Wheat germ agglutinin regulates cell division in wheat seedling roots

The mitogenic activity of wheat germ agglutinin (WGA) has been studied in roots of 4-day-old wheat seedlings. WGA had a more pronounced stimulating effect on cell division than the known mitogens concanavalin A and phytohemagglutinin whereas gliadin had no effect. Treatment of wheat seedling roots with exogenous WGA led to the accumulation of indoleacetic acid and cytokinins, hormones that play an important role in the activation of plant cell growth. The data on the combined effect of 24-epibrassinolide and WGA on cell division and accumulation of phytohormones in seedling roots support a possible link between the endogenous WGA level and hormonal regulation of cell division in the root meristem of wheat plants.     

Mechanisms of protective action of wheat germ agglutinin on cell growth in wheat seedling roots under salinity

Effects of 20 nM wheat germ agglutinin (WGA) on relative growth rate, mitotic index (MI) and the cell area in the root extension zone were investigated in seedling of Triticum aestivum L. under the influence of 2% NaCl. It was elucidated that pretreatment of wheat seedling with WGA prevented a salinity induced inhibition of root cell growth, and accelerated the restoration of cell growth after stress removal. The protective WGA effect on root cell growth may be due, presumably, to reorganization of phytohormone balance caused by WGA treatment, which could lead to accumulation of LAA and decrease in the ABA level.     

Lectin involvement in the development of wheat tolerance to cadmium toxicity

In the roots of bread wheat (Triticum aestivum L.) seedlings, the effects of pretreatment with 28 nM wheat germ agglutinin (WGA) and successive action of 1 mM cadmium acetate on growth, phytohormone balance, lignin deposition, and also cadmium accumulation and distribution were studied. Priority data on cadmium-induced ABA-mediated reversible accumulation of WGA in the roots, which was accompanied by its excretion in the medium of seedling incubation, were obtained. Pretreatment with WGA exerted a clear protective effect on seedling growth in the presence of cadmium, which was based on a decrease in the amplitude of stress-induced shifts in the balance between IAA and ABA and preventing the reduction in the cytokinin level. Acceleration of lignification of the cell walls in the basal parts of roots of seedlings pretreated with WGA and subjected to stress is shown, and this limits cadmium entry into the plant.     

The involvement of wheat and common bean lectins in the control of cell division in the root apical meristems of various plant species

The effects of wheat germ agglutinin (WGA) and phytohemagglutinin (PHA) at the concentration of 1 mg/l on the rate of cell division in the root apical meristem of wheat (Triticum aestivum L.), barley (Hordeum vulgare L.), rice (Oryza sativa L.), and common bean (Phaseolus vulgaris L.) seedlings were compared. WGA enhanced cell division in the roots of barley and rice approximately similarly as in wheat roots but did not affect division of meristematic cells in the roots of common bean seedlings. In contrast PGA enhanced mitotic activity in the root apical meristem of common bean seedlings but did not affect division in the wheat and barley roots. Seedling treatment with lectins shifted the hormonal balance in them toward accumulation of growth activators (IAA and cytokinins). The relationship between lectin and hormonal systems in the control of cell division is discussed.     

The role of polysaccharide-containing components of the Azospirillum brasilense capsule in adsorbing bacteria on wheat seedling roots

Azospirillum brasilense cells deprived of capsular exopolysaccharides completely lost their ability to bind wheat germ agglutinin (WGA) and much of their ability to attach to wheat seedling roots. The decapsulation of bacterial cells by washing them with a NaCl solution led to an increase in the relative hydrophobicity of the cell surface. The pretreatment of wheat seedling roots with N-acetyl-D-glucosamine (GlcNAc) or the GlcNAc-containing polysaccharide complexes stripped from Azospirillum cells reduced their attachment to the roots. Under the experimental conditions, 3-h incubation of wheat seedling roots with exponential-phase azospirilla, bacterial adsorption is mainly driven by the attachment of the cells to the roots, whose operation is due to the capsular polysaccharide components and the WGA present on the wheat seedling roots.     

Immunocytochemical localization of wheat germ agglutinin in wheat

Immunocytological techniques were developed to localize the plant lectin, wheat germ agglutinin (WGA), in the tissues and cells of wheat plants. In a previous study we demonstrated with a radioimmunoassay that the lectin is present in wheat embryos and adult plants both in the roots and at the base of the stem. We have now found, using rhodamine, peroxidase, and ferritin-labeled secondary antibodies, that WGA is located in cells and tissues that establish direct contact with the soil during germination and growth of the plant In the embryo, WGA is found in the surface layer of the radicle, the first adventitious roots, the coleoptile, and the scutellum. Although found throughout the coleorhiza and epiblast, it is at its highest levels within the cells at the surface of these organs. In adult plants, WGA is located only in the caps and tips of adventitious roots. Reaction product for WGA was not visualized in embryonic or adult leaves or in other tissues of adult plants. At the subcellular level, WGA is located at the periphery of protein bodies, within electron-translucent regions of the cytoplasm, and at the cell wall-protoplast interface. Since WGA is found at potential infection sites and is known to have fungicidal properties, it may function in the defense against fungal pathogens.     

Wheat germ agglutinin in wheat seedling roots: induction by elicitors and fungi

Summary Treatment of wheat (Triticum aestivum L.) seedlings with elicitors originating from either plant or fungal cell walls induces about a 2-fold increase of wheat germ agglutinin (WGA) in the roots. While the WGA content in roots of healthy plants normally decreases as a function of germination time, a transient accumulation of WGA could be observed in plants challenged with different fungi, including Rhizoctonia solani, Fusarium culmorum, Pythium ultimum and Neurospora crassa. Peak levels in challenged roots were 2 to 5 times as high as in control plants. Most of this induced WGA could be released from the roots by soaking them in a solution of the hapten N-acetylglucosamine. On the basis of the results obtained it is postulated that WGA may be involved in the defence of wheat against fungal attack.     

Role of the Polysaccharide Components of Azospirillum brasilense Capsules in Bacterial Adsorption on Wheat Seedling Roots

Azospirillum brasilense cells deprived of capsular exopolysaccharides completely lost their ability to bind wheat germ agglutinin (WGA) and much of their ability to attach to wheat seedling roots. The decapsulation of bacterial cells by washing them with a NaCl solution led to an increase in the relative hydrophobicity of the cell surface. The pretreatment of wheat seedling roots with N-acetyl-D-glucosamine (GlcNAc) or the GlcNAc-containing polysaccharide complexes stripped from Azospirillum cells reduced their attachment to the roots. Under the experimental conditions used (3-h incubation of wheat seedling roots with exponential-phase azospirilla), bacterial adsorption is mainly driven by the specific mechanisms attachment of the cells to the roots, whose operation is due to the capsular polysaccharide components and the WGA present on the wheat seedling roots.     

Stress-induced accumulation of wheat germ agglutinin and abscisic Acid in roots of wheat seedlings

Wheat germ agglutinin (WGA) levels in roots of 2-day-old wheat seedlings increased up to three-fold when stressed by air-drying. Similar results were obtained when seedling roots were incubated either in 0.5 molar mannitol or 180 grams per liter polyethylene glycol 6000, with a peak level of WGA after 5 hours of stress. Longer periods of osmotic treatment resulted in a gradual decline of WGA in the roots. Since excised wheat roots incorporate more [³⁵S]cysteine into WGA under stress conditions, the observed increase of lectin levels is due to de novo synthesis. Measurement of abscisic acid (ABA) levels in roots of control and stressed seedlings indicated a 10-fold increase upon air-drying. Similarly, a five- and seven-fold increase of ABA content of seedling roots was found after 2 hours of osmotic stress by polyethylene glycol 6000 and mannitol, respectively. Finally, the stress-induced increase of WGA in wheat roots could be inhibited by growing seedlings in the presence of fluridone, an inhibitor of ABA synthesis. These results indicate that roots of water-stressed wheat seedlings (a) contain more WGA as a result of an increased de novo synthesis of this lectin, and (b) exhibit higher ABA levels. The stress-induced increase of lectin accumulation seems to be under control of ABA.     

WGA reduces the level of oxidative stress in wheat seedlings under salinity

Protective effect of exogenous wheat germ agglutinin (WGA) on wheat seedling (Triticum aestivum L.) during salinity stress was studied. In particular, we examined the state of pro- and antioxidant systems as well as the level of peroxide oxidation of lipids and electrolyte leakage under control conditions and when stressed with NaCl. Generation of superoxide anions and activity of both superoxide dismutase (SOD) and peroxidase increased during saline stress. Accumulation of O₂ ^·− resulted in peroxide oxidation of lipids and electrolyte leakage in response to stress. The injurious effect of salinity on root growth of seedlings was manifested by a decreased mitotic index (MI) in apical root meristem. This study show that WGA pretreatment decreased salt-induced superoxide anion generation, SOD and peroxidase activities, levels of lipid peroxidation and electrolytes leakage as well as correlating with a reduction in the inhibition of root apical meristem mitotic activity in salt-treated plants. This suggests that exogenous WGA reduced the detrimental effects of salinity-induced oxidative stress in wheat seedlings. Thus WGA effects on a balance of reactive oxygen species (ROS) and activities of antioxidant enzymes may provide an important contribution to a range of the defense reactions induced by this lectin in wheat plants.     

Isolation and characterization of plant growth-promoting rhizobacteria from wheat roots by wheat germ agglutinin labeled with fluorescein isothiocyanate

Thirty-two isolates were obtained from wheat rhizosphere by wheat germ agglutinin (WGA) labeled with fluorescein isothiocyanate (FITC). Most isolates were able to produce indole acetic acid (65.6%) and siderophores (59.3%), as well as exhibited phosphate solubilization (96.8%). Fourteen isolates displayed three plant growth-promoting traits. Among these strains, two phosphate-dissolving ones, WS29 and WS31, were evaluated for their beneficial effects on the early growth of wheat (Triticum aestivum Wan33). Strain WS29 and WS31 significantly promoted the development of lateral roots by 34.9% and 27.6%, as well as increased the root dry weight by 25.0% and 25.6%, respectively, compared to those of the control. Based on 16S rRNA gene sequence comparisons and phylogenetic positions, both isolates were determined to belong to the genus Bacillus. The proportion of isolates showing the properties of plant growth-promoting rhizobacteria (PGPR) was higher than in previous reports. The efficiency of the isolation of PGPR strains was also greatly increased by WGA labeled with FITC. The present study indicated that WGA could be used as an effective tool for isolating PGPR strains with high affinity to host plants from wheat roots. The proposed approach could facilitate research on biofertilizers or biocontrol agents.     

The Role of Wheat Germ Agglutinin in Plant–Bacteria Interactions: A Hypothesis and the Evidence in Its Support

Wheat plants are known to develop the associative symbiosis with the rhizobacterium Azospirillum brasilense.We studied the interaction of a lectin, wheat germ agglutinin (WGA), which is also found in wheat roots, with A. brasilense, strain sp245. When added to the azospirillum culture to the final concentration of 10^–8to 10^–9M, WGA enhanced IAA production, dinitrogen fixation, and ammonium excretion by bacterial cells. WGA also promoted the synthesis of proteins, both new and those already present in bacterial cells. The hypothesis that WGA is a signal molecule rerouting the bacterial metabolism in the direction favorable for the growth and development of the host plant has been put forward. It is suggested that signal properties of WGA are the basis for one of the functions of this lectin and essential for the effective associative symbiosis.     

Wheat lectin as a factor in plant-microbial communication and a stress response protein

Wheat lectin (wheat germ agglutinin, WGA), a representative of a broad group of cereal lectins, is excreted by plant roots into the surrounding medium and interacts with both pathogenic microflora and growth-stimulating rhizobacteria. WGA was found to serve as a molecular signal for the rhizobacterium Azospirillum brasilense, which forms endophytic and associative symbioses with wheat plants. The bacterial response to the lectin was pleiotropic: WGA at concentrations from 10(-10) to 10(-6) M exerted a dose-dependent effect on a range of processes in the bacterium that are important for the establishment and functioning of symbiosis. Plants with different WGA content differed in their responses to severe nitrogen starvation and to seed treatment with Azospirillum.     

Effects of plant lectins on the adhesive properties of baby hamster kidney cells

We studied the effects of different lectins on the adhesive properties of baby hamster kidney (BHK) cells. The purpose of these studies was to learn more about the cell surface receptors involved in cell adhesion. Three adhesive phenomena were analyzed: 1) the adhesion of BHK cells to lectin-coated substrata; 2) the effects of lectins on the adhesion of cells to substrata coated by plasma fibronectin (pFN); and 3) the effects of lectins on the binding of pFN-coated beads to cells. Initial experiments with fluorescein-conjugated lectins indicated that concanavalin A (Con A), ricinus communis agglutinin I (RCA I), and wheat germ agglutinin (WGA) bound to BHK cells but peanut agglutinin (PNA), soybean agglutinin (SBA), and ulex europaeus agglutinin I (UEA I) dod not bind. All three of the lectins which bound to the cells promoted cell spreading on lectin substrata, and the morphology of the spread cells was similar to that observed with cells spread on pFN substrata. Protease treatment of the cells, however, was found to inhibit cell spreading on pFN substrata or WGA substrata more than on Con A substrata or RCA I substrata. In the experiment of cells with Con A or WGA inhibited cell spreading on pFN substrata, but RCA I treatment had no effect. Finally, treatment of cells with WGA inhibited binding to cells of pFN beads, but neither Con A nor RCA I affected this interaction. These results indicate that the lectins modify cellular adhesion in different ways, probably by interacting with different surface receptors. The possibility that the pFN receptor is a WGA receptor is discussed.     

Inhibition of human lymphocyte activation by wheat germ agglutinin: a model for saccharide-specific suppressor factors

The suppressive effect of wheat germ agglutinin (WGA) on lectin-stimulated blastogenesis and immunoglobulin production was studied. Addition of WGA at 10 micrograms/ml inhibited phytohemagglutinin (PHA)-, concanavalin-A (Con-A)-, and pokeweed mitogen (PWM)-induced mitogenic responses by 70-80%. PWM-driven immunoglobulin synthesis was suppressed by 45% with WGA. The inhibitory effects of WGA were not due to cell death or to interference with lectin binding at the cell surface. Inhibition was dependent on the presence of WGA in the cell culture during the first 24 hr of mitogen exposure and was observed in cultures of both monocyte-depleted peripheral blood mononuclear cells as well as T-cell-enriched populations. WGA-induced inhibition of blastogenesis was blocked by the addition of N-acetylglucosamine (GluNAc) which prevents WGA binding to the cell surface. WGA was found to mimic the suppressive effect of a soluble immune suppressor supernatant (SISS) derived from Con-A-activated mononuclear cell cultures. PHA responses were inhibited by 80 and 95% with SISS and WGA, respectively. The inhibition by both WGA and SISS was totally reversed with addition of GluNAc. Furthermore, WGA and SISS demonstrated competition for the same cell surface receptor site. WGA may therefore be useful as an in vitro model of a saccharide-specific, biologically relevant, soluble mediator for the investigation of mechanisms of immunologic suppression.     

Wheat lectin as a factor in plant-microbial communication and a stress response protein

Wheat lectin (wheat germ agglutinin, WGA), a representative of a broad group of cereal lectins, is excreted by plant roots into the surrounding medium and interacts with both pathogenic microflora and growth-stimulating rhizobacteria. WGA was found to serve as a molecular signal for the rhizobacterium Azospirillum brasilense, which forms endophytic and associative symbioses with wheat plants. The bacterial response to the lectin was pleiotropic: WGA at concentrations from 10^?10 to 10^?6 M exerted a dose-dependent effect on a range of processes in the bacterium that are important for the establishment and functioning of symbiosis. Plants with different WGA content differed in their responses to severe nitrogen starvation and to seed treatment with Azospirillum.     

Epidermal growth factor receptors on PC12 cells: Alteration of binding properties by lectins

The PC12 cell line displays cell surface receptors for both nerve growth factor (NGF) and epidermal growth factor (EGF). It has been previously shown that the lectin wheat germ agglutinin (WGA) alters the properties of NGF receptors on these cells. We now report that preincubations with either WGA or concanavalin A (Con A) decrease the binding of ¹²⁵I-EGF to PC12 cells by greater than 50%. The inhibition of binding occurred at 37°C and 4°C and could be blocked or reversed by the addition of sugars which bind specifically to WGA or Con A. Scatchard analysis revealed that these lectins decreased binding primarily by lowering the affinity of the receptor and to a lesser extent by decreasing receptor number. Succinylalion of Con A (sCon A) produced a derivative that was less effective than the native lectin in decreasing EGF binding; however, addition of an antibody against Con A restored the ability of sCon A to decrease binding. Similar to results obtained with ¹²⁵I-NGF binding, WGA but not Con A was found to increase, by scveralfold; the proportion of ¹²⁵I-EGF binding that is resistant to solubilization by Triton X-100 detergent. A potential association of the EGF receptor with cytoskeletal elements is discussed which could account for such results.