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Platycrater arguta is a rare and endangered deciduous shrub originating from the Tertiary Period. Understanding its drought tolerance is crucial for conservation efforts and enhancing its resilience to environmental stress. This study aimed to assess the effects of varying levels of drought stress on the phenotype and physiological–biochemical characteristics of P. arguta. The study subjected P. arguta to different levels of drought stress using 10%, 20%, and 30% polyethylene glycol-6000 (PEG-6000) over a 10-day period. Additionally, the effects of exogenous melatonin application at various concentrations (including 100 µM) were examined to determine its potential in alleviating drought-induced damage. Key parameters measured included leaf relative water content, net photosynthetic rate (Pn), antioxidant enzyme activity, and soluble sugar content. Drought stress significantly inhibited the growth of P. arguta. As PEG-6000 concentration increased, leaf relative water content and net photosynthetic rate decreased, while leaf wilting severity, membrane damage, antioxidant enzyme activity, and soluble sugar content increased. A 30% PEG-6000 concentration caused irreversible damage, leading to plant death. Exogenous application of 100 µM melatonin alleviated this damage by increasing leaf relative water content, enhancing photosynthetic efficiency, boosting antioxidant enzyme activity, accumulating osmotic regulators, and reducing leaf desiccation. The study demonstrated that P. arguta is sensitive to severe drought conditions, with 30% PEG-6000 causing irreversible damage. However, the application of 100 µM melatonin significantly improved the plant's drought tolerance by upregulating the expression of ABI1 and downregulating genes such as AUX1A-2, IAA2-2, and HP2-1. This finding highlights the potential of melatonin as a protective agent against drought stress, providing valuable insights for the conservation and enhancement of P. arguta's resilience to environmental challenges.

Clematis is the queen of the vines, being an ornamental plant with high economic value. Waterlogging stress reduces the ornamental value of the plant and limits its application. Melatonin plays an important role in plant resistance to abiotic stresses. In this study, the physiological responses and gene expression levels of two wild species, namely, Clematis tientaiensis and Clematis lanuginosa, and two horticultural varieties, namely, ‘Sen-No-Kaze’ and ‘Viva Polonia,’ under waterlogging stress were analyzed to determine the effect of melatonin on waterlogging tolerance. The results showed that the waterlogging tolerances of C. lanuginosa and ‘Sen-No-Kaze’ were relatively poor, but were significantly improved by concentrations of 100 μmol·L-1 and 50 μmol·L-1 melatonin. C. tientaiensis and ‘Viva Polonia’ had relatively strong tolerance to waterlogging, and this was significantly improved by 200 μmol·L-1 melatonin. Under waterlogging stress, the relative conductivity and H2O2 content of Clematis increased significantly; the photosynthetic parameters and chlorophyll contents were significantly decreased; photosynthesis was inhibited; the contents of soluble protein and soluble sugars were decreased. Effective improvement of waterlogging tolerance after exogenous melatonin spraying, the relative conductivity was decreased by 4.05%-27.44%; the H2O2 content was decreased by 3.84%-23.28%; the chlorophyll content was increased by 35.59%-103.36%; the photosynthetic efficiency was increased by 25.42%-45.86%; the antioxidant enzyme activities of APX, POD, SOD, and CAT were increased by 28.03%-158.61%; the contents of proline, soluble protein, and soluble sugars were enhanced, and cell homeostasis was improved. Transcription sequencing was performed on wild Clematis with differences in waterlogging tolerance, and nine transcription factors were selected that were highly correlated with melatonin and that had the potential to improve waterlogging tolerance, among which LBD4, and MYB4 were significantly positively correlated with the antioxidant enzyme system, and bHLH36, DOF36, and WRKY4 were significantly negatively correlated. Photosynthetic capacity was positively correlated with DOF36 and WRKY4 while being significantly negatively correlated with MYB4, MOF1, DOF47, REV1 and ABR1. Melatonin could enhance the flooding tolerance of Clematis by improving photosynthetic efficiency and antioxidant enzyme activity. This study provides an important basis and reference for the application of melatonin in waterlogging-resistant breeding of Clematis.

Clematis is a perennial ornamental vine known as the “Vine Queen” for its gorgeous floral color and rich flower shape. Clematis tientaiensis, an endangered plant, is a key protected wild plant and a rare breeding parent of Clematis because of its extremely high ornamental value. Light environment is one of the important environmental factors affecting the space distribution and the size of C. tientaiensis population. One-year-old homogenous and healthy potted C. tientaiensis plants were grown under four different light intensities (T1: 1800 ± 30/0 µmol m−2 s−1; T2: 1500 ± 30/0 µmol m−2 s−1; T3: 1200 ± 30/0 µmol m−2 s−1; T4: 900 ± 30/0 µmol m−2 s−1). This study analyzed the potential adaptive mechanism of C. tientaiensis in response to irradiance by investigating the photosynthesis, rapid light curve, chloroplast ultrastructure, Rubisco activase enzyme (RAC), Rubisco enzyme, amino acids, and gene expression under four irradiance treatments. High light caused the leaves chlorosis and yellowing, reduced the net photosynthetic rate (Pn), stomatal conductance (Gs), RAC and Rubisco enzyme activity; the quantum yield of unregulated energy dissipation [Y(NO)], and increased the content of eight amino acids content. The expression of psbA, psbB, psbC, and Psb(OEC) were down-regulated with decreasing irradiance. The results showed that C. tientaiensis plants grown under T1 (1800 ± 30 µmol m−2 s−1) irradiance were in danger of absorbing more light energy than they could use for photosynthesis, while they exhibited good adaptability to the T3 (1200 ± 30 µmol m−2 s−1) irradiance, and the PSII reaction center and Rubisco and RCA enzymes could be the key points in response to high light stress, which also emphasized the importance of appropriate light management practices for promoting the growth and population expansion of C. tientaiensis.

Clematis tientaiensis is an ornamental plant with beautiful flowers that belongs to the Ranunculaceae family. C. tientaiensis is endemic to Zhejiang Province in China. Five different colours of the C. tientaiensis flower have been observed, and to explore the reason for this flower colour variation, transcriptome and metabolome sequencing analyses were conducted in this study. The results indicate that 32 metabolites participate in anthocyanin biosynthesis, and that 24 metabolites were differentially accumulated among the five different flower colours. The transcriptome sequencing results enabled the identification of 13,559 differentially expressed genes. Further analysis indicated that cyanidin-3-O-galactosidea and cyanidin-3-O-sophoroside promote anthocyanin accumulation in the flowers of C. tientaiensis, whereas the pelargonidin-3-O-galactoside plays a negative role in anthocyanin synthesis. In addition, a combined transcriptome and metabolome analysis showed that the WDR2 gene plays an important regulatory role in anthocyanin biosynthesis. The results of this study provide a basis for further research into the biosynthesis and regulation of anthocyanins in C. tientaiensis flowers.

Clematis is a superior perennial ornamental vine known for varied colors and shapes of its flowers. Clematis crassifolia is sensitive to high temperature, whereas Clematis cadmia has a certain temperature adaptability. Here we analyzed the potential regulatory mechanisms of C. crassifolia and C. cadmia in response to heat stress by studying the photosynthesis, antioxidant parameters, amino acids, and gene expression patterns under three temperature treatments. Heat stress caused the fading of leaves; decreased net photosynthetic rate, stomatal conductance, superoxide dismutase, and catalase activity; increased 13 kinds of amino acids content; and up-regulated the expression of seven genes, including C194329_G3, C194434_G1, and C188817_g1, etc., in C. crassifolia plants. Under the treatments of heat stress, the leaf tips of C. cadmia were wilted, and the net photosynthetic rate and soluble protein content decreased, with the increase of 12 amino acids content and the expression of c194329_g3, c194434_g1, and c195983_g1. Our results showed that C. crassifolia and C. cadmia had different physiological and molecular response mechanisms to heat stress during the ecological adaptation.

Salt stress critically affects the physiological processes and morphological structure of plants, resulting in reduced plant growth. Salicylic acid (SA) is an important signal molecule that mitigates the adverse effects of salt stress on plants. Large pink Dianthus superbus L. (Caryophyllaceae) usually exhibit salt-tolerant traits under natural conditions. To further clarify the salt-tolerance level of D. superbus and the regulating mechanism of exogenous SA on the growth of D. superbus under different salt stresses, we conducted a pot experiment to examine the biomass, photosynthetic parameters, stomatal structure, chloroplast ultrastructure, reactive oxygen species (ROS) concentrations, and antioxidant activities of D. superbus young shoots under 0.3, 0.6, and 0.9% NaCl conditions, with and without 0.5 mM SA. D. superbus exhibited reduced growth rate, decreased net photosynthetic rate (Pn), increased relative electric conductivity (REC) and malondialdehyde (MDA) contents, and poorly developed stomata and chloroplasts under 0.6 and 0.9% salt stress. However, exogenously SA effectively improved the growth, photosynthesis, antioxidant enzyme activity, and stoma and chloroplast development of D. superbus. However, when the plants were grown under severe salt stress (0.9% NaCl condition), there was no significant difference in the plant growth and physiological responses between SA-treated and non-SA-treated plants. Therefore, our research suggests that exogenous SA can effectively counteract the adverse effect of moderate salt stress on D. superbus growth and development.