title: Photosystem I shows a higher tolerance to sorbitol-induced osmotic stress than photosystem II in the intertidal macro-algae Ulva prolifera (Chlorophyta).
abstract: The photosynthetic performance of the desiccation-tolerant, intertidal macro-algae Ulva prolifera was significantly affected by sorbitol-induced osmotic stress. Our results showed that photosynthetic activity decreased significantly with increases in sorbitol concentration. Although the partial activity of both photosystem I (PS I) and photosystem II (PS II) was able to recover after 30 min of rehydration, the activity of PS II decreased more rapidly than PS I. At 4 M sorbitol concentration, the activity of PS II was almost 0 while that of PS I was still at about one third of normal levels. Following prolonged treatment with 1 and 2 M sorbitol, the activity of PS I and PS II decreased slowly, suggesting that the effects of moderate concentrations of sorbitol on PS I and PS II were gradual. Interestingly, an increase in non-photochemical quenching occurred under these conditions in response to moderate osmotic stress, whereas it declined significantly under severe osmotic stress. These results suggest that photoprotection in U. prolifera could also be induced by moderate osmotic stress. In addition, the oxidation of PS I was significantly affected by osmotic stress. P700(+) in the thalli treated with high concentrations of sorbitol could still be reduced, as PS II was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), but it could not be fully oxidized. This observation may be caused by the higher quantum yield of non-photochemical energy dissipation in PS I due to acceptor-side limitation (Y(NA)) during rehydration in seawater containing DCMU.
authors.affiliation: Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
authors.forename: Shan
authors.initials: S
authors.lastname: Gao
authors.forename: Zhenbing
authors.initials: Z
authors.lastname: Zheng
authors.forename: Wenhui
authors.initials: W
authors.lastname: Gu
authors.forename: Xiujun
authors.initials: X
authors.lastname: Xie
authors.forename: Li
authors.initials: L
authors.lastname: Huan
authors.forename: Guanghua
authors.initials: G
authors.lastname: Pan
authors.forename: Guangce
authors.initials: G
authors.lastname: Wang
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects*; D003890:Desiccation; D004579:Electron Transport / Q000187:drug effects; D007700:Kinetics; D009997:Osmotic Pressure / Q000187:drug effects*; D010084:Oxidation-Reduction / Q000187:drug effects; D055668:Photochemical Processes / Q000187:drug effects; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D011789:Quantum Theory; D013012:Sorbitol / Q000494:pharmacology*; D013312:Stress, Physiological / Q000187:drug effects*; D044445:Ulva / Q000187:drug effects / Q000502:physiology*
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D013012:Sorbitol