Time Course Of Germination Research Articles

Exploring temperature and salinity effects on seed germination in North African pastoral grasses: A halo-thermal modeling approach in the context of climate change

Understanding how plant species respond to temperature and salt stress is crucial for ensuring successful seed germination and crop production. The ongoing effects of global climate change, such as temperature fluctuations, can have serious consequences for seed germination. This study aimed to investigate the impact of salinity (NaCl) and temperature (T), individually and in interaction, on the germination responses of four North African pastoral grass species Stipagrostis (S. ciliata, S. pungens, S. obtusa, and S. pulmosa) and the potential impact of climate change scenarios on their seed germination. Significant effects of NaCl, T, and their interaction (NaCl × T) were observed on both germination percentage and germination rate across the four species. The halotime and halothermal time models successfully predicted germination time courses for the four species (R2 > 0.86). The base T (Tb), optimum T (To), and ceiling T (Tc) were 13, 9.8, 9.0, and 10.7 °C; 25, 29, 28, and 27 °C; and 34, 35, 38, and 34 °C for S. ciliata, S. obtusa, S. pungens, and S. pulmosa, respectively. The predictions indicated that higher temperatures associated with climate change caused shorter germination times (i.e., 42 h for S. ciliata and 23–24 h for S. pulmosa, S. pungens, and S. obtusa) suggesting potential shifts in germination behavior in response to changing environmental conditions. Furthermore, the study assessed germination recovery after salt stress, revealing species-specific responses to both T and NaCl variations. The results highlighted the resilience of the studied grass species, as seeds were capable of recovering germination after exposure to salt stress. Therefore, the research provides comprehensive insights into the intricate relationships between T, NaCl, and germination in North African pastoral grasses. The findings contribute to our understanding of how these grasses may respond to changing environmental conditions, particularly under climate change scenarios.

Quantification of camelina germination niche to combined salinity and temperature stresses using a halothermal time model

The present work was carried out to quantify camelina germination niche under salinity and temperature ( T) stress using halotime and halothermal time models. Seed germination ( SG) time courses were recorded at six constant temperatures (5 °C, 10 °C, 15 °C, 20 °C, 25 °C, and 30 °C) and at each of the following levels of NaCl concentrations (0, 50, 100, 150, 200, and 250 mM). Halotime model could well describe the germination time courses across a range of NaCl concentrations ( R2 = 0.79–0.91). The median base NaCl concentration was approximately constant (231 mM) at suboptimal T followed by a linear decrease, with the rate of 17.4 mM °C−1, under supra-optimal T. However, the germination rate increased with increasing T, reaching its maximum at a fixed optimum temperature ( To = 20 °C), independent of NaCl concentration. Then it decreased linearly for T > To and intercepted the x-axis at the ceiling temperature values of 33.5 °C, 30 °C, 28 °C, 25 °C, and 22 °C under 0, 50, 100, 150, and 200 mM NaCl, respectively. Consequently, based on model estimation the adequate soil T for SG of camelina should be in the range of 0.4 °C–33.5 °C, and the To is 20 °C. Besides, the salinity should be less than 231 mM.

Seed germination thermal niche differs among nine populations of an annual plant: A modeling approach.

Germination timing is an important determinant of survival and niche breadth of plants. The annual plant Nigella sativa occurs in diverse environments along a steep temperature gradient and thus is a suitable model for the study of germination behavior in response to temperature. We used a modeling approach to compare the germination thermal niche of seeds of nine populations of N. sativa produced in a common garden. Germination time courses were obtained by a newly developed process‐based model, and thermal niche was visualized by plotting germination breadth as a function of after‐ripening time. Seeds were sampled five times: immature (2 weeks before maturity), mature, and afterripened for 1, 2, and 5 months. Immature and mature seeds had a greater depth of dormancy than afterripened seeds, as estimated by lower values of high‐limit temperatures (T h). Afterripening increased germination percentage, synchrony, and thermal niche breadth of all nine populations. The highest asynchrony was for immature and mature seeds, and afterripening enhanced synchrony. Based on the new graphical method, N. sativa has Type 1 nondeep physiological dormancy, and thus, the germination niche is narrow at seed maturity, leading to a delayed germination strategy that is highly dependent on thermal time accumulated during afterripening. Our findings show that there is considerable variation in the germination thermal niche among populations. Temperature regimes in the natural habitats of N. sativa have played a significant role in shaping variation in thermal niche breadth for seed germination of this annual species. The models used in our study precisely predict germination behavior and thermal niche under different environmental conditions. The germination synchrony model also can estimate germination pattern and degree of dormancy during the year, suggesting a useful method for quantification of germination strategies.

CHARACTERIZATION OF Exserohilum turcicum INFECTION SITES IN MAIZE GENOTYPES

ABSTRACT Northern leaf blight caused by Exserohilum turcicum is an important disease of maize (Zea mays L.), and its severity depends more closely on growth lesions than on spot number. Here, we characterized the infection sites of E. turcicum on resistant and susceptible maize genotypes by analyzing the histology of lesions as well as the structural and biochemical mechanisms of infection. Maize leaves were inoculated with the pathogen at specific points and incubated in a microhumidity chamber. Samples were obtained to follow fungal development and host tissue lignification using light and electron microscopy, and the activity and electrophoretic patterns of peroxidases were determined. The time course of spore germination and appressorium formation was essentially the same for both genotypes; however, a delay of 12 h in fungal penetration, accompanied by host tissue lignification, was noted in the resistant genotype, as opposed to that in the susceptible one. Scanning electron microscopy revealed fungal mycelium in the xylem vessels of both genotypes; however, in the resistant genotype, pathogen colonization was restricted to mesophyll cells around the penetration point, where chlorotic flecks were produced. Meanwhile, in the susceptible genotype, following penetration and chlorotic fleck formation, the pathogen continued to grow inside the xylem vessels and profusely colonized mesophyll tissue distant from the penetration point, resulting necrotic lesion development. Electrophoretic patterns of peroxidases were similar between the two genotypes, with three isoenzymes present in all tissues. In addition, two novel isoenzymes were detected in chlorotic flecks, necrotic lesions, and green tissue around the lesions.

Using Halothermal Time Model to Describe Barley (Hordeumvulgare L.) Seed Germination Response to Water Potential and Temperature.

Barley (Hordeum vulgare L.) is a salt-tolerant crop with considerable economic value in salinity-affected arid and semiarid areas. In the laboratory experiment, the halothermal time (HaloTT) model was used to examine barley seed germination (SG) at six constant cardinal temperatures (Ts) of 15, 20, 25, 30, 35, and 40 °C under five different water potentials (ψs) of 0, −0.5, −1.5, −1.0, and −2.0 MPa. Results showed that at optimum moisture (0 MPa), the highest germination percentage (GP) was recorded at 20 °C and the lowest at 40 °C. Moreover, GP increased with the accelerated aging period (AAP) and significantly (p ≤ 0.05) decreased with high T. In addition, with a decrease of ψ from 0 to −0.5, −1, 1.5, and −2.0 MPa, GP decreased by 93.33, 76.67, 46.67, and 33.33%, respectively, in comparison with 0 MPa. The maximum halftime constant (θHalo) and coefficient of determination (R2) values were recorded at 20 °C and 30 °C, respectively. The optimum temperature (To) for barley is 20 °C, base Ψ of 50th percentile (Ψb (50)) is −0.23 Mpa, and standard deviation of Ψb (σΨb) is 0.21 MPa. The cardinal Ts for germination is 15 °C (Tb), 20 °C (To), and 40 °C (Tc). The GP, germination rate index (GRI), germination index (GI), coefficient of the velocity of germination (CVG), germination energy (GE), seed vigor index I and II (SVI-I & II), Timson germination index (GI), and root shoot ratio (RSR) were recorded maximum at 0 MPa at 20 °C and minimum at −2.0 MPa at 40 °C. Mean germination time (MGT) and time to 50% germination (T 50%) were maximum at −2 MPa at 40 °C, and minimum at 20 °C, respectively. In conclusion, the HaloTT model accurately predicted the germination time course of barley in response to T, Ψ, or NaCl. Therefore, barley can be regarded as a salt-tolerant plant and suitable for cultivation in arid and semi-arid regions due to its high resistance to salinity.

Using mathematical models to evaluate germination rate and seedlings length of chickpea seed (Cicer arietinum L.) to osmotic stress at cardinal temperatures

Cicer arietinum is the 3rd most important cool season legume crop growing in vast arid and semi-arid regions of the world. A lab experiment was designed using hydrothermal time model (HTT) to investigate the chickpea seed germination (SG) behavior, cardinal temperatures and germination responses across fluctuating temperatures (Ts) and water potentials (Ψs). Seeds of chickpea var. NIFA 1995 were germinated at six constant Ts (7, 14, 21, 28, 35 and 42°C) each having the following five water potentials: 0, -0.2, -0.4-0.6 and -0.8 MPa. Germination percentage (G%) decreased significantly at (*P ≤ 0.05) from 86.7% at 28°C in -0.2 MPa to 10% in -0.2 MPa at 7°C. The germination rate (GR = 1/t50) against different T percentiles exhibited that linear increase was observed in the GR pattern above and below the To. Based on the confidence intervals of the model coefficients and (R2: 0.96), the average cardinal temperatures were 4.7, 23 and 44.2°C for the base (Tb), optimal (To) and ceiling (Tc) temperatures respectively. θT1 value was observed maximum at 28°C in -0.2 MPa and decreases with decreasing Ψ (-0.8 MPa). In comparison with control, the θT2 value was also highest in -0.2 MPa at 28°C. The thermal time (TT) concept is well fitted to germination fraction data in distilled water with an R2 value increasing 0.972. The hydro time constant (θH) increased with an increase in T to To and then decreased when T>To. The ѱb(50) irregularly varied with increasing T, σΨb was also recorded lowest (0.166 MPa) at 28°C and highest (0.457 MPa) at 7°C. Based on the statistical analysis, cardinal temperatures, hydrothermal time constant (θHTT) and germination findings the HTT gives an insight into the interactive effect of T and Ψ on seed germination time courses under varying environmental conditions.

Effects of environment, life-history and phylogeny on germination strategy of 789 angiosperms species on the eastern Tibetan Plateau

Germination strategies vary widely among species and significantly influence individual fitness and community diversity. Germination strategies are known to be influenced by environmental conditions, life-history traits and evolutionary history, but how these factors influence germination across species under natural conditions is poorly understood. Here, we characterized germination strategies of 789 angiosperm species from the eastern Tibetan Plateau based on germination time courses and the final germination proportion expressed in the field under three light treatments: high (i.e., natural) light, medium light and low light. Based on results of correlation analysis and cluster analysis, we found two major dimensions of germination strategies [early (fast) versus late (slow) germination and high versus low germination proportions]. We also characterized a “dormant” germination strategy (species with final germination proportion < 5%). Low light availability altered the frequencies of germination strategies, and tended to canalize germination strategy into the extreme categories of early germination or high levels of dormancy. Germination strategy varied significantly based on species life-history traits (seed mass and adult longevity) and local habitat conditions (elevation, water habitat and light habitat). Finally, germination strategy exhibited strong phylogenetic signal, such that related taxa exhibited similar germination strategies. In sum, the diversity of germination strategies we observed among these species is maintained by a combination of local habitat conditions, evolutionary history and the correlated selection acting on germination and key life-history traits.

Halothermal and hydrothermal time models describe germination responses of canola seeds to ageing.

Hydrothermal time (HTT) and halothermal time (HaloTT) models were used to quantitatively characterize the combined effects of temperature (T), water potential (ψ) and NaCl concentration on seed germination of canola after different accelerated ageing periods (AAP) at 42°C and 100% humidity. Seed germination time courses were observed and electrical conductivities of seed leachates were measured in all experiments. The cardinal temperatures estimated by both models were 4.6, 28 and 35°C for the base (Tb ), optimum (To ) and ceiling (Tc ) temperatures in water (0MPa), respectively, when the seeds were not aged. The Tb increased with AAP, while the Tc decreased and the To remained constant at all AAP. Below To , the median base water potentials (ψb (50)) were -1.07, -0.73, -0.48 and -0.39MPa for the AAP levels of 0, 24, 36 and 48h, respectively. These values were more negative when germination occurred in salt solutions (the base NaCl concentrations converted to ψ were -1.25, -0.81, -0.51 and -0.41MPa, respectively), due to uptake of salt ions. Thresholds became more positive above To and reached zero at Tc in all AAP. Seed osmotic adjustment capacity declined linearly with increasing AAP while the conductivity of seed leachates increased in association with the loss of seed vigour. Significant correlations between conductivity results and the parameters of HTT and HaloTT models suggest that they could be considered as effective descriptors of canola seed vigour.

Transcriptome and metabolite analysis reveal the drought tolerance of foxtail millet significantly correlated with phenylpropanoids-related pathways during germination process under PEG stress

BackgroundFoxtail millet [Setaria italica (L.) P. Beauv.] is an excellent crop known for its superior level of drought tolerance across the world. Especially, less water is needed during its germination period than the other cereal crops. However, the knowledge of the mechanisms underlying the abiotic stress effects on seed germination of foxtail millet is largely unknown.ResultsThe water uptake pattern of foxtail millet seeds was ploted during germination period, according to which the germination time course of millet was separated into three phases. We sequenced the transcriptome of foxtail millet seeds, which were treated by PEG during different germination phases after sowing. The transcriptional studies revealed that more DEGs were identified during the further increase in water uptake period (phase III) than during the rapid initial uptake period (phase I) and the plateau period (phase II) under PEG stress. The pathway analysis of DEGs showed that the highly enriched categories were related to phenylpropanoid biosynthesis, plant hormone signal transduction and phenylalanine metabolism during phase III. The 20 phenylpropanoids-related genes of germinating foxtail millet were found to be down-regulated during the further increase in water uptake period under PEG stress. Further expression analysis identified 4 genes of phenylalanine ammonia-lyase, 4-coumarate-CoA ligase 3, cinnamoyl-CoA reductase 1, cationic peroxidase SPC4 in phenylpropanoids-related pathway, which played important roles in foxtail millet in response to PEG stress during different germination periods. The studies of metabolites in phenylpropanoid biosynthesis pathway revealed that higher amount of cinnamic acid was accumulated in germinating seeds under PEG stress, while the contents of p-coumaric acid, caffeic acid, ferulic acid and sinapic acid were decreased. And the effects of five phenolic compounds on germination and growth of foxtail millet showed that 1 mM concentration of cinnamic acid inhibited shoot and root growth, especially root development. Ferulic acid, caffeic acid, sinapic acid and p-coumaric acid could increase the root length and root/sprout in lower concentration.ConclusionsThese findings suggest that key genes and metabolites of foxtail millet related with phenylpropanoids pathway may play prominent roles in the regulation of resistance to drought during germination. Foxtail millet can probably avoid drought by regulating the levels of endogenous allelochemicals.

Population-based threshold models: A reliable tool for describing aged seeds response of rapeseed under salinity and water stress

Rapeseed (Brassica napus L.; Brassicaceae) is the second largest source of oilseed crop which is used for food and industrial applications globally. The production of this plant will be affected by climate change, increasing heat, salt and water stresses, in the future. Therefore, this study aimed to quantify the seed germination responses of two spring (‘Dalgan’ and ‘Hyola 50′) and one winter (‘Ahmadi’) rapeseed cultivars with a range of seed vigor (artificially aged at 42 °C) under water and salt stresses using hydrotime and halotime models, respectively. Germination time courses were recorded and seed germination characteristics were calculated. Seed moisture content and electrical conductivity were measured and also osmotic adjustment value associated with accumulation of salt ions was estimated. Rapeseed germination was negatively influenced by the accelerated aging period (AAP), water potential (ψ) and salinity (NaCl concentration) in all cultivars (P < 0.01). The hydrotime and halotime models accurately describe rapeseed germination at a range of ψs and NaCls at each AAP, with R2 values of 0.80–0.96. The estimated median threshold water potential (ψb(50)) and salinity (NaClb(50)) were −1.291, −1.170 and −1.104 MPa and 373.3, 326.7 and 304.4 mM for Ahmadi, Dalgan and Hyola 50 cultivars at AAP = 0, respectively. With increasing AAP, the ψb(50) increased (become more positive) and NaClb(50) decreased (linearly in both), reached zero at 130, 85.5 and 77.3 h AAP. The ψb(50) estimated by the hydrotime model was higher after converting the NaCl concentrations to ψ as salt ions absorbed by the seeds in response to salt stress (–1.707, –1.455, –1.361 MPa, respectively). The highest osmotic adjustment value observed in Ahmadi (∼21−54 %, depending on AAP) than those obtained in other cultivars, suggesting that the seed mass/size is an effective factor for improving seed germination of rapeseed under saline conditions (r ≥ 0.86, osmotic adjustment value vs. seed mass). However, this value decreased linearly with AAP in all cultivars, reflecting the cell membrane damage and loss of seed vigor. It was confirmed by the increasing conductivity values at higher AAP. In conclusion, the models used in this study were able to accurately predict the rapeseed germination behavior at different levels of water and saline conditions.

Low temperature stimulates spatial molecular reprogramming of theArabidopsisseed germination programme

AbstractThe timing of the germination of seeds is highly responsive to inputs from the environment. Temperature plays a key role in the control of germination, with low temperatures acting to stimulate this developmental transition in many species. InArabidopsis, extensive gene expression changes have been reported at the whole seed level in response to cold, while much less is known about their spatial distribution across the diverse cell types of the embryo. In this study we examined the spatiotemporal patterns of promoter activity and protein abundance for key gibberellic acid (GA) and abscisic acid (ABA) factors which regulate the decision to germinate both during a time course of germination and in response to cold. Low temperature stimulated the spatial relocalization of these factors to the vasculature. The response of these seeds to dormancy-breaking stratification treatments therefore stimulates the distribution of both positive (GA) and negatively acting (ABA) components to this same cell type. This altered spatial pattern persisted following the transfer of seeds to 22°C, as well as after their rehydration, indicating that this alteration is persistent. These observations suggest that the vasculature plays a role in the low temperature-mediated stimulation of germination in this species, while novel cell types are recruited to promote germination in response to stratification.

Basic Features of the Analysis of Germination Data with Generalized Linear Mixed Models

Germination data are discrete and binomial. Although analysis of variance (ANOVA) has long been used for the statistical analysis of these data, generalized linear mixed models (GzLMMs) provide a more consistent theoretical framework. GzLMMs are suitable for final germination percentages (FGP) as well as longitudinal studies of germination time-courses. Germination indices (i.e., single-value parameters summarizing the results of a germination assay by combining the level and rapidity of germination) and other data with a Gaussian error distribution can be analyzed too. There are, however, different kinds of GzLMMs: Conditional (i.e., random effects are modeled as deviations from the general intercept with a specific covariance structure), marginal (i.e., random effects are modeled solely as a variance/covariance structure of the error terms), and quasi-marginal (some random effects are modeled as deviations from the intercept and some are modeled as a covariance structure of the error terms) models can be applied to the same data. It is shown that: (a) For germination data, conditional, marginal, and quasi-marginal GzLMMs tend to converge to a similar inference; (b) conditional models are the first choice for FGP; (c) marginal or quasi-marginal models are more suited for longitudinal studies, although conditional models lead to a congruent inference; (d) in general, common random factors are better dealt with as random intercepts, whereas serial correlation is easier to model in terms of the covariance structure of the error terms; (e) germination indices are not binomial and can be easier to analyze with a marginal model; (f) in boundary conditions (when some means approach 0% or 100%), conditional models with an integral approximation of true likelihood are more appropriate; in non-boundary conditions, (g) germination data can be fitted with default pseudo-likelihood estimation techniques, on the basis of the SAS-based code templates provided here; (h) GzLMMs are remarkably good for the analysis of germination data except if some means are 0% or 100%. In this case, alternative statistical approaches may be used, such as survival analysis or linear mixed models (LMMs) with transformed data, unless an ad hoc data adjustment in estimates of limit means is considered, either experimentally or computationally. This review is intended as a basic tutorial for the application of GzLMMs, and is, therefore, of interest primarily to researchers in the agricultural sciences.

Quantifying perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) seed germination responses to water potential and temperature with a hydrothermal time model

ABSTRACT In New Zealand, a commonly sown pasture combination is perennial ryegrass with white clover. The hydrothermal time model (HTT) was used to quantify germination under different temperature (T) and water potential (WP) conditions for white clover ‘Nomad’ and perennial ryegrass ‘Stellar AR1’. Seeds were germinated in vitro under a range of T × WP combinations, and HTT models were fitted to germination time course data. Rapid germination of white clover under optimum T and WP was reflected by a much lower value for its HTT constant compared with perennial ryegrass (10.8 vs 80.7 MPa °C d). However, the lower base water potential for perennial ryegrass (−1.29 vs −0.495 MPa) and a higher threshold temperature for thermoinhibition (21.8 vs 18.3°C), meant that predicted perennial ryegrass germination was more resilient in warm dry conditions. HTT models can be used to assist decisions about the timing of perennial ryegrass and white clover sowing.

Effect of salinity on seed germination of five mangroves from Sri Lanka: use of hydrotime modelling for mangrove germination

AbstractMangroves are highly adapted to extreme environmental conditions that occur at the interface of salt and fresh water. Adaptations to the saline environment during germination are a key to mangrove survival, and thereby, its distribution. The main objective of this research was to study the effect of salinity on seed germination of selected mangrove species and the application of a hydrotime model to explain the relationship between water potential of the medium and rate of seed germination. Germination of seeds was examined at 15, 25 and 35°C in light/dark over a NaCl gradient. Germination time courses were prepared, and germination data were used to investigate whether these species behave according to the principles of the hydrotime model. The model was fitted for the germination of Acanthus ilicifolius seeds at 25°C. Final germination percentage was significantly influenced by species, osmotic potential and their interaction at 25°C. Moreover, temperature had a clear effect on seed germination (Sonneratia caseolaris and Pemphis acidula) which interacted with osmotic potential. Only A. ilicifolius seeds behaved according to the hydrotime principles and thus its threshold water potential was –1.8 MPa. Optimum germination rates for seeds of the other species occurred at osmotic potentials other than 0 MPa. The descending order of salinity tolerance of the tested species was Aegiceras corniculatum &gt; Sonneratia caseolaris &gt; Acanthus ilicifolius &gt; Pemphis acidula &gt; Allophylus cobbe, suggesting that the viviparous species (A. corniculatum) is highly salt tolerant compared with the non-viviparous species. The results revealed that seeds of the study species exhibited facultative halophytic behaviour in which they can germinate over a broad range of saline environments. Use of a hydrotime model for mangroves was limited as germination of their seeds did not meet model criteria.

Quantification of Retama raetam seed germination response to temperature and water potential using hydrothermal time concept

Retama raetam (Forssk Webb; Fabaceae) is a xerophytic shrub that is distributed from northern to southern Tunisia and which is of interest for medical use and for revegetation. To quantify seed germination responses of R. raetam to temperature (T) and water potential (ψ), and to determine cardinal Ts, a hydrothermal time model (HTT) was used. The experiment was conducted at six constant Ts (5, 10, 15, 20, 25, and 30 °C) at each of the following ψs (0, –0.3, –0.7 and −1 MPa; provided by PEG 6000). Results showed that germination rate (GR) and germination percentage (GP) were significantly influenced by ψ, T and their interactions (P < 0.01). Cardinal Ts for R. raetam was 4.2 °C for Tb (the base T), 17 °C for To (the optimum T) and 30 °C for Tc (the ceiling T) in the control condition (0 MPa). The Td (the T at which ψb(50) starts to change) was estimated to be 10 °C. By increasing T to To, hydrotime constant (θH) decreased nonlinearly and then stabilized to 30 MPa °C h at Ts ranging from 15 to 30 °C. The study showed that when the HTT model is applied, it can accurately describe the time course of germination across all Ts and ψs for this plant (R2 = 0.90). Moreover, estimated parameters using HTT model were 388.6 MPa °C h for the hydrothermal time constant (θHTT), –0.913 MPa for the base water potential (ψb(50)) and 0.047 MPa °C h for the kT (the slope of the relationship between ψb(50) and T ≥ Td). The parameters presented in this study can easily be used in R. raetam SG simulation models for characterizing the physiological status of R. raetam seed populations and also for predicting germination time courses of this plant under different environmental conditions.

Effects of temperature and water limitation on the germination of Stipagrostis ciliata seeds collected from Sidi Bouzid Governorate in Central Tunisia

Most ecological studies in North Africa reveal a process of continuous degradation of rangeland ecosystems as a result of overgrazing. This degradation appears across the decreasing of perennial grass diversity. Indeed, the majority of steppe ecosystems are characterized by a low density of perennial grass species at present. This study evaluated the effects of temperature and water limitation on the seed germination of Stipagrostis ciliata (Desf.) de Winter, a perennial grass species. The seeds were collected from the Bou Hedma Park, Sidi Bouzid Governorate, Central Tunisia. The thermal time and hydrothermal time models were used to describe the seed germination of S. ciliata under different water potentials and temperatures. The germination response of S. ciliata seeds in darkness was evaluated over a range of temperatures (15°C, 20°C, 25°C, 30°C and 35°C) and across a wide range of osmotic potentials (0.0,–0.2,–0.6,–1.2,–1.6 and –2.0 MPa) of the polyethylene glycol (PEG6000) solutions at each temperature level. Among the tested temperatures, 25°C was found to be the optimal temperature to the germination of S. ciliata seeds. The final germination percentage (75.2%) was obtained with distilled water. The progressive decrease of osmotic potential of the PEG6000 solutions inhibited the seed germination. However, the number of days to first germination was increased with a reduction of osmotic potential. A significant positive relationship was identified between final germination percentage of S. ciliata seeds and osmotic potential of the PEG6000 solutions, with R2 ranging from 0.5678 to 0.8761. Furthermore, a high degree of congruency between predicted and observed germination time course curves was observed. In general, S. ciliata exhibits a significant adaptation capacity for water limitation and high temperature in arid ecosystems.

Application of hydrotime model to predict early vigour of rapeseed (Brassica napus L.) under abiotic stresses

Rapeseed (Brassica napus L.) is important for edible oil production in semi-arid areas. Abiotic stresses are threatening rapeseed production in such areas. This study was conducted to find tolerant genotypes of rapeseed and to determine which traits of crop establishment is related to abiotic stress tolerance. Hydrotime model parameters were determined in a laboratory germination test, and seedling emergence and growth were evaluated in pot experiments under control, drought, salinity, deep sowing, low and high temperatures for 19 rapeseed genotypes. Results indicated that the predicted germination time courses at the various water potentials generally fitted well with the observed germination data. The estimated values of θ H, ψb(50), and σψb differed significantly across genotypes. Seedling emergence and growth differed significantly under each environmental condition. PCA showed that genotypes of Hayola 401 and line 285 were the most tolerant to abiotic stresses during crop establishment and seedling growth. The first PC explained 40% of variations, and a correlation was observed between PC1 and ψb(50). Correlations among hydrotime model parameters and early seed vigour variables indicated that ψb(50) negatively correlated with seedling emergence percentage and rate (day−1) under all abiotic stresses. It shows that genotypes with more negative values of ψb(50) have more seedling emergence percentage and a larger seedling emergence rate (days−1) under a wide range of environmental conditions. Thus, it can be concluded that, to identify tolerant genotypes of rapesee to abiotic stresses, ψb(50) is a good trait and that breeders can focus on reducing ψb(50) to increase tolerance of abiotic stresses.

Analysis of multiple mass spectrometry images from different Phaseolus vulgaris samples by multivariate curve resolution

A new procedure based on the simultaneous analysis of multiple mass spectrometry images using multivariate curve resolution is presented in this work. Advantages of the application of the proposed approach are shown for three cases of plant studies demonstrating its potential usefulness in metabolomics studies, particularly in lipidomics. In the first dataset, a three stage germination time course process of green bean seeds is presented. The second example is a dose-response study where the stem bases of a non-exposed plant are compared to those of plants exposed to increasing concentrations of the pesticide chlorpyrifos. Finally, the third study is the simultaneous analysis of several sequential transversal and longitudinal cuts of the same green bean plant stem segment.The analysis of these three examples required the comprehensive adaptation of different chemometric methodologies including data compression by selection of the regions of interest (ROI strategy), appropriate data normalization and baseline correction, all of them before MCR-ALS simultaneous image analysis of multiple samples and post processing of the achieved results. MCR-ALS resolved components provided spatial information about the changes in the spatial composition and distribution of the different lipids on the surface of the investigated samples. These results enabled the identification of single lipids and the clustering of those lipids that behaved similarly in the different images simultaneously analyzed. The proposed strategy for MSI analysis represents a step forward in the simultaneous analysis of multiple sets of images providing an improved recovery of both spatial and structural information in environmental and biomedical studies.

Proteomic Analysis Reveals Different Involvement of Embryo and Endosperm Proteins during Aging of Yliangyou 2 Hybrid Rice Seeds.

Seed aging is a process that results in a delayed germination, a decreased germination percentage, and finally a total loss of seed viability. However, the mechanism of seed aging is poorly understood. In the present study, Yliangyou 2 hybrid rice (Oryza sativa L.) seeds were artificially aged at 100% relative humidity and 40°C, and the effect of artificial aging on germination, germination time course and the change in protein profiles of embryo and endosperm was studied to understand the molecular mechanism behind seed aging. With an increasing duration of artificial aging, the germination percentage and germination rate of hybrid rice seeds decreased. By comparing the protein profiles from the seeds aged for 0, 10 and 25 days, a total of 91 and 100 protein spots were found to show a significant change of more than 2-fold (P < 0.05) in abundance, and 71 and 79 protein spots were identified, in embryos and endosperms, respectively. The great majority of these proteins increased in abundance in embryos (95%) and decreased in abundance in endosperms (99%). In embryos, most of the identified proteins were associated with energy (30%), with cell defense and rescue (28%), and with storage protein (18%). In endosperms, most of the identified proteins were involved in metabolism (37%), in energy (27%), and in protein synthesis and destination (11%). The most marked change was the increased abundance of many glycolytic enzymes together with the two fermentation enzymes pyruvate decarboxylase and alcohol dehydrogenase in the embryos during aging. We hypothesize that the decreased viability of hybrid rice seeds during artificial aging is caused by the development of hypoxic conditions in the embryos followed by ethanol accumulation.

Single-seed oxygen consumption measurements and population-based threshold models link respiration and germination rates under diverse conditions

AbstractSeed germination is responsive to diverse environmental, hormonal and chemical signals. Germination rates (i.e. speed and distribution in time) reveal information about timing, uniformity and extent of germination in seed populations and are sensitive indicators of seed vigour and stress tolerance. Population-based threshold (PBT) models have been applied to describe germination responses to temperature, water potential, hormones, ageing and oxygen. However, obtaining detailed data on germination rates of seed populations requires repeated observations at frequent times to construct germination time courses, which is labour intensive and often impractical. Recently, instruments have been developed to measure repeatedly the respiration (oxygen consumption) of individual seeds following imbibition, providing complete respiratory time courses for populations of individual seeds in an automated manner. In this study, we demonstrate a new approach that enables the use of single-seed respiratory data, rather than germination data, to characterize the responses of seed populations to diverse conditions. We applied PBT models to single-seed respiratory data and compared the results to similar analyses of germination time courses. We found consistent and quantitatively comparable relationships between seed respiratory and germination patterns in response to temperature, water potential, abscisic acid, gibberellin, respiratory inhibitors, ageing and priming. This close correspondence between seed respiration and germination time courses enables the use of semi-automated respiratory measurements to assess seed vigour and quality parameters. It also raises intriguing questions about the fundamental relationship between the respiratory capacities of seeds and the rates at which they proceed toward completion of germination.