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Understanding the plant cell wall architecture is essential for elucidating its biological function and mechanical properties. This study employs a synthetic approach using spherical core–shell capsules with shells composed of deuterated bacterial cellulose (d-BC) and pectin. The shell structure was created via a bottom-up layer-by-layer assembly onto CaCO3 templates, followed by characterization through microscopy and scattering techniques. Small-angle X-ray scattering (SAXS) and confocal laser scanning microscopy revealed increased pore sizes in hydrated d-BC/pectin shells compared to those of hydrated wood-derived cellulose nanofiber (CNF)-based shells from a previous study. Using small-angle neutron scattering (SANS) with contrast variation, structural changes of individual wall components under varying salinities (0 or 10 mM NaCl) were analyzed. The presence of NaCl selectively influenced the pectin phase, while the d-BC network retained structural stability, highlighting its robustness as a wall component. This platform provides a useful tool for testing hypotheses and advancing our understanding of cell wall porosity and composition-dependent permeability.

Cellulose fibres are a sustainable alternative for development of new materials and with chemical modifications the material properties can be tailored for its intended application. To understand the impact of a modification characterisation techniques that reveal where the chemical alterations occur across the fibre are needed. Here we showcase how X-ray spectro-microscopy around the carbon K-edge can provide spatially resolved images of the chemical content of cellulose fibres and investigate the effect of different sample preparation strategies on the resulting data quality. We show that that one can spatially separate different lignin compositions over a single thermomechanical pulp fibre. The sample preparation is key for a successful experiment and requires sectioning of thin slices (~ 100 nm) of the sample which can be achieved by microtome sectioning. The effect of different embedding materials, including epoxies, cryo-embeddings with water and sucrose and elemental sulphur, is evaluated. The results show that epoxy embeddings are beneficial for homogenous sectioning, which is an advantage for imaging, while embedding strategies without carbon species, such as elemental sulphur or cryo-embedding with water, is better for evaluation of the chemical content in the fibre due to less overlap in the spectral signal from the embedding material. We also present measurement strategies for efficient data collection that minimise the inflicted radiation dose to provide guidelines for performing synchrotron-based spectro-microscopy around the carbon K-edge to characterise cellulose fibres.

Plant cell wall porosity regulates a number of critical functions in plants, and improved structural and molecular insights are key to understanding factors that influence porosity. Yet, measuring porosity of cell walls in the wet state is not straightforward. Here, simplified hollow core-shell structures were developed with shells composed of cellulose nanofibers (CNFs) and pectin, inspired by the composition of the plant primary cell wall. These structures were examined to evaluate the influence of salinity (sodium chloride) on shell porosity via the permeation of FITC-dextran molecules. Additionally, small angle X-ray scattering, dynamic vapor sorption and electron microscopy imaging were exploited to improve mechanistic understanding. Combined, these techniques covered the sub-nm to micron length scales, and the collective experimental results implicated that sodium chloride only mediates a small increase in pore diameter. The observed increase in FITC-dextran permeability is thus rather due to changes to charge-pairing interactions between the oppositely charged CNF and pectin, and pectin mobility. The approach developed provides a platform on which to enable other plant wall polysaccharides and external stress factors to be systematically investigated.

Leaf senescence can be induced by stress or aging, sometimes in a synergistic manner. It is generally acknowledged that the ability to withstand senescence-inducing conditions can provide plants with stress resilience. Although the signaling and transcriptional networks responsible for a delayed senescence phenotype, often referred to as a functional stay-green trait, have been actively investigated, very little is known about the subsequent metabolic adjustments conferring this aptitude to survival. First, using the individually darkened leaf (IDL) experimental setup, we compared IDLs of wild-type (WT) Arabidopsis (Arabidopsis thaliana) to several stay-green contexts, that is IDLs of two functional stay-green mutant lines, oresara1-2 (ore1-2) and an allele of phytochrome-interacting factor 5 (pif5), as well as to leaves from a WT plant entirely darkened (DP). We provide compelling evidence that arginine and ornithine, which accumulate in all stay-green contexts—likely due to the lack of induction of amino acids (AAs) transport—can delay the progression of senescence by fueling the Krebs cycle or the production of polyamines (PAs). Secondly, we show that the conversion of putrescine to spermidine (SPD) is controlled in an age-dependent manner. Thirdly, we demonstrate that SPD represses senescence via interference with ethylene signaling by stabilizing the ETHYLENE BINDING FACTOR1 and 2 (EBF1/2) complex. Taken together, our results identify arginine and ornithine as central metabolites influencing the stress- and age-dependent progression of leaf senescence. We propose that the regulatory loop between the pace of the AA export and the progression of leaf senescence provides the plant with a mechanism to fine-tune the induction of cell death in leaves, which, if triggered unnecessarily, can impede nutrient remobilization and thus plant growth and survival.

We study composites of cellulose nanocrystals (CNCs) in an ionomer matrix of poly(ethylene-stat-sodium acrylate) and find that direct cellulose/cellulose interactions in the composite are not a requirement for achieving reinforcement. While isotropic composites only show a slightly enhanced stiffness compared to the neat ionomer, a more substantial increase in Young's modulus by a factor of up to 5 is achieved by uniaxial alignment of the composites through melt spinning. The orientation of CNC in melt-spun composites reduces the probability of cellulose/cellulose interactions, which suggests that cellulose/polymer interactions must be present that lead to the observed reinforcement. Molecular dynamics simulations confirm strong cellulose/polymer interactions in the form of ionic interactions as well as hydrogen bonding. These cellulose/polymer interactions facilitate efficient stress transfer, leading to the high reinforcing effect of CNC, while cellulose/cellulose interactions play a minor role in the mechanical response of the composite.

The Gram-negative bacterium Porphyromonas gingivalis is a secondary colonizer of the oral biofilm and is involved in the onset and progression of periodontitis. Its fimbriae, of type-V, are important for attachment to other microorganisms in the biofilm and for adhesion to host cells. The fimbriae are assembled from five proteins encoded by the mfa1 operon, of which Mfa5 is one of the ancillary tip proteins. Here we report the X-ray structure of the N-terminal half of Mfa5, which reveals a von Willebrand factor domain and two IgG-like domains. One of the IgG-like domains is stabilized by an intramolecular isopeptide bond, which is the first such bond observed in a Gram-negative bacterium. These features make Mfa5 structurally more related to streptococcal adhesins than to the other P. gingivalis Mfa proteins. The structure reported here indicates that horizontal gene transfer has occurred among the bacteria within the oral biofilm.

Type 2 diabetes (T2D), alike Parkinson's disease (PD), belongs to the group of protein misfolding diseases (PMDs), which share aggregation of misfolded proteins as a hallmark. Although the major aggregating peptide in beta -cells of T2D patients is Islet Amyloid Polypeptide (IAPP), alpha-synuclein (alpha Syn), the aggregating peptide in substantia nigra neurons of PD patients, is expressed also in beta -cells. Here we show that alpha Syn, encoded by Snca, is a component of amyloid extracted from pancreas of transgenic mice overexpressing human IAPP (denoted hIAPPtg mice) and from islets of T2D individuals. Notably, alpha Syn dose-dependently promoted IAPP fibril formation in vitro and tail-vein injection of alpha Syn in hIAPPtg mice enhanced beta -cell amyloid formation in vivo whereas beta -cell amyloid formation was reduced in hIAPPtg mice on a Snca (-/-) background. Taken together, our findings provide evidence that alpha Syn and IAPP co-aggregate both in vitro and in vivo, suggesting a role for alpha Syn in beta -cell amyloid formation.

The functions of mitochondria during leaf senescence, a type of programmed cell death aimed at the massive retrieval of nutrients from the senescing organ to the rest of the plant, remain elusive. Here, combining experimental and analytical approaches, we showed that mitochondrial integrity in Arabidopsis (Arabidopsis thaliana) is conserved until the latest stages of leaf senescence, while their number drops by 30%. Adenylate phosphorylation state assays and mitochondrial respiratory measurements indicated that the leaf energy status also is maintained during this time period. Furthermore, after establishing a curated list of genes coding for products targeted to mitochondria, we analyzed in isolation their transcript profiles, focusing on several key mitochondrial functions, such as the tricarboxylic acid cycle, mitochondrial electron transfer chain, iron-sulfur cluster biosynthesis, transporters, as well as catabolic pathways. In tandem with a metabolomic approach, our data indicated that mitochondrial metabolism was reorganized to support the selective catabolism of both amino acids and fatty acids. Such adjustments would ensure the replenishment of alpha-ketoglutarate and glutamate, which provide the carbon backbones for nitrogen remobilization. Glutamate, being the substrate of the strongly up-regulated cytosolic glutamine synthase, is likely to become a metabolically limiting factor in the latest stages of developmental leaf senescence. Finally, an evolutionary age analysis revealed that, while branched-chain amino acid and proline catabolism are very old mitochondrial functions particularly enriched at the latest stages of leaf senescence, auxin metabolism appears to be rather newly acquired. In summation, our work shows that, during developmental leaf senescence, mitochondria orchestrate catabolic processes by becoming increasingly central energy and metabolic hubs.

Plants often have to cope with altered light conditions, which in leaves induce various physiological responses ranging from photosynthetic acclimation to leaf senescence. However, our knowledge of the regulatory pathways by which shade and darkness induce leaf senescence remains incomplete. To determine to what extent reduced light intensities regulate the induction of leaf senescence, we performed a functional comparison between Arabidopsis leaves subjected to a range of shading treatments. Individually covered leaves, which remained attached to the plant, were compared with respect to chlorophyll, protein, histology, expression of senescence-associated genes, capacity for photosynthesis and respiration, and light compensation point (LCP). Mild shading induced photosynthetic acclimation and resource partitioning, which, together with a decreased respiration, lowered the LCP. Leaf senescence was induced only under strong shade, coinciding with a negative carbon balance and independent of the red/far-red ratio. Interestingly, while senescence was significantly delayed at very low light compared with darkness, phytochrome A mutant plants showed enhanced chlorophyll degradation under all shading treatments except complete darkness. Taken together, our results suggest that the induction of leaf senescence during shading depends on the efficiency of carbon fixation, which in turn appears to be modulated via light receptors such as phytochrome A.