Lignin is a heterogeneous aromatic polymer responsible for cell wall stiffness and protection from pathogen attack. However, lignin represents a bottleneck to biomass degradation due to its recalcitrance related to the natural cell wall resistance to release sugars for fermentation or further processing. A biological approach involving genetics and molecular biology was used to disrupt lignin pathway synthesis and decrease lignin deposition. Here, we imaged three-dimensional fragments of the petioles of wild type and C4H lignin mutant Arabidopsis thaliana plants by synchrotron cryoptychography. the three-dimensional images revealed the heterogeneity of vessels, parenchyma, and fibre cell wall morphologies, highlighting the relation between disturbed lignin deposition and vessel implosion (cell collapsing and obstruction of water flow). We introduce a new parameter to accurately define cell implosion conditions in plants, and we demonstrate how cryo-ptychographic X-ray computed tomography (cryo-PXCT) provides new insights for plant imaging in three dimensions to understand physiological processes. Lignin is a hydrophobic and heterogeneous biopolymer fundamental for the development of an efficient water transport system in plants, conferring structural robustness and impermeability to conduits, essential for plant stiffness 1,2. Lignin is found in the plant cell wall, mainly in vessels and fibres, forming chemical bonds with hemicellulose, which adheres to cellulose microfibrils. This polymer plays a fundamental physiological role during pathogen infection by inducing cell wall coarsening, impeding the action of fungal and bacterial cellulolytic enzymes and consequently inhibiting the pathogen invasion of surrounding tissues 3. On the other hand, for lignocellulosic biofuel production, lignin is among the molecules that limit the value of biomass crops, impacting the cellulose breakdown to glucose, which is used for further fermentation steps 4,5. Different pretreatment approaches have been developed to change the physical and chemical nanostructure of lignocellulosic biomass to alter its three-dimensional structure, interactions and composition to improve hydrolysis rates 6-10. As an alternative, genetic manipulations of the lignin biosynthetic pathway can alter the composition and reduce the content of lignin, thereby decreasing biomass recalcitrance related to the natural cell resistance to release sugars for fermentation or further processing. This effect has been largely elucidated for both Arabidopsis thaliana, a model organism for plants, and other species 1,11-15. However, the compromised growth of manipulated plants has made the commercial use of these crops a problematic issue, since the lack of cellular rigidity makes the vessels more susceptible to embolism formation 11,16,17 or collapse (i.e., conduit implosion) 18 , preventing the water transport along the plant. Therefore, it is crucial to determine the three-dimensional distribution of lignin in the cell walls and in different tissues to understand ...

Permeability is the key parameter for quantifying fluid flow in porous rocks. Knowledge of the spatial distribution of the connected pore space allows, in principle, to predict the permeability of a rock sample. However, limitations in feature resolution and approximations at microscopic scales have so far precluded systematic upscaling of permeability predictions. Here, we report fluid flow simulations in pore-scale network representations designed to overcome such limitations. We present a novel capillary network representation with an enhanced level of spatial detail at microscale. We find that the network-based flow simulations predict experimental permeabilities measured at lab scale in the same rock sample without the need for calibration or correction. By applying the method to a broader class of representative geological samples, with permeability values covering two orders of magnitude, we obtain scaling relationships that reveal how mesoscale permeability emerges from microscopic capillary diameter and fluid velocity distributions.

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