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.
Physiol Plant. 2014 Oct;152(2):380-8. doi: 10.1111/ppl.12188. Epub 2014 Apr 17.
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.
耐干燥、潮间带大型海藻石莼的光合性能受山梨醇诱导的渗透胁迫显著影响。我们的结果表明，光合活性随山梨醇浓度的增加而显著下降。尽管 PS I 和 PS II 的部分活性在 30 分钟再水合后能够恢复，但 PS II 的活性比 PS I 下降得更快。在 4M 山梨醇浓度下，PS II 的活性几乎为 0，而 PS I 的活性仍约为正常水平的三分之一。在 1 和 2M 山梨醇的长时间处理后，PS I 和 PS II 的活性缓慢下降，表明中浓度山梨醇对 PS I 和 PS II 的影响是逐渐的。有趣的是，在这些条件下，中等渗透压胁迫会引起非光化学猝灭增加，而在严重渗透压胁迫下，非光化学猝灭会显著下降。这些结果表明，U. prolifera 中的光保护也可能是由适度的渗透压胁迫诱导的。此外，渗透压胁迫显著影响 PS I 的氧化。在高浓度山梨醇处理的藻体中，P700(+)仍可被还原，因为 PS II 被 3-(3,4-二氯苯基)-1,1-二甲基脲（DCMU）抑制，但不能完全氧化。这种观察结果可能是由于在含有 DCMU 的海水中再水合时，PS I 中的非光化学能量耗散量子产率较高，导致受体侧限制（Y(NA)）所致。
