Metal binding and resultant loss of phototoxicity of alpha-terthienyl: metal detoxification versus alpha-terthienyl inactivation.

The members of the plant family asteraceae are noted for their cosmopolitan distribution and their versatility is attributed to be largely due to their morphological adaptations. Interestingly members of this family are endowed with rich levels of secondary plant metabolites, many of which are photochemically active (Bakker et al. 1979; Kagan et al. 1989). The secondary plant metabolite alpha-terthienyl derived from the plant family asteraceae is among the new class of light activated insecticide. The photobiocidal effects associated with alpha-terthienyl in presence of sunlight and ultraviolet light (300-400 nm), has stimulated a great deal of interest in its toxic mechanism of action against a number of organisms including phytopathogenic fungi, nematodes and mosquito larvae. Trials under tropical conditions indicate a very high level of activity as a larvicide to mosquito. There is no cross resistance to this compound in malathion resistant mosquito larvae (Arnason et al. 1989). Even though many researchers feel that the phototoxicity of secondary plant metabolites has arisen independently many times in evolution as a defense mechanism, the physiological impact of such biologically active compounds in the plant producing them also should be addressed (Arnason et al. 1987). Moreover, the accumulation of secondary plant metabolites in the roots of many asteraceae members as is the case with alpha-terthienyl in marigold (Tagetes sp.) roots, hints towards their functional divergence. In this study, we demonstrate a potent heavy metal quenching activity of alpha-terthienyl.