Effect of abiotic stress on photosynthesis, respiration and antioxidant system in Chlamydomonas reinhardtii

Our results indicate that 200 mM NaCl, 0.2 mu M methyl viologen, 4 MM arsenite or 300 mu M of cadmim in the culture medium are highly toxic for C. reinhardtii productivity and they inhibit photosynthesis, while respiration remains in all cases relatively high. Salt stress bloks immediately the photosynthetic activity of the alga which is partially recovered, and it increases catalase, ascorbate peroxidase (APX) and glutathione reductase (GR) activities. Catalase activity was increased almost 20-fold during salt stress, reaching a value of 338.0 mu moles O-2 formed/min/mg Chl, after 24 h treatment. In MV-treated C. reinhardtii cells catalase, APX and GR activities result increased, while CAT and GR are the most efficiently induced activities by arsenite-stressed cells. Cadmium induces CAT and APX, but not GR, activities. These data support that abiotic stress induces in C. reinhardtii an increase of active oxygen species (AOS), which parallel a significant inhibition of the photosynthetic electron flow. On the other hand, nitrate and sulfate uptake rates by C. reinhardtii were significantly inhibited, under the indicated abiotic stresses. In addition, glutamate synthase (MVH-GOGAT), glutamate dehydrogenase (NADH-GDH) and O-acetylserine(thiol)lyase (OASTL) activities were differently affected by abiotic stress in C reinhardtii. Salt enhances MVH-GOGAT and OASTL activities; methyl viologen produces a 30-fold increase of NADH-GDH activity, while MVH-GOGAT and OASTL activities are moderately enhanced. Cadmium produces an increase in NADH-GDH and OASTL activities. However, the three mentioned activities decreased with respect to control in arsenite-treated cells. These data indicate that an active synthesis of glutamate and cysteine is produced in C. reinhardtii cells treated with salt, methyl viologen or cadmium.