leaf area. After the sporulation had started the uredia size was strongly dependent on the uredia density. The size of the uredia was approximately halved when the uredia density increased from about 10 to about 150 per cm². The urediospore production per uredium decreased much stronger with increased uredia density.     

Lectin Binding Studies on the Cell Walls of Soybean Rust (Phakopsora pachyrhizi Syd.)

Walls of uredospores, infection structures, intercellular hyphae and haustoria of the soybean rust fungus (Phakopsora pachyrhizi) were studied by electron microscopy using gold-labeled wheat germ lectin (WGL) and Concanavalin A (ConA) as cytochemical probes. Receptors for WGL (probably chitin) were detected in all fungal walls included in this study. WGL-binding occurred throughout the entire walls (uredospores, appressorial cone, penetration hyphae, haustorial mother cells) or only to the inner wall layers (germ tubes, appressoria, intercellular hyphae).     

小麦类根瘤中胞间细菌的运动及其对细胞壁的影响

用电子显微镜和光学显微镜观察了小麦类根瘤,以探讨小麦类根瘤中胞间细菌的运动及其对细胞壁的影响.结果表明:(1)小麦类根瘤由薄壁细胞、分生细胞和侵染细胞组成,它们中有许多胞间隙,其中一些还含有大量细菌;它们的胞间层常常彼此分离,形成间隙,间隙中有时也有细菌存在;(2)小麦类根瘤中没有侵入线,细菌运动主要在胞间进行;具有细菌的胞间隙和胞间层大小不等、形状各异,其细胞壁还常常出现不同程度的变化,变化的大小一般与它们中的细菌有关,且随细菌数量的增加而增加.     

Block-Surface Staining for Differentiation of Starch and Cell Walls in Wheat Endosperm

A staining technique for differentiating starch granules and cell walls was developed for computer-assisted studies of starch granule distribution in cells of wheat [Triticum aestivum L.] caryopses. Blocks of embedded caryopses were sectioned, exposing the endosperm tissue, and stained with iodine potassium iodide (IKI) and Calcofluor White. Excessive tissue hydration during staining was avoided by using stains prepared in 80% ethanol and using short staining times. The IKI quenched background fluorescence which facilitated the use of higher concentrations of Calcofluor White. Cell wall definition was improved with the IKI-Calcofluor staining combination compared to Calcofluor alone. The high contrast between darkly stained starch granules and fluorescent cell walls permitted computer assisted analysis of data from selected hard and soft wheat varieties. The ratio of starch granule area to cell area was similar for both wheat classes. The starch granule sizes ranged from 2.1 μm³ to 22,000 μm³ with approximately 90% of the granules measuring less than 752 μm³ (ca. 11 μm in diameter). Hard wheat samples had a greater number of small starch granules and a lower mean starch granule area compared to the soft wheat varieties tested. The starch size distribution curve was bimodal for both the hard and soft wheat varieties. Three-dimensional starch size distribution was measured for four cells near the central cheek region of a single caryopsis. The percentage of small granules was higher at the ends than at the mid-section of the cells.     

Effect of BYDV Infection on the Cell Surface Glycoproteins in Common Wheat,Wheatgrass and Octoploid Wheat-Wheatgrass

Changes in the cell surface glycoproteins in common wheat 3B-2, Agropyron intermedium and octoploid wheat-wheatgrass Zhong 5 after the inoculation with barley yellow dwarf virus (BYDV) were sdudied using electron microscopy and ruthenium red staining. The results indicated that, after the inoculation with BYDV, different changes in cell surface glycoproreins were observed in the plant species with different levels of resistance. In A. intermediurn which is immune to BYDV, inoculation with BYDV did not cause significant change in cell surface glycoprotein layer. In cotoploid wheat-wheatgrass Zhong 5 which is highly resistent to BYDV, BYDV infection caused significant thickening in most cell surface glycoprotein layer. In common wheat 3B-2 which is susceptible to BYDV, BYDV infection did not cause thickening in cell surface glycoprotein layer, but in most cells, glycoproteins on the cell surface were partially peeled off or disappeared completely. Therefore, it is suggested that the glycoproteins on cell surface play certain roles in BYDV resistance. The phenomenon of the thickening of cell surface glycoprotein layer caused by BYDV infection was possibly a resistant reaction to the virus.     

利用花药培养快速创制小麦条锈病和黄矮病抗性新种质

利用中间偃麦草与普通小麦杂交育成的部分双二倍体－中５为外源抗性基因供体,通过花药培养途径,在它与几个冬小麦品种的５个杂交组合中,诱导出试管花粉绿苗１４４株,移栽加倍后,形成了４９个加倍单倍体株系。通过小麦条锈病和黄矮病抗性鉴定获得了几个高抗黄矮病或者对条锈病近免疫的新材料。其中ＤＨ７２８对条锈病菌近免疫,２ｎ＝４４,减数分裂构型为０．７０１Ｖ＋０．０３５ＩＩＩ＋２１．５７９ＩＩ＋０．４５６Ｉ,为双     

Histopathology of Leaf Rust Infection and Development in Wheat Genotypes containing Lr12 and Lr13

Evidence exists that certain genes for resistance to leaf rust in wheat, e.g. Lr13 and Lr34 , may interact with other genes to condition higher levels of resistance than that conferred by each gene individually. In this study, the hypothesis that Lr12 and Lr13 , both genes for adult plant resistance to Puccinia recondita Roberge ex. Desmaz f. sp. tritici Eriks. and Henn., interact to confer an improved level of resistance, was investigated using fluorescence and phase-contrast microscopy. Flag leaf segments of monogenic and digenic Thatcher lines, sampled 64 and 240 h post-inoculation, were stained with Uvitex 2B and screened, using fluorescence microscopy, for development of infection structures or host response. To study cell wall appositions, specimens were stained with trypan blue and a solution of picric acid in methyl salicylate. Aborted penetration, consisting of nonpenetrating appressoria and aborted substomatal vesicles, showed that inhibition of fungal growth in wheat lines containing Lr12 and/or Lr13 was activated, to a certain degree, before haustoria were formed. At 240 h after inoculation colony size indicated that fungal colonies in the Lr gene combination lines were generally smaller than in the parents, but not necessarily smaller than those in a line with Lr13 only. Host cell necrosis was more frequently associated with infection sites, specifically of pathotype UVPrt2, in the combination lines than in the parents. The morphology of cell wall appositions varied considerably from a narrow, luminous zone slightly wider in the centre, to a thick central part opposite the haustorium mother cell, sharply decreasing towards both ends. Histological assessments could, however, not conclusively prove pronounced resistance enhancement or unconventional resistance mechanisms due to combining the genes Lr12 and Lr13 .     

The Effect of Rust Infection on Reproduction in a Tropical Tree (Faramea occidentalis)1

Fungal pathogens that infect reproductive structures of plants (e.g., flowers and fruits) can reduce the seed production and seedling recruitment of host plants. We report here on the effects of a rust, Aecidium farameae, that infects the ovaries and pedicels of mature flowers on Faramea occidentalis (Ruhiaceae), a small tree common on Barro Colorado Island, Republic of Panama. Rust infection of ovaries reduced the number of maturing fruit on infected trees. Trees with low rust incidence in June of 1992 had 68 percent fruit survival, compared to 17 percent fruit survival for those with high rust incidence. Infected fruits developed abnormally and were usually aborted long before uninfected fruits were mature. One hundred percent of the infected ovaries marked in July were diseased or missing in August. We conclude that infection by A. farameae has the potential to seriously decrease the reproductive output of Faramea occidentalis and may represent an important source of variation in the relative fitness of individual plants.     

Effect of Lytic Enzymes of Acanthamoeba castellanii on Bacterial Cell Walls

Extracts of Acanthamoeba castellanii (Neff) contain alpha- and beta-glucosidase, beta-galactosidase, beta-N-acetylglucosaminidase, amylase, and peptidase. All of these activities are optimal between pH 3 and 4. These extracts also were found to clarify suspensions of cell walls from nine different gram-positive bacteria, including Micrococcus lysodeikticus. The pH optimum for the lytic activity was between 3 and 4. The extent of lysis of the various cell walls did not correlate with the release of free amino groups and of free N-acetylated sugars from the walls during digestion with these extracts. Suspensions of cell walls of Escherichia coli (a gram-negative bacterium), Cordiceps militaris (a fungus), and Acanthamoeba cysts, as well as of colloidal chitin, were not clarified by incubation with these extracts, although reducing sugars were released from each of these materials. Exhaustive digestion of M. lysodeikticus walls by lysozyme released no free N-acetylglucosamine. The products of exhaustive digestion of this cell wall with Acanthamoeba extracts were free N-acetylglucosamine, free N-acetylmuramic acid, glycine, alanine, glutamic acid, lysine, and N-acetylmuramic acid peptide fragments. These results suggest that the amoeba extracts contain endo- and exo-hexosaminidases, in addition to beta-hexosaminidase and peptide hydrolases.     

抗条锈病小麦品种9365在抗病育种中的利用与评价

9365是陕西省小麦研究中心创制的抗条锈病小麦品种.经多年观察、利用发现,9365对条锈病表现高抗,其穗大、成穗率高、落黄好、高产、综合农艺性状好,是陕西省小麦抗条锈病育种可资利用的抗条锈小麦品种.其缺点是植株偏高、成熟偏晚、抗性受隐性基因控制.     

Effect of β-Lysin on Isolated Cell Walls and Protoplasts of Bacillus subtilis

The cytoplasmic membrane is the site of beta-lysin action. Protoplasts lysed rapidly in its presence, whereas cell walls and wall autolysis were unaffected.