Desiccation tolerance and recovery of the leafy liverwort Porella platyphylla (L.) Pfeiff.: chlorophyll-fluorescence measurements

Modulated chlorophyll fluorometry demonstrated rapid and complete recovery of maximum and effective quantum yield (F-v/F-m and Phi PSII) on remoisteni ng after 7 days in an air-dry stale. Both parameters returned to pre-desicc ation values within 2 h in either darkness or light (PPFD 100 mu mol m(-2) s(-1)), and the period of desiccation appeared as only a transitory interru ption of normal photosynthetic function. In the course of drying both param eters declined as cell water content fell below full turgor, steeply so bel ow RWC = 0.5, but photochemical quenching was little affected. Increase in non-photochemical quenching (NPQ) under water stress was almost all in the slow-relaxing ('photoinhibitory') component. During recovery in light, NPQ increased strongly with peaks at 2-3 h and 7-8 h (in both fast and slow-rel axing components), returning to pre-desiccation levels within 24 h. Progres sive fall in NPQ during recovery in the dark was mostly due to decline in t he slow-relaxing component. The results suggest that desiccation tolerance in Porella platyphylla is essentially constitutive. Increased photoprotecti on during recovery in light may reflect 'repair' processes which are essent ially complete within 24 h.