Changes in chlorophyll a fluorescence, photosynthetic CO2 assimilation andxanthophyll cycle interconversions during dehydration in desiccation-tolerant and intolerant liverworts

The interactions among water content, chlorophyll a fluorescence emission, xanthophyll interconversions and net photosynthesis were analyzed during de hydration in desiccation-tolerant Frullania dilatata (L.) Dum. and desiccat ion-intolerant Pellia endiviifolia (Dicks) Dum. Water loss led to a progres sive suppression of photosynthetic carbon assimilation in both species. The ir chlorophyll fluorescence characteristics at low water content were: low photosynthetic quantum conversion efficiency, high excitation pressure on p hotosystem II and strong non-photochemical quenching. However, dissipation activity was lower in P. endiviifolia and was not accompanied by a rise in the concentration of de-epoxidised xanthophylls as F. dilatata. The photosy nthetic apparatus of F. dilatata remained fully and speedily recuperable af ter desiccation in as indicated by the restoration of chlorophyll fluoresce nce parameters to pre-desiccation values upon rehydration. A lack of recove ry upon remoistening of P, endiviifolia indicated permanent and irreversibl e damage to photosystem II. The results suggest that F. dilatata possesses a desiccation-induced zeaxanthin-mediated photoprotective mechanism which m ight aid photosynthesis recovery when favourable conditions are restored by alleviating photoinhibitory damage during desiccation. This avoidance mech anism might have evolved as an adaptative response to repeated cycles of de siccation and rehydration that represent a real threat to photosynthetic vi ability.