ABSCISIC-ACID IN SPOROPHYTES OF 3 LAMINARIA SPECIES (PHAEOPHYTA)

Abscisic acid (ABA) was identified in tissue of Laminaria hyperborea ( Gunn.) Foslie, L. digitata (Huds.) Lamour. and L. saccharina (L.) Lamo ur, by GC-MS. Endogenous ABA levels in L. hyperborea, cultivated in an experimental daylength cycle simulating the natural year, showed a di stinct negative correlation between ABA contents and growth rates. Tis sue ABA ranged from 140 mu g kg(-1) DW during the resting phase in exp erimental autumn to 50 mu g kg(-1) DW in experimental winter when the new blade generation is formed. Application of ABA to culture medium o f beaker cultures L. hyperborea showed a significant inhibition of gro wth at 10(-6) and 10(-5) M ABA in culture under short-day conditions. The results offer evidence that ABA might act as a growth inhibitor in volved in control of the circannual growth rhythm of L. hyperborea.