Response mechanisms of domoic acid in Pseudo-nitzschia multiseries under copper stress.

Abstract

A complex relationship exists between copper stress and the accumulation and release of domoic acid (DA) in toxin-producing Pseudo-nitzschia cells. To clarify the changes and role of DA in this process, we exposed the toxin-producing P.multiseries and the non-toxin-producing P.pungens to copper stress (5 and 9μM) for 96h. Results showed that P.multiseries grew better than P.pungens under the two aforementioned copper concentrations. DA content in the cells of P.multiseries increased with increased copper stress, and the dissolved DA in the medium under the 9μM copper treatment increased. DA addition at a 9μM copper concentration reduced the copper content in P.multiseries cells and cell walls, but did not change the free copper ion content in culture medium. Adding DA to the medium reduced the malondialdehyde (MDA) content in the cells of P.multiseries under copper stress, DA addition also reduced the activities of catalase (CAT) and superoxide dismutase (SOD) at 5μM Cu, and the activity of peroxidase (POD) at 9μM Cu. This suggests that DA may not alleviate copper stress by improving the antioxidant defense system of algal cells, nor can it be complexed with copper ions in the medium to alleviate copper stress. Furthermore, the reactive oxygen species (ROS) scavenger N-tert-butyl-α-phenylnitrone (BPN) was used to study the DA accumulated in cells. The BPN addition significantly reduced the accumulation of DA in the cells under copper stress, suggesting that DA content in cells was closely related to ROS. Moreover, further experiments demonstrated that DA addition can improve the growth of P.multiseries under hydrogen peroxide stress. Our results indicate that DA alleviates P.multiseries oxidative damage when expose to copper stress.