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Research Containing: Cell wall

The actin cytoskeleton is a suppressor of the endogenous skewing behaviour of Arabidopsis primary roots in microgravity

by on 22 August 2016in Biology & Biotechnology No comment

Before plants can be effectively utilised as a component of enclosed life-support systems for space exploration, it is important to understand the molecular mechanisms by which they develop in microgravity. Using the Biological Research in Canisters (BRIC) hardware on board the second to the last flight of the Space Shuttle Discovery (STS-131 mission), we studied how microgravity impacts root growth in Arabidopsis thaliana. Ground-based studies showed that the actin cytoskeleton negatively regulates root gravity responses on Earth, leading us to hypothesise that actin might also be an important modulator of root growth behaviour in space. We investigated how microgravity impacted root growth of wild type (ecotype Columbia) and a mutant (act2-3) disrupted in a root-expressed vegetative actin isoform (ACTIN2). Roots of etiolated wild-type and act2-3 seedlings grown in space skewed vigorously toward the left, which was unexpected given the reduced directional cue provided by gravity. The left-handed directional root growth in space was more pronounced in act2-3 mutants than wild type. To quantify differences in root orientation of these two genotypes in space, we developed an algorithm where single root images were converted into binary images using computational edge detection methods. Binary images were processed with Fast Fourier Transformation (FFT), and histogram and entropy were used to determine spectral distribution, such that high entropy values corresponded to roots that deviated more strongly from linear orientation whereas low entropy values represented straight roots. We found that act2-3 roots had a statistically stronger skewing/coiling response than wild-type roots, but such differences were not apparent on Earth. Ultrastructural studies revealed that newly developed cell walls of space-grown act2-3 roots were more severely disrupted compared to space-grown wild type, and ground control wild-type and act2-3 roots. Collectively, our results provide evidence that, like root gravity responses on Earth, endogenous directional growth patterns of roots in microgravity are suppressed by the actin cytoskeleton. Modulation of root growth in space by actin could be facilitated in part through its impact on cell wall architecture.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/23952736

Cell wall-bound peroxidase activity and lignin formation in azuki bean epicotyls grown under hypergravity conditions

by on 9 June 2015in Biology & Biotechnology No comment

The effects of accelerated gravity stimuli on the cell wall-bound peroxidase activity and the lignin content were investigated along epicotyls of azuki bean (Vigna angularis) seedlings. The endogenous growth occurred primarily in the upper regions of the epicotyl, but no growth was detected in the middle or basal regions. Hypergravity treatment at 300g for 6h suppressed elongation growth and stimulated lateral expansion of the upper regions. The content of acetyl bromide-soluble lignin increased gradually from the apical to the basal regions of epicotyls. Hypergravity treatment stimulated the increase in the lignin content in epicotyls, particularly in the middle and basal regions. The peroxidase activity in the protein fraction extracted with a high ionic strength buffer from the cell wall preparation also increased gradually toward the basal region, and hypergravity treatment increased the activity in all epicotyl regions. There was a close correlation between the lignin content and the enzyme activity. These results suggest that hypergravity increases the activity of cell wall-bound peroxidase followed by increases of the lignin formation in epicotyl cell walls, which may contribute to increasing the rigidity of cell walls against the gravitational force.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/19195738

Modification of Cell Wall Architecture in Gramineous Plants under Altered Gravity Conditions

by on 9 June 2015in Biology & Biotechnology No comment

Gramineous plants, such as rice, wheat, and maize, are essential crops. The cell wall composition of gramineous plants is distinguished from that of dicotyledons, such as Arabidopsis, pea, and mung bean. In cell walls of gramineous plants, arabinoxylans and β-glucans are the major matrix polysaccharides and they make network structure within cell wall architecture. Gravitational stimuli affect the metabolism of β-glucans in gramineous shoots; hypergravity suppressed the β-glucan breakdown, when it inhibited shoot elongation. The opposite results were obtained under microgravity conditions in space. On the other hand, the arabinoxylan and diferulic acid (DFA) contents increased under continuous hypergravity conditions. Since arabinoxylans are cross-linked by DFA-bridges, continuous hypergravity may stimulate the formation of arabinoxylan-DFA network within cell walls. These findings suggest that the β-glucan metabolism is primarily involved in the mechanism of growth regulation, while the arabinoxylan-DFA network has a load-bearing function against the gravitational force. The modification of these wall constituents may contribute to the capacity of gramineous plants to sustain their structure and growth under altered gravity conditions.

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Cell wall oxalate oxidase modifies the ferulate metabolism in cell walls of wheat shoots

by on 9 June 2015in Biology & Biotechnology No comment

Oxalate oxidase (OXO) utilizes oxalate to generate hydrogen peroxide, and thereby acts as a source of hydrogen peroxide. The present study was carried out to investigate whether apoplastic OXO modifies the metabolism of cell wall-bound ferulates in wheat seedlings. Histochemical staining of OXO showed that cell walls were strongly stained, indicating the presence of OXO activity in shoot walls. When native cell walls prepared from shoots were incubated with oxalate or hydrogen peroxide, the levels of ester-linked diferulic acid (DFA) isomers were significantly increased. On the other hand, the level of ester-linked ferulic acid (FA) was substantially decreased. The decrease in FA level was accounted neither by the increases in DFA levels nor by the release of FA from cell walls during the incubation. After the extraction of ester-linked ferulates, considerable ultraviolet absorption remained in the hemicellulosic and cellulose fractions, which was increased by the treatment with oxalate or hydrogen peroxide. Therefore, a part of FA esters may form tight linkages within cell wall architecture. These results suggest that cell wall OXO is capable of modifying the metabolism of ester-linked ferulates in cell walls of wheat shoots by promoting the peroxidase action via supply of hydrogen peroxide.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/21684033

Phenylalanine ammonia-lyase and cell wall peroxidase are cooperatively involved in the extensive formation of ferulate network in cell walls of developing rice shoots

by on 9 June 2015in Biology & Biotechnology No comment

The relationship between the formation of cell wall-bound ferulic acid (FA) and diferulic acid (DFA) and the change in activities of phenylalanine ammonia-lyase (PAL) and cell wall-bound peroxidase (CW-PRX) was studied in rice shoots. The length and the fresh mass of shoots increased during the growth period from day 4 to 6, while coleoptiles ceased elongation growth on day 5. The amounts of FA and DFA isomers as well as cell wall polysaccharides continued to increase during the whole period. The activities of PAL and CW-PRX greatly increased in the same manner during the period. There were close correlations between the PAL activity and ferulate content or between the CW-PRX activity and DFA content. The expression levels of investigated genes for PAL and putative CW-PRX showed good accordance with the activities of these enzymes. These results suggest that increases in PAL and CW-PRX activities are cooperatively involved in the formation of ferulate network in cell walls of rice shoots and that investigated genes may be, at least in part, associated with the enzyme activities. The substantial increase in such network probably causes the maturation of cell walls and thus the cessation of elongation growth of coleoptiles.

Related URLs:
http://www.ncbi.nlm.nih.gov/pubmed/22118877

Increase in the level of arabinoxylan–hydroxycinnamate network in cell walls of wheat coleoptiles grown under continuous hypergravity conditions

by on 9 June 2015in Biology & Biotechnology No comment

Changes in the amount and composition of cell wall constituents in response to continuous hypergravity stimuli were studied in wheat (Triticum aestivum L.) coleoptiles. The lengths of coleoptiles grown under hypergravity (300 g) conditions for 2–4 days from germination stage were 60–70% of those of 1 g control. However, the net amounts of hemicellulosic polysaccharides and cellulose in hypergravity-treated coleoptiles increased progressively as much as those in the control coleoptiles. As a result, their contents per unit length of coleoptile largely increased under hypergravity conditions. In the hemicellulose fraction, the amounts of arabinose and xylose, the major components of the fraction, prominently increased in response to hypergravity. When hemicellulosic polysaccharides were separated into neutral and acidic polymers by an anion-exchange column, the amounts of the acidic fraction consisting of (glucurono)arabinoxylans were higher in hypergravity-treated coleoptiles than in control coleoptiles. The amounts of cell wall-bound ferulic acid and diferulic acid (DFA) increased dramatically in both 1 g control and hypergravity-treated coleoptiles. Particularly, the amounts of DFA in hypergravity-treated coleoptiles were significantly higher than those in control coleoptiles during the incubation period. These results suggest that continuous hypergravity increases the rigid network structures via arabinoxylan–hydroxycinnamate cross-links within cell wall architecture in wheat coleoptiles. These structures may have a load-bearing function and contribute to construct the stable cell wall against the gravitational force.

Related URLs:
http://dx.doi.org/10.1111/j.1399-3054.2005.00544.x

Cell Wall-Related Genes Involved in Supporting Tissue Formation and Transcriptional Regulation in Arabidopsis thaliana

by on 9 June 2015in Biology & Biotechnology No comment

The characteristic growth pattern of vascular plants largely depends on the intrinsic properties of their cell walls, which are flexible, but strong enough to support the plant body. The plant body is composed of various tissues each with a specific cell wall type. Different sets of enzymes are required for the construction of these individual cell wall types. The cell wall type-specific enzyme-set hypothesis has been described to explain the mechanisms underlying cell wall construction. This hypothesis suggests that specific sets of transcription factors are required for the construction of each of the cell-wall types. Recent reverse genetic studies investigating secondary wall formation in Arabidopsis thaliana have demonstrated the existence of a hierarchical transcriptional network that governs the regulation of secondary wall formation in cell wall types. The examination of the effects of mechanical stimuli on the expression of genes encoding a particular set of cell wall-related enzymes and transcriptional factors has shown that A. thaliana is able to perceive subtle changes in self-weight of the aerial portions, and use this information as a signal to regulate formation of cell walls in the supporting tissues. However, the mechanisms by which mechanical signals are perceived via sensors presumably located at the cell surface remain unknown. In addition, the pathways through which the signal is transmitted and integrated into the transcriptional network that governs the coordinated actions of cell wall-related genes are also yet to be described. Current reverse genetic approaches based on comprehensive expression analysis of cell wall-related genes may aid in the elucidation of the regulatory mechanisms underlying supporting tissue formation via mechanical signals. Such information may contribute not only to a further understanding of the molecular basis underlying evolution of the plant vascular system, but may also provide us with the knowledge required for the future development and utilization of plant cell walls as a sustainable resource.

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Germination and growth test in four strains of Arabidopsis thaliana in the reference model of European Modular Cultivation System

by on 9 June 2015in Biology & Biotechnology No comment

Japan Aerospace Exploration Agency (JAXA） has two plant physiological space experiments that utilize the European Modular Cultivation System (EMCS) facility of European Space Agency ESA). The theme of the two experiments, namely, Cell Wall and Resist Wall (CWRW) are aimed at understanding the formation of plant cell wall and the mechanism of gravity resistance in plants. A ground-based study for monitoring the germination and growth of Arabidopsis, science test, was performed for 50 days in the EMCS experiment reference model (ERM), as a preparation of the onboard CWRW space experiment. Four strains of Arabidopsis seeds were germinated and the seedlings were cultivated in the dedicated plant cultivation chamber (PCC) in the EMCS ERM until the inflorescence stems grew to approximately 10-cm long.. The objective of this science test was to successfully grow Arabidopsis seedlings in the EMCS ERM for determining the approximate duration of the　onboard CWRW space experiment. As a result, the PCC could be used to grow three strains, i.e., wild type, lefty mutant, and gene modified pCesA7::GUS, Arabidopsis plants from seeds to 10-cm-long inflorescence stems within 50 days. This science test confirmed that the PCC is biocompatible and a good support system for these strains growth during the entire experiment. On the other hand, the hmg mutant seeds, which are more delicate and susceptible to outer environment than other strains, failed to germinate. Therefore, increase the number of sowing hmg mutant seeds into the PCC and germination test using the PCC and the germination test using the PCC　for selection the hmg mutant seeds with best germination rate were essential for the future onboard CWRW space experiment.

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Reverse Genetic Approach to Exploring Genes Responsible for Cell-Wall Dynamics in Supporting Tissues of Arabidopsis thaliana under Microgravity Conditions

by on 9 June 2015in Biology & Biotechnology No comment

In 2008, the 'Cell Wall' experiment is scheduled to be launched and conducted on the International Space Station with the European Modular Cultivation System (EMCS). The main aim of this in-orbit plant science experiment is to elucidate the effect of gravitational conditions on supporting tissue formation in plants, thereby gaining new insight into the molecular mechanisms by which plants adapted to the land environment. In this first space experiment with in-orbit control experiments, we will specifically aim to elucidate the expression profiles of several candidate genes encoding proteins that are involved in the construction and restructuring of the secondary cell wall in the stem of Arabidopsis thaliana grown both in microgravity and 1G conditions. This review article deals with biological background pertinent to the 'Cell Wall' experiment, the anticipated experimental procedures to be used, together with a perspective of how this space experiment will extend our knowledge in both pure and applied life sciences.

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JAXA Space Plant Research on the ISS with European Modular Cultivation System

by on 9 June 2015in Biology & Biotechnology No comment

The European Modular Cultivation System (EMCS) installed within the US laboratory module, Destiny, and/or the European experiment module, Columbus, onboard the International Space Station (ISS), is an ESA facility available for plant research and biological experiments. The EMCS facility uses standard experiment containers (ECs) mounted on centrifuges and provides life support such as water and gas supply systems as well as observation systems. The experiment-specific hardware such as the plant cultivation chamber, root phototropism observation chamber, and plant root gravitropism observation chamber is integrated into the EC. JAXA has five themes concerning space plant research, of which two-Cell Wall and Resist Wall-will include conducting space experiments using the EMCS facility; according to the present shuttle flight schedule, they are due to be launched in mid February 2007. The objectives of the Cell Wall / Resist Wall experiment include in-orbit growth of 10-cm-long inflorescence stems of Arabidopsis and subsequent, post-flight morphology, biological, gene expression, and cell-wall properties analyses on the ground. In this article, we describe the EMCS facility, the plant cultivation and onboard chemical fixation system. Furthermore, we also discuss the verification experiments conducted by JAXA.

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