Photoautotrophic cell suspension cultures from Mesembryanthemum crystallinum and their response to salt stress

For the first time, photoautotrophic cell suspension cultures of Mesembryanthemum crystallinum have been established. The cells are growing in a sugar-free culture medium in the presence of 2% (v/v) CO2 as the sole carbon source. A 16 h light photoperiod is applied. Increase in fresh and dry weight during a 21 days growth cycle was more than 3-fold. Treatment of the cells with 200 mM NaCl from day 10 to day 21 of subculture stimulated cell culture growth, enhanced CO2 fixation and elicited an increase in the extractable activities of enzymes related to CO2 fixation (RubisCO; PEP carboxylase) and melic acid metabolism (NAD/NADP dependent malic enzyme and malic acid dehydrogenase). The cells performed osmotic adjustment to high salinity by uptake of K+, Na+, Cl- and formation of proline as well as by a reduction in cell size. Although sugar and starch content of the cells changed during light/dark transition, a CAM-related diurnal fluctuation of malic acid was not observed.