Control Of Dormancy Research Articles

β3-Adrenoreceptors Control Mitochondrial Dormancy in Melanoma and Embryonic Stem Cells.

The early phases of embryonic development and cancer share similar strategies to improve their survival in an inhospitable environment: both proliferate in a hypoxic and catecholamine-rich context, increasing aerobic glycolysis. Recent studies show that β3-adrenergic receptor (β3-AR) is involved in tumor progression, playing an important role in metastasis. Among β-adrenergic receptors, β3-AR is the last identified member of this family, and it is involved in cancer cell survival and induction of stromal reactivity in the tumor microenvironment. β3-AR is well known as a strong activator of uncoupling protein 1 (UCP1) in brown fat tissue. Interestingly, β3-AR is strongly expressed in early embryo development and in many cancer tissues. Induction of uncoupling protein 2 (UCP2) has been related to cancer metabolic switch, leading to accelerated glycolysis and reduced mitochondrial activity. In this study, for the first time, we demonstrate that β3-AR is able to promote this metabolic shift in both cancer and embryonic stem cells, inducing specific glycolytic cytoplasmic enzymes and a sort of mitochondrial dormancy through the induction of UCP2. The β3-AR/UCP2 axis induces a strong reduction of mitochondrial activity by reducing ATP synthesis and mitochondrial reactive oxygen species (mtROS) content. These effects are reverted by SR59230A, the specific β3-AR antagonist, causing an increase in mtROS. The increased level of mtROS is neutralized by a strong antioxidant activity in embryonic stem cells, but not in cancer stem cells, where it causes a dramatic reduction in tumor cell viability. These results lead to the possibility of a selective antitumor therapeutic use of SR59230A. Notably, we demonstrate the presence of β3-AR within the mitochondrial membrane in both cell lines, leading to the control of mitochondrial dormancy.

MPPT Controller for Solar PV Cells using GSAPSO Algorithm

Solar energy is a very general source of renewable energy due to some advantages. In many countries, Photovoltaic power systems have been mostly used. However, there are many urgent issues to tackle in the application of PV power systems. The main problem is how to improve efficiency. Since the PV arrays display a nonlinear Power–Voltage (P–V) characteristic curve which varies with insolation and temperature, how to achieve Maximum Power Point Tracking (MPPT) is a very significant technology. In this work, we have explored the optimization methods for efficient tracking such as PSO and GSA. The essential issue of MPPT control is an optimization problem which can be achieved by using evolutionary algorithms. PSO algorithm owns the characteristics of good robustness, parallel processing and high probability of finding global optimal solution. By combining GSA to PSO, the performance has been improved. The proposed GSAPSO algorithm greatly shortens the searching time, reduces the fluctuation of output waveform and improves the efficiency through particles dormancy and activation control, optimal number of particles algorithm and search sequence selection. It achieves a smooth starting for maximum power and achieves it in less time than the widely used other methods.

Photoperiod- and temperature-mediated control of growth cessation and dormancy in trees: a molecular perspective.

How plants adapt their developmental patterns to regular seasonal changes is an important question in biology. The annual growth cycle in perennial long-lived trees is yet another example of how plants can adapt to seasonal changes. The two main signals that plants rely on to respond to seasonal changes are photoperiod and temperature, and these signals have critical roles in the temporal regulation of the annual growth cycle of trees. This review presents the latest findings to provide insight into the molecular mechanisms that underlie how photoperiodic and temperature signals regulate seasonal growth in trees. The results point to a high level of conservation in the signalling pathways that mediate photoperiodic control of seasonal growth in trees and flowering in annual plants such as arabidopsis. Furthermore, the data indicate that symplastic communication may mediate certain aspects of seasonal growth. Although considerable insight into the control of phenology in model plants such as poplar and spruce has been obtained, the future challenge is extending these studies to other, non-model trees.

Awake1, an ABC-Type Transporter, Reveals an Essential Role for Suberin in the Control of Seed Dormancy.

The mother plant plays an important dynamic role in the control of dormancy of her progeny seed in response to environmental signals. In order to further understand the mechanisms by which this dormancy control takes place in Arabidopsis (Arabidopsis thaliana), we conducted a forward genetic screen to isolate mutants that fail to enter dormancy in response to variation in temperature during seed set. We show that, for the first of these mutants, designated awake1, the maternal allele is required for entry into strongly dormant states and that awake1 mutants show seed phenotypes shown previously to be associated with the loss of suberin in the seed. We identify awake1 as an allele of ABCG20, an ATP-binding cassette transporter-encoding gene required for the transport of fatty acids during suberin deposition, and show that further suberin-deficient mutants have seed dormancy defects. Seed coat suberin composition is affected by temperature during seed maturation, but this response appears to be independent of ABCG20. We conclude that seed coat suberin is essential for seed dormancy imposition by low temperature and that the exclusion of oxygen and water from the seed by the suberin and tannin layers is important for dormancy imposition.

QTL mapping for microtuber dormancy and GA3 content in a diploid potato population.

ABSTRACTThe genetic control of dormancy is poorly understood in most plant species, but dormancy is a prominent feature for the potato industry. We used the microtuber system, in which tubers were produced in vitro and stored at 20°C, to perform quantitative trait locus (QTL) analysis for dormancy and gibberellic acid (GA3) content in an F1 population consisting of 178 genotypes derived from an interspecific cross between Solanum chacoense acc. PI 320285 (long dormancy) and Solanum phureja acc. DM1-3 516 R44 (short dormancy). In this analysis, 163 markers were used to construct a genetic map with a total length of 591.8 cM. Through QTL analysis, we identified 22 markers closely linked to the timing of dormancy release and GA3 content. The male parent alleles were closely related with long dormancy, with the most significant effect on chromosome I, which accounted for 9.4% of phenotypic variation. The dormancy and GA3 QTLs localized to the same position in the genome, confirming that same genomic region controls GA3 content at different developmental stages or in dormant and sprouting tubers. The identified QTLs may be useful for future breeding strategies and studies of dormancy in potato.

Effects of Environmental Factors on Seed Germination and Seedling Emergence of Common Teasel (Dipsacus fullonum)

Common teasel is an invasive and widespread weed in Argentina. Germination experiments were carried out from 2011 to 2014 to determine the effect of various environmental factors on germination and emergence. Germination of recently dispersed seeds was 12% in darkness at constant temperature. In contrast, seed exposure to light and alternating temperatures enhanced germination to 95%. The requirement of light and alternating temperatures suggest that common teasel has physiological dormancy. Several experiments were carried out to determine whether (1) seed responses to light and alternating temperatures have a hormonal basis, (2) seed coats can suppress germination, and (3) time and thermal conditions during seed storage reduce light and alternating temperature requirements. Germination was reduced (≤ 13%) by a gibberellin synthesis inhibitor. In contrast, the presence of gibberellins and an abscisic acid synthesis inhibitor increased germination to 95 and 38%, respectively. Results suggest that a higher ratio among gibberellins and abscisic acid (GA/ABA) leads to a break in dormancy. Germination was 100% when embryos were excised, suggesting that seed coats may suppress germination by mechanical restriction. Likewise, germination was enhanced by hydrogen peroxide (70%). This compound is known to increase GA/ABA ratio in agreement with a hormonal control of dormancy proposed for common teasel. An increment of storage time reduces light and alternating temperature requirements, allowing seeds to germinate in darkness. Taking these results together confirms that common teasel has physiological dormancy. Seedling emergence was progressively reduced from 70 to 8% by increased burial depth from 0 to 3 cm. Information from these experiments may facilitate development of effective management for common teasel.

Diversity of insulin-like peptide signaling system proteins in Calanus finmarchicus (Crustacea; Copepoda) – Possible contributors to seasonal pre-adult diapause

Calanus finmarchicus, an abundant calanoid copepod in the North Atlantic Ocean, is both a major grazer on phytoplankton and an important forage species for invertebrate and vertebrate predators. One component of the life history of C. finmarchicus is the overwintering dormancy of sub-adults, a feature key for the annual recruitment of this species in early spring. While little is known about the control of dormancy in C. finmarchicus, one hypothesis is that it is an insect-like diapause, where the endocrine system is a key regulator. One group of hormones implicated in the control of insect diapause is the insulin-like peptides (ILPs). Here, C. finmarchicus transcriptomic data were used to predict ILP signaling pathway proteins. Four ILP precursors were identified, each possessing a distinct A- and B-chain peptide; these peptides are predicted to form bioactive heterodimers via inter-chain disulfide bridging. Two ILP receptors, which likely represent splice variants of a common gene, were identified. Three insulin-degrading enzymes were also discovered, as were proteins encoding the transcription factor FOXO, a downstream target of ILP that has been implicated in the regulation of insect diapause, and insulin receptor substrate, a protein putatively linking the ILP receptor and FOXO. RNA-Seq data suggest that some C. finmarchicus insulin pathway transcripts are differentially expressed across development. As in insects, the ILP signaling system may be involved in controlling C. finmarchicus’ organism-environment interactions (e.g., regulation of seasonal sub-adult diapause), a hypothesis that can now be investigated using these data.

Structural genomics and transcriptional characterization of the Dormancy-Associated MADS-box genes during bud dormancy progression in apple

The molecular control of bud dormancy establishment and release is still not well understood, although some genes have already been demonstrated to play important roles in this process. The dormancy-associated MADS-box (DAM) genes were first identified in the peach EVERGROWING locus and are considered the main regulators of bud dormancy control. In this work, the apple (Malus × domestica Borkh.), a perennial plant adapted to temperate climates that displays cycles of growth and bud dormancy, was screened for the presence of DAM genes. The candidate genes retrieved were characterized in comparison to DAM genes from other species. Four of them (MdDAM1–4) are structurally very similar to the reported DAM genes. When apple genomic segments containing these candidates were compared to the peach EVERGROWING locus, a highly conserved noncoding region was detected inside their largest intron. Similar sequences were also identified inside introns of apricot and pear DAM genes. Organ expression patterns revealed that MdDAM1–4 are mainly expressed in dormant buds and seeds, with low transcript accumulation in vegetative structures. In addition, the MdDAM genes showed seasonally oscillating patterns of steady-state messenger RNA (mRNA) levels and were downregulated by artificial chilling. Motif analyses in the promoter and in the intronic conserved region of the MdDAM genes disclosed some clues to the regulation of the expression patterns observed. Possible roles for the conserved intronic sequence in dormancy regulation are discussed.

On the language and physiology of dormancy and quiescence in plants.

The language of dormancy is rich and poetic, as researchers spanning disciplines and decades have attempted to understand the spell that entranced 'Sleeping Beauty', and how she was gently awoken. The misleading use of 'dormancy', applied to annual axillary buds, for example, has confounded progress. Language is increasingly important as genetic and genomic approaches become more accessible to species of agricultural and ecological importance. Here we examine how terminology has been applied to different eco-physiological states in plants, and with pertinent reference to quiescent states described in other domains of life, in order to place plant quiescence and dormancy in a more complete context than previously described. The physiological consensus defines latency or quiescence as opportunistic avoidance states, where growth resumes in favourable conditions. In contrast, the dormant state in higher plants is entrained in the life history of the organism. Competence to resume growth requires quantitative and specific conditioning. This definition applies only to the embryo of seeds and specialized meristems in higher plants; however, mechanistic control of dormancy extends to mobile signals from peripheral tissues and organs, such as the endosperm of seed or subtending leaf of buds. The distinction between dormancy, quiescence, and stress-hardiness remains poorly delineated, most particularly in buds of winter perennials, which comprise multiple meristems of differing organogenic states. Studies in seeds have shown that dormancy is not a monogenic trait, and limited study has thus far failed to canalize dormancy as seen in seeds and buds. We argue that a common language, based on physiology, is central to enable further dissection of the quiescent and dormant states in plants. We direct the topic largely to woody species showing a single cycle of growth and reproduction per year, as these bear the majority of global timber, fruit, and nut production, as well being of great ecological value. However, for context and hypotheses, we draw on knowledge from annuals and other specialized plant conditions, from a perspective of the major physical, metabolic, and molecular cues that regulate cellular activity.

Abstract B51: Extracellular matrix control of metastasis and dormancy

Abstract This abstract is being presented as a short talk in the scientific program. A full abstract is printed in the Proffered Abstracts section (PR14) of the Conference Proceedings. Citation Format: Lauren E. Barney, Ari Gilman, Arthur Mercurio, Shelly R. Peyton. Extracellular matrix control of metastasis and dormancy. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr B51.

Abstract PR14: Extracellular matrix control of metastasis and dormancy

Abstract Introduction: Paget's classical seed and soil hypothesis states that specific interactions between the metastatic cell (the seed) and the recipient tissue microenvironment (the soil) mediate the non-random patterns of spread observed in breast cancer (tropism). We hypothesize that the ability of metastatic cells to survive dormancy, exit quiescence, and colonize a specific tissue depends upon the ability of the soil to first sustain survival, and subsequently trigger outgrowth. To this end, we created a biomaterial platform that varies extracellular matrix (ECM) density and composition, and used integrin-mediated phenotyping to study how highly metastatic cells differentiate between secondary sites via integrin binding. With this relationship in hand, we have found that both the ECM and growth factors also mediate dormancy in cells that display metastatic latency in vivo. Methods: ECM microenvironments were created by linking combinations of ECM proteins to glass coverslips using silane chemistry. Human breast cancer cell lines were seeded onto the surfaces, and we quantified initial cell adhesion and long-term migration via microscopy. Using cell lines that only metastasize to the bone, brain, or lung (provided by J. Massagué), we created fingerprints of behavior characteristic of each tropism, and compared these with the phenotypes of other cell lines with known metastasis. Quiescence was induced on ECMs via culture in serum free medium for up to 14 days, and subsequent serum-stimulation for allowed for recovery and growth. Proliferation was assayed via immunofluorescent staining for Ki67, and cell number was determined via DAPI staining. Results: We identified unique phenotypes of bone, brain, and lung tropic subpopulations, and confirmed these in seven of nine other known, more heterogeneous, metastatic cell lines, establishing a connection between in vitro phenotype and in vivo fate. Function-affecting antibodies to integrins each shift a cell line's predicted tropism in vitro, and these in vitro phenotyping results mimic the clinical metastasis patterns dictated by both α2 and α6 integrin gene expression. Interestingly, however, our functional predictions regarding β1 integrin actually provide insights that are largely independent of clinical gene expression, potentially identifying new metastatic therapeutic targets, and emphasizing the need for this type of functional analysis. However, when we applied this approach to cell lines that display latency in vivo (e.g., ZR-75-1), our predictions were not correct. These cells were generally insensitive to ECM and growth factors in adhesion and motility, but instead, we found that these factors regulate entrance into dormancy. We uniformly observe that a laminin-coupled ECM is unable to permit survival of dormant cells, whereas binding to collagen I maintains cell survival for at least 14 days. Epidermal growth factor supplementation improves the entrance into dormancy on collagen alone. We have found that this collagen-specific, EGF-enhanced survival ability is mediated by β1 integrin binding and activation of ERK1/2, suggesting that β1 integrin function is critical both for aggressive metastasis and for permitting dormancy. Conclusions: We are the first to report that bone, brain, and lung tropism can be distinguished via simple integrin-mediated phenotyping, and that this approach can be used to predict in vivo tropism. We suggest that functional β1 integrin binding mediates both aggressive and latent metastasis. In sum, we propose that this functional screen of cell-matrix interactions can predict in vivo outcomes, and thus, is a valuable tool to provide insight toward integrins as druggable targets for metastatic disease. Citation Format: Lauren E. Barney, Ari Gilman, Arthur Mercurio, Shelly R. Peyton. Extracellular matrix control of metastasis and dormancy. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Metastasis; 2015 Nov 30-Dec 3; Austin, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(7 Suppl):Abstract nr PR14.

Differential effect of ethylene supplementation and inhibition on abscisic acid metabolism of potato (Solanum tuberosum L.) tubers during storage

Ethylene is used as a commercial potato sprout suppressant, but the role of ethylene in potato dormancy is unclear and contradictory. Two potato cultivars ‘Estima’ and ‘Marfona’ were treated with air or continuous ethylene (10μLL−1), transferred from air to ethylene or vice versa at first indication of sprouting (10% peeping of the control tubers), over three seasons. The ethylene binding inhibitor, 1-methylcyclopropene, was applied (1μLL−1 for 24h) either at harvest and/or at first indication of sprouting. Tubers were stored at 6°C for 30 weeks and assessed for sprout length and number, and non-structural carbohydrate content. Abscisic acid (ABA) metabolism in tubers throughout storage was monitored. Ethylene applied from harvest or the first indication of sprouting reduced sprout growth significantly for both cultivars while ethylene induced sugar accumulation was prevented by 1-MCP application prior to ethylene storage. Multiple applications of 1-MCP showed no additional benefit to ethylene induced sugar accumulation. A rise in ABA content in flesh tissue was observed in response to ethylene application while 1-MCP blocked the ethylene induced rise in ABA caused by exogenous and endogenous ethylene. The increase in ABA caused by ethylene may delay dormancy break yet 1-MCP blocked this rise in ABA with no apparent effect on sprout behaviour. Sucrose is a prerequisite signalling molecule for hormonal dormancy control. 1-MCP reduced the ethylene induced rise in sucrose content therefore although 1-MCP reduced ABA, the reduction in sucrose content may still have delayed sprout initiation. However, the level of sucrose in the 1-MCP treated tubers did not decrease below that of the control. Taken together, ABA and sucrose may play a role in the sprout suppressing ability of exogenously applied ethylene, but it is clear that other factors are involved.

Cancer-reactive memory T cells from bone marrow: Spontaneous induction and therapeutic potential (Review).

Cognate interactions between naïve tumor antigen (TA)-specific T cells and TA-presenting dendritic cells (DCs) are facilitated by secondary lymphoid organs such as lymph nodes or the spleen. These can result either in TA-specific tolerance or, depending on environmental costimulatory signals, in TA-specific immune responses. In the present review, we describe such events for the bone marrow (BM) when blood-borne TA, released from the primary tumor or expressed by blood circulating tumor cells or DCs enters the BM stroma and parenchyma. We argue that cognate T-DC interactions in the BM result in immune responses and generation of memory T cells (MTCs) rather than tolerance because T cells in the BM show an increased level of pre-activation. The review starts with the spontaneous induction of cancer-reactive MTCs in the BM and the involvement of such MTCs in the control of tumor dormancy. The main part deals with the therapeutic potency of BM MTCs. This is a new area of research in which the authors research group has performed pioneering studies which are summarized. These include studies in animal tumor models, studies with human cells in tumor xenotransplant models and clinical studies. Based on observations of an enormous expansion capacity, longevity and therapeutic capacity of BM MTCs, a hypothesis is presented which suggests the involvement of stem-like MTCs.

Analysis of a cancer dormancy model and control of immuno-therapy.

The goal of this paper is to analyze a model of cancer-immune system interactions from [16], and to show how the introduction of control in this model can dramatically improve the hypothetical patient response and in effect prevent the cancer from growing. We examine all the equilibrium points of the model and classify them according to their stability properties. We identify an equilibrium point corresponding to a survivable amount of cancer cells which are exactly balanced by the immune response. This situation corresponds to cancer dormancy. By using Lyapunov stability theory we estimate the region of attraction of this equilibrium and propose two control laws which are able to stabilize the system effectively, improving the results of [16]. Ultimately, the analysis presented in this paper reveals that a slower, continuous introduction of antibodies over a short time scale, as opposed to mere inoculation, may lead to more efficient and safer treatments.

Dormancy in cereals (not too much, not so little): about the mechanisms behind this trait

AbstractAs in other cultivated species, dormancy can be seen as a problem in cereal production, either due to its short duration or to its long persistence. Indeed, cereal crops lacking enough dormancy at harvest can be exposed to pre-harvest sprouting damage, while a long-lasting dormancy can interfere with processes that rely on rapid germination, such as malting or the emergence of a uniform crop. Because the ancestors of cereal species evolved under very diverse environments worldwide, different mechanisms have arisen as a way of sensing an appropriate germination environment (a crucial factor for winter or summer annuals such as cereals). In addition, different species (and even different varieties within the same species) display diverse grain morphology, allowing some structures to impose dormancy in some cereals but not in others. As in seeds from many other species, the antagonism between the plant hormones abscisic acid and gibberellins is instrumental in cereal grains for the inception, expression, release and re-induction of dormancy. However, the way in which this antagonism operates is different for the various species and involves different molecular steps as regulatory sites. Environmental signals (i.e. temperature, light quality and quantity, oxygen levels) can modulate this hormonal control of dormancy differently, depending on the species. The practical implications of knowledge accumulated in this field are discussed.

Grain dormancy loss is associated with changes in ABA and GA sensitivity and hormone accumulation in bread wheat,Triticum aestivum(L.)

AbstractKnowledge about the hormonal control of grain dormancy and dormancy loss is essential in wheat, because low grain dormancy at maturity is associated with the problem of pre-harvest sprouting (PHS) when cool and rainy conditions occur before harvest. Low GA (gibberellin A) hormone sensitivity and high ABA (abscisic acid) sensitivity were associated with higher wheat grain dormancy and PHS tolerance. Grains of two PHS-tolerant cultivars were very dormant at maturity, and insensitive to GA stimulation of germination. More PHS-susceptible cultivars were less sensitive to ABA inhibition of germination, and were either more GA sensitive or germinated efficiently without GA at maturity. As grain dormancy was lost through dry afterripening or cold imbibition, grains first gained GA sensitivity and then lost ABA sensitivity. These changes in GA and ABA sensitivity can serve as landmarks defining stages of dormancy loss that cannot be discerned without hormone treatment. These dormancy stages can be used to compare different cultivars, seed lots and studies. Previous work showed that wheat afterripening is associated with decreasing ABA levels in imbibing seeds. Wheat grain dormancy loss through cold imbibition also led to decreased endogenous ABA levels, suggesting that reduced ABA signalling is a general mechanism triggering dormancy loss.

Transcription profiling of the chilling requirement for bud break in apples: a putative role for FLC-like genes.

Apple production depends on the fulfilment of a chilling requirement for bud dormancy release. Insufficient winter chilling results in irregular and suboptimal bud break in the spring, with negative impacts on apple yield. Trees from apple cultivars with contrasting chilling requirements for bud break were used to investigate the expression of the entire set of apple genes in response to chilling accumulation in the field and controlled conditions. Total RNA was analysed on the AryANE v.1.0 oligonucleotide microarray chip representing 57,000 apple genes. The data were tested for functional enrichment, and differential expression was confirmed by real-time PCR. The largest number of differentially expressed genes was found in samples treated with cold temperatures. Cold exposure mostly repressed expression of transcripts related to photosynthesis, and long-term cold exposure repressed flavonoid biosynthesis genes. Among the differentially expressed selected candidates, we identified genes whose annotations were related to the circadian clock, hormonal signalling, regulation of growth, and flower development. Two genes, annotated as FLOWERING LOCUS C-like and MADS AFFECTING FLOWERING, showed strong differential expression in several comparisons. One of these two genes was upregulated in most comparisons involving dormancy release, and this gene's chromosomal position co-localized with the confidence interval of a major quantitative trait locus for the timing of bud break. These results indicate that photosynthesis and auxin transport are major regulatory nodes of apple dormancy and unveil strong candidates for the control of bud dormancy.

Effects of storage under low temperature, room temperature and in the soil on viability and vigour of Leucospermum cordifolium (Proteaceae) seeds

Seed longevity, the control of dormancy and the eventual fate of seeds were studied in two experiments simulating conditions in natural fynbos. In one experiment a batch of mature, freshly harvested, intact achenes (“seeds”) of the myrmecochorous species Leucospermum cordifolium was divided into lots, of which one was buried in mesic mountain fynbos (experiencing a mediterranean-type climate with hot summers). Other seed lots were stored open at room temperature and in closed nitrogen filled containers at 3°C, respectively. Stored seeds were sampled and germinated under optimal laboratory (viability estimate) and seed bed (vigour estimate in fynbos) conditions, during autumn, after 0 (control), 1, 2 and 4years. Low temperature stored seeds maintained a high viability and vigour for c. two years but ambient temperature storage led to a marked decline after 1year ending in almost complete mortality after 4years of shelf storage. Four year soil-stored seeds, by contrast, maintained a high viability and vigour, of 80% and 60% respectively of the original seed source values. The soft pericarp/elaiosome in soil-stored seeds disappeared completely whilst the testa became progressively scarified over time. The strongly increased germination rate (velocity) in soil-stored seeds was attributed to natural oxygenation mediated by testa scarification. In another experiment freshly matured intact achenes were oxygenated with 1% H2O2 and the pericarps removed. Disinfection and benzyladenine growth regulator soaking (200mgL−1 for 24h) were applied as separate treatments. The seeds were then sown at 1cm depth in a standard seed bed in autumn and germination was recorded in the first winter season and, in the undisturbed seed bed, in each subsequent winter for 5 germination seasons. H2O2 oxygenated seeds gave a much higher germination percentage and rate than non-oxygenated seeds, although sporadic germination continued over five germination seasons in all treatments. Seeds germinated only during autumn and early winter each year.The results of the combined experiments suggest that, in nature, Leucospermum seeds can persist underground for long periods. We propose a model of soil-stored seeds in which the intact testa of freshly dispersed seeds is gradually scarified, leading to uneven, extended germination of the young (mainly current season) seed cohort over the first (and possibly several) post-fire germination seasons; and the synchronous germination of the older (scarified), larger, portion of the seed bank, leading to massive species recruitment during the early stages of the first post-fire winter germination season. The numerous wet–dry cycles due to natural rainfall, over prolonged periods in fynbos, may contribute to seed longevity via cellular repair processes.

Tissue-specific hormonal profiling during dormancy release in macaw palm seeds.

Little is known about the control exerted by hormones in specific tissues during germination and post-germinative development in monocot seeds, whose embryos have complex structures and can remain dormant for long periods of time. Here the tissue-specific hormonal profile of macaw palm (Acrocomia aculeata) seeds overcoming dormancy and seedling during initial development was examined. Endogenous hormonal concentrations were determined in the cotyledonary petiole, haustorium, operculum, endosperm adjacent to the embryo and peripheral endosperm of dry dormant seeds, imbibed seeds trapped in phase I of germination, and germinating (phase 2 and phase 3) seeds 2, 5, 10 and 15 days after sowing. Evaluations were performed on seeds treated for overcoming dormancy by removal of the operculum and by immersion in a gibberellic acid (GA3 ) solution. Removal of the operculum effectively helped in overcoming dormancy, which was associated with the synthesis of active gibberellins (GAs) and cytokinins (CKs), as well as reductions of abscisic acid (ABA) in the cotyledonary petiole. In imbibed seeds trapped in phase I of germination, exogenous GA3 caused an increase in active GAs in the cotyledonary petiole and operculum and reduction in ABA in the operculum. Initial seedling development was associated with increases in the CK/auxin ratio in the haustorium and GA levels in the endosperm which is possibly related to the mobilization of metabolic reserves. Increases in salicylic acid (SA) and jasmonic acid (JA) concentrations were associated with the development of the vegetative axis. Hormones play a crucial tissue-specific role in the control of dormancy, germination and initial development of seedlings in macaw palm, including a central role not only for GAs and ABA, but also for CKs and other hormones.

In vitro embryo germination and interploidy hybridization of rose (Rosa sp)

In roses the problems associated with inter-specific breeding include low percent of seed set and lack or low percent of seed germination. Low seed set is usually due to non-amenable parents, which may have different ploidy level or other divergences that result in embryo abortion at early stages of development. Lack of seed germination is mostly attributed to the mechanical restrictions such as thick pericarp or the regulatory mechanisms such as the hormonal control of dormancy. The aims of the present investigation were to optimize in vitro embryo germination technique in rose and study the ploidy of progenies resulted from interploidy hybridizations. To optimize embryo germination, seeds were surface sterilized, whole pericarp and testa were removed and embryos were placed on half strength Murashige and Skoog media supplemented with different concentrations (0, 1, 2.5, 5 mg l−1) of benzyladenine (BA) in combination with different concentrations (0, 0.5, 1, 1.5 mg l−1) of gibberellic acid. The maximum percent of in vitro embryo germination (93.40 %) was observed on medium containing 2.5 mg l−1 BA. In order to select the most fertile seed parents which could be used in interspecific hybridization, 11 commercial rose cultivars (R. × hybrida) were employed in 36 reciprocal crosses. Three rose cultivars including ‘Golden Celebration’, ‘Tess of the d’Urbervilles’ and ‘Molineux’ were selected as the maternal parents. The selected seed parents were employed in crosses with one rose species from Gallicanae section [R. damascena (2n = 4x)] and four rose species form Caninae section [R. orientalis (2n = 5x), R. iberica (2n = 5x) R. canina (2n = 5x) and R. pulverulenta (2n = 6x)]. The highest percent of hip set and in vitro embryo germination were observed in crosses between tetraploid rose cultivars and R. damascena. In all of the crosses with R. canina, the percent of hip and seed set was 0 %. However, in the crosses between tetraploid rose cultivars and other pentaploid or hexaploid rose species from Caninae section both triploid and tetraploid offsprings were attained. Future morphological analysis of the progenies is necessary to show to what extent progenies demonstrate the characteristics of the pollen parents from the Caninae section. Nevertheless, progenies from interploidy hybridizations would be beneficial in future breeding programs in order to expand the relatively small gene pool of roses.