Vernalization in calabrese (Brassica oleracea var. italica) - a model for apex development

Using data from an experiment in controlled environment cabinets,with temperatures between 7 C and 23 C, a model of vernalizationwas developed which predicts the change in apex diameter ofcalabrese with temperature. The model does not include a juvenilephase and the rate of diameter growth is maximal at 15.8 C.When tested on field-grown crops of two cultivars, the modeldescribed apex expansion well. Key words: Model, cardinal temperatures, juvenility, vernalization, initiation     

MORPHOLOGY OF THE CURD OF CAULIFLOWER

Sadik , Sidki . (U. California, Davis.) Morphology of the curd of cauliflower. Amer. Jour. Bot. 49(3): 290–297. Illus. 1962.—The development of the curd and inflorescence of cauliflower, Brassica oleracea Linn., var. botrytis D.C., is described. The cultivars ‘Snowball M’ and ‘February-Early-March’ were studied. The curd has a nonfasciated and monopodial type of branching. Curd initiation of ‘Snowball M’ is not dependent on vernalization, but the curd of ‘February-Early-March’ and the floral primordia of both cultivars are initiated only after vernalization. Associated with flowering is the disruption of the curd by the elongation of some of the inflorescence branches. The initiation of leaves, branches, and floral primordia follows a 5 + 8 phyllotaxy throughout all stages of development. This system of phyllotaxy changes at the time of initiation of floral parts.     

基于生理生态过程的大麦顶端发育和物候期模拟模型

为改进已有的大麦生理发育时间模拟模型(YDmodel),以扬州地区5个品种春播条件下的顶端发育和物候发育观测资料和历史资料为依据,构建了基于生理发育时间的顶端发育和物候期机理模型.模型量化了热效应、光周期、春化效应对发育的影响,引入了7个遗传参数,分别为播种到出苗所需的有效积温、灌浆期发育基点温度、生理春化时间、临界日长、光周期反应起始点、最短苗穗期、最短灌浆期.本模型在YDmodel基础上的改进主要有3点:(1)将每日生理发育时间的增量乘以水肥丰缺因子,改为除以水肥丰缺因子表现水肥对大麦发育的影响,客观体现了大麦在水肥丰缺条件下的发育延迟或提早现象;(2)将三段线性函数改为非线性函数表达春化效应和相对热效应,确立了不同品种相对春化效应和相对热效应的曲线族;(3)将线性函数改为正弦函数表达不同品种光周期效应.经测算,各大麦品种到达单棱期、二棱期、雌雄蕊分化期、药隔形成期、雌蕊柱头二裂分叉期、雌蕊柱头毛状突起期等顶端发育阶段的生理发育时间分别为2.6、5.6、11.3、13.1、15.3、18.2、28.7d,到达出苗期、拔节期、抽穗期、灌浆期和成熟期等主要物候期的生理发育时间为0、13.1、28.7、32.8、51.5d,形成了不同大麦品种在不同气候和栽培条件下统一的衡量发育的定量尺度.     

Novel natural alleles at FLC and LVR loci account for enhanced vernalization responses in Arabidopsis thaliana

Vernalization, the induction of flowering by low winter temperatures, is likely to be involved in plant climatic adaptation. However, the genetic, molecular and ecological bases underlying the quantitative variation that tunes vernalization sensitivity to natural environments are largely unknown. To address these questions, we have studied the enhanced vernalization response shown by the Ll-0 accession of Arabidopsis thaliana. Quantitative trait locus (QTL) mapping for several flowering initiation traits in relation to vernalization, in a new Ler × Ll-0 recombinant inbred line (RIL) population, identified large effect alleles at FRI, FLC and HUA2, together with two small effect loci named as Llagostera vernalization response (LVR) 1 and 2. Phenotypic analyses of near isogenic lines validated LVR1 effect on flowering vernalization responses. To further characterize the FLC allele from Ll-0, we carried out genetic association analyses using a regional collection of wild genotypes. FLC-Ll-0 appeared as a low-frequency allele that is distinguished by polymorphism Del(-57), a 50-bp-deletion in the 5'-UTR. Del(-57) was significantly associated with enhanced vernalization responses and FLC RNA expression, as well as with altitude and minimum temperatures. These results are consistent with Del(-57) acting as a novel cis-regulatory FLC polymorphism that may confer climatic adaptation by increasing vernalization sensitivity.     

The quantitative response of wheat vernalization to environmental variables indicates that vernalization is not a response to cold temperature

The initiation of flowering is a crucial trait that allows temperate plants to flower in the favourable conditions of spring. The timing of flowering initiation is governed by two main mechanisms: vernalization that defines a plant's requirement for a prolonged exposure to cold temperatures; and photoperiod sensitivity defining the need for long days to initiate floral transition. Genetic variability in both vernalization and photoperiod sensitivity largely explains the adaptability of cultivated crop plants such as bread wheat (Triticum aestivum L.) to a wide range of climatic conditions. The major genes controlling wheat vernalization (VRN1, VRN2, and VRN3) and photoperiod sensitivity (PPD1) have been identified, and knowledge of their interactions at the molecular level is growing. However, the quantitative effects of temperature and photoperiod on these genes remain poorly understood. Here it is shown that the distinction between the temperature effects on organ appearance rate and on vernalization sensu stricto is crucial for understanding the quantitative effects of the environmental signal on wheat flowering. By submitting near isogenic lines of wheat differing in their allelic composition at the VRN1 locus to various temperature and photoperiod treatments, it is shown that, at the whole-plant level, the vernalization process has a positive response to temperature with complex interactions with photoperiod. In addition, the phenotypic variation associated with the presence of different spring homoeoalleles of VRN1 is not induced by a residual vernalization requirement. The results demonstrate that a precise definition of vernalization is necessary to understand and model temperature and photoperiod effects on wheat flowering. It is suggested that this definition should be used as the basis for gene expression studies and assessment of functioning of the wheat flowering gene network, including an explicit account of the quantitative effect of environmental variables.     

Interactions of temperature and photoperiod in the control of flowering of latitudinal and altitudinal populations of wild strawberry (Fragaria vesca)

Floral induction and development requirements of a range of latitudinal and altitudinal Norwegian populations of the wild strawberry Fragaria vesca L. have been studied in controlled environments. Rooted runner plants were exposed to a range of photoperiods and temperatures for 5 weeks for floral induction and then transferred to long day (LD) at 20°C for flower development. A pronounced interaction of temperature and photoperiod was shown in the control of flowering. At 9°C, flowers were initiated in both short day (SD) and LD conditions, at 15 and 18°C in SD only, whereas no initiation took place at 21°C regardless of daylength conditions. The critical photoperiod for SD floral induction was about 16 h and 14 h at 15 and 18°C, respectively, the induction being incomplete at 18°C. The optimal condition for floral induction was SD at 15°C. A minimum of 4 weeks of exposure to such optimal conditions was required. Although the populations varied significantly in their flowering performance, no clinal relationship was present between latitude of origin and critical photoperiod. Flower development of SD-induced plants was only marginally advanced by LD conditions, while inflorescence elongation and runnering were strongly enhanced by LD at this stage. The main shift in these responses took place at photoperiods between 16 and 17 h. Unlike all other populations studied, a high-latitude population from 70°N ('Alta') had an obligatory vernalization requirement. Although flowering and fruiting in its native Subarctic environment and after overwintering in the field in south Norway, this population did not flower in the laboratory in the absence of vernalization, even with 10 or 15 weeks of exposure to SD at 9°C. Flowering performance in the field likewise indicated a vernalization requirement of this high-latitude population.     

Ecological genetics of vernalization response in Bromus tectorum L. (Poaceae)

BACKGROUND AND AIMS: Bromus tectorum (cheatgrass or downy brome) is an exotic annual grass that is dominant over large areas of former shrubland in western North America. To flower in time for seed production in early summer, B. tectorum plants generally require vernalization at winter temperatures, either as imbibed seeds or as established seedlings. METHODS: Variation in response to increasing periods of vernalization as seeds or seedlings for progeny of ten full-sib families from each of four B. tectorum populations from contrasting habitats was studied. KEY RESULTS: As vernalization was increased from 0 to 10 weeks, the proportion of plants flowering within 20 weeks increased, weeks to initiation of flowering decreased, and seed yield per plant increased, regardless of whether plants were vernalized as seeds or seedlings. Most of the variation was accounted for by differences among populations. Plants of the warm desert population flowered promptly even without vernalization, while those of the cold desert, foothill and montane populations showed incremental changes in response variables as a function of vernalization period. Populations differed in among-family variance, with the warm desert population generally showing the least variance and the cold desert population the most. Variation among populations and among families within populations decreased as vernalization period increased, whereas the non-genetic component of variance showed no such pattern. CONCLUSIONS: Variation in vernalization response was found to be adaptively significant and apparently represents the result of contrasting selection regimes on a range of founder genotypes.     

Temperature Response of Vernalization in Wheat: Modelling the Effect on the Final Number of Mainstem Leaves

This paper outlines a modelling approach which predicts theeffect of both continuous and intermittent low temperature regimeson the final number of leaves in winter wheat. The model takesaccount of the balance between the concurrent processes of leafprimordium initiation and rate of saturation of vernalization,and their response to temperature. The inverse of the time tosaturation of vernalization, at which stage final leaf numberis set, is modelled as a linear function of vernalizing temperature,between 0 and 17 °C. The rate of leaf primordium initiationis modelled using the established linear relationship betweenrate and temperature above 0 °C. Final leaf number is hencethe product of the number of leaf primordia initiated once vernalizationis saturated. In the model, genotypes are characterized by (1)the slope and intercept of the linear response of the rate ofsaturation of vernalization to temperature in the vernalizingrange, and (2) by a development rate towards floral transitionat on-vernalizing temperatures (above 17 °C). The modelis tested against data from experiments where six cultivarsof winter wheat plants of different ages were exposed to a rangeof low temperature regimes, including continuous and intermittentvernalizing temperatures. Overall, the model predicted, withr ²values of 70–90%, the final leaf number across a rangeof six to 21 leaves. Prediction of final leaf number for somecultivars was better in continuous than in intermittent vernalizingregimes. This modelling approach can explain the often-conflictingreports of the effectiveness of different temperatures for vernalization,and the interaction of plant age and vernalization effectiveness. Triticum aestivum L.; wheat; vernalization; rate; temperature; leaf number; modelling; phenology; flowering     

Tagging and mapping candidate loci for vernalization and flower initiation in hexaploid oat

Flowering time is a decisive factor in the adaptation of oat. Some oat varieties require low temperatures for floral initiation, a process called vernalization. The objectives of this study were to clone, characterize, and map genes associated with vernalization in oat, and to identify markers linked to quantitative trait loci (QTL) that affect vernalization response. Genetic linkage maps were developed using Diversity Arrays Technology markers in recombinant inbred lines from the oat populations UFRGS 8?×?UFRGS 930605 and UFRGS 881971?×?Pc68/5*Starter. Flowering time and response to vernalization were characterized using field trials and controlled greenhouse experiments, and QTL were identified in two genetic regions on each of the two maps. PCR primer pairs anchored in the conserved coding regions of the Vrn1, Vrn2, and Vrn3 genes from wheat, barley, and Lolium were used to amplify and clone corresponding oat sequences. Cloned sequences corresponding to the targeted genes were recovered for both Vrn1 and Vrn3. A copy of the Vrn3 gene was mapped using a PCR amplicon, and an oat Vrn1 fragment was mapped by restriction fragment length polymorphism analysis. The location of the mapped Vrn1 locus was homologous to major QTL affecting flowering time in other work, and homoeologous to major QTL affecting response to vernalization in this study.     

Temperature Response of Vernalization in Wheat: A Developmental Analysis

The vernalization response of wheat ( Triticum aestivum L.)was reinterpreted from a developmental perspective, using currentconcepts of the developmental regulation of wheat morphologyand phenology. At temperatures above 0 °C, the effects ofthe process of vernalization per se in wheat are confoundedby the effects of concurrent vegetative development. These effectsare manifested by differences in the number of leaves initiatedby the shoot apex prior to floral initiation, which in turnaffects the subsequent rate of development to ear emergenceand anthesis. Leaf primordia development during vernalizationand total leaf number at flowering were used to develop criteriato define both the progress and the point of saturation of thevernalization response. These criteria were then used to reinterpretthe results of Chujo ( Proceedings of the Crop Science Societyof Japan 35 : 177–186, 1966), and derive the temperatureresponse of vernalization per se for plants grown under saturatinglong day conditions. The rate of vernalization increased linearlywith temperature between 1 and 11 °C, such that the timetaken to saturate the vernalization response decreased from70 d at 1 °C to 40 d at 11 °C. The rate declined againat temperatures above 11 °C, and 18 °C was apparentlyineffective for vernalization. Total leaf number at saturation,however, increased consistently with temperature, as a resultof the balance between the concurrent processes of leaf primordiuminitiation and vernalization. Total leaf number at saturationincreased from 6 at 1 °C to 13.3 at 15 °C, which inturn influenced the time taken to reach ear emergence. The advantagesof using this developmental interpretation of vernalizationas the basis for a mechanistic model of the vernalization responsein wheat are discussed. Triticum aestivum L.; wheat; vernalization; rate; temperature; primordia; leaf number; flowering     

Expression of Vernalization Genes in Near-isogenic Wheat Lines: Effects of Night Temperature

Four near-isogenic lines of wheat (Triticum aestivum L.em Thell)were used to compare selected night temperatures for their effectivenessas vernalizing temperatures. All treatments (conducted withina phytotron) had a common day temperature of 20 °C for 12h and night temperatures were 4, 7, 10, 13 and 20 °C. Interpretationof results for reproductive development was confounded by threeinteracting factors, their relative importance varying withgenotype. Firstly, development rate was generally slower atlower night temperatures. Secondly, in contrast, there was atendency for lower night temperatures to hasten developmentrate if vernalization requirements were satisfied. Thirdly,the lower night temperatures provided a more favourable environmentfor leaf production such that for some genotypes, vernalizedplants had higher final leaf numbers than unvernalized plants.Only for the genotype with the strongest vernalization response(vrn1 vrn2) did hastening of development due to vernalizationoverride any delaying effects. For this genotype, 4, 7 and 10°C were vernalizing temperatures. For the other three genotypes,any hastening of development due to vernalization was outweighedby delaying effects of lower night temperatures. Spikelet numberand days to anthesis were positively correlated in three ofthe four genotypes. It appeared that differences in spikeletnumber were a direct result of night temperature influencingthe duration of the spikelet phase and/or rate of spikelet initiation.Plant size at flowering was determined by the differential effectsof night temperature on growth and development rates. Triticum aestivum L., wheat, vernalization, night temperature, isogenic lines     

Winter Growth of Autumn-sown White Lupin (Lupinus albus L.) Main Apex Growth Model

The winter growth of winter white lupin (cv. Lunoble) was investigated.Over three consecutive years, 1987–1989, it was sown atdifferent times at Lusignan (France) and in 1989, at nine differentlocations with various sowing times. The production of primordia,the vernalization requirements and the final number of leaveson the main stem were related to field measurements of dailymaximum and minimum temperatures. A statistical model for the main apex growth with a system oftwo equations was developed, with a threshold level for leafprimordia production at 3°C. The number of leaf primordiaproduced by a vegetative apex (y) in terms of the cumulativesums of temperature over 3°C (x) followed the curvilinearregression y = 4.76+ 0.0268x + 0000015 6x². The upper and lowertemperature limits for vernalization were estimated as 14 and1°C respectively. The vernalization requirements of a vegetative apex (y) decreasedwhen the number of initials produced (x) increased accordingto the negative exponential regression y = exp (7.2— 0.02626.x). The two equations were used for the prediction of the finalnumber of leaves of a lupin crop. The predictive accuracy ofthe model was checked against independent data. The agreementbetween observed and predicted final leaf number was often close,but some deviations did occur with low leaf number. The modeldescribed most of the growth phenomena which occur during thephase sowing to floral initiation of the main stem of a winterlupin crop, and its possible uses are discussed Lupinus albus L, white lupin, growth, model, vernalization, primordia, apex, thermal time     

Factors controlling Flowering in the Chrysanthemum: III. FAVOURABLE EFFECTS OF LIMITED PERIODS OF LONG DAY ON INFLORESCENCE INITIATION

Experiments are described which indicate that Chrysanthemumcuttings derived from unvernalized long-day stock plants flowersooner and with lower leaf numbers after vernalization thansimilarly treated cuttings from short-day stock. Long-day treatmentof young cuttings also hastens inflorescence initiation providedthe period of such treatment is limited and given before orimmediately after vernalization. The effect of long day appearsto be maximal when vernalization is complete. Long-day treatmentcannot substitute for vernalization.     

The Influence of Genes for Vernalization Response on Development and Growth in Wheat

Studies were made of the influence of genes for vernalizationresponse on the growth and development of four near-isogeniclines of bread wheat (Triticum aestivum L.). The duration from sowing of flower initiation, terminal spikeletformation and ear emergence all increased with increasing vernalizationresponse. There was a close positive relationship between thedays from sowing to flower initiation and from sowing to earemergence, indicating that the duration of either phase of developmentis a useful measure of relative vernalization when daylengthdoes not limit the rate of development. Total spikelet number per ear and the duration of spikelet initationincreased with increasing vernalization response and there wasa correspondingly higher rate of spikelet initiation in thetwo lines with stronger vernalization response. Most of the differences in growth between the lines were associatedwith diferences in development caused by the vrn genes. Maximumtotal above-ground dry matter and total leaf area per plantincreased with increasing vernalization repsonse but relativegrowth rate and leaf area per plant were not significantly differentbetween the lines. There were no differences in net assimilationrate between the four lines until 40 d from sowing; thereafterit decreased, with the greatest decrease in the line with thestrongest vernalization response. Flower initiation, terminal spikelet formation, spikelet initiation, ear emergence, growth rate     

The expected effects of climate change on wheat development

Air temperature and the atmospheric concentrations of carbon dioxide are expected to rise. These two factor have a great potential to affect development, growth and yield of crops, including wheat. Rising air temperature may affect wheat development more than rising atmospheric CO₂ as there is not yet evidence that elevated CO₂ concentrations can directly induce changes in wheat development. In winter wheat, temperature has a complex effect on development due to its strong interaction with vernalization and photoperiod. In this paper, potential effects of rising temperature on the development of winter wheat from sowing to heading are considered in the light of this complex controlling mechanism. Data from a large series of field trials made in Romania is analysed at first and, subsequently, the IATA-Wheat Phenology model is used to calculate the impact of air warming on wheat development under different climate change scenarios. Data from the field trials showed very clearly the occurrence of a complex temperature/photoperiod/vernalization interaction for field sown crops and demostrated that the photoperiodic and vernalization responses have a key role in controlling the duration of the emergence-heading period. Temperature plays, instead, a central role in controlling seed germination and crop emergence as well as leaf inititiation and leaf appearance rate. The results of model analysis showed very well that the impact of an even or uneven distribution of warning effects may be very different. In the first case, the model predicted that the duration of the vegetative period was at least partly reduced in some years. In the second case, the model suggested that if warming will be more pronounced in winter than in spring, as predicted for some areas of the world by General Circulation Models, we may expect an increase in the duration of the vegetative phase of growth. On the contrary, in case of a spring warming but unchanged winter temperatures, we may expect a substantial decrease in the duration of the vegetative period.     

Winter Growth of Autumn-sown White Lupin (Lupinus albus L.) Main Apex Growth Model

The winter growth of winter white lupin (cv. Lunoble) was investigated.Over three consecutive years, 1987–1989, it was sown atdifferent times at Lusignan (France) and in 1989, at nine differentlocations with various sowing times. The production of primordia,the vernalization requirements and the final number of leaveson the main stem were related to field measurements of dailymaximum and minimum temperatures. A statistical model for the main apex growth with a system oftwo equations was developed, with a threshold level for leafprimordia production at 3 °C. The number of leaf primordiaproduced by a vegetative apex (y) in terms of the cumulativesums of temperature over 3 °C (x) followed the curvilinearregression y = 4.76 + 00268x + 00000156x². The upper and lowertemperature limits for vernalization were estimated as 14 andI °C respectively. The vernalization requirements of a vegetative apex (y) decreasedwhen the number of initials produced (x) increased accordingto the negative exponential regression y = exp (7.2 + 002626.x). The two equations were used for the prediction of the finalnumber of leaves of a lupin crop. The predictive accuracy ofthe model was checked against independent data. The agreementbetween observed and predicted final leaf number was often close,but some deviations did occur with low leaf number. The modeldescribed most of the growth phenomena which occur during thephase sowing to floral initiation of the main stem of a winterlupin crop, and its possible uses are discussed. Lupinus albus L., white lupin, growth, model, vernalization, primordia, apex, thermal time     

The Nature and Duration of Gene Action for Vernalization Response in Wheat

Four near-isogenic lines of wheat were studied to determinethe nature and duration of gene action for vernalization responseunder 2 weekly vernalization periods from 0 to 10 weeks. With time to floral initiation the Vrn 1 Vrn 2 and Vrn 1 vrn2 genotypes showed a cumulative response whereby days to floralinitiation decreased as the period of vernalization increased.The vrn 1 Vrn 2 and the vrn 1 vrn 2 genotypes also showed acumulative response for periods of vernalization less than 6weeks for the former and 8 weeks for the latter. Days to earemergence was closely related to days to floral initiation dueto the constancy of the period from floral initiation to earemergence across all lines and treatments and, consequently,they gave similar measures of the relative strength of vernalizationresponse. It appears that genes for vernalization response ceaseto act after floral initiation. The implications of these findings to breeding for increasedadaptability and yield in wheat are discussed. Triticum aestivum, wheat isogenic lines, vernalization, floral initiation, ear emergence, gene action     

The Effects of Vernalization on the Growth of the Wheat Shoot Apex

he effect of vernalization on the growth of the wheat shootapex was examined by comparing three genetic lines of ChineseSpring (CS) wheat having strong [CS (Hope 5D)], medium (CS Euploid),or no [CS (Hope 5A)] vernalization requirement. The mean volumeof the apical dome increased gradually in all lines, and thenthe apical dome enlarged rapidly as its relative growth rate(RGR) increased prior to double ridge formation. Phytomer volumeat initiation remained constant, so that the ratio of phytomerto apical dome at primordium initiation decreased in successiveplastochrons. In CS Euploid and in unvernalized CS (Hope 5D),the RGR of the apical dome tended to decrease at least untilinitiation of the collar primordium. The rate of primordiuminitiation at double ridge formation increased in proportionto the RGR of the apex at that time; i.e. it increased greatlyin CS (Hope 5A) and vernalized CS (Hope 5D), less so in CS Euploid,but no increase was observed in unvernalized CS (Hope 5D). Thetime of formation of double ridges seemed to be independentof the growth rate or size of the apical dome. The number oftillers present at ear emergence was inversely proportionalto vernalization requirement and was reduced by vernalization.Vernalization resulted in a decrease in the RGR of the newly-initiatedleaf primordia in relation to the RGR of the apical dome andthe axial part of the phytomer. Transfer of plants from longto short days at various times during growth showed that vernalizationincreased the number of labile primordia which could developinto either leaf, collar or spikelet. Vernalization thereforeseems to alter the ability of the apex to respond to subsequentphotoperiod rather than to affect its growth directly. Triticum aeslivum, wheat, chromosome substitution lines, shoot apex growth, vernalization