Distribution of polycyclic aromatic hydrocarbons in subcellular root tissues of ryegrass (Lolium multiflorum Lam.)

Background

Because of the increasing quantity and high toxicity to humans of polycyclic aromatic hydrocarbons (PAHs) in the environment, several bioremediation mechanisms and protocols have been investigated to restore PAH-contaminated sites. The transport of organic contaminants among plant cells via tissues and their partition in roots, stalks, and leaves resulting from transpiration and lipid content have been extensively investigated. However, information about PAH distributions in intracellular tissues is lacking, thus limiting the further development of a mechanism-based phytoremediation strategy to improve treatment efficiency.

Results

Pyrene exhibited higher uptake and was more recalcitrant to metabolism in ryegrass roots than was phenanthrene. The kinetic processes of uptake from ryegrass culture medium revealed that these two PAHs were first adsorbed onto root cell walls, and they then penetrated cell membranes and were distributed in intracellular organelle fractions. At the beginning of uptake (< 50 h), adsorption to cell walls dominated the subcellular partitioning of the PAHs. After 96 h of uptake, the subcellular partition of PAHs approached a stable state in the plant water system, with the proportion of PAH distributed in subcellular fractions being controlled by the lipid contents of each component. Phenanthrene and pyrene primarily accumulated in plant root cell walls and organelles, with about 45% of PAHs in each of these two fractions, and the remainder was retained in the dissolved fraction of the cells. Because of its higher lipophilicity, pyrene displayed greater accumulation factors in subcellular walls and organelle fractions than did phenanthrene.

Conclusions

Transpiration and the lipid content of root cell fractions are the main drivers of the subcellular partition of PAHs in roots. Initially, PAHs adsorb to plant cell walls, and they then gradually diffuse into subcellular fractions of tissues. The lipid content of intracellular components determines the accumulation of lipophilic compounds, and the diffusion rate is related to the concentration gradient established between cell walls and cell organelles. Our results offer insights into the transport mechanisms of PAHs in ryegrass roots and their diffusion in root cells.     

Rice RING protein OsBBI1 with E3 ligase activity confers broad-spectrum resistance against Magnaporthe oryzae by modifying the cell wall defence

Emerging evidence suggests that E3 ligases play critical roles in diverse biological processes, including innate immune responses in plants. However, the mechanism of the E3 ligase involvement in plant innate immunity is unclear. We report that a rice gene, OsBBI1, encoding a RING finger protein with E3 ligase activity, mediates broad-spectrum disease resistance. The expression of OsBBI1 was induced by rice blast fungus Magnaporthe oryzae, as well as chemical inducers, benzothiadiazole and salicylic acid. Biochemical analysis revealed that OsBBI1 protein possesses E3 ubiquitin ligase activity in vitro. Genetic analysis revealed that the loss of OsBBI1 function in a Tos17-insertion line increased susceptibility, while the overexpression of OsBBI1 in transgenic plants conferred enhanced resistance to multiple races of M. oryzae. This indicates that OsBBI1 modulates broad-spectrum resistance against the blast fungus. The OsBBI1-overexpressing plants showed higher levels of H(2)O(2) accumulation in cells and higher levels of phenolic compounds and cross-linking of proteins in cell walls at infection sites by M. oryzae compared with wild-type (WT) plants. The cell walls were thicker in the OsBBI1-overexpressing plants and thinner in the mutant plants than in the WT plants. Our results suggest that OsBBI1 modulates broad-spectrum resistance to blast fungus by modifying cell wall defence responses. The functional characterization of OsBBI1 provides insight into the E3 ligase-mediated innate immunity, and a practical tool for constructing broad-spectrum resistance against the most destructive disease in rice.     

Removal of some polycyclic aromatic hydrocarbons from petrochemical wastewater using low-cost adsorbents of natural origin

Removal of polycyclic aromatic hydrocarbons (PAHs) from petrochemical wastewater was investigated using various low-cost adsorbents of natural origin including sugar cane bagasse, green coconut shells, chitin, and chitosan. Adsorption experiments of mixtures of PAHs (5.0-15.0 mg/L) have been carried out at ambient temperature (28+/-2 degrees C) and pH 7.5. The adsorption isotherms of PAHs were in agreement with a Freundlich model, while the uptake capacity of PAHs followed the order: green coconut shells>sugar cane bagasse>chitin>chitosan. The adsorption properties of green coconut shells were comparable to those of some conventional adsorbents such as Amberlite T. The partition coefficients in acetone:water, the adsorption constants at equilibrium, and the molecular masses of the PAHs could be linearly correlated with octanol-water partition coefficients.     

Degradation of barley straw, ryegrass, and alfalfa cell walls by Clostridium longisporum and Ruminococcus albus

The recently isolated ruminal sporeforming cellulolytic anaerobe Clostridium longisporum B6405 was examined for its ability to degrade barley straw, nonlignified cell walls (mesophyll and epidermis) and lignified cell walls (fiber) of ryegrass, and alfalfa cell walls in comparison with strains of Ruminococcus albus. R. albus strains degraded 20 to 28% of the dry matter in barley straw in 10 days, while the clostridium degraded less than 2%. A combined inoculum of R. albus SY3 and strain B6405 was no more efficient than SY3 alone, and the presence of Methanobacterium smithii PS did not increase the amount of dry matter degraded. In contrast, with alfalfa cell walls as the substrate, the clostridium was twice as active (28% weight loss) as R. albus SY3 (15%). The percentages of dry matter degraded from ryegrass cell walls of mesophyll, epidermis, and fiber for the clostridium were 50, 47, and 32%, respectively, and for R. albus SY3 they were 77, 73, and 63%, respectively. Analyses of the predominant neutral sugars (arabinose, xylose, and glucose) in the plant residues after bacterial attack were consistent with the values for dry matter weight loss. Measurements of the amount of carbon appearing in the fermentation products indicated that R. albus SY3 degraded ryegrass mesophyll cell walls most rapidly, with epidermis and fiber cell walls being degraded at similar rates. Strain B6405 attacked alfalfa cell walls at a rate greater than that of any of the ryegrass substrates. These results indicate an unexpected degree of substrate specificity in the ability of C. longisporum to degrade plant cell wall material.     

Degradation of barley straw, ryegrass, and alfalfa cell walls by Clostridium longisporum and Ruminococcus albus.

The recently isolated ruminal sporeforming cellulolytic anaerobe Clostridium longisporum B6405 was examined for its ability to degrade barley straw, nonlignified cell walls (mesophyll and epidermis) and lignified cell walls (fiber) of ryegrass, and alfalfa cell walls in comparison with strains of Ruminococcus albus. R. albus strains degraded 20 to 28% of the dry matter in barley straw in 10 days, while the clostridium degraded less than 2%. A combined inoculum of R. albus SY3 and strain B6405 was no more efficient than SY3 alone, and the presence of Methanobacterium smithii PS did not increase the amount of dry matter degraded. In contrast, with alfalfa cell walls as the substrate, the clostridium was twice as active (28% weight loss) as R. albus SY3 (15%). The percentages of dry matter degraded from ryegrass cell walls of mesophyll, epidermis, and fiber for the clostridium were 50, 47, and 32%, respectively, and for R. albus SY3 they were 77, 73, and 63%, respectively. Analyses of the predominant neutral sugars (arabinose, xylose, and glucose) in the plant residues after bacterial attack were consistent with the values for dry matter weight loss. Measurements of the amount of carbon appearing in the fermentation products indicated that R. albus SY3 degraded ryegrass mesophyll cell walls most rapidly, with epidermis and fiber cell walls being degraded at similar rates. Strain B6405 attacked alfalfa cell walls at a rate greater than that of any of the ryegrass substrates. These results indicate an unexpected degree of substrate specificity in the ability of C. longisporum to degrade plant cell wall material.     

Chemometric analysis of in-line multi-wavelength fluorescence measurements obtained during cultivations with a lipase producing Aspergillus oryzae strain

The filamentous fungus, Aspergillus oryzae, was cultivated in batch and fed-batch cultivations in order to investigate the use of multi-wavelength fluorescence for monitoring course of events during filamentous fungi cultivations. The A. oryzae strain applied expressed a fungal lipase from Thermomyces lanuginosus. Spectra of multi-wavelength fluorescence were collected every 5 min with the BioView system (DELTA, Denmark) and both explorative and predictive models, correlating the fluorescence data with cell mass and lipase activity, were built. During the cultivations, A. oryzae displayed dispersed hyphal growth and under these conditions no fouling of the multi-wavelength fluorescence sensor was observed. The scores of a parallel factor analysis (PARAFAC) model, based on the fluorescence spectra, gave clear evidence of, for example, the on-set of the feeding phase. The predictive models, estimating the cell mass, showed correlations between 0.73 and 0.97 with root mean square error of cross validation (RMSECV) values between 1.48 and 0.77 g . kg(-1). A model estimating the lipase activity was also constructed for the fed-batch cultivations with a correlation of 0.93. The results presented here clearly show that multi-wavelength fluorescence is a useful tool for monitoring fed-batch cultivations of filamentous fungi.     

Effects of Cosolvent and Temperature on the Desorption of Polynuclear Aromatic Hydrocarbons from Contaminated Sediments of Chien-Jen River,Taiwan

This study evaluated the effects of the water-miscible cosolvent and temperature on the sorption-desorption of polynuclear aromatic hydrocarbons (PAHs) from contaminated sediments in Chien-Jen River, Taiwan. Sediment samples from five sampling stations of downstream section were utilized in this study. Phenanthrene and anthracene were selected as target compounds. The cosolvent effect on sorption of phenanthrene and anthracene was examined by the addition of various volume fractions of methanol (i.e., 0.3, 0.5, 0.7, and 0.9, respectively) in the sediment/water systems. The utility of the log-linear cosolvency model for predicting PAH sorption from solvent mixtures was evaluated. An inverse relationship was observed for sorption coefficients of phenanthrene and anthracene as a function of increasing cosolvent. The effect of temperature on sorption of phenanthrene and anthracene was conducted at temperature from 10°C to 40°C. The use of elevated temperatures in desorption experiments increased the PAH release from sediments. It was observed that sorption of phenanthrene and anthracene onto sediments decreased when temperature increased. The decrease of sorption coefficient of phenanthrene was more sensitive than that of anthracene. The magnitude of decreased sorption was attributed by the increased desorption rate constant, solubility, and heterogeneities of sediments.     

Immediate and delayed mortality of Rhyzopertha dominica (Coleoptera: Bostrichidae) and Sitophilus oryzae (Coleoptera: Curculionidae) adults exposed to spinosad-treated commodities

A series of tests was conducted to characterize differences in the mortality of the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), and rice weevil, Sitophilus oryzae (L.) (Coleoptera: Curculionidae), exposed to three commodities treated with a liquid and dry spinosad formulation. In laboratory bioassays, adults of the two insect species were exposed to untreated wheat, Triticum aestivum L., corn, Zea mays L., and sorghum, Sorghum bicolor (L.) Moench., and to commodities treated with 1 mg (AI)/kg of liquid and dry spinosad formulations. Mortality was assessed from independent samples examined at specific time intervals to determine immediate mortality and after 24 h of recovery on untreated grain at 28 degrees C and 65% RH to determine delayed mortality. Comparison of the time required for 50% (LT50) and 95% (LT95) mortality indicated that R. dominica adults were consistently and significantly more susceptible (died quickly) than S. oryzae adults when exposed to spinosad-treated commodities. In general, the toxicity of liquid and dry spinosad formulations was similar against R. dominica or S. oryzae. The toxicity of spinosad to each species varied slightly among the three commodities, and there were no consistent trends to suggest that spinosad was more effective on one commodity versus another. LT50 values based on immediate mortality for R. dominica on all commodities ranged from 0.45 to 0.74 d; corresponding values based on delayed mortality ranged from 0.04 to 0.23 d, suggesting delayed toxic action of spinosad in R. dominica. LT50 values based on immediate and delayed mortality for S. oryzae on all three commodities treated with the two spinosad formulations were essentially similar and ranged from 2.75 to 4.56 d. LT95 values for R. dominica based on immediate mortality on spinosad-treated commodities ranged from 1.75 to 3.36 d, and those based on delayed mortality ranged from 0.49 to 1.88 d. There were no significant differences in LT95 values based on immediate and delayed mortality for S. oryzae on spinosad-treated commodities, and the LT95 values ranged from 7.62 to 18.87 d. The toxicity of spinosad was enhanced during a 24-h holding period after removal from spinosad-treated commodities only against R. dominica adults, and possible reasons for increased postexposure mortality of R. dominica adults after brief exposures to spinosad warrant further study.     

Genetic alteration of pore size and other properties of the Neurospora cell wall

Trevithick, John R. (University of Wisconsin Medical School, Madison), Robert L. Metzenberg and Donald F. Costello. Genetic alteration of pore size and other properties of the Neurospora cell wall. J. Bacteriol. 92:1016-1020. 1966.-Several properties of the cell walls of wild type and the osmotic mutant of Neurospora crassa have been examined. The peameability of the isolated cell walls to polyethylene glycol and dextran polymers of different molecular weights was investigated by the volume of distribution technique. The exclusion thresholds were evaluated by a statistical treatment. The molecular weights corresponding to these thresholds for wild type and osmotic were approximately 4,750 and 18,500, respectively; these values are significantly different. The cell walls of osmotic appeared to be thinner, more easily broken, and more easily compressed to ribbonlike shapes, whereas those of wild type were tubular and strong. Chemical analysis showed that osmotic walls had roughly a 30-fold higher galactosamine-glucosamine ratio than did wild type. It is proposed that the osmotic mutant has a cell wall with abnormally large pores, and that this may account for the increased rate of egress of invertase and the decreased fractionation of light from heavy invertase in this strain.     

Measurement of biodegradability parameters for single unsubstituted and methylated polycyclic aromatic hydrocarbons in liquid bacterial suspensions

Substrate depletion experiments were conducted to characterize aerobic biodegradation of 20 single polycyclic aromatic hydrocarbons (PAHs) by induced Sphingomonas paucimobilis strain EPA505 in liquid suspensions. PAHs consisted of low molecular weight, unsubstituted, and methyl-substituted homologs. A material balance equation containing the Andrews kinetic model, an extension of the Monod model accounting for substrate inhibition, was numerically fitted to batch depletion data to estimate extant kinetic parameters including the maximal specific uptake rates, q(max), the affinity coefficients, K(S), and the substrate inhibition coefficients, K(I). Strain EPA505 degraded all PAHs tested. Applied kinetic models adequately simulated experimental data. A cell proliferation assay involving reduction of the tetrazolium dye WST-1 was used to evaluate the ability of strain EPA505 to utilize individual PAHs as sole energy and carbon sources. Of the 22 PAHs tested, 9 supported bacterial growth. Evaluation of the biokinetic data showed that q(max) correlated highly with transmembrane flux as theoretically estimated by a diffusion model, pointing to transmembrane transport as a potential rate-determining process. The biodegradability data generated in this study is essential for the development of quantitative structure-activity relationships (QSARs) for biodegradability and for modeling biodegradation of simple PAH mixtures.     

Mobility and Persistence of Petroleum Hydrocarbons in Peat Soils of Southeastern Mexico

Spilled crude petroleum from oil wells contains numerous hydrocarbons, some of which are toxic and threaten life. We have studied the mobility and persistence of hydrocarbons in waterlogged soils that contain large proportions of fermented organic matter (Histosols) and large concentrations of dissolved organic carbon (DOC) in the State of Tabasco, Mexico. We sampled soil and phreatic water at sites polluted by oil spills for several decades, as well as at sites that had only recently (few weeks) been polluted, and compared their hydrocarbon contents with those of unaffected sites in the same area. Samples were analyzed for 16 non-alkylated polyaromatic hydrocarbons (PAHs) and n-alkanes from nC9 to nC34. The spilled hydrocarbons had remained predominantly in the organic surface horizons of the soil where spillage occurred; there was little evidence of movement within the soil. The fraction of low molecular weight compounds was larger at sites of recent spills than where spills happened several decades ago. Nevertheless, sites of old spills still contained large concentrations of hydrocarbons, among which those of low molecular weight represented from 30 to 49% of total PAHs and from 50 to 84% of total n-alkanes, indicating that volatilization or microbial degradation is slow in these soils. In the peat horizons the measured organic carbon partition coefficients (K _oc ) for the higher molecular weight PAHs were consistently smaller than those estimated by empirical equations by up to two orders of magnitude. The dissolved organic carbon of these peat soils seems to influence this behavior. At sites of old spills, partition coefficients for the PAHs were larger than at sites of recent spills.     

Partitioning of polycyclic aromatic hydrocarbons between plant roots and water

Partition of phenanthrene between water and roots was determined for 13 plant species using a batch equilibration technique. Partition coefficients (K _rt) from 734 to 2,564 L/kg were measured. A simple model to estimate the partition of organic contaminants between roots and water was developed based on the composition of plant roots and the 1-octanol/water partitioning coefficient. The estimates were close to the observed results, with differences of < 14%. The partition coefficients of phenanthrene by root cell walls were 13–84% greater than sorption by the corresponding roots. The cell wall fraction—the dominant fraction of root organic components—was identified as the primary domain for partition of phenanthrene. The measured hydroponic uptake of phenanthrene into roots was always less than phenanthrene partition by plant roots. A modified sorption model containing a quasi-equilibrium factor (α_pt) could reasonably predict hydroponic uptake by plant roots. The results obtained from this study provide insights into partition of highly lipophilic organic chemicals in roots, and provide convenient methods to estimate this partition as well as uptake of such chemicals in root–water systems.     

Omiganan interaction with bacterial membranes and cell wall models. Assigning a biological role to saturation

Omiganan pentahydrochloride (ILRWPWWPWRRK-NH(2).5Cl) is an antimicrobial peptide currently in phase III clinical trials. This study aims to unravel the mechanism of action of this drug at the membrane level and address the eventual protective role of peptidoglycan in cell walls. The interaction of omiganan pentahydrochloride with bacterial and mammalian membrane models - large unilamellar vesicles of different POPC:POPG proportions - was characterized by UV-Vis fluorescence spectroscopy. The molar ratio partition constants obtained for the two anionic bacterial membrane models were very high ((18.9+/-1.3)x10(3) and (43.5+/-8.7)x10(3)) and about one order of magnitude greater than for the neutral mammalian models ((3.7+/-0.4)x10(3) for 100% POPC bilayers). At low lipid:peptide ratios there were significant deviations from the usual hyperbolic-like partition behavior of peptide vesicle titration curves, especially for the most anionic systems. Membrane saturation can account for such observations and mathematical models were derived to further characterize the peptide-lipid interaction under those conditions; a possible relation between saturation and MIC was deduced; this was supported by differential quenching studies of peptide internalization. Interaction with the bacterial cell wall was assessed using Staphylococcus aureus peptidoglycan extracts as a model. A strong partition towards the peptidoglycan mesh was observed, but not as large as for the membrane models.     

Changes in germ cell population in young and adult female mice from two inbred strains: CBA/Kw and KE

Female mice from two inbred strains CBA/Kw and KE differ markedly in fertility. The gametes of females from KE strain are of poorer quality than those of CBA/Kw. We analyzed the number of oocytes per ovary in KE and CBA/Kw mice aged 5, 25, 90, 180 and 360 days. The ovaries were dissected and processed according to the routine histological methods. In case of five-day-old females we used a modified distributed point counting method while in order to examine the gonads of older females, the nucleoli counting method was applied. In general, we observed gradual decrease in germ cell number throughout the whole life of females from both strains. The noticeable wave of oocyte loss occurs between 5th and 25th days of life. The mice from KE inbred strain on day 25th (1650 +/- 322 vs. 1140 +/- 210) and 90(th) (1040 +/- 211 vs. 692 +/- 89) days have significantly (p<0.005) more germ cells than the females from CBA/Kw strain. In older females the differences were not statistically significant. Interestingly, CBA/Kw females were found to have more rapid loss of primordial follicles throughout their lives. This can explain their shortened reproductive lifespan which was observed earlier.     

Lignification and cell wall thickening in nodes of Phyllostachys viridiglaucescens and Phyllostachys nigra

BACKGROUND AND AIMS: Bamboos are among the most important plants in the world. The anatomical structure and mechanical properties of the culm internode are well documented. Fewer details are available of the culm node. The aim of this study was a topochemical investigation on lignification and cell wall thickening in developing and maturing bamboo nodes. The deposition sequence and distribution of lignin structural units and cell wall thickening in different anatomical regions of the node of Phyllostachys viridiglaucescens and Phyllostachys nigra are discussed. METHODS: Cell wall thickening and lignification are investigated in the outer part of the nodal region and in the diaphragm of developing and maturing P. nigra culms and in maturing culms of P. viridiglaucescens of different age classes. The lignification during ageing was studied topochemically by means of cellular UV microspectrophotometry. A combination of light microscopy and image analysis techniques were used to measure cell wall thickness. KEY RESULTS: The fibre and parenchyma cell wall thickness does not significantly increase during ageing. In the diaphragm, the cell walls are thinner and the cell diameter is larger than in the outer part of the node. In shoots, the lignin content in the epidermis, hypodermis and in both fibre and parenchyma cells of the diaphragm is relatively low compared with older culms. The fibre and parenchyma cells of the diaphragm have higher values of p-coumaric and ferulic acids than fibre and parenchyma cells of the outer part of the node. CONCLUSIONS: It was hypothesized that the combination of more hydroxycinnamic acids and of thinner cell walls in combination with higher cell diameters (lower density and lower stiffness) in the diaphragm than in the outer part of the node may play an important role in the biomechanical function of the node by acting as a spring-like joint to support the culm by bending forces.     

Characterization of the last step of lignin biosynthesis in Zinnia elegans suspension cell cultures

The last step of lignin biosynthesis in Zinnia elegans suspension cell cultures (SCCs) catalyzed by peroxidase (ZePrx) has been characterized. The k(3) values shown by ZePrx for the three monolignols revealed that sinapyl alcohol was the best substrate, and were proportional to their oxido/reduction potentials, signifying that these reactions are driven exclusively by redox thermodynamic forces. Feeding experiments demonstrate that cell wall lignification in SCCs is controlled by the rate of supply of H(2)O(2). The results also showed that sites for monolignol beta-O-4 cross-coupling in cell walls may be saturated, suggesting that the growth of the lineal lignin macromolecule is not infinite.     

Plant and algal cell walls: diversity and functionality

Background

Although plants and many algae (e.g. the Phaeophyceae, brown, and Rhodophyceae, red) are only very distantly related they are united in their possession of carbohydrate-rich cell walls, which are of integral importance being involved in many physiological processes. Furthermore, wall components have applications within food, fuel, pharmaceuticals, fibres (e.g. for textiles and paper) and building materials and have long been an active topic of research. As shown in the 27 papers in this Special Issue, as the major deposit of photosynthetically fixed carbon, and therefore energy investment, cell walls are of undisputed importance to the organisms that possess them, the photosynthetic eukaryotes (plants and algae). The complexities of cell wall components along with their interactions with the biotic and abiotic environment are becoming increasingly revealed.

Scope

The importance of plant and algal cell walls and their individual components to the function and survival of the organism, and for a number of industrial applications, are illustrated by the breadth of topics covered in this issue, which includes papers concentrating on various plants and algae, developmental stages, organs, cell wall components, and techniques. Although we acknowledge that there are many alternative ways in which the papers could be categorized (and many would fit within several topics), we have organized them as follows: (1) cell wall biosynthesis and remodelling, (2) cell wall diversity, and (3) application of new technologies to cell walls. Finally, we will consider future directions within plant cell wall research. Expansion of the industrial uses of cell walls and potentially novel uses of cell wall components are both avenues likely to direct future research activities. Fundamentally, it is the continued progression from characterization (structure, metabolism, properties and localization) of individual cell wall components through to defining their roles in almost every aspect of plant and algal physiology that will present many of the major challenges in future cell wall research.