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Change in corpus allatum function during metamorphosis of the tobacco hornworm Manduca sexta : Regulation at the terminal step in juvenile hormone biosynthesis
Author(s) -
Bhaskaran Govindan,
Sparagana Steven P.,
Barrera Punnee,
Dahm Karl H.
Publication year - 1986
Publication title -
archives of insect biochemistry and physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.576
H-Index - 66
eISSN - 1520-6327
pISSN - 0739-4462
DOI - 10.1002/arch.940030402
Subject(s) - manduca sexta , corpus allatum , juvenile hormone , biology , endocrinology , medicine , sphingidae , metamorphosis , manduca , biochemistry , hormone , insect , larva , botany
Changes in activity of the corpora allata (CA) during larval‐pupal‐adult development of the tobacco hornworm Manduca sexta were studied by transplantation assays, measurements of in vitro juvenile hormone (JH) and JH acid synthesis, and determination of JH acid methyltransferase (JHAMT) and 3‐hydroxy‐3‐methylglutaryl coenzyme A (HMG‐CoA) reductase activities. The data from these assays demonstrate that the CA cease to secrete JH by day 4 of the last larval instar (wandering stage). With regard to JH synthesis, they remain inactive throughout the prepupal, pupal, and most of the pharate adult periods. CA of females, but not of males, resume JH synthesis shortly before eclosion. The biochemical basis of the inactivation process is the loss of JHAMT activity. However, prepupal CA produce JH acids, as shown by enzyme and in vitro assays. Pupal and pharate adult CA do not synthesize JH acids although levels of HMG‐CoA reductase activity seem to remain relatively high. Radiolabeled JH was recovered from hemolymph of allatectomized prepupae that had been injected with radiolabeled JH acid. These results provide further evidence that certain peripheral tissues (eg, imaginal discs) convert JH acid secreted by the prepupal CA to JH and, thus, that JH acid is a prohormone in the prepupal period. The CA change from hormone secretion to prohormone secretion during larval‐prepupal transformation, a unique functional alteration in an endocrine gland.