XVI International Botanical Congess

Bearing in mind that the deciduous family Salicaceae (genus Salix and Populus) is the most ancient among Dicotyledons and the primitive species in the willow subgenus Salix are derived from Populus-like forms we have chosen Populus alba, P. tremula and Salix pentandra to compare their ontogenetic change in leaf secondary metabolism with that of young, still developing species, S. myrsinifolia. A number of phenolic glucosides, cinnamic acid derivatives, flavonoid- glycosides and condensed tannins were analyzed in five or six apicalmost leaves of current-growth shoots of seedlings (current season old), saplings (six years old) and adult trees (15-20 years old). The old versus young species showed marked difference in strategy of secondary chemistry throughout the ontogenetic phases. Low molecular mass phenolic glucosides appeared to be strongly induced only in juvenile ontogenetic phases of old species while they were also very abundant in mature ontogenetic phases of young species. On the contrary, in mature phases of the old species phenolic glucosides were replaced by high molecular mass components (tannins) but in mature phases of young species the expression of high molecular mass components were low.