Interactive effects of different densities of Pedicularis kansuensis parasitism and Epichloё endophyte infection on the endogenous hormone levels and alkaloid contents of Stipa purpurea

doi:10.11686/cyxb2019313

Abstract

Abstract: Root hemiparasites of grasses in the natural environment impose a biotic stress on their hosts. Conversely, Epichloё endophytes enhance their hosts’ tolerance or resistance to biotic and abiotic stresses. However, only a few studies have explored the interactive effects of different densities of hemiparasite infection and the presence or absence of Epichloё endophyte on the growth, endogenous hormone levels and alkaloid contents of the host grasses. Therefore, we set up a two factor pot experiment with endophyte-infected (E+) and endophyte-free (E-) plants of Stipa purpurea as the host grass, grown without (control) or with one or three plants of the hemiparasite Pedicularis kansuensis. Various plant growth parameters and endogenous hormone levels were determined for E+ and E- S. purpurea, while alkaloid concentrations of endophyte-infected S. pupurea plants and their hemiparasites (where present) were measured. Comparing parasitized and unparasitized S. purpurea, biomass of parasitized plants was decreased 80%, plant height, tiller number and root length were reduced 25%, and indole-3-acetic acid and abscisic acid levels of S. purpurea were increased 43% and 51%, respectively. However, zeatin-riboside levels were decreased by 50%, while the growth parameters, and endogenous hormone levels of E+ host grasses were significantly higher than those of their E- counterparts. Furthermore, under parasitic stress, alkaloid production of Epichloё-endophyte-infected plants was enhanced, and alkaloids were transferred from E+ host grass plants to their root hemiparasites through the xylem bridge formed by haustoria. In conclusion, our results show that Epichloё endophyte has a potential role in improving its host grass resistance or tolerance to parasitic stress by up-regulating host grass alkaloid contents and endogenous hormone levels, especially those hormones typically sensitive to biotic stress. Our results also suggest that use of the Epichloё endophyte symbiont has potential as a tool to assist recovery of degraded grassland in the Qinghai Tibet Plateau where root hemiparasites are widely distributed.

Key words: root hemiparasite, endogenous hormone, alkaloid, Epichloë endophyte, Stipa purpurea, density

BAO Gen-sheng, SONG Mei-ling, WANG Yu-qin, LIU Jing, WANG Hong-sheng. Interactive effects of different densities of Pedicularis kansuensis parasitism and Epichloё endophyte infection on the endogenous hormone levels and alkaloid contents of Stipa purpurea[J]. Acta Prataculturae Sinica, 2020, 29(4): 147-156.

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