Isocitrate lyase activity patterns during cell cycle in synchronous cultures of Chlamydomonas reinhardtii (Chlorophyceae)
Paulson, Ruth; Knutsen, Gjert; Erga, Svein R.
The green alga Chlamydomonas reinhardtii is able to grow heterotrophically on acetate. When photoautotrophically grown cells are transferred to dark conditions, addition of acetate causes the induction of the glyoxylate cycle enzymes, the primary one being isocitrate lyase (ICL). The capacity of the cells to produce this enzyme during their life cycle was studied in synchronous cultures of C. reinhardtii. The ability to induce ICL followed a periodic peak pattern, with the maximum capacity around the midpoint of the life cycle. This pattern was found in cultures synchronized by light/dark cycles as well as in cultures synchronized by selection of zoospores. The appearance of changing adaptation ability during life cycle emphasizes the importance of using synchronous cultures as a tool in physiological studies. Environmental factors, such as light and acetate, are essential for induction of ICL, while variations in ICL induction capacity during life cycle must be explained by specific regulation of ICL, involving de novo synthesis of the enzyme. Our results may also contribute to a better understanding of how phytoplankton may survive during severe environmental conditions.