Corm Dormancy Research Articles

GhbZIP30-GhCCCH17 module accelerates corm dormancy release by reducing endogenous ABA under cold storage in Gladiolus.

Gladiolus hybridus is one of the most popular flowers worldwide. However, its corm dormancy characteristic largely limits its off-season production. Long-term cold treatment (LT), which increases sugar content and reduces abscisic acid (ABA), is an efficient approach to accelerate corm dormancy release (CDR). Here, we identified a GhbZIP30-GhCCCH17 module that mediates the antagonism between sugars and ABA during CDR. We showed that sugars promoted CDR by reducing ABA levels in Gladiolus. Our data demonstrated that GhbZIP30 transcription factor directly binds the GhCCCH17 zinc finger promoter and activates its transcription, confirmed by yeast one-hybrid, dual-luciferase (Dual-LUC), chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR) and electrophoretic mobility shift assay (EMSA). GhCCCH17 is a transcriptional activator, and its nuclear localisation is altered by surcose and cytokinin treatments. Both GhbZIP30 and GhCCCH17 positively respond to LT, sugars, and cytokinin treatments. Silencing GhbZIP30 or GhCCCH17 resulted in delayed CDR by regulating ABA metabolic genes, while their overexpression promoted CDR. Taken together, we propose that the GhbZIP30-GhCCCH17 module is involved in cold- and glucose-induced CDR by regulating ABA metabolic genes.

BASIC PENTACYSTEINE2 fine-tunes corm dormancy release in Gladiolus.

Bud dormancy is an important trait in geophytes that largely affects their flowering process and vegetative growth after dormancy release. Compared with seed dormancy, the regulation of bud dormancy is still largely unclear. Abscisic acid (ABA) acts as the predominant hormone that regulates the whole dormancy process. In Gladiolus (Gladiolus hybridus), cold storage promotes corm dormancy release (CDR) by repressing ABA biosynthesis and signaling. However, the mechanisms governing ABA-related processes during CDR via epigenetics are poorly understood. Here, we show that class I BASIC PENTACYSTEINE2, (GhBPC2) directly binds to 9-CIS-EPOXYCAROTENOID DIOXYGENASE (GhNCED) and ABA INSENSITIVE5 (GhABI5) loci and down-regulates their expression to accelerate CDR. During CDR, histone modifications change dramatically at the GhBPC2-binding loci of GhABI5 with an increase in H3K27me3 and a decrease in H3K4me3. GhBPC2 is involved in both H3K27me3 and H3K4me3 and fine-tunes GhABI5 expression by recruiting polycomb repressive complex 2 (PRC2) and the chromatin remodeling factor EARLY BOLTING IN SHORT DAYS (GhEBS). These results show GhBPC2 epigenetically regulates CDR in Gladiolus by mediating GhABI5 expression with PRC2 and GhEBS.

Flower induction and development in saffron: Timing and hormone signalling pathways

The demand for saffron is expected to rise in the coming years due to its nutraceutical and medicinal properties. To cope with this, it will be necessary to develop a mechanised production of saffron. Upgrading the production methods requires accurate control of the flowering time in this species. Nevertheless, little is known about the control of flowering time in Crocus sativus L. The aim of this study is to gain insight into the floral induction regulatory networks operating in this species. A transcriptomic analysis was performed from saffron main buds in different stages of development. The identification of putative integrators of flowering time signals, like FT, as well as meristem identity genes, such as LFY and TFL1, permitted the definition of the time of flowering induction of the buds, being able to use them as molecular markers. The identification of the transcripts encoded by a DROOPING LEAF-like (DL) gene is of particular relevance because this gene might be a novel factor for carpel specification in saffron.To elucidate the hormonal signalling networks working during flower induction, transcriptomic data were used, and the content of IAA, ABA and gibberellins was determined in competent and non-competent buds to flower, during the saffron life cycle. Our results suggested that ABA might be negatively regulating corm dormancy release, but its involvement in flower induction cannot be ruled out. ABI5 and the mediator of ABA regulated dormancy gene MARD1, could be key players of this pathway. In addition, a drop in GA4 levels may also be a necessary, but insufficient, condition for floral induction and development. DELLA, TFL1 and PIF3 genes might be involved in the gibberellin pathway. Notably, IAA seems to be a positive regulator of the process, involving MP/ARF5 and ANT genes in the pathway. Taken together, these results pave the way to the unveiling of the regulatory networks controlling the vegetative-to-reproductive phase change in saffron.

GhNAC83 inhibits corm dormancy release by regulating ABA signaling and cytokinin biosynthesis in Gladiolus hybridus.

Corm dormancy is an important trait for breeding in many bulb flowers, including the most cultivated Gladiolus hybridus. Gladiolus corms are modified underground stems that function as storage organs and remain dormant to survive adverse environmental conditions. Unlike seed dormancy, not much is known about corm dormancy. Here, we characterize the mechanism of corm dormancy release (CDR) in Gladiolus. We identified an important ABA (abscisic acid) signaling regulator, GhPP2C1 (protein phosphatase 2C1), by transcriptome analysis of CDR. GhPP2C1 expression increased during CDR, and silencing of GhPP2C1 expression in dormant cormels delayed CDR. Furthermore, we show that GhPP2C1 expression is directly regulated by GhNAC83, which was identified by yeast one-hybrid library screening. In planta assays show that GhNAC83 is a negative regulator of GhPP2C1, and silencing of GhNAC83 promoted CDR. As expected, silencing of GhNAC83 decreased the ABA level, but also dramatically increased cytokinin (CK; zeatin) content in cormels. Binding assays demonstrate that GhNAC83 associates with the GhIPT (ISOPENTENYLTRANSFERASE) promoter and negatively regulates zeatin biosynthesis. Taken together, our results reveal that GhNAC83 promotes ABA signaling and synthesis, and inhibits CK biosynthesis pathways, thereby inhibiting CDR. These findings demonstrate that GhNAC83 regulates the ABA and CK pathways, and therefore controls corm dormancy.

Influence of size and plant growth regulators on corm and cormel production of gladiolus (Gladiolus grandiflorus L.)

Gladiolus is an excellent cut flower grown throughout the world for its spikes with florets of massive form, brilliant colours, attractive shapes, varying size and long shelf life. However, major constraint for gladiolus cultivation is the corm dormancy. Plant growth regulators (PGRs) play an important role in breaking dormancy and promote more number of quality corm and cormel productions in gladiolus. Therefore, an experiment was conducted to study the influence of corm size and plant growth regulators on corm and cormel production of gladiolus during the period from October 2017 to April 2018 at the Landscaping section of the Department of Horticulture, Bangladesh Agricultural University, Mymensingh. The two-factor experiment included two corm sizes viz., 3-4 cm and 4.1-5 cm, and two PGRs viz., GA3 @ 250, 500 and 750 ppm; and NAA @ 100, 200 and 300 ppm along with tap water as control. The experiment was laid out in a randomised complete block design (RCBD) with three replications. The results revealed that the corm size and PGRs at different concentrations significantly influenced the corm and cormel producing attributes of gladiolus. Maximum number of corms and cormels per plant, maximum weight of single corm, maximum weight of corms and cormels per plant, biggest size of single corm, highest yield of corms and cormels per hectare were recorded from 4.1-5 cm sized corms and GA3 @ 500 ppm, compared to rest of the treatments. It was observed that combined treatments had significant influence on all the parameters studied. The treatment combination of 4.1-5 cm sized corms and GA3 @ 500 ppm was found to be best in terms of corm and cormel production of gladiolus.Progressive Agriculture 29 (2): 91-98, 2018

GhTCP19 Transcription Factor Regulates Corm Dormancy Release by Repressing GhNCED Expression in Gladiolus.

Dormancy is one of the least understood phenomena in plant biology; however, bud/corm dormancy is an important economic trait in agricultural/horticultural breeding. In this study, we isolated an ABA biosynthesis gene, GhNCED, from the transcriptome database of corm dormancy release (CDR), and characterized its negative role in regulating CDR. To understand transcriptional regulation of GhNCED, yeast one-hybrid screening was conducted and GhTCP19 was identified and shown to regulate GhNCED expression directly. An in planta assay showed that GhTCP19 negatively regulates GhNCED expression. GhTCP19 is dramatically induced by exogenous cytokinins (CKs) and is induced during CDR. Silencing of GhTCP19 in dormant cormels delayed CDR, resulting in higher expression of GhNCED and ABA levels. Meanwhile, endogenous CK biosynthesis and signaling were inhibited in GhTCP19-silenced cormels. Taken together, our results reveal that GhTCP19 is a positive regulator of the CDR process by repressing expression of an ABA biosynthesis gene (GhNCED), promoting CK biosynthesis (GhIPT) and signal transduction (GhARR) as well as inducing cyclin genes. This study expands our knowledge on CDR which is mediated by TCP family members.

Boosting saffron (Crocus sativus L.) micro-propagation through in vitro corm production

Lack of availability of quality planting material is hampering the National program of extending saffron area in Morocco. Tissue culture has been found to be a valuable substitute to vegetative propagation due to high proliferation ratio. Corm storage at 35°C has proved to be beneficial not only in making corms more responsive to shooting but also helps in extending corm dormancy thus enabling to remove the bottle neck of available tissue culture protocols being season dependent. These states of dormancy also facilitate the corms disinfection (100%) after been soaked in pure alcohol, and then in 50% bleach solution. Culturing of saffron corms on MS media supplemented with 1.5 mg L-1 BAP + 0.5 mg L-1 NAA helps to produce 12 shoots/corm after 4 weeks. Further sub-culturing on MS + 6.5 mg L-1 BAP + 0.2 mg L-1 NAA promotes shoot multiplication, and thereafter 16 weeks on a MS medium with 3 mg L-1 BAP in combination with 80 g L-1 sucrose leads to microcorm development up to 2 g weight without any dormancy and can be used successfully for a second multiplication cycle. Direct transfer of in vitro corms on peat substratum has been found promising. The in vitro micro-propagation seems to be a very promising technology for saffron production and will help in the diffusion of any genetic progress generated by the current participatory breeding program of saffron in Morocco.

Gladiolus hybridus ABSCISIC ACID INSENSITIVE 5 (GhABI5) is an important transcription factor in ABA signaling that can enhance Gladiolus corm dormancy and Arabidopsis seed dormancy.

The phytohormone abscisic acid (ABA) regulates plant development and is crucial for abiotic stress response. In this study, cold storage contributes to reducing endogenous ABA content, resulting in dormancy breaking of Gladiolus. The ABA inhibitor fluridone also promotes germination, suggesting that ABA is an important hormone that regulates corm dormancy. Here, we report the identification and functional characterization of the Gladiolus ABI5 homolog (GhABI5), which is a basic leucine zipper motif transcriptional factor (TF). GhABI5 is expressed in dormant vegetative organs (corm, cormel, and stolon) as well as in reproductive organs (stamen), and it is up-regulated by ABA or drought. Complementation analysis reveals that GhABI5 rescues the ABA insensitivity of abi5-3 during seed germination and induces the expression of downstream ABA response genes in Arabidopsis thaliana (EM1, EM6, and RD29B). Down-regulation of GhABI5 in dormant cormels via virus induced gene silence promotes sprouting and reduces the expression of downstream genes (GhLEA and GhRD29B). The results of this study reveal that GhABI5 regulates bud dormancy (vegetative organ) in Gladiolus in addition to its well-studied function in Arabidopsis seeds (reproductive organ).

Short communication. Phenological growth stages of saffron plant (Crocus sativus L.) according to the BBCH Scale

Phenological studies are important for understanding the influence of climate dynamics on vegetative growth, flowering and fruiting on plants and can be used in many scientific subjects, such as Agronomy, Botany and Plant Biology, but also Climatology as a result of the current global interest in climate change monitoring. The purpose of the detailed specific culture descriptions of the principal growth stages in plants is to provide an instrument for standardization of data recording. To date, there was no coding method to describe developmental stages on saffron plant (Crocus sativus L.). Because of the increasing world-wide interest on this crop, a novel growth development code based on the BBCH extended scale is proposed in this paper. Six principal growth stages were set up, starting from sprouting, cataphylls and flowers appearance, plant appearance and development, replacement corms development, plant senescence and corm dormancy. Each principal growth stage is subdivided into secondary growth stages. Descriptive keys with illustrations are included to make effective use of the system.

Developmental and stress regulation of gene expression for a 9-cis-epoxycarotenoid dioxygenase, CstNCED, isolated from Crocus sativus stigmas

Oxidative cleavage of cis-epoxycarotenoids by 9-cis-epoxycarotenoid dioxygenase (NCED) is the critical step in the regulation of abscisic acid (ABA) synthesis in higher plants. ABA has been associated with dormancy and flower senescence, while also regulating plant adaptive responses to various environmental stresses. An NCED gene, CstNCED, was cloned from Crocus sativus stigmas. The deduced amino acid sequence of the CstNCED protein shared high identity with other monocot NCEDs, and was closely related to the liliopsida enzymes. At the N-terminus of CstNCED a chloroplast transit peptide sequence is located. However, its expression in chloroplast-free tissues suggested localization in other plastid types. The relationship between expression of CstNCED and the endogenous ABA level was investigated in the stigma and corms, where it was developmentally regulated. The senescence of the unpollinated stigma is preceded by an increase in ABA levels and CstNCED expression. In corms, a correlation was observed between CstNCED expression and dormancy. Furthermore, CstNCED expression was correlated with the presence of zeaxanthin in the dormant corms. When detached C. sativus leaves and stigmas were water and salt stressed, increases in CstNCED mRNA were observed. The results provided evidence of the involvement of CstNCED in the regulation of ABA-associated processes such as flower senescence and corm dormancy in monocotyledonous saffron.

Chilling relieves corm dormancy in Calopogon tuberosus (Orchidaceae) from geographically distant populations

Many plant species require a chilling period to commence regrowth from overwintering structures such as buds, corms, tubers, and rhizomes. While the effects of chilling have been thoroughly studied in a horticultural context, little information exists regarding the relationship between ecotypic differentiation and chilling requirements. Effects of chilling storage organs on shoot emergence of widespread orchid species has not been examined, and ecotypic differentiation in the Orchidaceae has also received little attention. The effects of chilling on corm dormancy in Calopogon tuberosus, a widespread orchid of eastern North America, were studied. Seeds were collected from south Florida, north central Florida, South Carolina, and Michigan, and germinated in vitro to produce plants. After 20 weeks in vitro culture, corms were removed from seedlings and chilled for 0, 2, 4, 6, and 8 weeks. Corms were subsequently planted in a soilless potting mix and placed under ex vitro conditions in an environmental growth chamber. Shoot emergence was monitored bi-weekly for 16 weeks, and shoot length, leaf number, leaf width, root number, root length, and corm diameter were measured after 16 weeks. Longer chilling periods broke corm dormancy more effectively than shorter chilling treatments regardless of population. Shoots of all populations sprouted rapidly on corms after 6 and 8 weeks chilling. In addition, a higher percentage of shoots sprouted on corms after 8 weeks chilling. After 16 weeks, north central Florida and South Carolina plantlets were larger than Michigan and south Florida plantlets. Differing chilling requirements among C. tuberosus populations may reflect ecotypic differentiation resulting from varying environmental conditions at each site.

Temperature effects on corm dormancy and growth of Zephyra elegans D.Don

Experiments were performed with the Chilean geophyte Zephyra elegans, a potential cut flower, to evaluate the effect of corm weight and storage temperature on corm dormancy, and to determine the effect of day and night growing temperatures on its growth and flowering. Z. elegans has a deciduous and synanthous growth habit and the corm is replaced annually. Dormant corms were stored at different constant temperatures or temperature combinations from 20 to 40 °C. Corms released from their dormancy were grown at 15/10, 20/15, or 25/20 °C day/night temperatures. Corms of various weights were planted at the same date after being stored dry at 25 °C for 22 weeks. They all emerged 19–38 days after planting, showing that dormancy release was not affected by corm weight. A 20-week corm storage treatment at a constant 25 °C resulted in the most rapid corm sprouting. Sprouting percentage was reduced at higher or lower storage temperatures. Temperature also affected plant growth. When plants were grown at 15/10 or 20/15 °C they emerged and flowered more rapidly than when they were grown at 25/20 °C. The latter growing temperature also resulted in poor flower quality.

フリージア球茎に対する３℃処理の開花促進効果と３℃感応に影響を及ぼす要因

Corms of Freesia hybrida hort. 'Aladdin' (semi-late flowering cultivar) were exposed to 3°C for 0-4 weeks from August 7, and then to 9°C for 6 weeks, and finally grown at 21°C. Exposing corms to 3°C stopped leaf initiation, and it had no influence on the flower-bud initiation which occurred during the subsequent exposure to 9°C. However, the 3°C treatment hastened flower bud development at 21°C and decreased the number of days at 21°C to flowering by a maximum 10 days. This promotive after- effect of 3°C was not obvious in the early flowering cultivar, 'Rapid Yellow'. Small corms (3.5g) of 'Aladdin' were less responsive to 3°C than were the larger corms (6g). The sensitivity to chilling was gradually increased with time after the corm dormancy broke, indicating that juvenility governs it. Both wet and dry corms responded to the chilling treatment, but the response disappeared when the corms were chilled under controlled atmosphere (CA) at 3% O2, 3% CO2 and 94% N2 or modified atmosphere (MA) in 0.04mm in thick polyethylene bags.

Morphology of flower initiation of brodiaea

The main axis of dormant brodiaea corms ( Triteleia laxa) harvested from the field in the summer comprises a leaf sheath, two leaf primordia, and a vegetative meristem. Floral induction, as indicated by initiation of bracts on the flanks of the apical meristem, occurs after corm dormancy is broken. The bracts enlarge and enclose the reproductive dome, which then divides to form floral primordia of different ages. The daughter corm, which forms from the basal portion of the stem, starts to enlarge early in the growing season. Unlike many other geophytes, there is little competition, in brodiaea, for assimilates between the vegetative propagules (daughter corm and cormels) and the developing inflorescence.

The involvement of ethylene in liatris corm dormancy

The involvement of ethylene in liatris corm dormancy

Changes in abscisic acid levels during dormancy release in freesia corms

A high level of free-abscisic acid (ABA) was detected when corms were still in deep dormancy. The level of free-ABA decreased as the corm dormancy disappeared and increased temporarily after complete release from dormancy. A gradual slight increase of bound-ABA was observed during dormancy release. Treatment of dormant corms with benzyladenine (BA) increased sprouting but the sprouts did not show normal growth. Ethylene treatment induced complete sprouting and subsequent normal growth. Changes in ABA levels and ethylene production are discussed in relation to dormancy release in freesia corms.

Breaking Bud Dormancy in Corms and Trees with Sulfide Compounds in Garlic and Horseradish

Abstract Volatiles from garlic and horseradish paste broke corm dormancy of springflowering gladiolus (Gladiolus × Tubergenii Hort. Effective substances in garlic were allyl sulfide, methyl disulfide, n-propyl disulfide, and those in horseradish were allyl sulfide, allyl isothiocyanate, and n-propyl sulfide. Monosulfide extracted from garlic paste, allyl sulfide, and allyl disulfide were effective in breaking corm dormancy of summer-flowering gladiolus (Gladiolus spp.). Methyl disulfide promoted sprouting and flowering of tree peony (Paeonia suffruticosa Andr.) and flowering of ornamental cherry (Prunus spp.) without phytotoxic symptoms.

春咲きグラジオラスの生態的品種分類

Ecological characteristics of spring-flowering gladiolus were studied, using 5 cultivars with different 5 pedigrees (‘Comet’ of Herald, ‘Charm’ of Tubergenii, ‘Elvira’of Herald×Nanus, ‘Robinetta’ of Ramosus and‘Albus’of Colvillei) and compared with summer-flowering gladiolus.‘Comet’and‘Traveler’of summer-flowering gladiolus flowered earlier when grown at 30-25°C (day-night) than at 20°C (whole day), whereas‘Charm’flowered earlier when grown at 20°C.‘Robinetta’and‘Albus’flowered normally only when grown at 20°C.The effect of day length on flowering was small.‘Elvira’flowered a little earlier when grown under short day than under long day, whereas‘Comet’, ‘Charm’, ‘Robinetta’and‘Albus’flowered a little earlier when grown under long day.Flowering of‘Comet’was severely affected by low light intensity, resulting in 100% blasting. Flowering of‘Elvira’and‘Charm’were appreciably affected whereas flowering of‘Robinetta’was not affected at all.Flower bud initiation and development of‘Charm’, ‘Robinetta’and ‘Albus’ were promoted by low temperature treatment on the corms, whereas those of ‘Elvira’and‘Comet’were not.For breaking corm dormancy, high temperature storage (30°C) was more effective than low temperature storage (5°C) for all the cultivars.Cold hardiness was strongest in‘Robinetta’, intermediate in‘Charm’, ‘Albus’ and‘Comet’, and weakest in‘Elvira’.Drought resistance was strongest in‘Robinetta’, intermediate in‘Albus’and ‘Charm’, and weakest in‘Elvira’and‘Comet’.Thus, spring-flowering gladiolus, which has been regarded as one group, could be ecologically classified into 3 groups: a typical spring-flowering gladiolus type, ‘Albus’and‘Robinetta’, an intermediate type, ‘Charm’, and a summer-flowering type, ‘Comet’and‘Elvira’. Ecological characteristics of these groups well reflected those of their parental species.

DORMANCY IN HOMERIA BREYNIANA (L.) LEWIS

Summary. The variation in the percentage of dormant corms of Homeria breyniana between sites and years was shown for a 3‐year period. The highest dormancy count of 61 % was obtained at Wagin in 1959 while the lowest count of 1% was also obtained in 1959 at Muchea. It was demonstrated that soil surface cover plays an important part in corm dormancy. In 1961 the removal of the surface cover by burning almost eliminated dormancy. Removing the cover at three dates during the summer did not affect the germination of corms during the late autumn. Moreover, corms left in the soil throughout the summer exhibited no physiological dormancy in April. In laboratory tests the percentage germination steadily decreased as the test temperatures were reduced from 25 to 5° C. Soil temperatures follow a similar decline in Western Australia during April and May. Light rains of 12 and 14 points (100 points = 1 in.) gave a significant increase in soil moisture where the surface was bare. Sufficient moisture penetrated to cause a general germination of corms and this resulted in H. breyniana emerging on bare soil some 3 weeks earlier than where surface cover was present. The diurnal temperature range at this time was 54–68° F. The break of the season (the beginning of the growing season) did not occur until 17 days later, and the diurnal soil temperature range had dropped to 49–54° F. Corms subjected to germination tests at these two temperature ranges gave a 90% and 70% sprouting respectively. La dormance des bulbes de Homeria breyniana (L.) Lewis