ABSCISIC-ACID IN LICHENS - VARIATION, WATER RELATIONS AND METABOLISM

For the first time the well known drought stress hormone abscisic acid , which is involved in regulating processes increasing desiccation tol erance in many plant systems, was analysed in lichens. ABA was detecte d in all 26 species investigated. In contrast to higher plants and liv erworts, the ABA content increased after hydration of air dry lichen t halli and decreased in desiccating lichen material. Experiments with B aeomyces rufus (Huds.) Rebent indicated that the mycobiont might be th e major site of ABA biosynthesis. After incubation of hydrated lichen thalli with radioactive ABA for up to 72 h no metabolism to phaseic ac id and dihydrophaseic acid could be detected. Fluctuations of internal ABA might be a result of ABA release to the external medium.