Selenium can be absorbed and utilized by plants, influencing their growth by altering their physiological metabolism. In this study, based on plant physiology methods, compared to the CK treatment, the height and leaf length of oat seedlings under the T0.02 (0.02 g/kg Na₂SeO₃) treatment significantly increased by 18.36% and 15.81%, respectively (p < 0.05). Under the T0.1 (0.1 g/kg Na₂SeO₃) treatment, the levels of malondialdehyde (MDA), proline, soluble sugar content, and peroxidase (POD) activity significantly increased (p < 0.05). However, the seedling height and leaf length under the T0.1 treatment significantly decreased by 33.24% and 23.25%, respectively. Additionally, the contents of chlorophyll a, chlorophyll b, and carotenoids, as well as ascorbate peroxidase (APX) activity and the superoxide anion radical generation rate (O₂⁻) significantly decreased (p < 0.05). The total selenium, organic selenium, and inorganic selenium contents, as measured by the atomic fluorescence spectroscopy method, were also increased in oat seedling roots and leaves under T0.1 treatment (p < 0.05). Selenium had a high coefficient of mobility from root to leaf of 6.01 under T0.02 and 4.65 under T0.1 treatment, and from soil to leaf of 4.98 under T0.02 and 4.55 under T0.1 treatment. Through untargeted metabolomics, six differential phenylpropanoid compounds and 18 differential flavonoid compounds were found in oat seedlings. Based on transcriptomic analysis of oat seedlings, 29 DEGs associated with phenylpropanoid metabolism and 13 DEGs related to flavonoid biosynthesis were identified. Over 60% of the genes (25/42) in the phenylpropanoid and flavonoid biosynthesis pathway were associated with the accumulation of about 74% (20/27) of the compounds in oat leaves. Based on transcriptomic and metabolomics analysis, there were nine major genes (including PAL1, PAL4, CHS2, PAL7, POD3, PAL6, CCR1, CCR4, POD4) modulating the metabolism of phenylpropanoid and flavonoid biosynthesis pathway. This study offers novel insights and genetic resources for exploring the mechanisms underlying plant responses to selenium treatment, thereby further enhancing selenium tolerance in plants.

Lycium chinense is acknowledged for its substantial nutritional benefits, particularly attributed to the high levels of ascorbic acid (AsA) found in its fruits. The “Mengqi No.1” variety of L. chinense, which is cultivated in Qinghai, is known for its high yield and exceptional quality. We utilized the “Mengqi No.1” variety as experimental materials and combined metabolomic, transcriptomic, and physiological analyses to investigate the metabolites, genes, and enzymes related to AsA metabolism in L. chinense fruits. The results revealed nine differential metabolites associated with AsA metabolism in L. chinense fruits across three stages, including 1D-Myo-Inositol-1,4-Bisphosphate, D-Fructose, L-(+)-Arabinose, I-Inositol, L-Arabinitol, D-Galactose-1-P, lactose, α-D-Glucose, and D-Glucose-6-P. Notably, the contents of D-Glucose-6-P, D-Galactose-1-P, and D-Fructose were increased as the fruit developed. Additionally, fresh weight, longitudinal length, and radial width were increased, while the contents of AsA and DHA were decreased. GalDH and DHAR are critical enzymes for the accumulation of AsA and DHA, exhibiting positive correlation coefficient. Furthermore, PMM1, PMM5, GME2, and GME3 were identified as key regulatory genes in the L-Galactose pathway of AsA synthesis, influencing D-Galactose-1-P, D-Glucose-6-P, α-D-Glucose, and D-Fructose. DHAR1 and DHAR2 are considered key positive regulator genes of AsA and DHA in the AsA-GSH cycle. However, the majority of genes (nine) act as negative regulators of AsA and DHA. These findings provide a foundation for the understanding of the regulatory mechanism of AsA metabolism in L. chinense fruits and offer insights into the utilization of AsA from L. chinense.

Phlomoides rotata, a traditional medicinal plant, is commonly found on the Tibetan Plateau at altitudes of 3100–5200 m. Its primary active medicinal compounds, flavonoids and phenylethanol glycosides (PhGs), exhibit various pharmacological effects, including hemostatic, anti-inflammatory, antitumor, immunomodulatory, and antioxidant activities. This study analyzed flavonoid and PhG metabolites in the roots of P. rotata collected from Henan County (HN), Guoluo County (GL), Yushu County (YS), and Chengduo County (CD) in Qinghai Province. A total of differentially abundant metabolites (DAMs) including 38 flavonoids and 21 PhGs were identified. Six genes (UFGT1, CHS1, COMT2, C4H3, C4H8, and C4H5) and four enzymes (4CL, C4H, PPO, and ALDH) were found to play key roles in regulating flavonoid and PhG biosynthesis in P. rotata roots. With increasing altitude, the relative content of 15 metabolites, the expression of seven genes, and the activity of four enzymes associated with flavonoid and PhG metabolism increased. These findings enhance our understanding of the regulatory mechanisms of flavonoid and PhG metabolism in P. rotata and provide insights into the potential pharmaceutical applications of its bioactive compounds.

Phlomoides rotata, a traditional medicinal plant, always grows on the Tibetan Plateau at a high altitude of 3100–5200 m. The major active ingredients in P. rotata were used in medicines due to their diverse pharmacological effects, including hemostatic, anti-inflammatory, antitumor, immuno-modulatory, and antioxidant activities. This study screened 15 top endophytic genus through the analysis of OTUs and the top 30 metabolites with relatively high content in P. rotata roots from four different habitats (HN, GL, YS, and CD regions) in Qinghai Province. Twelve physicochemical indicators were measured and analyzed in the rhizosphere soils of P. rotata habitats. The results indicated that the top 30 metabolites compounds included 7 amino acids, 5 sugars and alcohols, 4 phenylpropanoids, 3 Organic acids, and 3 Alkaloids. Four endophytic bacteria (Acidibacter, Sphingomonas, Variovorax, and Sphingobium) and three endophytic fungi (Tetracladium, Cadophora, and Minimelanolocus) were dominant genera in P. rotata roots from four habitats. There were 109 positive significant correlations and 57 negative correlations between OTUs of endophytic bacteria and contents of top 30 metabolites, and 59 positive significant correlations and 58 negative correlations between OTUs of endophytic fungus and contents of top 30 metabolites. The OTUs of Acidibacter were significantly positively correlated with the content of 5 soil physicochemical indicators (total phosphorus, amylase, sucrase, total potassium, or soil organic carbon) and significantly negatively correlated with the content of acid protease. OTUs of Tetracladium or Cadophora showed a positive correlation with the content of total phosphorus and a negative correlation with that of alkaline phosphatase. This study provides a theoretical basis for the study of the correlation between endophytes and metabolites in P. rotata roots.

Selenium (Se), as a vital trace element, plays an important role in regulating the antioxidant systems of plants, strengthening photosynthetic capacity, and enhancing their stress resistance. Selenate and selenite are the dominant forms of Se available to plants in soils. This research takes highland barley as the research object, aiming to assess the impacts of plant growth, organic acid metabolite, and six transcription factor families in highland barley seedlings under varying concentrations of Na₂SeO₃. The study indicated that compared to the control group (CK), the plant height of highland barley seedlings under Se1 (0.02 g/kg Na₂SeO₃) treatment significantly increased by 66%. Under the Se2 (0.2 g/kg Na₂SeO₃) treatment, plant height significantly decreased by 28%. With Na₂SeO₃ concentration increased, the pigment content, O₂⁻ production rate, and soluble protein content in highland barley seedlings decreased, while the contents of soluble sugar, MDA, and H₂O₂ increased. Se1 treatment was found to be more beneficial for the growth and development of seedlings. The organic selenium in leaves and roots under Se2 treatment significantly increased by 1105-fold and 188-fold, respectively. The most effective migration capability from soil to leaf under Se1 or Se2 treatment was up to 6.15 or 6.56, respectively. Based on metabolomics, 30 differential metabolites of organic acids were screened from highland barley seedlings under Na₂SeO₃ treatment and showed positive correlationships with organic selenium, inorganic selenium, and total selenium in highland barley seedling leaves. Through transcriptome analysis, heatmap analysis on six major categories of transcription factors (bHLH, MYB, NAC, WRKY, GATA, and HSF) was performed. Under Se2 treatment, approximately two-thirds of the transcription factors showed high expressions. We further screened 26 differentially expressed genes (DEGs) related to Na₂SeO₃ concentration. Based on correlation analysis, there were six genes in the bHLH family, five in MYB, three in NAC, five in WRKY, and three in the GATA and HSF families that showed positive correlations with 30 differential organic acid metabolites. These results enhance our understanding of the relationship between the organic acid metabolites and transcription factor expression in highland barley seedlings under Na₂SeO₃ treatment.

Selenium (Se) influences plant growth, yet its molecular regulation of amino acid metabolism in oat seedlings remains unclear. Through transcriptomic and metabolomic analyses, this study identified three major affected pathways: tryptophan metabolism (16 differentially expressed genes [DEGs], 13 differentially expressed metabolites [DEMs]), glycine, serine, and threonine metabolism (19 DEGs, 10 DEMs), and arginine and proline metabolism (24 DEGs, 13 DEMs). The T0.02 treatment (0.02 g/kg Na₂SeO₃) precisely regulates metabolism by selectively upregulating dimethylglycine in the glycine, serine, and threonine pathway and activating key genes (PRODH2, amiE2, AMD2) in the arginine–proline pathway, thereby promoting the growth of oat seedlings. The T0.1 treatment (0.1 g/kg Na₂SeO₃), promoted the accumulation of glycerate and threonine by upregulating the expression of two key genes (HPR3, ItaE1) related to glycine, serine, and threonine metabolism. Simultaneously, it enhanced the accumulation of L-ornithine, putrescine, 4-guanidinobutyric acid, and γ-aminobutyric acid through the upregulation of four key genes (ARG, ODC1, amiE1, and ALDH3) associated with arginine and proline metabolism. Additionally, the upregulation of key genes (ALDH2, 5-HTP) involved in tryptophan metabolism facilitated the accumulation of 5-methoxyindoleacetic acid and serotonin. This study primarily reveals the accumulation patterns of amino acid metabolites in oat seedlings subjected to selenium treatment and identifies key genes and metabolic pathways involved in the molecular response process. Furthermore, the research preliminarily elucidates potential regulatory nodes through which selenium treatment enhances amino acid accumulation, providing significant insights for understanding the comprehensive effects of selenium treatment on the stress resistance mechanisms of oat seedlings.