RESUMEN
The biosynthesis of cyclic triterpenoids in ten saponin-deficient (sad) mutant varieties of the diploid oat Avena strigosa is reported. Two mutants were found to be deficient in 2,3-oxidosqualene:beta-amyrin cyclase (OSbetaAC) (EC 5.4.99) and thus unable to produce the beta-amyrin necessary for the production of avenacins. The other mutants studied had post beta-amyrin lesions. 2,3-Oxidosqualene:cycloartenol cyclase (OSCC) (EC 5.4.99.8) needed for sterol formation was present in all ten mutants.
Asunto(s)
Avena/química , Mutación , Saponinas/genética , Avena/enzimología , Avena/genética , Radioisótopos de Carbono , Cromatografía Líquida de Alta Presión , Transferasas Intramoleculares/metabolismo , Ácido Mevalónico/químicaRESUMEN
In keeping with the proposal that avenacin biosynthesis is restricted to the tips of primary roots of oat seedlings, the incorporation of radioactivity from R-[2-(14)C]mevalonic acid (MVA) into avenacins and beta-amyrin by serial sections of primary roots was found to be more-or-less restricted to root tip sections. Squalene synthase (SQS) (EC 2.5.1.21) and 2,3-oxidosqualene:beta-amyrin cyclase (OS beta AC) (EC 5.4.99) were also most active in these sections. The incorporation of radiolabel from R-[2-(14)C]MVA into cycloartenol and 24-methylene cycloartanol by, and the 2,3-oxidosqualene:cycloartenol cyclase (OSCC) (EC 5.4.99) activity in, the various serial sections were consistent with phytosterol biosynthesis occurring in all the sections of the root with some tailing-off in the rate of synthesis in the more distal sections.