PHOSPHOLIPID-SYNTHESIS IN THE FAT-BODY ENDOPLASMIC-RETICULUM DURING PRIMARY AND SECONDARY JUVENILE-HORMONE STIMULATION OF VITELLOGENESIS IN LEUCOPHAEA-MADERAE

Juvenile hormone (JH) treatment coordinately stimulated the dose-dependent synthesis of vitellogenin and endoplasmic reticulum (ER) membrane phospholipids in fat body cells from allatectomized adult females of L. maderae. Animals were pulse-labeled in vivo with [32P] to simultaneously measure the rates of synthesis of the phosphorylated subunits of vitellogenin and the structural phospholipids of the ER membranes. Phospholipid synthesis in ER membranes from nontarget tissues for JH such as thoracic muscle, midgut and larval fat body was unresponsive to hormaone treatment. The proliferation of ER in response to JH treatment was thus restricted to tissue that was competent to synthesize vitellogenin. Primary and secondary vitellogenin induction was measured in allatectomized adult females treated 12 days apart with JH-III. The time-course of the primary response for vitellogenin and ER phospholipid synthesis was characterized by a 24 h latent period, a rapid increase to a maximum at 72 h, and then a gradual decline. During secondary induction, vitellogenin accumulated in the hemolymph nearly twice as fast as before and peaked at a concentration of 38 .mu.g/.mu.l. This vitellogenin titer was .apprx. 2-fold higher than that found at the height of the primary response. During primary and secondary stimulation with JH, ER phospholipid synthesis, as measured by [14C]choline incorporation into microsomal phosphatidylcholine, was stimulated 5-fold over the untreated control animals. The amplified production of vitellogenin during the secondary response was associated with a 24 h-earlier peak of ER phospholipid synthesis in the fat body.