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. 2021 Aug;149(1-2):171-185. doi: 10.1007/s11120-021-00819-1. Epub 2021 Feb 3.
Alternative electron fluxes such as the cyclic electron flux (CEF) around photosystem I (PSI) and Mehler reaction (Me) are essential for efficient photosynthesis because they generate additional ATP and protect both photosystems against photoinhibition. The capacity for Me can be estimated by measuring O exchange rate under varying irradiance and CO concentration. In this study, mass spectrometric measurements of O exchange were made using leaves of representative species of C and C grasses grown under natural light (control; PAR ~ 800 µmol quanta m s) and shade (~ 300 µmol quanta m s), and in representative species of gymnosperm, liverwort and fern grown under natural light. For all control grown plants measured at high CO, O uptake rates were similar between the light and dark, and the ratio of Rubisco oxygenation to carboxylation (V/V) was low, which suggests little potential for Me, and that O uptake was mainly due to photorespiration or mitochondrial respiration under these conditions. Low CO stimulated O uptake in the light, V/V and Me in all species. The C species had similar V/V, but Me was highest in the grass and lowest in the fern. Among the C grasses, shade increased O uptake in the light, V/V and the assimilation quotient (AQ), particularly at low CO, whilst Me was only substantial at low CO where it may contribute 20-50% of maximum electron flow under high light.
替代电子流，如围绕光系统 I（PSI）的循环电子流（CEF）和 Mehler 反应（Me），对于高效光合作用至关重要，因为它们可以产生额外的 ATP，并保护两个光系统免受光抑制。可以通过测量不同光照和 CO 浓度下的 O 交换率来估计 Me 的能力。在这项研究中，使用在自然光（对照；PAR≈800 μmol 量子 m-2 s-1）和遮荫（≈300 μmol 量子 m-2 s-1）下生长的 C 和 C 禾本科植物以及在自然光下生长的代表裸子植物、苔藓和蕨类植物的叶片进行了质谱测量 O 交换。对于所有在高 CO 下测量的对照生长植物，在光照和黑暗下的 O 吸收速率相似，并且 Rubisco 氧合与羧化的比值（V/V）较低，这表明 Me 的潜力很小，并且在这些条件下 O 吸收主要是由于光呼吸或线粒体呼吸。低 CO 刺激所有物种在光照下的 O 吸收、V/V 和 Me。C 种具有相似的 V/V，但 Me 在草中最高，在蕨中最低。在 C 禾本科植物中，遮荫会增加光照下的 O 吸收、V/V 和同化商（AQ），特别是在低 CO 下，而 Me 仅在低 CO 下大量存在，在高光下，它可能贡献 20-50%的最大电子流。
