Oxidative Stress Response During The Resting Cells Formation In Marine Diatom Thalassiosira Pseudonana

As an important component of phytoplankton,diatoms have strong ecological adaptability.Among them,the formation of resting cells is an effective strategy for some diatoms to cope with unfavorable growth environments and maintain long-term survival.However,little is known about the various regulatory processes and mechanisms involved in the oxidative stress response during the formation of resting cells in diatoms.In this present study,the oxidative stress response and related regulatory mechanism involved in the formation of resting cells in marine diatom Thalassiosira pseudonana were investigated by combining the physiological and biochemical detection and proteomics methods.The results as following:The formation of resting cells in T.pseudonana was induced under the condition of dark and low temperature(4?)for three months.During the induction process,the levels of reactive oxygen species(ROS)and malondialdehyde(MDA),the peroxidation index of membrane lipid,were significantly increased.Correspondingly,the antioxidants(SOD,POD,CAT,GSH),and the de-epoxidation state(DES)in xanthophyll cycle reached the highest value in the early stage of induction(day 30),and then began to decrease.The results showed that ROS scavenging enzyme system and xanthophyll cycle were involved in antioxidant stress in the early stage of resting cells formation.Based on proteomics results,the electron transport pathway(ETC)in mitochondria of mature resting cells was not inhibited.Meanwhile,the expressions of proteins related to mitochondrial alternative oxidase(AOX)were up-regulated,which is involved in anti-oxidative stress in mitochondria,may play a role in reducing ROS production in mitochondrial electron transport chain.On the other hand,proteins related to PSI and PSII system,cytochrome b6f complex,fucoxanthin chlorophyll protein complex(FCP),and phytochrome DPh were all not affected.However,the chloroplast photosynthetic electron transport chain was restrained,which can inhibit cell photosynthetic capacity and could lead to accumulate some ROS in mature resting cells.This result is consistent with biochemical observation that there were still some levels of ROS accumulation in mature resting cells compared with that of vegetative cells.Proteomics also showed that chrysolaminaran polysaccharides have not been accumulated in the mature cells.However,the up-regulation of the proteins related to neutral lipid TAG biosynthesis suggested that neutral lipid could be used as primary energy for mature resting cells.The results indicate that the resting cells of T.pseudonana have an effective survival strategy and regulatory mechanism against stress,so as to maintain the longterm survival under an adverse growth environment.