Background

Soil salinity adversely affects plant growth. Microbial infection and exogenous polyamine application are effective approaches to ameliorate salt injury in plants. Our previous study showed that Epichloë endophytes play an important role in improving wild barley (Hordeum brevisubulatum) salinity tolerance through polyamine metabolism modification. However, the effects of polyamine (Spd) on Epichloë endophytes-induced host tolerance to salt stress are largely unknown. The aim of this work is to determine whether exogenous polyamine influences the function of Epichloë endophytes to improve salt tolerance of H. brevisubulatum plants.

Methods

Epichloë endophyte infected (E+) and endophyte free (E−) H. brevisubulatum plants were sprayed with distilled water or 1 mM spermidine (Spd) and treated with water or 200 mM NaCl. The experimental plots included four treatments: (a) CK, (b) NaCl, (c) Spd, and (d) Spd + NaCl. Dry weight, amino acid, sodium, potassium, calcium, nitrogen, phosphorus and carbon contents were quantified, Na⁺:K⁺ ratio and C:N:P stoichiometry were analyzed after 21 days exposure to NaCl treatment.

Results

There was greater accumulation of aspartic acid, threonine, glutamic acid, tyrosine, phenylalanine, histidine, arginine and proline but lower cysteine in endophyte-infected plants compared to endophyte-free counterparts in response to NaCl treatment. The presence of Epichloë endophyte also significantly increased dry weight, total amino acid, potassium, root calcium, nitrogen and phosphorus content but decreased sodium, shoot calcium content and ratios of sodium/potassium, carbon/nitrogen and carbon/phosphorus, nitrogen/phosphorus under NaCl stress. The effects of endophyte to decrease sodium content, sodium/potassium ratio and increase dry weight, total amino acid, potassium, nitrogen and shoot phosphorus were much more pronounced under dual application of NaCl and exogenous spermidine treatment compared to treatments only under NaCl treatment.

Conclusion

Epichloë endophytes may ameliorate the harmful effects of NaCl stress to H. brevisubulatum plants, whilst exogenous spermidine further enhanced this effect. Spermidine application to endophyte-infected seedlings decreased more of these harmful effects and mediated the function of the endophyte to suppress the negative effects of salinity stress.

中文翻译：

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外源亚精胺增强了 Epichloë 内生菌诱导的野生大麦（Hordeum brevisubulatum）对 NaCl 胁迫的耐受性

背景

土壤盐分对植物生长产生不利影响。微生物感染和外源多胺应用是改善植物盐害的有效方法。我们之前的研究表明，Epichloë内生菌通过多胺代谢修饰在提高野生大麦 ( Hordeum brevisubulatum ) 耐盐性方面发挥着重要作用。然而，多胺 (Spd) 对Epichloë内生菌诱导的宿主对盐胁迫的耐受性的影响在很大程度上是未知的。这项工作的目的是确定外源多胺是否影响Epichloë内生菌的功能，以提高H. brevisubulatum植物的耐盐性。

方法

用蒸馏水或 1 mM 亚精胺 (Spd) 喷洒被Epichloë内生菌感染 (E+) 和无内生菌 (E-) 的H. brevisubulatum植物，并用水或 200 mM NaCl 处理。实验地块包括四种处理：(a) CK、(b) NaCl、(c) Spd 和 (d) Spd + NaCl。干重、氨基酸、钠、钾、钙、氮、磷和碳含量被量化，Na ⁺ :K ⁺比率和 C:N:P 化学计量在暴露于 NaCl 处理 21 天后进行分析。

结果

与无内生菌对应物相比，响应于 NaCl 处理，内生菌感染植物中天冬氨酸、苏氨酸、谷氨酸、酪氨酸、苯丙氨酸、组氨酸、精氨酸和脯氨酸的积累更多，但内生菌感染的植物中半胱氨酸的积累量更低。Epichloë的存在在NaCl胁迫下，内生菌还显着增加干重、总氨基酸、钾、根钙、氮和磷含量，但降低钠、地上部钙含量和钠/钾、碳/氮和碳/磷、氮/磷的比例。与仅在NaCl处理下的处理相比，在NaCl和外源亚精胺双重处理下内生菌降低钠含量、钠/钾比和增加干重、总氨基酸、钾、氮和地上部磷的作用更显着。

结论

Epichloë内生菌可以改善 NaCl 胁迫对H. brevisubulatum植物的有害影响，而外源亚精胺进一步增强了这种影响。对受内生菌感染的幼苗施用亚精胺可减少更多这些有害影响，并介导内生菌抑制盐胁迫负面影响的功能。