Investigation of cell shape effect on the mechanical behaviour of open-cell metal foams

The mechanical behaviours of metal foams greatly depend on their cell topology, including cell shape, cell size etc. as well as relative density and material properties of the cell wall. However, the cell shape effect on the mechanical behaviours of such materials appears to be ignored in previous research. In this paper, both analytic and finite element models are developed and employed to investigate the effect of cell shape on the mechanical behaviour of open-cell magnesium alloy (AZ91) foams under compression, including deformation modes and failure modes. For numerical modelling, both two-dimensional (2-D) and three-dimensional (3-D) finite element models are developed to predict the compressive behaviours of typical open-cell metal foams and capture the deformation modes and failure mechanisms. Two typical cell shapes i.e. cubic and diamond are taken into consideration. To validate these models, the analytic and numerical results are compared to the experimental data. Both the numerical and experimental data indicate that the cell shape significantly affects the compression behaviour of open-cell metal foams. In general, numerical results from the three-dimensional solid-element model show better agreement with the experimental results than those from other finite element models.

Single cell stiffness measurement at various humidity conditions by nanomanipulation of a nano-needle

This paper presents a method for single cell stiffness measurement based on a nano-needle and nanomanipulation. The nano-needle with a buffering beam was fabricated from an atomic force microscope cantilever by the focused ion beam etching technique. Wild type yeast cells (W303) were prepared and placed on the sample stage inside an environmental scanning electron microscope (ESEM) chamber. The nanomanipulator actuated the nano-needle to press against a single yeast cell. As a result, the deformation of the cell and nano-needle was observed by the ESEM system in real-time. Finally, the stiffness of the single cell was determined based on this deformation information. To reveal the relationship between the cell stiffness and the environmental humidity conditions, the cell stiffness was measured at three different humidity conditions, i.e. 40, 70 and 100%, respectively. The results show that the stiffness of a single cell is reduced with increasing humidity.

Bioanalytical evaluation of Lactobacillus delbrueckii subsp. lactis 313 cell-envelope proteinase extraction

Lactobacilli cell-envelope proteinases (CEPs) have demonstrated numerous biopharmaceutical applications in the development of new streams of blockbuster nutraceuticals; thus, the development of efficient and commercially viable methods for CEP extraction will promote their full-scale application. In this study, the sub-cellular location of CEPs in Lactobacillus delbrueckii subsp. lactis 313 (LDL 313) was identified and the effects of different extraction methods were investigated for their ability to efficiently release CEPs from LDL 313. Significantly high relative proteinase activity of~95% was detected in cell-wall fractions and ~5% activity was observed for osmotic fluids, implying that proteinases in LDL 313 are cell-wall bound. CEPs were released from cell-wall via incubation in calcium-free buffer, indicating the enzyme is liable to self-digestion and ionic misfolding. Of the different extraction methods investigated, the use of 5 M LiCl was the most suitable, under the conditions of experimentation, for releasing high levels of CEPs from LDL 313.

Effect of storage on the biochemical and processing quality of Adzuki Bean (Vigna angularis)

Storage of adzuki beans and other pulse grains causes biochemical and physical changes that affect the hydration properties of the beans. This affects the quality of products made from the beans such as the Japanese bean paste “ann.” Storage, particularly under unfavourable conditions, leads to the “hard shell” phenomenon, where beans fail to imbibe water when soaked and remain hard, and the “hard-to-cook” phenomenon where the seeds hydrate normally, but the cotyledon fails to hydrate and soften during cooking. The hard shell phenomenon is attributable to impermeability of the seed coat to water, which is due to biochemical changes in the seed coat, such as the formation of protein-tannin complexes, and biophysical changes such as reduction in size or closure of the straphiole aperture in the hilum area—the main area for water entry into the adzuki bean. The hard-to-cook phenomenon is due to changes in the cotyledon tissue, which include formation of insoluble pectinates, lignification of the cell wall and middle lamella, interaction of condensed tannins with proteins and starch, and changes to the structure and functionality of the cellular proteins and starch.

Potassium phosphonate alters the defence response of Xanthorrhoea australis following infection by Phytophthora cinnamomi

Potassium phosphonate (phosphite) is widely used in the management of Phytophthora diseases in agriculture, horticulture and natural environments. The Austral grass tree, Xanthorrhoea australis, a keystone species in the dry sclerophyll forests of southern Australia, is susceptible to Phytophthora cinnamomi, but is protected by applications of phosphite. We examined the effect of phosphite application on the infection of X. australis seedlings and cell suspension cultures by zoospores of P. cinnamomi. Phosphite induced more intense cellular responses to pathogen challenge and suppressed pathogen ingress in both seedlings and cell cultures. In untreated X. australis seedlings, hyphal growth was initially intercellular, became intracellular 24 h after inoculation, and by 48 h had progressed into the vascular tissue. In phosphite-treated seedlings, growth of P. cinnamomi remained intercellular and was limited to the cortex, even at 72 h after inoculation. The cell membrane retracted from the cell wall and phenolic compounds and electron dense substances were deposited around the wall of infected and neighbouring cells. Suspension cells were infected within 6 h of inoculation. Within 24 h of inoculation, untreated cells were fully colonised, had collapsed cytoplasm and died. The protoplast of phosphite-treated suspension cells collapsed within 12 h of inoculation, and phenolic material accumulated in adjacent, uninfected cells. No anatomical response to phosphite treatment was observed before infection of plant tissues, suggesting that the phosphite-associated host defence response is induced following pathogen challenge. Anatomical changes provide evidence that phosphite stimulates the host defence system to respond more effectively to pathogen invasion.

Lignin production and monolignol pathway gene expression is suppressed by abscisic acid during defence reactions of Arabidopsis

The phytohormone, abscisic acid (ABA) has been shown to influence the outcome of the interactions between various hosts with biotrophic and hemibiotrophic pathogens. Susceptibility to avirulent isolates can be induced by addition of low physiological concentrations of ABA to plants. In contrast, addition of ABA biosynthesis inhibitors induced resistance following challenge of plants by virulent isolates. ABA deficient mutants of Arabidopsis, such as aba1-1, were resistant to virulent isolates of Peronospora parasitica. In interactions of Arabidopsis with avirulent isolates of Pseudomonas syringae pv. tomato, susceptibility was induced following addition of ABA or imposition of drought stress. These results indicate a pivotal, albiet undefined, role for ABA in determining either susceptibility or resistance to pathogen attack. We have found that the production of the cell wall strengthening compound, lignin, is increased during resistant interactions of aba1-1 but suppressed in ABA induced susceptible interactions. Using RT-PCR and microarray analysis we have found down-regulation by ABA of key genes of the phenylpropanoid pathway especially of those genes involved directly in lignin biosynthesis. ABA also down-regulates a number of genes in other functional classes including those involved in defence and cell signalling.

Suppression by abscisic acid of lignin production and monolignol pathway gene expression in interactions of Arabidopsis with oomycete and bacterial pathogens

The phytohormone, abscisic acid (ABA) has been shown to influence the outcome of the interactions between various hosts with biotrophic and hemibiotrophic pathogens. Susceptibility to avirulent isolates can be induced in plants by addition of low physiological concentrations of ABA. In contrast, addition of ABA biosynthesis inhibitors induced resistance following challenge of plants by virulent isolates. ABA deficient mutants of Arabidopsis, such as aba1-1, were resistant to virulent isolates of Peronospora parasitica. In interactions of Arabidopsis with avirulent isolates of Pseudomonas syringae pv. tomato, susceptibility was induced following addition of ABA or imposition of drought stress. These results indicate a pivotal, albiet undefined, role for ABA in determining either susceptibility or resistance to pathogen attack. We have found that the production of the cell wall strengthening compound, lignin, is increased during resistant interactions of aba1-1 but suppressed in ABA-induced susceptible interactions. Using RT-PCR and microarray analysis we have found down-regulation by ABA of key genes of the phenylpropanoid pathway especially of those genes involved directly in lignin biosynthesis. ABA also down-regulates a number of genes in other functional classes including those involved in defence and cell signalling.

Abscisic acid regulation of plant defence responses during pathogen attack

The plant hormone, abscisic acid (ABA), has previously been shown to have an impact on the resistance or susceptibility of plants to pathogens. In this thesis, it was shown that ABA had a regulatory effect on an extensive array of plant defence responses in three different plant and pathogen interaction combinations as well as following the application of an abiotic elicitor. In unique studies using ABA deficient mutants of Arabidopsis, exogenous ABA addition or ABA biosynthesis inhibitor application and simulated drought stress, ABA was shown to have a profound effect on the outcome of interactions between plants and pathogens of differing lifestyles and from different kingdoms. The systems used included a model plant and an important agricultural species: Arabidopsis thaliana (Arabidopsis) and Peronospora parasitica (a biotrophic Oomycete pathogen), Arabidopsis and Pseudomonas syringae pathovar tomato (a biotrophic bacterial pathogen) and an unrelated plant species, soybean (Glycine max) and Phytophthora sojae (a hemibiotrophic Oomycete pathogen), Generally, a higher than basal endogenous ABA concentration within plant tissues at the time of avirulent pathogen inoculation, caused an interaction shift towards what phenotypically resembled susceptibility. Conversely, a lower than basal endogenous ABA concentration in plants inoculated with a virulent pathogen caused a shift towards resistance. An extensive suppressive effect of ABA on defence responses was revealed by a range of techniques that included histochemical, biochemical and molecular approaches. A universal effect of ABA on suppression or induction of the phenylpropanoid pathway via regulation of the key entry point gene, phenylalanine ammonia-lyase (PAL), when stimulated by biotic or abiotic elicitors was shown. ABA also influenced a wide variety of other defence-related components such as: the development of a hypersensitive response (HR), the accumulation of the reactive oxyden species, hydrogen peroxide and the cell wall strengthening compounds lignin and callose, accumulation of SA and the phytoalexin, glyceollin and the transcription of the SA-dependent pathogenesis- related gene (PR-1). The near genome-wide microarray gene expression analysis of an ABA induced susceptible interaction also revealed an yet unprecedented insight into the great diversity of defence responses that were influenced by ABA that included: disease resistance like proteins, antimicrobial proteins as well as phenylpropanoid and tryptophan pathway enzymes. Subtle differences were found in the number and type of defence responses that were regulated by ABA in each type of plant and pathogen interaction that was studied. This thesis has clearly identified in plant/pathogen interactions previously unknown and important roles for ABA in the regulation of many defence responses.

Physiology and biochemistry of budburst in Vitis vinifera

Both the physiological and biochemical control of budburst in the grapevine, Vitis Vinifera L. were investigated. It was found that the accuracy of a predictive model for grapevine budburst based on ambient temperature was limited under the experimental conditions. There was a significant correlation of 4.7 ± 0.3 days between the days of maximal xylem exudation and budburst over the 3 years of investigation. The co-relationships between daily xylem exudate volume and a range of environmental parameters were considered. It was found that soil temperature was highly correlated against daily xylem exudation. Ambient temperature and soil moisture were significantly correlated with xylem exudation, however the coefficients of correlation were much lower than that of soil temperature. Rainfall showed only a very limited correlation with daily xylem exudate flow. Seasonal variations in the pH and the carbohydrate and inorganic nutrient concentrations of xylem exudate were investigated. Exudate carbohydrate concentrations fell from 660 µM before the day of maximal xylem exudation to zero levels within 4 weeks. Xylem exudate pH was found to consistently fall to a minimum at the time of maximal exudate flow. Exudate concentrations of the metallic cofactors Ca, K, Mg, Mn and Zn varied directly with daily exudate flow, suggesting some sort of flow-dependent mobilisation of these nutrients. A growth promontory oligosaccharide fraction was prepared by partial acid hydrolysis of grapevine primary cell wall material. This fraction significantly increased control growth of the Lemna minor L. bioassay over a limited ‘window’ of bioactivity. A growth inhibitory oligosaccharide fraction, similar in activity to abscisic acid was isolated from grapevine xylem exudate prior to budburst. The exudate concentration or efficacy of this substance declined after budburst such that there was no apparent growth inhibition. A model is proposed for grapevine budburst whereby an oligosaccharide growth inhibitor is gradually removed from the xylematic stream under the effects of soil temperature, allowing the surge of metabolic activity and vegetative growth that constitute budburst.

Tailoring enzymes for biofuel production with reference to Australian biomass

Manufacture of biofuels from existing biomass may provide a sustainable alternative to the extensive utilization of fossil fuels. Biomass offers environmental advantage over fossil fuels as it is a renewable energy source with low sulphur and nitrogen content and is carbon neutral over its production and utilization. Ranges of biomass are reported worldwide to be suitable raw material for bioethanol production. These can be generally classified into three groups; sucrose based (sugar cane), starch based (corn, wheat and barley) and lignocellulosic (which is mostly comprised of lignin, cellulose and hemicelluloses in grasses, wood and straw) materials. However, the limited supply of two biomass groups (sucrose and starch) will not satisfy society’s growing energy demands; thus biofuel technology based on lignocelluloses is under intense investigation. The main bottleneck in lignocellulosic biomass conversion for biofuel production is the enzymatic depolymerisation of cell wall polysaccharides into fermentable sugars. Protein engineering has recently been used to improve the performance of lignocelluloses degrading enzymes, as well as proteins involved in biofuel synthesis pathways. We have produced a recombinant enzyme that has the ability to produce monomeric sugars from a complex substrate. This presentation will summarize current efforts to develop an enzymatic treatment which would facilitate the economical processing of biomass available in Australia for bioenergy generation.

The role of oomycete effectors in plant–pathogen interactions

Plants constantly come into contact with a diverse range of microorganisms that are potential pathogens, and they have evolved multi-faceted physical and hemical strategies to inhibit pathogen ingress and establishment of disease. Microbes, however, have developed their own strategies to counteract plant defence responses. Recent research on plant–microbe interactions has revealed that an important part of the infection strategies of a diverse range of plant pathogens, including bacteria, fungi and oomycetes, is the production of effector proteins that are secreted by the pathogen and that promote successful infection by manipulating plant structure and metabolism, including interference in plant defence mechanisms. Pathogen effector proteins may function either in the extracellular spaces within plant tissues or within the plant cell cytoplasm. Extracellular effectors include cell wall degrading enzymes and inhibitors of plant enzymes that attack invading pathogens. Intracellular effectors move into the plant cell cytoplasm by as yet unknown mechanisms where, in incompatible interactions, they may be recognised by plant resistance proteins but where, in compatible interactions, they may suppress the plant’s immune response. This article presents a brief overview of our current understanding of the nature and function of effectors produced by oomycete plant pathogens.

Enzyme-assisted extraction of bioactives from plants

Demand for new and novel natural compounds has intensified the development of plant-derived compounds known as bioactives that either promote health or are toxic when ingested. Enhanced release of these bioactives from plant cells by cell disruption and extraction through the cell wall can be optimized using enzyme preparations either alone or in mixtures. However, the biotechnological application of enzymes is not currently exploited to its maximum potential within the food industry. Here, we discuss the use of environmentally friendly enzyme-assisted extraction of bioactive compounds from plant sources, particularly for food and nutraceutical purposes. In particular, we discuss an enzyme-assisted extraction of stevioside from Stevia rebaudiana, as an example of a process of potential value to the food industry.

The resurrection plant Sporobolus stapfianus: An unlikely model for engineering enhanced plant biomass?

The resurrection grass Sporobolus stapfianus Gandoger can rapidly recover from extended periods of time in the desiccated state (water potential equilibrated to 2% relative humidity) (Gaff and Ellis, Bothalia 11:305–308 1974; Gaff and Loveys, Transactions of the Malaysian Society of Plant Physiology 3:286–287 1993). Physiological studies have been conducted in S. stapfianus to investigate the responses utilised by these desiccation-tolerant plants to cope with severe water-deficit. In a number of instances, more recent gene expression analyses in S. stapfianus have shed light on the molecular and cellular mechanisms mediating these responses. S. stapfianus is a versatile research tool for investigating desiccation-tolerance in vegetative grass tissue, with several useful characteristics for differentiating desiccation-tolerance adaptive genes from the many dehydration-responsive genes present in plants. A number of genes orthologous to those isolated from dehydrating S. stapfianus have been successfully used to enhance drought and salt tolerance in model plants as well as important crop species. In addition to the ability to desiccate and rehydrate successfully, the survival of resurrection plants in regions experiencing short sporadic rainfall events may depend substantially on the ability to tightly down-regulate cell division and cell wall loosening activities with decreasing water availability and then grow rapidly after rainfall while water is plentiful. Hence, an analysis of gene transcripts present in the desiccated tissue of resurrection plants may reveal important growth-related genes. Recent findings support the proposition that, as well as being a versatile model for devising strategies for protecting plants from water-loss, resurrection plants may be a very useful tool for pinpointing genes to target for enhancing growth rate and biomass production.

Comparison of marine macrophytes for their contributions to blue carbon sequestration

Many marine ecosystems have the capacity for long-term storage of organic carbon (C) in what are termed "blue carbon" systems. While blue carbon systems (saltmarsh, mangrove, and seagrass) are efficient at long-term sequestration of organic carbon (C), much of their sequestered C may originate from other (allochthonous) habitats. Macroalgae, due to their high rates of production, fragmentation, and ability to be transported, would also appear to be able to make a significant contribution as C donors to blue C habitats. In order to assess the stability of macroalgal tissues and their likely contribution to long-term pools of C, we applied thermogravimetric analysis (TGA) to 14 taxa of marine macroalgae and coastal vascular plants. We assessed the structural complexity of multiple lineages of plant and tissue types with differing cell wall structures and found that decomposition dynamics varied significantly according to differences in cell wall structure and composition among taxonomic groups and tissue function (photosynthetic vs. attachment). Vascular plant tissues generally exhibited greater stability with a greater proportion of mass loss at temperatures > 300 degrees C (peak mass loss -320 degrees C) than macroalgae (peak mass loss between 175-300 degrees C), consistent with the lignocellulose matrix of vascular plants. Greater variation in thermogravimetric signatures within and among macroalgal taxa, relative to vascular plants, was also consistent with the diversity of cell wall structure and composition among groups. Significant degradation above 600 degrees C for some macroalgae, as well as some belowground seagrass tissues, is likely due to the presence of taxon-specific compounds. The results of this study highlight the importance of the lignocellulose matrix to the stability of vascular plant sources and the potentially significant role of refractory, taxon-specific compounds (carbonates, long-chain lipids, alginates, xylans, and sulfated polysaccharides) from macroalgae and seagrasses for their long-term sedimentary C storage. This study shows that marine macroalgae do contain refractory compounds and thus may be more valuable to long-term carbon sequestration than we previously have considered.