Inducible effects of abscisic acid on sporophyte discs from Laminaria japonica Areschoug (Laminariales, Phaeophyceae)

The effects of exogenous abscisic acid (ABA; 10(-7)-10(-5) M), a known plant growth regulator, on reproduction and growth were investigated by culturing discs from sporophytes of Laminaria japonica Areschoug. ABA plays a role in triggering sorus formation, and it was found that sorus formation of discs was fastest in 10(-5) M ABA. The application of 10(-5) M ABA to culturing discs also suppressed the expansion of surface area. ABA contents in sorus and vegetative parts of the sporophyte were determined by bioassay. The mean ABA content in sorus parts obtained from sporophytes was 0.222 +/- 0.053 mug equivalent-ABA g wet weight(-1), which was about five times higher than the content found in vegetative parts (0.048 +/- 0.009 mug equivalent-ABA g wet weight(-1)). Taken together these results suggest that sorus development requires an elevated level of ABA and is associated with decreasing vegetative growth and that the ABA level of the sporophyte may play a crucial role in reproduction.