RESPONSES TO CADMIUM- INDUCED OXIDATIVE STRESS IN MARINE MACROALGA ULVA LINZA.

The activities of antioxidant enzymes and gene expression of antioxidant enzymes were determined in Ulva linzaunder different Cdconcentrations (0, 50, 100, 200, 300, 400 𝜇MCdCl2) for 3 days. The results clearly demonstrated that Cdinduced stimulation of antioxidant activity. The Cdaccumulation in thalli increased linearly as Cdconcentration increased. The decrease in growth rate, photosynthetic efficiency and protein contents with increasing of H2O2 and malondialdehyde (MAD) contents in response to elevated Cdconcentrations indicates the induction of the oxidative stress. As in response to the increased oxidative stress, Cdtreatments induced the activities and transcripts of superoxide dismutase (SOD; EC 1.15.1.1), ascorbate peroxidase (APX; EC 1.11.1.11), catalase (CAT; EC 1.11.1.6) and glutathione reductase (GR; EC 1.6.4.2). In general the ascorbate pool increased by treatments with different Cdconcentrations. A steady slight decrease in glutathione content with increasing Cdconcentration was indicated. The oxidized glutathione (GSSG) content and the glutathione (GSH) /GSSG ratio were not significantly influenced by the tested Cd concentrations, except the concentration of 300 𝜇M, which caused a 18% decline in GSSG content and the concentration of 400 𝜇M which decreased GSH/GSSG ratio by 23%. The different Cdconcentrations induced a conspicuous increase in proline content of the investigated alga.