Phytoalexins alfalfa

Abiotic elicitors, examples, 48 Abscisic acid, plant-growth hormone inhibitor, I6f Active defense, definition, 37 Alfalfa, phytoalexins, 56 Allelochemicals... 

HPLC/PDA/MS analysis of an alfalfa root extract. The HPLC retention time, the UV absorbance spectrum, and the mass spectrum readily identify the peak eluting at 45 minutes as medicarpin, a known phytoalexin in alfalfa. 

He, X.Z. and Dixon, R.A., Genetic manipulation of isofiavone 7-0-methyltransferase enhances biosynthesis of 4 -0-methylated isofiavonoid phytoalexins and disease resistance in alfalfa. Plant Cell, 12, 1689, 2000. 

Paiva, N.L. et al.. Stress responses in alfalfa (Medicago sativa L.) 11. Molecular cloning and expression of alfalfa isofiavone reductase, a key enzyme of isofiavonoid phytoalexin biosynthesis. Plant Mol Biol, 17, 653, 1991. 

The biosynthesis of pterocarpans, which include well-known phytoalexins such as medicarpin in alfalfa (Medicago sativa) [Baker et al., 1989 Higgins, 1972 Oommen et al., 1994 He and Dixon, 2000] (Fig. 21.2), pisatin in pea... 

Higgins VJ. 1972. Role of the phytoalexin medicarpin in three leaf spot diseases of alfalfa. Physiol Plant Pathol 2 289-300. 

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,... 

Microsomal preparations from yeast-elicited cell cultures of chickpea catalyzed the hydroxylation of formononetin and biochanin A to their 2 - and 3 -hydroxy derivatives.43 44 Neither daidzein nor genistein were accepted as substrates. Both hydroxylation reactions seem to be catalyzed by two distinct enzymes, since they exhibited different physicochemical properties and induction kinetics in cell cultures and roots of chickpeas.45 Both 2 - and 3 -hydroxylations of formononetin are prerequisite reactions in the pathway for biosynthesis of the phytoalexins, medicarpin and maackiain in alfalfa and chickpea, respectively8. 

BALDRIDGE, G.D., O NEILL, N.R., SAMAC, D.A., Alfalfa (.Medicago sativa L.) resistance to the root-lesion nematode, Pratylenchus penetrans defense-response gene mRNA and isoflavonoid phytoalexin levels in roots, Plant Mol. Biol., 1998, 38,999-1010. 

Fig. 1. Biosynthetic pathway for alfalfa and clover phytoalexins. SAM, S-adenosyl methionine.

---