RESUMEN
Full-length protein disulfide isomerase (UfPDI) cDNA was cloned from the intertidal macroalga Ulva lactuca Linnaeus. Modulation of UfPDI expression by stresses and polyamines (PA) was studied. UfPDI transcription and enzyme activity were increased by hypersalinity (90) or high light illumination (1,200 µmol photons · m(-2) · s(-1) ), decreased by the addition of 100 µM CuSO4 . An exposure to a salinity of 90 decreased PA contents. Treating with PA biosynthetic inhibitors, D-arginine (D-Arg) or α-methyl ornithine (α-MO), led to a further decrease and also inhibited UfPDI expression and recovery of the growth rate. These results suggest that PAs are required to activate UfPDI expression with hypersalinity, even PA contents are decreased at a salinity of 90. The induction of UfPDI expression by hypersalinity of 90 and tolerance to hypersalinity could be enhanced if internal PA contents rise. Sung et al. (2011b) showed that PA contents could be increased by pretreating with putrescine (Put, 1 mM), spermidine (Spd, 1 mM), or spermine (Spm, 1 mM) at a salinity of 30. Therefore, PA pretreatment effect on UfPDI expression was examined. Pretreatment with Spd and Spm, but not with Put, enhanced UfPDI expression after transferred to a salinity of 90 and restored the growth rate. In conclusion, induction of UfPDI expression by Spd or Spm before exposure to hypersaline conditions and continuous up-regulation after hypersalinity exposure are required for the acquisition of hypersalinity tolerance in the intertidal green macroalga U. lactuca.
RESUMEN
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).