Submitted to: Recent Advances in Allelopathy - Volume 2
Publication Type: Book / chapter
Publication Acceptance Date: 8/15/2003
Publication Date: 10/1/2004
Citation: Romagni, J.G., Rosell, R.C., Nanayakkara, N.D., Dayan, F.E. 2004. Ecophysiology and potential modes of action for selected lichen secondary metabolites. In: Recent Advances in Allelopathy - Volume 2. Macias, F.A., Galindo, J.C.G., Molinillo, J.M.G., Cutler, H.G., Editors. Boca Raton, FL. CRC Press. 2:13-33. Interpretive Summary: Book chapter. No interpretive summary required.
Technical Abstract: Lichens, a symbiosis between a fungal and algal partner, produce secondary compounds that are unique to the symbiosis. Due to the high energy investment in these compounds, which can comprise up to 25% of the dry thallus weight, they must have an important role in lichen ecology. Our group is beginning to elucidate specific allelopathic roles and modes of action for these compounds. One lichen compound, (-)-usnic acid was found to inhibit 4-hydroxyphenylpyruvate dioxygenase, a key enzyme in carotenoid biosynthesis. A series of lichen emodin analogues have been found to cause bleaching in grasses. Continued research suggested a decrease in photosystem II (PSII) activity, but the putative mode of action for these compounds remains to be determined. Another group of anthraquinone analogues has been found to inhibit germination and primary root formation. The preliminary data suggests that each lichen secondary compound has several ecological roles. Many inhibit pathways crucial for seedling development. This may decrease interspecific competition, especially in the canopy. Finally, we determined several compounds to be effective against phloem-feeding insects, particularly whiteflies (Bemisia tabaci). Both (-)-usnic acid and vulpinic acid caused highly significant mortality in whiteflies. Other functions of the same compounds, such as (-)-usnic, may include antiherbivory mechanisms.