Abstract
Soybean is an important economic crop that is continually threatened by abiotic stresses, especially salt stress. Wild soybean is an important germplasm resource for the breeding of cultivated soybean. The root system plays a very important role in plant salt tolerance. To explore the salt tolerance-related mechanisms among Soja, we have demonstrated the seedling roots' growth and metabolomics in wild soybean, semi-wild soybean, and cultivated soybean under two types of salt stress by using gas chromatography-mass spectrometry. We characterized 47 kinds of differential metabolites under neutral salt stress, and isoleucine, serine, l-allothreonine, glutamic acid, phenylalanine, asparagines, aspartic acid, pentadecanoic acid, lignoceric acid, oleic acid, galactose, tagatose, d-arabitol, dihydroxyacetone, 3-hydroxybutyric acid, and glucuronic acid increased significantly in the roots of wild soybean seedlings. However, these metabolites were suppressed in semi-wild and cultivated soybeans. Amino acid, fatty acid, sugars, and organic acid synthesis and the secondary metabolism of antioxidants increased significantly in the roots of wild soybean seedling. Under alkaline salt stress, wild soybean contained significantly higher amounts of proline, glutamic acid, aspartic acid, l-allothreonine, isoleucine, serine, alanine, arachidic acid, oleic acid, cis-gondoic acid, fumaric acid, l-malic acid, citric acid, malonic acid, gluconic acid, 5-methoxytryptamine, salicylic acid, and fluorene than semi-wild and cultivated soybeans. Our study demonstrated that carbon and nitrogen metabolism, and the tricarboxylic acid (TCA) cycle and receiver operating characteristics (especially the metabolism of phenolic substances) of the seedling roots were important to resisting salt stress and showed a regular decreasing trend from wild soybean to cultivated soybean. The metabolomics's changes were critical factors in the evolution of salt tolerance among Soja. This study provides new insights into salt tolerance in soybean, and presents quantitative parameters for a salt tolerant soybean breeding system, which is conducive to the rational use and protection of wild soybean resources.
Highlights
Soybean is an important source of protein and fat in the human diet, as well as being an important livestock feed and industrial raw material (He and Chen, 2013)
Seedling root growth and biomass were significantly inhibited in the three kinds of soybean when exposed to both kinds of salt stress (Table 1)
The number of leaves and roots per plant decreased, the leaf area became smaller, the leaves turned yellow under both types of salt stress
Summary
Soybean is an important source of protein and fat in the human diet, as well as being an important livestock feed and industrial raw material (He and Chen, 2013). Soja includes wild soybean (Glycine soja), semi-wild soybean (Glycine gracilis), and cultivated soybean (Glycine max), which are phylogenetically related. Wild soybean can better adapt to a variety of adverse environments (Tuyen et al, 2010). Semi-wild soybean is a transition type in the evolution of Soja, having a physiological metabolism close to that of wild soybean and a phenotype closer to that of cultivated soybean (Shi et al, 2016). The cultivated soybean has been bred by artificial selection and domestication from wild soybean. Cultivated soybean is a typical glycophyte in which growth, quality, and yield are significantly reduced under salt stress (Wang and Li, 2011)
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