Fig. 4.

Time-dependent changes of NPQ and the de-epoxidation state (DES) of the Ddx cycle pigment pool [Dtx (Ddx+Dtx)⁻¹] in cell suspensions of T. pseudonana during prolonged dark incubation. The negative time period represents the time span required for oxygen depletion from the medium. NPQ and DES determined during that period represent the values obtained during dark-aerobic incubation. These values did not change between the onset of experiments and during 60 min of darkness when aerobic conditions were maintained. The grey area represents the reoxygenation period. Data presented are the average of 3–20 replicates with the respective standard errors. To suppress chlororespiratory activity the inhibitor of the terminal oxidase (PTOX) Propylgallate (PG, 1 mM) was added to cell suspensions directly at the start of the reoxygenation period (indicated by the arrow). A representative example of the time-course of NPQ before and after the addition of PG is shown. Three independent measurements were carried out which confirmed the results depicted in the figure.