Biochemical pathways lignins

A short discussion is also in order regarding the biochemical pathways to the polysaccharides (celluloses and hemicelluloses), which are the dominant organic components in most biomass, and the lignins, proteins (polypeptides), and triglycerides (lipids or fats) that are found in biomass. Most biomass on... 

FIGURE 2 Scheme of biochemical pathways and pools leading to carbohydrates, lignin, lipids, and other metabolites. 

To confuse matters further, several dimeric phenylpropanoid (neo)lignans have been implicated in lignin synthesis (12) (see later). Others splay potent antiviral (/j), antifungal (74), bactericidal (15), insecticidal (16) and putative cytokinin (17, 18) properties. Therefore, it is difficult at first inspection to determine whether phenylpropanoid metabolism initially evolved for water/nutrient conduction, structural support or defense. (Figure 1 shows the overall biochemical pathway to the different metabolic products from Phe 1/Tyr 2). 

Pteridophytes. Evolution of the biochemical pathway to the lignins proper apparently first occurred with the appearance of the pteridophytes, the earliest remains of which to date come from the Devonian period (27). In extant plants, lignins are seemingly present in the ferns (Filicopsida), clubmosses (Lycopsida), horsetails (Equisetopsida), and the Psilotopsida [see... 

In this chapter I will focus on biochemical and molecular aspects leading to lignin production. We have studied in detail phenylalanine ammonia lyase (PAL EC 4.3.1.5), the first enzyme of the general phenylpropanoid pathway, and cinnamyl alcohol dehydrogenase (CAD EC 1.1.1.195), an enzyme specific to the branch pathway leading to lignin formation. 

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