Wheat germ agglutinin participates in regulation of cell division in apical root meristem of wheat seedlings

A study was made of cell division activity and hormonal status in roots of 4 day old wheat seedling treated with wheat germ agglutinin (WGA). The revealed stimulating effect of WGA on mitotic index (MI) and cell area in root extension zone was specific for this lectin, because gliadin, taken as a control protein, caused no changes in growth parameters. Phytolectins (phytohemagglutinin and concanavalin A) possessing properties of mitogens rendered no such essential influence on cell growth of wheat. Immunoassay has shown that WGA-treatment leads to accumulation of auxins and cytokinins in roots. This suggest participation of WGA in regulation of MI of meristem cells in roots of seedlings during their interaction with phytohormones.     

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 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.     

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.     

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.     

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.     

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.     

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.     

Mechanisms of Extracellular NO and Ca<Superscript>2+</Superscript> Regulating the Growth of Wheat Seedling Roots

Our previous studies suggested the cross talk of nitric oxide (NO) with Ca²⁺ in regulating stomatal movement. However, its mechanism of action is not well defined in plant roots. In this study, sodium nitroprusside (SNP, a NO donor) showed an inhibitory effect on the growth of wheat seedling roots in a dose-dependent manner, which was alleviated through reducing extracellular Ca²⁺ concentration. Analyzing the content of Ca²⁺ and K⁺ in wheat seedling roots showed that SNP significantly promoted Ca²⁺ accumulation and inhibited K⁺ accumulation at a higher concentration of extracellular Ca²⁺, but SNP promoted K⁺ accumulation in the absence of extracellular Ca²⁺. To gain further insights into Ca²⁺ function in the NO-regulated growth of wheat seedling roots, we conducted the patch-clamped protoplasts of wheat seedling roots in a whole cell configuration. In the absence of extracellular Ca²⁺, NO activated inward-rectifying K⁺ channels, but had little effects on outward-rectifying K⁺ channels. In the presence of 2 mmol L⁻¹ CaCl₂ in the bath solution, NO significantly activated outward-rectifying K⁺ channels, which was partially alleviated by LaCl₃ (a Ca²⁺ channel inhibitor). In contrast, 2 mmol L⁻¹ CaCl₂ alone had little effect on inward or outward-rectifying K⁺ channels. Thus, NO inhibits the growth of wheat seedling roots likely by promoting extracellular Ca²⁺ influx excessively. The increase in cytosolic Ca²⁺ appears to inhibit K⁺ influx, promotes K⁺ outflux across the plasma membrane, and finally reduces the content of K⁺ in root cells.     

Protective effect of inhibitors of succinate dehydrogenase on wheat seedlings during osmotic stress

The effect of malonate and sedaxane, a compound with the fungicidal effect which act as succinate dehydrogenase inhibitors, on the resistance of etiolated wheat seedlings (Triticum aestivum L.) to osmotic stress caused by 12% PEG 6000 solution, was studied. The presowing treatment of seeds with 0.3 mM sedaxane solution significantly reduced the inhibitory effect of osmotic stress on seedling growth. The protective effect of 10 mM malonate was significant when it was added to the incubation medium of the roots; the effect of preseeding treatment with malonate was less significant. Unlike malonate, malate had no positive effect on seedling growth under osmotic stress. The activity of succinate dehydrogenase and the hydrogen peroxide content decreased in seedlings after the treatment of roots with malonate and sedaxane. Pretreatment with sedaxane and the addition of malonate to the incubation medium of roots prevented the accumulation of a lipid peroxidation product, malondialdehyde, which is caused by osmotic stress, and increased peroxidase activity. It was concluded that the stress-protective effect of sedaxane and malonate on wheat seedlings might be due to the inhibition of succinate dehydrogenase-dependent formation of reactive oxygen species and the prevention of oxidative cell damage.     

土壤-小麦生态系统的磁化效应及其生态指示

应用室外盆栽试验方法,将土壤磁效应与生物磁效应相结合,研究了磁处理土壤对土壤-小麦系统健康的影响．结果表明,磁处理棕壤后土壤-小麦系统的健康状况得到较为明显的好转,包括使小麦种子提前出苗,出苗整齐一致;增加小麦幼苗的株高、主茎叶片数、分蘖数、单株根数和单株叶面积;使小麦根系的总吸收面积、活跃吸收面积、活跃吸收面积占总吸收面积的百分比提高;增加成熟小麦的有效穗数、结实小穗数、平均穗粒数、千粒重,减少不孕小穗数,提高小麦的生物学产量．在此基础上,对土壤-小麦系统磁化健康效应的生态指示进行了理论探讨,其中,200mT磁场强度是适于小麦生长的最佳磁处理参数．     

Biosynthesis of lectin in roots of germinating and adult cereal plants

Root tips of wheat, rye, barley and rice seedlings contain lectins which are identical to the respective embryo lectins with respect to their molecular weight, sugar-specificity and serological properties. Using in vivo labelling techniques, it could be demonstrated that lectin is synthesized de novo in these tissues. The presence of lectin mRNA in seedlings was confirmed by in-vitro synthesis of lectin in root-tip extracts. Lectin synthesis occurs both in primary and first adventitious roots and is confined to the apical part (2mm) of the root. As seedling development proceeds, lectin synthesis in root tips gradually decreases. Adventitious roots of adult (five to six months old) wheat, rye and barley, but not rice, plants also contain lectins which are indistinguisable from the embryo lectins by the above-mentioned criteria. These lectins are synthesized in vivo in isolated root tips (5 mm) with labelled cysteine and in vitro in cell-free extracts prepared from root tips. Synthesis of lectin in roots of adult plants is also confined to the apical (2 mm) tip of the roots. At the molecular level, root lectin synthesis is very similar to that in embryos. All root lectins are synthesized as 23 000-M_r precursors which are post-translationally converted into the mature 18 000-M_r polypeptides. The observation that seedling roots and adventitious roots of six-month-old plants actively synthesize lectins strongly indicates that lectin genes are expressed in these tissues. In addition, since the root lectins are indistinguishable from the embryo lectins, we postulate that the same lectin genes are expressed.Abbreviations ABA abscisic acid - SDS-PAGE sodium dodecyl sulphate-polyacrylamide gel electrophoresis - WGA wheat-germ agglutinin     

Multiple Hormonal Control of the Lectin Content in Roots of Wheat Seedlings

The effects of 0.2 M GA, 4.4 M benzyladenine (BA), and 5.7 M IAA on the contents of wheat germ agglutinin (WGA) and ABA in the roots of four-day-old wheat (Triticum aestivumL.) seedlings were studied. All phytohormones tested almost doubled the level of WGA. BA and IAA evidently stimulated the WGA accumulation by inducing ABA accumulation, whereas GA affected the level of the WGA in an ABA-independent way. The authors conclude that phytohormones control the WGA level via several pathways.     

小麦根系过氧化氢积累与耐盐性的关系

以抗盐性不同的2个小麦品系为材料,对其在盐胁迫下根细胞膜的膜渗透率,MDA含量,H2O2积累以及POD,SOD相对活性进行了分析和对比。结果表明：盐胁迫下抗性低的小麦品系93029#POD活性下降,导致活性氧积累而引起膜脂的过氧化作用;而抗盐性强的906#,在盐胁迫下。POD活性显著升高,没有明显的活性氧积累和膜脂过氧化现象,植物的抗盐性与其活性氧代谢和H2O2水平有关,抗必品系具有较高的清除活性氧的能力,使得H2O2浓度处于较低的水平,不对细胞造成伤害,外施Ca^2 和Vc可部分缓解盐害。     

The allelopathic potential of alfalfa root medicagenic acid glycosides and their fate in soil environments

Summary The allelopathic effect of alfalfa (Medicago media Pers.) and red clover (Trifolium pratense L.) root saponins on winter wheat seedling growth and the fate of these chemicals in soil environments were studied. Seed germination, seedling and test fungus growth were suppressed by water and by alcohol extracts of alfalfa roots, and by crude saponins of alfalfa roots, indicating that medicagenic acid glycosides are the inhibitor. Powdered alfalfa roots inhibited wheat seedling growth when added to sand. At concentrations as low as 0.25% (w/w) the root system was completely destroyed whereas seedling shoots suffered little damage. Red clover roots caused some wheat growth inhibition when incorporated to sand, but their effect was much lower than in the alfalfa root treatment. Soil textures had a significant influence on the inhibitory effect of alfalfa roots. The inhibition of seedling growth was more pronounced on light than on heavy soils. This was attribted to the higher sorption of inhibitors by heavy soils. Incubation of alfalfa roots mixed into loose sand, coarse sand, loamy sand and clay loam for a period of 0–8 days resulted in decreased toxicity to bothT. viride and wheat seedlings. This decrease occurred more quickly in heavier soils than in loose sand, due to the hydrolysis of glycosides by soil microorganisms. Soil microbes were capable of detoxifying medicagenic acid glycosides by partial hydrolysis of sugar chain to aglycone. These findings illustrate the importance of medicagenic acid glycosides as an inhibitor of wheat seedling growth, and of their fate in different soil environments.     

Immunocytochemistry in plants with colloidal gold conjugates

Summary The chitin-binding lectin wheat germ agglutinin (WGA) is found at the periphery of wheat embryos, and a similar lectin is present at the root tips of older plants (Mishkind et al. 1982). Although a ferritin-conjugated secondary antibody is adequate for localizing WGA in embryos, native electron-opaque particles make the electron microscope identification of added label equivocal in other wheat tissues. As reported here, however, unambiguous ultrastructural localization of WGA-like lectin in adult wheat roots can be obtained with rabbit anti-WGA followed by colloidal gold-labeled goat anti-rabbit (GAR) IgG. Colloidal gold (CG) was prepared by the reduction of gold chloride with citrate, ascorbate or phosphorous. GAR IgG, prepared from serum by antigen affinity chromatograhy, was adsorbed to the gold particles to produce a stabilized suspension of GAR-CG. Localization was performed on 8–12 M frozen sections of tissue fixed in 4% paraformaldehyde, 0.3% glutaraldehyde, and 0.75% acrolein in phosphate-buffered saline containing 1M sucrose. Localization with GAR-CG was first compared to that ascertained in embryos using other probes and was then extended to the roots of adult plants. An advantage of the GARCG method is that it permits the visualization of antigen at both the light and electron microscope levels in the same section. At the light level, the anti-WGA-GAR-CG complex appears as a red stain that is localized in specific tissues of embryos and in the caps and outer layers of adult roots. Sections in which lectin was detected at the light microscope level were embedded in plastic and sectioned for subcellular examination. Electron dense gold particles indicative of WGA are found at the periphery of protein bodies in wheat embryos and in vacuoles of the roots of adult plants. Sections incubated with control IgG lack reaction product.     

咖啡因对小麦幼苗生长,过氧化物酶同工 酶及根尖细胞有丝分裂的影响

３０ｐｐｍ以下浓度的咖啡因对小麦种子萌发,幼苗生长和胚根长度均有明显抑制作用。随着咖啡因浓度的增加,根尖细胞有丝分裂指数明显下降。低浓度时,过氧化物酶同工酶和苹果,酸脱氢酶没有变化,但高浓度时,使得这两种酶的活性几乎消失。