Outer Cell Wall Research Articles

EFFECT OF THE PERISTOMATAL RIM UPON STOMATAL MOVEMENTS IN <i>POPULUS MEXICANA</i> (SALICACEAE)

Light and scanning electron microscopy were used to study the stomatal complexes of Populus mexicana, which has xeromorphic leaf structure. In this poplar, the stomatal complexes are laterocytic and paracytic. The subsidiary cell walls form the peristomatal rim, which rests upon the outer tangential walls of the guard cells. To elucidate the function of the peristomatal rim, we applied modelling using the finite element method. The modelling has shown that the inner and the outer tangential walls of the guard cells bend outward when the stoma is opening. The peristomatal rim hinders the movements of the outer tangential walls of the guard cells. Due to the peristomatal rim, the open stomatal pore sinks deeper into the epidermis. It is narrower and better covered with the outer stomatal ledges, than the one in the stomatal complex without peristomatal rim. The probability of influence of stomatal mechanics in P. mexicana upon water losses during transpiration is under discussion.

An ABCB transporter regulates anisotropic cell expansion via cuticle deposition in the moss Physcomitrium patens.

Anisotropic cell expansion is crucial for the morphogenesis of land plants, as cell migration is restricted by the rigid cell wall. The anisotropy of cell expansion is regulated by mechanisms acting on the deposition or modification of cell wall polysaccharides. Besides the polysaccharide components in the cell wall, a layer of hydrophobic cuticle covers the outer cell wall and is subjected to tensile stress that mechanically restricts cell expansion. However, the molecular machinery that deposits cuticle materials in the appropriate spatiotemporal manner to accommodate cell and tissue expansion remains elusive. Here, we report that PpABCB14, an ATP-binding cassette transporter in the moss Physcomitrium patens, regulates the anisotropy of cell expansion. PpABCB14 localized to expanding regions of leaf cells. Deletion of PpABCB14 resulted in impaired anisotropic cell expansion. Unexpectedly, the cuticle proper was reduced in the mutants, and the cuticular lipid components decreased. Moreover, induced PpABCB14 expression resulted in deformed leaf cells with increased cuticle lipid accumulation on the cell surface. Taken together, PpABCB14 regulates the anisotropy of cell expansion via cuticle deposition, revealing a regulatory mechanism for cell expansion in addition to the mechanisms acting on cell wall polysaccharides.

Numerical study on energy absorption performance of novel bionic helmet liner

In this paper, by introducing the pyramid-shaped spine configuration of durian shells and bidirectional corrugated configuration of jaw feet of mantis shrimps into the helmet liner, a bidirectional staggered rectangular frustum liner was designed. Finite element simulation of impact was carried out on liners with various pyramid-shaped cell structures, and the kinetic behavior of the liners of different structures during impact compression was studied. The results showed that the decrease in the inclination angle of the outer walls of pyramid-shaped cells and the bidirectional-cell design can both improve the specific energy absorption of the helmet, and that the bidirectional staggered rectangular frustum helmet has the highest specific energy absorption, 2.7 times that of the gradient lattice or 1.3 times that of the honeycomb helmet. This is because the bidirectional staggered rectangular frustum cell design enhances the connection between adjacent cell walls, resulting in a larger deformation area during the impact process and participation of more material in energy storage, thus significantly improving the overall energy absorption performance.

Exogenous N-hexanoyl-l-homoserine lactone mitigates acid rain stress effects through modulation of structural and functional changes in Triticum aestivum leaf

Acid rain (AR) is a global environmental problem that causes a number of morphological, physiological and molecular changes in plants. N-acyl homoserine lactones, as bacterial quorum sensing signal molecules, mediate a number of physiological processes in plants. In this study, we have demonstrated for the first time the stress-protective role of AHL foliar treatment under conditions of abiotic stress - acid rain. The effects of simulated acid rain (SAR), treatment of plants with N-hexanoyl-l-homoserine lactone (C6-HSL) solution, and a combination of these two factors on the microstructure of the leaf surface, photosynthetic pigments, secondary metabolites, and lipoxygenase activity in winter wheat plants were analyzed. It was established that on the fourth day following treatment of 14-day-old plants with C6-HSL, the thickness of the outer cell wall of the leaf epidermis, together with the cuticle layer, increased by 15 %. SAR treatment resulted in a significant thinning of the cell wall (33 %), while pretreatment with C6-HSL followed by SAR reduced cell wall thickness by only 9 %. Under SAR, the cuticular wax layer was destroyed and there were unequal wax lamellae on the epidermal surface, while in C6-HSL treated plants only partial cracking of the cuticular wax layer, slight destruction of the wax lamellae, and formation of wax crusts took place. C6-HSL induced a significant increase in total chlorophyll content under non-SAR conditions, and significantly mitigated the decrease of total chlorophyll content caused by SAR. Lipoxygenase activity, the content of total phenols, flavonoids, and proline increased after treatment of plants with C6-HSL solution alone and in combination with SAR. This is the first report on the possibility of using C6-HSL as an ecological biostimulator under conditions of AR.

Preparation of Teakwood Bending Components with Excellent Softening Properties by Vacuum Impregnation with Triethanolamine Compounding Solution

To study the softening bending properties and mechanism of teakwood, it was extractively pretreated by using superheated steam, the triethanolamine compound was used as a softening solution, which was infiltrated into the wood by vacuum impregnation and synergistically softened through saturated steam to improve the bending properties of teakwood. Analysis by Fourier transform infrared spectroscopy (FTIR), Carbon 13 nuclear magnetic resonance (13C NMR), and X-ray photoelectron spectroscopy (XPS) showed that the synergistic softening treatment elevated the content of O and N elements in the softening solution and together with the C elements in the wood, formed C-NH2 and C-N bonds, which increased the molecular activity and improved the softening properties of teakwood. Scanning electron microscope (SEM) observations revealed that the outer conduits, cell walls, and fibrous tissue structures of the teakwood were stretched after softening and bending, and even microcracks of different degrees were formed between the cell walls. According to the load–deformation relationship of teakwood softening bending, the stress–strain relationship was theoretically derived and the bifold constitutive model of teakwood bending was constructed after fitting the constitutive relationship data, the integrated correlation coefficient R2 was 96.25%, which proved that the present model can better simulate the constitutive relationship of teakwood in bending.

The Potential of Paulownia fortunei L. for the Phytoremediation of Pb

Pb endangers forest ecological health; phytoremediation is an effective Pb remediation technology. Woody plants with Pb tolerance provided a mechanism for the phytoremediation of Pb. Paulownia fortunei (L.), a fast-growing woody plant, has a good tolerance to Pb. However, its tolerance mechanism is unclear. The results in this study revealed that P. fortunei seedlings can withstand 400 mg·L−1 Pb stress. The quantification of Pb in different P. fortunei tissues showed an increasing trend of accumulation in root > leaf > stem; the transport coefficient and enrichment coefficient decreased with an increase in Pb concentration. The tolerance of P. fortunei to Pb may be related to cell partition and immobilization by the cell wall. Microstructural analysis performed using scanning electron microscopy showed that the absorbed Pb is mainly distributed in cell wall components, and when the concentration of Pb increases, it can be transferred to soluble parts and organelles. The Fourier transform infrared spectrometry results showed that excess hydroxyl groups occurred under Pb stress in the outer epidermis cell walls of roots and leaves adsorbing heavy metals. When the concentration of Pb was over 400 mg·L−1, the growth of P. fortunei was inhibited, the root cell wall was deformed, the plasmolysis occurred in the cauline cell, and the internal leaf capsule was ruptured. Furthermore, antioxidant enzyme activity was significantly reduced. Therefore, P. fortunei can transfer the underground part of Pb to the aboveground part up to the concentration of 400 mg·L−1. This study provides a theoretical basis and technical reference for fully utilizing woody plant resources to restore the ecological environment of forests.

Probing stress-regulated ordering of the plant cortical microtubule array via a computational approach

BackgroundMorphological properties of tissues and organs rely on cell growth. The growth of plant cells is determined by properties of a tough outer cell wall that deforms anisotropically in response to high turgor pressure. Cortical microtubules bias the mechanical anisotropy of a cell wall by affecting the trajectories of cellulose synthases in the wall that polymerize cellulose microfibrils. The microtubule cytoskeleton is often oriented in one direction at cellular length-scales to regulate growth direction, but the means by which cellular-scale microtubule patterns emerge has not been well understood. Correlations between the microtubule orientation and tensile forces in the cell wall have often been observed. However, the plausibility of stress as a determining factor for microtubule patterning has not been directly evaluated to date.ResultsHere, we simulated how different attributes of tensile forces in the cell wall can orient and pattern the microtubule array in the cortex. We implemented a discrete model with transient microtubule behaviors influenced by local mechanical stress in order to probe the mechanisms of stress-dependent patterning. Specifically, we varied the sensitivity of four types of dynamic behaviors observed on the plus end of microtubules – growth, shrinkage, catastrophe, and rescue – to local stress. Then, we evaluated the extent and rate of microtubule alignments in a two-dimensional computational domain that reflects the structural organization of the cortical array in plant cells.ConclusionOur modeling approaches reproduced microtubule patterns observed in simple cell types and demonstrated that a spatial variation in the magnitude and anisotropy of stress can mediate mechanical feedback between the wall and of the cortical microtubule array.

Hybrid materials based on chitosan functionalized with green synthesized copper nanoparticles: Physico-chemical and antimicrobial analysis

Recently, the development of materials with antimicrobial properties has become a challenge under scrutiny. The incorporation of copper nanoparticles (NpCu) into a chitosan matrix appears to represent a viable strategy to contain the particles and prevent their oxidation. Regarding the physical properties, the nanocomposite films (CHCu) showed a decrease in the elongation at break (5 %) and an increase in the tensile strength of 10 % concerning chitosan films (control). They also showed solubility values lower than 5 % while the swelling diminished by 50 %, on average. The dynamical mechanical analysis (DMA) of nanocomposites revealed two thermal events located at 113° and 178 °C, which matched the glass transitions of the CH-enriched phase and nanoparticles-enriched phase, respectively. In addition, the thermogravimetric analysis (TGA) detected a greater stability of the nanocomposites. Chitosan films and the NpCu-loaded nanocomposites demonstrated excellent antibacterial capacity against Gram-negative and Gram-positive bacteria, proved through diffusion disc, zeta potential, and ATR-FTIR techniques. Additionally, the penetration of individual NpCu particles into bacterial cells and the leakage of cell content were verified by TEM. The mechanism of the antibacterial activity of the nanocomposites involved the interaction of chitosan with the bacterial outer membrane or cell wall and the diffusion of the NpCu through the cells.These materials could be applied in diverse fields of biology, medicine, or food packaging.

A Clinically Selected Staphylococcus aureus clpP Mutant Survives Daptomycin Treatment by Reducing Binding of the Antibiotic and Adapting a Rod-Shaped Morphology.

Daptomycin is a last-resort antibiotic used for the treatment of infections caused by Gram-positive antibiotic-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA). Treatment failure is commonly linked to accumulation of point mutations; however, the contribution of single mutations to resistance and the mechanisms underlying resistance remain incompletely understood. Here, we show that a single nucleotide polymorphism (SNP) selected during daptomycin therapy inactivates the highly conserved ClpP protease and is causing reduced susceptibility of MRSA to daptomycin, vancomycin, and β-lactam antibiotics as well as decreased expression of virulence factors. Super-resolution microscopy demonstrated that inactivation of ClpP reduced binding of daptomycin to the septal site and diminished membrane damage. In both the parental strain and the clpP strain, daptomycin inhibited the inward progression of septum synthesis, eventually leading to lysis and death of the parental strain while surviving clpP cells were able to continue synthesis of the peripheral cell wall in the presence of 10× MIC daptomycin, resulting in a rod-shaped morphology. To our knowledge, this is the first demonstration that synthesis of the outer cell wall continues in the presence of daptomycin. Collectively, our data provide novel insight into the mechanisms behind bacterial killing and resistance to this important antibiotic. Also, the study emphasizes that treatment with last-line antibiotics is selective for mutations that, like the SNP in clpP, favor antibiotic resistance over virulence gene expression.

Diversity of staminal nectariferous appendages in disymmetric and zygomorphic flowers of Fumarioideae (Papaveraceae).

Staminal nectaries show diversity in their position, size, shape, color, and number in Ranunculales. In Papaveraceae, nectaries only appear at the base of stamen in these lineages with disymmetric and zygomorphic flowers. However, the diversity of the staminal nectaries' developmental characteristics and structure is unknown. The diversity of staminal nectaries of Hypecoum erectum, Ichtyoselmis macrantha, Adlumia asiatica, Dactylicapnos torulosa, Corydalis edulis, and Fumaria officinalis (six species belonging to six genera, respectively) in the Fumarioideae was investigated under scanning electron microscopy, light microscopy, and transmission electron microscopy. In all species studied, according to the developmental characteristics of the nectaries, four developmental stages can be divided into initiation, enlargement, differentiation, and maturation, and the number of nectaries can be determined at the stage of initiation (stage 1), and morphological differentiation occurs at the developmental stage 3. The staminal nectaries consist of secretory epidermis, parenchyma tissue, and phloem with some sieve tube elements reaching the secretory parenchyma cells; however, the number of cell layers of parenchyma can vary from 30 to 40 in I. macrantha and D. torulosa, to only 5 to 10 like in F. officinalis. Secretory epidermis cells are larger than secretory parenchyma cells with abundant microchannels on the outer cell wall. There were abundant mitochondria, Golgi bodies, rough endoplasmic reticulum, and plastids in secretory parenchyma cells. Nectar is stored in the intercellular space and exuded to the exterior via microchannels. In A. asiatica, according to the evidence of small secretory cell characteristics such as dense cytoplasm, and numerous mitochondria, together with the filamentous secretions present on the surface of epidermal cells on groove, it can be inferred that the U-shaped sulcate which is located in the white projection formed at the filament of triplets in A. asiatica is nectariferous.

Heterogeneity of Lipopolysaccharide as Source of Variability in Bioassays and LPS-Binding Proteins as Remedy.

Lipopolysaccharide (LPS), also referred to as endotoxin, is the major component of Gram-negative bacteria's outer cell wall. It is one of the main types of pathogen-associated molecular patterns (PAMPs) that are known to elicit severe immune reactions in the event of a pathogen trespassing the epithelial barrier and reaching the bloodstream. Associated symptoms include fever and septic shock, which in severe cases, might even lead to death. Thus, the detection of LPS in medical devices and injectable pharmaceuticals is of utmost importance. However, the term LPS does not describe one single molecule but a diverse class of molecules sharing one common feature: their characteristic chemical structure. Each bacterial species has its own pool of LPS molecules varying in their chemical composition and enabling the aggregation into different supramolecular structures upon release from the bacterial cell wall. As this heterogeneity has consequences for bioassays, we aim to examine the great variability of LPS molecules and their potential to form various supramolecular structures. Furthermore, we describe current LPS quantification methods and the LPS-dependent inflammatory pathway and show how LPS heterogeneity can affect them. With the intent of overcoming these challenges and moving towards a universal approach for targeting LPS, we review current studies concerning LPS-specific binders. Finally, we give perspectives for LPS research and the use of LPS-binding molecules.

Transcriptomic Profile of Penicillium digitatum Reveals Novel Aspects of the Mode of Action of the Antifungal Protein AfpB.

Antifungal proteins (AFPs) from filamentous fungi are promising biomolecules to control fungal pathogens. Understanding their biological role and mode of action is essential for their future application. AfpB from the citrus fruit pathogen Penicillium digitatum is highly active against fungal phytopathogens, including its native fungus. Our previous data showed that AfpB acts through a multitargeted three-stage process: interaction with the outer mannosylated cell wall, energy-dependent cell internalization, and intracellular actions that result in cell death. Here, we extend these findings by characterizing the functional role of AfpB and its interaction with P. digitatum through transcriptomic studies. For this, we compared the transcriptomic response of AfpB-treated P. digitatum wild type, a ΔafpB mutant, and an AfpB-overproducing strain. Transcriptomic data suggest a multifaceted role for AfpB. Data from the ΔafpB mutant suggested that the afpB gene contributes to the overall homeostasis of the cell. Additionally, these data showed that AfpB represses toxin-encoding genes, and they suggest a link to apoptotic processes. Gene expression and knockout mutants confirmed that genes coding for acetolactate synthase (ALS) and acetolactate decarboxylase (ALD), which belong to the acetoin biosynthetic pathway, contribute to the inhibitory activity of AfpB. Moreover, a gene encoding a previously uncharacterized extracellular tandem repeat peptide (TRP) protein showed high induction in the presence of AfpB, whereas its TRP monomer enhanced AfpB activity. Overall, our study offers a rich source of information to further advance in the characterization of the multifaceted mode of action of AFPs. IMPORTANCE Fungal infections threaten human health worldwide and have a negative impact on food security, damaging crop production and causing animal diseases. At present, only a few classes of fungicides are available due to the complexity of targeting fungi without affecting plant, animal, or human hosts. Moreover, the intensive use of fungicides in agriculture has led to the development of resistance. Therefore, there is an urgent need to develop antifungal biomolecules with new modes of action to fight human-, animal-, and plant-pathogenic fungi. Fungal antifungal proteins (AFPs) offer great potential as new biofungicides to control deleterious fungi. However, current knowledge about their killing mechanism is still limited, which hampers their potential applicability. AfpB from P. digitatum is a promising molecule with potent and specific fungicidal activity. This study further characterizes its mode of action, opening avenues for the development of new antifungals.

Changes in Density of Cellulose Microfibrils in Cell Wall Lamellae during Cell Growth in the Giant-Celled Green Alga <i>Valonia utricularis</i>

Cell walls in the giant-celled green alga Valonia are composed of multiple lamellae and designated as “crossed-fibril” type wherein each lamella contains cellulose microfibrils (CMFs) arranged in a uniform orientation. Outer, older lamellae are thinner than inner, younger lamellae, probably because the former are extended during cell growth more so than the latter without deposition of new cell wall materials. If this hypothesis is correct, the density of CMFs in the outer lamellae should be lower than that in the inner lamellae. In the present study, the density of CMFs in the outermost lamellae of the cell wall, in various sizes of Valonia utricularis growing cells, was calculated using images obtained with an atomic force microscope, and the densities were compared among the cells of different sizes. The CMF density ranged from 0.5 to 4.0 µm−1, which is lower than that previously recorded for the innermost lamellae (more than 10 µm−1). Moreover, the CMF density was negatively correlated with the cell size indicating that spacing between neighboring CMFs was increased by the cell surface extension due to cell growth. These findings may support the abovementioned hypothesis that the outer cell wall lamellae are extended by cell growth without the deposition of new CMFs.

Comparison between the anatomical structures of inhabited and uninhabited domatium in two species of genus Rhamnus L. (Rhamnaceae)

IntroductionDomatia are small structures usually located on the underside of leaf, in the axils of the major veins. They are related to a mutualism between plants and small animals (arthropods) such as mites or ants. There is a large ecological background on domatia, but only a few detailed reports on their anatomy, and less information on the histological changes resulting from plant-mite interaction within domatia. There are many species of the genus Rhamnus L. that have leaf domatia, which anatomical structure is known, but the anatomical differences between inhabited and uninhabited domatia have not been studied. In this work, Rhamnus alaternus L. and Rhamnus ludovici-salvatoris Chod. are studied to know the differences between the anatomy of inhabited and uninhabited domatia and to assess the plant response to the presence of domatium inhabitant. MethodAnatomical study focused on examining epidermis and subepidermal collenchyma in the leaf blade, uninhabited domatium and inhabited domatium and a comparison were performed. The anatomical structure of the non-domatia leaf lamina is used to contrast the changes and to better understand the domatia and the effect of inhabitants. ResultsThe structure of the domatium shows certain differences from the structure of the non-domatia leaf blade. In the domatium, there is a thickening of the outer cell walls of the epidermis, a disordered appearance of the epidermis and subepidermal collenchyma, and larger and more abundant trichomes. The inhabited domatia had more disorder in the epidermis and subepidermal collenchyma. ConclusionsThe presence of inhabitants in the domatium is related to a major alteration of the tissue structure. However, the location of the epidermis and collenchyma, as well as the presence, location and type of domatia do not vary.

A new species of the red alga Erythrotrichia (Erythropeltales, Rhodophyta) from Korea: Erythrotrichia johnawestii sp. nov. and observations in culture

Abstract Four species of Erythrotrichia (E. biseriata, E. reflexa, E. tetraseriata, E. carnea) have been reported in Korea, but phylogenetic studies have not been conducted on them. We analyzed two newly collected Erythrotrichia isolates using rbcL DNA sequences and determined their species status using four DNA-based species delimitation methods. One isolate (KNU-1) grouped with E. carnea in three methods: Assemble Species by Automatic Partitioning, both single-threshold and multiple-threshold general mixed yule coalescent, but grouped as a distinct species in the statistical parsimony network analysis. A second isolate (KNU-2) was considered a distinct species in all the above species-delimitation methods. We propose the name, Erythrotrichia johnawestii sp. nov., for this new species. The new species was different from E. carnea in lacking a thick outer cell wall layer and with a smaller cell size. Mature monosporangia produced raised openings that released monospores. Cell walls were not detected in newly released monospores but began to appear when the spore attached to the substratum and produced rhizoids. Sexual reproduction was not observed during the four-year culture period.

The plant cuticle

The plant cuticle is one of the key innovations that allowed plants to colonize terrestrial ecosystems. By limiting molecular diffusion, the cuticle provides an interface that ensures controlled interactions between plant surfaces and their environments. It confers diverse and sometimes astonishing properties upon plant surfaces at both the molecular level (from water and nutrient exchange capacities to almost complete impermeability), to the macroscopic level (from water repellence to iridescence). It takes the form of a continuous modification of the outer cell wall of the plant epidermis from early in plant development (surrounding the epidermis of the developing plant embryo) and is actively maintained and modified throughout the growth and development of most plant aerial organs - including non-woody stems, flowers, leaves, and even the root cap of emerging primary and lateral roots. The cuticle was first identified as a distinct structure in the early 19th century, and has since been the focus of intense research that, while revealing the fundamental role of the cuticle in the life of terrestrial plants, has also highlighted many unresolved mysteries regarding cuticle biogenesis and structure.

Apatite-coated Ag/AgBr/TiO2 nanocomposites: Insights into the antimicrobial mechanism in the dark and under visible-light irradiation

For the first time, titania-based photocatalysts with different crystalline compositions (anatase/rutile) and morphology (irregular and faceted nanoparticles) were modified with Ag/AgBr and apatite (HA). The antimicrobial activity was tested for Escherichia coli (E. coli) bacteria and Candida albicans (C. albicans) fungi under visible-light illumination and in the dark for HA-covered and uncovered nanocomposites. It has been found that antimicrobial inactivation mechanism follows two different pathways, depending on the conditions (dark vs. irradiation), i.e., HA loading on the photocatalyst surface affects only the microorganism nourishment from the surrounding media (growth inhibition) in the dark, but significantly induces outer cell wall destruction (leading even to the mineralization) in the presence of light. Furthermore, 2-propanol oxidative decomposition was also investigated. The obtained results suggest that the improved photocatalytic activity of HA-covered samples originates from phosphate anions in HA, hindering the charge carriers’ recombination. In bacteria case, titania's properties are key factor for high bactericidal effects, such as anatase form (electrostatic attraction between microorganisms and photocatalyst surface) and fine crystallites, as opposed to yeast inactivation resembling 2-propanol oxidation, i.e., photocatalytic mechanism, based on reactive oxygen species. Concluding, HA/Ag/AgBr/TiO2 samples are promising “green” materials for decomposition of both microbiological and chemical pollutants.

TolC-AcrA complex formation monitored by time dependent single-channel electrophysiology

Characterizing protein-protein interaction on a single molecular level is a challenge, experimentally as well as interpretation of the data. For example, Gram-negative bacteria contain protein complexes spanning the outer and inner cell wall devoted to efflux effectively cell toxic substances. Recent seminal work revealed the high-resolution structure of such a tripartic composition TolC-AcrA-AcrB suggesting to design inhibitors preventing efflux of antibiotics. To show that electrophysiology can provide supporting information here, we reconstitute single TolC homotrimer into a planar lipid membrane, apply a transmembrane voltage and follow the assembly of AcrA to TolC using the modulation of the ion current through TolC channel during binding. In particular, the presence of AcrA in solution increases the average ionic current through TolC and, moreover, reduces the ion-current fluctuations caused by flickering of TolC. Here, we show that statistical properties of ion-current fluctuations (the power spectral density) provide a complementary measure of the interaction of the TolC-AcrA complex in presence of putative efflux pump inhibitors. Both characteristics, the average ion current across TolC and the current noise, taken into consideration together, point to a stiffening of the tip of TolC which might reduce the formation of the complex.

Infection Biology of Bipolaris oryzae in Rice and Defence Responses in Compatible and Less Compatible Interactions

The infection biology of Bipolaris oryzae and the defence responses of its host rice were studied using the rice cv. MTL 189 inoculated with two isolates of B5 (highly compatible with MTL 189) and K2 (less compatible). In the former interaction, the hyphal progress was accompanied by tissue degradation and extensive sporulation after 8 days, whereas in the latter interaction, only very limited tissue degradation and sporulation was observed. Quantitative microscopy of the infection showed that the percentages of conidia and appressoria causing penetration and fluorescent epidermal cells (FEC) were lower for isolate K2 than for isolate B5 at 12 and 24 hours after inoculation (hai). Fluorescent papillae (FP) were only seen in the less compatible interaction and the percentage of conidia causing single FEC was highest in the less compatible interaction at 12 hai, but not at 24 hai. Qualitative examination of other defence responses showed that H2O2 started to accumulate at 4 hai in the less compatible interaction, whereas it appeared in the compatible interaction only at 12 hai. The level of H2O2 was generally higher in the less compatible than in the compatible interaction. Cross sections of leaves showed that H2O2 accumulated in the outer walls of epidermal cells. Likewise, accumulation of callose and polyphenolic substances was most pronounced in the less compatible interaction and occurred at the same places as H2O2. To our knowledge, this is the first report implicating H2O2 as an early defence response against the hemibiotrophic pathogen B. oryzae during early infection stages in rice. Understanding defence reactions may aid in resistance breeding.

EFFECT OF CO-DIGESTING PRETREATED CHICKEN - GOAT AND UNTREATED COW MANURE ON BIOGAS PRODUCTION IN FIXED DOME LABORATORY DIGESTER

The effect of hydro, mechanical and thermal pretreatment of chicken and goat manure on biogas production wasdone using a 0.15m3 laboratory scale batch digester. The feedstocks were subjected to 6, 12 and 18 hours ofsoaking, 2 mm, 3 mm and 4 mm of mechanical mincing, and 60 ̊C, 80 ̊C and 100 ̊C of heating. Pretreated feedstocks were co-digested with untreated cow manure from an extensive dairy rearing system. Experiments weredone at 8 % substrate total solids and a constant temperature of 35°C. Averagely, mechanical pretreatmentresulted in the highest increase in mean biogas production rate with 11.11%, over the co-digestion control (0.54m3/m3d), followed by thermal and hydro by 5.56% and1.85%. Maximal increase in production for eachpretreatment was at 6 hour soaking time (9.30%), 3 mm effective feed stock particle sizes (18.52%) and 80 ̊C ofheating (14.81%). Co-digestion increased mean biogas production rate over mono-digestion by 68.97%(chicken), 81.84% (goat) and 8.8% (cow manure). Superior outer cell wall and cover disruption of feed stocksfor easy hydrolysis advantaged mechanical pretreatment.