Fang Yang, Jiang Zhijian, Zhao Chunyu, Li Linglan, Ranvilage Chanaka Isuranga Premarathne Maha, Liu Songlin, Wu Yunchao, Huang Xiaoping
Key Laboratory of Tropical Marine Bio-resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China.
University of Chinese Academy of Sciences, Beijing, China.
Front Plant Sci. 2020 Nov 30;11:571627. doi: 10.3389/fpls.2020.571627. eCollection 2020.
Seagrasses inhabiting the intertidal zone experience periodically repeated cycles of air exposure and rehydration. However, little is known about the photoprotective mechanisms in photosystem (PS)II and PSI, as well as changes in carbon utilization upon air exposure. The photoprotective processes upon air exposure in Asch., an endangered seagrass species, were examined using the Dual-PAM-100 and non-invasive micro-test technology. The results showed that air exposure enhanced non-photochemical quenching (NPQ) in both PSII and PSI, with a maximum increase in NPQ and Y(ND) (which represents the fraction of overall P700 that is oxidized in a given state) of 23 and 57%, respectively, resulting in intensive thermal energy dissipation of excess optical energy. Moreover, cyclic electron transport driven by PSI (CEF) was upregulated, reflected by a 50 and 22% increase in CEF and maximum electron transport rate in PSI to compensate for the abolished linear electron transport with significant decreases in pmf (the proton motive force [pmf]) attributable solely to proton translocation by linear electron flow [LEF]). Additionally, H fluxes in mesophyll cells decreased steadily with increased air exposure time, exhibiting a maximum decrease of six-fold, indicating air exposure modified carbon utilization by decreasing the proton pump influxes. These findings indicate that efficient heat dissipation and CEF confer daily air exposure tolerance to the intertidal seagrass and provide new insights into the photoprotective mechanisms of intertidal seagrasses. This study also helps explain the extensive distribution of in intertidal zones.
栖息在潮间带的海草会周期性地经历反复的空气暴露和再水化循环。然而，对于光系统（PS）II和PSI中的光保护机制以及空气暴露后碳利用的变化知之甚少。利用双调制叶绿素荧光仪（Dual-PAM-100）和非损伤微测技术，研究了濒危海草物种阿氏草（Asch.）在空气暴露后的光保护过程。结果表明，空气暴露增强了PSII和PSI中的非光化学猝灭（NPQ），NPQ和Y(ND)（代表在给定状态下被氧化的总P700的比例）分别最大增加了23%和57%，导致过量光能的强烈热能耗散。此外，由PSI驱动的循环电子传递（CEF）上调，表现为CEF和PSI中的最大电子传递速率分别增加了50%和22%，以补偿线性电子传递的废除，pmf（质子动力势[pmf]）仅因线性电子流[LEF]的质子转运而显著降低。另外，叶肉细胞中的H通量随着空气暴露时间的增加而稳步下降，最大下降了六倍，表明空气暴露通过减少质子泵流入量改变了碳利用。这些发现表明，有效的散热和CEF赋予了潮间带海草对每日空气暴露的耐受性，并为潮间带海草的光保护机制提供了新的见解。这项研究也有助于解释阿氏草在潮间带的广泛分布。
