Graduation date: 1995

Thesis (M.S.)--Oregon State University, 1971. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Vernalization is defined as the response to prolonged cold exposure required for acquiring the molecular competence necessary to undergo floral transition. FLOWERING LOCUS C (FLC), a potent floral repressor in Arabidopsis, is highly expressed before vernalizing cold treatment but is repressed during prolonged vernalization. VERNALIZATION INSENSITIVE 3 (VIN3) is a Plant HomeoDomein (PHD)- containing protein that is required for establishing vernalization-mediated repression of FLC. The induction of VIN3 is one of the earliest molecular events in vernalization response and its expression is intimately linked to prolonged cold exposure. However, mechanisms underlying VIN3 induction remain poorly understood. The constitutive repression of VIN3 in the absence of cold is due to multiple repressive components, including a transposable element-derived sequence, LIKE-HETEROCHROMA TIN PROTEIN 1 (LHP1), and POLYCOMB REPRESSION COMPLEX 2 (PRC2). Furthermore, the full extent of VIN3 induction by vernalization requires activating complex components, including EARLY FLOWERING 7 (ELF7) and EARLY FLOWERING IN SHORT DAYS (EFS). Dynamic changes in the histone modifications present at VIN3 chromatin during vernalization were also observed, indicating that chromatin changes play a critical role in regulating VIN3 induction. However, VIN3 induction by vernalization still occurs in the absence of activation complexes and de- repression of VIN3 in the absence of the repressive complexes is not sufficient for achieving complete induction. Thus, unknown cold-influenced regulators responsible for achieving maximum VIN3 induction during vernalization must exist. Therefore, forward genetic screening was undertaken to elucidate upstream regulators of VIN3. Molecular characterization of T-DNA mutant populations elucidated two interesting mutants: a mutant that ectopically expressed VIN3 before cold (ectopic VIN3 induction, evi1) and mutants that failed to induce VIN3 during vernalization (defects in VIN3 induction, dvi1). FLC is over-expressed in dvi1 despite its failure to induce VIN3 expression during vernalization, suggesting that this mutant may regulate both VIN3 and FLC. In evi1, FLC is hyper-repressed after 40 days of vernalization, leading to an acceleration of flowering time. These results indicate that regulators of VIN3 in the vernalization pathway exist and that these regulators may use different mechanisms in order to influence VIN3 expression. / text

Winter canola (Brassica napus cv. Crystal) requires vernalization, exposure to chilling, to induce bolting and flowering. Since gibberellins (GAs) have been implicated in the regulation of stem elongation and reproductive development in numerous plants, the role of GAs in events induced by vernalization was investigated. Three classical approaches for studying GA physiology were taken. Plant growth regulators were applied and showed that: (i) GA application induced stem elongation but not flowering in nonvernalized plants and (ii) plant growth retardants that block GA biosynthesis prevented elongation and flowering in vernalized plants. Endogenous GAs were extracted from vernalized and nonvernalized shoot tips, chromatographically purified and quantified by gas chromatography-selected ion monitoring. GA1,3,8,19 and 20 concentrations were higher in the vernalized shoots following vernalization. Feeds of [3H]GA20 to vernalized and nonvernalized plants demonstrated higher rates of [3H]GA1 formation after vernalization, suggesting increased metabolism to the biologically active form. Collectively, these studies indicate a regulatory role of GAs in the control of stem elongation in winter canola, but the role of GAs in flowering was less clear. Vernalization apparently induces stem elongation by increasing GA synthesis and particularly the biosynthesis of GA1. / xii, 138 leaves : ill., ports. ; 28 cm.

Factors affecting flowering time have been extensively studied for decades. Greater understanding of flowering time has wider implications in agriculture and ecology as the trait is crucial to optimising reproductive success. It is best understood in the genetic model Arabidopsis thaliana (Arabidopsis), in which loss and gain of function mutations have identified several pathways that regulate flowering and its response to the environment. This has been complemented by studies of natural variation in flowering. Worldwide accessions of Arabidopsis have been used to identify additional flowering regulators and to examine the evolution of these genes and their potential involvement in adaptation to different environments. One of the most extensively studied pathways is responsible for accelerated flowering in response to an extended period of cold (vernalization). Several studies have attributed a substantial proportion of worldwide variation to the genes FRIGIDA (FRI) and FLOWERING LOCUS C (FLC), both of which are instrumental in conferring sensitivity to vernalization, though other genes have also been found. This study examines flowering time variation locally in populations of Arabidopsis from in and around Edinburgh. It identifies substantial, genetically determined variation in flowering time and in sensitivity to photoperiod and vernalization between local accessions. Variation in FRI and FLC sequences and in their levels of expression were detected in local accessions, but these were able to explain little of the phenotypic variation observed. Hybrids between local accessions showing extreme differences in flowering time or responses to photoperiod and vernalization were therefore used to map genes underlying their differences as quantitative trait loci (QTL). This analysis identified a locus in chromosome 5 that could account for differences in vernalization sensitivity. This region includes the VERNALIZATION INSENSITIVE 3 (VIN3) gene. Sequence differences between VIN3 alleles and their expression in response to vernalization supported the potential involvement of this gene in local flowering time variation.

Environmental signals such as photoperiod and temperature provide plants with seasonal information, allowing them to time flowering to occur in favourable conditions. Most ecotypes of the model plant Arabidopsis thaliana flower earlier in long photoperiods and after prolonged exposure to cold (vernalization). The vernalized state is stable through mitosis, but is not transmitted to progeny, suggesting that the vernalization signal may be transmitted via a modification of DNA such as cytosine methylation. The role of methylation in the vernalization response is investigated in this thesis. ¶ Arabidopsis plants transformed with an antisense construct to the cytosine methyltransferase METI (AMT) showed significant decreases in methylation. AMT plants flowered significantly earlier than unvernalized wildtype plants, and the promotion of flowering correlated with the extent of demethylation. The flowering time of mutants with decreased DNA methylation (ddm1) was promoted only in growth conditions in which wildtype plants showed a vernalization response, suggesting that the early flowering response to demethylation operated specifically through the vernalization pathway. ¶ The AMT construct was crossed into two late flowering mutants that differed in vernalization responsiveness. Demethylation promoted flowering of the vernalization responsive mutant fca, but not of the fe mutant, which has only a slight vernalization response. This supports the hypothesis that demethylation is a step in the vernalization pathway. ¶ The role of gibberellic acid (GA) in the early flowering response to demethylation was investigated by observing the effect of the gai mutation, which disrupts the GA signal transduction pathway, on flowering time in plants with demethylated DNA. The presence of a single gai allele delayed flowering, suggesting that the early flowering response to demethylation requires a functional GA signal transduction pathway, and that demethylation increases GA levels or responses, directly or indirectly. ¶ In most transgenic lines, AMT-mediated demethylation did not fully substitute for vernalization. This indicates that part of the response is not affected by METI-mediated methylation, and may involve a second methyltransferase or a factor other than methylation. A second Arabidopsis methyltransferase, METIIa, was characterized and compared to METI. The two genes are very similar throughout the coding region, and share the location of their eleven introns, indicating that they diverged relatively recently. Both are transcribed in all tissues and at all developmental stages assayed, but the level of expression of METI is significantly higher than that of METIIa. The possible functions of METI, METIIa, and other Arabidopsis cytosine methyltransferase genes recently identified are discussed.

Flowering time and flower quality of three nobile dendrobium hybrids in relation to vernalization duration and light intensity during vernalization were studied in the first experiment. Mature Dendrobium Red Emperor 'Prince', Dendrobium Sea Mary 'Snow King', and Dendrobium Love Memory 'Fizz' were cooled at 10 degrees C with 300 to 350 mol·m–2·s–1 photosynthetic photon flux (PPF) (12-h photoperiod) or darkness, each with four cooling durations (2, 4, 6, or 8 weeks). Plants were forced in a greenhouse after vernalization. At least 4 weeks of 10 degrees C cooling in light was needed for flower initiation of Red Emperor 'Prince'; whereas Sea Mary 'Snow King' and Love Memory 'Fizz' only needed 2 weeks of 10 degrees C cooling regardless of light. Darkness during vernalization slightly delayed flowering and resulted in fewer but larger flowers. Longer cooling duration delayed flowering, decreased the flower longevity, and produced larger and more flowers. In the second experiment, Love Memory 'Fizz' were cooled at 15 degrees C for 4 weeks with PPF of 0, 50, 100, or 200 mol·m–2·s–1 (12-h photoperiod). Compared to 200 mol·m–2·s–1, low PPF of 50 or 100 mol·m–2·s–1 did not affect flowering time or flower quality; however, darkness delayed flowering and reduced flower quality. The third experiment was aimed at developing a strategy to defer flowering of nobile dendrobium orchids by holding them under low temperature. Mature Den. Red Emperor 'Prince' and Den. Sea Mary 'Snow King' were held at 10 degrees C for various durations (0, 4, 8, 12 or 16 weeks) after vernalization (4 weeks at 10 degrees C). Plants were forced in a greenhouse after holding. Time to flowering, flower differentiation and flower quality were determined. Increase of low temperature holding duration from 0 to 16 weeks extended time to flowering up to 3 months and did not affect parameters of flower except producing larger flowers and reducing flower number per flowering node for Den. Red Emperor 'Prince'. Notably, the flower longevity was not adversely affected. Defoliation was aggravated in Den. Red Emperor 'Prince' by longer duration of cooling and was considered a detrimental effect of low temperature holding.

Orientador: Marcelo Agenor Pavan / Banca: Filipe Pereira Giardini Bonfim / Banca: Julio Massaharu Marubayashi / Resumo: O alho (Allium sativum L.) não possui semente verdadeiramente botânica, sendo assim, sua única via de propagação se dá vegetativamente, fato este que implica regularmente numa infecção viral mista, se tornando uma das principais causas da redução de produtividade. Alguns produtores já possuem acesso a semente de alho 'Livre de Vírus', no entanto, ainda utilizam de vernalização antiquada, preconizada pela pesquisa para alho semente infectada por vírus (material comum para maioria dos produtores nacionais), e quando utilizada pelos produtores em alho-semente 'Livre de Vírus', vem acarretando problemas principalmente para os produtores do cerrado, onde o plantio é antecipado. Neste estudo foi avaliado o efeito da temperatura de vernalização a 4ºC combinada por diferentes períodos (30, 40, 50 e 60 dias) em bulbilho-semente livre de vírus. O experimento foi conduzido de acordo coma a safra da cultura na região (março à outubro), em fazendas localizadas nos municípios de Santa Juliana (MG) e Campo Alegre de Goiás (GO): regiões de cerrado que se destacam atualmente pela produção de alho nobre no Brasil. Foram avaliadas três das principais cultivares existentes no mercado, sendo elas: Caçador, Quitéria e Ito. As maiores produtividades de bulbos comerciais para as cultivares Caçador em Campo Alegre de Goiás (GO) 2014 e Santa Juliana (MG) 2014 foram nos tratamentos de 30 e 40 dias de vernalização, respectivamente, conciliando produtividades de 11,3 t.ha-¹ e 12,4 t.ha-¹, com boa qualida... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract : Garlic (Allium sativum L.) does not really have truly botanic seeds; therefore, its only way of propagation is vegetatively, which regularly implies in a mixed viral infection that becomes the major cause of reduced productivity. Some producers already have access to garlic seed 'Virus Free', however, still use old-fashioned vernalization, recommended by the search for seed infected garlic virus (common material for most domestic producers), and when used by producers in garlic-seed 'Virus Free', has been causing problems especially for the cerrado producers, where planting is anticipated. This study evaluated the effect of vernalization temperature of 4 ° C combined for different periods (30, 40, 50 and 60 days) in virus free bulbil seed. The experiment was conducted in accordance eat the harvest of culture in the region (march to october), in farms located in the cities of Santa Juliana (MG) and Campo Alegre de Goiás (GO): cerrado regions which are currently out for garlic production noble in Brazil. Were evaluated three of the main existing cultivars on the market, which are: Caçador, Quiteria and Ito. The highest commercial bulbs for Caçador in Campo Alegre de Goiás (GO) 2014 and Santa Juliana (MG) in 2014 were the treatments of 30 and 40 days of vernalization, respectively, combining yields of 11.3 t ha-¹ and 12.4 t ha-¹, with good quality bulb. Quitéria in Campo Alegre de Goiás (GO) in 2014 achieved a better result with treatment of 51 days of vernalization, reaching productivity of 16.8 t ha-¹. 'Ito' 2015 Campo Alegre de Goiás (GO) and Santa Juliana (MG) ... / Mestre

Flower forcing to meet holiday market can increase the value of potted flowering plants. This study was to investigate the effects of chilling and post-chilling photoperiod treatments on flowering of banana shrub and the effects of water stress, daminozide, chlormequat, and ethephon on flowering of bougainvillea. Experiments were conducted at R.R. Foil Plant Science Research Center and MSU Dorman Greenhouse at Mississippi State University (MSU), Mississippi State, MS. Results from banana shrub experiment indicated that 8-week chilling at 8 ºC was necessary for banana shrub to break bud dormancy and a tank mix of daminozide and chlormequat was able to increase the number of flower buds on banana shrub. Results from bougainvillea experiment indicated that water stress, daminozide, and chlormequat enhanced flowering. In conclusion, this study provided fundamental information to future research on flower forcing of banana shrub and bougainvillea.

Flowering time is a carefully regulated trait that integrates cues from temperature and photoperiod to coordinate flowering at favorable times of the year. This dissertation aims to understand the evolution of genetic architecture that facilitated the transition of Pooideae, a subfamily of grass, from the tropics to the temperate northern hemisphere approximately 50 million years ago. Two traits hypothesized to have facilitated this evolutionary shift are the use of long-term low-temperature (vernalization) to ready plants for flowering, and long-day photoperiods to induce flowering. In chapter one I review literature on the regulation of grass flowering by vernalization and photoperiod, and in chapters two and three I determine the role of VERNALIZATION 1 (VRN1) and VRN2, known to confer vernalization responsiveness in core Pooideae crop species, in flowering time across Pooideae. In chapter four, I then test predictions of the hypothesis that the Brachypodium distachyon miR5200 ortholog in the ancestor of Pooideae was important for suppressing short day flowering through its negative regulation of flowering time integrator FLOWERING LOCUS T (FT)/VERNALIZATION3 (VRN3). In combination with other studies, my data demonstrate that VRN1-mediated vernalization responsiveness evolved early in the Pooideae, while VRN2-mediated vernalization responsiveness appears to have evolved much later in the diversification of Pooideae. Although miR5200 likely evolved early in the Pooideae, its transcriptional regulation by short day photoperiod appears derived within Brachypodium distachyon. This work answers important questions about the evolutionary origin of temperature- and photoperiod-mediated flowering in an economically important clade that contains crop species such as wheat (Triticum aestivum) and barley (Hordeum vulgare). Directions for future work on this topic are discussed in chapter 5.