Photosynthetic And Antioxidant Response Towards Stress In Bangiaceae

The algae industry is an important component of the Chinese economy,with a variety of species being cultivated,including: Saccharina japonica,Pyropia yezoensis,Pyropia haitanensis,Undaria pinnatifida,Gracilaria spp,Sargassum thunbergii,and Bangia.Because Pyropia yezoensis and Bangia grow in the intertidal zone,they face periodic environmental stresses,including water loss and changes in temperature,light,and salinity.In our study,we use P.yezoensis and Bangia as experimental material to measure the physiological and biochemical indexes of the algae under different stress conditions.Through these results,we can explore the antioxidant physiological mechanism of the algae under stress and to lay the foundation for understanding algae stress resistance mechanisms.Desiccation is the main abiotic stress for wild P.yezoensis.To reveal the mechanisms by which P.yezoensis protects against desiccation,the photosynthetic and antioxidant physiological response of wild P.yezoensis thallus during desiccation stress was investigated.The stress response to water loss was examined in wild P.yezoensis,with water loss ranging from 0% to 80%.The optimal chlorophyll fluorescence quantum yields of photosystem II（Fv/Fm）were measured,as well as levels of soluble proteins（SP）,malonaldehyde（MDA）,& enzymes.The results revealed that with the increase of water loss,Fv/Fm decreased until 60% water loss.However,the Fv/Fm can return to normal after 1 h of rehydration.The level of chlorophyll a,carotenoid,and SP decreased gradually with water loss.The level of R-phycoerythrin（R-PE）and R-phycocyanin（R-PC）decreased until 20% water loss,after which it increased and stayed stable from 30% to 80% water loss.The change in the ratio of phycobiliproteins to SP was similar to the change in the level of phycobiliproteins.The ratio increased to control level at water loss of 40% and was significantly higher than the control at water loss of 80%.There was no significant change in the level of MDA in either the control or the algae with water loss ≤ 30%,whereas the level of MDA increased significantly between water loss of 30% to 40%.However,there was no significant change among the algae with water loss from 40% to 80%.There was no significant change in the activity of superoxide dismutase（SOD）and catalase（CAT）at water loss ≤ 20%.The activity of peroxidase（POD）significantly increased at water loss 10-20%.When water loss increased to 30%,the activity of SOD,CAT and POD decreased significantly.There was no significant change among the algae with water loss from 50% to 80%.The above results suggested that during the early stage of water loss,the antioxidant enzymes POD,CAT and SOD played key roles in scavenging the reactive oxygen species,which inhibited the yield of excessive MDA;with water loss increasing,the water condition became disadvantageous for the antioxidant enzymes to operate,thus MDA accumulated.Based on the change in the ratio of phycobiliproteins to SP,we speculated that the function of phycobiliproteins became increasingly more important in protecting the algae against desiccation stress at water loss ≥ 30%,which helps in the rapid recovery of photosynthesis Fv/Fm during rehydration.In comparing desiccation stress for “periodically drying” and “without drying” cultured algae,we found that the thalli with “periodically drying” tolerated ⁷0% relative water loss（RWL）while those cultured “without drying” endured < 50% RWL.Pigment levels were higher in the thalli with “periodically drying” than those farmed “without drying”.Chlorophyll a and carotenoid levels from both treatments decreased significantly at RWL = 20%,kept steady at RWL 20-50%,and decreased at RWL = 60%.Phycoerythrin,phycocyanin,and SP levels from “periodically drying” decreased significantly at RWL = 20%,while those from “without drying” kept steady at RWL = 0-50%.The ratio of R-PE and R-PC to SPs for each treatment increased during dehydration and peaked at the critical point of desiccation-tolerance.SOD,CAT and POD activities peaked at RWL = 40-50% in the “without drying” treatment and = 60-70% in the “periodically drying”.The results suggested that SOD,CAT and POD played important roles in desiccation-tolerance.Through the critical point of these enzyme activity changes,we can speculate that the ability to resist desiccation is better in the “periodically drying” algae,than in the “without drying”.We cultured Bangia with different concentrations of marine water,75%,50%,25%,and 0%,and measuring the indexes of Fv/Fm,reactive oxygen species（ROS）,superoxide anion(O^2-),hydrogen peroxide（H₂O₂）,MDA,total antioxidant capacity（T-AOC）,POD,SOD,CAT,and glutathione reductase（GR）.We found that as the treatment time increased,the Fv/Fm of 75% marine water algae reduced gradually.After being cultured for 1 hour,the Fv/Fm of the 50% marine water algae significantly decreased compared with the control.At 2 d,the Fv/Fm of the 50% marine water algae significantly decreased,and from 2 d to 8 d,there were no significant changes.After being cultured for 1 hour,the Fv/Fm of the 25% marine water algae decreased significantly compared with the control.After being cultured for 2 d,the level decreased significantly and it decreased again at 6 d.For the 0% marine water algae,the Fv/Fm decreased significantly at 1 h and then increased significantly at 12 h,after which the level decreased gradually.The level of O^2-decreased significantly in 25% marine water algae,and there were no significant changes in the other three treatments.The peak level of H₂O₂ appeared at 3 d and 7 d in each culture treatment.For the 75% marine water algae,the level of MDA decreased significantly at 4 d,and then increased gradually.For the other treatments,the level of MDA increased gradually and was significantly higher than the control.The T-AOC activity of 0% marine water algae had a peak level at 5 d and then decreased significantly.The TAOC activity of other treatments fluctuated,but was always lower than the control.We also found that for the 0% marine water algae,the POD activity increased significantly.The SOD activity had a peak level at 4 d and 7 d,and the CAT activity fluctuated but was always lower than the control.The GR activity had a peak level at 3 h,1 d,and 5 d.In the 25% marine water algae,POD activity had a peak level at 3 h,3 d,and 6 d,and SOD activity had a peak level at 3 h,1 d,and 5 d.The CAT activity fluctuated but was always lower than the control.The GR activity had a peak level at 1 d and 7 d.In the 50% marine water algae,the POD activity had a peak level at 3 h,1 d,and 5 d,and the SOD activity had a peak level at 5 d and then decreased gradually.The CAT activity was the same as the SOD.The GR activity had a peak level at 3 h,5 d,and 6 d.In the 75% marine water algae,the POD activity had a peak level at 4 d,the SOD activity had no significant increase,and the CAT activity also had no significant increase.The GR activity had a peak level at 1 d and 5 d.The results showed that the Bangia cultured in different water suffered different stress.This stress caused the level of H₂O₂ to increase,which then resulted in membrane lipid peroxidation and the production of abundant MDA,which can damage the cells.Because of the stress,the activity of T-AOC decreased gradually,but the SOD,POD,CAT play an important role in the process of cleaning the O^2-and H₂O₂.