Tolerance and Response of Ornamental Plants to Abiotic Stress

Lavandula angustifolia is a promising essential oil and ornamental crop whose distribution in the temperate zone and northern regions is limited by its low winter hardiness. Analyzing the causes of low winter hardiness will facilitate the selection of the most winter-hardy hybrids. The study goal is to evaluate the climatic conditions and winter hardiness of narrow-leaved lavender and to determine critical conditions for the successful overwintering of plants in the conditions of Moscow. The studies were conducted in the laboratory of cultivated plants of MBG RAS from 2015 to 2022. The research objects were 72 lavender hybrids. The assessment of hybrids’ winter hardiness was carried out after complete snow melt. Average daily temperature, snow cover height, and precipitation were considered daily. Data statistical processing was carried out using Microsoft Excel and PAST 4.5 software. Optimal lavender overwintering conditions were formed in 2018 and the greatest plant damage was observed in 2017. The research years were grouped by winter hardiness structured into clusters, which allowed us to identify common features in climatic conditions and to identify critical periods of the winter period leading to a decrease in winter hardiness. Temperature fluctuations in winter, frequent temperature transitions over the 0 °C mark, high levels of snow cover and the formation of ice deposits led to severe damage to some lavender hybrids. Severe frosts in the absence of snow cover can lead to the death of lavender plants in the temperate zone. Lavender hybrids were grouped by winter hardiness into two clusters and 11 subclusters. A group of hybrids with consistently high resistance has been selected throughout the years of the study; these hybrids are the most promising for further hybridization. Full article

Manganese (Mn) is a toxic metal element that adversely affects plant growth. Hydrogen sulfide (H₂S) is considered an important signaling molecule with significant potential in alleviating various abiotic stresses. However, there is limited information available on the role of H₂S in alleviating manganese stress in plants. In this study, the effects of exogenous H₂S and its scavenger, homocysteine thiolactone (HT), on the physiological and biochemical parameters of Malus hupehensis var. pingyiensis seedlings were evaluated. Our results show that H₂S treatment significantly alleviates growth inhibition and oxidative damage induced by manganese stress in Malus hupehensis seedlings, primarily by enhancing antioxidant enzyme activity and up-regulating the ascorbate-glutathione (ASA-GSH) cycle. H₂S treatment increased photosynthetic pigment content and helped maintain osmotic balance in leaves, thereby enhancing key gas exchange parameters and mitigating manganese-induced suppression of photosynthesis. H₂S treatment enhanced the absorption of Ca, Mg, Fe and Zn under manganese stress, significantly reduced manganese accumulation in Malus hupehensis seedlings, and modulated the transcriptional expression of MTPs, facilitating the transfer of manganese to the leaves. Thus, H₂S reduces oxidative damage and promotes growth under Mn stress, highlighting its important role in plant stress tolerance. Full article

Isopentenyl diphosphate isomerase (IPI) is a key enzyme in the synthesis of isoprenoids. In this paper, the in vivo biological activity of the IPI gene from Fritillaria unibracteata (FuIPI) was investigated. Combining a color complementation experiment with High-Performance Liquid Chromatography analysis showed that the FuIPI gene could accumulate β-carotene in Escherichia coli, and Glu190 was identified as a key residue for its catalytic activity. Bioinformatics analysis together with subcellular localization indicated that the FuIPI protein was localized in chloroplasts. Compared with wild-type Arabidopsis thaliana, FuIPI transgenic plants had higher abscisic acid content and strengthening tolerance to drought and salt stress. Overall, these results indicated that the FuIPI gene had substantial biological activity in vivo, hopefully laying a foundation for its further research and application in liliaceous ornamental and medicinal plants. Full article

Owing to the poor cold tolerance of Stenotaphrum Trin and the urgent need for shade-tolerant grass species in temperate regions of East China, this study evaluated the cold tolerance of 55 Stenotaphrum accessions, aiming to provide shade-tolerant materials for temperate regions. A fine cold-tolerant turfgrass should have both the advantages of delayed fall dormancy and early spring green-up. However, previous research on the cold resistance of turfgrass has mainly focused on the performance of the spring green-up, with less attention paid to the fall dormancy, which has affected the ornamental and application value of turfgrass. This study first dynamically investigated the leaf colour of each accession during the fall dormancy and the coverage during the spring green-up and evaluated the cold resistance of the accession through membership functions and cluster analysis. Significant differences in the cold resistance were found with the assignment of breeding lines to four categories. The weak correlation (R² = 0.1682) between leaf colour during the fall dormancy and coverage during the spring green-up indicates that using the performance of a single period to represent the cold resistance of accessions is not appropriate. To test whether using the laboratory-based LT50 and stolon regrowth rating analysis can replace the above-improved method, we conducted a related analysis and found that the fit between these two methods is very poor. This phenomenon is attributed to the poor correlation between the laboratory-based parameters and the pot-investigated data. Therefore, this study presents a cold resistance evaluation method for Stenotaphrum that integrates performance in both the fall dormancy and spring green-up periods. This improved evaluation method cannot be simplified by the growth performance of a single period or replaced by using laboratory-based LT50 and stolon regrowth tests. With the help of this improved method, several excellent cold tolerance accessions (ST003, S13, and S12) were identified for temperate regions of East China. Full article

Hydrangea macrophylla, a celebrated ornamental worldwide, thrives in semi-shaded growth environments in its natural habitat. This study utilizes Hydrangea macrophylla ‘Endless Summer’ as the experimental material to delve into its molecular mechanisms for adapting to semi-shaded conditions. Transcriptome analysis was conducted on leaves from four different natural light growth scenarios, showcasing phenotypic variations. From each sample, we obtained over 276,305,940 clean reads. Following de novo assembly and quantitative assessment, 88,575 unigenes were generated, with an average length of 976 bp. Gene ontology analysis of each control group elucidated the terms associated with the suitable environmental conditions for normal growth, development, and flowering, such as “reproductive bud system development” and “signal transduction”. The exploration of gene interactions and the identification of key genes with strong connectivity were achieved by constructing a protein–protein interaction (PPI) network. The results indicate that hydrangea grows vigorously and blooms steadily under semi-shaded conditions; the photosynthetic efficiency of hydrangea is stabilized through genes related to photosynthesis, such as PHYB, PSBR, FDC, etc. Hormone signal transduction genes like PIN3, LAX2, TIF6B, and EIN3 play important roles in responding to environmental stimulation and regulating growth and development, while genes such as SOC1, COL4/5/16, and AGL24 promote flowering. The expression of genes such as BGLUs and TPSs provides additional energy substances to support flowering. Full article

Saline water has been proposed as a solution to partially supply plants with their water requirements due to a lack of fresh water for cultivation in arid and semi-arid sites. Gamma-aminobutyric acid (GABA) is a non-protein amino acid participating in numerous metabolic processes to mitigate the undesirable effects of salinity. A pot experiment was carried out during 2021 and 2022 at Sakha Horticulture Research Station to investigate the effect of foliar application of GABA at 20 and 40 mM on vegetative growth and biochemical changes in French lavender under increasing levels of sea water salinity irrigation treatments (0, 1000, 2000, and 3000 ppm). Results indicated that increasing salinity concentration noticeably decreased plant height, number of branches, herb fresh and dry weight, root length, root fresh and dry weights, photosynthetic pigments, relative water content, and essential oil percentage. On the other hand, accumulation of proline and antioxidant enzymes was increased under increasing salinity concentrations. We conclude that foliar application of GABA acid at 40 mM can alleviate the adverse effects of salinity on the abovementioned French lavender plant characteristics by improving vegetative growth and root characteristics, as well as diminishing chlorophyll degradation, maintaining high leaf relative water content, increasing proline accumulation and antioxidant activity. Full article

Conifers are a common type of plant used in ornamental horticulture. The prompt diagnosis of the phenological state of coniferous plants using remote sensing is crucial for forecasting the consequences of extreme weather events. This is the first study to identify the “Vegetation” and “Dormancy” states in coniferous plants by analyzing their annual time series of spectral characteristics. The study analyzed Platycladus orientalis, Thuja occidentalis and T. plicata using time series values of 81 vegetation indices and 125 spectral bands. Linear discriminant analysis (LDA) was used to identify “Vegetation” and “Dormancy” states. The model contained three to four independent variables and achieved a high level of correctness (92.3 to 96.1%) and test accuracy (92.1 to 96.0%). The LDA model assigns the highest weight to vegetation indices that are sensitive to photosynthetic pigments, such as the photochemical reflectance index (PRI), normalized PRI (PRI_norm), the ratio of PRI to coloration index 2 (PRI/CI2), and derivative index 2 (D2). The random forest method also diagnoses the “Vegetation” and “Dormancy” states with high accuracy (97.3%). The vegetation indices chlorophyll/carotenoid index (CCI), PRI, PRI_norm and PRI/CI2 contribute the most to the mean decrease accuracy and mean decrease Gini. Diagnosing the phenological state of conifers throughout the annual cycle will allow for the effective planning of management measures in conifer plantations. Full article

Carnation is one of the most important ornamental plants worldwide; however, heat stress is a problem, which affects carnation cultivation. The harmful effects of heat stress include impaired vegetative development and reduced floral induction. In this study, to enhance carnation growth under conditions of heat stress, various concentrations of melatonin were added to in vitro culture media. The mechanism by which melatonin reduced heat stress damage was then studied by taking measurements of morphological parameters, levels of reactive oxygen species (ROS), antioxidant enzymes, and malondialdehyde (MDA), as well as differential gene expression, in carnation plants during in vitro culture. These data revealed that untreated carnation plants were more harmed by conditions of heat stress than plants treated with melatonin. Melatonin at concentrations of 5 and 10 mM increased chlorophyll content, fresh weight, and plant height to a greater extent than other concentrations. Melatonin may, thus, be used to alleviate damage to carnations caused by heat stress. The application of melatonin was also found to reduce oxidative damage and enhance antioxidant defense mechanisms. In addition, the expression of heat-related genes was found to be upregulated; in melatonin-treated plants, an upregulation was recorded in the expression of GAPDH, DcPOD1, DcPOD2, DcPOD3, Gols1, MBF1c, HSF30, HSP101, HSP70, and sHSP (MT) genes. In short, we found that melatonin treatment increased heat tolerance in carnation plants. The data presented here may serve as a reference for those seeking to enhance the growth of plants in conditions of heat stress. Full article

The genus Rhododendron is known for its preference for acidic soils, although some genotypes can tolerate a more neutral or alkaline pH. In this study, a greenhouse experiment was set up for 140 days to examine different parameters to assess pH stress in the progeny of R. fortunei and the cross combination R. ‘Pink Purple Dream’ x ‘Belami’. Additional cultivars ‘Gomer Waterer’ and ‘Cunningham’s White’ were included in the greenhouse test. The plants were divided into two groups. One group was planted in a substrate with a neutral pH (treatment, pH 6.3) and the other group of plants was planted in an acidic pH substrate (control, pH 4.5). Tolerance to pH stress was evaluated for the individual genotypes on both substrates 140 days after the start of the experiment. The following parameters were analyzed: shoot length, root development, chlorophyll fluorescence (Fv/Fm), leaf color and weight (fresh and dry). In intolerant genotypes, all parameters except for number of shoots were negatively affected by pH stress; especially, the development of roots was negatively impacted by the neutral pH, resulting in above-ground symptoms of pH stress, including decreased height and lower fresh and dry weight. The results show variation in pH tolerance within the genotypes tested and point to the potential for the selection of Rhododendron genotypes with improved tolerance to neutral pH. Full article

In recent years, there has been a significant growth in scholarly attention to the effects of Cd stress on horticultural plants, as reflected by the abundance of research articles on this issue in academic publications. Therefore, it is necessary to conduct a review of current research and provide a comprehensive perspective to quickly grasp the latest developments and future trends in the research field of “horticultural plants-Cd responses”. By utilizing a visualizing bibliometric analysis software CiteSpace, this study integrated and analyzed a total of 4318 relevant research records—2311 from the Web of Science (WOS) database and 2007 from the China National Knowledge Infrastructure (CNKI) database—related to “horticultural plants-Cd responses”, covering the period from 1999 to 2024. A visual analysis was conducted in the form of knowledge mappings, including the current research status of “horticultural plants-Cd responses”, as well as the differences in publications’ temporal distribution, spatial distribution (cooperation networks) and intellectual base between China and foreign countries, precisely uncovering the core aspects of research topics related to the field. The results indicated the following: (1) Scientific research on “horticultural plants-Cd responses” has experienced a significant increase in publication volume and has entered a phase of rapid development. Globally, there has been an annual average increase of 217 articles in the WOS since 2019, while in China, the annual average increase has been 134 articles in the CNKI since 2015. (2) China is the most productive country in terms of publication volume (1165 articles, 52.79%), engaging in active partnerships with other countries worldwide. Chinese scholars (Lin L. and Liao M.) are leading researchers in both domestic and international research fields of “horticultural plants-Cd responses”. The network of collaborations among authors and institutions in the WOS database seemed denser compared to that in the CNKI database. (3) International research hotspots have focused on accumulation, tolerance and oxidative stress, while domestically, the focus has been on antioxidant enzymes, growth and seed germination. Phytoremediation, subcellular distribution and the transcriptome are the world’s emerging topics, while in China, growth and physiological characteristics are still emerging topics. (4) In comparison, China exhibited a lagging development trend, which is reflected in the fact that it began to focus on gene expression and transcriptome research only after the global frontier shifted towards biochar and cadmium co-stress and yield response. Based on these, this study provides a systematic theoretical basis for subsequent research on “horticultural plants-Cd responses”, aiding scholars in their efforts to understand the dynamic frontiers and address the challenges in this field. Full article