The effect of light on the number of chloroplast nucleoids in daughter cells of the algaScenedesmus quadricauda

Summary Synchronous cultures of the green algaScenedesmus quadricauda (Turp.) Bréb. grown at mean irradiances 25Wm^–2, 75Wm^–2, and 130Wm^–2 PhAR were exposed to different illumination regimes (ratio of light to dark interval varied from 2:22 to 24:0 hours). The populations of daughter cells released under these conditions differed markedly in their progress in the cell cycle. The cells from these populations were stained with DAPI and the shape, localization and number of chloroplast nucleoids were examined. The nucleoids were of spherical shape, divided asynchronously having dumbbell shape during fission. In the chloroplast, nucleoids were located symmetrically about the transverse axis of the cells. The mean number of nucleoids varied from two in the least developed daughter cells to 16 in the daughter cells of the highest developmental stage. The progress of these cells and thus also the number of nucleoids were proportional to the portion of the light energy amount which these daughter cells shared from the total light energy amount obtained by their mother cells.Abbreviations DAPI 4, 6-diamidino-2-diphenylindole - PhAR photosynthetically active radiation (400–700 nm)