Fluorescence induction curves registered from individual microalgae cenobiums in the process of population growth

Registration of chlorophyll fluorescence induction curves (IC) from individual microalgae cenobiums was performed during Scenedesmus quadricauda culture growth. Emphasis was placed on the analysis of patterns of the slow phase of IC, since these slow fluorescence transitions reflect complex interactions between primary and secondary photosynthetic processes. A classification was performed of the ICs obtained according to the patterns of their slow phase. Four different types of such patterns were distinguished. The microalgae population structure with respect to IC patterns was investigated at different stages of culture growth. The distribution of microalgae cenobiums over the patterns of IC was found to change in accordance with the stage of population development. At the stage of the population growth enhancement, nonmonotonous IC dominated with a high steady-state level of fluorescence. The stage of linear growth was characterized by IC with monotonous decay kinetics and low steady-state level of fluorescence. At the third stage including the phases of growth inhibition, stationary state and the beginning of cell death the population structure was the most heterogeneous, with all IC patterns observed.Abbreviations CO₂ carbon dioxide - ETC electron transfer chain - Fl fluorescence - FNR ferredoxin-NADPH reductase - IC induction curve of chlorophyll fluorescence - PQ plastoquinone - PS I Photosystem I - PS II Photosystem II - Q_A primary quinone acceptor of PS II