Abstract

Relationships between changes in the levels of intracellular cAMP and H₂O₂ were studied in various growth zones of pea (Pisumsativum L.) seedling roots upon infection with Rhizobium leguminosarum bv. viceae (Rlv), Pseudomonas syringae pv. pisi (Psp), or Clavibacter michiganensis ssp. sepedonicus (Cms). Previous studies have shown that these root zones are differentially sensitive to Rlv. In the present work, the highest level of H₂O₂ in growth zones of pea roots was observed after a short-term (5 min) inoculation with Rlv. In roots treated with Psp and Cms, the H₂O₂ contents were lower and showed little variation between Psp and Rlv treatments as well as between various growth zones. In all three treatments, the H₂O₂ content in seedling epicotyls decreased by approximately 20% with respect to the control level. Under these conditions, the level of intracellular cAMP increased substantially in almost all growth zones of pea seedling roots. The largest increase was observed upon the inoculation with Cms. The intracellular cAMP level was artificially increased by applying various concentrations of exogenous n-butyryl-cAMP known to readily permeate into the cells. At concentrations of 5 and 10 nM, n-butyryl-cAMP induced equal increases of H₂O₂ content in all analyzed zones, whereas the treatment with 50 nM n-butyryl-cAMP diminished H₂O₂ content in root zones and epicotyls. A 30-min incubation of samples in the presence of 10 or 50 nM n-butyryl-cAMP followed by a 5‑min infection with Rlv, Psp, and Cms significantly modified the H₂O₂ level in root growth zones. In order to decrease the intracellular content of cAMP, an inhibitor of transmembrane adenylate cyclase, suramin was applied. Under the action of suramin, the cAMP concentration in the root growth zones decreased by approximately 40%; in addition, the intracellular H₂O₂ content increased in the same root zones and in epicotyls. The treatment of seedlings with suramin followed by a 5-min incubation of plants in the presence of Rlv and Psp microorganisms led to insignificant lowering in the content of a signaling molecule H₂O₂, whereas the “suramin + Cms” treatment induced a larger decrease in H₂O₂ content, thus shifting it to the control level. It is concluded that, in plant cells exposed to biotic stressors, a certain concentration status of secondary messengers is established by virtue of their mutual influence on the components of other plant signaling systems.

中文翻译：

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cAMP对生物胁迫下豌豆幼苗根中过氧化氢水平的调节作用

摘要

在豌豆根瘤菌感染后，研究了豌豆（Pisum sativum L.）幼苗各个生长区细胞内cAMP水平与H ₂ O ₂变化之间的关系。Vicese（Rlv），丁香假单胞菌PV。皮氏（Psp）或密歇根州的Clavibacter ssp。sepedonicus（Cms）。先前的研究表明，这些根区对Rlv的敏感性不同。在目前的工作中，最高水平的H ₂ O ₂短期（5分钟）接种Rlv后，在豌豆根的生长区中观察到生长激素。在用Psp和Cms处理的根中，H ₂ O ₂含量较低，在Psp和Rlv处理之间以及各个生长区之间几乎没有变化。在所有三种处理中，幼苗上胚轴中的H ₂ O ₂含量相对于对照水平降低了约20％。在这些条件下，豌豆幼苗根部几乎所有生长区的细胞内cAMP含量均显着增加。Cms接种后观察到最大的增加。通过应用已知易于渗透到细胞中的各种浓度的外源正丁酰-cAMP，可以人工提高细胞内cAMP的水平。在5和10 nM的浓度下，正丁酰cAMP引起所有分析区域中H ₂ O ₂含量的均等增加，而50 nM正丁酰cAMP处理降低了根区域和上胚轴中H ₂ O _2的含量。在存在10或50 nM正丁酰cAMP的情况下孵育30分钟，然后用Rlv，Psp和Cms感染5分钟会显着修饰H ₂ O ₂根生长区的水平。为了降低cAMP的细胞内含量，使用了跨膜腺苷酸环化酶苏拉明的抑制剂。在苏拉明的作用下，根部生长区中的cAMP浓度降低了约40％。另外，在相同的根区和上胚轴中细胞内H ₂ O ₂含量增加。用苏拉明处理幼苗，然后在Rlv和Psp微生物存在下孵育植物5分钟，导致信号分子H ₂ O ₂含量降低不明显，而“苏拉明+ Cms ”处理则诱导了更大的释放。 H ₂减少O ₂含量，因此将其转移到控制水平。结论是，在暴露于生物胁迫下的植物细胞中，次级信使由于它们对其他植物信号系统组件的相互影响而建立了一定的浓度状态。