Methyl jasmonate (MeJA) is an airborne signaling phytohormone that can induce changes in endogenous jasmonates (JAs) and cause photosynthetic responses. However, the response of these two aspects of citrus plants at different MeJA concentrations is still unclear. Four MeJA concentrations were used in two citrus varieties, Huangguogan (C. reticulata × C. sinensis) and Shiranuhi [C. reticulata × (C. reticulata × C. sinensis)], to investigate the effects of MeJA dose on the endogenous JAs pathway and photosynthetic capacity. We observed that MeJA acted in a dose-dependent manner, and its stimulation in citrus leaves showed a bidirectional character at different concentrations. This work demonstrates that MeJA at only a concentration of 2.2 mM or less contributed to the activation of magnesium protoporphyrin IX methyltransferase (ChlM, EC 2.1.1.11) and protochlorophyllide oxidoreductase (POR, EC 1.3.1.11) and the simultaneous accumulation of Chla and Chlb, which in turn contributed to an improved photosynthetic capacity and PSII photochemistry efficiency of citrus. Meanwhile, the inhibition of endogenous JAs synthesis by exogenous MeJA was observed. This was achieved by reducing the ratio of monogalactosyl diacylglycerol (MGDG) to diagalactosyl diacylglycerol (DGDG) and inhibiting the activities of key enzymes in JAs synthesis, especially 12-oxo-phytodienoic acid reductase (OPR, EC 1.3.1.42). Another noteworthy finding is that there may exist a JA-independent pathway that could regulate 12-oxo-phytodienoic acid (OPDA) synthesis. This study jointly analyzed the internal hormone regulation mechanism and the external physiological response, as well as revealed the effects of exogenous MeJA on promoting the photosynthesis and inhibiting the endogenous JAs synthesis. This article is protected by copyright. All rights reserved.

中文翻译：

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外源茉莉酸甲酯对柑橘内源茉莉酸合成及光合作用调控的影响

茉莉酸甲酯 (MeJA) 是一种空气传播信号植物激素，可诱导内源性茉莉酸 (JA) 发生变化并引起光合反应。然而，柑橘植物在不同 MeJA 浓度下这两个方面的反应仍不清楚。四种 MeJA 浓度用于两个柑橘品种黄果干 (C. reticulata × C. sinensis) 和 Shiranuhi [C. reticulata × (C. reticulata × C. sinensis)]，研究 MeJA 剂量对内源性 JAs 途径和光合能力的影响。我们观察到 MeJA 以剂量依赖性方式起作用，其对柑橘叶的刺激在不同浓度下表现出双向特征。这项工作表明，仅 2.2 mM 或更低浓度的 MeJA 有助于激活镁原卟啉 IX 甲基转移酶（ChlM，EC 2.1.1. 11) 和原叶绿素酸氧化还原酶 (POR, EC 1.3.1.11) 以及 Chla 和 Chlb 的同时积累，这反过来又有助于提高柑橘的光合能力和 PSII 光化学效率。同时，观察到外源性MeJA对内源性JAs合成的抑制。这是通过降低单半乳糖二酰基甘油 (MGDG) 与二半乳糖二酰基甘油 (DGDG) 的比例并抑制 JA 合成中关键酶的活性来实现的，尤其是 12-氧代-植物二烯酸还原酶 (OPR, EC 1.3.1.42)。另一个值得注意的发现是，可能存在一条独立于 JA 的途径，可以调节 12-氧代植物二烯酸 (OPDA) 的合成。本研究联合分析了内在激素调节机制和外在生理反应，并揭示了外源性MeJA对促进光合作用和抑制内源性JAs合成的影响。本文受版权保护。版权所有。