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

Abstract

Modulated chlorophyll fluorometry demonstrated rapid and complete recovery of maximum and effective quantum yield (F_v/F_m and ΦPSII)on remoistening after 7 days in an air-dry state. Both parameters returned to pre-desiccation values within 2 h in either darkness or light (PPFD 100 μmol m⁻² S^−l), and the period of desiccation appeared as only a transitory interruption of normal photosynthetic function. In the course of drying both parameters declined as cell water content fell below full turgor, steeply so below 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 hand 7-8 h (in both fast and slowrelaxing components), returning to pre-desiccation levels within 24 h. Progressive fall in NPQ during recovery in the dark was mostly due to decline in the slow-relaxing component. The results suggest that desiccation tolerance in Porella platyphylla is essentially constitutive. Increased photoprotection during recovery in light may reflect ‘repair’ processes which are essentially complete within 24 h.