Distribution and biosynthesis of 20-hydroxyecdysone in plants of Achyranthes japonica Nakai.

There is increasing interest in phytoecdysteroids (PEs) because of their potential role in plant defense against insects. To understand the mechanism regulating their levels in plants, the fluctuation, distribution, and biosynthesis of PE 20-hydroxyecdysone (20E) examined in Achyranthes japonica. The total amount of 20E per individual plant initially remained at a constant level, and increased markedly after the first leaf pair (LP) stage, while the concentration of 20E in a given plant decreased rapidly during vegetative growth. In addition, the incorporation of [2-(14)C]-mevalonic acid into 20E did not differ significantly depending on plant organs and developmental stages, suggesting that biosynthesis of 20E is not restricted to particular organs or growth stages.