The responses of Scrippsiella acuminata to the stresses of darkness: antioxidant activities and formation of pellicle cysts

Abstract

In order to understand the strategy of Scrippsiella acuminata to cold dark environment, the antioxidant responses and the formation of pellicle cysts of S. acuminata to darkness at 8°C and 20°C were investigated. Cell densities decreased significantly after 96 h dark treatment, and no live cells were observed after 9-days dark treatments. The darkness stress generally resulted in an increase of antioxidant defenses, including soluble protein, superoxide dismutase (SOD), glutathione (GSH), and malondialdehyde (MDA). Cellular soluble protein and SOD activity increased sharply under 20°C darkness, which protected algal cells against the oxidative stress from darkness, and resulted in relatively lower MDA levels. Soluble protein and SOD activity were enhanced under 8°C darkness as well however not in a sharp rise, and higher levels of MDA and GSH were recorded. The results suggested high SOD and protein levels protected cells against harsh darkness stress, while high GSH not only helped algae cells resist dark stress, but also played an important role in low temperature stress. Darkness promoted the formation of pellicle cysts of S. acuminata, and the maximum formation rates were 16.06% to 21.74% at 8°C and 20°C, respectively. Germination of pellicle cysts occurred within 24 h after light exposure, however pellicle cysts could not withstand long-time darkness stress, and all pellicle cysts died after 9-days darkness exposure. The results of this study suggest that S. acuminata is able to overcome temporary cold darkness through forming pellicle cysts.