24-epibrassinolide overcame the inhibitory effect of brassinazole on the barley growth and the content of brassinosteroids. The present work demonstrates the occurrence of mainly castasterone, brassinolide and cathasterone and lower amounts of 24-epibrassinolide, 24-epicastasterone, 28-homobrassinolide, typhasterol, 6-deoxocastasterone and 6-deoxotyphasterol in 14-day-old de-etiolated barley (Hordeum vulgare L. cv. Golden Promise). We also investigated the endogenous level of brassinosteroids (BRs) in barley seedlings treated with 24-epibrassinolide (EBL) and/or brassinazole (Brz). To our knowledge, this is the first report related to the occurrence of BRs and application of EBL and Brz in terms of the endogenous content of BRs in barley. Brz as a specific inhibitor of BR biosynthetic reactions decreased the level of BRs in the leaves. Application of EBL showed a weak promotive effect on the BR content in Brz-treated seedlings. Brz also inhibited growth of the seedlings; however, addition of EBL overcame the inhibition. The EBL applied alone at 0.01-1 µM increased the BR level in the leaves but at 10 µM lowered the BR content. In opposition to leaves, the Brz in the concentration range from 0.1 to 1 µM did not significantly affect the content of BRs in the roots. However, application of 10 µM Brz caused BRs to decrease, but treatment of EBL concentrations overcame the inhibitory effect of Brz.
Keywords: Barley; Distribution; Inhibition; Interaction; Promotive effect.