Cun Zhu, Wu Hong-Min, Zhang Jin-Yan, Shuang Sheng-Pu, Hong Jie, Chen Jun-Wen
College of Agronomy and Biotechnology, Yunnan Agricultural University, Kunming, China.
Key Laboratory of Medicinal Plant Biology of Yunnan Province, Yunnan Agricultural University, Kunming, China.
Front Plant Sci. 2022 Feb 15;13:796931. doi: 10.3389/fpls.2022.796931. eCollection 2022.
Nitrogen (N) is a primary factor limiting leaf photosynthesis. However, the mechanism of N-stress-driven photoinhibition of the photosystem I (PSI) and photosystem II (PSII) is still unclear in the N-sensitive species such as , and thus the role of electron transport in PSII and PSI photoinhibition needs to be further understood. We comparatively analyzed photosystem activity, photosynthetic rate, excitation energy distribution, electron transport, OJIP kinetic curve, P700 dark reduction, and antioxidant enzyme activities in low N (LN), moderate N (MN), and high N (HN) leaves treated with linear electron flow (LEF) inhibitor [3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU)] and cyclic electron flow (CEF) inhibitor (methyl viologen, MV). The results showed that the increased application of N fertilizer significantly enhance leaf N contents and specific leaf N (SLN). Net photosynthetic rate ( ) was lower in HN and LN plants than in MN ones. Maximum photochemistry efficiency of PSII ( / ), maximum photo-oxidation P700 ( ), electron transport rate of PSI (ETRI), electron transport rate of PSII (ETRII), and plastoquinone (PQ) pool size were lower in the LN plants. More importantly, K phase and CEF were higher in the LN plants. Additionally, there was not a significant difference in the activity of antioxidant enzyme between the MV- and HO-treated plants. The results obtained suggest that the lower LEF leads to the hindrance of the formation of ΔpH and ATP in LN plants, thereby damaging the donor side of the PSII oxygen-evolving complex (OEC). The over-reduction of PSI acceptor side is the main cause of PSI photoinhibition under LN condition. Higher CEF and antioxidant enzyme activity not only protected PSI from photodamage but also slowed down the damage rate of PSII in grown under LN.
氮（N）是限制叶片光合作用的主要因素。然而，在诸如[未提及的物种名称]等对氮敏感的物种中，氮胁迫驱动的光系统I（PSI）和光系统II（PSII）光抑制的机制仍不清楚，因此需要进一步了解电子传递在PSII和PSI光抑制中的作用。我们比较分析了用线性电子流（LEF）抑制剂[3-(3,4-二氯苯基)-1,1-二甲基脲（DCMU）]和循环电子流（CEF）抑制剂（甲基紫精，MV）处理的低氮（LN）、中氮（MN）和高氮（HN）叶片的光系统活性、光合速率、激发能分布、电子传递、OJIP动力学曲线、P700暗还原和抗氧化酶活性。结果表明，增加氮肥施用量显著提高了叶片氮含量和比叶氮（SLN）。HN和LN植株的净光合速率（ ）低于MN植株。LN植株中PSII的最大光化学效率（ / ）、最大光氧化P700（ ）、PSI的电子传递速率（ETRI）、PSII的电子传递速率（ETRII）和质体醌（PQ）库大小较低。更重要的是，LN植株中的K相和CEF较高。此外，MV处理和HO处理的植株之间抗氧化酶活性没有显著差异。所得结果表明，较低的LEF导致LN植株中ΔpH和ATP形成受阻，从而损害PSII放氧复合体（OEC）的供体侧。PSI受体侧过度还原是LN条件下PSI光抑制的主要原因。较高的CEF和抗氧化酶活性不仅保护PSI免受光损伤，还减缓了LN条件下生长的[未提及的物种名称]中PSII的损伤速率。
