Low Germination Temperatures Research Articles

Seed Germination Characteristics of a Critically Endangered Evergreen Oak—Quercus marlipoensis (Fagaceae) and Their Conservation Implications

Seed germination is among the most crucial and vulnerable stages in plant life cycles. Quercus marlipoensis is a critically endangered sclerophyllous oak. Only one population has ever been found worldwide in the tropical montane cloud forests of southeastern Yunnan, China, and it has shown difficulties with regeneration. However, its seed biological traits and key restrictive germination factors remain unknown. We investigate the impacts of scarification, temperature, and water potential on the seed germination of Q. marlipoensis. Results show that the seeds show typical epicotyl dormancy. The seed germination increased when removing part or all of the pericarp and part of the cotyledon (one-third and two-thirds). The seeds can germinate at 5 to 30 °C, but the highest T50 was achieved at 25 °C. When the water potential decreased from 0 to −1.0 MPa, the germination rate decreased but the germination time increased. Q. marlipoensis seeds are typically recalcitrant and highly sensitive to moisture loss, but the species can tolerate animal predation and low germination temperatures. The more frequent climatic extremes and droughts in the Indo-China region will severely degrade its natural habitats. Therefore, ex situ conservation to preserve its germplasm and introduce seedlings into a suitable habitat are essential for its conservation management.

Seed Priming Improves Enzymatic and Biochemical Performances of Rice During Seed Germination under Low and High Temperatures

As an abiotic stress, adverse germination temperatures cause serious disruptions in physiological and biochemical processes involved in seed germination. Using a factorial experiment, we examined the effects of different seed priming treatments on enzymatic and biochemical performances of rice seed germination under different temperatures. Each of the rice genotypes (Hashemi, Sadry-domsefid, IRON-70-7053-7 and NORIN-22) was primed with hydro-hardening, KCl, CaCl2 and ascorbic acid (AsA) and without a priming agent as a control at low (15 ºC), optimum (25 ºC) and high (35 ºC) germination temperatures. The results showed that the enzymatic and biochemical performances of all the rice genotypes were affected by the seed priming agents, especially under the low germination temperature. At 15 ºC, seed priming with AsA was found to be the best agent for the activities of amylase, α-amylase, catalase (CAT), peroxidase (POX), ascorbate peroxidase (APOX) and superoxide dismutase (SOD) as well as the content of soluble sugars in the NORIN-22 genotype, and for protease activity and soluble protein content in the IRON-70-7053-7 genotype. SOD at the low germination temperature and CAT, POX and protease at the optimum and high germination temperatures were the most important enzymes in occurrence of germination potential in terms of seedling length, vigor index, normal seedling rate and germination rate. Under the priming agents, the highest changes in normal seedling rate were observed at the low and optimum germination temperatures by AsA priming in the Hashemi and NORIN-22 genotypes, and at the high germination temperature under KCl priming in the Hashemi genotype.

MAPK11 regulates seed germination and ABA signaling in tomato by phosphorylating SnRKs.

Seed germination is a critical stage in the plant life cycle and it plays an important role in the efficiency of agricultural production. However, our knowledge of the mechanisms that regulate seed germination remains limited. In this study, we identified a novel gene, MAPK11, that encodes mitogen-activated protein kinase 11; its expression was significantly higher in seeds of tomato varieties with a low optimum germination temperature than in those with a high optimum germination temperature. In tests at 25 °C, overexpression of MAPK11 in an accession with optimum germination at 25 °C resulted in a decrease in germination, whereas RNAi of MAPK11 in an accession with optimum germination at 15 °C resulted in increased germination. Furthermore, we found that lines overexpressing MAPK11 exhibited hypersensitivity to ABA during germination. These observations were at least partially explained by the fact that MAPK11 up-regulated both NCED1 expression and ABA biosynthesis, and that it also affected ABA signaling and negatively regulated germination by influencing the phosphorylation of SnRK2.2 in vivo. In addition, we found that MAPK11 interacts with and phosphorylates SnRK1 in vivo, thereby potentially inhibiting its activation. SnRK1 interacted with ABI5 and suppressed the transcription of ABI5, thereby affecting ABA signaling and the regulation of germination. Our results demonstrate that ABA signaling in tomato is affected by a mechanism that depends on MAPK11 phosphorylating SnRKs, and this ultimately influences seed germination.

Gene expression and genetic control to cold tolerance during maize seed germination

BackgroundThe study of cold tolerance in maize seeds and seedlings through physiological quality assessments, as well as the genetic control associated with this trait, allows an early characterization of genotypes. Here we studied the genetic control for cold tolerance during the germination process in maize seeds and genes influenced by this stress.ResultsSix maize lines were used, three classified as tolerant and three as susceptible to low germination temperature. A field was developed to produce the hybrid seeds, in a partial diallel scheme including the reciprocal crosses. For the expression analysis, seeds from two contrasting lines were used, as well as their hybrid combination and their reciprocal crosses, on dried and moistened seeds at 10 °C for 4 and 7 days. It was evaluated the catalase (CAT) and esterase (EST) enzymes, heat-resistant proteins and the genes Putative stearoyl-ACP desaturase (SAD), Ascorbate Peroxidase (APX), Superoxide Dismutase (SOD) and Mitogen Activated Protein Kinase (ZmMPK5). The estimated values ​​for heterosis, general and specific combining abilities and reciprocal maternal and non-maternal effects were carried out and it showed that there is heterosis for germination at low temperatures, also the non-additive genes were more important and there was a reciprocal effect.ConclusionsThere is a greater expression of the CAT and EST enzymes in moistened seeds at seven days and there is less expression of heat-resistant proteins and the SAD gene at seven days of moistening. Also, there are variations in the expression of the APX, SOD and ZmMPK5 genes in dried and moistened seeds, as well as among the genotypes studied.

Effect of Soil Temperature in the Emergence of Maize Seeds

Temperature is one of the most important factors in the germination process, which influences the absorption of nutrients required for growth and development of the plant, germination uniformity, and seed vigor maintenance. Low temperatures can result in deformation of the leaves and the apex of the plant, and high temperatures hamper the development of them. The objective of this work was to evaluate the ideal temperature values for germination in each genetic material used, highlighting the most suitable for each condition. The experiment was conducted at the Central Seed Laboratory at the Department of Agriculture of the Lavras Federal University, where germination percentage, first germination count, seedling emergence and emergence speed were evaluated. The experimental design was completely randomized, with a factorial scheme of 4 × 5, in which it was analyzed four lines (L30, L64, L63, and L91) at five different germination temperatures (15, 20, 25, 30 and 35 ºC). An analysis of variance was done and for the comparison between means, the Scott Knott test was used, at a 5% probability. It can be observed that the lines L63 and L91 were more susceptible to low germination temperatures and lines L30 and L64 do not tolerate high temperatures. Also, the evaluation of temperature-controlled substrate germination proved to be a promising technique to identify tolerant and susceptible lines for germination in both high and low temperatures.

English

The study was conducted on dry maize seed and seed subjected to sub optimal germination temperature. Four lines of maize seeds were used, two were classified as susceptible to low temperature (44 and 54) and two tolerant to low temperature (64 and 91°C). Water content and germination tests were performed at different temperatures (10 and 25°C) to evaluate the physical and physiological quality of maize seeds. For molecular study, activity of heat-resistant proteins, esterase, superoxide dismutase, catalase and α-amylase enzymes were assessed. Study of AOX1, ZmMPK5, SOD, APX, SAD, ENR and LEA genes with real time polymerase chain reaction (PCR) were carried out. AOX, SAD and LEA genes that are related as tolerant to abiotic stress showed higher expression in line 64, which was classified as tolerant to low germination temperature. The ZmMPK5 gene is associated with increased production of abscisic acid and expressed more in line 54, which was considered as susceptible to low germination temperature.  Key words: Zea mays, seed vigor, abiotic stress.

Multiple paths to similar germination behavior in Arabidopsis thaliana

Germination timing influences plant fitness, and its sensitivity to temperature may cause it to change as climate shifts. These changes are likely to be complex because temperatures that occur during seed maturation and temperatures that occur post-dispersal interact to define germination timing. We used the model organism Arabidopsis thaliana to determine how flowering time (which defines seed-maturation temperature) and post-dispersal temperature influence germination and the expression of genetic variation for germination. Germination responses to temperature (germination envelopes) changed as seeds aged, or after-ripened, and these germination trajectories depended on seed-maturation temperature and genotype. Different combinations of genotype, seed-maturation temperature, and after-ripening produced similar germination envelopes. Likewise, different genotypes and seed-maturation temperatures combined to produce similar germination trajectories. Differences between genotypes were most likely to be observed at high and low germination temperatures. The germination behavior of some genotypes responds weakly to maternal temperature but others are highly plastic. We hypothesize that weak dormancy induction could synchronize germination of seeds dispersed at different times. By contrast, we hypothesize that strongly responsive genotypes may spread offspring germination over several possible germination windows. Considering germination responses to temperature is important for predicting phenology expression and evolution in future climates.

Future challenge for endangered arable weed species facing global warming: Low temperature optima and narrow moisture requirements

As a result of the intensification of agriculture in Central Europe, many arable weed species have declined. Global climate change may further challenge the adaptability of arable weeds since plants may be more often subjected to higher temperatures and lower soil moisture during the germination period.A climate chamber experiment analysed the response of four familial pairs of common and endangered arable weeds from Germany. To this end we used a large range of temperatures and water potentials to assess specific traits defining their germination requirements. Using a simple response surface approach, we predicted germination response under three climate change scenarios.Results supported our expectation that endangered species, owing to their narrow germination requirements, may be more negatively affected by global warming than common species. Endangered species germinated significantly less than the common arable weeds, except at very low temperatures (3°C and 5°C). The preference of endangered arable weed species for low germination temperatures was confirmed by their low optimal germination temperature (15.8°C±0.4). In contrast, common species germinated at significant higher temperatures (optimal temperature 18.4°C±0.2), had a significantly wider range of germination temperature (endangered: 24°C±3.5, common: 31°C±0.5) and were also more flexible towards changes in water potential.Calculations based on response surfaces for three climate change scenarios indicated that endangered arable weed species may benefit less from climate warming than common species.

The dynamics of acid-soluble phosphorus compounds in the course of winter and spring wheat germination under various thermic conditions. Part II. Labile phosphorus after hydrolysis of the acid-soluble fraction

The changes in labile phosphorus compounds content during germination of wheat were investigated. These compounds were determined in acid-soluble germ extracts separated into fractions according to the solubility of their barium salts. Low germination temperature was found to raise the labile phosphorus content in the fraction of insoluble barium salts. If we assume that labile P of this fraction consisted mainly of adenosinedi- and triphosphates, it would seem that the rise, in the ATP and ADP level under the influence of low temperature may be essential for initiating flowering in winter varieties.

Investigation of the Germination of Barley and Wheat Grains with a Design of Experiments for the Production of Hydrolases.

The production of hydrolases from cereals has been examined in order to investigate food-derived enzymes as an alternative source to microbial enzymes for the use in food processes. For that, the influence of temperature on the pretreatment, imbibition and germination of barley and wheat grains was determined by measuring the β-glucosidase, β-galactosidase and lipase activities using a design of experiments. The evaluation of the statistical model showed an increase of the β-glucosidase activity with low imbibition and low germination temperature for barley grains and low imbibition and high germination temperature for wheat grains. The maximum β-glucosidase activity in wheat extracts was (585±151) nkat per g of dry mass (dm), while in barley extracts it was (109±15) nkat per g of dm. The maximum β-galactosidase activities in barley and wheat extracts were (34±12) and (63±23) nkat per g of dm, respectively. The maximum lipase activities of (6.7±0.1) and (4.6±4.4) nkat per g of dm in barley and wheat extracts, respectively, were rather low compared to the glycosidase activities. The extracts were also tested for other hydrolase activities (e.g. peptidase and α-amylase activities). The insights obtained enable the basis for the potential use of cereal hydrolases in food processing, which might be attractive to consumers.

Expression of genes related to tolerance to low temperature for maize seed germination

The aim of this study was to characterize maize lines tolerant to cold temperatures during the germination process. Seeds from lines with different levels of tolerance to low temperatures were used; 3 lines were classified as tolerant and 3 as susceptible to low germination temperatures. A field was set up to multiply seeds from selected lines. After the seeds were harvested and classified, we conducted physiological tests and analyzed fatty acid content of palmitic, stearic, oleic, linoleic, linolenic, and eicosenoic acids. In proteomic analysis, the expression of heat-resistant proteins, including catalase, peroxidase, esterase, superoxide dismutase, and α-amylase, were evaluated. Transcript analysis was used to measure the expression of the genes AOX1, AOX2, ZmMPK-17, and ZmAN-13. The material showing the highest susceptibility to low germination temperatures contained high saturated fatty acid content. Expression of α-amylase in seeds soaked for 72 h at a temperature of 10°C was lower than expression of α-amylase when soaked at 25°C for the same amount of time. We observed variation in the expression of heat-resistant proteins in seeds of the lines evaluated. The genes AOX and Zm-AN13 were promising for use in identifying maize materials that are tolerant to low germination temperatures.

Mapping QTLs for grain dormancy on wheat chromosome 3A and the group 4 chromosomes, and their combined effect

A major QTL for grain dormancy, QPhs.ocs-3A.1, derived from the highly dormant wheat Zenkoujikomugi (Zen), has been identified in a study made under a controlled environment. Further investigations were needed to dissect the precise position and expression of QPhs.ocs-3A.1 under different field conditions because the ability to detect genetic loci for grain dormancy traits is compromised by environmental effects and genotype/environment interactions. Group 4 chromosomes have also been shown to be possible sites of QTLs for grain dormancy. The objectives of this study were (1) to locate additional molecular markers in the QPhs.ocs-3A.1 region, (2) to identify QTLs on the group 4 chromosomes and (3) to elucidate their combined effects. We examined the recombinant inbred lines (RILs) from a cross between Chinese Spring (CS) and Zen over a 3-year period in one location and 1 year in a different location. In an interval mapping study QPhs.ocs-3A.1 was mapped to within the 4.6 cM region flanked by Xbarc310 and Xbcd907 at the proximal end of the short arm of chromosome 3A. QPhs.ocs-3A.1 was confirmed to be the predominant dormancy QTL since it explained a large portion (11.6-44.8%) of the phenotypic variation, and was strongly displayed under dormancy-breaking conditions or at low germination temperatures. For QPhs.ocs-4A.1, identified on the long arm of chromosome 4A, and QPhs.ocs-4B.1, on the centromeric region of the long arm of Chr 4B, the LOD peak positions and the desirable allele were consistent between the trials, while the LOD scores and contribution to the phenotypic variation varied. Transgressive segregants were observed among the 125 RILs and most of them had a combination of the three alleles conferring a higher dormancy: the Zen alleles at QPhs.ocs-3A.1 and QPhs.ocs-4A.1 and the CS allele at QPhs.ocs-4B1. This demonstrated a combined effect of the desirable alleles on accelerating grain dormancy, with their total effect being superior to that of Zen.

Effects of desiccation and a change in temperature on germination of immature grains of wheat (Triticum aestivum L.)

A study was made of the effects of desiccation and a change in temperature on the germination of wheat grains harvested 20 days after anthesis. When the germination test was performed immediately after harvesting, germination percentages ranged from 5.2% to 10.7%. Germination percentages increased to 48.2% to 90.3% after grain had been desiccated at 20 °C and then hydrated at 10 °C. This increase occurred even if grains had been desiccated in an atmosphere of high relative humidity. The germination percentage of non-desiccated grains depended on the germination temperature. When the pericarp and testa were removed from embryos, the germination percentage of grains incubated at 20 °C and then at 10 °C was higher than that of grains incubated at 10 °C. In general, a low germination temperature is believed to be effective in breaking dormancy of wheat grains. However, a change in temperature stimulated germination to a greater extent than a constant low temperature. The germination percentage of 5-day cycle alternating temperature was greater than that with 1-day, 2-day and 10-day cycles. Although the germination of immature wheat grains was stimulated by both high and low germination temperatures, it is likely that cycles shorter and, also, longer than a critical period induce limited germination. Loss of dormancy commonly occurs when development of wheat grains proceeds at a high temperature, with imbibition at a low temperature. However, germination ability of non-desiccated immature wheat grain was enhanced by a change in temperature during germination.

THE EFFECT OF HEAT TREATMENT OF WATERMELON SEED ON GERMINATION, HYPOCOTYL EMERGENCE AND ABSCISIC ACID CONTENT

Seeds of watermelon (Citrullus lanatus) with a moisture content of 7.2% were heat treated at 60°C for 15 or 20 h, and their performances compared with that of untreated seeds. Radicle emergence of treated seeds was only slightly lower than that of the control when germinated at 25°C. To ascertain the effect of the treatments on hypocotyl growth (emergence) per se, radicle emergence was synchronized in all treatments and emergence from deep plantings in sand determined. Small differences in emergence were observed when seeds were germinated at 25°C, but seed treatment resulted in large reductions in emergence at 15°C. This demonstrates that the hypocotyls developing from heat-treated, germinated seeds are less able to withstand low germination temperatures, which could be an important factor in emergence failure. Levels of free abscisic acid (ABA) were higher at 15°C than at 25°C, with hypocotyls of treated seeds containing more free ABA and its breakdown products than the control at the lower temperature.

Variation in temperature requirements for germination and early seedling root development in Chamaecrista rotundifolia and three allied species.

Two experiments are discussed. In the first, rates of root elongation during the first four days of growth at 25 °C were studied in Chamaecrista rotundifolia (34 accessions), C. nictitans (2 accessions), C. pilosa (1 accession) and C. serpens (3 accessions). In the second, a comparison was made of germination characteristics of 14 accessions of C. rotundifolia and one of C. pilosa at nine constant temperatures (11–27 °C). Entries included accessions from a wide latitudinal range. There were statistically significant differences in root length on all four days of measurement. No accession had significantly longer roots than the commercial cultivar cv. Wynn on day 1, but over the following three days, 4, 10 and 13 accessions had significantly longer roots, respectively. Root length on day 4 was positively correlated with latitude of origin. In the second experiment, maximum germination occurred at 25.5–27 °C, with progressively lower percentages at lower temperatures. There were highly significant differences between accessions at each temperature (P<0.001), and a highly significant accession × temperature interaction. No accession had a higher germination percentage than cv. Wynn at any temperature. Percentage mortality differed significantly (P<0.05) at all temperatures except 27 °C. Mortality at low temperature was negatively correlated with latitude of provenance. Increased temperatures up to 22.5 °C reduced the time taken to reach 50% of maximum germination (T50), and thereafter it was reasonably constant. With one exception (22.5 °C), no accession germinated significantly more quickly than cv. Wynn, and at 13 °C cv. Wynn germinated significantly more rapidly than all other entries. Over all temperatures, there was a significant negative correlation between days to 50% germination and latitude of provenance. Estimated base temperature for germination (Tb) ranged from 10.6 °C to 13.6 °C. Tb was positively correlated with latitude of provenance. It is argued that accessions from higher latitudes have developed mechanisms for survival of soft seed at low temperatures, low base germination temperature, germination rates and root elongation rates that adapt them to an environment with summer-dominant rainfall and winters which are too cool to support growth.

Germination depth vs. temperature requirements in naturally dispersed seeds of Leucospermum cordifolium and L. cuneiforme (Proteaceae)

Myrmecochory (ant dispersal) and the requirement for both low and high diurnal soil temperatures during seed germination after fire, are important ecological determinants in the seedling recruitment phase of Leucospermum R. Br. species. A crucial unknown parameter linking these two factors is the effective burial depth (i.e. germination depth) of seeds stored in the subterranean seed bank. The germination depth of seedlings was effectively determined in a nursery trial by measuring the length of the hypocotyl between the radicle end and ground level. Using this method the germination depth of Leucospermum cordifolium (Salisb. ex Knight) Fourcade and L. cuneiforme (Burm. f.) Rourke seedlings emerging during winter, after summer burns in three localities was estimated. Average estimated germination depths varied between 30 and 45 mm. Daily minimum and maximum temperatures were measured at various soil depths during winter in burnt and unburnt mesic mountain fynbos. Temperatures measured at 10, 20 and 40 mm depths during winter were close to the known optimum daily low and high germination temperatures in L. cordifolium , in burnt fynbos, but not in unburnt fynbos. These temperatures in burnt fynbos prevailed especially during early winter. It was concluded that a high proportion of the Leucospermum cordifolium seed bank will germinate only during the first early winter following a fire. Other aspects of natural seed dispersal were studied. These included seedling dispersal numbers and patterns around burnt mother plants. Evidence for seed dispersal and burial by ants was found.

Germination Promotor and Inhibitor in Leachates from Tomato Seeds1

Abstract The leachate from seed of tomato (Lycopersicon esculentum Mill., PI 341984), an accession whose seeds germinate well at low temperatures, promoted the germination of seeds of the same and other tomato cultivars. The leachate from ‘Red Rock’ seed, a cultivar whose seeds germinate poorly at low temperatures, inhibited the germination of seeds of the same and other tomato cultivars. The promotive and inhibitory effects of these leachates on seed germination is apparently highly specific and restricted to tomato seeds. The activity was highest in fresh seeds and the responses were best exhibited at low germination temperatures.

Influence of temperature on seed dormancy in lettuce

In certain lettuce cultivars seed dormancy occurs. Research on the influence of temperature on the occurrence of this dormancy was carried out with the cultivars ‘Magiola’, ‘Portato’, ‘Deci-Minor’ and ‘Valore’, the first 2 with seed dormancy, the last 2 without. The optimum germination temperature for the expression of seed dormancy was found to be between 23 and 26°C. By temperature treatments of dry seeds a better expression of the genotype for seed dormancy could sometimes be obtained. A temperature of 30°C during seed formation did not result in dormancy. Temperatures from 23 to 17°C and certain day and night temperatures such as 30°C/20°C resulted in much dormancy. During their later phases of development, seeds are sensitive to these temperatures. There are indications that no qualitative differences exist between dormancy which occurs at rather low germination temperatures and dormancy occurring at high temperatures. Between cultivars, only quantitative differences for dormancy seem to occur.

Secondary Dormancy in Cotton1

This study was undertaken to evaluate the effect of low temperature and high soluble salts on the germination of cotton (Gossypium hirsutum L.) seeds. Stress conditions consisting of either low germination temperature (13 C) or high concentrations of soluble salts (18,000 ppm) in the germination substrate, induced a secondary dormancy in newly harvested cotton seeds. Seeds from seven cotton‐producing states responded similarly, and dormancy under identical conditions decreased as the seeds aged. Three‐year‐old seeds showed little or no dormancy under either salt or cold germination conditions.