ARC Centre of Excellence for Translational Photosynthesis, Hawkesbury Institute for the Environment, Western Sydney University, Hawkesbury Campus, Locked Bag 1797, Penrith, NSW, 2751, Australia.
ARC Centre of Excellence for Translational Photosynthesis, Research School of Biology, Australian National University, Canberra, ACT, 2601, Australia.
Photosynth Res. 2019 Dec;142(3):321-334. doi: 10.1007/s11120-019-00666-1. Epub 2019 Sep 13.
Cyclic electron flow (CEF) around photosystem I (PSI) is essential for generating additional ATP and enhancing efficient photosynthesis. Accurate estimation of CEF requires knowledge of the fractions of absorbed light by PSI (f) and PSII (f), which are only known for a few model species such as spinach. No measures of f are available for C grasses under different irradiances. We developed a new method to estimate (1) f in vivo by concurrently measuring linear electron flux through both photosystems [Formula: see text] in leaf using membrane inlet mass spectrometry (MIMS) and total electron flux through PSII (ETR2) using chlorophyll fluorescence by a Dual-PAM at low light and (2) CEF as ETR1-[Formula: see text]. For a C grass, f was 0.5 and 0.4 under control (high light) and shade conditions, respectively. C species belonging to NADP-ME and NAD-ME subtypes had f of 0.6 and PCK subtype had 0.5 under control. All shade-grown C species had f of 0.6 except for NADP-ME grass which had 0.7. It was also observed that f ranged between 0.3 and 0.5 for gymnosperm, liverwort and fern species. CEF increased with irradiance and was induced at lower irradiances in C grasses and fern relative to other species. CEF was greater in shade-grown plants relative to control plants except for C NADP-ME species. Our study reveals a range of CEF and f values in different plant functional groups. This variation must be taken into account for improved photosynthetic calculations and modelling.
循环电子流（CEF）围绕光系统 I（PSI）对于产生额外的 ATP 和增强高效光合作用是必不可少的。准确估计 CEF 需要了解 PSI（f）和 PSII（f）吸收的光分数，这仅在少数模式物种（如菠菜）中已知。在不同辐照度下，C 类禾本科植物没有 f 的测量值。我们开发了一种新方法，通过同时测量叶片中两个光系统[公式：见文本]的线性电子通量[Formula: see text]和使用叶绿素荧光在低光下通过 Dual-PAM 测量 PSII 的总电子通量（ETR2），来估算（1）活体中的 f；以及（2）CEF 作为 ETR1-[公式：见文本]。对于 C 类禾本科植物，在对照（高光）和遮荫条件下，f 分别为 0.5 和 0.4。属于 NADP-ME 和 NAD-ME 亚型的 C 物种在对照条件下的 f 为 0.6，而 PCK 亚型的 f 为 0.5。除 NADP-ME 草外，所有遮荫生长的 C 物种的 f 均为 0.6，而 NADP-ME 草的 f 为 0.7。还观察到，裸子植物、苔藓和蕨类植物的 f 范围在 0.3 到 0.5 之间。CEF 随辐照度增加而增加，并在 C 类禾本科植物和蕨类植物中在较低的辐照度下被诱导，而在其他物种中则不然。与对照植物相比，遮荫植物的 CEF 较高，但 NADP-ME 物种除外。我们的研究揭示了不同植物功能群中 CEF 和 f 值的范围。在进行光合作用计算和建模时，必须考虑这种变化。
