The modulation of manganese superoxide dismutase (MnSOD), FeSOD, ascorbate peroxidase (APX), glutathione reductase (GR), and catalase (CAT) gene expression and activities and antioxidants in Ulva fasciata against hypersalinity (90 per thousand)-induced oxidative stress was studied. Increases in H(2)O(2) contents but no changes in lipid peroxidation and protein carbonyl group contents suggest oxidative damage did not occur in 90 per thousand condition. Antioxidants were consumed for reactive oxygen species (ROS) scavenging indicated by decreased ascorbate and glutathione contents by 90 per thousand. Antioxidant enzymes were differently expressed by 90 per thousand for ROS removal. MnSOD activity and transcript increased 1 h after 90 per thousand treatment with a peak at hour 3, while FeSOD activity increased fast to the plateau after 1 h and its transcript increased after 3 h. APX activity increased 1 h after 90 per thousand but its transcript rose till 3 h, and GR activity increased after 1 h with a peak at hour 3 but its transcript increased till 3 h. CAT activity and transcript increased after 12 h. Enzyme activity is transcriptionally regulated by 90 per thousand except a fast increase in FeSOD, APX, and GR activities during 1 h. APX is responsible for early H(2)O(2) decomposition while CAT scavenges H(2)O(2) in the later period. The inhibition of 90 per thousand induced increase of H(2)O(2) content and FeSOD activity and transcript by treatment of a H(2)O(2) scavenger, dimethylthiourea, and the increase of FeSOD transcript of 30 per thousand grown thalli by H(2)O(2) treatment suggest that H(2)O(2) mediates the upregulation of FeSOD by hypersalinity while other enzymes is modulated by factors other than H(2)O(2).
Transcripts and enzyme activities of antioxidative enzymes were increased by hypersalinity (90‰) in a marine macroalga, Ulva fasciata Delile (Lu et al. 2006, Sung et al. 2009). This study examined the effects of polyamines (PAs) on the induction of hypersalinity tolerance through the modulation of expression of antioxidative defense enzymes. Incubation of U. fasciata grown under 30‰ in the presence of putrescine (Put), spermidine (Spd), or spermine (Spm) (1 mM) for 12 h increased internal PA contents prior to 90‰ treatment. Spd or Spm pretreatments reduced H O accumulation and lipid peroxidation during 90‰ treatment and improved the recovery growth rate after transfer from 90‰ to 30‰. Increases in iron superoxide dismutase (FeSOD; EC 1.15.1.1) activity and transcript levels observed under 90‰ were further increased by Spd and Spm pretreatments, while Put pretreatment had no effect. Increases in MnSOD activity and transcript levels observed under 90‰ were enhanced by Spd and Put pretreatment. An observed increase in catalase (CAT; EC 1.11.1.6) activity and transcript levels under 90‰ was not affected by Spd and Spm pretreatments but was inhibited by Put pretreatment. Observed increases in ascorbate peroxidase (APX; EC 1.11.1.11) activity and transcript levels under 90‰ were inhibited by Put, Spd, and Spm pretreatments. In conclusion, Spd and Spm treatment affords U. fasciata protection against hypersalinity through the up-regulation of FeSOD gene expression, thereby alleviating oxidative damage.
The molecular acclimation of intertidal green macroalga Ulva fasciata Delile to high salinity stress were examined by the construction of a forward cDNA library via the suppressive subtractive hybridization between 30‰ and 90‰ (24 h) and by the time course dynamics of several abundantly expressed genes. Among the genes with known sequences, the expressed sequence tags are abundant in the function of protein synthesis (ribosomal protein) and destination. The cDNAs of ATP-dependent Clp protease (UfClpC), 20S proteasome β-subunit type 1 domain (UfPbf1), ubiquitin-conjugating enzyme E2 I (UfUbc9), and heat shock protein 90A (UfHsp90A) were cloned. UfClpC transcript increased 3 h after 90‰ treatment, followed by a decrease, while UfPbf1 and UfUbc9 transcripts increased after 12 h and decreased at 48 h. The transcripts of UfHsp90A increased 1 h after 90‰ treatment, followed by a drop and to the control level at 48 h. Protease activity increased 3 h after 90‰ treatment and decreased to the control level at 48 h. H₂O₂ contents increased 1 h after 90‰ treatment and then remained unchanged, but protein carbonyl group contents increased after 48 h. The treatments of reactive oxygen species scavengers partially alleviated 90‰ damage (partial growth rescue) and suppressed the increases in H₂O₂ content, protein carbonyl group content, protease activity, and UfClpC, UfPbf1, UfUbc9, and UfHsp90A transcripts by 90‰. The induction of specific chaperones and proteases at the molecular level for protein quality control can be considered as one of the molecular mechanisms of hypersalinity acclimation in U. fasciata.
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