Germination responses to temperature and water potential in Jatropha curcas seeds: a hydrotime model explains the difference between dormancy expression and dormancy induction at different incubation temperatures

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.

Seed Germination Ecology of the Medicinal Plant Peganum harmala (Zygophyllaceae)

Seed germination is a crucial stage in the life cycle of annuals in arid, saline regions and is particularly vulnerable to abiotic stresses. Peganum harmala, a valuable medicinal plant, has limited research on its seed germination response to different environmental stresses in the arid, saline regions of Central Asia. To investigate this, we studied the effects of various temperature regimes (ranging from 20/5 to 35/20 °C), light exposure (12 hours light/12 hours dark and continuous dark), seven levels of polyethylene glycol (PEG-6000) concentration (ranging from 0-30%), and four types of salinity (ranging from 0-600 mmol L^-1). Our findings show that photoperiod and temperature significantly influence germination. Optimal temperature range for seed germination was observed at 30/15 °C, with simulated critical and limit values of drought tolerance being highest (17.30% and 24.98%). However, higher temperatures (35/20 °C) and lower temperatures (20/5 °C) reduced the critical and limit values of drought tolerance. Additionally, the type and concentration of salinity had a significant effect on the seed germination, shoot, and root lengths of P. harmala. Regression analysis indicated that the critical values of NaCl, Na₂SO₄, NaHCO₃, and Na₂CO₃ tolerance during germination were 178 mmol L^-1, 101 mmol L^-1, 106 mmol L^-1, and 54 mmol L^-1, respectively. Salinity inhibition on seed germination followed the order: NaCl < NaHCO₃ < Na₂SO₄ < Na₂CO₃. Moreover, NaCl, Na₂SO₄, NaHCO₃, and Na₂CO₃ significantly inhibited the growth of P. harmala seedlings in both shoots and roots. Our study demonstrates the sensitivity of P. harmala to environmental factors such as light, temperature, drought, and salinity. The study provides valuable information on the germination ecology of P. harmala under diverse ecological scenarios, which can be useful in developing efficient propagation and utilization of this medicinal plant.

Hydrotime Model Parameters Estimate Seed Vigor and Predict Seedling Emergence Performance of Astragalus sinicus under Various Environmental Conditions

Seed vigor is an important aspect of seed quality. High-vigor seeds show rapid and uniform germination and emerge well, especially under adverse environmental conditions. Here, we determined hydrotime model parameters by incubating seeds at different water potentials (0.0, -0.2, -0.4, -0.6, and -0.8 MPa) in the laboratory, for 12 seed lots of Chinese milk vetch (Astragalus sinicus) (CMV), a globally important legume used as forage, green manure, and a rotation crop. Pot experiments were conducted to investigate the seedling emergence performance of 12 CMV seed lots under control, water stress, salinity stress, deep sowing, and cold stress conditions. Meanwhile, the field emergence performance was evaluated on two sowing dates in June and October 2022. Correlation and regression analyses were implemented to explore the relationships between hydrotime model parameters and seedling emergence performance under various environmental conditions. The seed germination percentage did not differ significantly between seed lots when seeds were incubated at 0.0 MPa, whereas it did differ significantly between seed lots at water potentials of -0.2, -0.4, and -0.6 MPa. The emergence percentage, seedling dry weight, and simplified vigor index also differed significantly between the 12 seed lots under various environmental conditions. Ψ_b(50) showed a significant correlation with germination and emergence performance under various environmental conditions; however, little correlation was observed between θ_H or σ_φb and germination and emergence. These results indicate that Ψ_b(50) can be used to estimate seed vigor and predict seedling emergence performance under diverse environmental conditions for CMV and similar forage legumes. This study will enable seed researchers, plant breeders, and government program directors to target higher seed vigor more effectively for forage legumes.

The Effects of Temperature and Water on the Seed Germination and Seedling Development of Rapeseed (Brassica napus L.)

The seed germination and seedling growth of rapeseed are crucial stages in plant life, especially when facing abiotic stresses. In the present work, the effects of water and temperature on seed germination and seedling growth were investigated in a rapeseed crop (Brassica napus L.). The plants were examined under different temperature levels (5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, and 35 °C) and water levels (twenty-nine levels based on either one-milliliter intervals or as a percentage of the thousand-kernel weight (TKW)). Moreover, planting densities and antifungal application techniques were investigated in the study. The findings demonstrated substantial variations between all the growth parameters investigated at all the tested temperatures, and 20 °C was considered the optimum within a broad range of 15-25 °C. Water availability plays a significant role in germination, which can be initiated at 0.65 mL, corresponding to 500% of the TKW. The method of TKW is a more accurate aspect of water application because of the consideration of the seed weight and size. The optimal water range for the accumulation of dry weight, 3.85-5.9 mL (2900-4400% of TKW), was greater than that required for seedling growth, 1.45-3.05 mL (1100-2300% of TKW). Twenty to twenty-five seeds per 9 cm Petri dish exhibited the most outstanding values compared to the others, which provides an advantage in breeding programs, especially when there are seed limitations. Seed priming is a more effective antifungal application strategy. These data can be incorporated into future rapeseed germination in vitro studies, breeding programs, and sowing date predictions.

Quantifying Temperature and Osmotic Stress Impact on Seed Germination Rate and Seedling Growth of Eruca sativa Mill. via Hydrothermal Time Model

Germination models are quite helpful in predicting emergence times, dormancy periods, and their applications in crop management. This study investigated the germination behaviors of Eruca sativa Mill. in response to fluctuations in temperatures (T_s) and water potentials (ψ_s). Germination percentage (GP) increased 95% with rising temperature within the range of 20–30 °C, and decreased 25% at 5 °C. Moreover, each ψ and T resulted in a decrease in GP as ψ decreased. Further, we noted that the θT1 value was substantially high at 30 °C and in (0 MPa), whereas the θT2 value was maximum at 10 °C (−0.02 MPa) and it decreased with decreasing Ψ. The maximum hydrothermal time constant (θHTT) and hydrotime (θH) values were obtained at 10 and 30 °C, respectively. In addition, a linear increase in the GR_(g) pattern was observed at T_b and a decrease below the T_o. The calculated cardinal T_s was 5 °C for the base T, and 30 °C for both the optimum and ceiling T. The germination characteristics were higher at 30 °C having (0 MPa). Therefore, using cardinal temperatures, germination results, and the hydrothermal time model (HTT) could reveal the independent and interactive impacts of both T and the Ψ on the response of seed germination subjected to diverse environmental conditions.

Water Dynamics on Germinating Diaspores: Physiological Perspectives from Biophysical Measurements

We demonstrated that classical biophysical measurements of water dynamics on germinating diaspores (seeds and other dispersal units) can improve the understanding of the germination process in a simpler, safer, and newer way. This was done using diaspores of cultivated species as a biological model. To calculate the water dynamics measurements (weighted mass, initial diffusion coefficient, velocity, and acceleration), we used the mass of diaspores recorded over germination time. Weighted mass of germinating diaspores has a similar pattern, independent of the physiological quality, species, or genetic improvement degree. However, the initial diffusion coefficient (related to imbibition per se), velocity, and acceleration (related to the whole germination metabolism) are influenced by species characters, highlighting the degree of genetic improvement and physiological quality. Changes in the inflection of velocity curves demonstrated each phase of germination sensu stricto. There is no pattern related to the number of these phases, which could range between three and six. Regression models can demonstrate initial velocity and velocity increments for each phase, giving an idea of the management of germinative metabolism. Our finds demonstrated that germination is a polyphasic process with a species-specific pattern but still set by the degree of genetic improvement and (or) physiological quality of diaspores. Among the biophysical measurements, velocity has the greatest potential to define the germination metabolism.

Modeling the influence of temperature and water potential on seed germination of Allium tenuissimum L

Allium tenuissimum L. is a widely distributed perennial herbaceous species in temperate and desert steppes. Relative to other wild Allium species, it produces unique sweet flavors, more biomass in arid and cold environments, and has generated greater interest for crop production. Successful crop establishment, however, will depend on rapid and uniform seed germination. Our study aimed to characterize seed germination of A. tenuissimum under various temperature regimes (11, 15, 20, 24 and 28 °C) and water potential levels (0, −0.2, −0.4 and −0.6 MPa), and model germination by hydrotime (HT) and hydrothermal time (HTT) analysis. Final germination percentage (FGP) increased within the range of 11 to 20 °C, yet it declined within the range of 24 to 28 °C and generally decreased as water potential became more negative within each temperature setting. Maximum FGP was observed at 20 °C at all water potential settings and ranged from 55.0 ± 5.3 to 94.8 ± 1.4%. According to HT and HTT models, the base (T_b) and optimum temperatures (T_o) for seed germination were 7.0 and 20.5 °C, respectively. In addition, base water potential for the fraction of germination within the seed lot (Ψ_b(g)) shifted to 0 MPa as temperature increased from T_b to ceiling temperature (T_c). For obtaining 50 % seed germination, Ψ_b(50) and T_c(50) were estimated to be −0.67 MPa and 27.2 °C, respectively. These values for T_b and Ψ_b(50) suggest seed germination of A. tenuissimum is both cold and drought tolerant and suitable for production in semi-arid regions. Our characterization of the ideal sowing conditions for A. tenuissimum, i.e., 20.5 °C and soil water potential less negative than −0.67 MPa offers information to forecast suitable settings to enhance crop production.

Germination Energy and Capacity of Maize Seeds Following Low-Temperature Short Storage

The present research attempts to characterize the effect of low temperatures, and the moisture content of maize (Kosmo 230) meant for sowing on its energy and capacity to germinate. Seeds were moistened to varying degrees and stored under various conditions; then, their germination energy and capacity were assessed. Sowing material with 15% moisture content showed slightly declined germination ability when stored at −25–−20 °C for over three days, while the storage of seeds with a 25 and 30% moisture content at −5–0 °C for 1–3 days had the effect of seed conditioning. Seedlings obtained from conditioned seeds showed sustainability characterized by faster growth, and demonstrated nearly twice the size as other plants. Warehousing and storage of maize grains with a 11.12% moisture content at temperatures up to −25 °C did not significantly affect seed germination capacity or energy, irrespective of storage time.

Revisão: Jatropha curcas L.: aspectos morfofisiológicos e químicos

Resumo Jatropha curcas L. (pinhão-manso) é uma espécie vegetal oleaginosa cujo óleo, extraído de suas sementes, apresenta múltiplas aplicações para comunidades locais, além da sua potencial aplicação em diferentes setores industriais, dentre os quais a indústria de biodiesel, constituindo-se, assim, em mais uma fonte de matéria-prima dentro do elenco de espécies oleaginosas úteis. Aspectos morfofisiológicos e físico-químicos são de grande importância quando se tem interesse na prospecção de espécies vegetais visando sua domesticação e exploração comercial. O objetivo deste estudo foi realizar uma revisão do estado da arte sobre a J. curcas, compilando estudos acerca da caracterização morfofisiológica, assim como acerca da composição química das sementes, gerando assim informações que auxiliem na exploração do potencial de produção e cultivo da espécie, a fim de subsidiar estudos que propiciem a exploração comercial sustentável dessa cultura. O conhecimento morfológico disponível sobre J. curcas possibilita o entendimento preciso do ciclo biológico da planta, entretanto, estudos fisiológicos ainda necessitam ser desenvolvidos para uma melhor compreensão do comportamento dela, principalmente em termos de armazenamento, condições ótimas de germinação e formação de mudas, assim como sobre o comportamento da espécie quando sob condições adversas, tais como excessiva insolação, restrição hídrica e temperaturas elevadas, dentre outras. A descrição da composição química, caracterização de compostos tóxicos e fatores antinutricionais da semente já existentes forneceram informações que podem dar suporte a produção e exploração comercial de J. curcas, porém estudos e testes com animais devem ser conduzidos para confirmar com maior segurança suas aplicações comerciais.

Field Sandbur (Cenchrus pauciflorus) Seeds in the Same Bur Respond Differently to Temperature and Water Potential in Relation to Germination in a Semi-Arid Environment, China

The success of a biological invasion relies on the environment and is closely linked to factors such as water and temperature. Invasive plant species display different seed characteristics, including shape. Field sandbur (Cenchrus pauciflorus) is a globally widespread invasive species capable of adapting to broad environmental conditions. However, its germination response to water and temperature still remains unclear. C. pauciflorus contains two seeds in the same bur that differ in size: big seeds (M) and small seeds (P). Separate greenhouse experiments were conducted under different temperature regimes (0/10°C, 5/15°C, 10/20°C, 15/25°C, 18/28°C, 20/30°C and 25/35°C) and water potentials (-1.50Mpa, -1.00Mpa, -0.75Mpa, -0.50Mpa, -0.25Mpa and 0Mpa) for M and P seeds. The results support the hypothesis that germination of C. pauciflorus is significantly influenced by seed type, temperature and water potential. M and P seeds responded differently to varied alternative temperatures and water potentials. However, M and P seeds were more sensitive to water potential than to temperature. Optimal conditions for M and P seed germination were measured at 25/35°C (night temperature/day temperature) and 20/30°C, respectively. In contrast, the highest germination rate was observed for the 0Mpa of the water potential treatment. Additionally, base temperature (T_base) and base water potential (W_base) were lower for M (7.7°C, -1.11Mpa at 10/20°C, and -1.07Mpa at 20/30°C) than for P (9.4°C, -0.92Mpa at 10/20°C, and -0.52Mpa at 20/30°C). These different germination strategies of M and P seeds with respect to temperature and water potential increased overall plant propagation. These results indicate that tropical and subtropical regions water potentials beyond -0.50Mpa (10/20°C) or -1.00Mpa (20/30°C) face a potential risk of C. pauciflorus invasion.

Osmoconditioning prevents the onset of microtubular cytoskeleton and activation of cell cycle and is detrimental for germination of Jatropha curcas L. seeds

Jatropha curcas is an oilseed crop renowned for its tolerance to a diverse range of environmental stresses. In Brazil, this species is grown in semiarid regions where crop establishment requires a better understanding of the mechanisms underlying appropriate seed, seedling and plant behaviour under water restriction conditions. In this context, the objective of this study was to investigate the physiological and cytological profiles of J. curcas seeds in response to imbibition in water (control) and in polyethylene glycol solution (osmoticum). Seed germinability and reactivation of cell cycle events were assessed by means of different germination parameters and immunohistochemical detection of tubulin and microtubules, i.e. tubulin accumulation and microtubular cytoskeleton configurations in water imbibed seeds (control) and in seeds imbibed in the osmoticum. Immunohistochemical analysis revealed increasing accumulation of tubulin and appearance of microtubular cytoskeleton in seed embryo radicles imbibed in water from 48 h onwards. Mitotic microtubules were only visible in seeds imbibed in water, after radicle protrusion, as an indication of cell cycle reactivation and cell proliferation, with subsequent root development. Imbibition in osmoticum prevented accumulation of microtubules, i.e. activation of cell cycle, therefore germination could not be resumed. Osmoconditioned seeds were able to survive re-drying and could resume germination after re-imbibition in water, however, with lower germination performance, possibly due to acquisition of secondary dormancy. This study provides important insights into understanding of the physiological aspects of J. curcas seed germination in response to water restriction conditions.

Development of a threshold model to predict germination of Populus tomentosa seeds after harvest and storage under ambient condition

Effects of temperature, storage time and their combination on germination of aspen (Populus tomentosa) seeds were investigated. Aspen seeds were germinated at 5 to 30°C at 5°C intervals after storage for a period of time under 28°C and 75% relative humidity. The effect of temperature on aspen seed germination could not be effectively described by the thermal time (TT) model, which underestimated the germination rate at 5°C and poorly predicted the time courses of germination at 10, 20, 25 and 30°C. A modified TT model (MTT) which assumed a two-phased linear relationship between germination rate and temperature was more accurate in predicting the germination rate and percentage and had a higher likelihood of being correct than the TT model. The maximum lifetime threshold (MLT) model accurately described the effect of storage time on seed germination across all the germination temperatures. An aging thermal time (ATT) model combining both the TT and MLT models was developed to describe the effect of both temperature and storage time on seed germination. When the ATT model was applied to germination data across all the temperatures and storage times, it produced a relatively poor fit. Adjusting the ATT model to separately fit germination data at low and high temperatures in the suboptimal range increased the models accuracy for predicting seed germination. Both the MLT and ATT models indicate that germination of aspen seeds have distinct physiological responses to temperature within a suboptimal range.