Cadmium increases the activity levels of glutamate dehydrogenase and cysteine synthase in Chlamydomonas reinhardtii

The presence of 300 μM Cd2+ in culture medium was found to be toxic to Chlamydomonas reinhardtii, reducing growth and productivity by about 48%. Approximately 30% of the total cadmium in the medium was accumulated by the alga resulting in 0.88% of the algal dried biomass. Elemental analysis indicated a cadmium-dependent decrease in the C (about 3.2%) and N content (about 7.1%) within C. reinhardtii, while the S content increased by approximately 7.5%. In parallel, Cd2+ produced a significant activation of the aminating glutamate dehydrogenase (EC 1.4.1.2) activity and also NAD+- and NADP+-isocitrate dehydrogenase (EC 1.1.1.41 and 1.1.1.42, respectively) activities upon 24 h of the exposure to 150 μM of the metal. These data are consistent with the key role of the glutamate dehydrogenase/isocitrate dehydrogenase system to supply the glutamate required for the Cd2+-induction of phytochelatin synthesis in the alga. Moreover, the presence of cadmium in the culture medium enhances the sulfate uptake rate and the components of the cysteine synthase complex within the cells such as the serine acetyltransferase (EC 2.3.1.30) and O-acetyl-L-serine (thiol)lyase (EC 4.2.99.8) activities.