Conversion of a radiolabelled ecdysone precursor, 2,22,25-trideoxyecdysone, by embryonic and larval tissues of Locusta migratoria.

A high specific activity tritiated ecdysone precursor, 2,22,25-trideoxyecdysone, was used to probe the capacity of various embryonic and larval tissues to perform the last 3 hydroxylation steps in ecdysone biosynthesis. Embryos at early stages of development, prior to the differentiation of their endocrine glands and embryonic heads, thoraces and abdomens of later stages, were found to have the capacity to hydroxylate the precursor to ecdysone. Larval epidermis and fat body are also able to transform 2,22,25-trideoxyecdysone into ecdysone; Malpighian tubules and midgut hydroxylate the precursor at C-2 but are apparently unable to hydroxylate both at C-22 and C-25. Larval prothoracic glands convert the precursor to ecdysone at a very efficient rate, which is 1-2 magnitudes higher than that of the other tissues investigated; several data argue for the existence of a privileged sequence of hydroxylations, C-25, C-22, C-2, in the larval prothoracic glands.