Abstract
Soil alkalization is a major environmental threat that affects plant distribution and yield in northeastern China. Puccinellia tenuiflora is an alkali-tolerant grass species that is used for salt-alkali grassland restoration. However, little is known about the molecular mechanisms by which arbuscular mycorrhizal fungi (AMF) enhance P. tenuiflora responses to alkali stress. Here, metabolite profiling in P. tenuiflora seedlings with or without arbuscular mycorrhizal fungi (AMF) under alkali stress was conducted using liquid chromatography combined with time-of-flight mass spectrometry (LC/TOF-MS). The results showed that AMF colonization increased seedling biomass under alkali stress. In addition, principal component analysis (PCA) and orthogonal projections to latent structures discriminant analysis (OPLS-DA) demonstrated that non-AM and AM seedlings showed different responses under alkali stress. A heat map analysis showed that the levels of 88 metabolites were significantly changed in non-AM seedlings, but those of only 31 metabolites were significantly changed in AM seedlings. Moreover, the levels of a total of 62 metabolites were significantly changed in P. tenuiflora seedlings after AMF inoculation. The results suggested that AMF inoculation significantly increased amino acid, organic acid, flavonoid and sterol contents to improve osmotic adjustment and maintain cell membrane stability under alkali stress. P. tenuiflora seedlings after AMF inoculation produced more plant hormones (salicylic acid and abscisic acid) than the non-AM seedlings, probably to enhance the antioxidant system and facilitate ion balance under stress conditions. In conclusion, these findings provide new insights into the metabolic mechanisms of P. tenuiflora seedlings with arbuscular mycorrhizal fungi under alkali conditions and clarify the role of AM in the molecular regulation of this species under alkali stress.
Highlights
Soil salinization and alkalization are some of the most severe ecological and agricultural problems throughout the world and severely limit plant growth, development and yield [1,2]
Yu et al (2013) found 43 differentially expressed proteins in P. tenuiflora seedlings under alkali stress using proteomic technology, and the results suggested that their alkali response mechanisms include a decline in photosynthesis, the activation of multiple antioxidant mechanisms and an enhanced energy supply [17]
Two-way analysis of variance (ANOVA) results showed that dry weight of seedlings was affected by the alkalinity concentration (p < 0.001) and the presence of arbuscular mycorrhizal fungi (p < 0.001, Table 1)
Summary
Soil salinization and alkalization are some of the most severe ecological and agricultural problems throughout the world and severely limit plant growth, development and yield [1,2]. It has been reported that almost 831 million hectares of land have been affected by salt in the soil [3]. In northeastern China, the most remarkable feature is that the soil consists mainly of alkaline salts (e.g., NaHCO3 and Na2CO3), and alkaline meadows cover more than 70% of the land area [4]. Alkaline stress has the same inhibitory effects as saline stress and has the unique influence of high pH, which inhibits ion uptake and disrupts the ionic balance of plant cells [8,9]. To the best of our knowledge, the majority of studies have emphasized the toxic effects of salt stress and paid little attention to alkaline stress, and the specific alkali-tolerance mechanisms of halophytes are still not fully understood
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