Aims

Root hemiparasite infection is considered a potential biotic stress that affects the growth of cool-season grasses, and the damage caused by a hemiparasitic plant to host grasses is largely determined by the density of the hemiparasite. Epichloë endophytes have been shown to be mutualistic symbionts of cool-season grasses under most environmental conditions. Although cool-season grasses can be host to both Epichloë endophytes and hemiparasites, little attention has been given to how Epichloë infection regulates the physiological and phytohormone responses of host grasses under parasitic stress.

Methods

We performed a pot experiment with an endophyte-infected and endophyte-free host grass, Stipa purpurea, and a facultative hemiparasite, Pedicularis kansuensis. The grasses were grown together under different densities of the hemiparasite (control, one or three plants per pot). Grass growth as well as physiological and phytohormone parameters were determined following parasitic stress.

Results

Successful parasitism increased the biomass and survival of P. kansuensis while suppressing the growth of S. purpurea. The reduction in the growth of S. purpurea was dependent on the density of P. kansuensis. Epichloë infection of S. purpurea improved the tolerance of this grass to parasitic stress, resulting in more tillers, longer roots, higher shoot and root biomasses and a higher root:shoot ratio compared with those of the endophyte-free grass. Interestingly, Epichloë infection increased proline, indole-3-acetic acid and abscisic acid production as well as superoxide dismutase, peroxidase and catalase activities and reduced the malondialdehyde content, root vitality and zeatin riboside content under root hemiparasitic stress.

Conclusions

Our results demonstrate that the growth of the host grass was severely reduced under parasitic stress; the negative effects of hemiparasitic plants on the host grass were largely determined by the density of the hemiparasite. The findings also indicate that the Epichloë endophytes greatly alleviated the damage caused by the hemiparasite to the cool-season grass by producing more antioxidant enzymes, enhancing root viability, synthesizing certain phytohormones and suppressing haustorium formation.

中文翻译：

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Epichloë内生菌感染通过调节抗氧化剂和植物激素增强紫花针茅对寄生虫胁迫的耐受性

宗旨

根部半寄生虫感染被认为是影响冷季草生长的潜在生物胁迫，半寄生植物对寄主草造成的损害在很大程度上取决于半寄生虫的密度。在大多数环境条件下，Epichloë内生菌已被证明是冷季草的共生体。尽管冷季草可以是Epichloë内生菌和半寄生虫的宿主，但很少有人关注Epichloë感染如何调节寄主草在寄生压力下的生理和植物激素反应。

方法

我们对受内生菌感染且无内生菌的寄主草Stipa purpurea和兼性半寄生虫Pedicularis kansuensis进行了盆栽试验。草在不同密度的半寄生虫（对照，每盆一株或三株植物）下一起生长。在寄生胁迫后测定草生长以及生理和植物激素参数。

结果

成功的寄生增加了P的生物量和存活率。kansuensis同时抑制S的生长。紫癜。S. purpurea生长的减少取决于P的密度。甘肃。与无内生菌的草相比，S. purpurea 的Epichloë感染提高了这种草对寄生胁迫的耐受性，导致更多的分蘖、更长的根、更高的枝条和根生物量以及更高的根：枝条比。有趣的是，埃皮克洛 感染增加了脯氨酸、吲哚-3-乙酸和脱落酸的产生以及超氧化物歧化酶、过氧化物酶和过氧化氢酶的活性，并降低了根偏寄生胁迫下的丙二醛含量、根活力和玉米素核苷含量。

结论

我们的结果表明寄主草的生长在寄生胁迫下严重减少；半寄生植物对寄主草的负面影响很大程度上取决于半寄生植物的密度。研究结果还表明，Epichloë内生菌通过产生更多抗氧化酶、增强根系活力、合成某些植物激素和抑制吸器形成，大大减轻了半寄生虫对冷季草造成的损害。