The variation of photosynthetic activity (Fv/Fm). (A) The decay of Fv/Fm ratio as a function of the time of heat treatment. (B) The variations of the Fv/Fm of heat-treated cells are plotted as functions of the time of recultivation in the dark (○), and those with light (150 μmol photon m-2 s-1) turned on at 12 (∇), 24 (■), 36 (Δ), 48 (□), 60 (◊) and 72 h (♦), respectively. The Fv/Fm of untreated cells as a function of the time of dark cultivation is also shown (●). Each data point represents the mean ±SD of three independent measurements with two replicates each. The dotted line indicates the Fv/Fm (0.74 ± 0.02) of untreated cells at the beginning of dark cultivation.