Plant cell lignification

All secondary cell walls develop from primary cell walls. Cells no longer grow once lignin is added to their wails. Lignification, which is a key step in the conversion of a primary cell wall into a secondary cell wall, results in terminal differentiation of the encased cell. Indeed, many cells with lignified walls die. The totipotency of plant cells is limited to cells enveloped in primary walls. 

One or several of these mechanisms may be involved in resistance responses when lignification takes place in the plant cell walls. In the case of biotrophic parasites which rely on functional mature haustoria within living host cells for their development (33-36), lignification of the whole cell contents leading to rapid host cell death may in itself be a decisive factor in the expression of resistance. 

Lignin, a phenolic polymer, is also incorporated into the wall during the secondary-thickening phase. This component permeates the spaces between the plant cells, thereby strengthening the tissue. Lignification is a result of enzymic dehydrogenation and subsequent polymerization of coumaryl, coniferyl, and sinapyl alcohols, the relative proportions of which differ in the lignins from different plants.23-28... 

Phenolic compounds may be involved in plant responses to cold stress and in plant acclimation to low temperature. Acclimation of apple trees to cold climates was found to be associated with a seasonal accumulation of chlorogenic acid [102]. Strengthened frost tolerance in a variety of plants were attributed to thicker cell-wall lignification or suberization [102]. Thickening of cell walls and increased production of suberin-type lipids were observed in cold-acclimated winter rye leaves [103]. The presence of suberin in cell walls may favour membrane cell-wall adhesion, a major factor in the resistance of plant cells to freezing [104]. 

Ogawa, K., Kanematsu, S., and Asada, K., 1997, Generation of superoxide anion and localization of CuZn-superoxide dismutase in the vascular tissue of spinach hypocotyls their association with lignification, Plant Cell Physiol. 38 1118-1126. 

The plasma membranes of plant cells possess several redox activities that can be related to both plant nutrition and cell wall formation and lignification (Liithje et al., 1997 Berczi and Mpller, 2000). In this context, it has been shown that in oat roots, HMS humic fractions inhibited NADH oxidation in either the presence or absence of an artificial electron acceptor (ferricyanide), whereas LMS fractions inhibited this oxidase only if the electron donor (NADH) and acceptor (ferricyanide) were added at the same time (Pinton et al., 1995). While the first effect could be related to the activity of surface peroxidases that can be involved in cell wall formation and thickening (Vianello and Macri, 1991), the second seems to be exerted on a different redox system with an unknown function (Nardi et al., 2002). 

Hosel, W., Fiedler-Preiss, A. and Borgmann, E. (1982) Relationship of coniferin p-glucosidase to lignification in various plant cell suspension cultures. Plant Cell Tiss. Org. Cult, 1,137-48. 

Lignification so called is the polymerization process in plant cell walls that takes phenolic monomers, produces radicals, and couples them with other monomer radicals (only during initiation reactions), or more typically cross-couples them with the growing lignin oligomer, to build up a phenylpropanoid polymer [44-47]. 

Wardrop, A.B. Lignification of the plant cell wall. Appl. Polym. Symp 28, 1041-1063... 

The secondary compounds or enzymes accumulated in the neighborhood of the plasma membrane, e.g., the constituents of the cell wall and the epidermis of plant cells, are either insoluble due to polymerization (cellulose, hemicellulose, lignin, cutin, suberin, sporopoUenin) or are trapped by a sieve effect due to the network of ceU wall constituents. Certain enzymes, however, such as the malate dehydrogenase involved in lignification (D 22.2.3), are also covalently bound to the cell wall. Low molecular compounds are able to penetrate the cell wall and may be washed out into the surroundings. 

Most heavy metal resistant plants belong to the so-called excluders , they prevent the accumulation of heavy metals inside their tissues [5]. Metal exclusion can function in several different ways. The probably most simple way is a reduction of the unselective permeability of cells. This is typically reached by lignification of plant cell walls, and the enhancement of lignifying enzymes is a well-known response to cadmium toxicity [6]. In addition, exclusion can occur by precipitation... 

Bast fibers contain a bit lower amount of cellulose (about 70%) than cotton ones. Moreover, they contain such components as lignin (10%), wax and trace amonnts of antibiotics, some of which increase biostability of the fiber. The presence of lignins induces coarsening (lignifications) of plant cells that promotes the loss of softness, flexibility, elasticity, and increased friability of fibers. 

It may be that the presence of this isoform promotes the strengthening of calli cell walls through a special mechanism, since cultured cells have mainly undifferentiated cell walls missing lignification and suberin deposition, similar to meristematic cells in plants. 

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