Ecdysteroids during ovarian development and embryogenesis in solitary and gregarious schistocerca gregaria
Maternal ecdysteroids identified in the vitellogenic oocytes of Schistocerca gregaria included more than 80% polar conjugates, up to 5% free ecdysteroids, and up to 15% non-hydrolyzable polar metabolites. The representations of ecdysone (E), 20-hydroxyecdysone (20E), and 2-deoxyecdysone (2dE) in the conjugates was about 16:3:1, and in the free ecdysteroids about 3:1:1. The quantity of ecdysteroids in the ovaries before egg-laying reached 2.3 ng 20E equiv. per mg tissue in the solitary, and 8.9 ng/mg in the gregarious females. Newly laid eggs contained 14 ng and 89 ng, respectively, of 20E equiv. per egg. Nearly all egg ecdysteroids were in form of conjugates and their content declined during the first half of embryonic development. The amount of ecdysteroids sharply increased to over 70 ng 20E equiv./egg in the solitary, and to nearly 400 ng/egg in the gregarious phase. In the second half of embryonic development, the representation of conjugates in total ecdysteroids was reduced to 45-55%, whereas that of free E + 20E rose to 30-40%. Free 2dE remained low but, in the gregarious embryos, free 26E increased to 10% of all ecdysteroids. The conjugates of solitary embryos contained nearly exclusively E and 20E (in ratio 2:1), whereas those of the gregarious embryos included E, 20E, 2dE, and 26E (in ratio 12:7:4:1). Towards the end of embryonic development, the amounts of conjugates and of free ecdysteroids decreased, while that of polar metabolites rose. A sharp drop in ecdysteroid content was associated with hatching but the more than five times higher ecdysteroid level in the gregarious than in the solitary phase was maintained in the newly hatched larvae. Arch. Copyright 1999 Wiley-Liss, Inc.
Zoology Department, Assiut University, Assiut, Egypt.
AI
Tawfik
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Vedrova
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Sehnal