Vernalization Requirement Research Articles

Natural Variation of Barley Vernalization Requirements: Implication of Quantitative Variation of Winter Growth Habit as an Adaptive Trait in East Asia

In many temperate plant species, prolonged cold treatment, known as vernalization, is one of the most critical steps in the transition from the vegetative to the reproductive stage. In contrast to recent advances in understanding the molecular basis of vernalization in Arabidopsis non-vernalization mutants or the spring growth habits of cereal crops such as wheat and barley, natural variations in winter growth habits and their geographic distribution are poorly understood. We analyzed varietal variation and the geographic distribution of the degree of vernalization requirements in germplasms of domesticated barley and wild barley collections. We found a biased geographic distribution of vernalization requirements in domesticated barley: Western regions were strongly associated with a higher degree of spring growth habits, and the extreme winter growth habits were localized to Far Eastern regions including China, Korea and Japan. Both wild accessions and domesticated landraces, the regions of distribution of which overlapped each other, mainly belonged to the moderate class of winter growth habit. As a result of quantitative evaluations performed in this study, we provide evidence that the variation in the degree of winter growth habit in recombinant inbred lines was controlled by quantitative trait loci including three vernalization genes (VRN1, VRN2 and VRN3) that account for 37.9% of the variation in vernalization requirements, with unknown gene(s) explaining the remaining two-thirds of the variation. This evidence implied that the Far Eastern accessions might be a genetically differentiated group derived for an evolutionary reason, resulting in their greater tendency towards a winter growth habit.

HvFT1 (VrnH3) drives latitudinal adaptation in Spanish barleys

In barley, three genes are responsible for the vernalization requirement: VrnH1, VrnH2 and VrnH3. The winter growth habit of barley requires the presence of a recessive VrnH1 allele, together with an active VrnH2 allele. The candidate for VrnH3 (HvFT1) has been recently identified, with evidences pointing at a central role in the integration of the vernalization and photoperiod pathways. Functional polymorphisms have been proposed, but experimental evidence of their role on agronomic performance and adaptation is needed. We examined allelic variation at the promoter and intron 1 of the HvFT1 gene in a landrace collection of barley, finding a high diversity level, with its geographic distribution correlated with latitude. Focusing on genotypes with winter alleles in VrnH1 and VrnH2, an association analysis of the four main HvFT1 haplotypes found in the landrace collection detected differences in time to flowering. Landraces with the intron 1 TC allele, prevalent in the south, flowered 6-7days earlier than those with the AG allele, under natural conditions. These results were validated in an independent F(2) population. In both data sets, the effect found was similar, but in opposite direction to that described in literature. The polymorphism reported at intron 1 contributes to variation in flowering time under field conditions. We have found that polymorphisms at the promoter also contribute to the effect of the gene on flowering time under field and controlled conditions. The variety of HvFT1 alleles described constitutes an allelic series that may have been a factor in agro-ecological adaptation of barley.

Redox changes during cold acclimation affect freezing tolerance but not the vegetative/reproductive transition of the shoot apex in wheat

Cold acclimation is necessary for winter wheat (Triticum aestivum L.) to achieve its genetically determined maximum freezing tolerance, and cold also fulfils the vernalisation requirement. Chromosome 5A is a major regulator of these traits. The aim of the present study was to discover whether changes in the half-cell redox potential of the glutathione/glutathione disulphide (GSH/GSSG) and ascorbate/dehydroascorbate (AA/DHA) couples induced by cold acclimation are related to freezing tolerance and vernalisation requirement in a specific genetic system including chromosome 5A substitution lines. The amounts of H₂O₂ and AA, and the AA/DHA ratio showed a rapid and transient increase in the crown of all genotypes during the first week of acclimation, followed by a gradual increase during the subsequent 2 weeks. The amount of GSH and its ratio compared to GSSG quickly decreased during the first day, while later these parameters showed a continuous slow increase. The H₂O₂, AA and GSH concentrations, AA/DHA and GSH/GSSG ratios and the half-cell reduction potential of the GSH/GSSG couple were correlated with the level of freezing tolerance after 22 days at 2 °C; hence these parameters may have an important role in the acclimation process. In contrast to H₂O₂ and the non-enzymatic antioxidants, the lipid peroxide concentration and activity of the four antioxidant enzymes exhibited a transient increase during the first week, with no significant difference between genotypes. None of the parameters studied showed any relationship with the vegetative/generative transition state monitored as apex morphology and vernalisation gene expression.

Cross‐genome map based dissection of a nitrogen use efficiency ortho‐metaQTL in bread wheat unravels concerted cereal genome evolution

Monitoring nitrogen use efficiency (NUE) in plants is becoming essential to maintain yield while reducing fertilizer usage. Optimized NUE application in major crops is essential for long-term sustainability of agriculture production. Here, we report the precise identification of 11 major chromosomal regions controlling NUE in wheat that co-localise with key developmental genes such as Ppd (photoperiod sensitivity), Vrn (vernalization requirement), Rht (reduced height) and can be considered as robust markers from a molecular breeding perspective. Physical mapping, sequencing, annotation and candidate gene validation of an NUE metaQTL on wheat chromosome 3B allowed us to propose that a glutamate synthase (GoGAT) gene that is conserved structurally and functionally at orthologous positions in rice, sorghum and maize genomes may contribute to NUE in wheat and other cereals. We propose an evolutionary model for the NUE locus in cereals from a common ancestral region, involving species specific shuffling events such as gene deletion, inversion, transposition and the invasion of repetitive elements.

Time course and amplitude of DNA methylation in the shoot apical meristem are critical points for bolting induction in sugar beet and bolting tolerance between genotypes

An epigenetic control of vernalization has been demonstrated in annual plants such as Arabidopsis and cereals, but the situation remains unclear in biennial plants such as sugar beet that has an absolute requirement for vernalization. The role of DNA methylation in flowering induction and the identification of corresponding target loci also need to be clarified. In this context, sugar beet (Beta vulgaris altissima) genotypes differing in bolting tolerance were submitted to various bolting conditions such as different temperatures and/or methylating drugs. DNA hypomethylating treatment was not sufficient to induce bolting while DNA hypermethylation treatment inhibits and delays bolting. Vernalizing and devernalizing temperatures were shown to affect bolting as well as DNA methylation levels in the shoot apical meristem. In addition, a negative correlation was established between bolting and DNA methylation. Genotypes considered as resistant or sensitive to bolting could also be distinguished by their DNA methylation levels. Finally, sugar beet homologues of the Arabidopsis vernalization genes FLC and VIN3 exhibited distinct DNA methylation marks during vernalization independently to the variations of global DNA methylation. These vernalization genes also displayed differences in mRNA accumulation and methylation profiles between genotypes resistant or sensitive to bolting. Taken together, the data suggest that the time course and amplitude of DNA methylation variations are critical points for the induction of sugar beet bolting and represent an epigenetic component of the genotypic bolting tolerance, opening up new perspectives for sugar beet breeding.

Clinal Variation in Flowering Time and Vernalisation Requirement across a 3000-M Altitudinal Range in Perennial Arabidopsis kamchatica Ssp.Kamchatica and Annual Lowland Subspecies Kawasakiana

Clines in ecologically important traits across environmental gradients provide evidence of historical natural selection. Among the many adaptive traits that are relevant in natural habitats, flowering timing is a primary determinant of a plant’s lifetime fitness. In a laboratory experiment, we studied the divergence in flowering time and vernalisation requirement among 38 populations of two Arabidopsis subspecies: perennial A. kamchatica ssp. kamchatica across an altitudinal gradient from 30 to nearly 3000 m in the Japanese Alps, and its annual lowland subspecies, kawasakiana. Flowering time with vernalisation was not different and flowering time without vernalisation was slightly different between the subspecies; however, the altitude of the source populations was the dominant determinant of the variation in these traits for the species as a whole. The flowering time increased linearly and the effect of vernalisation to shorten the flowering time increased non-linearly with increasing altitude of the source population. Low-altitude populations of ssp. kamchatica from laboratory-collected seeds showed a stronger response to vernalisation than field-collected seeds, suggesting an effect of the maternal environment. By replicating the altitudinal gradient and explicitly accounting for the maternal effect, our results clearly suggest the existence of genetically based clinal patterns that provide signs of adaptive evolution. Early flowering is probably advantageous to completing reproduction before the hot summer at low altitudes. In ssp. kamchatica, which is perennial and can reproduce even if it does not flower in its first year, the strong vernalisation requirement may delay the first reproduction at high altitudes, where the growing season is short.

Selection of double purpose wheat genotypes. Vernalization requirements

Selection of double purpose wheat genotypes. Vernalization requirements

Identification of a large deletion in the first intron of the Vrn-D1 locus, associated with loss of vernalization requirement in wild wheat progenitor Aegilops tauschii Coss.

Vernalization promotes flowering in winter wheat cultivars, whereas spring wheat cultivars are able to transition from vegetative to reproductive phase without vernalization. The wheat vernalization requirement is mainly controlled by the major locus Vrn-1, an APETALA1/FRUITFULL MADS-box gene homolog. To study natural variation of the vernalization requirement in a wild progenitor of common wheat, we sequenced the Vrn-D(t)1 locus in four accessions of Aegilops tauschii Coss. Some structural mutations were found in the promoter and first intron regions of Vrn-D(t)1, and haplotype analysis was conducted to examine the distribution of each identified mutation within 211 accessions of Ae. tauschii germplasm. Out of the total, nine accessions, which were originally collected in Afghanistan and Pakistan, contained deletions of a 5.4-kb sequence in the critical region of the Vrn-D(t)1 first intron. The 5.4-kb deletion mutation appeared independently of the dominant allele of the common wheat Vrn-D1 locus. The large deletion was absolutely associated with a lack of vernalization requirement for flowering under long-day conditions, but had no influence on heading date under field growth conditions. The levels of Vrn-1 and WFT transcript increased in the Ae. tauschii accessions having the large deletion. Identification of natural mutant accessions with a loss of vernalization requirement indicates the agricultural significance of Ae. tauschii as a genetic resource for wheat breeding.

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.

Environmental and molecular analysis of the floral transition in the lower eudicot Aquilegia formosa

BackgroundFlowering is a critical transition in plant development, the timing of which can have considerable fitness consequences. Until recently, research into the genetic control of flowering time and its associated developmental changes was focused on core eudicots (for example, Arabidopsis) or monocots (for example, Oryza). Here we examine the flowering response of Aquilegia formosa, a member of the eudicot order Ranunculales that is emerging as an important model for the investigation of plant ecology and evolution.ResultsWe have determined that A. formosa has a strong vernalization requirement but little or no photoperiod response, making it a day neutral (DN) plant. Consistent with this, the Aquilegia homolog of FLOWERING LOCUS T (AqFT) is expressed in both long and short days but surprisingly, the locus is expressed before the transition to flowering. In situ hybridizations with homologs of several Arabidopsis Floral Pathway Integrators (FPIs) do not suggest conserved functions relative to Arabidopsis, the potential exceptions being AqLFY and AqAGL24.2.ConclusionsIn Aquilegia, vernalization is critical to flowering but this signal is not strictly required for the transcriptional activation of AqFT. The expression patterns of AqLFY and AqAGL24.2 suggest a hypothesis for the development of Aquilegia's determinate inflorescence whereby their differential expression controls the progression of each meristem from inflorescence to floral identity. Interestingly, none of the Aquilegia expression patterns are consistent with a function in floral repression which, combined with the lack of a FLC homolog, means that new candidate genes must be identified for the control of vernalization response in Aquilegia.

‘Tainan No. 1’ Statice: An Early Flowering Limonium Cultivar

Statice [Limonium sinuatum (L.) Mill.] is commercially grown as a cut-flower crop and used for both fresh and dry flower arrangements. Exposure to low temperatures at 11 ± 2 C at the seedling stage promotes flowering. Vernalization requirements differ among cultivars (Semeniuk and Krizek, 1973) and even in a population within the same cultivar (Shillo and Zamski, 1985). The genetic diversity is the result of floral dimorphism in the structure of pollen and stigma. The two known phenotypes, A/cob and B/papillate, exhibit self-incompatibility, whereas crosses between them are fully compatible and produce seeds (Baker, 1953, 1966). Most current statice cultivars are planted in the fall, experience natural cooling in winter, and then flower from spring to summer in the lowlands of Taiwan or other subtropical areas. However, growers have been seeking early-flowering statice cultivars that will produce cut flowers in the winter when the price is higher. Mass selection is often applied in breeding for a lower vernalization requirement to obtain earlier flowering populations (Cohen et al., 1995). In this present work, ‘Tainan No. 1’ was developed through eight continuous generations of mass selection from the parental cultivar Fortress Mix. The horticultural traits of this newly released cultivar are described subsequently.

Conservation and divergence of autonomous pathway genes in the flowering regulatory network of Beta vulgaris

The transition from vegetative growth to reproductive development is a complex process that requires an integrated response to multiple environmental cues and endogenous signals. In Arabidopsis thaliana, which has a facultative requirement for vernalization and long days, the genes of the autonomous pathway function as floral promoters by repressing the central repressor and vernalization-regulatory gene FLC. Environmental regulation by seasonal changes in daylength is under control of the photoperiod pathway and its key gene CO. The root and leaf crop species Beta vulgaris in the caryophyllid clade of core eudicots, which is only very distantly related to Arabidopsis, is an obligate long-day plant and includes forms with or without vernalization requirement. FLC and CO homologues with related functions in beet have been identified, but the presence of autonomous pathway genes which function in parallel to the vernalization and photoperiod pathways has not yet been reported. Here, this begins to be addressed by the identification and genetic mapping of full-length homologues of the RNA-regulatory gene FLK and the chromatin-regulatory genes FVE, LD, and LDL1. When overexpressed in A. thaliana, BvFLK accelerates bolting in the Col-0 background and fully complements the late-bolting phenotype of an flk mutant through repression of FLC. In contrast, complementation analysis of BvFVE1 and the presence of a putative paralogue in beet suggest evolutionary divergence of FVE homologues. It is further shown that BvFVE1, unlike FVE in Arabidopsis, is under circadian clock control. Together, the data provide first evidence for evolutionary conservation of components of the autonomous pathway in B. vulgaris, while also suggesting divergence or subfunctionalization of one gene. The results are likely to be of broader relevance because B. vulgaris expands the spectrum of evolutionarily diverse species which are subject to differential developmental and/or environmental regulation of floral transition.

Cold Acclimation Proteome Analysis Reveals Close Link between the Up-Regulation of Low-Temperature Associated Proteins and Vernalization Fulfillment

Low-temperature (LT) stress is one of the major limiting factors in cereal production in cold high-altitude mountainous areas of Iran where cereals are exposed to variable periods of temperatures in the vernalization range during the autumn season. Cereals regulate their development through adaptive mechanisms that are responsive to low but nonfreezing temperatures. We exploited a proteomic approach to determine the interrelationship between vernalization fulfillment and expression of low-temperature (LT)-induced protein in most hardy Norstar and semi-hardy Azar2 wheat (Triticum aestivum L. em. Thell). These cultivars were subjected to 12 h of cold acclimating temperature (2 °C) over a period of 0-89 days. LT tolerance, as measured by LT50, and vernalization fulfillment, as estimated from final leaf number (FLN), was determined at intervals throughout the acclimation period. A significant decrease in FLN associated with LT treatment indicated that Norstar and Azar2 had vernalization responses. Azar2 achieved its vernalization fulfillment and maximum LT tolerance (∼ -8 °C) by 28 days of acclimation. However, Norstar had a longer vernalization requirement (between 35 and 42 days) and reached vernalization fulfillment and maximum LT tolerance (∼ -18.7 °C) about the same time as vernalization fulfillment. We applied a two-dimensional electrophoresis-based proteomics approach to analyze changes in the leaf proteome of two genotypes, Norstar and Azar2, during cold acclimation. Using MALDI-TOF/TOF mass spectrometry, 66 LT-associated proteins could significantly be identified. These proteins were categorized into cold-regulated proteins, antifreezing proteins, oxidative stress defense, photosynthesis, chloroplast post-transcriptional regulation, metabolisms, and protein synthesis. A close association between the vernalization fulfillment and the start of a decline in the protein accumulation of hardy Norstar with a long vernalization requirement and semi-hardy Azar2 with a short vernalization requirement was observed. This finding supported the hypothesis that developmental trait which was regulated by vernalization had a regulatory influence over LT proteome response and highlight a close link between the up-regulation of LT-associated proteins and vernalization fulfillment at the molecular level in wheat.

Modelling cold hardening and dehardening in timothy. Sensitivity analysis and Bayesian model comparison

Timothy ( Phleum pratense L.) is the most important forage grass in Scandinavia and it is therefore highly interesting to study how it will perform in a changing climate. In order to model winter survival, the dynamics of hardening and dehardening must be simulated with satisfactory precision. We investigated an early timothy frost tolerance model (LT50 model), and an LT50 model for winter wheat. Based on the assumption that timothy has no vernalization requirement, unlike winter wheat, but does have the ability to adapt to cold temperatures in a process linked to stage of development, two alternative versions of the winter wheat model were also constructed. In total, these four candidate models were calibrated by a Bayesian approach for the timothy cultivar Engmo. The candidate models were validated using independent observations on LT50 in timothy at different locations reflecting differences in climate. A sensitivity analysis, using the Morris method, to identify important model parameters suggested that there is a connection between frost tolerance and stage of plant development, even if there is no vernalization requirement. The simplified winter wheat model was selected as the best candidate model for LT50 in timothy based on model selection criteria and its ability to capture the hardening and dehardening processes. The results from the Bayesian calibration suggest that there are no major regional differences in Norway calling for regional calibration. However, cultivar-specific calibration is probably required, since there are hardy and less hardy cultivars within the same species. A functional LT50 model would allow risk assessments to be made of future winter survival using specifically tailored and downscaled climate scenarios.

Introgression of an intermediate VRNH1 allele in barley (Hordeum vulgare L.) leads to reduced vernalization requirement without affecting freezing tolerance

The process of vernalization is mainly controlled by two genes in winter barley (Hordeum vulgare L.), VRNH1 and VRNH2. A recessive allele at VRNH1 and a dominant allele at VRNH2 must be present to induce a vernalization requirement. In addition, this process is usually associated with greater low-temperature tolerance. Spanish barleys originated in areas with mild winters and display a reduced vernalization requirement compared with standard winter cultivars. The objective of this study was to investigate the genetic origin of this reduced vernalization requirement and its effect on frost tolerance. We introgressed the regions of a typical Spanish barley line that carry VRNH1 and VRNH2 into a winter cultivar, Plaisant, using marker-assisted backcrossing. We present the results of a set of 12 lines introgressed with all four possible combinations of VRNH1 and VRNH2, which were evaluated for vernalization requirement and frost tolerance. The reduced vernalization requirement of the Spanish parent was confirmed, and was found to be due completely to the effect of the VRNH1 region. The backcross lines showed no decline in frost tolerance compared with that of the recurrent parent unless they carried an extra segment of chromosome 5H. This extra segment, a carryover of the backcross process, apparently contained the well-known frost tolerance quantitative trait locus Fr-H2. We demonstrate that it is possible to manipulate the vernalization requirement with only minor effects on frost tolerance. This finding opens the path to creating new types of barley cultivars that are better suited to specific environments, especially in a climate-change scenario.

Cold-induced changes of enzymes, proline, carbohydrates, and chlorophyll in wheat

Quantitative changes in total leaf soluble proteins, proline, carbohydrate content, chlorophyll fluorescence, guaiacol peroxidase (POD) and catalase (CAT) activities were determined in a less cold-hardy (LCH) spring cv. Kohdasht (LT50 = −6°C), a semi cold-hardy (SCH) facultative cv. Azar 2 (LT50 = −15°C), and a cold-hardy (CH) winter cv. Norstar (LT50 = −26°C) of wheat (Triticum aestivum L.) exposed to 4°C for 9 weeks. Seedlings were grown in a controlled growth room for 14 days at 20°C and then transferred to 4°C (experimental day 0) for 63 days (cold treatment); otherwise they were maintained continuously at 20°C (control treatment). The samples were harvested 0, 2, 21, 28, 42, and 63 days after exposure to 4°C. The results showed significant low temperature (LT)-induced accumulation of total soluble proteins, proline, and carbohydrates and elevation in activities of CAT and POD in leaves of SCH and CH winter cultivars rather than in LCH spring cultivar. In contrast, the chlorophyll fluorescence (Fv/Fm) declined during LT treatment irrespective of cultivar. The results suggest that developmental traits such as vernalization requirement of wheat affects on cold-tolerance expression system of plants.

A survey of EMS-induced biennial Beta vulgaris mutants reveals a novel bolting locus which is unlinked to the bolting gene B

Beta vulgaris is a facultative perennial species which exhibits large intraspecific variation in vernalization requirement and includes cultivated biennial forms such as the sugar beet. Vernalization requirement is under the genetic control of the bolting locus B on chromosome II. Previously, ethyl methanesulfonate (EMS) mutagenesis of an annual accession had yielded several mutants which require vernalization to bolt and behave as biennials. Here, five F2 populations derived from crosses between biennial mutants and annual beets were tested for co-segregation of bolting phenotypes with genotypic markers located at the B locus. One mutant appears to be mutated at the B locus, suggesting that an EMS-induced mutation of B can be sufficient to abolish annual bolting. Co-segregation analysis in four populations indicates that the genetic control of bolting also involves previously unknown major loci not linked to B, one of which also affects bolting time and was genetically mapped to chromosome IX.

Plant responses to cold: transcriptome analysis of wheat

Temperature and light are important environmental stimuli that have a profound influence on the growth and development of plants. Wheat varieties can be divided on the basis of whether they require an extended period of cold to flower (vernalization). Varieties that have a requirement for vernalization also tend to be winter hardy and are able to withstand quite extreme subzero temperatures. This capacity, however, is not constitutive and plants require a period of exposure to low, non-freezing temperatures to acquire freezing tolerance: this process is referred to as cold acclimation. Cold acclimation and the acquisition of freezing tolerance require the orchestration of many different, seemingly disparate physiological and biochemical changes. These changes are, at least in part, mediated through the differential expression of many genes. Some of these genes code for effector molecules that participate directly to alleviate stress. Others code for proteins involved in signal transduction or transcription factors that control the expression of further banks of genes. In this review, we provide an overview of some of the main features of cold acclimation with particular focus on transcriptome reprogramming. In doing so, we highlight some of the important differences between cold-hardy and cold-sensitive varieties. An understanding of these processes is of great potential importance because cold and freezing stress are major limiting factors for growing crop plants and periodically account for significant losses in plant productivity.

Floral ontogeny of Brunonia australis (Goodeniaceae) and Calandrinia sp. (Portulacaceae)

Floral ontogeny of Brunonia australis Sm. ex R.Br. (blue pincushion) and Calandrinia sp. (not yet fully classified) was investigated by scanning electron microscopy to assist further efforts for manipulating flowering of these potential floriculture crops. This is the first work to study floral initiation and the stages of flower development for these species. Floral initiation of B. australis commenced 28 days after seed germination when grown at 25/10 or 35/20°C (day/night) under long days (11 h of ambient light at 553 ± 45 µmol m–2 s–1, plus a 5-h night break at <4.5 µmol m–2 s–1). Leaf number at floral initiation reflected differences in the accumulated thermal time between treatments so that about double the number of leaves formed at 35/20°C. This suggested differing temperature responses for leaf and phenological development, and that leaf number was not a good indicator of floral initiation. For Calandrinia sp., floral initiation commenced 47 days after seed germination when grown at 25/10°C. Hot temperatures (35/20°C) inhibited flowering; indicating a vernalisation requirement. For B. australis, the pattern of floret development was centripetal, with flowers organised into five whorls. Four bracts surrounded each flower, whereas the sepals, petals and stamens showed a pentamerous arrangement. A central style was terminated by an indusial stigmatic presenter. Flowers of Calandrinia sp. consisted of four whorls, namely two sepals, 8–10 petals, numerous stamens produced centrifugally and a central syncarpous gynoecium with four stigmatic branches.

Bolting and flowering control in sugar beet: relationships and effects of gibberellin, the bolting gene B and vernalization

Bolting, the first visible sign of reproductive transition in beets (Beta vulgaris), is controlled by the dominant bolting gene B (B allele), which allows for flowering under long days (LDs, >14 h light) without prior vernalization. The B-locus carries recessive alleles (bb) in sugar beet (Beta vulgaris L. spp. vulgaris), so that vernalization and LDs are required for bolting and flowering. Gibberellin growth hormones (GAs) control stem elongation and reproductive development, but their role during these processes in sugar beet is not defined. We aimed to investigate the involvement of GAs in bolting and flowering in sugar beet, and also its relationship with the vernalization requirement as defined by the B-gene. Plants segregating for the B allele were treated with exogenous GA(4) under inductive (16 h light) and non-inductive (8 h light) photoperiods, with and without prior vernalization treatment. A co-dominant polymerase chain reaction (PCR) marker was used to genotype the B-gene locus. Bolting and flowering dates were scored, and bolt heights were measured as appropriate. Analysis of variance was used to determine the effects and interactions of GAs, the B allele and vernalization on bolting and flowering. The effects of the B allele on bolting were also verified in the field. Application of GAs or the B allele could initiate bolting independently. When the B allele was absent, the applied GAs promoted stem growth, but did so only in vernalized plants, irrespective of photoperiod. Under LDs, bolt height before flowering in plants carrying the B allele (BB; Bb) was not significantly influenced by GAs. The timing and frequency of flowering were influenced by the B allele without interactive effects from GAs. In sugar beet, GA acts independently of the B allele and photoperiod to induce bolting. Vernalization enables GA action independently of the B allele; hence, the dominant B allele may not directly participate in vernalization-induced bolting.