Osmotic and atmospheric dehydration effects in the lichens Hypogymnia physodes, Lobaria pulmonaria, and Peltigera aphthosa:: an in vivo study of the chlorophyll fluorescence induction

Inactivation of photosynthesis during atmospheric and osmotic (highly concentrated NaCl or sucrose solutions) dehydration was monitored by measurement of chlorophyll fluorescence induction (OIP-phase, Kautsky-curves) in three lichen species. The induction curves were changed in a very similar way by all three treatments. all dehydration effects were rapidly reversible after rehydration. At relatively mild water stress, the rise time to the transient peak F-p was prolonged, and the variable part of fluorescence was diminished. In addition, at severe water stress, a considerable decline of the F-0 value was observed. For NaCl treatment this effect started at water potentials <-8.5 MPa in P. aphthosa, <-12 MPa in H. physodes, and <-21 MPa in L. pulmonaria. Above these water potentials, our observations are in agreement with values from desiccation-tolerant algae, higher plants, and lichens, where an inactivation on the photosystem 2 (PS2) donor side has been postulated. At very low water potentials, the decrease in F-0 probably monitors changes in the organization of the antenna apparatus of PS2.