School of Life Sciences, University of KwaZulu-Natal, Scottsville, South Africa.
Open Lab 'Biomarker', Kazan (Volga Region) Federal University, Kazan, Russia.
Physiol Plant. 2023 Mar;175(2):e13904. doi: 10.1111/ppl.13904.
The photosynthetic apparatus of lichen photobionts has been well-characterized by chlorophyll fluorescence analysis (e.g., by pulse amplitude modulation [PAM]), which provides a proxy of the activity of photosystem II (PSII) and its antenna. However, such kinetics are unable to directly characterize photosystem I (PSI) activity and the associated alternative electron pathways that may be involved in photoprotection. Instead, PSI can be probed in vivo by near-infrared absorption, measured at the same time as standard chlorophyll fluorescence (e.g., using the WALZ Dual PAM). Here, we used the Dual PAM to investigate cyclic electron flow and photoprotection in a range of mostly temperate lichens sampled from shaded to more open microhabitats. Sun species displayed lower acceptor side limitation of PSI (Y[NA]) early in illumination when compared to shade species, indicative of higher flavodiiron-mediated pseudocyclic electron flow. In response to high irradiance, some lichens accumulate melanin, and Y[NA] was lower and NAD(P)H dehydrogenase (NDH-2)-type cyclic flow was higher in melanised than pale forms. Furthermore, non-photochemical quenching (NPQ) was higher and faster relaxing in shade than sun species, while all lichens displayed high rates of photosynthetic cyclic electron flow. In conclusion, our data suggest that (1) low acceptor side limitation of PSI is important for sun-exposed lichens; (2) NPQ helps shade species tolerate brief exposure to high irradiance; and (3) cyclic electron flow is a prominent feature of lichens regardless of habitat, although NDH-2-type flow is associated with high light acclimation.
藻菌共生体的光合作用装置已经通过叶绿素荧光分析（例如，通过脉冲振幅调制 [PAM]）得到了很好的描述，它提供了光系统 II (PSII) 及其天线活性的替代物。然而，这种动力学无法直接表征光系统 I (PSI) 的活性以及可能涉及光保护的相关替代电子途径。相反，可以通过近红外吸收原位探测 PSI，同时测量标准叶绿素荧光（例如，使用 WALZ Dual PAM）。在这里，我们使用 Dual PAM 研究了从荫蔽到更开阔微生境的一系列主要温带地衣中的循环电子流和光保护。与荫蔽种相比，太阳种在光照早期表现出较低的 PSI 受体侧限制（Y[NA]），这表明黄素二铁介导的拟循环电子流较高。在高光辐照下，一些地衣会积累黑色素，并且黑色素化和苍白形式之间的 NAD(P)H 脱氢酶 (NDH-2)-型循环流较高，Y[NA] 较低。此外，荫蔽种的非光化学猝灭（NPQ）高于太阳种，并且在荫蔽种中更快放松，而所有地衣都显示出高的光合循环电子流。总之，我们的数据表明：（1）PSI 受体侧限制低对暴露在阳光下的地衣很重要；（2）NPQ 有助于荫蔽种耐受短暂的高光辐照；（3）无论栖息地如何，循环电子流都是地衣的一个突出特征，尽管 NDH-2 型流与高光适应有关。
