Cell cultures
Micrasterias denticulata cells were grown in liquid Desmidiacean culture medium (Schlösser, 1982) in Erlenmeyer flasks under semi-sterile conditions. The medium contained a substantial amount of soil extract providing good pH buffering properties. Cells were kept at 20 ± 1 °C at a photoperiod of 14 h light:10 h dark. Every 4–6 weeks the cells were sub-cultured. 3–4 week old cultures during exponential growth were used for experiments (for detailed culture conditions see