The effect of abscisic acid on chlorophyll fluorescence in lichens under extreme water regimes

Chlorophyll fluorescence measurements were used to test whether externally applied abscisic acid (ABA) has an effect on the desiccation tolerance of l ichens and their sensitivity to constant water saturation. A surplus of ABA did not decrease the time required to regain full photosynthetic capacity after prolonged dry periods. However, an effect of ABA could be observed wh en lichens were permanently hydrated at moderately high temperatures. Liche ns suffered less from constant saturation if ABA was added to the incubatio n medium. These results suggest a positive effect of ABA on membrane functi on.