Seed Dormancy Mechanisms Research Articles

Integrated analyses provide insights into the seed dormancy mechanisms of the endangered plant Sinojackia sarcocarpa.

Sinojackia sarcocarpa, an endangered ornamental plant endemic to China, faces germination challenges that contribute to its endangered status. The mechanisms of its seed dormancy are not well understood. This study used morphological, physiological, transcriptomic, and gene function analyses to investigate these mechanisms. Our research shows that seed dormancy in Sinojackia sarcocarpa involves both physical and physiological factors. We found that removing the hard endocarp and applying gibberellic acid can effectively break dormancy. Transcriptomic analysis identified 2218 up-regulated and 374 down-regulated genes during germination. Notably, DOG1-domain genes SsDOGL4, SsTGA9, and SsTGA10 were significantly downregulated, while SsDOG1 was not. Additionally, overexpression of SsDOGL4 in Arabidopsis endosperm was found to enhance seed dormancy. Collectively, these findings offer significant insights into the mechanisms underlying seed dormancy in this endangered plant species.

Unraveling the role of PlARF2 in regulating deed formancy in Paeonia lactiflora.

PlARF2 can positively regulate the seed dormancy in Paeonia lactiflora Pall. and bind the RY cis-element. Auxin, a significant phytohormone influencing seed dormancy, has been demonstrated to be regulated by auxin response factors (ARFs), key transcriptional modulators in the auxin signaling pathway. However, the role of this class of transcription factors (TFs) in perennials with complex seed dormancy mechanisms remains largely unexplored. Here, we cloned and characterized an ARF gene from Paeonia lactiflora, named PlARF2, which exhibited differential expression levels in the seeds during the process of seed dormancy release. The deduced amino acid sequence of PlARF2 had high homology with those of other plants and contained typical conserved Auxin_resp domain of the ARF family. Phylogenetic analysis revealed that PlARF2 was closely related to VvARF3 in Vitis vinifera. The subcellular localization and transcriptional activation assay showed that PlARF2 is a nuclear protein possessing transcriptional activation activity. The expression levels of dormancy-related genes in transgenic callus indicated that PlARF2 was positively correlated with the contents of PlABI3 and PlDOG1. The germination assay showed that PlARF2 promoted seed dormancy. Moreover, TF Centered Yeast one-hybrid assay (TF-Centered Y1H), electrophoretic mobility shift assay (EMSA) and dual-luciferase reporter assay analysis (Dual-Luciferase) provided evidence that PlARF2 can bind to the 'CATGCATG' motif. Collectively, our findings suggest that PlARF2, as TF, could be involved in the regulation of seed dormancy and may act as a repressor of germination.

Low‐cost tools for large‐scale seed scarification: efficiency in two species from South American arid lands

The use of native plants for arid land restoration requires the application of pre‐germination treatments to alleviate seed dormancy mechanisms. As it is known, scarification allows several valuable species to overcome the primary forms of dormancy. However, supplying large quantities of scarified seeds at a low cost represents a significant challenge. In this context, our objective was to evaluate locally constructed machines accessible to people of degraded lands in a state of poverty. The effectiveness was evaluated by comparing two native shrubs from South American arid lands, Larrea divaricata and L. cuneifolia. Four treatments were applied: control (T0), mechanical scarification with a hand drill equipped with sandpaper on its head (T1), and mechanical scarification for 15 seconds (T2) and 30 seconds (T3) with a self‐constructed machine, capable of regulating pressure and speed. For both species, the germination probability was higher with T2 (0.82 ± 0.02) compared to T0 (0.28 ± 0.03) and T1 (0.65 ± 0.03). T3 presented intermediate values (0.75 ± 0.03) but did not differ significantly from T1 and T2. Our results show the effectiveness of a locally constructed seed scarification tool to upscale seed‐based restoration in arid lands.

Transcriptome and Proteome Co-Profiling Offers an Understanding of Pre-Harvest Sprouting (PHS) Molecular Mechanisms in Wheat (Triticum aestivum).

While wheat (Triticum aestivum L.) is a widely grown and enjoyed crop, the diverse and complex global situation and climate are exacerbating the instability of its supply. In particular, pre-harvest sprouting (PHS) is one of the major abiotic stresses that frequently occurs due to irregular climate conditions, causing serious damage to wheat and its quality. In this study, transcriptomic analysis with RNA-seq and proteomic analysis with LC-MS/MS were performed in PHS-treated spikes from two wheat cultivars presenting PHS sensitivity and tolerance, respectively. A total of 13,154 differentially expressed genes (DEGs) and 706 differentially expressed proteins (DEPs) were identified in four comparison groups between the susceptible/tolerant cultivars. Gene function and correlation analysis were performed to determine the co-profiled genes and proteins affected by PHS treatment. In the functional annotation of each comparative group, similar functions were confirmed in each cultivar under PHS treatment; however, in Keumgang PHS+7 (K7) vs. Woori PHS+7 (W7), functional annotations presented clear differences in the "spliceosome" and "proteasome" pathways. In addition, our results indicate that alternative splicing and ubiquitin-proteasome support the regulation of germination and seed dormancy. This study provides an advanced understanding of the functions involved in transcription and translation related to PHS mechanisms, thus enabling specific proposals for the further analysis of germination and seed dormancy mechanisms and pathways in wheat.

Breaking Seed Dormancy of Jaltomata procumbens (Cav.) J. L. Gentry Seeds with the Use of KNO3

Jaltomata procumbens (Cav.) J. L. Gentry presents seed dormancy mechanisms in its two populations, erect and decumbent, that make its germination and obtaining of plants difficult. Potassium nitrate (KNO3) is used as a seed germination promoter by soaking in an osmotic solution. The objective was to break the dormancy of Jaltomata seeds by evaluating KNO3. Treatments included: 2 populations (erect and decumbent), 2 soaking times (4 and 6 days) in 2 concentrations of KNO3 solution (0.1% and 0.2%) and in distilled water used as a control. Days of germination including starting (DGS) and ending (DGE), energy period (EP), germination energy (GE), germination percentage (GP) and rate (GR) were measured. The erect population presented a more uniform germination and a lower number of DGS and DGE as well as 100% germination with the highest GR (2.56 seeds day−1). No statistical differences were observed between KNO3 and control; however, the positive effect of the KNO3 and 4 days of soaking on the germinated seed was observed. The decumbent population exhibited a more variable germination; however, the same trend of the solution type and soaking days was observed, reaching 93.1 GP. Considering the economic and accessibility aspects of substances that promote germination on J. procumbens, distilled water imbibition and KNO3 are recommended to accelerate the germination process.

Physiology of Seed Dormancy and Germination-A Review

Seed dormancy is considered as an inherent property which outlines the environmental conditions in which the seed is accomplished to evolve. To better understand seed dormancy mechanisms, a series of rigorous studies examining seed metabolism in relation to gibberellin and abscisic acid have been organised. Abscisic acid is a hormone involved in the formation of primary dormancy, whereas gibberellins are a hormone involved in the induction of germination. During changes in dormancy certain variations in sensitivity can be observed. In the higher plants as the dormancy is present across all climatic regions differing responses in the environment has resulted due to adaptation. As a result of this variance, incubation is timed to avoid adverse weather conditions in order to promote reproductive growth and plant establishment. All molecular mechanisms emphasizing kernel latency initiation, conservation and improvement play a large part in the evolution and adaptation of these seeds and plants and their importance is indescribable. Together genetic and environmental factors are liable for triggering seed dormancy. For the induction of seed dormancy and besides its release the balance between the intensity of ABA plus GA remain in charge. There is a triphasic pattern of germination including imbibition i.e rapid uptake of water, enzyme activation and initiation of embryo growth resulting in the radicle protrusion. The dormancy state is regulated not only by the seed maturation environment, but it also changes over time after shedding in a way that is determined by the ambient environment.

Integrating GWAS and transcriptomics to identify genes involved in seed dormancy in rice.

Several QTLs and genes responsible for seed dormancy were detected and SNP candidates were shown to cause changes in seed germination. Seed dormancy is a key agricultural trait to prevent pre-harvest sprouting in crop plants such as rice (Oryza sativa L.), wheat (Triticum aestivum), and barley (Hordeum vulgare L.). However, our knowledge of seed dormancy is hampered by the complexities of studying a trait that changes over time after seed harvest, and is complicated by interactions between phytohormones, seed coat components and the environment. Here, we have conducted a genome-wide association study using a panel of 311 natural accessions of cultivated rice, examining a total of 519,158 single nucleotide polymorphisms (SNPs). Eight quantitative trait loci (QTLs) were found to associate with seed dormancy in the whole panel and five in the Japonica and Indica subpanel; expression of candidate genes within 100kb of each QTL was examined in two published, germination-specific transcriptomic datasets. Ten candidate genes, differentially expressed within the first four days post-imbibition, were identified. Five of these genes had previously been associated with awn length, heading date, yield, and spikelet length phenotypes. Two candidates were validated using Quantitative Reverse Transcription (qRT)-PCR. In addition, previously identified genes involved in hormone signaling during germination were found to be differentially expressed between a japonica and an indica line; SNPs in the promoter of Os9BGlu33 were associated with germination index, with qRT-PCR validation. Collectively, our results are useful for future characterization of seed dormancy mechanism and crop improvement, and suggest haplotypes for further analysis that may be of use to boost PHS resistance in rice.

The importance of fire season when managing threatened plant species: A long-term case-study of a rare Leucopogon species (Ericaceae)

Implemented burns are a primary source of fire in natural systems and occur outside of the wildfire season. However, the impacts of fire season shift on native plant species are rarely studied. Understanding fire season effects are particularly important for managing threatened species, which are often the focus of managed burns. To assess the impacts of fire seasonality and identify potential limiting traits, I studied the threatened Leucopogon exolasius and two common congeners, all of which persist via fire-driven population dynamics. All species were monitored over a 16 year period to assess seedling survival, growth and primary juvenile period after fire. For L. exolasius and the common L. esquamatus, comparisons of survival, growth and maturation were made after winter and summer fires, to assess the effects of season of burn. A key difference was found in primary juvenile period, which was exceptionally long for L. exolasius (>11 years for 80% of the population to flower) compared to the common congeners (3.2–7.57 years). Seasonal seed dormancy mechanisms meant that winter fires delayed emergence, leading to increases in primary juvenile period for both species. A long primary juvenile period may limit L. exolasius population persistence because plants are more likely to be killed by subsequent fire before maturation, while seasonal dormancy cues is a trait that would exacerbate the effects of this interval squeeze. In fire-prone systems, fire frequency is the key factor assumed to drive persistence, however, interactions with fire season can influence recruitment success. There are scant data on recruitment variation in response to fire seasonality, a factor that may have broad implications for rare and common species with seasonal germination requirements.

Diversity of epicotyl dormancy among tropical montane forest species in Sri Lanka.

Fruiting season of many Sri Lankan tropical montane species is not synchronised and may not occur when conditions are favourable for seedling establishment. We hypothesised that species with different fruiting seasons have different seed dormancy mechanisms to synchronise timing of germination with a favourable season for establishment. Using six species with different fruiting seasons, we tested this hypothesis. Germination and imbibition of intact and manually scarified seeds were studied. Effect of GA3 on germination was examined. Embryo length:seed length (E:S) ratio of freshly matured seeds and of those with a split seed coat was determined. Time taken for radicle and plumule emergence and morphological changes of the embryos were recorded. The radicle emerged from Ardisia missionis, Bheza nitidissima and Gaetnera walkeri seeds within 30days, whereas it took >30days in other species. Embryos grew in seeds of B.nitidissima and G.walkeri prior to radicle emergence but not in Microtropis wallichiana, Nothapodytes nimmoniana and Symplocos cochinchinensis. A considerable delay was observed between radicle and plumule emergence in all six species. Warm stratification and/or GA3 promoted germination of all species. All the tested species have epicotyl dormancy. Seeds of B.nitidissima and G.walkeri have non-deep simple morphophysiological epicotyl dormancy, and the other four species have non-deep physiological epicotyl dormancy. Differences in radicle and epicotyl dormancy promote synchronisation of germination to a favourable time for seedling development. Therefore, information on dormancy-breaking and germination requirements of both radicle and epicotyl are needed to determine the kind of dormancy of a particular species.

Ecological niche and bet-hedging strategies for Triodia (R.Br.) seed germination.

Regeneration dynamics in many arid zone grass species are regulated by innate seed dormancy mechanisms and environmental cues (temperature, moisture and fire) that result in infrequent germination following rainfall. This study investigated bet-hedging strategies associated with dormancy and germination in arid zone Triodia species from north-west Australia, by assessing (1) the effects of the mechanical restriction imposed by the indehiscent floral bracts (i.e. floret) covering the seed and (2) the impact of dormancy alleviation on florets and cleaned seeds (i.e. florets removed) when germinated under water stress. The initial dormancy status and germination for six species were tested on intact florets and cleaned seeds, across temperatures (10-40 °C) with and without the fire-related stimulant karrikinolide (KAR1), and under alternating light or constant dark conditions. Physiological dormancy alleviation was assessed by wet/dry cycling florets over a period of 10 weeks, and germination was compared against untreated florets, and cleaned seeds across a water potential gradient between 0 and -1.5 MPa. Florets restricted germination (<45 %) at all temperatures and, despite partial alleviation of physiological dormancy (wet/dry cycling for 8 weeks), intact florets germinated only at high water potentials. Cleaned seeds showed the highest germination (40-90 %) across temperatures when treated with KAR1, and germinated at much lower water potentials (-0.4 and -0.9 MPa). Triodia pungens was the most responsive to KAR1, with both seeds and florets responding, while for the remaining five species, KAR1 had a positive effect for seeds only. Only after seed dormancy was alleviated by removing florets and when KAR1 was applied did germination under water stress increase. This suggests that seeds of these Triodia species are cued to recruit following fire and during periods of high precipitation. Climate change, driven by large shifts in rainfall patterns, is likely to impact Triodia recruitment further in arid zone grasslands.

Timing of seed germination in two alpine herbs on the southeastern Tibetan plateau: the role of seed dormancy and annual dormancy cycling in soil

Germination timing strongly affects the probability of seedling survival and the conditions for subsequent plant growth and reproduction. For alpine species, timing of germination should be restricted to a period that ensures seedlings will attain a critical size during the short growing season and thus survive winter. Thus, we hypothesized that seeds of herbaceous alpine perennials germinate only at the beginning of the growing season in spring, when temperatures are low, and the seed dormancy mechanism helps synchronize the germination event to the beginning of the growing season. Seed traits and effects of light, temperature, cold stratification and GA3 on germination of Primula alpicola and Pedicularis fletcheri were tested in the laboratory and germination responses to temperature of seeds buried in the field at 4500 m a.s.l. and exhumed over a 2-year period were investigated. Fresh seeds were dormant, and cold stratification and GA3 overcame dormancy in seeds of both species and the light requirement for germination of P. alpicola seeds. Buried seeds of both species exhibited an annual dormancy/nondormancy/dormancy cycle. Seeds of P. alpicola and P. fletcheri have nondeep physiological dormancy and dormancy cycling. Dormancy cycling was coordinated with seasonal environmental conditions, and seeds germinated soon after snowmelt in late spring. This is the first comprehensive demonstration of regulation of germination timing by dormancy cycling in alpine plants.

Seed coat thinning during horsegram (Macrotyloma uniflorum) domestication documented through synchrotron tomography of archaeological seeds

Reduction of seed dormancy mechanisms, allowing for rapid germination after planting, is a recurrent trait in domesticated plants, and can often be linked to changes in seed coat structure, in particular thinning. We report evidence for seed coat thinning between 2,000 BC and 1,200 BC, in southern Indian archaeological horsegram (Macrotyloma uniflorum), which it has been possible to document with high precision and non-destructively, through high resolution x-ray computed tomography using a synchrotron. We find that this trait underwent stepped change, from thick to semi-thin to thin seed coats, and that the rate of change was gradual. This is the first time that the rate of evolution of seed coat thinning in a legume crop has been directly documented from archaeological remains, and it contradicts previous predictions that legume domestication occurred through selection of pre-adapted low dormancy phenotypes from the wild.

Seed Dormancy Mechanisms in Basalt Milkvetch and Western Prairie Clover

A greater diversity of native legumes and forbs is desirable for rangeland restoration practice in the Intermountain Region of the western United States. But for such diversity to materialize in the seed marketplace and to be effective in restoration practice, seeds that germinate reliably in seed fields and on restoration sites are needed. We measured germination response of two native legumes, basalt milkvetch (Astragalus filipes Torr. ex A. Gray) and western prairie clover (Dalea ornata [Douglas] Eaton & Wright), after eight germination treatments. Treatments were a factorial combination of 1) seed scarification with sandpaper (or unscarified), 2) a substrate of moist sand (or blotter paper), and 3) a 3-wk prechill at 5° (or nonprechilled). Cumulative germination increased linearly throughout the 10-wk course of the experiment for all treatment combinations in both species. Scarification increased germination of western prairie clover, but prechilling and substrate had no effect. In contrast, prechilling, scarification, and a sand substrate all increased germination of basalt milkvetch. Hence, for this species the prechilled/scarified/sand treatment combination displayed the numerically highest germination for all 10 wk (30−43%), and the nonprechilled/unscarified/blotter paper treatment combination always germinated lowest (1−3%). Results were consistent with physical dormancy (hard-seededness) limiting germination of western prairie clover and combinational dormancy (i.e., co-occurrence of physical and physiological dormancy) limiting germination of basalt milkvetch. Of the two species, we have found basalt milkvetch to be the more difficult to establish from seed. By prechilling acid-scarified seed in moist sand, basalt milkvetch was successfully established in two field trials seeded in mid-April. Nonprechilled mechanically (sandpaper) scarified seed germinated as high as prechilled acid-scarified seed. By scarifying and prechilling basalt milkvetch seed to address physical and physiological dormancy mechanisms, respectively, this seed-treatment protocol may be “scaled up” to produce large quantities of germinable seed.

Expression of ABA Metabolism-Related Genes Suggests Similarities and Differences Between Seed Dormancy and Bud Dormancy of Peach (Prunus persica).

Dormancy inhibits seed and bud growth of perennial plants until the environmental conditions are optimal for survival. Previous studies indicated that certain co-regulation pathways exist in seed and bud dormancy. In our study, we found that seed and bud dormancy are similar to some extent but show different reactions to chemical treatments that induce breaking of dormancy. Whether the abscisic acid (ABA) regulatory networks are similar in dormant peach seeds and buds is not well known; however, ABA is generally believed to play a critical role in seed and bud dormancy. In peach, some genes putatively involved in ABA synthesis and catabolism were identified and their expression patterns were studied to learn more about ABA homeostasis and the possible crosstalk between bud dormancy and seed dormancy mechanisms. The analysis demonstrated that two 9-cis-epoxycarotenoid dioxygenase-encoding genes seem to be key in regulating ABA biosynthesis to induce seed and bud dormancy. Three CYP707As play an overlapping role in controlling ABA inactivation, resulting in dormancy-release. In addition, Transcript analysis of ABA metabolism-related genes was much similar demonstrated that ABA pathways was similar in the regulation of vegetative and flower bud dormancy, whereas, expression patterns of ABA metabolism-related genes were different in seed dormancy showed that ABA pathway maybe different in regulating seed dormancy in peach.

我国北方草地6种乡土植物抗逆机理与应用

It is a long term work to assemble the knowledge needed to utilize the rich native plant resources to assist social and economic development in China. The progress of the research results and their application of mechanisms underlying the stress-tolerance in native plants including Zygophyllum xanthoxylum, Artemisia sphaerocephala, Microula sikkimensis, Achnatherum inebrians, Cleistogenes songorica and Leymus chinensis were reviewed in this paper. The main results and findings are as follows: based on discovering the physiological mechanism of drought tolerance of Z. xanthoxylum, the key genes involved in drought tolerance were cloned and applied into the genetic improvement of important legume forage lucerne (Medicago sativa) and lotus (Lotus corniculatus); the desert shrub A. sphaerocephala and alpine species M. sikkimensis contain high contents of polyunsaturated fatty acids, the highest contents being found in the seeds; the diversity of drunken horse grass fungal endophyte symbiont was investigated on a national scale. The alkaloids produced by the symbiont are the main reason for both increased plant stress tolerance and the toxicity symptoms observed after intake by grazing animals; the biological, physiological and molecular genetic characteristics of C. songorica were studied. As a result, the species is expected to be domesticated successfully. Technical information on procedures for pasture establishment and seed production of this species has been developed; the seed dormancy mechanisms of L. chinensis were explored, and techniques to effectively break dormancy were developed. © 2016, Science Press. All right reserved.

Conservation biology of two endemic Beyeria species (Euphorbiaceae) from southern Western Australia

Beyeria cockertonii Halford &amp; R.J.F.Hend. and Beyeria villosa Halford &amp; R.J.F.Hend. (Euphorbiaceae) are two short-range endemic monoecious congeners from southern Western Australia. We sought to determine whether life-history characteristics were responsible for their limited distribution and to identify aspects of their ecology that might render them vulnerable to current threatening processes. We investigated reproductive phenology in relation to climate, pollinator activity and synchronicity of male and female flowering. In addition seed dispersal, regeneration, demography and seed viability were examined and ex situ germination experiments conducted to determine seed-dormancy mechanisms. Flowering in the conservation-listed B. cockertonii was significantly correlated with temperature, whereas fruit set was correlated with pollinator abundance and movement; male and female flowering showed limited synchrony. The presence of soil-stored seeds lacking a caruncle at sites absent of adult plants of either species suggests that seed may be ant-dispersed (myrmecochory). Fresh seeds of B. cockertonii were significantly more viable than those of its more common congener, B. villosa (72 vs 0.5%, P &lt; 0.001). Fresh B. cockertonii seeds would not germinate with an intact caruncle; caruncle removal elicited germination of 64% and 60% (10°C and 15°C, respectively). Aqueous smoke further stimulated germination to 72% and 83% germination (10°C and 15°C, respectively), providing a link between fire and germination. Beyeria villosa was affected by high levels of pre-dispersal predation (up to 70%) and seed abortion (88%) and appeared to have lower reproductive fitness than B. cockertonii. Life-history strategies did not explain the greater abundance and wider distribution of B. villosa than those of the conservation-listed B cockertonii, nor was the greater rarity of B. cockertonii fully explained by habitat specificity, with both species being restricted to ultra-mafic volcanic rock associated with Achaean greenstone. However, an apparent dependence of B. cockertonii on a specific insect pollinator from the family Miridae may render this species vulnerable to threatening processes.

Seed dormancy and germination-emerging mechanisms and new hypotheses.

Seed dormancy has played a significant role in adaptation and evolution of seed plants. While its biological significance is clear, molecular mechanisms underlying seed dormancy induction, maintenance and alleviation still remain elusive. Intensive efforts have been made to investigate gibberellin and abscisic acid metabolism in seeds, which greatly contributed to the current understanding of seed dormancy mechanisms. Other mechanisms, which might be independent of hormones, or specific to the seed dormancy pathway, are also emerging from genetic analysis of “seed dormancy mutants.” These studies suggest that chromatin remodeling through histone ubiquitination, methylation and acetylation, which could lead to transcription elongation or gene silencing, may play a significant role in seed dormancy regulation. Small interfering RNA and/or long non-coding RNA might be a trigger of epigenetic changes at the seed dormancy or germination loci, such as DELAY OF GERMINATION1. While new mechanisms are emerging from genetic studies of seed dormancy, novel hypotheses are also generated from seed germination studies with high throughput gene expression analysis. Recent studies on tissue-specific gene expression in tomato and Arabidopsis seeds, which suggested possible “mechanosensing” in the regulatory mechanisms, advanced our understanding of embryo-endosperm interaction and have potential to re-draw the traditional hypotheses or integrate them into a comprehensive scheme. The progress in basic seed science will enable knowledge translation, another frontier of research to be expanded for food and fuel production.

In vitrobacterial decontamination ofKelussia odoratissimaseed during dormancy breaking

Kelussia odoratissima (Apiaceae) is an endangered medicinal plant indigenous to Iran. Seeds of this plant have a long-term dormancy. This study aimed at obtaining in vitro method to reduce microbial contamination, overcome seed dormancy and to disclose the type of classification system of seed dormancy. After using completely randomized design and Duncan's Multiple Range Test, the significance of between individual group's means was assessed. Results revealed that only one gram negative bacterium strain, Klebsiella sp., was isolated from the contaminated culture. Applying 500 mg/l copper sulphate for 6 min during seed sterilization, the contamination was eradicated. During cold stratification, to estimate the effect of exogenous application of cytikinin hormones, N6-furfurylaninopurine (Kin) and 6-benzylaminopurine (BAP) alone or in combination with each other, pre-soaking treatment with tioureae as a nitrogen compound and seed osmopriming with polyethylene glycole (PEG 6000), alone or in combination with BAP, the highest final seed germination (92.5%) was obtained on medium containing 1 mg/l BAP combined with 1 mg/l Kin. The lowest mean germination time (45.81 days) was also obtained on medium containing 0.25 mg/l BAP. Since using tiourea was simple and economical, with 80% final seed germination (using 0.2% thiourea) this can be an excellent way to promote seed germination of this plant. Considering the efficacy of treatments and growing of zygotic embryo without cold temperature exposure, seed dormancy mechanism identified as non-deep physiological dormancy and particularly chemical dormancy classification.

Seed dormancy mechanism as a factor influencing seed physiological quality in alfalfa (Medicago sativa) cv. Baralfa 85

Seed dormancy mechanism as a factor influencing seed physiological quality in alfalfa (Medicago sativa) cv. Baralfa 85

Seed germination, hydrothermal time models and the effects of global warming on a threatened high Andean tree species

AbstractSeed germination is a crucial event in a plant's life cycle. Because temperature and water availability are important regulators of seed germination, this process will likely be influenced by global warming. Insight into the germination process under global warming is thus crucial, and requires the study of a wide range of water availability and temperature conditions. As hydrothermal time (HTT) models evaluate seed germination for any combination of water potential and temperature, they can be suitable to predict global warming effects on seed germination. We studied the germination characteristics of the high Andean endemic tree speciesPolylepis besseri(Rosaceae), using HTT models. We were especially interested in the potential effects of global warming on seed germination. Assembly of HTT models forP. besseriwas fairly straightforward due to the lack of a seed dormancy mechanism. The models allowed prediction ofPolylepisgermination under constant and alternating temperatures. Initially, a global warming induced increase in the field minimum and mean temperature will increaseP. besserigermination, but as maximum temperatures rise above the optimum temperature for the species, seed germination will become jeopardized. Effects of global warming on seed germination are currently considerably underexplored. HTT models prove to be useful tools to study a plant species' general germination characteristics, and how they may become affected under global warming. For the endemic mountain tree speciesP. besseri, we predict an increase, followed by a decrease of seed germination under global warming.