Flavonoids nodulation

A. Nodulation genes—production of nod factors Flavonoids Rhizobium spp. 90,91.92... 

Flavonoid levels in plants can be affected by their nutritional status. Low nitrate concentrations, for example, induce flavonoid accumulation, which then serve as chemoattractants to nitrogen-fixing bacteria. Nodulation then restores the nitrogen economy of the plant.In L. pedunculatus, proanthocyanidins are not formed under high-nitrogen conditions, presumably because the requirement for nodulation is not so critical. 

FIGURE 8.7 Model for the role of Rhizobium- nd xnodule formation in white clover. (Redrawn from Mathesius, U., J. Exp. Bot., 52, 419, 2001. With permission of Oxford University Press.)... 

Further studies are required to fully elucidate the role of flavonoids in auxin regulation in vivo to determine, for example, whether changes in the synthesis or deposition of specific flavonoids within the cell act to change the rate or direction of auxin transport. There is the question of how such different organs or developmental outcomes as nodules, lateral roots,... 

Jain, V. and Nainawatee, H.S., Plant flavonoids signals to legume nodulation and soil microorganisms, J. Plant Biochem. Biotechnol, 11, 1, 2002. 

Firmin, J.L. et al., Flavonoid activation of nodulation genes in Rhizobium reversed by other compounds present in plants. Nature, 324, 90, 1986. 

Mathesius, U. et al., Flavonoids synthesized in cortical cells during nodule initiation are early developmental markers in white clover. Mol. Plant-Microbe Interact., 11, 1223, 1998. 

Mathesius U. 2001. Flavonoids induced in cells undergoing nodule organogenesis in white clover are regulators of auxin breakdown by peroxidase. J Exp Bot 52 419-426. 

Mathesius U, Schlaman FIRM, Spaink PIP, Sautter C, Rolfe BG, Djordjevic MA. 1998. Auxin transport inhibition precedes root nodule formation in white clover roots and is regulated by flavonoids and derivatives of chitin oligosaccharides. Plant J 14 23-34. 

Wasson AP, Pellerone FI, Mathesius U. 2006. Silencing the flavonoid pathway in Medicago truncatula inhibits root nodule formation and prevents auxin transport regulation by rhizobia. Plant Cell 18 1617-1629. 

Apigenin (70b), luteolin (70c) and related polyhydroxyflavones can activate the nodulation genes of the nitrogen-fixation bacteria (genus Rhizobium) in the leguminous plants such as peas. This is the first time that simple flavonoids have been shown to be involved in gene regulation [367-369]. 

This rhamnan OPS is induced when the bacterium is cultured in the presence of flavonoids (molecules produced by die host legume that induce expression of die rhizobial nod genes) (Reuhs, et al., 2005), and a similar rhamnan was detected in bacteroids obtained from die host legume root nodule (Fraysse, et al., 2002, Jabbouri, et al., 1996). 

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