Abstract:

Effects of low environmental temperature on the activities of superoxide dismutase (SOD), peroxidase (POD)
and catalase (CAT), and the contents of glutathione peroxidase (GSH), malondialdehyde (MDA), docosahexaenoic acid
(DHA) and reactive oxygen species (ROS) in Isochrysis galbana 3011 were investigated for exploring the relationship
among antioxidant enzyme activities, ROS levels and DHA contents at different temperatures. The enzyme activities were
determined by corresponding kits. ROS levels were detected by flow cytometry and inverted fluorescence microscope, and
DHA contents were determined by gas chromatography (GC). The results showed that activities of SOD, CAT and POD
increased firstly and then decreased with increasing culture time at 15, 18 and 21 ℃. Lower temperature could result in
earlier and higher enzyme activity peaks followed by a faster decline. The profile of GSH was similar to that of antioxidant
enzyme activities, while content of MDA increased continuously. ROS levels showed a complex change with declining
temperature, and ROS burst was appeared after induction for 16 h at 15 and 18 ℃, with maximum values of (14.11 ± 0.11)%
and (14.74 ± 0.58)% at 20 h, respectively (P < 0.05). DHA was 0.105 mg/g at 18 ℃ for 24 h, which was higher than that
at 24 ℃ for 24 h by 0.06 mg/g. Therefore, low environmental temperature can improve the levels of metabolic products by
activating microalgae defense responses, increasing ROS-related enzyme activities, ROS levels and DHA contents.

Key words: Isochrysis galbana 3011, antioxidant, low temperature, reactive oxygen species (ROS), docosahexaenoic acid