BIOSYNTHESIS OF ECDYSTEROIDS IN ZEA-MAYS

The incubation of several radiolabelled substrates with Zea mays plant s demonstrated the incorporation of radiolabels into ecdysteroid conju gates. Radiolabelled [C-14]ecdysone and [C-14]20-hydroxyecdysone, were biosynthesized from [2-C-14]mevalonic acid (MVA) in Z. mays. These ec dysteroids can be released from their conjugates by treatment with whe at germ acid phosphatase or mild acid hydrolysis. The C-24 reduced sid e chain sterols, lathosterol and cholesterol were endogenously biosynt hesized from [2-C-14]MVA and were identified by H-1 NMR. Lathosterol a ccounts for ca 0.5% of the total sterol composition, whereas cholester ol; is present at 2.5%. However, lathosterol was consistently found to have a specific activity three to six times that of cholesterol. Incu bation of [4-C-14]cholesterol with Z. mays leaves also demonstrated in corporation into a 20-hydroxyecdysone conjugate. Incubation of [22,23- H-3]ecdysone with Z. mays demonstrated incorporation into radiolabelle d ecdysone diphosphate and ecdysone polyphosphate, which were cleaved upon acid phosphatase treatment. Z. mays biosynthesizes primarily ecdy steroid conjugates and does not appear to produce detectable levels of non-conjugated ecdysteroids.