Figure 1.

Kinetics of PSII activation in desert crusts following rehydration in the light. Rehydration of a dried crust disc of 2-cm diameter was carried out at room temperature and 20 μmol photon m⁻² s⁻¹. A, Kinetics of the fluorescence parameter Fo elicited by the measuring modulated beam and of Fm induced by 1-s saturating light pulses as a function of the rehydration time (upper trace) and desiccated dried crust (lower trace). Note the low Fo level prior to the initiation of rehydration (oblique arrow, R). B, The variable fluorescence (Fv = Fm − Fo) as a function of rehydration time. The 100% corresponded to the value obtained after 55 min in A. The data presented are the average of four independent experiments; the sds were smaller than 5% of the average.