Accumulation of the ZRP3 mRNA in the root and coleorhiza of germinating maize (Zemays,Poaceae)

The evolutionary origin of the coleorhiza of species of Poaceae is unclear. The zrp3 gene, which codes for a protein of an as yet unknown function, is expressed in the roots of maize early in development. The sequence of zrp3 is similar to the sequences of three other genes isolated from dicot species. The pattern of accumulation of ZRP3 mRNA was examined in embryos of maize. No ZRP3 mRNA can be detected in the dry seeds; however, 1.5 d after inhibition, ZRP3 mRNA accumulated in both the roots and the coleorhiza of the embryo but not in other regions of the seed. In the roots, ZRP3 mRNA accumulates specifically in the cortical ground meristem and the pro-pith tissues. In the coleorhiza, ZRP3 mRNA accumulates in the parenchymal cells but not in the epidermal cells, thus distinguishing two tissue types in this organ. The accumulation of ZRP3 mRNA in the coleorhiza as well as in the root is molecular evidence consistent with the homology of these two organs.     

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.     

Hydroxyproline-rich glycoprotein mRNA accumulation in maize root cells colonized by an arbuscular mycorrhizal fungus as revealed by in situ hybridization

Summary To determine whether the expression of cell wall related genes changes during the establishment of an arbuscular mycorrhizal symbiosis (AM), we studied the expression of a maize hydroxyproline-rich glycoprotein (HRGP) gene. In situ hybridization showed that, in differentiated cells of maize roots, mRNA accumulation corresponding to the gene encoding for HRGP was only found when the cells were colonized by the endomycorrhizal fungusGlomus versiforme.     

Accumulation of reactive oxygen species in arbuscular mycorrhizal roots

We investigated the accumulation of reactive oxygen species (ROS) in arbuscular mycorrhizal (AM) roots from Medicago truncatula, Zea mays and Nicotiana tabacum using three independent staining techniques. Colonized root cortical cells and the symbiotic fungal partner were observed to be involved in the production of ROS. Extraradical hyphae and spores from Glomus intraradices accumulated small levels of ROS within their cell wall and produced ROS within the cytoplasm in response to stress. Within AM roots, we observed a certain correlation of arbuscular senescence and H₂O₂ accumulation after staining by diaminobenzidine (DAB) and a more general accumulation of ROS close to fungal structures when using dihydrorhodamine 123 (DHR 123) for staining. According to electron microscopical analysis of AM roots from Z. mays after staining by CeCl₃, intracellular accumulation of H₂O₂ was observed in the plant cytoplasm close to intact and collapsing fungal structures, whereas intercellular H₂O₂ was located on the surface of fungal hyphae. These characteristics of ROS accumulation in AM roots suggest similarities to ROS accumulation during the senescence of legume root nodules.     

Cultivar variation in the effect of chlorsulfuron in depressing the uptake of copper in wheat

The application of herbicides has induced symptoms of nutrient deficiencies under some circumstances. This glasshouse study examined the effect of chlorsulfuron on the uptake and utilization of copper (Cu) in four cultivars of wheat plants (Triticum aestivum L. cvs. Kulin, Cranbrook, Gamenya and Bodallin) on a Cu-responsive soil. Application of chlorsulfuron depressed the concentration of Cu in wheat plants receiving either inadequate or adequate Cu. In plants with inadequate Cu supply, chlorsulfuron increased the severity of Cu deficiency. Shoot weight was markedly decreased by chlorsulfuron at all levels of Cu, through decreasing the number of tillers and the elongation of leaves. This decreased growth of shoots occurred prior to the effect on Cu concentration in tissues. The retranslocation of Cu in old tissues over time was unaffected by chlorsulfuron. In all wheat cultivars, the decreased growth of shoots were correlated with the concentration of Cu in the youngest fully emerged leaf blade with critical levels of 1.6−1.7 at day 25 and 0.9−1.0 μg g⁻¹ d. wt. at day 60. The application of chlorsulfuron tended to increase the critical level at day 25 but not at day 60. In addition, Kulin seems to be most, and Cranbrook least, sensitive to chlorsulfuron. This sensitivity was associated with the sensitivity of the cultivars to Cu deficiency. It is suggested that chlorsulfuron application induces Cu deficiency in wheat plants mainly due to effects on the uptake of Cu. This revised version was published online in June 2006 with corrections to the Cover Date.     

A role for gibberellic acid in orienting microtubules and regulating cell growth polarity in the maize root cortex

The role of gibberellins and cortical microtubules in determining the polarity of cell growth in the root cortex of maize (Zea mays L.) was examined. Inhibition of gibberellin biosynthesis, either naturally through mutation (d5 mutant) or by means of chemicals such as 2S,3S paclobutrazol, caused thickening of root apices and increased their starch content. Immunofluorescence microscopy of cortical microtubules, coupled with a comparison of cell widhts, lengths and shapes, indicated that the meristem and immediate post-mitotic zone were the targets of gibberellin deficiency. Cortical cells in these regions were impaired in their ability to develop highly ordered transversal arrays of cortical microtubules. Consequently, the cells became wider and shorter. Application of gibberellic acid re-established the arrangements of cortical microtubules and the polarity of cell growth characteristic for roots having normal levels of gibberellins, it also decreased the starch content. These results indicate that gibberellins are morphogenetically active substances, not only in shoots but also in roots of maize.Abbreviations CMT cortical microtubule - GA gibberellin - GA₃ gibberellic acid - MT microtubule - PIG postmitotic isodiametric growth The authors acknowledge the support to F.B. from the Royal Society (London UK). We also thank Dr. J. Lenton (University of Bristol, Long Ashton Research Station) who kindly supplied us with 2S,3S paclobutrazol and grains of the GA-deficient d5 mutant of maize.     

Suppression of gravitropic response of primary roots by submergence

Primary roots of six plant species were placed horizontally either in humid air or under water, and their growth and gravitropic responses were examined. In air, all the roots showed a normal gravitropic curvature. Under water without aeration, roots of rice (Oryza sativa L.), oat (Avena sativa L.), azuki bean (Vigna angularis Ohwi et Ohashi), and cress (Lepidium sativum L.) curved downward at almost same rate as in air, whereas the curvature of roots of maize (Zea mays L.) and pea (Pisum sativum L.) was strongly suppressed. Submergence did not cause a decrease in growth rate of these roots. When roots of maize and pea were placed horizontally under water without aeration and then rotated in three dimensions on a clinostat in air, they showed a significant curvature, suggesting that the step suppressed by submergence is not graviperception but the subsequent signal transmission or differential growth process. Constant bubbling of air through the water partly restored the gravitropic curvature of maize roots and completely restored that of pea roots. The curvature of pea roots was also partly restored by the addition of an inhibitor of ethylene biosynthesis, aminooxyacetic acid. In air, ethylene suppressed the gravitropic curvature of roots of maize and pea. Furthermore, the level of ethylene in the intercellular space of the roots was increased by submergence. These results suggest that the accumulation of ethylene in the tissue is at least partly involved in suppression of transmission of the gravity signal or of differential growth in maize and pea roots under conditions of submergence.Abbreviations AOA aminooxyacetic acid - 3-D three-dimensional Dedicated to Professor Andreas Sievers on the occasion of his retirementWe thank Professor H. Suge and Drs. H. Takahashi and H. Kataoka, Tohoku University and Dr. T. Suzuki, Yamagata University, for helpful suggestions. The present study was supported in part by a Grant for Basic Research in Space Station Utilization from the Institute of Space and Astronautical Science, Japan.     

Zeta potential of protoplasts from gravireacting maize roots

Protoplasts were isolated from cortical cells of the elongating zone of maize (Zea mays L. cv. LG 11) roots and submitted to microelectrophoresis. Significant and transient differences in zeta potential between protoplasts from upper and lower root sides were compared with the gravireaction and the differential elongation of these roots. The maximum difference in the zeta potential was obtained between protoplasts from the upper and lower cortical cells after 90 min, exactly the time of gravipresentation for which the maximum rate of gravireaction was observed. In addition, this almost corresponded to the time for which the difference between the elongation rates of upper and lower sides of the extending zone began to increase. Consequently, the changes in the charges of the plasmalemma of the cortical cells from the growing part of roots could be more or less directly related to the root graviresponse.     

Roots,soil water and crop yield: tree crop interactions in a semi-arid agroforestry system in Kenya

Variations in soil water, crop yield and fine roots of 3–4 year-old Grevillea robusta Cunn. and Gliricidia sepium (Jacq.) Walp. growing in association with maize (Zea mays L.) were examined in semiarid Kenya during the long rains of 1996 and 1997. Even although tree roots penetrated more deeply than maize roots, maximum root length densities for both tree species and maize occurred in the top 200 mm of the soil profile where soil moisture was frequently recharged by rains. Populations of roots in plots containing trees were dominated by tree roots at the beginning of the growing season but because tree roots died and maize root length increased during the cropping season, amounts of tree and maize roots were similar at the end of the season. Thus, there was evidence of temporal separation of root activity between species, but there was no spatial separation of the rooting zones of the trees and crops within that part of the soil profile occupied by crop roots. Tree root length density declined with increasing distances from rows of trees and with depth in the soil profile. Although Grevillea trees were largest, plots containing G. sepium trees always contained more tree roots than plots containing G. robusta trees and Gliricidia was more competitive with maize than Grevillea. Overall, Gliricidia reduced crop yield by about 50% and Grevillea by about 40% relative to crop yield in control plots lacking trees and reductions of crop yield were greatest close to trees. There was less soil moisture in plots containing trees than in control plots. Such difference between control plots and plots containing trees were maximal at the end of the dry season and there was always less soil moisture close to trees than elsewhere in the plots. Plots containing Gliricidia trees contained less soil water than plots containing Grevillea trees.     

Accumulation of zeatin O-glycosyltransferase in Phaseolus vulgaris and Zea mays following cold stress

Zeatin O-glycosides have been reported as inactive and stable storage forms of cytokinins whose concentrations increase in cold stressed plants. Zeatin O-glycosides accumulation in developing bean seeds has been correlated with an increase of zeatin O-glycosyltransferase , which is specific to trans-zeatin, and catalyzes the conjugation of zeatin O-glycosides. When Phaseolus vulgaris and Zea mays seedlings were grown for 3 days at 25 and then incubated at 4 or 10 for 6 days no further growth was observed in roots. Hypertrophy was observed in the root tips of both species. In shoot-hypocotyl complexes, in contrast, growth occurred when seedlings were incubated at 10 . Western analysis, with Mabs specific to zeatin O-glycosyltransferase, detected antigenically related proteins in roots, shoot tips and cotyledons after seedlings were cold stressed for 1–6 days at 4 or 10 . Immunolocalization, of both maize and bean root sections grown at 25 revealed antigenically related proteins that were detected at low levels in cortical cells. The signal intensified upon cold stress. The localization of zeatin O-glycosyltransferase in Z. mays root tips was directly comparable to the distribution of the zeatin O-glycosides. The enzyme was detected in the nucleus, cytoplasm, and closely associated with the plasma membrane and in the cell wall of Z. mays root cells. Southern analysis suggested that more than one gene in Z. mays that were homologous to zeatin O-glycosyltransferase in P. vulgaris. Zeatin O-glycosyltransferase may be involved in modulation of cytokinins under cold stress.     

Enhanced production of phytoestrogenic isoflavones from hairy root cultures of Psoralea corylifolia L. Using elicitation and precursor feeding

The effect of biotic elicitors (yeast extract, chitosan), signaling molecule (salicylic acid), and polyamines (putrescine and spermidine) was studied with respect to isoflavones accumulation in hairy root cultures of Psoralea corylifolia L. Untreated hairy roots (control) accumulated 1.55% dry wt of daidzein and 0.19% dry wt of genistein. In precursor feeding experiment, phenylalanine at 2 mM concentration led to 1.3 fold higher production of daidzein (1.91% dry wt) and genistein (0.27% dry wt). In biotic elicitors, chitosan (2 mg/L) was found to be the most efficient elicitor to induce daidzein (2.78% dry wt) and genistein (0.279% dry wt) levels in hairy roots. Salicylic acid at 1 mM concentration stimulated the maximum accumulation of daidzein (2.2% dry wt) and genistein (0.228% dry wt) 2 days after elicitation. In case of polyamines, putrescine (50 mM) resulted in highest accumulation of daidzein (3.01% dry wt) and genistein (0.227% dry wt) after 5 days of addition. Present results indicated the effectiveness of elicitation and precursor feeding on isoflavones accumulation in hairy roots of P. corylifolia. This is the first report of elicitation on isoflavones production by hairy roots of P. corylifolia.     

Cereal phosphate transporters associated with the mycorrhizal pathway of phosphate uptake into roots

A very large number of plant species are capable of forming symbiotic associations with arbuscular mycorrhizal (AM) fungi. The roots of these plants are potentially capable of absorbing P from the soil solution both directly through root epidermis and root hairs, and via the AM fungal pathway that delivers P to the root cortex. A large number of phosphate (P) transporters have been identified in plants; tissue expression patterns and kinetic information supports the roles of some of these in the direct root uptake pathways. Recent work has identified additional P transporters in several unrelated species that are strongly induced, sometimes specifically, in AM roots. The primary aim of the work described in this paper was to determine how mycorrhizal colonisation by different species of AM fungi influenced the expression of members of the Pht1 gene families in the cereals Hordeum vulgare (barley), Triticum aestivum (wheat) and Zea mays (maize). RT-PCR and in-situ hybridisation, showed that the transporters HORvu;Pht1;8 (AY187023), TRIae;Pht1;myc (AJ830009) and ZEAma;Pht1;6 (AJ830010), had increased expression in roots colonised by the AM fungi Glomus intraradices,Glomus sp. WFVAM23 and Scutellospora calospora. These findings add to the increasing body of evidence indicating that plants that form AM associations with members of the Glomeromycota have evolved phosphate transporters that are either specifically or preferentially involved in scavenging phosphate from the apoplast between intracellular AM structures and root cortical cells. Operation of mycorrhiza-inducible P transporters in the AM P uptake pathway appears, at least partially, to replace uptake via different P transporters located in root epidermis and root hairs. Electronic Supplementary Material Supplementary material is available for this article at     

Structure and expression of the lignin O-methyltransferase gene from Zea mays L.

The isolation and characterization of cDNA and homologous genomic clones encoding the lignin O-methyltransferase (OMT) from maize is reported. The cDNA clone has been isolated by differential screening of maize root cDNA library. Southern analysis indicates that a single gene codes for this protein. The genomic sequence contains a single 916 bp intron. The deduced protein sequence from DNA shares significant homology with the recently reported lignin-bispecific caffeic acid/5-hydroxyferulic OMTs from alfalfa and aspen. It also shares homology with OMTs from bovine pineal glands and a purple non-sulfur photosynthetic bacterium. The mRNA of this gene is present at different levels in distinct organs of the plant with the highest accumulation detected in the elongation zone of roots. Bacterial extracts from clones containing the maize OMT cDNA show an activity in methylation of caffeic acid to ferulic acid comparable to that existing in the plant extracts. These results indicate that the described gene encodes the caffeic acid 3-O-methyltransferase (COMT) involved in the lignin biosynthesis of maize.     

Nitrate uptake by bean (Phaseolus vulgaris L.) roots under phosphate deficiency

Bean (Phaseolus vulgaris L.) plants were cultured for 19 d on complete or on phosphate deficient culture media. Low inorganic phosphate concentration in the roots decreased ATP level and nitrate uptake rate. The mechanisms which may control nitrate uptake rate during phosphate deficiency were examined. Plasma membrane enriched fractions from phosphate sufficient and phosphate deficient plants were isolated and compared. The decrease in total phospholipid content was observed in plasma membranes from phosphate deficient roots, but phospholipid composition was similar. No changes in ATPase and proton pumping activities measured in isolated plasma membrane of phosphate sufficient and phosphate deficient bean roots were noted. The electron microscope observations carried out on cortical meristematic cells of the roots showed that active ATPases were found in plasma membrane of both phosphate sufficient and phosphate deficient plants. The decrease in inorganic phosphate concentration in roots led to increased nitrate accumulation in roots, accompanied by a corresponding alterations in NO₃ distribution between shoots and roots. Nitrate reductase activity in roots of phosphate deficient plants estimated in vivo and in vitro was reduced to 50–60% of the control. The increased NO₃ concentration in root tissue may be explained by decreased NR activity and lower transport of nitrate from roots to shoots. Therefore, the reduction of nitrate uptake during phosphate starvation is mainly a consequence of nitrate accumulation in the roots.     

Anaerobic induction and tissue-specific expression of maize Adh1 promoter in transgenic rice plants and their progeny.

Summary In order to analyze expression of the maize alcohol dehydrogenase 1 gene (Adh1), its promoter was fused with the gusA reporter gene and introduced into rice by protoplast transformation. Histochemical analysis of transgenic plants and their progeny showed that the maize Adh1 promoter is constitutively expressed in root caps, anthers, anther filaments, pollen, scutellum, endosperm and shoot and root meristem of the embryo. Induction of expression by the Adh1 promoter was examined using seedlings derived from selfed progeny of the transgenic plants. The results showed that expression of the Adh1 promoter was strongly induced (up to 81-fold) in roots of seedlings after 24 h of anaerobic treatment, concomitant with an increase in the level of gusA mRNA. 2,4-D also induced Adh1 promoter-directed expression of gusA to a similar extent. In contrast, little induction by anaerobic treatment was detected in transformed calli, leaves or roots of primary transformants or shoots of seedlings. A detailed examination of seedling roots during anaerobic treatment revealed that the induction started first at the meristem and after 3 h there was strong induction in the elongation zone which is located 1–2 mm above the meristem; the induction then progressed upward from this region. Our results suggest that transgenic rice plants carring the gusA reporter gene fused with promoters are useful for the study of anaerobic regulation of genes derived from graminaceous species.     

Expression of a stilbene synthase gene in Nicotiana tabacum results in synthesis of the phytoalexin resveratrol

A gene from groundnut (Arachis hypogaea) coding for stilbene synthase was transferred together with a chimaeric kanamycin resistance gene. It was found to be rapidly expressed after induction with UV light and elicitor in tobacco cells (Nicotiana tabacum). Comparative studies of stilbene synthase mRNA synthesis in groudnut and transgenic tobacco suspension cultures revealed the same kinetics of gene expression. Stilbene synthase specific mRNA was detectable 30 minutes after elicitor induction and 10 minutes after UV irradiation. The maximum of mRNA accumulation was between 2 and 8 hours post induction. 24 hours after induction stilbene synthase mRNA accumulation ceased. Furthermore, in transgenic tobacco plants, the gene was found to be inducible in sterile roots, stems and leaves. Stilbene synthase was demonstrated in crude protein extracts from transgenic tobacco cell cultures using specific antibodies. Resveratrol, the product of stilbene synthase, was identified by HPLC and antisera raised against resveratrol.     

玉米ZmNPR1基因的克隆及表达分析

该研究从玉米高抗自交系D863F中克隆了ZmNPR1基因(GenBank登录号为MH619241)的gDNA和cDNA序列,开放阅读框长1 866 bp,编码621个氨基酸,相对分子质量67.61 kD,等电点为5.46。系统进化树比对表明,玉米ZmNPR1蛋白和高粱SbNPR1蛋白的亲缘关系较近,相似性高达97%。实时荧光定量PCR结果表明,ZmNPR1在叶片中能够被水稻黑条矮缩病毒诱导并显著上调表达。同时ZmNPR1在玉米叶片、茎、根、雄穗、雌穗以及花丝中均有表达,在雌穗和叶片中的表达量较高。研究表明,ZmNPR1可能在玉米粗缩病抗病过程中起着重要作用。