Legumes biosynthesis

Production sites for vitamin E biosynthesis occur in nuts, seeds, cereal germ, green leaves, legumes. Biosynthesis also occurs in some microorganisms. Precursors for biosynthesis include mevalonic acid and phenylalanine (probably these compounds with side chains). Considerably more research is required to pinpoint the exact precursors. Tocotnenol occuis as ail intermediate in the biosynthesis. 

A more detailed understanding of the biochemical pathways and enzymes involved in saponin biosynthesis will facilitate the development of plants with altered saponin content. In some cases, enhanced levels of saponins or the synthesis of novel saponins may be desirable (for example, for drug production 4 or improved disease resistance3,5,6), while for other plants, reduction in the content of undesirable saponins would be beneficial (for example, for legume saponins that are associated with antifeedant properties in animal feed7). This chapter is concerned with recent progress that has been made in the characterization of the enzymes and genes involved in the synthesis of these complex molecules and focuses on triterpenoid saponins. 

Site of alkaloid formation, transport, and accumulation. QA are formed in the aerial green parts of legumes, especially in the leaves (.9) In lupin leaves we succeeded in localizing the key enzymes of QA biosynthesis in the chloroplast (10, 11), where the formation of the precursor lysine also takes place. Like most of the processes that are located in the chloroplast, QA biosynthesis is regulated by light (.8) and QA formation fol lows a light-dependent diurnal rhythm (, 13). The alkaloids formed in the leaves are translocated via the phloem (13, 14) all over a lupin plant, so that all plant parts contain alkaloids. QA are accumulated and stored preferentially in epidermal and subepidermal tissues of stems and leaves (15, 16). Especially rich in alkaloids are the seeds, which may contain up to 5% (dry weight) alkaloid (equivalent to 200 mmol/ kg). ... 

Some species contain a closely related enzyme activity to DFR that can act on tlavanones, termed the flavanone 4-reductase (FNR), which may represent a variant DFR form. This is discussed in more detail in Section 3.4.7. 5-Deoxyleucoanthocyanidin compounds are known to occur in legumes, and analysis of two recombinant DFR proteins (MtDFRl and MtDFR2) from Medicago truncatula (barrel medic) has found activity on the 5-deoxyDHF substrates fustin and dihydrorobinetin. Indeed, fustin was the preferred substrate of both recombinant enzymes. MtDFRl and MtDFR2 showed distinct enzyme characteristics, and overexpression of MtDFRl but not MtDFR2 promoted anthocyanin biosynthesis in flowers of N. tabacum. 

A characteristic of legumes is the biosynthesis of 6 -deoxychalcones (chalcones lacking a hydroxyl at the C-6 position), which are the substrates for the production of 5-deoxyflavo-noids. The formation of 6 -deoxychalcones requires the activity of polyketide reductase (PKR) (also known as chalcone reductase or chalcone ketide reductase) in conjunction with CHS. It is thought that CoA-linked polyketide intermediates diffuse in and out of the CHS active site, and while unbound are reduced to alcohols by PKR. The resultant hydroxyl groups are then removed from the PKR products in the final cyclization and aromatization steps catalyzed by CHS. 

HI4 OMT protein showed activity against the 3-hydroxyl of a compound related to (+)-6a-hydroxymaackiain, ( + )-medicarpin, suggesting HM OMT may be functionally identical to HM30MT. However, the HM30MT substrate is only found in species making (+)-pisatin. The G. echinata HM OMT cDNA was used to isolate HM OMT cDNAs from L. japonicus, M. truncatula, and other legumes. Both HM OMT and lOMT may be involved in formono-netin biosynthesis, perhaps in the same tissues, and the formation of heterodimers of similar OMTs has been reported. 

Shimada, N. et al., A cluster of genes encodes the two types of chalcone isomerase involved in the biosynthesis of general flavonoids and legume-specific 5-deoxy(iso)flavonoids in Lotus japonicus. Plant Physiol, 131, 941, 2003. 

Tanner, G.J. et al., Proanthocyanidin biosynthesis in plants. Purification of legume leucoantho-cyanidin reductase and molecular cloning of its cDNA. J. Biol. Chem., 278, 31647, 2003. 

Jung W, Yu O, Lau SM, O Keefe DP, Odell J, Fader G, McGonigle B. 2000. Identification and expression of isofavone synthase, the key enzyme for biosynthesis of isofavones in legumes. Nature Biotechnol 18 208-212. 

Pang Y, Peel G, Wright E, Wang Z, Dixon RA. 2007. Early steps in proanthocyanidin biosynthesis in the model legume Medicago truncatula. Plant Physiol 145 601-615. 

Shimada N, Akashi T, Aoki T, Ayabe S. 2000. Induction of isoflavonoid pathway in the model legume Lotus japonicus Molecular characterization of enzymes involved in phytoalexin biosynthesis. Plant Sci 160 37-47. 

Secondly, the deacetylated form of chitin, chitosan, does not induce phytoalexin formation in the rice system but is active in other plant culture systems [99]. Glucan elicitors induce phytoalexins in legumes (soybean, chickpea, bean, alfalfa, pea) and solanaceous sp. (potato, sweet pepper) [100]. However, anthraquinone biosynthesis was stimulated in Morinda citrifolia by both chitin and chitosan. The degree of acetylation was found to be important in inducing defense responses. During the first few days of incubation after adding elicitor,... 

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