In this paper, the effects of different CO₂ concentrations (400 and 800 μmol·mol⁻¹) on photosynthetic gas exchange and chlorophyll fluorescence of mulberry (Morus alba L.) seedling leaves under drought stress were studied using an artificial climate chamber. The results showed that under non-drought conditions, the stomatal concentrations (G_s) and transpiratration rate (T_r) of mulberry seedling leaves decreased slightly with increased CO₂ concentrations, but the net photosynthetic rate (P_n) increased significantly. Under mild drought stress (5 days of drought), higher CO₂ concentrations significantly affected the photosynthetic gas exchange of mulberry seedling leaves, but had little effect on chlorophyll fluorescence. Under severe drought stress (10 das of drought), increased CO₂ concentrations not only alleviated drought stress by increasing the WUE of mulberry seedling leaves, but also significantly increased its PSII photochemical activity, which promoted electron transfer on the PSII acceptor side. In conclusion, increased CO₂ concentrations could raise the WUE of mulberry seedling leaves under normal water conditions and drought stress, and this effect was more significant under drought stress. Under severe drought stress, increased CO₂ concentrations improved the drought resistance of mulberry seedlings by improving their PSII function.

The northern highbush blueberry variety ‘Duke’ was used as the test material, and different concentrations of 2,4-Epibrassinolide (EBR) (0, 0.2, 0.4, 0.6, and 0.8 mg·L^-1) were applied during the bud expansion stage, with a second application administered at one-day intervals following the first. Samples were collected at the bud, flower, and fruit stages and subsequently treated with artificial low temperatures (2°C) after sampling. The effects of various concentrations of exogenous EBR on the physiological indices of cold resistance and the expression of the cold resistance gene VcCBF3 in blueberry buds, flowers, and young fruits were investigated through comprehensive evaluation and correlation analysis. The objective was to identify the optimal concentration of EBR to enhance the cold resistance of blueberries. The results indicate that: (1) Under low temperature stress, the contents of soluble sugar, soluble protein and proline increased, along with the activities of superoxide dismutase, peroxidase, and catalase. The expression of the VcCBF3 gene expression and the ascorbate-glutathione cycling system were up-regulated, and with the increase of EBR concentration, the expression of the VcCBF3 gene initially rose and then declined. The content of malondialdehyde and the production rate of superoxide anion radicals decreased, and with the increase of EBR concentration, the content of malondialdehyde first decreased and then increased. (2) Overall low temperature resistance, flowers > buds > young fruits. (3) Appropriate concentrations of exogenous EBR can effectively mitigate freezing damage in blueberries caused by low temperatures. A comprehensive evaluation and correlation analysis of each cold tolerance index and the expression of the VcCBF3 gene revealed that a treatment concentration of 0.4 mg·L^-1 had the most significant mitigating effect among the sprayed EBR concentrations of 0, 0.2, 0.4, 0.6, and 0.8 mg·L^-1.

Cerasus humilis, a small shrub of the Cerasus genus within the Rosaceae family, is native to China and renowned for its highly nutritious and medicinal fruits, robust root system, and remarkable drought resistance. This study primarily employed association transcriptome and metabolome analyses to assess changes in abscisic acid (ABA) levels and identify key regulatory genes in C. humilis subjected to varying degrees of drought stress. Notably, we observed distinct alterations in transcription factors across different drought intensities. Specifically, our transcriptome data indicated noteworthy shifts in GATA, MYB, MYC, WRKY, C2H2, and bHLH transcription factor families. Furthermore, combined transcriptomic and metabolomic investigations demonstrated significant enrichment of metabolic pathways, such as ‘Carbon metabolism’, ‘Biosynthesis of amino acids’, ‘Biosynthesis of cofactors’, ‘Phenylpropanoid biosynthesis’, ‘Starch and sucrose metabolism’, and ‘Plant hormone signal transduction’ under moderate (Mod) or severe (Sev) drought conditions. A total of 11 candidate genes involved in ABA biosynthesis and signaling pathways were identified. The down-regulated genes included secoisolariciresinol dehydrogenase-like and PYL2. Conversely, genes including FAD-dependent urate hydroxylase-like, cytochrome P450 97B2, carotenoid cleavage dioxygenase 4 (CCD4), SnRK2.2, ABI 5-like protein 5, PP2C 51, and SnRK2.3, were up-regulated under Mod or Sev drought stress. This study lays the genetic foundation for ABA biosynthesis to enhance drought tolerance and provides genetic resources for plant genetic engineering and breeding efforts.

To understand the response of hazelnut to the increased concentration of carbon dioxide (CO₂) under cadmium (Cd) pollution stress, this paper used an artificial open top chamber to control the CO₂ concentration (at 370 and 750 μmol·mol⁻¹) and to study the effects of an elevated CO₂ concentration on the growth and photosynthetic capacity of hazelnut leaves under different levels of Cd stress. The results showed that the increase in atmospheric CO₂ concentration has a tendency to alleviate the inhibition of plant growth caused by Cd. The net photosynthetic rate rose significantly, although the transpiration rate and stomatal conductance of hazelnut leaves decreased slightly with the rise in CO₂ concentration. The rise in CO₂ concentration had no significant effect on the activity of the photosystem Ⅱ (PSII) reaction center in hazelnut leaves. Under Cd stress conditions, the rise in CO₂ concentration significantly enhanced the PSII hazelnut leaves’ photochemical activity, which promotes the PSII receptor’s electron transfer capacity side and alleviates the degree of damage to the oxygen-evolving complex and the thylakoid membrane of the PSII donor side. The number of active reaction centers per unit area of hazelnut leaves, and the proportion of energy absorbed by PSII that is used for photosynthetic electron transfer, increased under severe stress conditions, which in turn reduced the energy proportion that was used for heat dissipation, providing CO₂’s effective fixation energy in the dark reaction. In conclusion, the rise in the CO₂ concentration enhances hazelnut’s heavy metal resistance by improving the PSII function under Cd stress conditions.

Canker is a destructive fungal disease that adversely affects plant growth, triggering leaf drop, branch dieback and even plant death. For the blueberry industry, fungal canker reduces blueberry yield and quality. In this study, diseased branches of the ‘Bluegold’ blueberry cultivar collected from open-field plantations in Jilin Province, China, were used to isolate and identify the pathogen, characterize its biological properties, and investigate the physiological and metabolomic responses of blueberry shoots to pathogen infection. Based on morphological characteristics and internal transcribed spacer sequence analysis, the pathogen was preliminarily identified as Diaporthe eres. Biological characterization showed that the optimal temperature and pH for mycelial growth of the isolate were 25 °C and 6, respectively, while light conditions had no significant effect on fungal growth. Pathogenicity results demonstrated that infection by the isolate significantly induced the accumulation of superoxide anions (O₂^.−) and hydrogen peroxide (H₂O₂) in blueberry new shoots, which led to lipid peroxidation and subsequently resulted in significant increases in malondialdehyde content and relative electrical conductivity. Concurrently, the plant’s antioxidant enzyme system was disrupted, and the activities of peroxidase and superoxide dismutase remained significantly elevated throughout the infection period, while catalase activity exhibited an initial increase followed by a gradual decline. Metabolomic analysis identified 541 differentially accumulated metabolites, with key metabolites including ferulic acid, quercetin and kaempferol showing marked abundance changes. These were primarily enriched in pathways closely associated with plant resistance, such as phenylpropanoid biosynthesis and flavonoid biosynthesis. Combined analysis of physiological and metabolomic data showed that reactive oxygen species accumulation and antioxidant enzyme responses were accompanied by significant enrichment of phenylpropanoid and flavonoid metabolism, indicating coordinated antioxidant regulation and secondary metabolic reprogramming in blueberry shoots following pathogen infection. Overall, this study preliminarily identified a D. eres isolate associated with blueberry canker in Jilin Province, and systematically characterized the physiological and metabolic responses of blueberry to pathogen infection, providing a theoretical basis for understanding blueberry—Diaporthe interactions and for developing effective disease management strategies.

Fragaria pentaphylla, a unique wild strawberry species in China, is rich in various fruit colors and a valuable resource for studying color genes. Fruits of different colors from F. pentaphylla were selected as the experimental material. Liquid chromatography-mass spectrometry (LC-MS) and high-throughput RNA sequencing (RNA-seq) were employed to identify key genes responsible for the development of different fruit colors. Metabolite analysis revealed that 3249 metabolites were detected, including nine differential metabolites related to anthocyanin synthesis and five biological pathways. Additionally, an analysis combining transcriptome and metabolome data showed that the structural genes FpDFR, FpCHS, FpCHI, and FpUFGT were upregulated in red fruit, with significantly higher expression levels compared to pink and white fruits, actively promoting anthocyanin production in red fruit. Conversely, genes FpANR and FpLAR were upregulated in white fruit, enhancing catechin synthesis and inhibiting anthocyanin formation. The gene FpPAL was upregulated in pink fruit. Transcription factors FpbHLH18, FpMYB1, FpMYB24, and FpMYB114 collaborate with structural genes to enhance the synthesis of anthocyanins in red fruit. The findings improve our understanding of the molecular mechanisms that control anthocyanin production in F. pentaphylla. The identified key candidate genes may be utilized in the molecular breeding of strawberries.