Effect of soil compaction on photosynthesis and carbon partitioning within a maize–soil system

Soil compaction is known to affect plant growth. However, most of the information regarding the effects of this factor on carbon partitioning has been obtained on young plants while little is known about the evolution of these effects with plant age. The objective of this work was to investigate how soil compaction affects carbon assimilation, photosynthate partitioning and morphology of maize plants during vegetative growth up to tassel initiation. A pressure was applied on moist soil to obtain a bulk density of 1.45 g cm⁻³ (compacted soil (CS) treatment) while the loose soil (LS) treatment (bulk density of 1.30 g cm⁻³) was obtained by gentle vibration of soil columns. Plants were grown in a growth chamber for 3–6 weeks and carbon partitioning in the plant–soil system was evaluated using ¹⁴C pulse-labelling techniques. Soil compaction greatly hampered root elongation and delayed leaf appearance rate, thereby decreasing plant height, shoot and root dry weights and leaf area. The increase in soil bulk density decreased carbon assimilation rate especially in early growth stages. The main effect of soil compaction on assimilate partitioning occurred on carbon exudation, which increased considerably to the detriment of root carbon. Furthermore, soil microbial biomass greatly increased in CS. Two hypotheses were formulated. The first was that increasing soil resistance to root penetration induced a sink limitation in roots and this increased carbon release into the soil and resulted in a root feedback that regulated carbon assimilation rate. The second hypothesis relies on soil–plant water relations since, due to compaction, the pore size distribution has to be considered. In a compacted soil, the peak of the pore size distribution curve is shifted towards the small pore size. The volume of small pores increases and the unsaturated conductivity decreases substantially, when compared to non-compacted soil. Due to small hydraulic conductivity, the inflow into the roots is well below optimum and the plant closes stomata thus reducing carbon assimilation rate. The effects of soil compaction persisted with plant age although the difference between the two treatments, in terms of percentage, decreased at advanced growth stages, especially in the case of root parameters.     

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.     

Flavonols and anthocyanins of bush butter, Dacryodes edulis (G. Don) H.J. Lam, fruit. changes in their composition during ripening

Dacryodes edulis is a multipurpose tree presently undergoing domestication in central Africa and the countries bordering the Gulf of Guinea, the fruits of which are a good source of essential fatty acids. Polyphenols were characterized in the skin zone and in the pulp of bush butter [Dacryodes edulis (G. Don) H.J. Lam] fruits at different stages of ripeness, from unripe to soft fruits. Total polyphenols, assayed according to the Folin-Ciocalteu method, accounted for 3.0-4.2 mg/g of fresh skin, corresponding to 18.6-21.6 mg/g of defatted dry skin, higher concentrations than in the pulp, with 1.1-1.4 mg/g of fresh weight, corresponding to 5.4-12.3 mg/g of defatted dry weight. Reversed-phase high-performance liquid chromatography revealed the presence of flavonols and anthocyanins. Flavonols appeared to be the main class, with quercitrin as the main individual compound, and the highest concentrations occurred in the skin zone. Hyperin, isoquercitrin, isorhamnetin rhamnoside, and isorhamnetin hexoside were also present in relatively high amounts. Petunidin, cyanidin, and peonidin hexosides were identified by mass spectrometry. In the course of ripening, the total polyphenols as well as the major flavonols increased slightly between unripe and preripe stages and then declined gradually as ripening progressed. Anthocyanin profiles also showed a substantial change during ripening, concomitant with the color change from pink to purple.     

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.     

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.

     

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.     

Detection of Coxiella burnetii, the agent of Q fever, in oviducts and uterine flushing media and in genital tract tissues of the non pregnant goat

The aim of the present study was the detection and quantification of Coxiella burnetii DNA in the flushing media (oviducts and uterine horns) and genital tract tissues of non pregnant goats from 20 goats chosen at random from 86 goats originating from 56 different breeding herds in south-west France. The serological prevalence rate of C. burnetii in the study population was 70.3%.The DNA of C. burnetii was identified using conventional PCR in the flushing media from the oviducts and uterus in 8/20 goats (40%) and in genital tract tissues (oviduct, uterus and ovary) in 5/20 goats (25%). This study clearly shows for the first time that the media used to flush the oviducts or uterine horns, collected using the standard embryo harvesting technique in goats, are susceptible to infection with C. burnetii. The 16 conventional PCR-positive samples were also analyzed using real-time PCR. The bacterial load of the oviduct and uterine flushing media varied from 2.9 × 10⁴ to 7.5 × 10⁶ bacteria per flushing medium, while the bacterial load of the tissue samples varied from 1.0 × 10² to 1.5 × 10⁵ bacteria per mg of tissue. The infection of genital tract flushing media and tissues is a risk factor for the transmission of C. burnetii from donor to recipient during embryo transfer or to the embryo and fetus when gestation is pursued to term.     

Evidence of Brucella sp. infection in marine mammals stranded along the coast of southern New England.

After recent isolations of Brucella sp. from pinnipeds and cetaceans, a survey was initiated to investigate the prevalence of Brucella sp. infections and serologic evidence of exposure in marine mammals stranded along the coasts of Connecticut and Rhode Island. One hundred and nineteen serum samples from four species of cetaceans and four species of pinnipeds were collected from 1985 to 2000 and tested for antibodies to Brucella sp. using the brucellosis card test, buffered acidified plate antigen test, and rivanol test. In addition, 20 of these were necropsied between 1998 and 2000, with lymphoid and visceral tissues cultured for Brucella sp. Three of 21 (14%) harbor seals (Phoca vitulina) and four of 53 (8%) harp seals (Phoca groenlandica) were seropositive. Brucella sp. was isolated from two of four (50%) harbor seals and three of nine (33%) harp seals. Of the five animals with positive cultures, two were seropositive and three seronegative. Brucella sp. was most frequently cultured from the lung and axillary, inguinal, and prescapular lymph nodes. Tissues from which Brucella sp. was isolated showed no gross or histopathologic changes. These results indicate that marine mammals stranded along the coast of southern New England can be exposed to and infected with Brucella sp.     

Monoclonal antibodies to lymphocyte surface antigens for cetacean homologues to CD2, CD19 and CD21.

CD2 is a pan-T cell marker, while CD19 and CD21 are important molecules in signal transduction of B lymphocytes. CD19 and CD21 are both present on mature B cells, while CD19 is also present in developing B cells and plasma cells. Monoclonal antibodies (mAbs) against cetacean lymphocyte putative homologues to CD2 (two different antibodies), CD19 and CD21 were characterized. The proteins immunoprecipitated were as follows: F21.I (putative anti-CD2), 43 and 59kDa; F21.B (putative anti-CD19), 83 and 127kDa; F21.F (putative anti-CD21), 144kDa. The second putative anti-CD2 (F21.C) selectively inhibited the binding of F21.I. Both the putative anti-CD2 (T cell markers) stained T-cell zones on lymph node sections, while both the B cell markers (putative CD19 and CD21) stained B-cell zones. F21.B and F21.F were absent from thymus single cell suspension but labeled 63 and 65% mesenteric lymph node lymphocytes, respectively, while both F21.C and F21.F were present on 100% thymocytes and fewer lymph node lymphocytes. B and T cell markers were mutually exclusive on double labeling using flow cytometry. These mAbs are foreseen as possible valuable diagnostic and research tools to assess immune functions of captive and wild cetaceans.