The low temperature induced physiological responses of Avena nuda L., a cold-tolerant plant species

Expression Profiling Analysis of the SWEET Gene Family in In Vitro Pitaya Under Low-Temperature Stress and Study of Its Cold Resistance Mechanism

Pitaya (Hylocereus undatus) fruit is an attractive, nutrient-rich tropical fruit with commercial value. However, low-temperature stress severely affects the yield and quality of pitaya. The relevant mechanisms involved in the response of pitaya to low-temperature stress remain unclear. To study whether the SWEET gene family mediates the response of H. undatus to low-temperature stress and the related mechanisms, we performed genome-wide identification of the SWEET gene family in pitaya, and we used 'Baiyulong' tissue-cultured plantlets as material in the present study. We identified 28 members of the SWEET gene family from the H. undatus genome and divided these family members into four groups. Members of this gene family presented some differences in the sequences of introns and exons, but the gene structure, especially the motifs, presented relatively conserved characteristics. The promoter regions of most HuSWEETs have multiple stress- or hormone-related cis-elements. Three duplicated gene pairs were identified, including one tandem duplication gene and two fragment duplication gene pairs. The results revealed that the SWEET genes may regulate the transport and distribution of soluble sugars in plants; indirectly regulate the enzyme activities of CAT, POD, and T-SOD through its expression products; and are involved in the response of pitaya to low-temperature stress and play vital roles in this process. After ABA and MeJA treatment, the expression of HuSWEETs changed significantly, and the cold stress was also alleviated. This study elucidated the molecular mechanism and physiological changes in the SWEET gene in sugar metabolism and distribution of pitaya when it experiences low-temperature stress and provided a theoretical basis for cold-resistant pitaya variety breeding.

Influence of Foliar Application of Nanoparticles on Low Temperature Resistance of Rice Seedlings

Chilling stress, a common abiotic factor, adversely affects the growth and biomass of rice seedlings during the early stages, ultimately reducing the yield. Effective strategies to mitigate these negative impacts are essential for improving rice productivity. The application of nanotechnology in agriculture, particularly nanoparticles (NPs), has shown a promising effect in alleviating chilling stress in plants. This study evaluates the effects of various nanoparticles, ZnO (0, 50, 100, and 200 mg/L), Fe2O3 (0, 50, 75, and 100 mg/L), TiO2 (0, 50, 75, and 100 mg/L), and CeO2 (0, 50, 75, and 100 mg/L) on the chilling resistance with one control (a water spray) under a normal temperature. Four rice cultivars: LLY-7108 and XZX-6 (Low-temperature-tolerant), and LLY-32 and ZJZ-17 (Low-temperature-susceptible) were tested in this experiment. Rice seedlings were subjected to low temperature conditions (12 h light 14 °C/12 h dark, at 10 °C) for five days, followed by seven days of recovery. The results of this study demonstrate that NPs significantly enhanced seedling height fresh/dry weight and root length compared to untreated controls under chilling stress. NP treatment also reduced the reactive oxygen species (ROS), malondialdehyde (MDA), and proline content, while enhancing superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities, thereby mitigating oxidative damage. The four rice varieties exhibited clear signs of rapid growth recovery and positive physiological changes due to NPs' application. Among the tested cultivars, LLY-7108 showed the most substantial recovery and physiological responses, while ZJZ-17 exhibited the least. The findings of this study indicate that the foliar application of ZnO (100 mg/L), Fe2O3 (50 mg/L), TiO2 (50 mg/L), and CeO2 (75 mg/L) NPs effectively mitigates chilling stress in rice seedlings, likely by enhancing the antioxidant enzymatic activity while reducing the oxidative damage. This study highlights the potential of NPs as effective agents in reducing the adverse effects of chilling stress on rice.

Evaluation of different bermudagrass germplasm at physiological and molecular level under shade along longitudinal and latitudinal gradients

Responses of turfgrass to shade vary in individual species, and the degree and quality of low light; therefore, the selection of low light tolerant cultivars of turfgrass is important and beneficial for turf management rather than other practices. The stolons of thirteen bermudagrass genotypes were planted with two treatments and three replications of each treatment to establish for one month in the Yangzhou University Jiangsu China greenhouse. The established plants were transferred outside of the greenhouse, and 50% shading was applied to them with a black net. After 30 days of stress treatment, the morpho-physiological and biochemical analyses were performed. The expression of genes such as HEMA, HY5, PIF4, and Cu/ZnSOD was assessed. Cynodon dactylon is a C4, and perennial that grows as lawn grass and is used as forage. Based on different indicator measurements, the most shade-tolerant germplasm was L01 and L06 along the longitudes and L09 and L10 along the latitudes. At the same time, L02 and L08 were more susceptible, respectively. However, germplasm showed greater tolerance in higher latitudes while longitudinal plants showed less stress response. The current study aimed (1) to screen out the most shade-tolerant Cynodon dactylon genotype among 13 along longitudinal and latitudinal gradients in China. (2) to examine morpho-physiological indicators of different bermudagrassgenotypes; (3) to evaluate if and how differences in various indicators of bermudagrass correlated with geographic region. This study will significantly advance the use of Cynodon germplasm in breeding, genomics, management, nomenclature, and phylogeographical study. It will decisively define whether natural selection and migration can drive evolutionary responses for populations to adapt to their new environments effectively.

Arbuscular Mycorrhizal Fungi-Mediated Modulation of Physiological, Biochemical, and Secondary Metabolite Responses in Hemp (Cannabis sativa L.) under Salt and Drought Stress

The increasing impact of global climate change has resulted in adversity stresses, like salt and drought, gradually becoming the main factors that limit crop growth. Hemp, which contains numerous medicinal active components and multiple bioactive functions, is widely used in the agricultural, industrial, and medical fields, hence promoting the rapid development of related industries. Arbuscular mycorrhizal fungi (AMF) can establish a symbiotic relationship with 80% of vascular plants. This symbiosis promotes host plant growth, regulates plant physiology and biochemistry, facilitates secondary metabolite synthesis, and enhances resistance to abiotic stresses. However, the effects of salt stress, drought stress, and AMF interaction in hemp are not well understood. In this study, to investigate this, we performed a study where we cultured hemp that was either inoculated or uninoculated with Funneliformis mosseae and determined changes in effective colonization rate, growth, soluble substances, photosynthesis, fluorescence, ions, and secondary metabolites by cultivating hemp under different concentrations of NaCl (0 mM, 100 mM, and 200 mM) and different soil moisture content (45%, 25%, and 15%). The results showed that salt, drought stress, or salt-drought interaction stress all inhibited colonization rate after stress, plant growth, mainly due to ion toxicity and oxidative damage. Inoculation with F. mosseae effectively alleviated plant growth inhibition under 100 mM NaCl salt stress, drought stress, and salt-drought interaction stress conditions. It also improved osmoregulation, photosynthetic properties, fluorescence properties, and ion homeostasis, and promoted the accumulation of secondary metabolites. However, under 200 mM NaCl salt stress conditions, inoculation with F. mosseae negatively affected plant physiology, biochemistry, and secondary metabolite synthesis, although it did alleviate growth inhibition. The results demonstrate that there are different effects of salt-drought interaction stress versus single stress (salt or drought stress) on plant growth physiology. In addition, we provide new insights about the positive effects of AMF on host plants under such stress conditions and the effects of AMF on plants under high salt stress.

Effects of appropriate low-temperature treatment on the yield and quality of pigmented potato (Solanum tuberosum L.) tubers

Temperature is one of the important environmental factors affecting plant growth, yield and quality. Moreover, appropriately low temperature is also beneficial for tuber coloration. The red potato variety Jianchuanhong, whose tuber color is susceptible to temperature, and the purple potato variety Huaxinyangyu, whose tuber color is stable, were used as experimental materials and subjected to 20 °C (control check), 15 °C and 10 °C treatments during the whole growth period. The effects of temperature treatment on the phenotype, the expression levels of structural genes related to anthocyanins and the correlations of each indicator were analyzed. The results showed that treatment at 10 °C significantly inhibited the potato plant height, and the chlorophyll content and photosynthetic parameters in the leaves were reduced, and the enzyme activities of SOD and POD were significantly increased, all indicating that the leaves were damaged. Treatment at 10 °C also affected the tuberization of Huaxinyangyu and reduced the tuberization and coloring of Jianchuanhong, while treatment at 15 °C significantly increased the stem diameter, root-to-shoot ratio, yield and content of secondary metabolites, especially anthocyanins. Similarly, the expression of structural genes were enhanced in two pigmented potatoes under low-temperature treatment conditions. In short, proper low temperature can not only increase yield but also enhance secondary metabolites production. Previous studies have not focused on the effects of appropriate low-temperature treatment during the whole growth period of potato on the changes in metabolites during tuber growth and development, these results can provide a theoretical basis and technical guidance for the selection of pigmented potatoes with better nutritional quality planting environment and the formulation of cultivation measures.

Assessment of the changes in growth, photosynthetic traits and gene expression in Cynodon dactylon against drought stress

Drought stress considered a key restrictive factor for a warm-season bermudagrass growth during summers in China. Genotypic variation against drought stress exists among bermudagrass (Cynodon sp.), but the selection of highly drought-tolerant germplasm is important for its growth in limited water regions and for future breeding. Our study aimed to investigate the most tolerant bermudagrass germplasm among thirteen, along latitude and longitudinal gradient under a well-watered and drought stress condition. Current study included high drought-resistant germplasm, "Tianshui" and "Linxiang", and drought-sensitive cultivars; "Zhengzhou" and "Cixian" under drought treatments along longitude and latitudinal gradients, respectively. Under water deficit conditions, the tolerant genotypes showed over-expression of a dehydrin gene cdDHN4, antioxidant genes Cu/ZnSOD and APX which leads to higher antioxidant activities to scavenge the excessive reactive oxygen species and minimizing the membrane damage. It helps in maintenance of cell membrane permeability and osmotic adjustment by producing organic osmolytes. Proline an osmolyte has the ability to keep osmotic water potential and water use efficiency high via stomatal conductance and maintain transpiration rate. It leads to optimum CO2 assimilation rate, high chlorophyll contents for photosynthesis and elongation of leaf mesophyll, palisade and thick spongy cells. Consequently, it results in elongation of leaf length, stolon and internode length; plant height and deep rooting system. The CdDHN4 gene highly expressed in "Tianshui" and "Youxian", Cu/ZnSOD gene in "Tianshui" and "Linxiang" and APX gene in "Shanxian" and "Linxiang". The genotypes "Zhongshan" and "Xiaochang" showed no gene expression under water deficit conditions. Our results indicate that turfgrass show morphological modifications firstly when subjected to drought stress; however the gene expression is directly associated and crucial for drought tolerance in bermudagrass. Hence, current research has provided excellent germplasm of drought tolerant bermudagrass for physiological and molecular study and future breeding.

Comparative Transcriptomics and Metabolomics Analyses of Avicennia marina and Kandelia obovata under Chilling Stress during Seedling Stage

One of the most productive ecosystems in the world, mangroves are susceptible to cold stress. However, there is currently insufficient knowledge of the adaptation mechanisms of mangrove plants in response to chilling stress. This study conducted a comparative analysis of transcriptomics and metabolomics to investigate the adaptive responses of Kandelia obovata (chilling-tolerant) and Avicennia marina (chilling-sensitive) to 5 °C. The transcriptomics results revealed that differentially expressed genes (DEGs) were mostly enriched in signal transduction, photosynthesis-related pathways, and phenylpropanoid biosynthesis. The expression pattern of genes involved in photosynthesis-related pathways in A. marina presented a downregulation of most DEGs, which correlated with the decrease in total chlorophyll content. In the susceptible A. marina, all DEGs encoding mitogen-activated protein kinase were upregulated. Phenylpropanoid-related genes were observed to be highly induced in K. obovata. Additionally, several metabolites, such as 4-aminobutyric acid, exhibited higher levels in K. obovata than in A. marina, suggesting that chilling-tolerant varieties regulated more metabolites in response to chilling. The investigation defined the inherent distinctions between K. obovata and A. marina in terms of signal transduction gene expression, as well as phenylpropanoid and flavonoid biosynthesis, during exposure to low temperatures.

The role of nitric oxide and hydrogen sulfide in regulation of redox homeostasis at extreme temperatures in plants

Nitric oxide and hydrogen sulfide, as important signaling molecules (gasotransmitters), are involved in many functions of plant organism, including adaptation to stress factors of various natures. As redox-active molecules, NO and H₂S are involved in redox regulation of functional activity of many proteins. They are also involved in maintaining cell redox homeostasis due to their ability to interact directly and indirectly (functionally) with ROS, thiols, and other molecules. The review considers the involvement of nitric oxide and hydrogen sulfide in plant responses to low and high temperatures. Particular attention is paid to the role of gasotransmitters interaction with other signaling mediators (in particular, with Ca²⁺ ions and ROS) in the formation of adaptive responses to extreme temperatures. Pathways of stress-induced enhancement of NO and H₂S synthesis in plants are considered. Mechanisms of the NO and H₂S effect on the activity of some proteins of the signaling system, as well as on the state of antioxidant and osmoprotective systems during adaptation to stress temperatures, were analyzed. Possibilities of practical use of nitric oxide and hydrogen sulfide donors as inductors of plant adaptive responses are discussed.

Exogenous melatonin improved the growth and development of naked oat seedlings under cadmium stress

Heavy metal pollution has become a global problem, which affect more and more crop yields. Melatonin (MT) is widely used in plant stress resistance to alleviate the toxicity caused by heavy metals and other stresses. In this paper, the effects of exogenous 50 μM and 100 μM MT on the growth and development of naked oat seedlings under cadmium stress (25 mg L^-1) were studied. The results showed that different concentrations of MT could promote the growth of naked oat seedlings under 25-mg L^-1 cadmium stress. The application of exogenous melatonin could significantly increase the plant height, fresh weight, dry weight, chlorophyll, and proline contents of naked oats. MT could also reduce the contents of hydrogen peroxide, superoxide anion, and malondialdehyde in the cells of naked oat seedlings, and increase the activities of SOD, POD, and CAT. In addition, exogenous melatonin could affect the gene expression of LOX, POX, and Asmap1 in MAPK family and NAC and WRKY1 in TFS family in naked oat seedlings, thus promoting the growth and development of naked oat seedlings. In conclusion, this study is the first to demonstrate that MT is able to alleviate the negative effects to treat naked oat seedlings with cadmium stress. Therefore, melatonin has the potential to be applied in crops threatened by heavy metals.

Bolstered plant tolerance to low temperatures by overexpressing NAC transcription factors: identification of critical variables by meta-analysis

The potential biotechnological application of NAC overexpression has been challenged by meta-analysis, establishing a correlation between the magnitudes of several physiological and biochemical parameters and the enhanced tolerance to cold. Overexpression of various NAC (NAM/ATAF/CUC) transcription factors in different plant systems was shown to confer enhanced tolerance to low temperatures by inducing both common and distinctive stress response pathways. However, lack of consensus on the type of parameters evaluated, their magnitudes, and direction of the responses complicates drawing general conclusions on the effects of NAC expression in plant physiology. We report herein a meta-analysis summarizing the most critical response variables used to study the effect of overexpressing NAC regulators on cold stress tolerance. We found that NAC overexpression affected all of the outcome parameters in stressed plants, and one response in control conditions. Transformed plants displayed an increase of at least 40% in positive responses, while negative outcomes were reduced by at least 30%. The most reported parameters included survival, electrolyte leakage, and malondialdehyde contents, whereas the most sensitive to the treatments were the F_v/F_m parameter, survival, and the activity of catalases. We also explored how different experimental arrangements affected the magnitudes of the responses. NAC-mediated improvements were best observed after severe stress episodes and during brief treatments (ranging from 5 to 24 h), especially in terms of antioxidant activities, accumulation of free proline, and parameters related to membrane integrity. Use of heterologous expression also favored several indicators of plant fitness. Our findings should help both basic and applied research on the influence of NAC expression on enhanced tolerance to cold.

Response characteristics of highland barley (Hordeum vulgare) seedlings to the stress of salinity and artemisinin under freeze–thaw environment

In Qinghai-Tibet Plateau, crops are commonly subjected to freeze-thaw and salt stress factors simultaneously, and allelopathy is common, which affects the growth of highland barley (Hordeum vulgare L.), the largest food crop in Tibet. In order to explore the effects of artemisinin, salt and freeze-thaw (FAS) stress on physiological characteristics of highland barley seedlings, hydroponic experiment was carried out with the addition of 20mg/L artemisinin and 150mMNaCl as well as the simulation of freeze-thaw environment. The results suggested that under combined stress, the soluble protein content in combined stresses of artemisinin, FAS increased by 97.8%, the variation of relative conductivity in FAS group was lower than that in combined salt and freeze-thaw stress (FS), the relative water content decreased significantly (P <0.05), the malondialdehyde (MDA), H2 O2 and soluble sugar content in FAS group accumulated but less than those in FS group, and the superoxide dismutase (SOD) activity in combined artemisinin and freeze-thaw stress (FA) and FAS groups decreased. In addition, after freeze-thaw treatment, photosynthesis was weakened, and internal CO2 conentration (C i ) in FAS group significantly decreased (P <0.05). This study proved that appropriate amount of artemisinin can alleviate the damage of salt and freeze-thaw stress on barley seedlings.

Cold Stress, Freezing Adaptation, Varietal Susceptibility of Olea europaea L.: A Review

Olive (Olea europaea L.) is an evergreen xerophytic tree characterizing vegetative landscape and historical-cultural identity of the Mediterranean Basin. More than 2600 cultivars constitute the rich genetic patrimony of the species cultivated in approximately 60 countries. As a subtropical species, the olive tree is quite sensitive to low temperatures, and air temperature is the most critical environmental factor limiting olive tree growth and production. In this present review, we explored the detrimental effects caused of low temperatures on olive cultivars, and analyzed the most frequently experimental procedures used to evaluate cold stress. Then, current findings freezing stress physiology and gene are summarized in olive tree, with an emphasis on adaptive mechanisms for cold tolerance. This review might clear the way for new research on adaptive mechanisms for cold acclimation and for improvement of olive growing management.

Effects of Liquid Phase Nano Titanium Dioxide (TiO2) on Seed Germination and Seedling Growth of Camphor Tree

It is of great significance to popularize and apply nanotechnology in forest plantations for the high-quality development of such areas. Camphor trees have good ecological and environmental benefits and are economic, which makes them worthy of widespread popularization and promotion. In this paper, we successfully synthesized bulk and rod-like TiO₂ powder and used it to study the influence of camphor seed germination and seedling growth. The germination rate, germination potential, germination index activity index of camphorwood seed during germination were measured by TiO₂ solution with different morphology. Meanwhile, the fresh weight, root length and seedling height of seedlings, as well as the activities of CAT, SOD and POD and MDA content in the seedlings were measured in detail. The difference in the promoting effect between bulk and rod TiO₂ powder was compared. The possible reasons are also explained. The results showed that bulk and rod-like TiO₂ solution improved the activities of SOD, POD and CAT, and increased the resilience of camphor seedlings. Moreover, the rod-like TiO₂ solution has a stronger osmotic effect on seed, and has a better effect on promoting seed germination and seedling growth. The study on the influence of nano-TiO₂ concentration also further showed that the treatment of nano-TiO₂ solution with appropriate concentration could effectively promote seed germination and seedling growth, and enhance its adoptability to adversity; but excessive concentration will bring some side effects, which was not conducive to seed germination and seedling growth. In general, the results of this study provide a theoretical basis and technical guidance for the practical application of nanotechnology in camphor seedling and afforestation production.

Physiological and Biochemical Responses of Kandelia obovata to Upwelling Stress

Mangroves growing in intertidal areas are faced with various stresses caused by coastal human activities and oceanic and atmospheric sources. Although the study of the physiological and biochemical characteristics of mangroves has been developing over the past four decades, the effect of upwelling on mangroves in plants stress resistance has seldom been investigated. Here, changes in the physiological and biochemical characteristics of the leaves of Kandelia obovata seedlings in response to upwelling were investigated (air temperature: 25 °C; water temperature: control 25 °C, 13 °C, and 5 °C; salinity: 10‰). The results revealed that upwelling treatment caused an increase in chlorophyll content but a decrease in photosynthetic fluorescence parameters. Hydrogen peroxide (H2O2) production and malondialdehyde activity (MDA) increased with the decrease in upwelling temperature. The proline content increased under upwelling stress, whereas the soluble sugar content decreased. Further, the activities of antioxidant enzymes, such as superoxide dismutase activity (SOD) and peroxidase activity (POD), showed an increasing trend during the treatment, while catalase activity (CAT) decreased. It was evidenced that upwelling stress triggered the physiological and biochemical responses of Kandelia obovata seedlings. This effect became more intense as the upwelling temperature decreased, and all these indicators showed different responses to upwelling stress. Through synthesizing more energy and regulating enzyme activity and osmotic pressure, the leaves of K. obovata formed a resistance mechanism to short-term upwelling.

Antioxidative enzymes in root and leaf of Rumex obtusifolius L. grown on ash amended soil

Antioxidant enzymes are one of the most important links in the plant defense system to various types of environmental stress, so their response to a particular type of stress may indicate the sensitivity or tolerance of the plant species. Our paper studied the difference in antioxidative enzyme [catalase (CAT, EC 1.11.1.6), superoxide dismutase (SOD, EC 1.15.1.1) and Class III peroxidases (POD, EC 1.11.1.7)], isoenzyme pattern and activities between Rumex obtusifolius L. (Polygonaceae) plants grown on ash amended and uncontaminated soil. Modified SDS-PAGE electrophoresis revealed the presence of a new POD isoform in leaf samples growing on ash-amended soil, although the activity of POD in the leaves did not change significantly compared to control plants. On the other hand, in the roots of ash-growing plants POD activity decreased by 90%. Single CAT isoform was detected in both leaf samples, and results indicate 47% higher CAT activity in leaves of ash growing plants. Native electrophoresis detected two SOD isoforms in leaves and roots from the control plant. SOD isoforms were inhibited in the roots of plants grown on ash. The paper indicates the possible role of CAT, SOD and POD in the adaptive response of R. obtusifolius plants on ash amended soil.

Alleviation of Postharvest Chilling Injury of Carambola Fruit by γ-aminobutyric Acid: Physiological, Biochemical, and Structural Characterization

Chilling injury is a physiological disorder affecting the quality of carambola fruit. In the present study, the effect of exogenous γ-aminobutyric acid (GABA) on CI development in carambola fruit during storage at 4°C for 15 days was investigated. The results showed that 2.5-mM GABA reduced CI index, maintained pericarp lightness, and decreased the electrolyte leakage (EL) and malondialdehyde content (MDA) while increased the superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) enzyme activities. Endogenous GABA content was significantly higher in the treated fruit than in the control fruit during the whole storage. Besides, the treatment promoted the accumulation of proline and ascorbic acid (AsA) under chilling stress. Compared to the control, GABA-treated fruit exhibited a higher activity of phenylalanine ammonia-lyase (PAL) and total phenolic compounds, and a lower activity of polyphenol oxidase (PPO). In addition, the Safranin O/fast green staining revealed via microscopic images that the GABA treatment reduced the cell walls degradation of carambola fruit. Moreover, the results displayed a lower activity of phospholipase D (PLD) and lipoxygenase (LOX) enzymes, which coincided with a higher content of oleic acid (C18:1), linoleic acid (C18:2n6), and α-linolenic acid (C18:3n3) after 15 days of treatment, leading to the maintenance of the integrity and prevention of the membrane of the rapid softening of carambola fruit. The findings of the present work showed particularly new insights into the crosstalk between GABA and fatty acids. GABA might preserve the pericarp of carambola fruit by increasing the content of the unsaturated fatty acid (UFA) γ-linolenic acid and reducing the saturated fatty acid (SFA) such as caproic acid (C6:0), caprylic acid (C8:0), myristic acid (C14:0), and palmitic acid (C16:0) progressively. GABA can be used as an appropriate postharvest technology for improving the quality of carambola fruit during low-temperature storage.

iTRAQ-based quantitative proteome analysis insights into cold stress of Winter Rapeseed (Brassica rapa L.) grown in the field

Winter rapeseed (Brassica rapa L.) is a major oilseed crop in Northern China, where its production was severely affected by chilling and freezing stress. However, not much is known about the role of differentially accumulated proteins (DAPs) during the chilling and freezing stress. In this study, isobaric tag for relative and absolute quantification (iTRAQ) technology was performed to identify DAPs under freezing stress. To explore the molecular mechanisms of cold stress tolerance at the cellular and protein levels, the morphological and physiological differences in the shoot apical meristem (SAM) of two winter rapeseed varieties, Longyou 7 (cold-tolerant) and Lenox (cold-sensitive), were explored in field-grown plants. Compared to Lenox, Longyou 7 had a lower SAM height and higher collar diameter. The level of malondialdehyde (MDA) and indole-3-acetic acid (IAA) content was also decreased. Simultaneously, the soluble sugars (SS) content, superoxide dismutase (SOD) activity, peroxidase (POD) activity, soluble protein (SP) content, and collar diameter were increased in Longyou 7 as compared to Lenox. A total of 6330 proteins were identified. Among this, 98, 107, 183 and 111 DAPs were expressed in L7 CK/Le CK, L7 d/Le d, Le d/Le CK and L7 d/L7 CK, respectively. Quantitative real-time PCR (RT-qPCR) analysis of the coding genes for seventeen randomly selected DAPs was performed for validation. These DAPs were identified based on gene ontology enrichment analysis, which revealed that glutathione transferase activity, carbohydrate-binding, glutathione binding, metabolic process, and IAA response were closely associated with the cold stress response. In addition, some cold-induced proteins, such as glutathione S-transferase phi 2(GSTF2), might play an essential role during cold acclimation in the SAM of Brassica rapa. The present study provides valuable information on the involvement of DAPs during cold stress responses in Brassica rapa L, and hence could be used for breeding experiments.

Physiological Responses and Proteomic Analysis on the Cold Stress Responses of Annual Pitaya (Hylocereus spp.) Branches

In this study, the physiological response of the annual branches of three varieties of pitaya (Xianmi, Fulong, and Zihonglong) in cold stress was investigated using a multivariate statistical method. Physiological change results showed that cold stress could decrease the moisture and chlorophyll contents, on the contrary, increase the relative electric conductivity, the contents of malonadehyde, soluble protein, soluble sugar, and free proline, and enhance the enzyme activities of peroxidase, superoxide dismutase, and catalase. Meanwhile, a comparative proteomic approach was also conducted to clarify the cold resistance-related proteins and pathways in annual pitaya branches. Proteomics results concluded that the cold tolerance of annual pitaya branches could be improved by modulating autophagy. Therefore, we hypothesized that an increased autophagy ability may be an important characteristic of the annual pitaya branches in response to cold stress conditions. Our results provide a good understanding of the physiological responses and molecular mechanisms of the annual pitaya branches in response to cold stress.

Ectopic expression of a novel cold-resistance protein 1 from Brassica oleracea promotes tolerance to chilling stress in transgenic tomato

Cold stress is considered as one of the major environmental factors that adversely affects the plant growth and distribution. Therefore, there arises an immediate need to cultivate effective strategies aimed at developing stress-tolerant crops that would boost the production and minimise the risks associated with cold stress. In this study, a novel cold-responsive protein1 (BoCRP1) isolated from Brassica oleracea was ectopically expressed in a cold susceptible tomato genotype Shalimar 1 and its function was investigated in response to chilling stress. BoCRP1 was constitutively expressed in all the tissues of B. oleracea including leaf, root and stem. However, its expression was found to be significantly increased in response to cold stress. Moreover, transgenic tomato plants expressing BoCRP1 exhibited increased tolerance to chilling stress (4 °C) with an overall improved rate of seed germination, increased root length, reduced membrane damage and increased accumulation of osmoprotectants. Furthermore, we observed increased transcript levels of stress responsive genes and enhanced accumulation of reactive oxygen species scavenging enzymes in transgenic plants on exposure to chilling stress. Taken together, these results strongly suggest that BoCRP1 is a promising candidate gene to improve the cold stress tolerance in tomato.

Responses of Grain Yield and Yield Related Parameters to Post-Heading Low-Temperature Stress in Japonica Rice

There is unprecedented increase in low-temperature stress (LTS) during post-heading stages in rice as a consequence of the recent climate changes. Quantifying the effect of LTS on yields is key to unraveling the impact of climatic changes on crop production, and therefore developing corresponding mitigation strategies. The present research was conducted to analyze and quantify the effect of post-heading LTS on rice yields as well as yield and grain filling related parameters. A two-year experiment was conducted during rice growing season of 2018 and 2019 using two Japonica cultivars (Huaidao 5 and Nanjing 46) with different low-temperature sensitivities, at four daily minimum/maximum temperature regimes of 21/27 °C (T1), 17/23 °C (T2), 13/19 °C (T3) and 9/15 °C (T4). These temperature treatments were performed for 3 (D1), 6 (D2) or 9 days (D3), at both flowering and grain filling stages. We found LTS for 3 days had no significant effect on grain yield, even when the daily mean temperature was as low as 12 °C. However, LTS of between 6 and 9 days at flowering but not at filling stage significantly reduced grain yield of both cultivars. Comparatively, Huaidao 5 was more cold tolerant than Nanjing 46. LTS at flowering and grain filling stages significantly reduced both maximum and mean grain filling rates. Moreover, LTS prolonged the grain filling duration of both cultivars. Additionally, there was a strong correlation between yield loss and spikelet fertility, spikelet weight at maturity, grain filling duration as well as mean and maximum grain filling rates under post-heading LTS (p < 0.001). Moreover, the effect of post-heading LTS on rice yield can be well quantified by integrating the canopy temperature (CT) based accumulated cold degree days (ACDDCT) with the response surface model. The findings of this research are useful in modeling rice productivity under LTS and for predicting rice productivity under future climates.

Yield, Physiological Performance, and Phytochemistry of Basil (Ocimum basilicum L.) under Temperature Stress and Elevated CO2 Concentrations

Early season sowing is one of the methods for avoiding yield loss for basil due to high temperatures. However, basil could be exposed to sub-optimal temperatures by planting it earlier in the season. Thus, an experiment was conducted that examines how temperature changes and carbon dioxide (CO₂) levels affect basil growth, development, and phytonutrient concentrations in a controlled environment. The experiment simulated temperature stress, low (20/12 °C), and high (38/30 °C), under ambient (420 ppm) and elevated (720 ppm) CO₂ concentrations. Low-temperature stress prompted the rapid closure of stomata resulting in a 21% decline in net photosynthesis. Chlorophylls and carotenoids decreased when elevated CO₂ interacted with low-temperature stress. Basil exhibited an increase in stomatal conductance, intercellular CO₂ concentration, apparent quantum yield, maximum photosystem II efficiency, and maximum net photosynthesis rate when subjected to high-temperature stress. Under elevated CO₂, increasing the growth temperature from 30/22 °C to 38/30 °C markedly increased the antioxidants content of basil. Taken together, the evidence from this research recommends that varying the growth temperature of basil plants can significantly affect the growth and development rates compared to increasing the CO₂ concentrations, which mitigates the adverse effects of temperature stress.

Transcriptomic, proteomic, and physiological comparative analyses of flooding mitigation of the damage induced by low-temperature stress in direct seeded early indica rice at the seedling stage

BACKGROUND

Low temperature (LT) often occurs at the seedling stage in the early rice-growing season, especially for direct seeded early-season indica rice, and using flooding irrigation can mitigate LT damage in rice seedlings. The molecular mechanism by which flooding mitigates the damage induced by LT stress has not been fully elucidated. Thus, LT stress at 8 °C, LT accompanied by flooding (LTF) and CK (control) treatments were established for 3 days to determine the transcriptomic, proteomic and physiological response in direct seeded rice seedlings at the seedling stage.

RESULTS

LT damaged chloroplasts, and thylakoid lamellae, and increased osmiophilic bodies and starch grains compared to CK, but LTF alleviated the damage to chloroplast structure caused by LT. The physiological characteristics of treated plants showed that compared with LT, LTF significantly increased the contents of rubisco, chlorophyll, PEPCK, ATP and GA3 but significantly decreased soluble protein, MDA and ABA contents. 4D-label-free quantitative proteomic profiling showed that photosynthesis-responsive proteins, such as phytochrome, as well as chlorophyll and the tricarboxylic acid cycle were significantly downregulated in LT/CK and LTF/CK comparison groups. However, compared with LT, phytochrome, chlorophyllide oxygenase activity and the glucan branching enzyme in LTF were significantly upregulated in rice leaves. Transcriptomic and proteomic studies identified 72,818 transcripts and 5639 proteins, and 4983 genes that were identified at both the transcriptome and proteome levels. Differentially expressed genes (DEGs) and differentially expressed proteins (DEPs) were significantly enriched in glycine, serine and threonine metabolism, biosynthesis of secondary metabolites, glycolysis/gluconeogenesis and metabolic pathways.

CONCLUSION

Through transcriptomic, proteomic and physiological analyses, we determined that a variety of metabolic pathway changes were induced by LT and LTF. GO and KEGG enrichment analyses demonstrated that DEGs and DEPs were associated with photosynthesis pathways, antioxidant enzymes and energy metabolism pathway-related proteins. Our study provided new insights for efforts to reduce the damage to direct seeded rice caused by low-temperature stress and provided a breeding target for low temperature flooding-resistant cultivars. Further analysis of translational regulation and metabolites may help to elucidate the molecular mechanisms by which flooding mitigates low-temperature stress in direct seeded early indica rice at the seedling stage.

Cold stress in the harvest period: effects on tobacco leaf quality and curing characteristics

BACKGROUND

Weather change in high-altitude areas subjects mature tobacco (Nicotiana tabacum L.) to cold stress, which damages tobacco leaf yield and quality. A brupt diurnal temperature differences (the daily temperature dropping more than 20 °C) along with rainfall in tobacco-growing areas at an altitude above 2450 m, caused cold stress to field-grown tobacco.

RESULTS

After the flue-cured tobacco suffered cold stress in the field, the surface color of tobacco leaves changed and obvious large browning areas were appeared, and the curing availability was extremely poor. Further research found the quality of fresh tobacco leaves, the content of key chemical components, and the production quality were greatly reduced by cold stress. We hypothesize that cold stress in high altitude environments destroyed the antioxidant enzyme system of mature flue-cured tobacco. Therefore, the quality of fresh tobacco leaves, the content of key chemical components, and the production quality were greatly reduced by cold stress.

CONCLUSION

This study confirmed that cold stress in high-altitude tobacco areas was the main reason for the browning of tobacco leaves during the tobacco curing process. This adverse environment seriously damaged the quality of tobacco leaves, but can be mitigated by pay attention to the weather forecast and pick tobacco leaves in advance.

Comparative analysis of two phytochrome mutants of tomato (Micro-Tom cv.) reveals specific physiological, biochemical, and molecular responses under chilling stress

Background

Phytochromes are plant photoreceptors that have long been associated with photomorphogenesis in plants; however, more recently, their crucial role in the regulation of variety of abiotic stresses has been explored. Chilling stress is one of the abiotic factors that severely affect growth, development, and productivity of crops. In the present work, we have analyzed and compared physiological, biochemical, and molecular responses in two contrasting phytochrome mutants of tomato, namely aurea (aur) and high pigment1 (hp1), along with wild-type cultivar Micro-Tom (MT) under chilling stress. In tomato, aur is phytochrome-deficient mutant while hp1 is a phytochrome-sensitive mutant. The genotype-specific physiological, biochemical, and molecular responses under chilling stress in tomato mutants strongly validated phytochrome-mediated regulation of abiotic stress.

Results

Here, we demonstrate that phytochrome-sensitive mutant hp1 show improved performance compared to phytochrome-deficient mutant aur and wild-type MT plants under chilling stress. Interestingly, we noticed significant increase in several photosynthetic-related parameters in hp1 under chilling stress that include photosynthetic rate, stomatal conductance, stomatal aperture, transpiration rate, chlorophyll a and carotenoids. Whereas most parameters were negatively affected in aur and MT except a slight increase in carotenoids in MT plants under chilling stress. Further, we found that PSII quantum efficiency (Fv/Fm), PSII operating efficiency (Fq′/Fm′), and non-photochemical quenching (NPQ) were all positively regulated in hp1, which demonstrate enhanced photosynthetic performance of hp1 under stress. On the other hand, Fv/Fm and Fq′/Fm′ were decreased significantly in aur and wild-type plants. In addition, NPQ was not affected in MT but declined in aur mutant after chilling stress. Noticeably, the transcript analysis show that PHY genes which were previously reported to act as molecular switches in response to several abiotic stresses were mainly induced in hp1 and repressed in aur and MT in response to stress. As expected, we also found reduced levels of malondialdehyde (MDA), enhanced activities of antioxidant enzymes, and higher accumulation of protecting osmolytes (soluble sugars, proline, glycine betaine) which further elaborate the underlying tolerance mechanism of hp1 genotype under chilling stress.

Conclusion

Our findings clearly demonstrate that phytochrome-sensitive and phytochrome-deficient tomato mutants respond differently under chilling stress thereby regulating physiological, biochemical, and molecular responses and thus establish a strong link between phytochromes and their role in stress tolerance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-020-00091-1.

Response of Mycorrhizal 'Touriga Nacional' Variety Grapevines to High Temperatures Measured by Calorespirometry and Near-Infrared Spectroscopy

Heat stress negatively affects several physiological and biochemical processes in grapevine plants. In this work, two new methods, calorespirometry, which has been used to determine temperature adaptation in plants, and near-infrared (NIR) spectroscopy, which has been used to determine several grapevine-related traits and to discriminate among varieties, were tested to evaluate grapevine response to high temperatures. 'Touriga Nacional' variety grapevines, inoculated or not with Rhizoglomus irregulare or Funneliformis mosseae, were used in this study. Calorespirometric parameters and NIR spectra, as well as other parameters commonly used to assess heat injury in plants, were measured before and after high temperature exposure. Growth rate and substrate carbon conversion efficiency, calculated from calorespirometric measurements, and stomatal conductance, were the most sensitive parameters for discriminating among high temperature responses of control and inoculated grapevines. The results revealed that, although this vine variety can adapt its physiology to temperatures up to 40 °C, inoculation with R. irregulare could additionally help to sustain its growth, especially after heat shocks. Therefore, the combination of calorespirometry together with gas exchange measurements is a promising strategy for screening grapevine heat tolerance under controlled conditions and has high potential to be implemented in initial phases of plant breeding programs.

Influence of sodium chloride on growth and metabolic reprogramming in nonprimed and haloprimed seedlings of blackgram (Vigna mungo L.)

Salinity hinders agricultural productivity worldwide by distressing plant metabolism. Growth of blackgram (Vigna mungo L. var. Sulata), an adverse climate-resistant pulse, is arrested under salinity. Present research integrates study of physio-biochemical parameters and non-targeted metabolomics approach to explore the alterations in metabolic pathway during adaptive responses of nonprimed and haloprimed blackgram seedlings grown hydroponically under NaCl stress. Salinity provoked accumulation of peroxides, compatible solutes and phenolics which increased free radical scavenging activities of nonprimed seedlings under salinity. Pre-germination seed halopriming abrogated NaCl-mediated adversities in haloprimed plantlets favouring better growth. Thus, farmers may adopt seed halopriming technique to improve blackgram productivity in saline-prone fields. Additionally, metabolomics study uncovered numerous metabolites amongst which 35 compounds altered significantly under salinity. The candidate metabolites were aspartic acid, L-glutamic acid, L-proline, L-asparagine, DL-isoleucine, L-homoserine, citrulline, L-ornithine, D-altrose, D-allose, N-acetyl-D-mannosamine, fructose, tagatose, sucrose, D-glucose, maltose, glycerol-1-phosphate, D-sorbitol, benzoic acid, shikimic acid, 4-hydroxycinnamic acid, arbutin, succinic acid, pipecolic acid, fumaric acid, nicotinic acid, L-pyroglutamic acid, oxalic acid, glyceric acid, maleamic acid, adenine, guanosine, lauric acid, stearic acid and porphine. Comparing metabolic responses of nonprimed and haloprimed seedlings, it was clear that efficient alteration in carbohydrate metabolism, phenolics accumulation, amino acid, organic acid and nucleic acid metabolism were the key places of metabolic reprogramming for tolerating salinity. Overall, we report, for the first time, 35 contributory candidate compounds that constituted core fundamental metabolome invoking salinity tolerance in nonprimed and haloprimed blackgram. These metabolites may be targeted by biotechnologists to produce high vigour salt-tolerant transgenic blackgram via genetic engineering.

Identification, characterization and functional differentiation of the NAC gene family and its roles in response to cold stress in ginseng, Panax ginseng C.A. Meyer

The NAC gene family is one of the important plant-specific transcription factor families involved in variety of physiological processes. It has been found in several plant species; however, little is known about the gene family in ginseng, Panax ginseng C.A. Meyer. Here we report identification and systematic analysis of this gene family in ginseng. A total of 89 NAC genes, designated PgNAC01 to PgNAC89, are identified. These genes are alternatively spliced into 251 transcripts at fruiting stage of a four-year-old ginseng plant. The genes of this gene family have five conserved motifs and are clustered into 11 subfamilies, all of which are shared with the genes of the NAC gene families identified in the dicot and monocot model plant species, Arabidopsis and rice. This result indicates that the PgNAC gene family is an ancient and evolutionarily inactive gene family. Gene ontology (GO) analysis shows that the functions of the PgNAC gene family have been substantially differentiated; nevertheless, over 86% the PgNAC transcripts remain functionally correlated. Finally, five of the PgNAC genes, PgNAC05-2, PgNAC41-2, PgNAC48, PgNAC56-1, and PgNAC59, are identified to be involved in plant response to cold stress, suggesting that this gene family plays roles in response to cold stress in ginseng. These results, therefore, provide new insights into functional differentiation and evolution of a gene family in plants and gene resources necessary to comprehensively determine the functions of the PgNAC gene family in response to cold and other abiotic stresses in ginseng.

Morpho-physiological integrators, transcriptome and coexpression network analyses signify the novel molecular signatures associated with axillary bud in chrysanthemum

BACKGROUND

Axillary bud is an important agronomic and economic trait in cut chrysanthemum. Bud outgrowth is an intricate process controlled by complex molecular regulatory networks, physio-chemical integrators and environmental stimuli. Temperature is one of the key regulators of bud's fate. However, little is known about the temperature-mediated control of axillary bud at molecular levels in chrysanthemum. A comprehensive study was designed to study the bud outgrowth at normal and elevated temperature in cut chrysanthemum. Leaf morphology, histology, physiological parameters were studied to correlate the leaf activity with bud morphology, sucrose and hormonal regulation and the molecular controllers.

RESULTS

Temperature caused differential bud outgrowth along bud positions. Photosynthetic leaf area, physiological indicators and sucrose utilization were changed considerable due to high temperature. Comparative transcriptome analysis identified a significant proportion of bud position-specific genes.Weighted Gene Co-expression Network Analysis (WGCNA) showed that axillary bud control can be delineated by modules of coexpressed genes; especially, MEtan3, MEgreen2 and MEantiquewhite presented group of genes specific to bud length. A comparative analysis between different bud positions in two temperatures revealed the morpho-physiological traits associated with specific modules. Moreover, the transcriptional regulatory networks were configured to identify key determinants of bud outgrowth. Cell division, organogenesis, accumulation of storage compounds and metabolic changes were prominent during the bud emergence.

CONCLUSIONS

RNA-seq data coupled with morpho-physiological integrators from three bud positions at two temperature regimes brings a robust source to understand bud outgrowth status influenced by high temperature in cut chrysanthemum. Our results provide helpful information for elucidating the regulatory mechanism of temperature on axillary bud growth in chrysanthemum.

Correlation analysis of cold-related gene expression with physiological and biochemical indicators under cold stress in oil palm

Oil palm (Elaeis guineensis Jacq.) is a representative tropical oil crop that is sensitive to low temperature. Oil palm can experience cold damage when exposed to low temperatures for a long period. During these unfavorable conditions, a series of gene induction/repression and physico-chemical changes occur in oil palm. To better understand the link between these events, we investigated the expression levels of various genes (including COR410, COR413, CBF1, CBF2, CBF3, ICE1-1, ICE1-2, ICE1-4, SIZ1-1, SIZ1-2, ZAT10, ZAT12) and the accumulation of osmolytes (proline, malondialdehyde and sucrose). Likewise, the activity of superoxide dismutase (SOD) in oil palm under cold stress (4°C, 8°C and 12°C) was examined. The results showed a clear link among the expression of CBFs (especially CBF1 and CBF3) and the all genes examined under cold stress (12°C). The expression of CBF1 and CBF2 also exhibited a positive link with the accumulation of sucrose and proline under cold stress in oil palm. At 4°C, the proline content exhibited a very significant correlation with electrolyte leakage in oil palm. The results of this study provide necessary information regarding the mechanism of the response and adaption of oil palm to cold stress. Additionally, they offer clues for the selection or development of cold-tolerant cultivars from the available germplasms of oil palm.

Genetic Screening and Expression Analysis of Psychrophilic Bacillus spp. Reveal Their Potential to Alleviate Cold Stress and Modulate Phytohormones in Wheat

Abiotic stress in plants pose a major threat to cereal crop production worldwide and cold stress is also notorious for causing a decrease in plant growth and yield in wheat. The present study was designed to alleviate cold stress on plants by inoculating psychrophilic PGPR bacteria belonging to Bacillus genera isolated from extreme rhizospheric environments of Qinghai-Tibetan plateau. The genetic screening of psychrophilic Bacillus spp. CJCL2, RJGP41 and temperate B. velezensis FZB42 revealed presence of genetic features corresponding to cold stress response, membrane transport, signal transduction and osmotic regulation. Subsequently, the time frame study for the expression of genes involved in these pathways was also significantly higher in psychrophilic strains as analyzed through qPCR analysis at 4 ℃. The inoculated cold tolerant Bacillus strains also aided in inducing stress response in wheat by regulating abscisic acid, lipid peroxidation and proline accumulation pathways in a beneficial manner. Moreover, during comparative analysis of growth promotion in wheat all three Bacillus strains showed significant results at 25 ℃. Whereas, psychrophilic Bacillus strains CJCL2 and RJGP41 were able to positively regulate the expression of phytohormones leading to significant improvement in plant growth under cold stress.

Genes, pathways and transcription factors involved in seedling stage chilling stress tolerance in indica rice through RNA-Seq analysis

BACKGROUND

Rice plants show yellowing, stunting, withering, reduced tillering and utimately low productivity in susceptible varieties under low temperature stress. Comparative transcriptome analysis was performed to identify novel transcripts, gain new insights into different gene expression and pathways involved in cold tolerance in rice.

RESULTS

Comparative transcriptome analyses of 5 treatments based on chilling stress exposure revealed more down regulated genes in susceptible and higher up regulated genes in tolerant genotypes. A total of 13930 and 10599 differentially expressed genes (DEGs) were detected in cold susceptible variety (CSV) and cold tolerant variety (CTV), respectively. A continuous increase in DEGs at 6, 12, 24 and 48 h exposure of cold stress was detected in both the genotypes. Gene ontology (GO) analysis revealed 18 CSV and 28 CTV term significantly involved in molecular function, cellular component and biological process. GO classification showed a significant role of transcription regulation, oxygen, lipid binding, catalytic and hydrolase activity for tolerance response. Absence of photosynthesis related genes, storage products like starch and synthesis of other classes of molecules like fatty acids and terpenes during the stress were noticed in susceptible genotype. However, biological regulations, generation of precursor metabolites, signal transduction, photosynthesis, regulation of cellular process, energy and carbohydrate metabolism were seen in tolerant genotype during the stress. KEGG pathway annotation revealed more number of genes regulating different pathways resulting in more tolerant. During early response phase, 24 and 11 DEGs were enriched in CTV and CSV, respectively in energy metabolism pathways. Among the 1583 DEG transcription factors (TF) genes, 69 WRKY, 46 bZIP, 41 NAC, 40 ERF, 31/14 MYB/MYB-related, 22 bHLH, 17 Nin-like 7 HSF and 4C3H were involved during early response phase. Late response phase showed 30 bHLH, 65 NAC, 30 ERF, 26/20 MYB/MYB-related, 11 C3H, 12 HSF, 86 Nin-like, 41 AP2/ERF, 55 bZIP and 98 WRKY members TF genes. The recovery phase included 18 bHLH, 50 NAC, 31 ERF, 24/13 MYB/MYB-related, 4 C3H, 4 HSF, 14 Nin-like, 31 bZIP and 114 WRKY TF genes.

CONCLUSIONS

Transcriptome analysis of contrasting genotypes for cold tolerance detected the genes, pathways and transcription factors involved in the stress tolerance.

Genes, pathways and transcription factors involved in seedling stage chilling stress tolerance in indica rice through RNA-Seq analysis

BACKGROUND

Rice plants show yellowing, stunting, withering, reduced tillering and utimately low productivity in susceptible varieties under low temperature stress. Comparative transcriptome analysis was performed to identify novel transcripts, gain new insights into different gene expression and pathways involved in cold tolerance in rice.

RESULTS

Comparative transcriptome analyses of 5 treatments based on chilling stress exposure revealed more down regulated genes in susceptible and higher up regulated genes in tolerant genotypes. A total of 13930 and 10599 differentially expressed genes (DEGs) were detected in cold susceptible variety (CSV) and cold tolerant variety (CTV), respectively. A continuous increase in DEGs at 6, 12, 24 and 48 h exposure of cold stress was detected in both the genotypes. Gene ontology (GO) analysis revealed 18 CSV and 28 CTV term significantly involved in molecular function, cellular component and biological process. GO classification showed a significant role of transcription regulation, oxygen, lipid binding, catalytic and hydrolase activity for tolerance response. Absence of photosynthesis related genes, storage products like starch and synthesis of other classes of molecules like fatty acids and terpenes during the stress were noticed in susceptible genotype. However, biological regulations, generation of precursor metabolites, signal transduction, photosynthesis, regulation of cellular process, energy and carbohydrate metabolism were seen in tolerant genotype during the stress. KEGG pathway annotation revealed more number of genes regulating different pathways resulting in more tolerant. During early response phase, 24 and 11 DEGs were enriched in CTV and CSV, respectively in energy metabolism pathways. Among the 1583 DEG transcription factors (TF) genes, 69 WRKY, 46 bZIP, 41 NAC, 40 ERF, 31/14 MYB/MYB-related, 22 bHLH, 17 Nin-like 7 HSF and 4C3H were involved during early response phase. Late response phase showed 30 bHLH, 65 NAC, 30 ERF, 26/20 MYB/MYB-related, 11 C3H, 12 HSF, 86 Nin-like, 41 AP2/ERF, 55 bZIP and 98 WRKY members TF genes. The recovery phase included 18 bHLH, 50 NAC, 31 ERF, 24/13 MYB/MYB-related, 4 C3H, 4 HSF, 14 Nin-like, 31 bZIP and 114 WRKY TF genes.

CONCLUSIONS

Transcriptome analysis of contrasting genotypes for cold tolerance detected the genes, pathways and transcription factors involved in the stress tolerance.

Seed mineral reserves and vigour of Bambara groundnut (Vigna subterranea L.) landraces differing in seed coat colour

A newly emerged seedling, given light and water, but no external source of minerals, uses its internal mineral nutrient reserves effectively for an early establishment. This research sought to investigate the influence of seed coat colour on the abundance of mineral elements in Bambara groundnut. Four landraces (G340A, Kazai, Kazuma, and Mana) varying in seed coat colour were analysed for differences in seed mineral composition using energy dispersive x-ray (EDX) analysis and atomic absorption spectrometry (AAS). Seeds were germinated at 10 °C and 25 °C, and various indices including, (1) mean emergence time, (2) mean germination rate, (3) coefficient of velocity of germination, and (4) final germination percentage (FGP) were calculated. The importance of seed mineral elements in the establishment of Bambara groundnut was examined by measuring root length (RL), shoot length (SL), shoot dry mass (SDM), and root dry mass (RDM). Plant tissue elemental analysis was done using flame atomic emission spectrometry (FAES) for K and flame atomic absorption spectrometry (FAAS) for Mg, Cu, Mn, and Zn. There were significant differences (P < 0.001) in mineral element content of dry seeds. G340A and Kazai had the highest and the lowest K, P, Mg, Mn, and Zn (11.65 gkg^-1, 7.2 gkg^-1, 2.33 gkg^-1, 59.56 mgkg^-1, and 44.42 mgkg^-1), and (8.82 gkg^-1, 4.75 gkg^-1, 1.38 gkg^-1, 48.9 mgkg^-1, and 42.6 mgkg^-1), respectively. Cold test germination indices were significantly different, the highest FGP was 73.3% in G340A and the lowest was 57.8% in Kazai. There were strong positive correlations between seed mineral concentration and plant growth parameters (p < 0.001). We concluded that (1) seed mineral concentration has a significant impact on the early establishment of Bambara groundnut and (2) the dark-coloured landraces (hue 8º) used in this study have the highest concentration of macro and micro elements compared to light coloured seeds (hue 38º).

Genome-wide identification and characterization of abiotic-stress responsive SOD (superoxide dismutase) gene family in Brassica juncea and B. rapa

Background

Abiotic stresses like drought, heat, cold and salinity cause major productivity loss in the rapeseed-mustard crops (Brassica). Major efforts have been made in the past to identify genes that provide resistance against such stresses. Superoxide dismutase (SOD) proteins, member of the metallo-enzyme family play vital role in protecting plants against abiotic stresses. In the present study, genome-wide analysis of abiotic stress responsive SOD gene family has been done in B. juncea and B. rapa.

Results

A total of 29 and 18 SOD genes were identified in B. juncea and B. rapa respectively and chromosome location mapping indicated their wide distribution across genome. On the basis of domain composition, the SODs were phylogenetically classified into sub-groups which was also substantiated by the gene structure and sub-cellular locations of SOD proteins. Functional annotation of SODs was also done by Gene Ontology (GO) mapping and the result was corroborated by the identified cis-regulatory elements in the promoter region of SOD genes. Based on FPKM analysis of SRA data available for drought, heat and salt stress, we identified 14 and 10 abiotic stress responsive SOD genes in B. rapa and B. juncea respectively. The differential expression analysis under drought and heat stress of identified abiotic-stress responsive SOD genes was done through quantitative Real Time PCR.

Conclusion

We identified abiotic-stress responsive genes that could help in improving the plant tolerance against abiotic stresses. This was the first study to describe the genome-wide analysis of SOD gene family in B. rapa and B. juncea, and the results will help in laying basic ground for future work of cloning and functional validation of SOD genes during abiotic stresses leading to Brassica crop improvement.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5593-5) contains supplementary material, which is available to authorized users.

Identification and Functional Characterization of a Cold-Related Protein, BcHHP5, in Pak-Choi (Brassica rapa ssp. chinensis)

In plants, heptahelical proteins (HHPs) have been shown to respond to a variety of abiotic stresses, including cold stress. Up to the present, the regulation mechanism of HHP5 under low temperature stress remains unclear. In this study, BcHHP5 was isolated from Pak-choi (Brassica rapa ssp. chinensis cv. Suzhouqing). Sequence analysis and phylogenetic analysis indicated that BcHHP5 in Pak-choi is similar to AtHHP5 in Arabidopsis thaliana. Structure analysis showed that the structure of the BcHHP5 protein is relatively stable and highly conservative. Subcellular localization indicated that BcHHP5 was localized on the cell membrane and nuclear membrane. Furthermore, real-time quantitative polymerase chain reaction (RT-qPCR) analysis showed that BcHHP5 was induced to express by cold and other abiotic stresses. In Pak-choi, BcHHP5-silenced assay, inhibiting the action of endogenous BcHHP5, indicated that BcHHP5-silenced might have a negative effect on cold tolerance, which was further confirmed. All of these results indicate that BcHHP5 might play a role in abiotic response. This work can serve as a reference for the functional analysis of other cold-related proteins from Pak-choi in the future.

Perspective Research Progress in Cold Responses of Capsella bursa-pastoris

Plants respond to cold stress by modulating biochemical pathways and array of molecular events. Plant morphology is also affected by the onset of cold conditions culminating at repression in growth as well as yield reduction. As a preventive measure, cascades of complex signal transduction pathways are employed that permit plants to endure freezing or chilling periods. The signaling pathways and related events are regulated by the plant hormonal activity. Recent investigations have provided a prospective understanding about plant response to cold stress by means of developmental pathways e.g., moderate growth involved in cold tolerance. Cold acclimation assays and bioinformatics analyses have revealed the role of potential transcription factors and expression of genes like CBF, COR in response to low temperature stress. Capsella bursa-pastoris is a considerable model plant system for evolutionary and developmental studies. On different occasions it has been proved that C. bursa-pastoris is more capable of tolerating cold than A. thaliana. But, the mechanism for enhanced low or freezing temperature tolerance is still not clear and demands intensive research. Additionally, identification and validation of cold responsive genes in this candidate plant species is imperative for plant stress physiology and molecular breeding studies to improve cold tolerance in crops. We have analyzed the role of different genes and hormones in regulating plant cold resistance with special reference to C. bursa-pastoris. Review of collected data displays potential ability of Capsella as model plant for improvement in cold stress regulation. Information is summarized on cold stress signaling by hormonal control which highlights the substantial achievements and designate gaps that still happen in our understanding.

Physiological and Molecular Mechanism of Nitric Oxide (NO) Involved in Bermudagrass Response to Cold Stress

Bermudagrass is widely utilized in parks, lawns, and golf courses. However, cold is a key factor limiting resource use in bermudagrass. Therefore, it is meaningful to study the mechanism of bermudagrass response to cold. Nitric oxide (NO) is a crucial signal molecule with multiple biological functions. Thus, the objective of this study was to investigate whether NO play roles in bermudagrass response to cold. Sodium nitroprusside (SNP) was used as NO donor, while 2-phenyl-4,4,5,5-tetramentylimidazoline-l-oxyl-3-xide (PTIO) plus NG-nitro-L-arginine methyl ester (L-NAME) were applied as NO inhibitor. Wild bermudagrass was subjected to 4 °C in a growth chamber under different treatments (Control, SNP, PTIO + L-NAME). The results indicated lower levels of malondialdehyde (MDA) content and electrolyte leakage (EL), higher value for chlorophyll content, superoxide dismutase (SOD) and peroxidase (POD) activities after SNP treatment than that of PTIO plus L-NAME treatments under cold stress. Analysis of Chlorophyll (Chl) a fluorescence transient displayed that the OJIP transient curve was higher after treatment with SNP than that of treated with PTIO plus L-NAME under cold stress. The values of photosynthetic fluorescence parameters were higher after treatment with SNP than that of treated with PTIO plus L-NAME under cold stress. Expression of cold-responsive genes was altered under cold stress after treated with SNP or PTIO plus L-NAME. In summary, our findings indicated that, as an important strategy to protect bermudagrass against cold stress, NO could maintain the stability of cell membrane, up-regulate the antioxidant enzymes activities, recover process of photosystem II (PSII) and induce the expression of cold-responsive genes.

De Novo Transcriptome Sequencing of Low Temperature-Treated Phlox subulata and Analysis of the Genes Involved in Cold Stress

Phlox subulata, a perennial herbaceous flower, can survive during the winter of northeast China, where the temperature can drop to −30 °C, suggesting that P. subulata is an ideal model for studying the molecular mechanisms of cold acclimation in plants. However, little is known about the gene expression profile of P. subulata under cold stress. Here, we examined changes in cold stress-related genes in P. subulata. We sequenced three cold-treated (CT) and control (CK) samples of P. subulata. After denovo assembly and quantitative assessment of the obtained reads, 99,174 unigenes were generated. Based on similarity searches with known proteins in public protein databases, 59,994 unigenes were functionally annotated. Among all differentially expressed genes (DEGs), 8302, 10,638 and 11,021 up-regulated genes and 9898, 17,876, and 12,358 down-regulated genes were identified after treatment at 4, 0, and −10 °C, respectively. Furthermore, 3417 up-regulated unigenes were expressed only in CT samples. Twenty major cold-related genes, including transcription factors, antioxidant enzymes, osmoregulation proteins, and Ca²⁺ and ABA signaling components, were identified, and their expression levels were estimated. Overall, this is the first transcriptome sequencing of this plant species under cold stress. Studies of DEGs involved in cold-related metabolic pathways may facilitate the discovery of cold-resistance genes.