Analysis of polysaccharides and monosaccharides in the root mucilage of maize (Zea mays L.) by gas chromatography

Identification of genetic and environmental factors influencing aerial root traits that support biological nitrogen fixation in sorghum

Plant breeding and genetics play a major role in the adaptation of plants to meet human needs. The current requirement to make agriculture more sustainable can be partly met by a greater reliance on biological nitrogen fixation by symbiotic diazotrophic microorganisms that provide crop plants with ammonium. Select accessions of the cereal crop sorghum (Sorghum bicolor (L.) Moench) form mucilage-producing aerial roots that harbor nitrogen-fixing bacteria. Breeding programs aimed at developing sorghum varieties that support diazotrophs will benefit from a detailed understanding of the genetic and environmental factors contributing to aerial root formation. A genome-wide association study of the sorghum minicore, a collection of 242 landraces, and 30 accessions from the sorghum association panel was conducted in Florida and Wisconsin and under 2 fertilizer treatments to identify loci associated with the number of nodes with aerial roots and aerial root diameter. Sequence variation in genes encoding transcription factors that control phytohormone signaling and root system architecture showed significant associations with these traits. In addition, the location had a significant effect on the phenotypes. Concurrently, we developed F2 populations from crosses between bioenergy sorghums and a landrace that produced extensive aerial roots to evaluate the mode of inheritance of the loci identified by the genome-wide association study. Furthermore, the mucilage collected from aerial roots contained polysaccharides rich in galactose, arabinose, and fucose, whose composition displayed minimal variation among 10 genotypes and 2 fertilizer treatments. These combined results support the development of sorghums with the ability to acquire nitrogen via biological nitrogen fixation.

Preparation of polysaccharide-conjugated selenium nanoparticles from spent mushroom substrates and their growth-promoting effect on rice seedlings

Selenium nanoparticles (SeNPs) have gained significant attention in the agricultural field due to their favorable bioavailability and low toxicity, making them a highly researched subject. In this study, crude polysaccharides from spent mushroom substrate of Agrocybe aegerita (AaPs) were extracted for preparing the polysaccharide‑selenium-nanoparticles (AaPs-SeNPs) by ascorbic acid reduction method. The structure of AaPs-SeNPs was analyzed and their growth-promoting effects on rice seedlings were studied by adopting different application methods. The results revealed that AaPs-SeNPs exhibited improved free radical scavenging ability, with a lower half-maximal inhibitory concentrations compared to AaPs. Rice seedlings treated with AaPs-SeNPs showed significant enhancements in growth characteristics when compared to AaPs treatment, and foliar application exhibited a better growth-promoting effect compared to root application. Moreover, the growth performance and antioxidant enzyme activities of rice seedlings were enhanced by the addition of AaPs-SeNPs, and the absorption efficiency of essential nutrients such as N/P/K and Fe/Zn/Mn was also improved at appropriate concentrations, which could be one of the key factors contributing to the improved growth performance of plants. This study provides new aspects for the utilization of SMS, and also offers new insights from the perspective of nutrient absorption on how polysaccharide-conjugated selenium nanoparticles enhance crop growth.

Running the numbers on plant synthetic biology solutions to global problems

Synthetic biology and metabolic engineering promise to deliver sustainable solutions to global problems such as phasing out fossil fuels and replacing industrial nitrogen fixation. While this promise is real, scale matters, and so do knock-on effects of implementing solutions. Both scale and knock-on effects can be estimated by 'Fermi calculations' (aka 'back-of-envelope calculations') that use uncontroversial input data plus simple arithmetic to reach rough but reliable conclusions. Here, we illustrate how this is done and how informative it can be using two cases: oilcane (sugarcane engineered to accumulate triglycerides instead of sugar) as a source of bio-jet fuel, and nitrogen fixation by bacteria in mucilage secreted by maize aerial roots. We estimate that oilcane could meet no more than about 1% of today's U.S. jet fuel demand if grown on all current U.S. sugarcane land and that, if cane land were expanded to meet two-thirds of this demand, the fertilizer and refinery requirements would create a large carbon footprint. Conversely, we estimate that nitrogen fixation in aerial-root mucilage could replace up to 10% of the fertilizer nitrogen applied to U.S. maize, that 2% of plant carbon income used for growth would suffice to fuel the fixation, and that this extra carbon consumption would likely reduce grain yield only slightly.

Mucilage secretion by aerial roots in sorghum (Sorghum bicolor): sugar profile, genetic diversity, GWAS and transcriptomic analysis

Aerial root mucilage can enhance nitrogen fixation by providing sugar and low oxygen environment to the rhizosphere microbiome in Sierra Mixe maize. Aerial root mucilage has long been documented in sorghum (Sorghum bicolor), but little is known about the biological significance, genotypic variation, and genetic regulation of this biological process. In the present study, we found that a large variation of mucilage secretion capacity existed in a sorghum panel consisting of 146 accessions. Mucilage secretion occurred primarily in young aerial roots under adequately humid conditions but decreased or stopped in mature long aerial roots or under dry conditions. The main components of the mucilage-soluble were glucose and fructose, as revealed by sugar profiling of cultivated and wild sorghum. The mucilage secretion capacity of landrace grain sorghum was significantly higher than that of wild sorghum. Transcriptome analysis revealed that 1844 genes were upregulated and 2617 genes were downregulated in mucilage secreting roots. Amongst these 4461 differentially expressed genes, 82 genes belonged to glycosyltransferases and glucuronidation pathways. Sobic.010G120200, encoding a UDP-glycosyltransferase, was identified by both GWAS and transcriptome analysis as a candidate gene, which may be involved in the regulation of mucilage secretion in sorghum through a negative regulatory mechanism.

Biological nitrogen fixation and prospects for ecological intensification in cereal-based cropping systems

The demand for nitrogen (N) for crop production increased rapidly from the middle of the twentieth century and is predicted to at least double by 2050 to satisfy the on-going improvements in productivity of major food crops such as wheat, rice and maize that underpin the staple diet of most of the world's population. The increased demand will need to be fulfilled by the two main sources of N supply - biological nitrogen (gas) (N2) fixation (BNF) and fertilizer N supplied through the Haber-Bosch processes. BNF provides many functional benefits for agroecosystems. It is a vital mechanism for replenishing the reservoirs of soil organic N and improving the availability of soil N to support crop growth while also assisting in efforts to lower negative environmental externalities than fertilizer N. In cereal-based cropping systems, legumes in symbiosis with rhizobia contribute the largest BNF input; however, diazotrophs involved in non-symbiotic associations with plants or present as free-living N2-fixers are ubiquitous and also provide an additional source of fixed N. This review presents the current knowledge of BNF by free-living, non-symbiotic and symbiotic diazotrophs in the global N cycle, examines global and regional estimates of contributions of BNF, and discusses possible strategies to enhance BNF for the prospective benefit of cereal N nutrition. We conclude by considering the challenges of introducing in planta BNF into cereals and reflect on the potential for BNF in both conventional and alternative crop management systems to encourage the ecological intensification of cereal and legume production.

Assembly Patterns of the Rhizosphere Microbiome Along the Longitudinal Root Axis of Maize (Zea mays L.)

It is by now well proven that different plant species within their specific root systems select for distinct subsets of microbiota from bulk soil - their individual rhizosphere microbiomes. In maize, root growth advances several centimeters each day, with the locations, quality and quantity of rhizodeposition changing. We investigated the assembly of communities of prokaryotes (archaea and bacteria) and their protistan predators (Cercozoa, Rhizaria) along the longitudinal root axis of maize (Zea mays L.). We grew maize plants in an agricultural loamy soil and sampled rhizosphere soil at distinct locations along maize roots. We applied high-throughput sequencing, followed by diversity and network analyses in order to track changes in relative abundances, diversity and co-occurrence of rhizosphere microbiota along the root axis. Apart from a reduction of operational taxonomic unit (OTU) richness and a strong shift in community composition between bulk soil and root tips, patterns of microbial community assembly along maize-roots were more complex than expected. High variation in beta diversity at root tips and the root hair zone indicated substantial randomness of community assembly. Root hair zone communities were characterized by massive co-occurrence of microbial taxa, likely fueled by abundant resource supply from rhizodeposition. Further up the root where lateral roots emerged processes of community assembly appeared to be more deterministic (e.g., through competition and predation). This shift toward significance of deterministic processes was revealed by low variability of beta diversity, changes in network topology, and the appearance of regular phylogenetic co-occurrence patterns in bipartite networks between prokaryotes and their potential protistan predators. Such patterns were strongest in regions with fully developed laterals, suggesting that a consistent rhizosphere microbiome finally assembled. For the targeted improvement of microbiome function, such knowledge on the processes of microbiome assembly on roots and its temporal and spatial variability is crucially important.

Mucilage Polysaccharide Composition and Exudation in Maize From Contrasting Climatic Regions

Mucilage, a gelatinous substance comprising mostly polysaccharides, is exuded by maize nodal and underground root tips. Although mucilage provides several benefits for rhizosphere functions, studies on the variation in mucilage amounts and its polysaccharide composition between genotypes are still lacking. In this study, eight maize (Zea mays L.) genotypes from different globally distributed agroecological zones were grown under identical abiotic conditions in a randomized field experiment. Mucilage exudation amount, neutral sugars and uronic acids were quantified. Galactose (∼39-42%), fucose (∼22-30%), mannose (∼11-14%), and arabinose (∼8-11%) were the major neutral sugars in nodal root mucilage. Xylose (∼1-4%), and glucose (∼1-4%) occurred only in minor proportions. Glucuronic acid (∼3-5%) was the only uronic acid detected. The polysaccharide composition differed significantly between maize genotypes. Mucilage exudation was 135 and 125% higher in the Indian (900 M Gold) and Kenyan (DH 02) genotypes than in the central European genotypes, respectively. Mucilage exudation was positively associated with the vapor pressure deficit of the genotypes' agroecological zone. The results indicate that selection for environments with high vapor pressure deficit may favor higher mucilage exudation, possibly because mucilage can delay the onset of hydraulic failure during periods of high vapor pressure deficit. Genotypes from semi-arid climates might offer sources of genetic material for beneficial mucilage traits.

A Model for Nitrogen Fixation in Cereal Crops

Nitrogen-fixing microbial associations with cereals have been of intense interest for more than a century (Roesch et al., Plant Soil 2008;302:91-104; Triplett, Plant Soil 1996;186:29-38; Mus et al., Appl. Environ. Microbiol. 2016;82:3698-3710; Beatty and Good, Science 2011;333:416-417). A recent report demonstrated that an indigenous Sierra Mixe maize landrace, characterized by an extensive development of aerial roots that secrete large amounts of mucilage, can acquire 28-82% of its nitrogen from atmospheric dinitrogen (Van Deynze et al., PLoS Biol. 2018;16:e2006352). Although the Sierra Mixe maize landrace is unique in the large quantity of mucilage produced, other cereal crops secrete mucilage from underground and aerial roots and we hypothesize that this may represent a general mechanism for cereals to support associations with microbial diazotrophs. We propose a model for the association of nitrogen-fixing microbes with maize mucilage and identify the four main functionalities for such a productive diazotrophic association.

Sticky mucilages and exudates of plants: putative microenvironmental design elements with biotechnological value

Plants produce a wide array of secretions both above and below ground. Known as mucilages or exudates, they are secreted by seeds, roots, leaves and stems and fulfil a variety of functions including adhesion, protection, nutrient acquisition and infection. Mucilages are generally polysaccharide-rich and often occur in the form of viscoelastic gels and in many cases have adhesive properties. In some cases, progress is being made in understanding the structure-function relationships of mucilages such as for the secretions that allow growing ivy to attach to substrates and the biosynthesis and secretion of the mucilage compounds of the Arabidopsis seed coat. Work is just beginning towards understanding root mucilage and the proposed adhesive polymers involved in the formation of rhizosheaths at root surfaces and for the secretions involved in host plant infection by parasitic plants. In this article, we summarise knowledge on plant exudates and mucilages within the concept of their functions in microenvironmental design, focusing in particular on their bioadhesive functions and the molecules responsible for them. We draw attention to areas of future knowledge need, including the microstructure of mucilages and their compositional and regulatory dynamics.

Strategy for Structural Elucidation of Polysaccharides: Elucidation of a Maize Mucilage that Harbors Diazotrophic Bacteria

The recruitment of a bacterial consortium by the host is a strategy not limited to animals but is also used in plants. A maize aerial root mucilage has been found that harbors nitrogen fixing bacteria that are attracted to the carbohydrate rich environment. This synbiotic relationship is facilitated by a polysaccharide, whose complicated structure has been previously unknown. In this report, we present the characterization of the maize polysaccharide by employing new analytical strategies combining chemical depolymerization, oligosaccharide sequencing, and monosaccharide and glycosidic linkage quantitation. The mucilage contains a single heterogeneous polysaccharide composed of a highly fucosylated and xylosylated galactose backbone with arabinan and mannoglucuronan branches. This unique polysaccharide structure may select for the diazotrophic community by containing monosaccharides and linkages that correspond to the glycosyl hydrolases associated with the microbial community. The elucidation of this complicated structure illustrates the power of the analytical methods, which may serve as a general platform for polysaccharide analysis in the future.

Triterpenoid Saponins from Clematis graveolens and Evaluation of their Insecticidal Activities

A new hederagenin based triterpenoid saponin, clematograveolenoside A (1), along with three known saponins, tomentoside A (2), huzhangoside D (3) and clematoside S (4), were isolated from the roots and rhizomes of Clematis graveolens. The structure of new compound was elucidated on the basis of detailed analysis of chemical and spectroscopic data including 1D- and 2D NMR spectra. Compound 2 was found the most effective against aphid ( Aphis craccivora) with an LC50 of 1.2 and 0.5 mg/mL after treatment for 72 and 96 h, respectively and was followed by compound 4 (LC50 = 2.3 and 1.9 mg/mL) and 1 (LC50 = 3.2 and 2.6 mg/mL). In case of termite ( Coptotermis homii), compound 1 was found more toxic with an LC50 of 0.1 mg/L after 24 h of treatment followed by compound 2, 3 and 4 (LC50 = 0.1, 0.2 and 0.2 mg/mL, respectively).

Structural characterization of organic intermediates arising from xylenol degradation by laboratory-scale constructed wetlands

A mixture of xylenols (2,6-, 3,4-, 3,5-) was subjected to laboratory-scale constructed wetland treatment using helophytes. Conversion efficiencies under aerobic conditions ranged from 89% to 94%; the corresponding numbers under anaerobic conditions were lower. The studies were focused on the identification of stable organic intermediates. Identification was performed by a combination of GC/MS analysis and pre-chromatographic derivatization of the lyophilizates. In addition to common intermediates including citraconate, succinate and dimethyl benzenediols, an array of α- and β-ketoadipic acid carboxylates could be identified. The ketoadipic acid carboxylates have not been known to be formed in bioremediation of phenols including xylenols so far. Mechanisms for the formation of ketoadipic acid carboxylates are proposed. Chemotaxonomic considerations using diagnostic fatty acids provided mounting evidence that organic matter originating from plants prevailed over bacterial organic matter. Biomarkers indicated a virtual absence of fungi and algae.

Screening and comparison of antioxidant activities of polysaccharides from Coriolus versicolor

Six polysaccharide fractions (Coriolus versicolor polysaccharides: CVPS-1, CVPS-2, CVPS-3, CVPS-4, CVPS-5 and CVPS-6) were isolated and purified from the fruiting bodies of C. versicolor by ion exchange chromatography and gel chromatography. Their chemical and physical characteristics were determined by chemical methods, high performance liquid chromatography, and high-performance gel-permeation chromatography. Finally, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical assay, superoxide radical assay, and hydroxyl radical assay were carried out to test the antioxidant activities of CVPS in vitro. The results indicated that the six CVPS fractions were acidic heteropolysaccharides, composed of mannose, rhamnose, glucuronic acid, glucose and fructose with different ratios. The molecular weights of CVPS-1, CVPS-2, CVPS-3, CVPS-4, CVPS-5 and CVPS-6 were 1740, 1480, 568, 880, 1260 and 1840kDa and the protein contents were 4.2%, 6.4%, 8.5%, 7.8%, 6.5% and 3.9%, respectively. Among the six fractions, CVPS with lower molecular weight, higher protein content and larger uronic acid amount, basically exhibited higher radical scavenging effects at the same concentration. Compared with other fractions, CVPS-3 exhibited the highest antioxidant activities. The effects of the molecular weight, protein content and uronic acid amount of the polysaccharides appeared to be significant on the improvement of the bioactivities.

Isolation, purification and characterisation of selenium-containing polysaccharides and proteins in selenium-enriched Radix puerariae

BACKGROUND

Selenium (Se) is an essential dietary mineral and Radix puerariae (RP) (the dried root of Pueraria lobata Willd.) is a botanical supplement widely used as a nutraceutical. Food enriched with Se provides a feasible and economic approach for production of organic Se compounds. However, little is known about Se-enriched RP and the structure of Se-containing polysaccharides and proteins derived from Se-enriched RP.

RESULTS

The organic form of Se accounted for 82.42% of total content. Purification by DEAE-52 and Sephadex G-100 column chromatography yielded three single fractions--RP-SeP-11, RP-SeP-22 and RP-SeP-33--with Se contents of 0.9562 × 10⁻³, 0.6113 × 10⁻³ and 0.3827 × 10⁻³ g kg⁻¹, respectively. RP-SeP-11 (3.5 kDa) was made of glucose, RP-SeP-22 (19.6 kDa) was composed of xylose and glucose, and RP-SeP-33 (97.9 kDa) was made up galactose, mannose and glucose. Two Se-containing proteins were obtained with Se content of 3.175 × 10⁻³ and 4.328 × 10⁻³ g kg⁻¹, respectively. One appeared as three subunits with molecular masses of 43.0, 29.0 and 17.8 kDa while the other appeared as two subunits with molecular masses of 43.0 and 26.3 kDa.

CONCLUSION

The results provide a basis for promoting the utilisation of RP resources enriched with Se as a promising tool for the food industry and are significant for its contribution to Se biochemistry in plants.

Immobilization of aluminum with mucilage secreted by root cap and root border cells is related to aluminum resistance in Glycine max L

The root cap and root border cells (RBCs) of most plant species produced pectinaceous mucilage, which can bind metal cations. In order to evaluate the potential role of root mucilage on aluminum (Al) resistance, two soybean cultivars differing in Al resistance were aeroponic cultured, the effects of Al on root mucilage secretion, root growth, contents of mucilage-bound Al and root tip Al, and the capability of mucilage to bind Al were investigated. Increasing Al concentration and exposure time significantly enhanced mucilage excretion from both root caps and RBCs, decreased RBCs viability and relative root elongation except roots exposed to 400 μM Al for 48 h in Al-resistant cultivar. Removal of root mucilage from root tips resulted in a more severe inhibition of root elongation. Of the total Al accumulated in root, mucilage accounted 48-72 and 12-27 %, while root tip accounted 22-52 and 73-88 % in Al-resistant and Al-sensitive cultivars, respectively. A (27)Al nuclear magnetic resonance spectrum of the Al-adsorbed mucilage showed Al tightly bound to mucilage. Higher capacity to exclude Al in Al-resistant soybean cultivar is related to the immobilization and detoxification of Al by the mucilage secreted from root cap and RBCs.

Culture medium optimization of a new bacterial extracellular polysaccharide with excellent moisture retention activity

A new kind of extracellular polysaccharide (EPS) from Pseudomonas fluorescens PGM37 was obtained and culture media was optimized using the statistical methods single factor experiments and response surface methodology (RSM) design. As a result, the optimum cultivation conditions initial pH value, medium volume, inoculum size, temperature, and rotation speed were 7.5, 100 mL/250 mL, 5%, 28 °C, and 180 rpm, respectively. The optimized media: sucrose 36.23 g L(-1), yeast extract 3.32 g L(-1), sodium chloride 1.13 g L(-1), and calcium chloride 0.20 g L(-1). The maximum predicted yield of EPS was 10.1163 g L(-1) under these conditions. The validation data was 10.012 g L(-1), which could strongly confirm the correlation between the experimental and theoretical values. Gas Chromatography analysis revealed that the polymer was made up of mannose and glucose in the ratio of 1:1. Infrared spectroscopy showed that the polysaccharide had β-D-pyranoid configuration and contained no other substituent. Graded by different multiples of alcohol after specific degradation by enzyme and then detected by LC-ESI-MS, the EPS structure was β-D-Glcp-(1, 4)-β-D-Manp-(1, 4)-β-D-Glcp-(1, 4)-β-D-Manp. The moisture retention ability of the EPS was found to be superior to glycerol and only a little inferior to hyaluronic acid (HA), which presented potential application value in cosmetics and clinical medicine fields.

Movement of newly assimilated 13C carbon in the grass Lolium perenne and its incorporation into rhizosphere microbial DNA

One of the key processes that drives rhizosphere microbial activity is the exudation of soluble organic carbon (C) by plant roots. We describe an experiment designed to determine the impact of defoliation on the partitioning and movement of C in grass (Lolium perenne L.), soil and grass-sterile sand microcosms, using a (13)CO(2) pulse-labelling method. The pulse-derived (13)C in the shoots declined over time, but that of the roots remained stable throughout the experiment. There were peaks in the atom% (13)C of rhizosphere CO(2) in the first few hours after labelling probably due to root respiration, and again at around 100 h. The second peak was only seen in the soil microcosms and not in those with sterilised sand as the growth medium, indicating possible microbial activity. Incorporation of the (13)C label into the microbial biomass increased at 100 h when incorporation into replicating cells, as indicated by the amounts of the label in the microbial DNA, started to increase. These results indicate that the rhizosphere environment is conducive to bacterial growth and replication. The results also show that defoliation had no impact on the pattern of movement of (13)C from plant roots into the microbial population in the rhizosphere.

Anticancer activity of rhamnoallosan against DU-145 cells is kinetically complementary to coexisting Polyphenolics in Psidium guajava budding leaves

Psidium guajava L. is a valuable farm fruit plant having many medicinal uses. Previously its budding leaves (PE) were shown to contain huge amounts of soluble polyphenolics (SP) including (in mg/g) gallic acid (348), catechin (102), epicatechin (60), rutin (100), quercetin (102), and rutin (100) and to exhibit potent anticancer activity. However, reconstitution of these polyphenolics recovered only 40% of the original bioactivity, and the soluble carbohydrate (SC) portion in PE was suspected to contribute the remaining. PE contained a novel rhamnoallosan, which had a carbohydrate/protein (w/w) ratio = 29.06%/10.27% (=2.83, average molecular mass of 5029 kDa), characteristically evidencing a peptidoglycan, consisting of a composition (mole % ratio) of rhamnose/allose/arabinose/tallose/xylose/fucose/glucose/mannose/galactose = 36.05:24.24:8.76:7.95:7.37:5.90:3.69:3.19:2.85 and of amino acid (in wt %) glycine/leucine/proline/alanine/methionine/isoleucine/valine/histidine/tyrosine/phenylalanine/cysteine/aspartic acid/lysine/glutamic acid = 37.12:12.68:10.05:8.97:5.99:4.89:4.83:4.25:4.05:2.78:1.86:1.10:0.73:0.70. Kinetic analysis showed comparable apparent cell-killing rate coefficients (k(app)) to be 4.03 x 10(3) and 2.92 x 10(3) cells mg(-1) h(-1), respectively, by SP and SC, evidencing the complementary anti-DU-145 bioactivity in nature.

Exudation of alcohol and aldehyde sugars from roots of defoliated Lolium perenne L. grown under sterile conditions

Root exudates were collected over a 27 day period from defoliated and non-defoliated Lolium perenne L. plants grown under sterile conditions in microlysimeters. Eleven individual sugars, including both aldehyde and alcohol sugars, were identified and quantified with a gas chromatograph-mass spectrometer (GC-MS). There was no change in the number of sugars present between 7 and 27 days, but the exudation of alcohol sugars decreased rapidly at about day 12. Xylose and glucose were present in the largest amounts. Defoliation initially increased the total amount of sugars in the exudates, but continuous defoliation reduced total sugar exudation by 16% and induced changes in the exudation patterns of individual sugars. Defoliation enhanced exudation of erythritol, threitol, and xylitol, reduced exudation of glucose and arabitol, but had little effect on the amounts of other sugars exuded. The more complex 6 C, 5 OH aldehyde sugars, especially glucose, showed changes earlier and to a greater extent (17 days), than the 5 C, 4 OH (xylose and ribose) and 6 C 4 OH (fucose) aldehyde groups. These findings confirm the general finding that repeated defoliation reduces the quantity of total sugars exuded, but the pattern of release of individual sugars is complex and variable.

Determination of aldoses and ketoses by GC-MS using differential derivatisation

A method has been established by which to determine aldoses and ketoses in plant material simultaneously. Monosaccharides were extracted by sonication with 80% ethanol and sugar oximes formed by treatment of the resultant extract with hydroxylamine and pyridine at 90 degrees C. After reaction, one aliquot of the product was derivatised with acetic anhydride at 90 degrees C, whilst a second aliquot was silylated with HMDS and TMCS at 80 degrees C. Both reaction mixtures were analysed by GC-MS in the SIM mode. Quantivation was linear within the range 1-4 microg/mL and the detection limit for monosaccharides was 5-25 ng/mL. The absolute recoveries were between 73.0 and 90.2% and the RSDs were 3.1-10.0%. This method was applied to analyse the free monosaccharides in Lyceum barbarum L.; eight monosaccharides were present in amounts between 0.26 and 368.65 microg/mg.

Influence of maize mucilage on the diversity and activity of the denitrifying community

In order to understand the effect of the maize rhizosphere on denitrification, the diversity and the activity of the denitrifying community were studied in soil amended with maize mucilage. Diversity of the denitrifying community was investigated by polymerase chain reaction (PCR) amplification of total community DNA extracted from soils using gene fragments, encoding the nitrate reductase (narG) and the nitrous oxide reductase (nosZ), as molecular markers. To assess the underlying diversity, PCR products were cloned and 10 gene libraries were obtained for each targeted gene. Libraries containing 738 and 713 narG and nosZ clones, respectively, were screened by restriction fragment analysis, and grouped based on their RFLP (restriction fragment length polymorphism) patterns. In all, 117 and 171 different clone families have been identified for narG and nosZ and representatives of RFLP families containing at least two clones were sequenced. Rarefaction curves of both genes did not reach a clear saturation, indicating that analysis of an increasing number of clones would have revealed further diversity. Recovered NarG sequences were related to NarG from Actinomycetales and from Proteobacteria but most of them are not related to NarG from known bacteria. In contrast, most of the NosZ sequences were related to NosZ from alpha, beta, and gammaProteobacteria. Denitrifying activity was monitored by incubating the control and amended soils anaerobically in presence of acetylene. The N2O production rates revealed denitrifying activity to be greater in amended soil than in control soil. Altogether, our results revealed that mucilage addition to the soil results in a strong impact on the activity of the denitrifying community and minor changes on its diversity.

Sucrose synthase isozyme SUS1 in the maize root cap is preferentially localized in the endopolyploid outer cells

The structure of the maize (Zea mays L.) root cap was studied to quantitatively evaluate the relationship among the size of the cells, their endopolyploidy level, and the abundance of the sucrose synthase isozyme SUS1. Median longitudinal root cap sections were analysed using immunolocalization, quantitative DNA staining, and image cytometry. Both the immunolocalization signal for the SUS1 protein and the endopolyploidy level increased from calyptrogen towards the root cap periphery and were thus the highest in the outer cells. These cells had a nuclear DNA content of mostly 8C or higher and the largest volumes of all root cap cells. The high amount of SUS1 protein in the outer, endopolyploid cells suggests an association between endoreduplication and the abundance of this enzyme. The outer cells are involved in mucilage production; hence, there is a possibility that sucrose synthase provides monosaccharide precursors for mucilage synthesis.Key words: nuclear DNA amount, endoreduplication, immunolocalization, image cytometry, Zea mays L.

Plant roots release phospholipid surfactants that modify the physical and chemical properties of soil

• Plant root mucilages contain powerful surfactants that will alter the interaction of soil solids with water and ions, and the rates of microbial processes. • The lipid composition of maize, lupin and wheat root mucilages was analysed by thin layer chromatography and gas chromatography-mass spectrometry. A commercially available phosphatidylcholine (lecithin), chemically similar to the phospholipid surfactants identified in the mucilages, was then used to evaluate its effects on selected soil properties. • The lipids found in the mucilages were principally phosphatidylcholines, composed mainly of saturated fatty acids, in contrast to the lipids extracted from root tissues. In soil at low tension, lecithin reduced the water content at any particular tension by as much as 10 and 50% in soil and acid-washed sand, respectively. Lecithin decreased the amount of phosphate adsorption in soil and increased the phosphate concentration in solution by 10%. The surfactant also reduced net rates of ammonium consumption and nitrate production in soil. • These experiments provide the first evidence we are aware of that plant-released surfactants will significantly modify the biophysical environment of the rhizosphere.