Effects of Cold Acclimation and Exogenous Pytohormone Abscisic Acid Treatment on Physiological Indicators of Winterness Wheat

Full-length transcriptome reveals the pivotal role of ABA and ethylene in the cold stress response of Tetrastigma hemsleyanum

Tetrastigma hemsleyanum is a valuable herb widely used in Chinese traditional and modern medicine. Winter cold severely limits the artificial cultivation of this plant, but the physiological and molecular mechanisms upon exposure to cold stress in T. hemsleyanum are unclear. T. hemsleyanum plants with different geographical origins exhibit large differences in response to cold stress. In this research study, using T. hemsleyanum ecotypes that exhibit frost tolerance (FR) and frost sensitivity (FS), we analyzed the response of cottage seedlings to a simulated frost treatment; plant hormones were induced with both short (2 h) and long (9 h) frost treatments, which were used to construct the full-length transcriptome and obtained 76,750 transcripts with all transcripts mapped to 28,805 genes, and 27,215 genes, respectively, annotated to databases. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed enrichment in plant hormone signaling pathways. Further analysis shows that differently expressed genes (DEGs) concentrated on calcium signaling, ABA biosynthesis and signal transduction, and ethylene in response to cold stress. We also found that endogenous ABA and ethylene content were increased after cold treatment, and exogenous ABA and ethylene significantly improved cold tolerance in both ecotypes. Our results elucidated the pivotal role of ABA and ethylene in response to cold stress in T. hemsleyanum and identified key genes.

Dissecting the effect of ethylene in the transcriptional regulation of chilling treatment in grapevine leaves

Ethylene (ETH) plays important roles in various development programs and stress responses in plants. In grapevines, ETH increased dramatically under chilling stress and is known to positively regulate cold tolerance. However, the role of ETH in transcriptional regulation during chilling stress of grapevine leaves is still not clear. To address this gap, targeted hormone profiling and transcriptomic analysis were performed on leaves of Vitis amurensis under chilling stress with and without aminoethoxyvinylglycine (AVG, a inhibitor of ETH synthesis) treatment. APETALA2/ETHYLENE RESPONSIVE FACTOR (AP2/ERF) and WRKY transcription factors (TF) were only the two highly enriched TF families that were consistently up-regulated during chilling stress but inhibited by AVG. The comparison of leaf transcriptomes between chilling treatment and chilling with AVG allowed the identification of potential ETH-regulated genes. Potential genes that are positively regulated by ETH are enriched in solute transport, protein biosynthesis, phytohormone action, antioxidant and carbohydrate metabolism. Conversely, genes related to the synthesis and signaling of ETH, indole-3-acetic acid (IAA), abscisic acid (ABA) were up-regulated by chilling treatment but inhibited by AVG. The contents of ETH, ABA and IAA also paralleled with the transcriptome data, which suggests that the response of ABA and IAA during chilling stress may regulate by ETH signaling, and together may belong to an integrated network of hormonal signaling pathways underpinning chilling stress response in grapevine leaves. Together, these findings provide new clues for further studying the complex regulatory mechanism of ETH under low-temperature stress in plants more generally and new opportunities for breeding cold-resilient grapevines.

Role of exogenous abscisic acid in freezing tolerance of mangrove Kandelia obovata under natural frost condition at near 32°N

BACKGROUND

Mangroves possess substantial ecological, social, and economic functions in tropical and subtropical coastal wetlands. Kandelia obovata is the most cold-resistance species among mangrove plants, with a widespread distribution in China that ranges from Sanya (18° 12' N) to Wenzhou (28° 20' N). Here, we explored the temporal variations in physiological status and transcriptome profiling of K. obovata under natural frost conditions at ~ 32^oN, as well as the positive role of exogenous abscisic acid (ABA) in cold resistance.

RESULTS

The soluble sugar (SS) and proline (Pro) functioned under freezing stress, of which SS was more important for K. obovata. Consistently, up-regulated DEGs responding to low temperature were significantly annotated to glycometabolism, such as starch and sucrose metabolism and amino sugar and nucleotide sugar metabolism. Notably, the top 2 pathways of KEGG enrichment were phenylpropanoid biosynthesis and flavonoid biosynthesis. For the antioxidant system, POD in conjunction with CAT removed hydrogen peroxide, and CAT appeared to be more important. The up-regulated DEGs responding to low temperature and ABA were also found to be enriched in arginine and proline metabolism, starch and sucrose metabolism, and peroxisome. Moreover, ABA triggered the expression of P5CS and P5CR, but inhibited the ProDH expression, which might contribute to Pro accumulation. Interestingly, there was no significant change in malondialdehyde (MDA) content during the cold event (P > 0.05), suggesting foliar application of ABA effectively alleviated the adverse effects of freezing stress on K. obovata by activating the antioxidant enzyme activity and increasing osmolytes accumulation, such as Pro, and the outcome was proportional to ABA concentration.

CONCLUSIONS

This study deepened our understanding of the physiological characters and molecular mechanisms underlying the response of K. obovata to natural frost conditions and exogenous ABA at the field level, which could provide a sound theoretical foundation for expanding mangroves plantations in higher latitudes, as well as the development coastal landscape.

Addressing the challenge of cold stress resilience with the synergistic effect of Rhizobium inoculation and exogenous melatonin application in Medicago truncatula

Cold stress is an adverse environmental condition that limits the growth and yield of leguminous plants. Thus, discovering an effective way of ameliorating cold-mediated damage is important for sustainable legume production. In this study, the combined use of Rhizobium inoculation (RI) and melatonin (MT) pretreatment was investigated in Medicago truncatula plants under cold stress. Eight-week-old seedlings were divided into eight groups: (i) CK (no stress, noninoculated, no MT), (ii) RI (Rhizobium inoculated), (iii) MT (75 μM melatonin), (iv) RI+MT, (v) CS (cold stress at 4 °C without Rhizobium inoculation and melatonin), (vi) CS+RI, (vii) CS+MT, and (viii) CS+RI+MT. Plants were exposed to cold stress for 24 hrs. Cold stress decreased photosynthetic pigments and increased oxidative stress. Pretreatment with RI and MT alone or combined significantly improved root activity and plant biomass production under cold stress. Interestingly, chlorophyll contents increased by 242.81% and MDA levels dramatically decreased by 34.22% in the CS+RI+MT treatment compared to the CS treatment. Moreover, RI+MT pretreatment improved the antioxidative ability by increasing the activities of peroxidase (POD; 8.45%), superoxide dismutase (SOD; 50.36%), catalase (CAT; 140.26%), and ascorbate peroxidase (APX; 42.63%) over CS treated plants. Additionally, increased osmolyte accumulation, nutrient uptake, and nitrate reductase activity due to the combined use of RI and MT helped the plants counteract cold-mediated damage by strengthening the nonenzymatic antioxidant system. These data indicate that pretreatment with a combined application of RI and MT can attenuate cold damage by enhancing the antioxidation ability of legumes.

The Influence of Soil Acidity on the Physiological Responses of Two Bread Wheat Cultivars

The recent study was conducted to examine the influence of acidic soil on the activities of ascorbate (APX) and guaiacol peroxidase (POD), proline, protein as well as malon-dialdehyde (MDA) content, in two commercial spring wheat cultivars (PAN3497 and SST806) at different growth stages (tillering and grain filling). A cultivar effect was significant only for MDA content, while the treatment effect was highly significant for proline, protein, and MDA. The sampling time effect was significant for most characteristics. MDA, antioxidative capacity, as well as protein content increased with maturity. At grain filling, MDA and proline contents were significantly higher at pH 5 than pH 6 and 7 for both cultivars, with the highest content in SST806. Similarly, SST806 had significantly higher APX and POD when growing at pH 5. There were no significant differences in protein content at grain filling between either genotype or treatments affected by low pH. This study showed that growth stage and soil pH influence the rate of lipid peroxidation as well as the antioxidative capacity of wheat, with a larger effect at grain filling, at pH 5. Although SST806 had higher proline, POD, and APX content than PAN3497 at this growth stage, this coincided with a very high MDA content. This shows that the high antioxidative capacity observed here, was not associated with a reduction of lipid peroxidation under low soil pH. Further research should, therefore, be done to establish the role of the induced antioxidant system in association with growth and yield in wheat.

Exogenous Melatonin Enhances Cold, Salt and Drought Stress Tolerance by Improving Antioxidant Defense in Tea Plant (Camellia sinensis (L.) O. Kuntze)

Melatonin is a biological hormone that plays crucial roles in stress tolerance. In this study, we investigated the effect of exogenous melatonin on abiotic stress in the tea plant. Under cold, salt and drought stress, increasing malondialdehyde levels and decreasing maximum photochemical efficiency of PSII were observed in tea leaves. Meanwhile, the levels of reactive oxygen species (ROS) increased significantly under abiotic stress. Interestingly, pretreatment with melatonin on leaves alleviated ROS burst, decreased malondialdehyde levels and maintain high photosynthetic efficiency. Moreover, 100 μM melatonin-pretreated tea plants showed high levels of glutathione and ascorbic acid and increased the activities of superoxide dismutase, peroxidase, catalase and ascorbate peroxidase under abiotic stress. Notably, melatonin treatments can positively up-regulate the genes (CsSOD, CsPOD, CsCAT and CsAPX) expression of antioxidant enzyme biosynthesis. Taken together, our results confirmed that melatonin protects tea plants against abiotic stress-induced damages through detoxifying ROS and regulating antioxidant systems.

Interaction of polyamines, abscisic acid and proline under osmotic stress in the leaves of wheat plants

The exact relationship between polyamine, abscisic acid and proline metabolisms is still poorly understood. In the present study, the effects of putrescine and abscisic acid treatments alone or in combination with polyethylene glycol-induced osmotic stress were investigated in young wheat plants. It was observed that abscisic acid plays a role in the coordinated regulation of the proline and polyamine biosynthetic pathways, which compounds are related to each other through a common precursor. Abscisic acid pre-treatment induced similar alteration of polyamine contents as the osmotic stress, namely increased the putrescine, but decreased the spermidine contents in the leaves. These changes were mainly related to the polyamine cycle, as both the synthesis and peroxisomal oxidation of polyamines have been induced at gene expression level. Although abscisic acid and osmotic stress influenced the proline metabolism differently, the highest proline accumulation was observed in the case of abscisic acid treatments. The proline metabolism was partly regulated independently and not in an antagonistic manner from polyamine synthesis. Results suggest that the connection, which exists between polyamine metabolism and abscisic acid signalling leads to the controlled regulation and maintenance of polyamine and proline levels under osmotic stress conditions in wheat seedlings.

Genome-wide transcriptome profiling provides overwintering mechanism of Agropyron mongolicum

BACKGROUND

The mechanism of winter survival for perennials involves multiple levels of gene regulation, especially cold resistance. Agropyron mongolicum is one important perennial grass species, but there is little information regarding its overwintering mechanism. We performed a comprehensive transcriptomics study to evaluate global gene expression profiles regarding the winter survival of Agropyron mongolicum. A genome-wide gene expression analysis involving four different periods was identified. Twenty-eight coexpression modules with distinct patterns were performed for transcriptome profiling. Furthermore, differentially expressed genes (DEGs) and their functional characterization were defined using a genome database such as NT, NR, COG, and KEGG.

RESULT

A total of 79.6% of the unigenes were characterized to be involved in 136 metabolic pathways. In addition, the expression level of ABA receptor genes, regulation of transcription factors, and a coexpression network analysis were conducted using transcriptome data. We found that ABA receptors regulated downstream gene expression by activating bZIP and NAC transcription factors to improve cold resistance and winter survival.

CONCLUSION

This study provides comprehensive transcriptome data for the characterization of overwintering-related gene expression profiles in A. mongolicum. Genomics resources can help provide a better understanding of the overwintering mechanism for perennial gramineae species. By analyzing genome-wide expression patterns for the four key stages of tiller bud development, the functional characteristics of the DEGs were identified that participated in various metabolic pathways and have been shown to be strongly associated with cold tolerance. These results can be further exploited to determine the mechanism of overwintering in perennial gramineae species.

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.

Alleviation of cold damage to photosystem II and metabolisms by melatonin in Bermudagrass

As a typical warm-season grass, Bermudagrass [Cynodon dactylon (L).Pers.] is widely applied in turf systems and animal husbandry. However, cold temperature is a key factor limiting resource utilization for Bermudagrass. Therefore, it is relevant to study the mechanisms by which Burmudagrass responds to cold. Melatonin is a crucial animal and plant hormone that is responsible for plant abiotic stress responses. The objective of this study was to investigate the role of melatonin in cold stress response of Bermudagrass. Wild Bermudagrass pre-treated with 100 μM melatonin was subjected to different cold stress treatments (-5°C for 8 h with or without cold acclimation). The results showed lower malondialdehyde (MDA) and electrolyte leakage (EL) values, higher levels of chlorophyll, and greater superoxide dismutase and peroxidase activities after melatonin treatment than those in non-melatonin treatment under cold stress. Analysis of chlorophyll a revealed that the chlorophyll fluorescence transient (OJIP) curves were higher after treatment with melatonin than that of non-melatonin treated plants under cold stress. The values of photosynthetic fluorescence parameters increased after treatment with melatonin under cold stress. The analysis of metabolism showed alterations in 46 metabolites in cold-stressed plants after melatonin treatment. Among the measured metabolites, five sugars (arabinose, mannose, glucopyranose, maltose, and turanose) and one organic acid (propanoic acid) were significantly increased. However, valine and threonic acid contents were reduced in melatonin-treated plants. In summary, melatonin maintained cell membrane stability, increased antioxidant enzymes activities, improved the process of photosystem II, and induced alterations in Bermudagrass metabolism under cold stress.

Growth and cesium uptake responses of Phytolacca americana Linn. and Amaranthus cruentus L. grown on cesium contaminated soil to elevated CO2 or inoculation with a plant growth promoting rhizobacterium Burkholderia sp. D54, or in combination

Growth and cesium uptake responses of plants to elevated CO(2) and microbial inoculation, alone or in combination, can be explored for clean-up of contaminated soils, and this induced phytoextraction may be better than the natural process. The present study used open-top chambers to investigate combined effects of Burkholderia sp. D54 inoculation and elevated CO(2) (860 μL L(-1)) on growth and Cs uptake by Phytolacca americana and Amaranthus cruentus grown on soil spiked with various levels of Cs (0-1000 mg kg(-1)). Elevated CO(2) and bacterial inoculation, alone or in combination, significantly increased biomass production with increased magnitude, ranging from 22% to 139% for P. americana, and 14% to 254% for A. cruentus. Total tissue Cs in both plants was significantly greater for bacterial inoculation treatment singly, and combined treatments of bacterial inoculation and elevated CO(2) than for the control treatment in most cases. Regardless of CO(2) concentrations and bacterial inoculation, A. cruentus had higher tissue Cs concentration, Cs transfer factors and concentration ratios than P. americana, but they had slightly different contents of antioxidant enzymes. It is concluded that combined effects of elevated CO(2) and microbial inoculation with regard to plant ability to grow and remove radionuclides from soil can be explored for CO(2)- and microbe-assisted phytoextraction technology.