Allelochemical induction of cytochrome P450 monooxygenases and amelioration of xenobiotic toxicity in Helicoverpa zea.
Polyphagous herbivores encounter allelochemicals as complex mixtures in their host plants, and the toxicity of an individual compound may be influenced by the chemical matrix in which it is encountered. Certain plant constituents may reduce toxicity of cooccurring compounds by inducing detoxification systems, including cytochrome P450s, which can metabolize a broad range of substances. The polyphagous corn earworm Helicoverpa zea encounters a diversity of plant allelochemicals in its many host plants and, as well, can encounter aflatoxins, mycotoxins produced by Aspergillus flavus and Aspergillus parasiticus that infect damaged grains. Dietary supplementation of each of three plant allelochemicals that are frequently (coumarin, COU), occasionally (indole-3-carbinol, 13C), or rarely (xanthotoxin, XAN) encountered by H. zea larvae substantially reduced the toxicity of aflatoxin B1 (AFB1) to H. zea. Compared to fourth instars on diets containing 1 microg/g AFB1 that failed to develop and pupate, fourth instars on diets containing I3C and XAN increased in mass by 216.1 and 700% after 6 days, and pupated at rates of 40 and 88%, respectively. Diets containing COU or XAN also significantly reduced the mortality rates of caterpillars exposed to the insecticides, diazinon and carbaryl. Diets containing COU and XAN increased CYP6B8 transcripts 2.6-fold; CYP321A1 transcripts increased 20.7, 8.3, and 10.6-fold in response to COU, I3C, and XAN, respectively. These results indicate that consumption of plant allelochemicals can ameliorate toxicity of natural and synthetic toxins encountered by insects, and they suggest that P450s induced by these allelochemicals contribute to detoxification of these chemicals in H. zea.
Zeng
Ren Sen
RS
Key Lab of Pesticide and Chemical Biology, Ministry of Education, South China Agricultural University, Guangzhou 510642, People's Republic of China. rszeng@scau.edu.cn
Wen
Zhimou
Z
Niu
Guodong
G
Schuler
Mary A
MA
Berenbaum
May R
MR
D000818:Animals; D001483:Base Sequence; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis* / Q000235:genetics; D017931:DNA Primers; D004790:Enzyme Induction; D009036:Moths / Q000187:drug effects*; D010675:Pheromones / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic / Q000187:drug effects; D015262:Xenobiotics / Q000633:toxicity*
D017931:DNA Primers; D010675:Pheromones; D012333:RNA, Messenger; D015262:Xenobiotics; D003577:Cytochrome P-450 Enzyme System