The middle lamella—more than a glue

Abstract

In plant tissues, cells are glued to each other by a pectic polysaccharide rich material known as middle lamella (ML). Along with many biological functions, the ML plays a crucial role in maintaining the structural integrity of plant tissues and organs, as it prevents the cells from separating or sliding against each other. The macromolecular organization and the material properties of the ML are different from those of the adjacent primary cell walls that envelop all plant cells and provide them with a stiff casing. Due to its nanoscale dimensions and the extreme challenge to access the structure for material characterization, the ML is poorly characterized in terms of its distinct material properties. This review explores the ML beyond its functionality as a gluing agent. The putative molecular interactions of constituent macromolecules within the ML and at the interface between ML and primary cell wall are discussed. The correlation between the spatiotemporal distribution of pectic polysaccharides in the different portions of the ML and the subcellular distribution of mechanical stresses within the plant tissue are analyzed.

The Genome of the Charophyte AlgaPenium margaritaceumBears Footprints of the Evolutionary Origins of Land Plants

“…This is exemplified by the substantially expanded repertoire of genes involved in the metabolism of pectins. These apparently ancient macromolecules contribute to cell expansion and cell differentiation, as well as forming the middle lamella that mediates intercellular adhesions, allowing tissue and organ formation in land plants (Zamil and Geitmann, 2017; Cosgrove, 2014). Addionally, while most terrestrial plant life requires more extensive depsoition of hydrophobic biopolymers to reinforce the walls of specialized cells, the origins of their building blocks can increasingly be traced back to aquatic ancestors.…”

Rhamnogalacturonan‐I is a determinant of cell–cell adhesion in poplar wood

“…In woody species, lignification is initiated in, and propagates from, the CML (Donaldson, 2001;Zamil and Geitmann, 2017). Consequently, treatments such as acidic chlorite would be expected to disrupt cell-cell adhesion.…”

The Middle Lamella of Plant Fibers Used as Composite Reinforcement: Investigation by Atomic Force Microscopy

“…These images not only provide values of the indentation modulus but also information about the morphology of the middle lamellae. In References [40,41], the authors made a distinction between the middle lamella (ML) and the compound middle lamella (CML), especially referring to the wood samples, but this distinction is also applicable to other plant fibers [13]. In fact, the middle lamella between two primary walls of two different cells is often not distinguishable [13], and the small tripartite layer appears as a single layer, such as in Figure 2b or Figure 2d.…”

“…An elementary fiber is a single cell, and several fibers are linked to each other to form a bundle of several dozens of single fibers having a multilayer structure, as illustrated in Figure 1a: (1) the lumen is the central hollow part of the cell and its shape and diameter vary with the maturity of the plant and the environmental conditions during growth; (2) the secondary cell wall is the thickest layer, divided into two to three sub-layers (S 1 , S 2 or G, and S 3 ) rich in cellulose where the thinner and not always visible S 3 can also be assimilated to unmatured Gn layer instead of a real S 3 [10]; (3) the primary cell wall is the external layer enriched in hemicelluloses, pectins, and lignin [11]. Between the fibers, there is another layer called middle lamella (ML), which cements the primary cell walls of adjacent cells together and is mainly composed of pectic polysaccharides, lignin, and a small amount of proteins [12][13][14]. This binder layer between two cells acts as a very thin and efficient interfacial matrix in the plant [13,15].…”

“…Between the fibers, there is another layer called middle lamella (ML), which cements the primary cell walls of adjacent cells together and is mainly composed of pectic polysaccharides, lignin, and a small amount of proteins [12][13][14]. This binder layer between two cells acts as a very thin and efficient interfacial matrix in the plant [13,15].…”