Polyamine effects on protein disulfide isomerase expression and implications for hypersalinity stress in the marine alga U lva lactuca Linnaeus 1

Full‐length protein disulfide isomerase ( Uf PDI ) c DNA was cloned from the intertidal macroalga U lva lactuca Linnaeus. Modulation of Uf PDI expression by stresses and polyamines ( PA ) was studied. Uf PDI 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 CuSO 4 . 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 Uf PDI expression and recovery of the growth rate. These results suggest that PA s are required to activate Uf PDI expression with hypersalinity, even PA contents are decreased at a salinity of 90. The induction of Uf PDI 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 Uf PDI expression was examined. Pretreatment with Spd and Spm, but not with Put, enhanced Uf PDI expression after transferred to a salinity of 90 and restored the growth rate. In conclusion, induction of Uf PDI 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 .