The Control of Flowering, Growth, and Dormancy in Kleinia articulata by Photoperiod

Kleinia articulata subjected to different photoperiods becomesdormant in long days (continuous light) and grows uninterruptedlyin short days (8 h). Dormancy results from the rapid cessationof leaf differentiation and expansion. By contrast stem growthis faster in long days and continues until all leaves have died.In long days growth is not halted permanently but flushes ofleaf production and stem elongation occur. Resumption of growthis stimulated rapidly by total darkness or short-day treatmentof the extreme stem tips for some days. This species is a strictshort-day plant in its flowering behaviour, depending on thisdaylength for normal inflorescence development also.     

Interaction of Daylength and Applied Gibberellins on Stem Growth and Leaf Production in Three Varieties of Celery

Pressman, E. and Negbi, M. 1987. Interaction of daylength andapplied gibberellins on stem growth and leaf production in threevarieties of celery.—J. exp. Bot. 38: 968–971. Exogenous application of gibberellins (GAs) stimulated stemlength. The extent of this stimulation was less in long photoperiods,as long days (LD) or as long nights interrupted by night breaks(NB), than it was in short days (SD). Long photoperiods increasedthe length and erectness of leaves and reduced leaf number.Similar morphological changes were stimulated by applied GAs,which were more effective on plants grown in SD than on thosein LD. It is suggested that long photoperiods cause these morphologicalchanges via the production or metabolism of endogenous GAs,but it is not clear how endogenous GAs interact with the appliedones. Key words: Daylength, gibberellins, stem growth, leaf production, celery     

Duration and Rate of Development Phases in Wheat in Two Environments

Six cultivars of bread wheat (Triticum aestivum ssp. vulgareL. amend. Thell.) of diverse climatic origin and different developmentalpatterns were studied under two environments, (a growth roomand an outdoors sowing) for the duration and rate of completionof their developmental phases. The need for vernalization in the cultivar Cappelle Desprezsubstantially increased the length of the vegetative phase,particularly in the growth room. Large differences in the durationof reproductive initiation and stem elongation phases betweenCappelle Desprez and the other cultivars in the growth roomsowing suggests an influence of veralization beyond the vegetativephase. Differences between the two environments influenced the durationof all phases of development, giving pronounced between-cultivarvariation in both the stem elongation and ripening phases. Rates of reproductive initiation and stem elongation for thecultivars, within and between the two environments appearedto be largely independent. The rate of spikelet initiation wassignificantly decreased in the growth room compared with theoutdoor sowing. The duration of the phases of development withineach cultivar appeared to be independent of each other, indicatingthe possibility for adjusting the rate, or duration, of a phaseof development comparatively free of a compensatory change inthe rate, or duration, of other phases. Triticum aestivum ssp, vulgare, wheat, vegetative phase, flower initiation, vernalization, photoperiodism     

Effect of Flowering on the Photosynthetic Capacity of Ryegrass Leaves Grown With and Without Natural Shading

The photosynthetic capacity of newly expanded leaves of vernalizedor non-vernalized plants of S24 perennial ryegrass (Lolium perenneL.), grown in long or short photoperiods, was measured in twoexperiments. In the first, leaves were protected from shadingduring development, while in the second, the natural shade ofneighbouring tillers in a sward was allowed. In the first experiment there was little effect of vernalization,day length or flowering, and leaves in all treatments had photosyntheticrates at 250 W m^–2 of between 28 and 32 mg CO₂ dm^–2h_–1.In the second experiment the photosynthetic rate of successiveleaves fell as sward leaf area increased. This downward trendwas reversed, however, in flowering tillers in the vernalizedlong-day treatment, while in the other treatments, which didnot flower, photosynthetic capacity continued to fall. It isconcluded that the leaves of reproductive tillers have highphotosynthetic capacities because stem extension carries themto the top of the canopy where they are well illuminated duringexpansion. Lolium perenneL, ryegrass, photosynthetic capacity, flowering, shading, vernalization     

Flowering Behaviour of Four Annual Grass Species in Relation to Temperature and Photoperiod

Populations of four co-habiting annual grass species Bromusmollis L. (Soft brome), Hordeum hystrix Roth (Mediterraneanbarley grass), Lolium rigidum Gaud. (Wimmera ryegrass) and Vulpiabromoides (L.) S. F. Gray (Squirrel-tail fescue) were examinedfor the presence and comparative levels of vernalization andphotoperiod response. This was evaluated as the number of daysfrom sowing to heading in both long (16 h) and short (normal,over-winter) photoperiods at two levels of temperature. Wide variation among the species in both vernalization and photoperiodicresponse was detected. L. rigidum possessed a high level ofvernalization response and was comparatively sensitive to photoperiodwhile V. bromoides possessed little or no vernalization responseand was comparatively insensitive to photoperiod. B. mollisand H. hystrix appeared to be intermediate between these twospecies for both responses. There were wide differences in timeto heading under long photoperiod (16 h) and high temperature(20 °C) of plants derived from seed of three of the speciesripened under non-vernalizing temperatures. This variation indicatesthe likely existence of genetic differences in vernalizationresponse between plants of these populations. The implications of these findings to the adaptability of thesespecies to the Australian environment have been outlined. Bromus mollis L., soft brome, Hordeum hystrix Roth, Mediterranean barley grass, Lolium rigidum Gaud, Wimmera ryegrass, Vulpia bromoides (L.) S. F. Gray, Squirrel-tail fescue, flowering, vernalization, photoperiod, temperature     

Effects of Photoperiod, Nitrogen Nutrition and Temperature on Inflorescence Initiation and Development in Onion (Allium cepa L.)

The effects of photoperiod, nitrogen nutrition and temperatureon inflorescence initiation and development in onion cv. Rijnsburgerand cv. Senshyu Semi-globe Yellow were studied in controlledenvironments. Rates of inflorescence initiation were estimatedusing the data for leaf numbers formed prior to flower formationand the rates of leaf initiation. At 9 °C inflorescenceinitiation was accelerated by long photoperiods particularlyfor cv. Rijnsburger where the average time for initiation was86 days in 8 h and 38 days in 20 h photoperiods. Initiationwas as rapid at 12 °C as at 9 °C but was slower at 6°C. A reduction in the nitrate concentration in the nutrientsolution from 0.012 to 0.0018 M greatly accelerated inflorescenceinitiation particularly in photoperiods and temperatures notconducive to rapid initiation. Cv. Senshyu initiated more slowlythan cv. Rijnsburger and was less sensitive to photoperiod andnitrogen level. The development rate of inflorescences afterinitiation was accelerated by long photoperiods and increasesin temperature from 6 to 12 °C but was retarded by the lowernitrogen level. Allium cepa L., onion, flower initiation, inflorescence development, photoperiod, nitrogen nutrition, temperature, vernalization     

Control of Stem Elongation and Flowering in Scrophularia marilandica

The influence of temperature, photoperiod. and certain metabolities was determined for stem elongation and flowering in Scrophularia marilandica. Induction for flowering did not occur until several weeks after the beginning of rapid stem elongation. From the experiments reported it is concluded that S. marilandica is a high-temperature quantitative long-day plant. Temperatures above 20°C negate the absolute requirement for long days for flowering. Plants exposed to photoperiods as brief as 4 hours flowered, given high temperatures. Stem elongation was found to be a necessary prerequisite for flowering. The process of stem elongation was somewhat more sensitive to inhibition by low temperatures than flowering and to a great extent more sensitive than leaf formation and leaf growth. Vernalization was found to be unnecessary for stem elongation and flowering. Gibberellic acid promoted stem elongation and branching without flowering under conditions resembling cool short days. Other metabolities were tested but had no observable effects.     

Photothermal Time for Flowering in Faba Bean (Vicia faba) and the Analysis of Potential Vernalization Responses

One cultivar and one land-race of faba bean were subjected to18 potentially vernalizing pre-treatments (constant temperaturesof 1, 5 or 9 °C factorially combined with photoperiods of8 or 16 h d^–1 for 10, 30 or 60 d), and then transferredinto four different growing regimes (‘day’/‘night’temperatures of 18/5 °C or 24/13 °C factorially combinedwith photoperiods of 11 or 16 h d–1). Control plants weregrown entirely in the latter four regimes. The times from sowingto appearance of first open flowers were recorded for all plants.Control plants of the land-race Zeidab Local flowered soonerin long days and in the warmer regime. Pre-treatment reducedthe subsequent time to flower in the four growing-on regimesbut most of the variation in the total time to first flowerfor the pre-treated plants was accounted for by differencesin the combined photothermal time accumulated in the two successiveenvironments - which was predicted by a simple photothermalmodel. Thus, there was neither a specific low-temperature nora short-day vernalization response in this accession. Similarly,no true low-temperature or short-day vernalization responsewas detected in the cv. Maris Bead. However, this UK cultivarflowered later than predicted in the 24/13 °C regime, indicatingthat the 24 °C ‘day’ temperature was supraoptimal.Delays to flowering at 24/13 °C were, however, less evidentwhen plants were grown in long days or following prolonged (30–60d) pre-treatments at cool temperatures. Viciafaba faba, bean, flowering, photoperiodism, vernalization, photothermal time, screening germplasm.     

Vernalization in Chickpea (Cicer arietinum); Fact or Artefact?

Various cool treatments of imbibing seeds reduced the subsequenttimes taken to flower in two genotypes of chickpea (Cicer arietinumL.). These reductions were greater in the kabuli cv. Rabat thanin the desi accession ICC 5810. Nevertheless, in both genotypes,the hastening of flowering was entirely accounted for by thephotothermal time accumulated during each cool temperature pretreatment,provided it was recognized that the ceiling photoperiods wereapproximately 10 and 8 h d^–1, respectively; i.e. neithergenotype shows a true vernalization response. A thorough reevaluationof ‘ responsiveness to vernalization’ in the chickpeagermplasm might now be prudent. Cicer arietinum L, chickpea, vernalization, photothermal time, screening germplasm     

Effects of Interactions between Low-temperature Treatments, Gibberellin (GA3) and Photoperiod on Flowering and Stem Height of Spring Rape (Brassica napus var. annua)

Exogenous gibberellin A₃(GA₃) reduced the number of leaf nodesat flowering and time to flowering and increased the stem heightat flowering in three genotypes of spring rape (Brassica napusvar.annua L.). The responses to GA₃were similar to those forlong days (LD) and low-temperature treatments, suggesting thatthe effect of photoperiod and the vernalization response areprobably mediated through gibberellins. The response to exogenousGA₃was greatest in non-cold-treated plants in short days (SD)suggesting that endogenous GAs are limiting in these conditions.CCC, an inhibitor of gibberellin biosynthesis, caused a smallincrease in the number of leaf nodes at flowering and time toflowering and a small decrease in the stem height at flowering,but unexpectedly, its effect was hardly influenced by the applicationof exogenous GA₃. Genotypes that showed the clearest responsesto the treatments with regard to the number of leaf nodes atflowering and time to flowering did not show the clearest responseswith regard to the stem height at flowering; the pattern ofresponses of the number of leaf nodes at flowering and timeto flowering was distinct from that of stem height at flowering.This indicates that flower formation and stem elongation areseparable developmental processes which may be controlled bydifferent endogenous gibberellins, different levels of a specificendogenous gibberellin, or different responses to gibberellin.Copyright 1999 Annals of Botany Company Brassica napus var. annua, gibberellin, photoperiod, spring rape, vernalization.     

Environmental Control of Flowering in Barley (Hordeum vulgare). III. Analysis of Potential Vernalization Responses, and Methods of Screening Germplasm for Sensitivity to Photoperiod and Temperature

Three genotypes of barley were subjected to 18 potentially vernalizingpre-treatments, comprising constant temperatures of 1, 5 or9 °C in factorial combination with photoperiods of 8 or16 h d^–1 for 10, 30 or 60 d^–1. These pre-treatedseeds or seedlings, together with non-pre-treated seeds as controls,were then transferred to each of four growing-on regimes, namelyday/night temperatures of 18/5 °C or 24/3 °C in factorialcombination with photoperiods of 11 or 16 h d^–1. The timesfrom sowing to awn emergence were recorded. The warmer growing-onregime (mean 19 °C) was not supra-optimal in long days,but in short days it considerably delayed awn emergence in allthree genotypes. In cv. Athenais there was no specific responseto the potentially vernalizing pre-trcatments: the rate of progresstowards awn emergence could be treated as a linear functionof the integrated responses to temperature and photoperiod actingindependently throughout development. In addition to these responses,cv. Gerbel B and the land-race Arabi Abiad also responded tolow-temperature vernalization and the response became saturatedduring the longer-duration pre-treatments. In Arabi Abiad, therate at which vernalization occurred, and the period requiredto saturate the response, were not greatly influenced by differencein pre-treatment temperature between 1 and 9 °C. In contrast,in Gerbel B the cooler the temperature of pre-treatment thegreater the saturated response to vernalization, the greaterthe effect of each day of pre-treatment, and the shorter theperiod required to saturate the response. Models of the photothennaland vernalization responses were combined in a single entitywhich described the influence of environment on rate of development.Simple germplasm-screening techniques are proposed for genotypecharacterization so that the phenotypic flowering response canbe estimated for any environment Hordeum vulgare L., barley, flowering, phtoperiodism, vernalization, photothennal time, germplasm screening     

Carbon Dioxide and Flowering in Pharbitis nil Choisy

The effects of photoperiod on floral and vegetative development of Pharbitis nil were modified by atmospheric CO₂ concentrations maintained during plant growth. Short day (SD) photoperiods caused rapid flowering in Pharbitis plants growing in 0.03 or 0.1% CO₂, while plants in long day (LD) conditions remained vegetative. At 1 or 5% CO₂, however, flower buds were developed under both the SD and LD photoperiods. Flowering was earliest in the plants exposed to SD at low CO₂ concentrations which formed floral buds at stem node 3 or 4. At high CO₂ concentrations, floral buds did not form until stem node 6 or 7. Both high CO₂ concentrations and LD photoperiods tended to enhance stem elongation and leaf formation.     

Effects of ambient temperature in association with photoperiod on phenology and on the expressions of major plant developmental genes in wheat (Triticum aestivum L.)

In addition to its role in vernalization, temperature is an important environmental stimulus in determining plant growth and development. We used factorial combinations of two photoperiods (16H, 12H) and three temperature levels (11, 18 and 25 °C) to study the temperature responses of 19 wheat cultivars with established genetic relationships. Temperature produced more significant effects on plant development than photoperiod, with strong genotypic components. Wheat genotypes with PPD‐D1 photoperiod sensitive allele were sensitive to temperature; their development was delayed by higher temperature, which intensified under non‐inductive conditions. The effect of temperature on plant development was not proportional; it influenced the stem elongation to the largest extent, and warmer temperature lengthened the lag phase between the detection of first node and the beginning of intensive stem elongation. The gene expression patterns of VRN1, VRN2 and PPD1 were also significantly modified by temperature, while VRN3 was more chronologically regulated. The associations between VRN1 and VRN3 gene expression with early apex development were significant in all treatments but were only significant for later plant developmental phases under optimal conditions (16H and 18 °C). Under 16H, the magnitude of the transient peak expression of VRN2 observed at 18 and 25 °C associated with the later developmental phases.     

Arabidopsis late-flowering fve mutants are affected in both vegetative and reproductive development

The development of wild-type Arabidopsis thaliana (L.) Heyhn and two late-flowering fve mutants has been analysed under different environmental conditions. In wild-type plants, short-day photoperiods delay the floral transition as a consequence of lengthening all the developmental phases of the plant. Moreover, short days also alter the inflorescence structure by reducing the internode elongation and delaying the establishment of the floral developmental programme in the lateral meristems of the inflorescence and co-florescences. Mutations at the FVE locus cause a delay in flowering time, and a change in the inflorescence structure, similar to the effect of short photoperiods on wild-type plants. However, the effect of the fve mutations is additive to the effect of short days, and all the aspects of the Fve phenotype are corrected by vernalization. These results seem to indicate that FVE is not simply involved in timing the transition from vegetative to reproductive growth, but that it could play a role during all stages of plant development.     

Flowering in Faba Bean: Genotypic Differences in Photoperiod Sensitivity, Similarities in Temperature Sensitivity, and Implications for Screening Germplasm

Reanalyses of extensive results from three separate controlledenvironment studies show that the rate of progress towards floweringin plants of the Sudanese faba bean (Vicia faba L.) land-raceZeidab Local responds consistently and without interaction tophotoperiod and sub-optimal temperatures across all investigations,with no specific low-temperature vernalization response. Moreover,the additive model developed to describe the photothermal responseis sufficiently robust to show that the range between the twoboundary photoperiods is substantial, and so covers most agriculturalenvironments: the critical photoperiod, below which floweringis delayed, is     

FLC or not FLC: the other side of vernalization

Vernalization is the promotion of the competence for floweringby long periods of low temperatures such as those typicallyexperienced during winters. In Arabidopsis, the vernalizationresponse is, to a large extent, mediated by the repression ofthe floral repressor FLC, and the stable epigenetic silencingof FLC after cold treatments is essential for vernalization.In addition to FLC, other vernalization targets exist in Arabidopsis.In grasses, vernalization seems to be entirely independent ofFLC. Here, the current understanding of FLC-independent branchesof the vernalization pathway in Arabidopsis and vernalizationwithout FLC in grasses is discussed. This review focuses onthe role of AGL19, AGL24, and the MAF genes in Arabidopsis.Interestingly, vernalization acts through related molecularmachineries on distinct targets. In particular, protein complexessimilar to Drosophila Polycomb Repressive Complex 2 play a prominentrole in establishing an epigenetic cellular memory for cold-regulatedexpression states of AGL19 and FLC. Finally, the similar networktopology of the apparently independently evolved vernalizationpathways of grasses and Arabidopsis is discussed. Key words: AGL19, Arabidopsis, chromatin, epigenetics, FLC, flowering time, polycomb, PRC2, vernalization Received 19 December 2007; Revised 11 February 2008 Accepted 15 February 2008     

Temperature and photoperiodic control of developmental responses in climatic races of Mimulus

Two strongly differentiated climatic races of the Mimulus cardinalis-lewisiicomplex were grown at a variety of temperatures (3–27°C)and photoperiods (8 and 16 hr) under controlled environmentalconditions. M. cardinalis (the lowland race, 400 m) and M. lewisii(the sub-alpine race, 3200 m) were found to differ in theirphysiological responses to the varied environments in severalsignificant ways: 1) At 27°C (16 hrphotoperiod), M. lewisiisustained 100% mortality in contrast to the substantial growthand flowering of M. cardinalis under these conditions; 2) In8 hr photoperiods at all temperatures, there was little growthand no flowering in M. lewisii whereas there was considerablegrowth at all temperatures, and flowering at 23 and 27°Cin M. cardinalis; 3) At low temperatures (7–15°C),16 hr photoperiods, flowering occurred a week or two earlierin M. lewisii than in M. cardinalis. The lowland race has asignificantly wider temperature and photoperiodic tolerancethan has the sub-alpine race. Applications of gibberellic acidto rosette Mimulus plants under non-inductive conditions (15°C,8 hr photoperiod) promoted vigorous stem elongation withoutflowering. The application of steroids, other hormones and metaboliteshad no observable effects. ¹Present address: Faculty of Botany, Ohio State University,Columbus, Ohio, U.S.A. (Received March 16, 1970; )     

Influence of Vernalization and Photoperiod on Supernumerary Spikelet Expression in Wheat

Two tetraploid (Triticum turgidum L.emend gr. turgidum and gr.durum) and five hexaploid wheats (Triticum x aestivum L. emendgr. aestivum) with reported tendencies for ‘branched heads’(supernurnerary spikelets) exhibited variation in its expressionunder different vernalization photoperiod and temperature regimes. Two main types of supernumerary spikelets were identified, multiplesessile spikelets (MSS) with two or more complete spikeletsat a rachis node and indeterminate rachilla spikelets (IRS)with two to 13 spikelets on an extended rachilla. The degree of supernumerary spikelet expression in wheats withvernalization response differed from those without. Short photoperiods(9–14 h) both outdoors and in a glasshouse environment,were more conducive to supernumerary spikelet expression than24 h photoperiod in both environments. The 24 h photoperiodglasshouse environment (higher mean temperatures) was leastconducive to its expression except in lines with a strong vernalizationresponse. The high stability of supernumerary spikelet expression in certaingenotypes in the different environments indicated the feasibilityof incorporating this character in breeding and selecting commercialwheats to increase grain number per head. Triticum, wheat, ear-branching, supernumerary spikelets, vernalization, photoperiod, temperature     

Studies with Liatris spicata Willd. 2. Effects of Photoperiod on Stem Extension, Flowering and Gibberellin Content

Flower formation in Liatris spicata Willd. was not affectedby photoperiodic treatments, but long days (16 h) had a pronouncedeffect on elongation of the flowering stem. An illuminance of2 Ix was sufficient to produce near maximal elongation. Long days caused a decrease in endogenous gibberellins in thetips of rapidly elongating stems and decreased the number offlowering stems per corm. Liatris spicata, elongation, flowering, gibberellin, light, photoperiod     

Developmental Regulation of Low-temperature Tolerance in Winter Wheat

Vernalization and photoperiod genes have wide-ranging effectson the timing of gene expression in plants. The objectives ofthis study were to (1) determine if expression of low-temperature(LT) tolerance genes is developmentally regulated and (2) establishthe interrelationships among the developmental stages and LTtolerance gene expression. LT response curves were determinedfor three photoperiod-sensitive LT tolerant winter wheat (Triticumaestivum L. em Thell) genotypes acclimated at 4 °C under8 h short-day (SD) and 20 h long-day (LD) photoperiods from0 to 112 d. Also, three de-acclimation and re-acclimation cycleswere used that bridged the vegetative/reproductive transitionpoint for each LD and SD photoperiod treatment. A vernalizationperiod of 49 d at 4 °C was sufficient for all genotypesto reach vernalization saturation as measured by minimum finalleaf number (FLN) and confirmed by examination of shoot apicesdissected from crowns that had been de-acclimated at 20 °CLD. Before the vegetative/reproductive transition, both theLD- and SD-treated plants were able to re-acclimate to similarLT₅₀(temperature at which 50% of the plants are killed by LTstress) levels following de-acclimation at 20 °C. De-acclimationof LD plants after vernalization saturation resulted in rapidprogression to the reproductive phase and limited ability tore-acclimate. The comparative development of the SD (non-flowering-inductivephotoperiod) de-acclimated plants was greatly delayed relativeto LD plants, and this delay in development was reflected inthe ability of SD plants to re-acclimate to a lower temperature.These observations confirm the hypothesis that the point oftransition to the reproductive stage is pivotal in the expressionof LT tolerance genes, and the level and duration of LT acclimationare related to the stage of phenological development as regulatedby vernalization and photoperiod requirements. Copyright 2001Annals of Botany Company Triticum aestivum L., wheat, low-temperature tolerance, vernalization, photoperiod, phenological development