The plants grow extremely fast, look spindly and pale and break off easily. It was termed gibberellin . Roughly 30 percent of all known gibberellins are biologically active. All higher plants contain presumably at least one, but usually several active and inactive gibberellins that exist in different concentrations depending on the respective tissue.
Gibberellins are diterpenoids derived from four isoprenoid units forming a system of four rings.
It is distinguished between gibberellins of 19 and such of 20 C-atoms. Both enumeration and the illustration below show, how the single structures differ. Young, growing meristematic cauline tissue, apical root cells, young fruits, as well as unripe or germinating seeds are all rich in gibberellins. In sun flowers is the gibberellin content highest in the young leaves and in the uppermost internodes while it decreases continuously towards the basal leaves and internodes. Gibberellin content and growth velocity of a tissue are correlated.