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Elucidation of a novel mode of action for a lichen anthraquinone analogue .
Rivera, Christin*,1, Romagni, Joanne1, 1 University of St Thomas, Houston, TX, USA
ABSTRACT- Bioactivity of lichen secondary metabolites has generally been ignored. Lichens, a symbiosis between an alga and fungal bionts, produce a variety of secondary compounds. Elucidation of novel modes of action for lichen natural products may begin to explain the roles of these metabolically expensive compounds. In this study, we are attempting to determine the putative mode of action for DNA3-15-1, an analogue of the anthraquinone, emodin. These derivatives of emodin may play a significant role in interspecific competition and/or herbivory. This specific analogue was highly specific for monocots (grasses) causing severe growth inhibition and bleaching. Our previous experiments have shown that this analogue is not an acetyl CoA carboxylase (ACCase) inhibitor, the only other known mode of action specific for monocots. DNA3-15-1 causes an increase in carotenoid content (ca. 250%) and a general decrease (ca. 80%) in chlorophyll content. We found no enzymes involved in chlorophyll or carotenoid biosynthesis inhibited. There is some photosystem (PSII) inhibition (50% of controls), though it is probably a secondary phytotoxic effect. We are continuing to investigate possible sites of inhibition, including destabilization of the mitotic spindle disruption of the light harvesting complex (LHC II).
KEY WORDS: anthraquinone, phytotoxin, lichen