ECDYSTEROID DISTRIBUTION DURING DEVELOPMENT OF SPINACH

During the growth and development of spinach (Spinacia oleracea), phytoecdysteroids are dynamically cycled between various leaves with an overall increase in total ecdysteroid content per plant. Within seeds, the embryo possesses 17-mu-g ecdysteroid per seed whereas the seed coat has only 1-mu-g ecdysteroid per seed. During the first 20 days of development the level of ecdysteroids on a mu-g per plant basis remains constant. After 20 days ecdysteroid content (mu-g per plant) increases with age. The physiological level of ecdysteroids within specific leaves cycles up and down with development on mu-g ecdysteroid per gram fresh weight basis. During this cycling ecdysteroids are synthesized in leaves subtending their site of accumulation, which is in the apical most leaves, as demonstrated by [2-C-14]MVA radiolabel feed experiments. Movement of a post-sterol product, possibly ecdysteroids, is also supported by the radiolabel experiments. Transport of these products during growth and development of spinach would account for the physiological accumulation of ecdysteroids in the apical parts of the plant. The physiology of ecdysteroids observed in spinach provides the basis for a consistent interpretation of most previous reports of ecdysteroid levels in higher plants.