Indolic and Phenolic Compounds

Soil microbial production of indolic and phenolic compounds derived from aromatic amino acids is regarded as an important factor in plant development. Plant growth was promoted upon the addition of L-tryptophan (Trp) to soil (Frankenberger et al. 1990; Frankenberger and Arshad 1991a,b). Environmental fluctuations cause increased Trp contents in soil and regulate the microbial production of indole-3-acetic acid (auxin), of its storage product indole-3-ethanol, and of anthranilic acid from the precursor Trp (Lebuhn et al. 1994). Microbial auxin and indole-3-ethanol exert auxin-phytohormone effects on plants (Martin et al. 1989; Müller et al. 1989; Selvadurai et al. 1991). Auxin also seems to control the induction of plant resistance mechanisms (Jouanneau et al. 1991).