Time-series responses in photosynthetic activity, 2-cysteine peroxiredoxin gene expression, and proteomics of Chattonella marina var. antiqua under different oxidative stress

Chattonella spp. are known to produce large amounts of reactive oxygen species (ROS); however, little is known about the mechanisms involved in mitigating the intracellular accumulation of ROS. In this study, a time-series of biological responses in C. marina var. antiqua under different oxidative stress conditions, induced by adding H₂O₂ at the initial concentrations of 100 and 500 µM, was investigated. Although the added exogenous H₂O₂ was rapidly consumed at 3 h post-exposure (hpe), intracellular ROS levels were enhanced in the 500 µM H₂O₂ group but decreased in the 100 µM H₂O₂ group. Accompanied by increased intracellular ROS levels, the photosynthetic activity of C. marina var. antiqua was considerably inhibited in the 500 µM H₂O₂ group, but not in the 100 µM H₂O₂ group. The F_v/F_m ratio and PI_ABS were negatively correlated with the intracellular ROS level, while the ABS/RC, TR₀/RC, and DI₀/RC were positively correlated with the intracellular ROS level. Expression of the gene encoding 2-cysteine peroxiredoxin (2-Cys Prx) was up-regulated in 100 µM H₂O₂ group at 6 hpe, but was down-regulated in 100 µM H₂O₂ group at 3 and 6 hpe. A negative relationship between the 2-Cys Prx transcript levels and intracellular ROS levels was detected. Results of the 2-DE proteomic analysis confirmed that the 500 µM H₂O₂ treatment down-regulated the expression of 2-Cys Prx and induced more damage to photosynthetic abilities of C. marina var. antiqua.