Nitrogen (N) is an essential component of photosynthetic apparatus. However, the mechanism that photosynthetic capacity is suppressed by N is not completely understood. Photosynthetic capacity and photosynthesis-related genes were comparatively analyzed in a shade-tolerant species Panax notoginseng grown under the levels of low N (LN), moderate N (MN) and high N (HN). Photosynthetic assimilation was significantly suppressed in the LN- and HN-grown plants. Compared with the MN-grown plants, the HN-grown plants showed thicker anatomic structure and larger chloroplast accompanied with decreased ratio of mesophyll conductance (gm) to Rubisco content (gm/Rubisco) and lower Rubisco activity. Meanwhile, LN-grown plants displayed smaller chloroplast and accordingly lower internal conductance (gi). LN- and HN-grown individuals allocated less N to light-harvesting system (NL) and carboxylation system (NC), respectively. N surplus negatively affected the expression of genes in Car biosynthesis (GGPS, DXR, PSY, IPI and DXS). The LN individuals outperformed others with respect to non-photochemical quenching. The expression of genes (FBA, PGK, RAF2, GAPC, CAB, PsbA and PsbH) encoding enzymes of Calvin cycle and structural protein of light reaction were obviously repressed in the LN individuals, accompanying with a reduction in Rubisco content and activity. Correspondingly, the expression of genes encoding RAF2, RPI4, CAB and PetE were repressed in the HN-grown plants. LN-induced depression of photosynthetic capacity might be caused by the deceleration on Calvin cycle and light reaction of photosynthesis, and HN-induced depression of ones might derive from an increase in the form of inactivated Rubisco.

中文翻译：

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氮条件下耐荫物种三七的光合作用性能和光合作用相关基因表达的协调。


氮（N）是光合作用装置的重要组成部分。然而，氮抑制光合能力的机制尚不完全清楚。对低氮（LN）、中氮（MN）和高氮（HN）条件下生长的耐荫树种三七的光合能力和光合作用相关基因进行了比较分析。在 LN 和 HN 生长的植物中，光合同化作用受到显着抑制。与MN生长的植物相比，HN生长的植物表现出更厚的解剖结构和更大的叶绿体，同时叶肉导度（gm）与Rubisco含量（gm/Rubisco）的比率降低，并且Rubisco活性降低。与此同时，液氮生长的植物叶绿体较小，内电导 (gi) 也相应较低。 LN 和 HN 生长的个体分别向光捕获系统（NL）和羧化系统（NC）分配较少的氮。氮过剩对汽车生物合成基因（GGPS、DXR、PSY、IPI 和 DXS）的表达产生负面影响。 LN 个体在非光化学猝灭方面优于其他个体。 LN个体中卡尔文循环酶和光反应结构蛋白编码基因(FBA、PGK、RAF2、GAPC、CAB、PsbA和PsbH)的表达受到明显抑制，伴随着Rubisco含量和活性的降低。相应地，编码 RAF2、RPI4、CAB 和 PetE 的基因的表达在 HN 生长的植物中受到抑制。 LN引起的光合能力下降可能是由于卡尔文循环和光合作用光反应的减速引起的，而HN引起的光合能力下降可能是由于失活的Rubisco形式的增加所致。