Influence of microflora and composition of root bathing solution on root exudation of maize plants

Root exudation of carbon (C) plays a major role in processes occurring in the plant rhizosphere. Environmental factors affecting root exudation have been identified but their effects are rarely quantified. The purpose of this work was to evaluate the impact of both the microflora and the chemical composition of the growth medium on root exudation, taking into account soluble exudates and mucilage fraction. Maize plants (Zea mays L.) were grown for 12 days in hydroponic conditions and then transferred in three root bathing solutions (demineralized water, KCl or nutrient solution) during 24 hours. In each case, presence of microflora was tested with a comparison between plants inoculated with maize rhizospheric strain and axenic plants. Exudation was measured in terms of C and biomass production. A strong interaction was noticed between microflora and chemical composition of the root bathing solution. In fact, the presence of rhizospheric microflora induces a stimulation of soluble exudates only in KCl and Nutrient solutions. In demineralized water, a different response was observed with a higher C release for axenic plants, probably due to the osmotic shock induced to the roots. Concerning mucilage fractions, small quantities were recovered on all treatments. This work demonstrates that the chemical composition of the root bathing solution and presence of microorganisms significantly modify the amount of soluble exudates. Attention must therefore be paid to the cultural conditions when exudation is studied because of the sensitivity of this process to root environment.     

Characterization of plum procyanidins by thiolytic depolymerization

The phenolic compounds of 'Green Gage' (GG) plums ( Prunus domestica L.), "Rainha Claudia Verde", from a 'protected designation of origin' (PDO), in Portugal, were quantified in both flesh and skin tissues of plums collected in two different orchards (GG-V and GG-C). Analyzes of phenolic compounds were also performed on another GG European plum obtained in France (GG-F) and two other French plums, 'Mirabelle' (M) and 'Golden Japan' (GJ). Thiolysis was used for the first time in the analysis of plum phenolic compounds. This methodology showed that the flesh and skin contain a large proportion of flavan-3-ols, which account, respectively, for 92 and 85% in GJ, 61 and 44% in GG-V, 62 and 48% in GG-C, 54 and 27% in M, and 45 and 37% in GG-F. Terminal units of procyanidins observed in plums are mainly (+)-catechin (54-77% of all terminal units in flesh and 57-81% in skin). The GJ plums showed a phenolic composition different from all of the others, with a lower content of chlorogenic acid isomers and the presence of A-type procyanidins as dimers and terminal residues of polymerized forms. The average degree of polymerization (DPn) of plum procyanidins was higher in the flesh (5-9 units) than in the skin (4-6 units). Procyanidin B7 was observed in the flesh of all GG plums and in the skin of the Portuguese ones. Principal component analysis of the phenolic composition of the flesh and skin of these plums obtained after thiolysis allowed their distinction according to the variety and origin, opening the possibility of the use of phenolic composition for variety/origin identification.     

Rhizosphere effects of <Emphasis Type="Italic">Populus euramericana</Emphasis> Dorskamp on the mobility of Zn,Pb and Cd in contaminated technosols

Purpose

This study aimed at investigating the rhizosphere effects of Populus euramericana Dorskamp on the mobility of Zn, Pb and Cd in contaminated technosols from a former smelting site.

Materials and methods

A rhizobox experiment was conducted with poplars, where the plant stem cuttings were grown in contaminated technosols for 2 months under glasshouse conditions. After plant growth, rhizosphere and bulk soil pore water (SPW) were sampled together. SPW properties such as pH, dissolved organic carbon (DOC) and total dissolved concentrations of Zn, Pb and Cd were determined. The concentrations of Zn, Pb and Cd in plant organs were also determined.

Results and discussion

Rhizosphere SPW pH increased for all studied soils by 0.3 to 0.6 units compared to bulk soils. A significant increase was also observed for DOC concentrations regardless of the soil type or total metal concentrations, which might be attributed to the plant root activity. For all studied soils, the rhizosphere SPW metal concentrations decreased significantly after plant growth compared to bulk soils which might be attributed to the increase in pH and effects of root exudates. Zn, Pb and Cd accumulated in plant organs and the higher metal concentrations were found in plant roots compared to plant shoots.

Conclusions

The restricted transfer of the studied metals to the plant shoots confirms the potential role of this species in the immobilization of these metals. Thus, P. euramericana Dorskamp can be used for phytostabilization of technosols.

     

Contribution of phytoecological data to spatialize soil erosion: Application of the RUSLE model in the Algerian atlas

Among the models used to assess water erosion, the RUSLE model is commonly used. Policy makers can act on cover (C-factor) and conservation practice (P-factor) to reduce erosion, with less costly action on soil surface characteristics. However, the widespread use of vegetation indices such as NDVI does not allow for a proper assessment of the C-factor in drylands where stones, crusted surfaces and litter strongly influence soil protection. Two sub-factors of C, canopy cover (CC) and soil cover (SC), can be assessed from phytoecological measurements that include gravel-pebbles cover, physical mulch, annual and perennial vegetation. This paper introduces a method to calculate the C-factor from phytoecological data and, in combination with remote sensing and a geographic information system (GIS), to map it over large areas. A supervised classification, based on field phytoecological data, is applied to radiometric data from Landsat-8/OLI satellite images. Then, a C-factor value, whose SC and CC subfactors are directly derived from the phytoecological measurements, is assigned to each land cover unit. This method and RUSLE are implemented on a pilot region of 3828 km² of the Saharan Atlas, composed of rangelands and steppe formations, and intended to become an observatory. The protective effect against erosion by gravel-pebbles (50%) is more than twice that of vegetation (23%). The C-factor derived from NDVI (0.67) is higher and more evenly distributed than that combining these two contributions (0.37 on average). Finally, priorities are proposed to decision-makers by crossing the synthetic map of erosion sensitivity and a decision matrix of management priorities.     

Effect of fertilization of a biochar and compost amended technosol: Consequence on Ailanthus altissima growth and As- and Pb-specific root sorption

The remediation of metal(loid) polluted soil using plants (i.e. phytoremediation) often requires the application of amendments, as well as chemical fertilizer. However, such fertilizers can have negative effects when applied alone and can thus be applied together with other organic amendments to diminish this negative effect. Finally, plants to be used in phytoremediation should be selected based on their adaptive capacity and tolerance to poor and highly contaminated soils, characteristics that possesses Ailanthus altissima. The objective of this study was to evaluate the effects of osmocote fertilization on the amended mining technosol properties and plant growth parameters, as well as to study the accumulation pattern of As and Pb in plant roots. Results showed that osmocote ameliorated soil conditions, but increased Pb mobility. It also greatly improved plant growth. Finally, different behaviours of metal(loid) accumulation were observed in the roots: As was absorbed mainly in the roots because of its similarity with P, with very low amounts in the leaves, whereas Pb was adsorbed mainly on the root surface, with lesser proportion absorbed inside the root system.     

Composition of phenolic compounds in a Portuguese pear (Pyrus communis L. var. S. Bartolomeu) and changes after sun-drying

The composition of phenolic compounds of a Portuguese pear cultivar (Pyrus communis L. var. S. Bartolomeu) was determined by HPLC after thioacidolysis. The average concentration of phenolic compounds in pear harvested at commercial maturity stage was 3.7 g per kg of fresh pulp. Procyanidins were the predominant phenolics (96%), with a mean degree of polymerization (mDP) of 13-44; hydroxycinnamic acids (2%), arbutin (0.8%), and catechins (0.7%) were also present. The most abundant monomer in the procyanidin structures was (-)-epicatechin (99%), which was found as extension and terminal units; (+)-catechin (1%) was found only as a terminal unit. Sun-drying of these pears caused a decrease of 64% (on a dry pulp basis) in the total amount of native phenolic compounds. Hydroxycinnamic acids and procyanidins showed the largest decrease; the B2 procyanidin was not found at all in the sun-dried pear. Less affected were arbutin and catechins. In the sun-dried pear, the procyanidins with high mDP became unextractable in the solvents used.     

Effectiveness of steam pasteurization in controlling microbiological hazards of cull cow carcasses in a commercial plant

The purpose of the study, carried out in a beef processing plant, was to evaluate the effectiveness of a new prototype for steam pasteurization treatment in controlling microbiological hazards. Samples were taken by swabbing randomly selected sites before and after pasteurization and again after chilling to obtain total aerobic counts (TAC), total coliform counts (TCC), and generic Escherichia coli counts (ECC) on Petrifilm plates and to determine the prevalence of Salmonella spp., Listeria monocytogenes, and E. coli O157:H7 using standard enrichment techniques. Escherichia coli and L. monocytogenes strains were tested for various factors associated with their virulence by using colony hybridization and polymerase chain reaction (PCR), respectively. Antimicrobial susceptibility was determined for each isolate that was potentially pathogenic to humans by using the disk-diffusion method. Mean values for TAC, TCC, and ECC were 2.18, 0.16, and 0.06 log10 CFU/cm2, respectively, before pasteurization; 1.17, 0.03, and 0.01 log10 CFU/cm2 after pasteurization; and 0.89, 0.02, and 0.01 log10 CFU/cm2 after chilling. Prevalence of L. monocytogenes, Salmonella spp., and E. coli O157:H7 on carcasses was 0.8%, 0.0%, and 0.0%, respectively, before pasteurization; 2.6%, 0.0%, and 0.0% after pasteurization; and 3.1%, 0.1%, and 0.0% after chilling. The prevalence of E. coli containing > or = 1 virulence gene was 14.7%. More specifically, 11.88% of the isolates obtained before pasteurization, 22.2% obtained after pasteurization, and 31.2% obtained after chilling had virulence genes. All L. monocytogenes isolates tested positive for the presence of 3 major virulence factors (hlyA, inlB, and plcB). Antibiograms showed that certain isolates were susceptible to all antibiotics, some showed an intermediate sensitivity, and others were multiresistant. Overall, these results suggest that steam pasteurization is an effective means of improving safety quality of beef carcasses. However, pasteurization may indirectly contribute to the growth of some pathogenic microorganisms, such as L. monocytogenes.     

Inhibition of apple polyphenol oxidase activity by procyanidins and polyphenol oxidation products

The rate of consumption of dissolved oxygen by apple polyphenol oxidase in cider apple juices did not correlate with polyphenol oxidase activity in the fruits and decreased faster than could be explained by the decrease of its polyphenolic substrates. The kinetics parameters of a crude polyphenol oxidase extract, prepared from apple (Braeburn cultivar), were determined using caffeoylquinic acid as a substrate. Three apple procyanidin fractions of n 80, 10.5, and 4 were purified from the parenchyma of cider apples of various cultivars. Procyanidins, caffeoylquinic acid, (-)-epicatechin, and a mixture of caffeoylquinic acid and (-)-epicatechin were oxidized by reaction with caffeoylquinic acid o-quinone in order to form oxidation products. All the fractions were evaluated for their inhibitory effect on PPO activity. Native procyanidins inhibited polyphenol oxidase activity, the inhibition intensity increasing with n. The polyphenol oxidase activity decreased by 50% for 0.026 g/L of the fraction of n 80, 0.17 g/L of the fraction of n 10.5, and 1 g/L of the fraction of n 4. The inhibitory effect of oxidized procyanidins was twice that of native procyanidins. Oxidation products of caffeoylquinic acid and (-)-epicatechin also inhibited polyphenol oxidase.     

Characterization and estimation of proanthocyanidins and other phenolics in coffee pulp (Coffea arabica) by thiolysis-high-performance liquid chromatography

Fresh and 3-day-old coffee pulp of the Arabica variety were analyzed for polyphenol composition followed by characterization by two different methods. The first method consisted in subjecting coffee pulp powder to direct thiolysis. For the second method, coffee pulp was subjected to successive solvent extractions, followed by thiolysis. Quantification of phenolic compounds was then achieved by high-performance liquid chromatography (HPLC) analysis of thiolysis products. Four major classes of polyphenols were identified: flavan-3-ols (monomers and procyanidins), hydroxycinnamic acids, flavonols, and anthocyanidins. Differences in concentration of procyanidins were observed between fresh and 3-day-old coffee pulp. Constitutive units were mainly epicatechin, representing more than 90% of the proanthocyanidin units, with average degrees of polymerization in the range of 3.8-9.1. Monomer to hexamer units of flavan-3-ols from fresh coffee pulp were separated by normal-phase HPLC. Molecular size of oligomeric proanthocyanidins was obtained by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Results obtained confirm the presence of oligomers of the flavan-3-ol (-)-epicatechin.