Tan Shun-Ling, Vera-Vives Antoni M, Alboresi Alessandro, Morosinotto Tomas
Department of Biology, University of Padova, Padova, Italy.
Department of Biology, University of Padova, Padova, Italy.
Plant Physiol Biochem. 2025 Jul;224:109904. doi: 10.1016/j.plaphy.2025.109904. Epub 2025 Apr 16.
Photosynthetic organisms exploit sunlight to drive an electron transport chain and obtain the chemical energy supporting their metabolism. In highly dynamic environmental conditions, excitation energy and electron transport need to be continuously modulated to prevent over-reduction and the consequent damage. An essential role in the regulation of electron transport is played by alternative electron transport mechanisms such as cyclic electron transport (CET) facilitated by PGRL1/PGR5 and NDH complex and pseudo-cyclic electron transport (PCET) mediated by the flavodiiron proteins (FLV) and the Mehler reaction. In this work mutant lines of the moss Physcomitrium patens depleted in PCET (flva KO) or CET (pgrl1/ndhm KO) were compared to wild-type plants for their ability to regulate photosynthetic electron transport in response to light fluctuations of different intensities. FLV activity enables a very fast increase in electron transport capacity but its impact is transient and becomes undetectable after 3 min from a light change. The FLV electron transport capacity is saturated at 100 μmol photons m s and does not increase even if exposed to stronger illumination. On the other hand, CET activation after an increase in illumination has a smaller contribution on electron transport capacity, but it provides a steady contribution for several minutes after a change in illumination intensity. Overall, these results demonstrate that light adapted plants CO fixation capacity needs approx. 3 min to adjust to different illumination intensities. In this interval CET and PCET enable adjusting temporary unbalances in electron transport, fully responding to 2-4 time increases in illumination. In case of larger increases, these mechanisms still contribute to protection from light damage by reducing the accumulation of electrons at PSI acceptor side. While the two mechanisms play an overlapping function, their activity shows distinctive kinetics and electron transport capacity thus they are complementary in ensuring optimal photoprotection.
光合生物利用阳光驱动电子传递链，并获取支持其新陈代谢的化学能量。在高度动态的环境条件下，激发能和电子传递需要不断调节，以防止过度还原及随之而来的损伤。替代电子传递机制在电子传递调节中起着至关重要的作用，例如由PGRL1/PGR5和NDH复合物促进的循环电子传递（CET），以及由黄素二铁蛋白（FLV）和梅勒反应介导的伪循环电子传递（PCET）。在这项工作中，将PCET（flva KO）或CET（pgrl1/ndhm KO）缺失的小立碗藓突变体系与野生型植物进行比较，以研究它们响应不同强度光波动调节光合电子传递的能力。FLV活性使电子传递能力能非常快速地增加，但其影响是短暂的，在光照变化3分钟后就变得无法检测到。FLV电子传递能力在100 μmol光子·m⁻²·s⁻¹时达到饱和，即使暴露在更强的光照下也不会增加。另一方面，光照增加后CET的激活对电子传递能力的贡献较小，但在光照强度变化后几分钟内它能持续提供稳定的贡献。总体而言，这些结果表明适应光照的植物的CO₂固定能力大约需要3分钟来适应不同的光照强度。在此期间，CET和PCET能够调节电子传递中的暂时不平衡，对光照增加2 - 4倍能完全响应。在光照增加幅度更大的情况下，这些机制仍有助于通过减少PSI受体侧电子的积累来保护免受光损伤。虽然这两种机制发挥重叠功能，但其活性表现出独特的动力学和电子传递能力，因此它们在确保最佳光保护方面是互补的。
