The variation of chlorophyll content. (A) The relative chlorophyll contents of heat-treated (○) and untreated (●) cells are plotted as functions of the time of dark cultivation. All the data are normalized with respect to that of untreated cells at the beginning of dark cultivation. Each data point represents the mean ±SD of three independent measurements with two replicates each. (B) The frequency distribution histograms of Scenedesmus cells analyzed for chlorophyll a fluorescence from (i) untreated cells at the beginning of dark cultivation and cells subjected to a heat treatment followed by cultivation in the dark for (ii) 0, (iii) 48 and (iv) 72 h, respectively.