CHANGES OF FLUORESCENCE AND XANTHOPHYLL PIGMENTS DURING DEHYDRATION IN THE RESURRECTION PLANT SELAGINELLA-LEPIDOPHYLLA IN LOW AND MEDIUM LIGHT INTENSITIES

The changes in photosynthetic efficiency and photosynthetic pigments during dehydration of the resurrection plant Selaginella lepidophylla (from the Chiuhahuan desert, S.W. Texas, USA) were examined under different light conditions. Changes in the photosynthetic efficiency were deduced from chlorophyll a fluorescence measurements (F(o), F(m), and F(v)) and pigment changes were measured by HPLC analysis. A small decrease in F(v)/F(m) was seen in hydrated stems in high light (650 mumol photons . m-2 . s-1) but not in low light (50 mumol photons . m-2 . s-1). However, a pronounced decline in F(v)/F(m) was observed during dehydration in both light treatments. after one to two hours of dehydration. A rise in F(o) was observed only after six to ten hours of dehydration. Concomitant with the decrease in photosynthetic efficiency during dehydration a rise in the xanthophyll zeaxanthin was observed, even in low-light treatments. The increase in zeaxanthin can be related to previously observed photoprotective non-photochemical quenching of fluorescence in dehydrating stems of S. lepidophylla. We hypothesize that under dehydrating conditions even low light levels become excessive and zeaxanthin-related photoprotection is engaged. We speculate that these processes, as well as stem curling and self shading (Eickmeier et al. 1992) serve to minimize photoinhibitory damage to S. lepidophylla during the process of dehydration.