Effects Of Temperature Stress Research Articles

Screening methods for thermotolerance in pollen.

Plant reproduction is highly susceptible to temperature stress. The development of the male gametophyte in particular represents a critical element in the reproductive cycle with high sensitivity to elevated temperatures. Various methods have been used to test the effect of temperature stress on pollen performance or to determine the degree of susceptibility of given species and genotypes. The information gained informs the development of new crop varieties suited to grow under warmer conditions arising through climate change and facilitates predicting the behavior of natural populations under these conditions. The characterization of pollen performance typically employs the terms pollen viability and pollen vigor, which, however, are not necessarily used consistently across studies. Pollen viability is a nominal parameter and is often assayed relying on cellular features as proxy to infer the capability of pollen grains to germinate and complete double fertilization. Alternatively, pollen germination can be determined through in vitro growth assays, or by monitoring the ability of pollen tubes to complete different progamic steps in vivo (ability to reach an ovule, release sperm cells, lead to seed set). Pollen vigor is an ordinal parameter that describes pollen tube growth rate or the efficiency of pollen tube growth as inferred by its morphology or growth pattern. To ensure consistent and relevant terminology, this review defines these terms and summarizes the methodologies used to assess them.

Computing the effects of temperature and osmotic stress on the seed germination of Helianthus annuus L. by using a mathematical model

An extremely important oil crop in the world, Helianthus annuus L. is one of the world's most significant members of the Asteraceae family. The rate and extent of seed germination and agronomic features are consistently affecting by temperature (T) and changes in water potential (ψ). A broad hydrothermal time model with T and ψ components could explain sunflower responses over suboptimal T and ψ. A lab experiment was performed using the HTT model to discover both T and ψ and their interactive effects on sunflower germination and also to figure out the cardinal Ts values. The sunflower seeds were germinated at temperatures (15 °C, 20 °C, 25 °C and 30 °C); each Ts had five constant ψs of 0, 0.3, 0.6, 0.9, and 1.2 MPa via PEG 6000 as osmotic stress inducer. The results revealed that highest germination index was found in seed grown at 20 °C in distilled water (0 MPa) and the lowest at 30 °C with osmotic stress of (− 1.2 MPa). The highest value of germination rate index was found in seed grown at 20 °C in distilled water (0 MPa) and the lowest at 15 °C with an osmotic stress of (− 1.2 MPa). In conclusion, water potential, temperature, and their interactions have a considerable impact on seed germination rate, and other metrics (GI, SVI-I, GRI, GE, SVI-II, and MGT). Seeds sown at 20 °C with zero water potential showed high germination metrics such as GE, GP, GRI, and T50%. The maximum value to TTsub noted at 30 °C in − 0.9 MPa osmotic stress and the minimum value was calculated at 15 °C in − 1.2 MPa osmotic stress. The result of TTsupra recorded highest at 15 °C in controlled group (0 MPa). Moreover, θH was highest at 30 °C in controlled condition (0 MPa) and minimum value was observed at 20 °C under − 1.2 MPa osmotic stress. The value of θHTT were maximum at 30 °C in controlled group (0 MPa) and minimum value was recorded at 15 °C under − 1.2 MPa osmotic potential. The base, optimum and ceiling temperatures for sunflower germination metrics in this experiment were noted 6.8, 20 and 30 °C respectively.

An integrated analysis of transcriptome and metabolome to reveal the effects of temperature stress on energy metabolism and physiological responses in Schizothorax wangchiachii muscles

The unique hydrological situation of Jinsha River and the construction and operation of large hydropower stations may cause resident Schizothorax wangchiachii to experience acute changes in water temperature. To reveal the response mechanisms of S. wangchiachii to high and low temperature stress, we conducted a stress experiment. Compared with the control group, the activity of antioxidant enzymes (SOD\\CAT) increased first and then decreased at high temperature, while MDA activity in the low temperature group continued to increase slowly. The activities of glycolytic enzymes were increased initially and then decreased including HK and PFK, but PK activity continued to increase throughout the stress period. Transcriptome sequencing showed that a large number of genes in muscle tissues were differentially expressed after high and low temperature stress, and the main enriched pathways included glycosaminoglycan biosynthesis, lysine degradation, glycerolipid metabolism, the PPAR signaling pathway, and the adipocytokine signaling pathway. Significant metabolic pathways were identified as enriched according to the metabolic differences,such as glycerophospholipid metabolism, qRT-PCR was used to verify gene expression. The results suggested that both high temperature and low temperature stress induced physiological responses in S. wangchiachii that maintained homeostasis by regulating glucolipid metabolism and amino acid degradation. This study revealed the response mechanisms of S. wangchiachii to high and low temperature stress, information that may serve as a reference for the study of responses in other fish to environmental changes in the upper reaches of the Yangtze River or where they are displaced by hydropower station construction.

Impact of temperature stress on Pyropia yezoensis and its inhabitant microbiota to promote aquaculture

The diverse inhabitant microbiota of Pyropia yezoensis can establish both beneficial and harmful interactions that effect community structure. It is complex to understand the seaweed microbial diversity and their ecological and functional regulations which are affected by numerous environmental factors. In this study, temperature stress was focused to understand the metagenomics of P. yezoensis microbiota, its functional annotation and the metabolites regulation of P. yezoensis. The samples of P. yezoensis from yellow sea of China were divided into two groups i.e low temperature 5°C (LT) and High temperature 25°C (HT). The genes and functional level analysis were followed by using metagenomic sequencing analysis and sequencing of 16sRNA gene. The Pyropia yezoensis samples were also analyzed through LCMS for metabolites regulation due to effects of microbiota and temperature stress. According to taxonomic classification analysis, Proteobacteria, Bacteroidetes, and Firmicutes were predominant in both samples with over-representation of these species in high temperature stress samples. A diverse relationship between the bacterial communities residing in the LT and HT samples was explored through discriminant analysis. The functional prediction of bacterial communities from KEGG analysis revealed a notable increase in HT predicted genes associated to amino acid metabolism, carbohydrate metabolism, energy metabolism, co-factors and vitamins metabolism, membrane transport, and nucleotide metabolism. The provoked chemical signaling and transportation response from the bacterial community, leading to activation of metabolic genes to utilize the available substrates of seaweed. The LCMS illustrated that the primary metabolites of Pyropia yezoensis were down regulated due to effect of high temperature which indicates a negative effect on the growth and health of Pyropia, while the secondary metabolites were up-regulated showing the defensive mechanism against unbearable stress. These up and down regulated metabolites also activated their respective pathways, suggesting the adoptive mechanism of P. yezoensis in response of high temperature.

Low temperature and excess moisture affect seed germination of soybean (Glycine max L.) under controlled environments

Cold and excess moisture pose a serious threat to soybean production especially during seed germination in short-season environments. In this study, the effects of low temperature and excess moisture stress on seed germination were investigated in 187 soybean accessions originating from 18 countries. The experiment used a combination of three temperature conditions (i.e., 20 °C/14 °C, 14 °C/10 °C, and 10 °C/10 °C day/night) and two moisture levels (i.e., normal and excess). The seed germinability traits measured included germination rate (GR), germination index, germination time, germination uniformity, and coefficient of velocity of germination. Overall, GR was lowest in the 20 °C/14 °C + excess moisture and germination time was longest in the 10 °C/10 °C + excess moisture. When compared with 20 °C/14 °C + normal moisture treatment, GR at 10 °C/10 °C + excess moisture decreased by 38%; germination time increased by 20 days; seed viability decreased by 83%; germination uniformity decreased by 70%; germination speed decreased by 73%. Differences in GR, germination index, and germination velocity under different treatments were affected by temperature, moisture, and their interaction. Variation in germination time uniformity was determined by temperature, with no significant effects of moisture conditions and the interaction of temperature and moisture. It was shown that the temperature–excess moisture interaction led to a sharp decrease in seed germination. Two genotypes including PI 603147 and PI 507702 were identified with a GR over 90% at 10 °C/10 °C + excess moisture. This study generated new knowledge and data to further the understanding of genetic resistance to cold and excess moisture stress in soybean.

Influence of structure-forming agent on rheological properties of polymer mixture based on low and high density polyethylene

The paper considers the effect of a structure-forming agent (titanium dioxide) on the rheological characteristics of a polymer mixture based on low and high density polyethylene, taken in a 50/50 ratio. The titanium dioxide concentration was 1 wt%. The rheological behavior of melts of polymer composites was studied using a CEAST MF50 capillary rheometer (Instron, Italy) at temperatures of 190, 210, 230, 250 °С and loads of 3.8, 5.0, 10.0, 12.5, and 21.6 kg. The effect of temperature and shear stress on the regularity of changes in effective viscosity and shear rate has been established. According to the Arrhenius – Frenkel – Eyring model, the activation energy of the viscous flow of composites is determined. The “apparent” activation energy of the viscous flow varies within 16.04–33.10 kJ/mol for the initial polyethylene mixture and in the range of 6.96–33.10 kJ/mol for composites modified with a structurant based on a mixture of low and high density polyethylene. A universal temperature-invariant characteristic of the viscosity properties of polymeric materials has been constructed, which makes it possible, by extrapolating this dependence to the region of high shear rates, to predict the technological mode of their processing by injection molding and extrusion.

Impact of Environmental Conditions on the Concentrations of Trichothecenes, Their Glucosides, and Emerging Fusarium Toxins in Naturally Contaminated, Irradiated, and Fusarium langsethiae Inoculated Oats.

Trichothecenes produced by Fusarium species are commonly detected in oats. However, the ratios of the concentrations of free trichothecenes and their conjugates and how they are impacted by different interacting environmental conditions are not well documented. This study aims to examine the effect of water activity (0.95 and 0.98 aw) and temperature (20 and 25 °C) stress on the production of T-2 and HT-2 toxins, deoxynivalenol and their conjugates, as well as diacetoxyscirpenol (DAS). Multiple mycotoxins were detected using liquid chromatography-tandem mass spectrometry from 64 contaminated oat samples. The highest concentrations of HT-2-glucoside (HT-2-Glc) were observed at 0.98 aw and 20 °C, and were higher than other type A trichothecenes in the natural oats' treatments. However, no statistical differences were found between the mean concentrations of HT-2-Glc and HT-2 toxins in all storage conditions analysed. DAS concentrations were generally low and highest at 0.95 aw and 20 °C, while deoxynivalenol-3-glucoside levels were highest at 0.98 aw and 20 °C in the naturally contaminated oats. Emerging mycotoxins such as beauvericin, moniliformin, and enniatins mostly increased with a rise in water activity and temperature in the naturally contaminated oats treatment. This study reinforces the importance of storage aw and temperature conditions in the high risk of free and modified toxin contamination of small cereal grains.

Combined Effects of Drought and Low Temperature on Germination and Seedling Growth of Melon Cultivars

The study aimed to determine the effects of drought (0.0, -2.0, -4.0, and -6.0 bar PEG 6000) and low temperature (18°C) on the germination and early seedling growth of three melon cultivars (Kırkağaç 589, Hasanbey 1, and Toros Sarıbal). Germination percentage, mean germination time, germination index, root length, shoot length, fresh and dry weight of the seedling, and vigor index of the melon cultivars were investigated. The results showed significant effects of low temperature and drought stress on the germination and seedling growth of melon cultivars. As temperature decreased and drought increased, the germination percentage decreased, and mean germination time was delayed. Drought stress led to a decrease in germination percentage, index, and all investigated seedling growth parameters, while the response of melon cultivars to drought stress varied. Seedling growth was more affected by low temperature than germination. Low temperature decreased germination percentage from 87.2% to 63.7% and seedling fresh weight from 140 mg/plant to 64 mg/plant. Each increase in drought levels resulted in a decrease in germination and seedling growth parameters of melon cultivars. Any seedling growth was not observed in Hasanbey 1 and Toros Sarıbal at -6.0 bar at 18°C. Melon cultivars showed different levels of tolerance to drought stress during germination and seedling growth stages, while they could maintain it up to -4.0 bar. It was concluded that Kırkağaç 589 germinated and grew better under drought stress at both optimum and low temperatures.

Mechanical Behavior of Secondary Lining in Super Large-Span Tunnels Considering Temperature Effects

Temperature stress has a significant impact on the structural stress of (super) large-span tunnel lining, which can easily lead to structural fatigue damage and premature cracking. With the increasing scale and quantity of super large-span tunnels, the issue of temperature stress in secondary lining has attracted widespread attention. Previous studies have paid little attention to the influence of temperature stress on the structural internal forces of ordinary small–medium-span tunnels, but this influence cannot be ignored for super large-span tunnels. We take the Letuan Tunnel (a double-hole eight-lane tunnel) of the Binzhou-Laiwu expressway renovation and expansion project in Shandong Province as a case study and analyze the mechanical response of the secondary lining through on-site measurement. Moreover, a numerical simulation was conducted to evaluate the effects of self-weight and temperature stress on the secondary lining of the case tunnel. The results indicate that: the stress of the secondary lining concrete and steel bars is greatly affected by seasonal temperature changes. The compressive stress of the concrete and steel bars is significantly greater in summer than in winter, and the tensile stress is greater in winter than in summer. Furthermore, multiple measurement points have shown a phenomenon of transition between tensile and compressive stress states. The stress of concrete and steel bars fluctuates periodically with a sine function over time, with a fluctuation period of one year. The structural stress increases with the increase of summer temperature and decreases with the decrease of winter temperature. The fluctuation amplitude of stress in the inner side of the lining concrete and steel bars is greater than that on the outer side. Among them, the stress amplitudes of the inner and outer sides of the concrete are between 0.77–1.75 MPa and 0.44–1.07 MPa, respectively, and the stress amplitudes of the inner and outer steel bars are between 5–31 MPa and 7–13 MPa, respectively. The safety factors in summer are lower than those in winter. The minimum safety factors for secondary lining in summer and winter are 3.4 and 4.6, respectively, which can meet the safety requirements for service. The average axial forces of the secondary lining under the coupling effects of self-weight and temperature in winter and summer are 528 MPa and 563 MPa, respectively, which are significantly greater than the combined axial forces under their individual effects. The bending moment distribution of the secondary lining at the tunnel vault, inverted arch, wall spring and other positions under the coupling effect of self-weight and temperature is different from or even opposite to the bending moment superposition result under the two individual actions. The achieved results reveal that the influence of temperature stress on the service performance of the lining structure cannot be ignored, and the research results can provide useful reference for similar tunnels and related studies.

Integrated transcriptomic and proteomic analyses reveal the molecular mechanism underlying the thermotolerant response of Spodoptera frugiperda

Spodoptera frugiperda (Lepidoptera: Noctuidae) is a highly destructive invasive pest with remarkable adaptability to extreme climatic conditions, posing a substantial global threat. Although the effects of temperature stress on the biological and ecological properties of S. frugiperda have been elucidated, the molecular mechanisms underlying its responses remain unclear. Herein, we combined transcriptomic and proteomic analyses to explore the key genes and proteins involved in thermotolerance regulation in S. frugiperda larvae at 42 °C. Overall, 1528 differentially expressed genes (DEGs) and 154 differentially expressed proteins (DEPs) were identified in S. frugiperda larvae under heat stress, including antioxidant enzymes, heat shock proteins (Hsps), cytochrome P450s, starch and sucrose metabolism genes, and insulin signaling pathway genes, indicating their involvement in heat tolerance regulation. Correlation analysis of DEGs and DEPs revealed that seven and eight had the same and opposite expression profiles, respectively. After nanocarrier-mediated RNA interference knockdown of SfHsp29, SfHsp20.4, SfCAT, and SfGST, the body weight and mortality of S. frugiperda larvae significantly decreased and increased under heat stress, respectively. This indicates that SfHsp29, SfHsp20.4, SfCAT, and SfGST play a crucial role in the thermotolerance of S. frugiperda larvae. These results provide insight into the mechanism of heat tolerance in S. frugiperda.

Temperature stress (cold and heat) strongly affect the phytotoxicity of polycyclic aromatic hydrocarbon (phenanthrene) to wheat

AbstractAnthropogenic activity could create different threats leading to irreversible changes in the global environment and, as a consequence, posing varied stressful conditions acting together (combined stress) on organisms. Our research concerned the combined stress of two of the main threats to soil health and plant health: temperature stress and pollution. The aim of this research was the quantitative assessment of the impact of temperature stress on the phytotoxicity of PAHs (polycyclic aromatic hydrocarbons; specifically, phenanthrene, which is a widespread, harmful organic contamination of soil) on the growth of wheat seedlings in relation to the level of soil contamination by phenanthrene (0–1000 mg kg−1 dry mass of soil) and the type of temperature stress: cold (10°C) and heat (35°C) stress, in three different soils. Earlier studies have investigated the effect of temperature stress on PAH toxicity mainly on soil invertebrates. However, the impact of temperature stress on PAH phytotoxicity towards crop plants, which are important for human food security but could be affected by chemical soil degradation, is still poorly understood. Our results indicated that the phenanthrene phytotoxicity was significantly enhanced by cold stress and heat stress. The effects of cold and heat temperature stress increased with increasing phenanthrene level. Our research is important for improving the risk assessment of PAH and food security forecasting.

Elevated CO2 ameliorates the high temperature stress effects on physio-biochemical, growth, yield traits of maize hybrids

The rising temperatures and levels of carbon dioxide in the atmosphere are anticipated to have a significant impact on the productivity of agricultural crops. Although, the individual effects of elevated CO2 and temperature have been extensively studied in C3 and C4 crops, there remains a scarcity of research investigating their interactive effects specifically on maize hybrids. The impact of elevated temperature and its interaction with elevated CO2 on phenology, physiology, biomass, and grain yield of maize hybrids was assessed in a field experiment using Free Air Temperature Elevation (FATE) facility. The results showed that elevated temperature (eT) increased the anthesis silking interval (ASI), while the presence of elevated CO2 along with elevated temperature (eT + eCO2) mitigated this effect. The differential expression were observed between hybrids depending on their genetic potential. Furthermore, the net photosynthetic rate (Anet), stomatal conductance (gs), and transpiration rate (Tr) of hybrids decreased under elevated temperature but eT + eCO2 condition helped in reverting its impact to some extent. In term of leaf composition, the highest level of total soluble sugars (TSS) and starch was observed under eT + eCO2 conditions, possibly due to improved Anet in the presence of elevated eCO2. The negative impact of eT was also evident through increased proline and MDA content, but eT + eCO2 ameliorated the adverse effect of eT. The biomass and grain yield also responded similarly, among the hybrids 900M GOLD recorded superior performance for grain yield at eT condition exceeding 35 °C. On the other hand, DHM117 experienced a significant reduction in grain yield under eT, but performed better under eT + eCO2 due to its improved physiological response to eCO2. The study indicated that elevated levels of carbon dioxide can actually mitigate the detrimental effects of elevated temperature on maize crop. This positive impact on maize crop can be attributed to an enhanced physiological performance in the presence of eCO2 which enables the plants to maintain satisfactory yield levels despite the challenging environmental conditions.

Effect of Temperature and Water Stress on the Antioxidant and Antidiabetic Activities of Thymus vulgaris Essential Oil

Effect of Temperature and Water Stress on the Antioxidant and Antidiabetic Activities of Thymus vulgaris Essential Oil

Effect of temperature and shear stress on properties of nanovesicles carrying hydrolyzed pollen protein

In this study, the effect of storage (65 °C, 24 h) and shear rates (2-100 s−1, 10 min) on the particle size, poly-dispersity index (PDI), encapsulation efficiency (EE), Angiotensin-converting enzyme (ACE) and DPPH radical inhibition, iron ion reduction ability and flow behavior of nanovesicles containing hydrolyzed bee pollen (produced by alcalase and pepsin) were evaluated. Nanoliposomes were coated by chitosan (0.2 % w/w). After storage at 65 °C, the size of the nanovesicles raised 2–2.5 folds while EE showed 5–8 % decline. ACE and DPPH radical inhibition activity were also decreased. After applying the shear stress, PDI was increased significantly (P<0.05), while EE of the nanoniosomes showed a drastic decline (P<0.05). Nanoliposomes and nanoniosomes exhibited decline in the ACE inhibitory and antioxidant activity. At low shear rates Newtonian-like and weak pseudo-plastic behavior of the chitosan-coated nanoliposomes were observed. The flow index (n), (k) and (R2) indicated the suitability of power law model for describing the flow characteristics.

Effects of cadmium exposure on haemocyte immune function of clam Ruditapes philippinarum at different temperatures

Haemocytes are crucial for the immune defence of mollusks. It is important to explore the immune performance of haemocytes of mollusks under the stress of heavy metals with global warming. In order to study the effects of cadmium (Cd) exposure and temperature stress on the haemocyte immune function of clam Ruditapes philippinarum, clams were exposed to different Cd concentrations (0.05, 0.10 and 0.25 mg/L) at 20 °C, 25 °C and 30 °C respectively. Haemocyte mortality, reactive oxygen species (ROS) and superoxide dismutase (SOD) activity were measured at day 1, day 3, day 5 and day 7. The results showed that the changes of the three indexes were not obvious when exposed to 0.05 mg/L of Cd at 20 °C, while significant differences were observed with the increase of temperature, Cd concentration and exposure time. Under a condition of relative high temperature coupling with high concentration of Cd, the clams were significantly influenced, showing an obvious synergistic effect. Selected indexes reflect the clam's response to the combined stress of temperature and Cd. Moreover, R. philippinarum might be an ideal biological index species to the Cd pollution.

Proteome trait regulation of marine Synechococcus elemental stoichiometry under global change.

Recent studies have demonstrated regional differences in marine ecosystem C:N:P with implications for carbon and nutrient cycles. Due to strong co-variance, temperature and nutrient stress explain variability in C:N:P equally well. A reductionistic approach can link changes in individual environmental drivers with changes in biochemical traits and cell C:N:P. Thus, we quantified effects of temperature and nutrient stress on Synechococcus chemistry using laboratory chemostats, chemical analyses, and data-independent acquisition mass spectrometry proteomics. Nutrient supply accounted for most C:N:Pcell variability and induced tradeoffs between nutrient acquisition and ribosomal proteins. High temperature prompted heat-shock, whereas thermal effects via the "translation-compensation hypothesis" were only seen under P-stress. A Nonparametric Bayesian Local Clustering algorithm suggested that changes in lipopolysaccharides, peptidoglycans, and C-rich compatible solutes may also contribute to C:N:P regulation. Physiological responses match field-based trends in ecosystem stoichiometry and suggest a hierarchical environmental regulation of current and future ocean C:N:P.

Quality monitoring and control for plasticization of acrylonitrile‐butadiene‐styrene regrind polymer in injection molding

AbstractTo meet net‐zero carbon emissions in injection molding, it is desirable to use regrind polymers in plastic parts fabrication. However, the quality of regrind polymer differs from virgin polymer due to the effects of temperature, pressure, and shear stress in the prior molding process. Consequently, the molded components differ in quality compared to those made from virgin material. This study investigates the feasibility of enhancing the quality consistency of regrind plastic components by controlling melt quality in plasticization. The evaluation of melt quality involves extracting two quality metrics from the pressure signal (i.e., the peak pressure and the pressure integral). They are then used to adjust the plasticization parameters as required to ensure that the weight and dimensions of the final regrind parts approach those of parts produced using virgin polymer. The experimental results show that the pressure integral effectively indicates the quality variation of the molded part during the injection molding of regrind polymer. Notably, by adjusting the back pressure, the quality of the molded part closely resembles that of the part made from virgin feedstock after six shots.

Physiological and Biochemical Effect of Elevated Night Temperature Stress on Bread Wheat (Triticum aestivum L.)

A laboratory experimentation was done in the Department of Plant Physiology, Institute of Agricultural Sciences, Banaras Hindu University to evaluate elevated night temperature effect in wheat (Triticum aestivum L.) to see the response in some antioxidant and biochemical parameters in two wheat cultivars viz. HUW-234 (comparatively tolerant to heat stress) and sonalika (comparatively susceptible to heat stress). A significance difference was recorded in the parameters pertaining to antioxidant system includes catalase, SOD and APX activity were found to increase substantially when the plants kept under stress conditions (250C/ 240C day and night temperature) than the plants kept under controlled condition (250C/150C day and night temperature). The percent increase in the antioxidant enzyme activity was found to be more in the tolerant genotype (HUW-234) than in the susceptible genotype (Sonalika). There was 23.52 % increase was reported in the catalase activity by tolerant genotype when kept under stress conditions than those kept under control. Significant reductions were reported in most of the photosynthetic and membrane parameters viz., chlorophyll ‘a’, chlorophyll ‘b’ and membrane thermostability index. Similar percent reduction was reported with respect to biochemical parameters (total protein content, starch content and soluble sugar content) in the susceptible variety kept under high night temperature regime. Based on the pooled data of two-year experimentation it can be concluded that variety HUW-234 was found to be more tolerant than variety sonalika to HNT stress.&#x0D; Key Words: High night temperature, Wheat, Catalase activity, Anti-oxidant system.

Influence of environmental factors on seed germination and seedling emergence of Amaranthus blitoides S. Watson and A. hybridus L.

AbstractAmaranthus blitoides S. Watson and A. hybridus L. are common herbaceous annual summer weeds in different regions of Iran, which produce a large number of small seeds per plant. The goal of these experiments was to determine seed germination cardinal temperature and investigate the effect of constant temperature, osmotic and salt stresses, stratification, flooding duration, after‐ripening and seed planting depth on seed germination and seedling emergence. Two‐piece segmented, dent‐like and beta four‐parameter models were used to investigate the relationship between germination rate and constant temperature. The dent‐like model showed the best description of the effect of constant temperature on seed germination rate of both A. blitoides and A. hybridus. Optimal seed germination of A. blitoides occurred at 35°C, but in A. hybridus optimum germination was observed in a range of constant temperatures from 30 to 40°C. Osmotic and salt stresses and flooding adversely affected seed germination of both species. After ripening for 6 months increased germination percentage of both A. blitoides and A. hybridus. Maximum seedling emergence of A. blitoides (42.8%) and A. hybridus (44.9%) occurred at a planting depth of 3.3 cm, whereas further increased planting depth minimized seedling emergence of both weeds. Information obtained from this study will help us to develop effective techniques for management of A. blitoides and A. hybridus.

Effect of temperature, pretreatments, gibberellin (GA3), salt and drought stress on germination of Thymus satureioides coss of Morocco

Thymus satureioides Cosson is an endemic medicinal and aromatic plant species of both Morocco and Algeria, holds significant cultural and economic importance. It is used in traditional medicine to treat various diseases and also as a culinary spice herb. T. satureioides has become a key export for Morocco. However, increasing market demand and the effects of climate change have led to a decline in its wild populations, raising concerns about the scarcity of this valuable natural resource. To address these challenges, a comprehensive understanding of the environmental requirements for the germination of T. satureioides is essential for planning and prioritizing conservation efforts in its native habitats. In this context, the aim of this study was to assess the combined effects of various pretreatments and temperature and of salinity, drought stress, and gibberellin on the germination parameters of T. satureioides. Seeds were collected from a wild plant population in the Anti-Atlas Mountains. The tests included five pretreatments (mechanical scarification, sulfuric acid (95%), dry heat, boiling water and hydrogen peroxide) in conjunction with five temperature conditions (10, 15, 20, 25 and 30 °C). Additionally, six concentrations of sodium chloride (0, 25, 50, 100, 150 and a 200 mM), six water potential levels of polyethylene glycol (PEG-6000) (0, −0.07, −0.14, −0.22, −0.32 and - 0.53 MPa) and six concentrations of gibberellin (0, 50, 100, 500, 1000 and 2000 ppm) were tested. Results showed that seeds can germinate without any treatment. However, seeds treated with dry heat followed by incubation at 20 °C improved all the germination parameters. In addition, germination parameters progressively decreased and delayed with increasing levels of both salt and water stress. Without stress, the germination percentage was 100%, with increasing salt stress to 200 mM germination was completely inhibited. Although, seeds showed a low germination percentage (5,67%) at the highest osmotic potential (−0.53 MPa).