Detection of root mucilage using an anti-fucose antibody

Plant root mucilage is known to enhance soil quality by contributing towards the soil carbon pool, soil aggregation, detoxification of heavy metal ions and interactions with rhizospheric microflora. Mucilage consists of many monosaccharide units, including fucose which can be used as an indicator for plant root based polysaccharides. This is the first report of an immunological technique developed to use anti-fucose antibodies as markers for probing and localizing fucosyl residues in mucilage polysaccharide and, in turn, for localization of plant root mucilage. Fucose was complexed with bovine serum albumin to raise antibodies against fucose. A fucose-directed antibody was shown to cross-react with root cap mucilages from grasses. This antibody was used to localize root mucilage polysaccharide in maize and wheat root caps using immunogold electron microscopy. Abundant labelling could be localized on the cell wall, and in the intercellular matrix and vesicles of the peripheral root cap cells. Labelling was less intense in cells towards the centre of the root cap tissue. Control experiments confirmed that immunogold localization of fucose was specific and reliable.     

Signal transmission during gravitropic curvature of primary roots of Zea mays

Primary roots of Zea mays cv. Ageotropic are nonresponsive to gravity and elongate approximately 0.80 mm h^?1. Applying mucilage-like material (K-Y Jelly) to the terminal 1.5 cm of these roots induces graviresponsiveness and slow elongation 28% (i.e. from 0.80 to 0.58mm h^?1). Applying mucilage-like material to one side of the terminal 1.5 cm of the root induces curvature toward the mucilage, irrespective of the root's orientation to gravity. Applying a 2-mm-wideband of mucilage-like material to a root's circumference 8 to 10 mm behind the root cap neither induces gravicurvature nor affects elongation significantly. Similarly, applying mucilage-like material to only the root cap does not significantly affect elongation or graviresponsiveness. Gravicurvature of mutant roots occurs only when mucilage-like material is applied to the root/root-cap junction. Reversing the caps of wild-type and mutant roots produces gravitropic responses characteristic of the root cap rather than the host root. These results are consistent with the suggestion that gravitropic effectors are growth inhibitors that move apoplastically through mucilage between the root cap and root.     

Contribution of root cap mucilage and presence of an intact root cap in maize (Zea mays) to the reduction of soil mechanical impedance

BACKGROUND AND AIMS: The impedance to root growth imposed by soil can be decreased by both mucilage secretion and the sloughing of border cells from the root cap. The aim of this study is to quantify the contribution of these two factors for maize root growth in compact soil. METHODS: These effects were evaluated by assessing growth after removing both mucilage (treatment I -- intact) and the root cap (treatment D -- decapped) from the root tip, and then by adding back 2 micro L of mucilage to both intact (treatment IM -- intact plus mucilage) and decapped (treatment DM -- decapped plus mucilage) roots. Roots were grown in either loose (0.9 Mg m(-3)) or compact (1.5 Mg m(-3)) loamy sand soils. Also examined were the effects of decapping on root penetration resistance at three soil bulk densities (1.3, 1.4 and 1.5 Mg m(-3)). KEY RESULTS: In treatment I, mucilage was visible 12 h after transplanting to the compact soil. The decapping and mucilage treatments affected neither the root elongation nor the root widening rates when the plants were grown in loose soil for 12 h. Root growth pressures of seminal axes in D, DM, I and IM treatments were 0.328, 0.288, 0.272 and 0.222 MPa, respectively, when the roots were grown in compact soil (1.5 Mg m(-3) density; 1.59 MPa penetrometer resistance). CONCLUSIONS: The contributions of mucilage and presence of the intact root cap without mucilage to the lubricating effect of root cap (percentage decrease in root penetration resistance caused by decapping) were 43 % and 58 %, respectively. The lubricating effect of the root cap was about 30 % and unaffected by the degree of soil compaction (for penetrometer resistances of 0.52, 1.20 and 1.59 MPa).     

The expansion of maize root-cap mucilage during hydration. 1. Kinetics

The conventional view of root-cap mucilage as an expanded blob of mucilage is characteristic only of root tips in contact with free water. In soil, the mucilage is almost always a dry coating over the tip to which soil particles adhere. The kinetics of expansion of root-cap mucilage of Zea mays roots grown in field soil, in soil in pots, and axenically on agar, were determined when the mucilage was exposed to water. On the soil-grown roots the increase in mucilage volume was linear with time, sometimes reaching a constant volume during the 6 h of measurement, but sometimes not. This linear expansion is interpreted as limited by the rate at which the condensed mucilage in the periplasmic and intercellular spaces of the root cap passes to the exterior of the cap, expanding as fast as it arrives outside in the water. The height of the plateau is interpreted as a measure of the amount of mucilage initially present in the interior spaces. Because of the greater availability of water in the axenic roots grown on 1% agar, the mucilage was already outside the root cap, and it expanded more rapidly. It reached a final volume about 10-fold greater than that on the soil-grown roots. The volume increase was curvilinear with time. An analysis of these curves suggested that this swelling on axenic roots was a diffusion of mucilage outwards from the flanks of the root cap, and the diffusivity of the mucilage was estimated as 4 × 10^?8 cm² s^?1. The molecular radius derived from this diffusivity was 34 nm, and the estimated molecular weight was 1.6 × 10⁸ Da.     

玉米根冠粘胶和铝的结合及有机酸累积

玉米根系分泌较多的植物粘胶 ,用 0 .0 1%中性红溶液使粘胶染成红色。 30 μmol/L的AlCl3 处理根系 1h后 ,不除去粘胶的根尖的铝含量大于除去粘胶的根尖的铝含量。粘胶的铝含量随着处理的铝浓度的增加而增加。用高效液相色谱仪能使粘胶 铝复合物分离成均含糖和铝的两种组分。 5 μmol/L的AlCl3 处理根系 2 4h后 ,粘胶中积累了铝诱导分泌的有机酸。粘胶中含有酸性磷酸酶 ,它的活性随着处理的铝浓度的增加而降低。这些结果证明了植物粘胶能够和铝结合、粘胶液滴能够积累有机酸及磷酸酶的假说     

Tribology of the root cap in maize (Zea mays) and peas (Pisum sativum)

Frictional resistance to a penetrating body can account for more than 80% of the total resistance to penetration of soil. We measured the frictional resistance between growing root caps of maize and pea and ground and smooth glass surfaces, which was linearly correlated to load, allowing calculation of the coefficient of kinetic friction and adhesion. Coefficients of kinetic friction between the root caps and the ground and smooth glass surfaces were approximately 0.04 and 0.02, respectively, the first measurements of the frictional properties of root tips at rates approaching those of root elongation, and an order of magnitude smaller than those previously reported. Results suggest that roots are well designed for penetrating soil, and encounter only small frictional resistance on the root cap. These data provide important parameters for modelling soil stresses and deformation around growing root tips.     

广东和巴西玉米气候生态条件比较分析

随着畜牧业的发展 ,广东玉米 (ＺｅｅｍａｙｓＬ .)的需求量也日增 ,发展玉米生产日益受到重视。引进优良品种是解决问题的重要途径之一。近几年来巴西玉米生产发展很快 ,由玉米进口国变为出口大国 ,玉米大面积高产稳产 ,其中重要的原因之一是培育出了一系列新的优良品种。巴西和广东地理纬度相似 ,同处热带亚热带 ,引种巴西的优良玉米品种理应在优先考虑的范围。气候生态条件是引种的关键因素之一。虽然广东和巴西的地理纬度相近 ,但地理纬度只是影响气候的因素之一 ,气候还受其它多种因素的影响。通过分析两地的气候特点及其对玉米生长发…     

Influence of microgravity on cellular differentiation in root caps of Zea mays

We launched imbibed seeds of Zea mays into outer space aboard the space shuttle Columbia to determine the influence of microgravity on cellular differentiation in root caps. The influence of microgravity varied with different stages of cellular differentiation. Overall, microgravity tended to 1) increase relative volumes of hyaloplasm and lipid bodies, 2) decrease the relative volumes of plastids, mitochondria, dictyosomes, and the vacuome, and 3) exert no influence on the relative volume of nuclei in cells comprising the root cap. The reduced allocation of dictyosomal volume in peripheral cells of flight-grown seedlings correlated positively with their secretion of significantly less mucilage than peripheral cells of Earth-grown seedlings. These results indicate that 1) microgravity alters the patterns of cellular differentiation and structures of all cell types comprising the root cap, and 2) the influence of microgravity on cellular differentiation in root caps of Zea mays is organelle specific.     

Depolymerization of cortical microtubules is not a primary cause of chilling injury in corn (Zea mays L. cv Black Mexican Sweet) suspension culture cells

Cold-induced depolymerization of cortical microtubules were examined in suspension culture cells of corn (Zea mays L. cv Black Mexican Sweet) at various stages of chilling. In an attempt to determine whether microtubule depolymerization contributes to chilling injury, experiments were carried out with and without abscisic acid (ABA) pretreatment, since ABA reduces the severity of chilling injury in these cells. Microtubule depolymerization was detectable after 1 h at 4°C and became more extensive as the chilling was prolonged. There was little chilling injury after 1 d at 4°C in either ABA-treated or non-ABA-treated cells. After 3 d at 4°C, there was about 26% injury for ABA-treated and 40% injury for non-ABA-treated cells, as evaluated by 2,3,5-triphenyl-tetrazolium chloride reduction and by regrowth. After 1d at 4°C, less than 10% of cells retained full arrays of microtubules in both ABA-treated and non-ABA-treated cells, the remainder having either partial arrays or no microtubules. After 3d at 4°C, about 90% of cells showed complete or almost complete depolymerization of microtubules in both ABA-treated and non-ABA-treated cells. ABA did not stabilize the cortical microtubules against cold-induced depolymerization. In about 66% of ABA-treated cells and 57% of non-ABA-treated cells that had been held at 4°C for 3d, repolymerization of cortical microtubules occurred after 3h at 28°C. These results argue against the hypothesis that depolymerization of cortical microtubules is a primary cause of chilling injury.     

玉米(Zea mays L.)叶脉发育的研究

玉米的叶脉在单子叶植物中有一定的代表性,叶脉由四级组成,粗细不同的一、二、三级叶脉均从叶基向叶尖方向延伸,属叶片的纵向叶脉,四级脉横向与一、二、三级叶脉连接,是横向的叶脉,各级叶脉有各自的形成方式,由于它们有规律的分布,从而构成了叶片的输导网络,各级叶脉的发生和发育与叫片的生长有直接的关系。     

Chilling stress and oxygen metabolizing enzymes in Zea mays and Zea diploperennis*

Abstract. The activities of five active-oxygen scavenging enzymes were compared for cold-lability and three were compared for chilling induction in two Zea genotypes of contrasting susceptibility to photoinhibition during chilling. Activities of superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and glutathione reductase (GTR, EC 1.6.4.2) in leaf extracts from plants grown without chilling stress were assayed at 19°C and 5°C. Enzymes from the chilling-susceptible Z. Mays cv. LG11 had lower specific activities at 5°C than did enzymes from the chilling-tolerant Z. diploperennis, except for MDHAR where no significant differences were observed. The activities of SOD and APX from Z. diploperennis were double those of Z. mays at both assay temperatures. Monodehydroa-scrobate reductase and glutathione reductase activities in both species were reduced by 63–78% at a 5°C assay temperature. The dehydroascorbate reductase (DHAR) showed the greatest low-temperature lability losing 96% (Z. diploperennis) and 100% (Z. mays) of its activity at 5°C. To examine possible chilling-induced changes in levels of enzyme activity, plants of both Zea genotypes were transferred to growth chambers at 10°C at moderate light intensities. Glutathione reductase activity was found to increase within 24h in Z. diploperennis, but it decreased slightly in Z. mays. MDHAR activity decreased by 50% in Z. diploperennis but showed only a transient increase in activity in Z. mays.     

Immunocytochemical localization of indole-3-acetic acid in primary roots of Zea mays

Colloidal gold-labelled antibody was used to localize indole-3-acetic acid in caps of primary roots of Z. mays cv. Kys. Gold particles accumulated on the nucleus, vacuoles, mitochondria, and some dictyosomes and dictyosome-derived vesicles. This is the first localization of indole-3-acetic acid in dictyosomes and dictyosome-derived vesicles and indicates that dictyosomes and vesicles constitute a pathway for indole-3-acetic acid movement in and secretion from root cap cells. Our findings provide cytochemical evidence to support the hypothesis that indole-3-acetic acid plays an important role in root gravitropism.     

玉米化感物质异羟肟酸的研究进展

介绍了异羟肟酸在玉米植株中的分布和玉米根系分泌物中异羟肟酸的分析方法．丁布(DIM-BOA)是玉米植株中含量最大的异羟肟酸．不同玉米品种之间异羟肟酸含量的差异很大．种子不含异羟肟酸;但萌发后其含量迅速增加,在萌芽几天后的幼苗植株其含量达最大值,随后逐渐下降;在玉米生长发育的不同时期,幼嫩叶片内异羟肟酸含量始终较高;地上部分异羟肟酸的浓度高于根系．植株异羟肟酸的浓度受生长环境条件影响显著,在紫外辐射、黑暗条件或水分胁迫下其含量明显增加．在各种禾谷类作物中,玉米根系分泌物内含异羟肟酸较高;铁的存在能显著增加玉米根系分泌物中异羟肟酸的含量．     

Nitric oxide is involved in nitrate-induced inhibition of root elongation in Zea mays

BACKGROUND AND AIMS: Root growth and development are closely dependent upon nitrate supply in the growth medium. To unravel the mechanism underlying dependence of root growth on nitrate, an examination was made of whether endogenous nitric oxide (NO) is involved in nitrate-dependent growth of primary roots in maize. METHODS: Maize seedlings grown in varying concentrations of nitrate for 7 d were used to evaluate the effects on root elongation of a nitric oxide (NO) donor (sodium nitroprusside, SNP), a NO scavenger (methylene blue, MB), a nitric oxide synthase inhibitor (N(omega)-nitro-L-arginine, L-NNA), H(2)O(2), indole-3-acetic acid (IAA) and a nitric reducatse inhibitor (tungstate). The effects of these treatments on endogenous NO levels in maize root apical cells were investigated using a NO-specific fluorescent probe, 4, 5-diaminofluorescein diacetate (DAF-2DA) in association with a confocal microscopy. KEY RESULTS: Elongation of primary roots was negatively dependent on external concentrations of nitrate, and inhibition by high external nitrate was diminished when roots were treated with SNP and IAA. MB and L-NNA inhibited root elongation of plants grown in low-nitrate solution, but they had no effect on elongation of roots grown in high-nitrate solution. Tungstate inhibited root elongation grown in both low- and high-nitrate solutions. Endogenous NO levels in root apices grown in high-nitrate solution were lower than those grown in low-nitrate solution. IAA and SNP markedly enhanced endogenous NO levels in root apices grown in high nitrate, but they had no effect on endogenous NO levels in root apical cells grown in low-nitrate solution. Tungstate induced a greater increase in the endogenous NO levels in root apical cells grown in low-nitrate solution than those grown in high-nitrate solution. CONCLUSIONS: Inhibition of root elongation in maize by high external nitrate is likely to result from a reduction of nitric oxide synthase-dependent endogenous NO levels in maize root apical cells.     

The expansion of maize root-cap mucilage during hydration. 3. Changes in water potential and water content

Root-cap mucilage from aerial nodal roots of maize has been found to have water potential values of −11 MPa or lower when air dried. The value approaches 0 MPa within 2 min of hydration in distilled water. In this time the expanding gel absorbs only about 0.3% of the water content of fully expanded mucilage. It is concluded that the root-cap mucilage per se has almost no capacity to retain water in the rhizosphere. Any function that it may play in the slowing of root desiccation would be indirect. For example, mucilage might decrease pore size between and within soil aggregates by pulling the particles together in a cycle of nocturnal efflux of water from the root surface, and diumal dyring during transpiration.     

Nitrate-uptake capacity of different root zones of Zea mays (L.) in vitro and in situ

The close relationship between nitrate depletion of the subsoil and root-length densities found in field experiments could not be explained by mathematical models simulating nitrate uptake (Wiesler and Horst, 1994). The objective of the present study was the validation of some of the assumptions made in these models namely uniform nitrate-uptake rates (NURs) independent on root age and daytime.Different techniques were developed and compared for the measurement of NUR of different root zones: (i) isolated root segments, (ii) compartmented uptake cuvettes, (iii) depletion of nitrate (water) from agarose blocks placed on specific zones of roots growing in nutrient solution and (iv) in rhizotrones filled with soil over the whole growing cycle of maize plants. All methods yielded a similar magnitude of NUR (10 - 30 pmol cm-2 s-1). However, only intact plants growing in nutrient solution as well as in soil, but not isolated root segments, showed higher NUR at apical root zones compared to more mature branching root zones by a factor of 2 - 8. The NUR of the root apex was particularly sensitive to the nitrogen demand of the plant and the assimilate supply from the shoots as affected by light intensity. At suboptimal, but not at optimal light conditions during preculture, NUR was lower in the dark than in the light. As plants matured, NUR of soil grown plants became increasingly dependent on water uptake. But even if nitrate uptake by mass flow was subtracted from total nitrate uptake, mature roots showed a surprisingly high nitrate-uptake capacity.The results indicate that the formation of root-age classes with different NUR and the assumption of lower NUR at night could improve the modelling of nitrate uptake.     

萌发玉米种子脱水耐性与胚根细胞超微结构的变化

玉米种子脱水试验表明,25℃下萌发24h种子脱水耐性开始丧失,丧失50％和100％的时间分别为33h、58h。萌发过程中随着吸胀时间增加,玉米种子脱水耐性逐步丧失。显微观察显示,种子吸胀过程中,胚根细胞的贮藏物质逐步减少,线粒体等细胞器的分化程度则不断提高,尤其是脂类物质的分解程度与脱水耐性变化的关系似乎更明显。     

Global and grain-specific accumulation of glycoside hydrolase family 10 xylanases in transgenic maize (Zea mays)

In planta expression of cell wall degrading enzymes is a promising approach for developing optimized biomass feedstocks that enable low-cost cellulosic biofuels production. Transgenic plants could serve as either an enzyme source for the hydrolysis of pretreated biomass or as the primary biomass feedstock in an autohydrolysis process. In this study, two xylanase genes, Bacillus sp. NG-27 bsx and Clostridium stercorarium xynB, were expressed in maize (Zea mays) under the control of two different promoters. Severe phenotypic effects were associated with xylanase accumulation in maize, including stunted plants and sterile grains. Global expression of these xylanases from the rice ubiquitin 3 promoter (rubi3) resulted in enzyme accumulation of approximately 0.01 mg enzyme per gram dry weight, or approximately 0.1% of total soluble protein (TSP). Grain-specific expression of these enzymes from the rice glutelin 4 promoter (GluB-4) resulted in higher-level accumulation of active enzyme, with BSX and XynB accumulating up to 4.0% TSP and 16.4% TSP, respectively, in shriveled grains from selected T0 plants. These results demonstrate the potential utility of the GluB-4 promoter for biotechnological applications. The phenotypic effects of xylanase expression in maize presented here demonstrate the difficulties of hemicellulase expression in an important crop for cellulosic biofuels production. Potential alternate approaches to achieve xylanase accumulation in planta without the accompanying negative phenotypes are discussed.