Indirect defense compounds

Viral infections continue to be significant causes of morbidity and mortality and at the same time continue to be resistant to treatment by small molecules. Avridine (6) is an antiviral compound which has shown some activity in a variety of animal tests apparently based upon its ability to stimulate a number of cells to produce the high molecular weight endogenous antiviral substance interferon. Thus, the compound is believed to operate indirectly by stimulating the body s own natural defenses against viral penetration into host cells. Avridine is synthesized by... 

Despite the act that the new compounds have been known and available for years, relatively little is known about their mode of action. Table VI reflects the state of the art. The lack of information is particularly surprising in the case of fosetyl and metalaxyl as far as their indirect effect is concerned, that is, the stimulation of the host plant s defense reactions (e.g. formation of phytoalexins). It is for the first time in the history of fungicides that such effects have been reported. 

Experimental compounds were evaluated in a dose-response format. Azoxystrobin or other fungicides that have both protective and curative activity were used as a standard, and a solvent control was used in every study. The number of disease lesions per leaf was used to determine the ability of the test compounds to prevent infections. The size of the lesions was used to determine the curative activity of compounds. Each fungicide concentration is replicated four times and the experiment is repeated at least once. This bioassay does not differentiate between direct effects on the fungus and indirect effects through induction of plant defenses. However, if a compound is much more active in this in vivo assay than than the in vitro microtiter assay, induction activity is indicated. 

Upon infestation of lima bean leaves (Phaseolus lunatus) with two-spotted spider mites (Tetranychus urticae), induction of ( )-P-ocimene (47) and a homomonoterpene, -4,8-dimethyl-l,3,7-nonatriene, occurs. A homosesquiterpene, (3 , 7 )-4,8,12-trimethyl-l,3,7,ll-tridecatetraene also has been observed (Dicke et al., 1990). These compounds attract another mite, Phytoseiulus persimilis, which is a predator of the two-spotted spider mite, a phenomenon known as indirect defense (Dicke et al., 1990 Takabayashi et al., 1991). When uninfested leaves are placed on moist cotton that had previously come into contact with leaves that had been infested (but had the mites removed), production of these compounds again occurred, providing evidence that induction of these kairomones occurs (Takabayashi et al., 1991). The... 

Indirect defense Chemical compounds attract natural enemies of an herbivore to locate a suitable prey after attack (also termed top-down effects or multitrophic Interactions) Indirect defense Is normally inducible and thus cost effective under a low herbivore environment. Effective only if natural enemies are within the range of spreading signals... 

---