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.     

Protective effect of wheat germ agglutinin on the course of mitosis in the roots of <Emphasis Type="Italic">Triticum aestivum</Emphasis> seedlings exposed to cadmium

Effect of pretreatment with 28 nM wheat germ agglutinin (WGA) on cell divisions in the root apical meristem of 4-day-old seedlings of wheat (Triticum aestivum L.), distribution of cells among mitotic phases, cadmium-induced disruptions of normal progression through mitosis, and activity of nucleolar organizer regions (NOR) of the chromosomes was studied after 7-h-long exposure to 1 mM cadmium acetate. Pretreatment with WGA has a pronounced protective effect on divisions of root meristem cells exposed to cadmium. Progression of the cells through mitotic phases was normalized, abnormal mitoses became much less numerous, and the share of binuclear cells decreased. Activity of NOR remained at the control level that much depended on the ability of WGA to prevent reduction in cytokinin content under cadmium stress.     

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.     

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.     

Phytotoxic, clastogenic and bioaccumulation effects of the environmental endocrine disruptor bisphenol A in various crops grown hydroponically

The effects of the endocrine disruptor bisphenol A (BPA) at concentrations of 10 and 50 mg l⁻¹ were evaluated on the germination and morphology, micronuclei (MN) content in root tip cells and BPA bioaccumulation of hydroponic seedlings of broad bean (Vicia faba L.), tomato (Lycopersicon esculentum Mill.), durum wheat (Triticum durum Desf.) and lettuce (Lactuca sativa L.) after 6 and 21 days of growth. In general, BPA at any dose used did not inhibit germination and early growth (6 days) of seedlings of the species examined, with the exception of primary root length of tomato which decreased at the higher BPA dose. In contrast, an evident phytotoxicity was induced by BPA in all species after 21 days of growth with evident morphological anomalies and significant reductions of the lengths and fresh and dry weights of shoots and roots of seedlings. With respect to the nutrient medium without seedlings, BPA concentration decreased markedly during the growth period in the presence of broad bean and tomato seedlings, and limitedly in the presence of durum wheat and, especially, lettuce. Further, the presence of BPA measured in roots and shoots of broad bean and tomato after 21-day growth indicated that bioaccumulation of BPA had occurred. The number of MN in broad bean and durum wheat root tip cells increased markedly by treatment with BPA at both concentrations, thus suggesting a potential clastogenic activity of BPA in these species.     

Rice DECUSSATE controls phyllotaxy by affecting the cytokinin signaling pathway

Phyllotaxy is defined as the spatial arrangement of leaves on the stem. The mechanism responsible for this extremely regular pattern is one of the most fascinating enigmas in plant biology. In this study, we identified a gene regulating the phyllotactic pattern in rice. Loss‐of‐function mutants of the DECUSSATE (DEC) gene displayed a phyllotactic conversion from normal distichous pattern to decussate. The dec mutants had an enlarged shoot apical meristem with enhanced cell division activity. In contrast to the shoot apical meristem, the size of the root apical meristem in the dec mutants was reduced, and cell division activity was suppressed. These phenotypes indicate that DEC has opposite functions in the shoot apical meristem and root apical meristem. Map‐based cloning revealed that DEC encodes a plant‐specific protein containing a glutamine‐rich region and a conserved motif. Although its molecular function is unclear, the conserved domain is shared with fungi and animals. Expression analysis showed that several type A response regulator genes that act in the cytokinin signaling pathway were down‐regulated in the dec mutant. In addition, dec seedlings showed a reduced responsiveness to exogenous cytokinin. Our results suggest that DEC controls the phyllotactic pattern by affecting cytokinin signaling in rice.     

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     

Characterization of a cDNA encoding a proline-rich 14 kDa protein in developing cortical cells of the roots of bean (Phaseolus vulgaris) seedlings

A cDNA clone, corresponding to mRNAs preferentially expressed in the roots of bean (Phaseolus vulgaris L.) seedlings, was isolated. This clone contains a 381 bp open reading frame encoding a polypeptide of 13.5 kDa, designated PVR5 (Phaseolus vulgaris root 5). The amino acid sequence of this clone is rich in proline (13.5%) and leucine (12.7%) and shares significant amino acid sequence homology with root-specific and proline-rich proteins from monocots (maize and rice), and proline-rich proteins from dicots (carrot, oilseed rape, and Madagascar periwinkle). The precise biological roles of these polypeptides are unknown. PVR5 mRNA accumulation is developmentally regulated within the root, with high levels at the root apex and declining levels at distances further from the root tip. In situ hybridization shows that PVR5 mRNA specifically accumulates in the cortical ground meristem in which maximal cell division occurs. Southern blot analysis suggests that genomic DNA corresponding to PVR5 cDNA is encoded by a single gene or a small gene family.     

Mechanisms of primordium formation during adventitious root development from walnut cotyledon explants

 In walnut (Juglans regia L.), an otherwise difficult-to-root species, explants of cotyledons have been shown to generate complete roots in the absence of exogenous growth regulators. In the present study, this process of root formation was shown to follow a pattern of adventitious, rather than primary or lateral, ontogeny: (i) the arrangement of vascular bundles in the region of root formation was of the petiole type; (ii) a typical root primordium was formed at the side of the procambium within a meristematic ring of actively dividing cells located around each vascular bundle; (iii) the developing root apical meristem was connected in a lateral way with the vascular bundle of the petiole. This adventitious root formation occurred in three main stages of cell division, primordium formation and organization of apical meristem. These stages were characterized by expression of LATERAL ROOT PRIMORDIUM-1 and CHALCONE SYNTHASE genes, which were found to be sequentially expressed during the formation of the primordium. Activation of genes related to root cell differentiation started at the early stage of primordium formation prior to organization of the root apical meristem. The systematic development of adventitious root primordia at a precise site gave indications on the positional and biochemical cues that are necessary for adventitious root formation. Received: 30 July 1999 / Accepted: 16 February 2000     

The extent and differences in mitotic activity of the root tip ofVicia faba L.

Mitotic activity does not stop for different meristematic cells of the root apex at the same distance from the initials. The differences are connected with the functional heterogeneity of the apical meristem of the root. The arrangement of vascular bundles,i.e. the alternation of independent xylem and phloem groups, is of major importance. In broad bean roots, the protophloem sieve elements stop dividing first. The centre of the stelei. e. late metaxylem elements stop dividing next. Division in the stele gradually ceases centrifugally, while it ceases centripetally in the peripheral part of the root. The cylindrical region with prolonged cell division includes internal layers of the cortex including endodermis, pericycle and adjoining cells of the stele. Proximally apical meristem is reduced to isolated strands of cells adjacent to the protoxylem poles. Pericycle cells stop dividing last at a distance of approx. 9–10 mm from the initials. The number of the division cycles is limited and is specific for individual cell types. Epidermal and cortical cells divide in broad bean roots transversely approximately seven times, cells of late metaxylem approximately five times. Root apical meristem is an asynchronous cell population with a different duration of the mitotic cycle. We determined local variations in the duration of the mitotic cycle in the apical meristem of broad bean root by means of colchicine-induced polyploidy. The cells of the quiescent centre had the longest mitotic cycle after colchicine treatment. The region of the proper root adjacent to the quiescent centre was mixoploid (2n and 4n). Isolated cells with a long cycle occurred also in the cortex and in the central cylinder. Cells with a division cycle of 18h were found in the root cap, in the epidermis, in the cortex and in the central cylinder. Relatively numerous cells with the shortest division cycle, approx. 12 h, occurred farther of the quiescent centre in the epidermis, in the cortex, in the pericycle, and in adjacent layers of the stele through-out the entire meristematic region. The results derived from the analysis of the apical meristem are discussed in connection with the ontogenesis of different types of cells taking part in the primary structure of the root.     

Changes in cytokinin,auxin, and abscisic acid contents in wheat seedlings treated with the growth regulator Stifun

The growth regulator Stifun at all concentrations tested (0.033, 0.33, 3.3, and 33 mg/L) affected the hormonal status of wheat seedlings (Triticum aestivum L., cv. Zhnitsa) and stimulated plant growth. This was evident in activation of cell division and elongation, as well as in the increase in shoot and root length, water content, and dry weight. Effects of Stifun on roots and shoots depended on concentration. Application of Stifun at the optimal growth-stimulating concentration (0.033 mg/L) elevated the levels of zeatin, zeatin riboside, dihydrozeatin riboside, isopentenyladenosine, and IAA in roots of 2-day-old seedlings, but reduced the ABA content. The levels of ABA, IAA, dihydrozeatin, and dihydrozeatin riboside in shoots increased, while the levels of zeatin riboside, isopentenyl adenine, and isopentenyladenosine decreased. The results indicate that the hormonal system plays a part in the plant response to growth-stimulating action of Stifun.     

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.     

Impact of the exodermis on infection of roots byFusarium culmorum

Patterns of infection withFusarium culmorum (W G Smith) Saccardo were observed in seedling roots of barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), maize (Zea mays L.) and asparagus (Asparagus officinalis L). Apical regions of the main roots were not infected. Since penetration into the root occurred several days after inoculation and the roots were growing during the experiment, these regions had apparently not been in existence long enough to be infected. In older regions of barley, wheat and asparagus, hyphae entered through the tips of lateral roots. In barley and wheat, which had not developed any suberin lamellae in their subepidermal layer, infection occurred randomly over the remainder of the root. In maize, the fungus penetrated the epidermis at many sites but did not breach the exodermis in which all cells possessed both Casparian bands and suberin lamellae. Maize roots, therefore, sustained only minimal infections. In asparagus, the fungus grew through the short (passage) cells but never the long cells of the exodermis. In doing so, it penetrated cells possessing Casparian bands but lacking suberin lamellae. The results support the hypothesis that suberin lamellae provide effective barriers to the growth ofF. culmorum hyphae.     

Improving of oilseed rape lateral root formation by physiological analogues of auxin

The aim of the present work was to study the effect of auxin physiological analogue TA-12 [1-(2-chloroethoksicarbonylmethyl)-4-naphthalenesulfonic acid calcium salt] on the formation of oilseed rape lateral root and on the mitotic activity of apical meristem cells. Spring oilseed rape (Brassica napus L. ssp. oleifera annua Metzg.) cultivar ‘Mascot’ was chosen as a test object. Anatomical, cytological and histological studies on root development suggest that compound TA-12 induces the activity of parent root pericycle cells, stimulates the formation of lateral roots and enhances the division of apical meristem cells. The auxin transport inhibitor 2,3,5-triiodobenzoic acid suppresses the division of apical meristem cells, while this process is restored by the auxin physiological analogue TA-12 and naphthaleneacetic acid. The compound TA-12, by stimulating primary root growth and lateral root induction, optimised the formation of the oilseed rape root system.     

MITOTIC ACTIVITY IN THE ROOT APICAL MERISTEM OF AZOLLA FILICULOIDES LAM., WITH SPECIAL REFERENCE TO THE APICAL CELL

The meristematic activity of the apical cell and its derivatives (merophytes) in the unbranched, determinate roots of Azolla filiculoides Lam. was investigated. The plane of division of the apical cell indicates that it is the initial of each merophyte. The division plane of each newly formed merophyte is strictly periclinal to the root surface and provides confirmation that the immediate derivatives of the apical cell cannot be the ultimate root initials. The frequency of cell division as determined by the mitotic index, and by the duration of the cell cycle as determined by the colchicine method, confirmed the meristematic activity of the apical cell. As roots increase in length, the duration of the cell cycle in the total meristem increases, with the apical cell possessing the longest cell cycle, whereas the immediate derivatives maintain approximately the same cycle duration as in shorter roots. In determinate Azolla roots, cell division appears to play a major role up to a certain root length, then increase in length is produced mainly by cell elongation.     

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 Development of Leaf Heat-Tolerance during the Local Heating of Seedling Organs

Experiments using cucumber (Cucumis sativusL.), wheat (Triticum aestivumL.), and barley (Hordeum vulgareL.) seedlings showed that actinomycin D partially inhibited an increase in the heat-tolerance of leaves heated at 38°C for 7 h but did not affect this index when the roots were heated. Exogenous ABA increased heat-tolerance in both cases. These results, with regard to the data demonstrating an important contribution of protein synthesis to the specific increase in heat-tolerance during the heat acclimation of intact plants, make it possible to conclude that the development of leaf heat-tolerance resulting from the local heating of shoots depends on the induced synthesis of mRNAs and respective proteins. At the same time, there is little or no such dependence during root heating. ABA manifested itself as a factor of a general, nonspecific increase in heat-tolerance during the local heating of both shoots and roots.     

Incidence of inhibitory pseudomonads in the Pacific Northwest

Incidence of pseudomonads inhibitory to the root growth of till and no-till seeded crops winter wheat (Triticum aestivum L.), pea (Pisum sativum), lentil (Lens culinaris), and no-till winter barley (Hordeum vulgare), top and bottom of a seeded slope, and on the weed downy brome (Bromus tectorum) was investigated. Pseudomonads on the rhizoplane of these plants ranged from 10⁶ to 10⁸ colony-forming units (cfu) per gram dry weight of root. Neither tillage management nor site on a seeded slope affected colonizing numbers. Total numbers of pseudomonads were reduced in a second sampling, particularly on winter barley roots. However, more inhibitory pseudomonads were found in the second sampling. Several of the isolates, both inhibitory and stimulatory from different host plants, were bioassayed against winter wheat seedlings. Generally, the effect was different on the winter wheat than on the host plant indicating the organisms had some specificity. Several pseudomonads were isolated that severely reduced downy brome root growth and not that of winter wheat. Contribution from Agric. Res. Serv., U S Dep. of Agric., in cooperation with the College of Agric, and Home Economics, Agric. Res. Center, Washington State Univ., Pullman, WA 99164. Scientific Paper No. 7491.