Cloning and expression of isoenzymes of superoxide dismutase in Haematococcus pluvialis (Chlorophyceae) under oxidative stress

Increasing evidence indicates that the biosynthesis and accumulation of the keto-carotenoid astaxanthin represents a chronic (in days or weeks) molecular defense mechanism in the green alga, Haematococcus pluvialis, to protect cells from abiotic stress. However, information with regard to the acute (in minutes or hours) response of the cells to stress is scarce. In this study, two cDNAs encoding manganese superoxide dismutase (MnSOD) were cloned and their full length nucleotide sequences were obtained. Quantitative real-time RT-PCR analysis revealed a general increase in MnSOD transcriptions in response to various abiotic stressors, e.g., high light, excessive amounts of iron or sodium acetate, either singly or in combination. Meanwhile, four isoforms of MnSOD were detected by a nondenaturing polyacrylamide gel electrophoresis approach. In addition, an iron-containing superoxide dismutase (FeSOD) was detected in the cells using the same technique. Differential expressions of SOD isoenzymes under different abiotic stressors were also investigated and discussed, at both mRNA and protein levels.