Weeks Of Vernalization Research Articles

Metabolic Profiling in Tuberous Roots of Ranunculus asiaticus L. as Influenced by Vernalization Procedure.

Ranunculus asiaticus L. is an ornamental geophyte. In commercial practice, it is mainly propagated by rehydrated tuberous roots. Vernalization before planting is a common practice to overcome the natural dormancy of tuberous roots; however, little is known about the mechanisms underlying the plant's response to low temperatures. We investigated the influence of three preparation procedures of tuberous roots, only rehydration (control, C), and rehydration plus vernalization at 3.5 °C for 2 weeks (V2) and for 4 weeks (V4), on plant growth, leaf photosynthesis, flowering, and metabolism in plants of two hybrids, MBO (early flowering, pale orange flower) and MDR (medium earliness, bright orange flower), grown in pots in an unheated greenhouse. We reported the responses observed in the aerial part in a previous article in this journal. In this paper, we show changes in the underground organs in carbohydrate, amino acids, polyphenols, and protein levels throughout the growing cycle in the different plant stages: pre-planting, vegetative growth, and flowering. The metabolic profile revealed that the two hybrids had different responses to the root preparation procedure. In particular, MBO synthesized GABA and alanine after 2 weeks and sucrose after 4 weeks of vernalization. In contrast, MDR was more sensitive to vernalization; in fact, a higher synthesis of polyphenols was observed. However, both hybrids synthesized metabolites that could withstand exposure to low temperatures.

Vernalization Promotes GA-Mediated Bolting Initiation via the Inhibition of ABA and JA Biosynthesis

To understand the relationship between vernalization and endogenous phytohormones on bolting, phytohormone levels and transcriptome changes were measured by LC-MS/MS and RNA sequencing before vernalization (CK), at the end of 16 weeks of vernalization (Vel) and at 5 days after vernalization (Re). A total of 32 phytohormone compounds significantly changed after vernalization; especially, the content of abscisic acid (ABA) and jasmonic acid (JA) was dramatically decreased more than sixteen and three times in the Vel and Re samples. In addition, GA19 accumulated after vernalization, while the content of GA53 and GA20 decreased. A total of 7471 differentially expressed genes (DEGs) were identified in response to vernalization. These DEGs were enriched with GO terms including response to stimulus (GO:0050896), response to hormone (GO:0009725) and shoot system development (GO:0048367). KEGG mapping indicated that 16, 13 and 11 DEGs were involved in gibberellic acid (GA), ABA and JA biosynthesis, suggesting a negative role of vernalization in phytohormone biosynthesis. Vernalization also repressed the expression of BvABFs and BvMYC2s, implying the inhibition of ABA and JA signalling. Additionally, vernalization plays a positive role in GA signalling, owing to the down-regulation of BvDELLAs. We also found that GA3-induced bolting could be retarded by exogenous ABA and methyl jasmonate (MeJA). In total, our results suggest that vernalization can promote GA-induced bolting by decreasing BvDELLA repressors of GA signalling and eliminating the antagonistic effects of ABA and JA.

Flowering Times of Wild Arabidopsis Accessions From Across Norway Correlate With Expression Levels of FT, CO, and FLC Genes.

Temperate species often require or flower most rapidly in the long daylengths, or photoperiods, experienced in summer or after prolonged periods of cold temperatures, referred to as vernalization. Yet, even within species, plants vary in the degree of responsiveness to these cues. In Arabidopsis thaliana, CONSTANS (CO) and FLOWERING LOCUS C (FLC) genes are key to photoperiod and vernalization perception and antagonistically regulate FLOWERING LOCUS T (FT) to influence the flowering time of the plants. However, it is still an open question as to how these genes vary in their interactions among wild accessions with different flowering behaviors and adapted to different microclimates, yet this knowledge could improve our ability to predict plant responses in variable natural conditions. To assess the relationships among these genes and to flowering time, we exposed 10 winter-annual Arabidopsis accessions from throughout Norway, ranging from early to late flowering, along with two summer-annual accessions to 14 weeks of vernalization and either 8- or 19-h photoperiods to mimic Norwegian climate conditions, then assessed gene expression levels 3-, 5-, and 8-days post vernalization. CO and FLC explained both FT levels and flowering time (days) but not rosette leaf number at flowering. The correlation between FT and flowering time increased over time. Although vernalization suppresses FLC, FLC was high in the late-flowering accessions. Across accessions, FT was expressed only at low FLC levels and did not respond to CO in the late-flowering accessions. We proposed that FT may only be expressed below a threshold value of FLC and demonstrated that these three genes correlated to flowering times across genetically distinct accessions of Arabidopsis.

The transition to flowering in winter rapeseed during vernalization.

Flowering time is a major determinant of adaptation, fitness and yield in the allopolyploid species rapeseed (Brassica napus). Despite being a close relative to Arabidopsis thaliana, little is known about the timing of floral transition and the genes that govern this process. Winter, semi-winter and spring type plants have important life history characteristics that differ in vernalization requirements for flowering and are important for growing rapeseed in different regions of the world. In this study, we investigated the timing of vernalization-driven floral transition in winter rapeseed and the effect of photoperiod and developmental age on flowering time and vernalization responsiveness. Microscopy and whole transcriptome analyses at the shoot apical meristems of plants grown under controlled conditions showed that floral transition is initiated within few weeks of vernalization. Certain Bna.SOC1 and Bna.SPL5 homeologs were among the induced genes, suggesting that they are regulating the timing of cold-induced floral transition. Moreover, the flowering response of plants with shorter pre-vernalization period correlated with a delayed expression of Bna.SOC1 and Bna.SPL5 genes. In essence, this study presents a detailed analysis of vernalization-driven floral transition and the aspects of juvenility and dormancy and their effect on flowering time in rapeseed.

Developmental and Molecular Changes Underlying the Vernalization-Induced Transition to Flowering in Aquilegia coerulea (James).

Reproductive success in plants is dependent on many factors but the precise timing of flowering is certainly among the most crucial. Perennial plants often have a vernalization or over-wintering requirement in order to successfully flower in the spring. The shoot apical meristem undergoes drastic developmental and molecular changes as it transitions into inflorescence meristem (IM) identity, which then gives rise to floral meristems (FMs). In this study, we have examined the developmental and gene expression changes underlying the transition from the vegetative to reproductive phases in the basal eudicot Aquilegia coerulea, which has evolved a vernalization response independently relative to other established model systems. Results from both our histology and scanning electron studies demonstrate that developmental changes in the meristem occur gradually during the third and fourth weeks of vernalization. Based on RNAseq data and cluster analysis, several known flowering time loci, including AqFT and AqFL1, exhibit dramatic changes in expression during the fourth week. Further consideration of candidate gene homologs as well as unexpected loci of interest creates a framework in which we can begin to explore the genetic basis of the flowering time transition in Aquilegia.

Annualization of the Long Day Onion Breeding Cycle through Threshold Vernalization and Dormancy Disruption

Background: Genetic gain is a function of several parameters including generation time. Onion is a biennial crop that typically requires two full calendar years per generation or breeding cycle. Annualization of onion breeding could double the rate of genetic gain but is technically difficult because of bulb vernalization and dormancy requirements. Methods: Based on recent results that demonstrate vernalization thresholds for long-day onion, we conducted an experiment to assess whether shorter vernalization times could result in faster, uniform flowering with dormancy-broken onion bulbs. Bulbs from eight varieties were subjected to a 15% hydrogen peroxide treatment for 4 h in order to break dormancy. This treatment was followed by either 6 or 12 weeks of vernalization after the first physical signs of dormancy release. The vernalized plants were transferred to 16-h daylengths in a 20 °C greenhouse for flowering. Results: The treatments imposed in this study resulted in the completion of a full generation in less than 12 months for all eight varieties examined. As the length of vernalization at 10 °C increased, we observed greater uniformity in floral initiation and a higher proportion of scape emergence. Plants that were vernalized for 6 weeks flowered 24% earlier than those in the 12-week treatment group. However, we observed greater uniformity in scape emergence both within and among varieties when vernalized for 12 weeks. conclusions: We have developed a framework for an annual cycle breeding system that offers the ability to phenotype bulb traits. We have also identified aspects of the system that will benefit from further refinements. Overall, this annualization system may be useful for advancing generations in onion breeding and reducing the time required to produce new varieties.

Expression of FLOWERING LOCUS C and a frameshift mutation of this gene on chromosome 20 differentiate a summer and winter annual biotype of Camelina sativa.

The nature of the vegetative to reproductive transition in the shoot apical meristem of Camelina sativa summer annual cultivar CO46 and winter annual cultivar Joelle was confirmed by treating seedlings with or without 8 weeks of vernalization. True to their life cycle classification, Joelle required a vernalization treatment to induce bolting and flowering, whereas CO46 did not. In this study, whole genome sequence, RNAseq, and resequencing of PCR‐amplified transcripts for a key floral repressor were used to better understand factors involved in the flowering habit of summer and winter biotypes at the molecular level. Analysis of transcriptome data indicated that abundance for one of the three genes encoding the floral repressor FLOWERING LOCUS C (FLC; Csa20 g015400) was 16‐fold greater in Joelle compared to CO46 prior to vernalization. Abundance of this transcript decreased only slightly in CO46 postvernalization, compared to a substantial decrease in Joelle. The results observed in the winter annual biotype Joelle are consistent with repression of FLC by vernalization. Further characterization of FLC at both the genome and transcriptome levels identified a one base deletion in the 5th exon coding for a keratin‐binding domain in chromosome 20 of CO46 and Joelle. The one base deletion detected in chromosome 20 FLC is predicted to result in a frameshift that would produce a nonfunctional protein. Analysis of whole genome sequence indicated that the one base deletion in chromosome 20 FLC occurred at a greater ratio in the summer biotype CO46 (2:1) compared to the winter biotype Joelle (1:4); similar trends were also observed for RNAseq and cDNA transcripts mapping to chromosome 20 FLC of CO46 and Joelle.

Vernalization Requirement and the Chromosomal VRN1-Region can Affect Freezing Tolerance and Expression of Cold-Regulated Genes in Festuca pratensis.

Plants adapted to cold winters go through annual cycles of gain followed by loss of freezing tolerance (cold acclimation and deacclimation). Warm spells during winter and early spring can cause deacclimation, and if temperatures drop, freezing damage may occur. Many plants are vernalized during winter, a process making them competent to flower in the following summer. In winter cereals, a coincidence in the timing of vernalization saturation, deacclimation, downregulation of cold-induced genes, and reduced ability to reacclimate, occurs under long photoperiods and is under control of the main regulator of vernalization requirement in cereals, VRN1, and/or closely linked gene(s). Thus, the probability of freezing damage after a warm spell may depend on both vernalization saturation and photoperiod. We investigated the role of vernalization and the VRN1-region on freezing tolerance of meadow fescue (Festuca pratensis Huds.), a perennial grass species. Two F2 populations, divergently selected for high and low vernalization requirement, were studied. Each genotype was characterized for the copy number of one of the four parental haplotypes of the VRN1-region. Clonal plants were cold acclimated for 2 weeks or vernalized/cold acclimated for a total of 9 weeks, after which the F2 populations reached different levels of vernalization saturation. Vernalized and cold acclimated plants were deacclimated for 1 week and then reacclimated for 2 weeks. All treatments were given at 8 h photoperiod. Flowering response, freezing tolerance and expression of the cold-induced genes VRN1, MADS3, CBF6, COR14B, CR7 (BLT14), LOS2, and IRI1 was measured. We found that some genotypes can lose some freezing tolerance after vernalization and a deacclimation–reacclimation cycle. The relationship between vernalization and freezing tolerance was complex. We found effects of the VRN1-region on freezing tolerance in plants cold acclimated for 2 weeks, timing of heading after 9 weeks of vernalization, expression of COR14B, CBF6, and LOS2 in vernalized and/or deacclimated treatments, and restoration of freezing tolerance during reacclimation. While expression of VRN1, COR14B, CBF6, LOS2, and IRI1 was correlated, CR7 was associated with vernalization requirement by other mechanisms, and appeared to play a role in freezing tolerance in reacclimated plants.

Studies on the flowering biology of red sorrel (Rumex acetosella) ramets from lowbush blueberry (Vaccinium angustifolium) fields in Nova Scotia, Canada

Red sorrel (Rumex acetosella L.) is a ramet-producing herbaceous creeping perennial species commonly found as a weed in commercially managed lowbush blueberry (Vaccinium angustifolium Aiton) fields in Nova Scotia, Canada. Flowering and seed production occur primarily in overwintering ramets of this species, indicating a potential vernalization requirement for flowering. This study was therefore initiated to examine the role of vernalization, photoperiod, and pre-vernalization stimulus on ramet flowering. Red sorrel ramets propagated from creeping roots and seeds collected from established red sorrel populations in lowbush blueberry had an obligate requirement for vernalization to flower. Ramet populations maintained under pre- and post-vernalization photoperiods of 16 h flowered following 12 weeks of vernalization at 4 ± 0.1 °C, whereas those maintained under constant 16, 14, or 8 h photoperiods without vernalization did not flower. Vernalization for 10 weeks maximized, but did not saturate, the flowering response. Pre-vernalization photoperiod affected flowering response, with increased flowering frequency observed in ramet populations exposed to decreasing, rather than constant, photoperiod prior to vernalization. This study represents the first attempt to determine the combined effects of vernalization and photoperiod on red sorrel flowering, and the results provide a benchmark for the future study of flowering and sexual reproduction in this economically important perennial weed species.

Vernalization responses and subsequent fertility of two climatically distinct populations of rattail fescue (Vulpia myuros [L.] C.C. Gmel.)

Rattail fescue has become increasingly problematic in North America as a result of the greater adoption of no‐till practices. While rattail fescue is described generally as a winter annual, there exists a wide variation in the life history documentation of the species. In some instances, rattail fescue has been observed behaving as a spring annual. In order to assess the vernalization plasticity of rattail fescue, laboratory‐germinated seedlings from two climatically different rattail fescue populations, eastern versus western Oregon, were exposed to 4, 7 or 10°C temperatures for 0, 2, 4, 5, 6, 6.5, 7 or 8 weeks of vernalization. Following vernalization, the seedlings were transferred to a greenhouse and the developmental stages were recorded. After 13 weeks, the emergent inflorescences were clipped and the seeds were tested for germinability. The initiation of sexual development in the eastern population was affected significantly by the vernalization temperature and length, while the western population only responded to the vernalization length. In general, a faster progression through the reproductive stages of development was associated with longer vernalization lengths. Lastly, there was an increase in the germination rate of the seeds that were produced on the parent plants that were subjected to longer vernalization lengths, regardless of the population or vernalization temperature. The level of plasticity in the vernalization response between the two tested populations indicates that land managers should monitor local population life history traits in order to ensure that effective weed control is implemented at the correct growth stage.

Length of vernalization period affects flowering time in three lupin species

With 2 figures and 2 tablesAbstractLupin is a long‐day plant, and its flowering time can be affected by prolonged exposure to cold, ambient temperatures and photoperiod. The vernalization response was investigated in three species of lupins, Lupinus albus L., L. luteus L. and L. mutabilis Sweet., under varying vernalization regimes in glasshouse conditions over summer. A range of genotypes were included from each species. Three weeks after emergence, each line was vernalized for 0–4 weeks in a cool room at 6°±1°C with 14h photoperiod. Vernalization did not affect flowering time in early‐season genotypes of all lupin species. However, significant differences occurred in mid to late‐season genotypes. All genotypes including very late wild types flowered after 2 weeks of vernalization, indicating 2‐week cold treatment was enough to induce flowering. Vernalization synchronized flowering for mid and late‐season genotypes of L. luteus, giving greater flexibility of phenology in long growing season environments where vernalization occurs naturally. Vernalization reduced leaf node number in late‐flowering lines of all species including mid‐season L. luteus.

Variety responses to vernalization and photoperiod in double purpose wheat varieties

The wheat vernalization response is controlled by three recessive alleles identified and located, that allows to characterize varieties through genetic analysis. However, it is unknown whether the same genetic constitution at a loci scale in different varieties implies the same (1) requirement of cold hours, and (2) interaction with the photoperiod for induction. Therefore, we conducted an experiment with varieties carrying the alleles (vrn-A1, vrn-B1 vrn-D1), extreme condition of vernalization requirements, to compare the duration of the vegetative phase under different photoperiods. The study was conducted in a greenhouse with four varieties of double purpose wheat. The treatments were 8, 6, 4, 2 and 0 weeks of vernalization, and two photoperiods: natural - Fn - (approximately 10 h), and extended - Fe - (18 h). At the time of anthesis the number of days to flowering (DaF) since transplantation date was determined. We demonstrated that: (1) the presence of the three recessive alleles does not guarantee an identical performance in the varieties under the tested light regimes; (2) all varieties saturated their requirements with comparable amounts of chilling hours. However, shortening of the flowering period did not determine the same response in all varieties, and (3) our results suggest potential complementary effects of vernalization and photoperiod. However, some regulation coming from the residual genotype of each variety should not be overlooked on genes accountable for responses to vernalization.

Contents of polyamines during vernalization in wheat and the effect of zearalenone

The contents of endogenous free and conjugated polyamines, putrescine (Put) and spermidine (Spd), were determined during 9 week of vernalization (at 5 °C) in winter wheat seedlings cultivated on Murashige and Skoog media without (MS0) and with 2 mg dm−3 zearalenone (MSZEN). At the 4th week of chilling treatment, which is sufficient to induce generative development in 30 % of plants, the marked increase in free and conjugated forms of Put and free Spd were observed. The presence of ZEN in medium significantly accelerated the vernalization. About 20 % of plants treated with ZEN flowered already after 2 weeks and 40 % after 3 weeks of chilling. Significantly higher content of free Put was determined in roots grown on MSZEN compared with MS0 during the first 5 weeks of vernalization with maximum at the 4th week. After germination, a marked decrease in free Spd content was observed both in plants grown on MS0 and MSZEN. Application of ZEN significantly slowed down the Spd decline in leaves and roots during the first and second week of vernalization. The content of Spd and its conjugates decreased in vernalized plants after 1 week of cultivation at 20 °C.

EFFECT OF TEMPERATURE AND PSEUDOBULB MATURITY ON FLOWERING OF THE ORCHID MILTONIOPSIS AUGRES 'TRINITY'

ISHS XXVII International Horticultural Congress - IHC2006: International Symposium on Ornamentals, Now! EFFECT OF TEMPERATURE AND PSEUDOBULB MATURITY ON FLOWERING OF THE ORCHID MILTONIOPSIS AUGRES 'TRINITY'

Temperature and Photoperiod Regulate Flowering of Potted Miltoniopsis Orchids

Miltoniopsis orchids have appealing potted-plant characteristics, including large, fragrant, and showy pansylike flowers that range from white and yellow to shades of red and purple. Scheduling orchid hybrids to flower on specific dates requires knowledge of how light and temperature regulate the flowering process. We performed experiments to determine whether a 9- or 16-h photoperiod [short day (SD) or long day (LD)] before vernalization and vernalization temperatures of 8, 11, 14, 17, 20, or 23 °C under SD or LD regulate flowering of potted Miltoniopsis orchids. Flowering of Miltoniopsis Augres `Trinity' was promoted most when plants were exposed to SD and then vernalized at 11 or 14 °C. Additional experiments were performed to determine how durations of prevernalization SD and vernalization at 14 °C influenced flowering of Miltoniopsis Augres `Trinity' and Eastern Bay `Russian'. Plants were placed under SD or LD at 20 °C for 0, 4, 8, 12, or 16 weeks and then transferred to 14 °C under SD for 8 weeks. Another set of plants was placed under SD or LD at 20 °C for 8 weeks and then transferred to 14 °C with SD for 0, 3, 6, 9, or 12 weeks. After treatments, plants were grown in a common environment at 20 °C with LD. Flowering of Miltoniopsis Augres `Trinity' was most complete and uniform (≥90%) when plants were exposed to SD for 4 or 8 weeks before 8 weeks of vernalization at 14 °C. Flowering percentage of Miltoniopsis Eastern Bay `Russian' was ≥80 regardless of prevernalization photoperiod or duration. This information could be used by greenhouse growers and orchid hobbyists to more reliably induce flowering of potted Miltoniopsis orchids.

Coreopsis grandiflora `Sunray' Flowers in Response to Short Days or Vernalization

Coreopsis grandiflora `Sunray' has been reported to flower under long days (LD) following vernalization or short days (SD). The objectives of this study were to characterize the effective duration of vernalization and SD and to determine if photoperiod during vernalization influences flowering. Vegetative cuttings taken from stockplants developed from one seedling were rooted for 2 weeks and grown for 5 weeks. Plants were provided with a 9-hour photoperiod for 2, 4, 6, or 8 weeks or were vernalized at 5 °C under a 16-hour photoperiod for 2, 4, 6 or 8 weeks or under a 9-hour photoperiod for 2 or 8 weeks. Following treatments, plants were grown in a greenhouse at 20 °C under a 16-hour photoperiod. Control plants were grown under constant 9- or 16-hour photoperiod. Leaf development, days to first visible bud (DVB), days to first open flower (DFLW), and height and total number of flower buds at FLW were recorded. No plants flowered under continuous SD. Under continuous LD, two plants flowered on axillary shoots but only after 95 days. All vernalized and SD-treated plants flowered on both terminal and axillary shoots. Photoperiod during vernalization did not affect subsequent flowering. DFLW decreased from 56 to 42 and from 50 to 42 after 2 to 8 weeks of vernalization and SD treatments, respectively. Following 2, 4, 6, and 8 weeks of vernalization, plants had 116, 116, 132, and 204 flower buds, respectively. Plant height at FLW of all SD-treated and vernalized plants was similar. Thus, 2 weeks of 9-hour SD or vernalization at 5 °C followed by LD was sufficient for flowering of our clone of C.`Sunray', although longer durations hastened flowering and increased flower bud number.

(75) Quantifying the Vernalization Response of Dianthus gratianopolitanus `Bath's Pink'

Two experiments were conducted to quantify the effect of vernalization temperature and duration on flowering of Dianthusgratianopolitanus `Bath's Pink'. In Expt. 1, plants were vernalized at 5 °C for 0, 3, 6, 9, 12, or 15 weeks and in Expt. 2, plants were vernalized at 0, 5 or 10 °C for 0, 2, 4, 6 or 8 weeks. After treatments, plants were forced in a greenhouse at 20 °C. Node development, days to first visible bud (DVB), days to first open flower (DFLW), number of buds and height at FLW were recorded. In Expt. 1, 10% of nonvernalized plants flowered and 100% of vernalized plants flowered. As vernalization duration increased from 3 to 15 weeks, DTVB decreased from 24 to 13. Average DFLW were 114, 41, 34, 33, 33, and 28 for 0-, 3-, 6-, 9-, 12-, and 15-week treatments, respectively. In Expt. 2, 40% of plants flowered without vernalization. Following 2 weeks of vernalization at 0 °C, 80% of plants flowered and as the duration of vernalization increased to ≥4 weeks, all plants flowered. Average DFLW decreased from 38 to 28 following 2 or 4 weeks of vernalization at 0 °C. Longer vernalization did not further reduce DFLW. All plants cooled at 5 °C flowered and vernalization duration did not affect DFLW. Percent flowering after vernalization at 10 °C for 2, 4, 6, and 8 weeks was 20%, 60%, 90%, and 100%, respectively, and average DFLW were 46, 45, 35, and 33, respectively. In conclusion, vernalization is required to force D.`Bath's Pink'. To achieve complete flowering, plants should be vernalized at 5 °C for ≥2 weeks or at 0 °C for 4 weeks or at 10 °C for 8 weeks. Qualitative effects of vernalization such as node development and number of buds and height at FLW will be discussed.

Vernalization and Devernalization of Campanula `Birch Hybrid' and Leucanthemum ×superbum `Snow Cap'

The influence of vernalization temperature and duration and devernalization treatments on subsequent growth and flower development of Campanula `Birch Hybrid' and Leucanthemum ×superbum Bergman ex J. Ingram `Snow Cap' was determined. In the vernalization experiment, plants of `Birch Hybrid' were vernalized at 0, 2.5, 5, 7.5, or 10 °C for 2, 4, 6, or 8 weeks. `Snow Cap' was vernalized at 0, 2.5, 5, or 10 °C for 2, 4, 6, or 8 weeks. In another devernalization experiment, plants of both species were moved to a high temperature (30/10 °C, day/night) growth chamber for 2 or 4 days at various times during or after the 6-week vernalization period. A 6-week vernalization was necessary to obtain 100% flowering in `Birch Hybrid', and 8 weeks of vernalization decreased time to flower by 7 to 10 days compared with 6-week vernalization. Exposure to high temperature for 2 days during or immediately after vernalization did not devernalize `Birch Hybrid' plants, while a 4-day exposure decreased flowering percentage in some treatments and delayed flowering by 7 to 10 days. There were no significant differences in flowering characteristics of `Snow Cap' plants vernalized at 0 to 5 °C for 4 to 8 weeks. A 2-week vernalization at 0, 2.5, 5, or 10 °C or 4 to 8 week vernalization at 10 °C delayed flowering by 5 to 10 days compared with those vernalized at 0 to 5 °C for 4 to 8 weeks. Exposure to high temperature for 2 d did not devernalize `Snow Cap' plants regardless of exposure times, but a 4-day exposure delayed flowering by 4 to 5 days in some treatments. Combined, the data indicate that `Birch Hybrid' has an obligate 6-week vernalization requirement and `Snow Cap' has a facultative 4-week vernalization requirement that can be fulfilled in the 0 to 10 °C range. Exposure to temperatures of 30 °C (9 h·d-1) for 12 out of 42 days did not devernalize either species but in some cases caused a small delay in time to flower.

Vernalization and Growing Degree-day Requirements of Thalictrum delavayi `Hewitt's Double'

Vernalization and growing degree-day requirements of Thalictrum delavayi `Hewitt's Double' were determined to improve the production scheduling of this cut flower crop. Two-year-old crowns of T. delavayi `Hewitt's Double', lifted in the fall, were exposed to cold storage for 0, 3, 6, 9, 12, or 15 weeks at 8 ± 1°C. After storage, the containerized plants were grown at Massey Univ., Palmerston North (40°20.S) in a greenhouse heated at 15°C and vented at 20°C, under a natural photoperiod (11 h increasing to 13 h) plus a 4-h night interruption between 2200 and 0200 HR. As buds continued to develop during storage at 8°C, growing degree-days calculations were made over both storage and greenhouse forcing periods. All plants flowered, but T. delavayi `Hewitt's Double' nevertheless showed a quantitative vernalization requirement, being fully saturated after 6 weeks of cold storage at 8°C. With a base temperature of 0°C, time to flowering reduced from 3338 degree-days without vernalization to an average 2804 degree-days subsequent to the saturation of the vernalization response (6 to 15 weeks of vernalization). Flower yield averaged between three and five stems per plant, with stem lengths ranging between 140 and 200 cm. Differences in flower yield and quality among storage durations were minor and not commercially significant.

Identification of genes expressed in the shoot apex ofBrassica campestris during floral transition

The vegetative-to-floral transition ofBrassica campestris cv. Osome was induced by vernalization. Poly(A)+RNA was isolated from the transition shoot apex after 6 weeks of vernalization, the floral apex after 12 weeks of vernalization and the expanded leaves just before vernalization, and cDNAs were synthesized. These cDNAs were used for subtraction and differential screening to select cDNA preferentially present in the transition and floral apices. Nucleotide sequences of the resulting 14 cDNA clones were determined, and northern blot analysis was carried out on six cDNAs. Two cDNA clones which did not show significant similarity to known genes were shown to be preferentially expressed in the floral apex.