Ecdysone
The molting hormone of insects. It is a derivative of cholesterol. The most striking physiological activity of ecdysone is the induction of puffs (zones of gene activity) in giant chromosomes of the salivary glands and other organs of the midge Chironomus. The induction of puffs has been visualized as primary action of the hormone, indicating that ecdysone controls the activity of specific genes. It has been shown that ecdysone stimulates the synthesis of messenger RNA, among which is the messenger for dopa decarboxylase. This enzyme is involved in the biosynthesis of the sclerotizing agent N-acetyl-dopamine. See Insecta
Ecdysone
any of the group of steroid hormones that stimulate molting and metamorphosis in arthropods. Some varieties—especially α-ecdysone and ecdysterone, either separately or together—function as molting hormones in different groups of arthropods.
In 1954, A. Butenandt isolated α-ecdysone from silkworm cocoons; in 1965 the chemical structure of the hormone was determined by chemical methods and by X-ray diffraction analysis. α-Ecdysone has the structural formula
where R = H and R′ = OH. (In ecdysterone, R = R′ = OH, and in ponasterone, R = OH and R′ = H.) Ecdysones are solid, optically active substances that are slightly soluble in water but readily soluble in polar organic solvents. They contain 27 or 28 carbon atoms. Four structural features are characteristic of most ecdysones: the cis linkage of rings A and B, the cis-glycol group in ring A, the α-and β-unsaturated ketone groups in ring B, and at least one hydroxyl group (usually two or three) in the sterol side chain.
Ecdysones are formed by the thoracic gland in insects and by the Y organ in crustaceans; the activity of the organ increases at the time the shell is shed. Ecdysones cause the epidermis to release the molting secretion that causes the formation and hardening of a new cutícula. Ecdysones also initiate pupal molting, which is accompanied by the transformation of the larvae into pupae and by the formation of a special melting cocoon (puparium). For this reason, ecdysones are used by sericulturists in Japan to hasten the formation of silkworm cocoons and facilitate manual sorting. At present, the use of ecdysones as insecticides that work by hormonal action does not appear promising.
Ecdysones act on insects by inducing chromosome puffs (zones of genetic activity). Successively arising puffs sequentially activate genes involved in the transmission of genetic information. In this manner ecdysones activate, for example, dioxyphenylalanine decarboxylase, an enzyme needed to synthesize the substances responsible for sclerotization of the insects’ cutícula. Ecdysones induce the formation of protein by stimulating the biosynthesis of messenger ribonucleic acids (mRNA). The balanced action of ecdysones, combined with that of the juvenile hormones, regulates the stages of insect development.
The concentration of ecdysones in arthropods is very low, ranging from 0.1 microgram per gram (μg/g) to 1.0μg/g. Certain ecdysones, including amarosterone and cyasterone, are also found in plants in concentrations ranging from 0.1 percent to 1–2 percent, but their physiological function is still unknown. Plant ecdysones contain 27, 28, or 29 carbon atoms. The assumption that the hormones protect plants against herbivorous insects has not been experimentally proved. It is worth noting that ecdysones stimulate the growth of such plants as peas and rice and that the plant hormone gibberellin induces molting in the locust.
REFERENCES
Akhrem, A. A., I. S. Levina, and Iu. A. Titov. Ekdizony—steroidnye gormony nasekomykh. Minsk, 1973.Heftmann, E. Biokhimiia steroidov. Moscow, 1972. (Translated from English.)
E. P. SEREBRIAKOV
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