Low-temperature acclimation of barley cultivars used as parents in mapping populations: response to photoperiod,vernalization and phenological development

Six barley (Hordeum vulgare L.) accessions, previously used as parents of mapping populations, were evaluated for characters potentially affecting the location of low-temperature (LT) tolerance QTLs. Three were of winter growth habit (Kompolti Korai, Nure, and Strider), one was facultative (Dicktoo) and two were spring (Morex and Tremois). Final leaf number (FLN) and LT₅₀ were determined at weekly intervals from 0 to 98 days of LT acclimation/vernalization under both long day (LD) and short day (SD) photoperiods. The point of vegetative/reproductive transition was determined from measurements of double ridge (DR) formation and FLN. With the exception of Nure, SD delayed development by increasing leaf production. Dicktoo was extremely SD sensitive lengthening its vegetative phase by more than 63 days relative to the LD photoperiod. SD had the opposite effect on Nure, causing an accelerating of flowering exhibiting the characteristic of ‘short day vernalization’. All accessions except Dicktoo and Kompolti Korai acclimated rapidly in the first 7 days of LT exposure, approaching their maximum LT tolerance in 14–21 days. Dicktoo and Kompolti Korai continued to slowly acclimate until reproductive transition. The results emphasize two important points: (1) the location of QTLs for LT tolerance, and as a consequence the identification of putative candidate genes, will be a function of the genotypes sampled, the experimental conditions used, and the quality of the phenotypic data and (2) the barley LT tolerance pathway reaches an early impediment relative to closely related more hardy members of the Triticeae such as wheat and rye.     

Developmental traits affecting low-temperature tolerance response in near-isogenic lines for the Vernalization locus Vrn-A1 in wheat (Triticum aestivum L. em Thell)

Investigation of low-temperature (LT) tolerance in cereals has commonly led to the region of the vyn-A1 vernalization gene or its homologue in related genomes. Two cultivars, one a non-hardy spring wheat and one a very cold-hardy winter wheat, whose growth habits are determined by the Vrn-A1 (spring habit) and vrn-A1 (winter habit) alleles, were chosen to produce reciprocal near-isogenic lines (NILs). These lines were then used to determine the relationship between rate of phenological development and the degree and duration of LT tolerance gene expression. Each allele was isolated in the genetic backgrounds of the non-hardy spring wheat 'Manitou' and the very cold-hardy winter wheat 'Norstar'. The effects of each allele on phenological development and low-temperature tolerance (LT50) were determined at regular intervals over a 4 degrees C acclimation period of 0-98 d. The vegetative/reproductive transition, as determined by final leaf number (FLN), was found to be a major developmental factor influencing LT tolerance. Possession of a vernalization requirement increased both the length of the vegetative growth phase and LT tolerance. Similarly, increased FLN in spring Norstar and winter Manitou NILs delayed their vegetative/reproductive transition and increased their LT tolerance relative to Manitou. Although the winter Manitou NILs had a lower FLN than the spring Norstar NILs, they were able to extend their vegetative stage to a similar length by increasing the phyllochron (interval between the appearance of successive leaves). Cereal plants have four ways of increasing the length of the vegetative phase, all of which extend the time that low-temperature tolerance genes are more highly expressed: (1) vernalization; (2) photoperiod responses; (3) increased leaf number; and (4) increased length of the phyllochron.     

Photoperiod and temperature interactions regulate low-temperature-induced gene expression in barley.

Vernalization and photoperiod (PP) responses are developmental mechanisms that allow plants to synchronize their growth and reproductive cycles with the seasonal weather changes. Vernalization requirement has been shown to influence the length of time that low-temperature (LT)-induced genes are up-regulated when cereal species are exposed to acclimating temperatures. The objective of the present study was to determine whether expression of LT-induced Wcs and Wcor gene families is also developmentally regulated by PP response. The LT-tolerant, highly short-day (SD)-sensitive barley (Hordeum vulgare L. cv Dicktoo) was subjected to 8-h SD and 20-h long-day PPs at cold-acclimating temperatures over a period of 70 d. A delay in transition from the vegetative to the reproductive stage under SD resulted in an increased level and longer retention of LT tolerance. Similar WCS and WCOR protein homologs were expressed, but levels of expression were much higher in plants acclimated under SD, indicating that the poor LT tolerance of long-day plants was the result of an inability to maintain LT-induced genes in an up-regulated state. These observations indicate that the PP and vernalization genes influence the expression of LT-induced genes in cereals through separate pathways that eventually converge to activate genes controlling plant development. In both instances, the delay in the transition from the vegetative to the reproductive stage produces increased LT tolerance that is sustained for a longer period of time, indicating that the developmental genes determine the duration of expression of LT-induced structural genes.     

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.     

Low-temperature tolerance and genetic potential in wheat (Triticum aestivum L.): response to photoperiod, vernalization, and plant development

It is frequently observed that winter habit types are more low-temperature (LT) tolerant than spring habit types. This raises the question of whether this is due to pleiotropic effects of the vernalization loci or to the linkage of LT-tolerance genes to these vernalization loci. Reciprocal near-isogenic lines (NILs) for alleles at the Vrn-A1 locus, Vrn-A1 and vrn-A1, determining spring and winter habit respectively, in two diverse genetic backgrounds of wheat (Triticum aestivum L.) were used to separate the effects of vernalization, photoperiod, and development on identical, or near identical, genetic backgrounds. The vrn-A1 allele in the winter lines allowed full expression of genotype dependent LT tolerance potential. The winter allele (vrn-A1) in a very cold tolerant genetic background resulted in 11°C, or a 2.4-fold, greater LT tolerance compared to the spring allele. Similarly, the delay in development caused by short-day (SD) versus long-day (LD) photoperiod in the identical spring habit NIL resulted in an 8.5°C or 2.1-fold, increase in LT tolerance. The duration of time in early developmental stages was shown to underlie full expression of genetic LT-tolerance potential. Therefore, pleiotropic effects of the vernalization loci can explain the association of LT tolerance and winter habit irrespective of either the proposed closely linked Fr-A1 or the more distant Fr-A2 LT-tolerance QTLs. Plant development progressively reduced LT-acclimation ability, particularly after the main shoot meristem had advanced to the double ridge reproductive growth stage. The Vrn-1 genes, or other members of the flowering induction pathway, are discussed as possible candidates for involvement in LT-tolerance repression.     

Flowering Responses of Contrasting Ecotypes of Poa annua and their Putative Ancestors Poa infirma andPoa supina

Flowering responses of two Australian and six Norwegian populationsof Poa annua and their putative ancestors P. infirma and P.supina were studied in controlled environments. The two Australianpopulations originating from suburban parks in Canberra hadopposite daylength flowering responses across the range of temperaturestested (9–21 °C), one being a quantitative short-day(SD) plant with no response to vernalization, the other a quantitativelong-day (LD) plant with a quantitative vernalization requirement(winter annual type). Variation in earliness of flowering withinthe former population was shown to be genetically determined,and testing of selfed progenies indicated that the populationis an aggregate of several largely homozygous lines with divergentflowering responses. Two lowland populations from southern Norwaywere both quantitative LD plants with no vernalization response,while two alpine snowbed populations from southern Norway andtwo high-latitude, subarctic populations from northern Norwaywere quantitative SD plants with an obligatory plant vernalizationor SD requirement for flowering. Two populations of P. supinaexhibited the same flowering responses as the alpine and high-latitudepopulations of P. annua with an obligatory plant vernalizationor SD requirement for flowering. A combination of SD and lowtemperature (9–12 °C) for 8–10 weeks was optimalfor induction and inflorescence initiation. On the other hand,P. infirma was found to be an early-flowering quantitative SDplant which flowered freely across the range of temperatures(9–21 °C) as a typical summer annual. The experimentsdemonstrate that virtually any kind of photoperiodic and vernalizationresponses can be found among populations of P. annua. Theseversatile flowering responses reflect the contrasting floweringresponses of P. supina and P. infirma, and add strong supportto the hypothesis that P. annua has originated from these species.Copyright 2001 Annals of Botany Company Adaptation, evolution, flowering, Poa annua, P. infirma, P. supina, photoperiod, vernalization     

The Interactive Effects of Carbon Dioxide Enrichment and Daylength on Growth and Development inPetunia hybrida

Plants were grown at either 350 or 1000 µl l^-1CO₂and inone of three photoperiod treatments: continuous short days (SD),continuous long days (LD), or short switched to long days atday 41 (SD–LD). All plants received 9 h of light at 450µmol m^-2s^-1and LD plants received an additional 4 h oflight at 8 µmol m^-2s^-1. Growth of SD plants respondedmore positively to elevated CO₂than did LD plants, due largelyto differences in the effect of CO₂on unit leaf rate. High CO₂increasedheight and decreased branching under SD conditions, but hadno effect under LD conditions. Elevated CO₂also increased thenumber of buds and open flowers, the effect for flower numberbeing greater in short than in long days. The specific leafarea of plants grown at 1000 µl l^-1CO₂was reduced regardlessof daylength. High CO₂also decreased leaf and increased reproductiveallocation, the magnitude of these effects being greater underSD conditions. Bud formation and flower opening was advancedunder high CO₂conditions in SD plants but bud formation wasdelayed and there was no effect on flower opening under LD conditions.The effects of CO₂on plants switched from SD to LD conditionswere largely intermediate between the two continuous treatments,but for some parameters, more closely resembled one or the other.The results illustrate that daylength is an important factorcontrolling response of plants to elevated CO₂. Petunia hybridaHort. ex Vilm; carbon dioxide; photoperiod; functional growth analysis; daylength; global change; development; phenology     

A Model of Photoperiod × Temperature Interaction Effects on Plant Development

The recent whole-plant research reviewed suggests the commonly applied paradigms about vernalization and photoperiodism should be replaced. A simple equation based on new paradigms predictively models with excellent fit the published days to flowering of at least six plant species. The paradigm that the response to photoperiod of the days to flowering (DTF) of crop plants is revealed adequately by comparing a range of photoperiods at just one temperature should be replaced with the following concepts. There is a base (lowest) temperature below which photoperiod gene activity does not occur, and, when the temperature is high enough to allow activity, there is always a photoperiod × temperature × genotype interaction effect on the days to flowering. Similarly, the paradigm that vernalization gene activity occurs at low temperature and promotes development should be replaced as follows. Vernalization gene activity occurs only if the temperature is above a base (lowest) temperature that allows activity of the vernalization gene(s), and this activity delays development to flowering. Development to flowering is accelerated by low-temperature vernalization, because the low temperature prevents vernalization gene activity, thereby preventing delay of the DTF. The phenomena called long-day (LD) vernalization and short-day (SD) vernalization are reinterpreted as follows. The apparent replacement by short or long daylength of a requirement for low-temperature vernalization is actually a replacement by the low temperature of a requirement for long or short day. Just as true low-temperature vernalization results from prevention of vernalization gene activity, these SD and LD promotions of the DTF occur because the photoperiod gene activity is prevented by the low temperature. Rather than requiring an environment that induces flowering, an inherent capability for rapid development to flowering is expressed, if there is no delay of the DTF by the activity of either or both of the vernalization and photoperiod gene(s). All the above-mentioned effects of temperature are due to the Q₁₀ effect on the specified photoperiod or vernalization gene activity. The effect of thermal time (due to the accumulated growing degree days) is the integrated Q₁₀ effect on all additional genes that partially control the rate of development to the reproductive stage.     

Nitrogen Assimilation and Leaf Development in Indeterminate Soybeans as Influenced by Post-Flowering Photoperiod

Guiamét, J. J., Balatti, P. A. and Montaldi, E. R. 1986.Nitrogen assimilation and leaf development in indeterminatesoybeans as influenced by post-flowering photoperiod.—J.exp. Bot. 37: 1611–1618. The effects of photoperiod on nitrogen fixation and leaf developmentin indeterminate soybeans were studied during early reproductivegrowth. Soybean plants cv. Williams were grown under short days(SD: 8 h-natural daylight (N.D.)+16 h-darkness) or long days(LD: 8 h-N.D. + 8 h-low intensity artificial light+ 8 h-darkness)from full bloom until mid pod filling. Long days greatly increased plant growth, both on the basisof leaf area or weight, mainly due to higher net assimilationrate. Average daily rates of N₂-fixation increased under LD;however, average N₂-fixation rates on a nodule weight or N basisdid not vary, suggesting that changes were not in nodule efficiencybut in nodule biomass. As compared to SD, LD reduced N contentin vegetative parts (pooled roots, stems and leaves), individualleaf blades and fruits. This seemed to be due to greater drymatter accumulation relative to N₂-fixation. The 2nd and 5th trifoliolate leaves showed larger specific leafweight (SLW) under LD. Soluble protein content on a dry weightbasis was higher in the 5th (younger) leaf than in the 2nd,but did not vary due to photoperiod. On the other hand, chlorophylland Fraction I protein content decreased in terms of dry weightunder LD. A larger proportion of leaf N was allocated to solubleproteins under LD, thus compensating for the lower N content.On the whole, growth enhancement by LD seemed unrelated to increasedavailability of N or to greater leaf soluble protein or FractionI content. Key words: Photoperiod, leaf development, soybean, nitrogen fixation     

Changes in the Pattern of Cell Division in the Shoot and Root Meristems of Lolium perenne during the Transition from Vegetative to Floral Growth

For Lolium perenne cv. Cropper, a system which resulted in 100%flowering comprised 90 short days (SD) at 4 ?C (vernalization)and 30 SD at 18 ?C followed by 8 long days (LD). The mitoticindex and G1 and G2 percentages were measured in the shoot androot apices of plants following 2, 5 or 8 LD and in SD controlssampled at the beginning and end of induction. Identical measurementswere made in plants given 48 SD at 18 ?C followed by 2, 5 or8 LD; plants remained vegetative in response to this treatmentlacking vernalization. Significant increases in both mitoticindex and meristem size occurred in the shoot apex in LD followingthe vernalizing, but not the non-vernalizing, treatment. A clusterof mitoses in the apical dome of the shoot apex was unique tothe vernalized plants given 5 or 8 LD. However, an increasein root meristem size occurred regardless of vernalization,but a significant increase in the mitotic index was limitedto vernalized plants given 5 or 8 LD. Whilst the vernalization-LDtreatment resulted in an increase in the G2 percentage in theshoot apex following 2, 5 or 8 LD, no such alteration was observedin the root meristem. Thus, the changes to the cell cycle whichcorrelated with flowering were increased mitotic indices andG2 percentages in the shoot apex at each sampling time and increasedmitotic indices in the root apex following 5 and 8 LD. Key words: Cell division, flowering, Lolium perenne L.     

Starch Accumulation in Leaves of Potato (Solanum tuberosum L.) during the First 18 Days of Photoperiod Treatment

Potato (Solanum tuberosum L.) plants were grown under long days(LD) of 18 h before a subset of the plants was transferred to10-h photosynthetic periods with either a dark night (SD) oran 8-h dim photoperiod extension with incandescent lamps (DE).Temperature was constant at 21 °C. Leaves were sampled atthe beginning and end of the high density light period for starchanalyses. Potato leaves accumulated starch more rapidly underSD than under LD; and this difference continued after a secondmajor sink, the tuber, began to develop. Starch accumulationover 10 h in SD leaves was three times higher than in LD leaves,even after 17 d of treatment. By this time SD gave higher wholeplant relative growth rates than LD, and the tuber mass of SDplants exceeded 30% of their total plant biomass. The DE treatmentresulted in starch accumulation intermediate to the LD and SDtreatments. Genotypes likewise differed: the earlier genotype,more strongly induced to tuberize, had higher leaf starch accumulationthan the later genotype. The effects of photoperiod and genotypewere also present when potatoes were grown at 27 °C, a temperatureunfavourable for tuberization under LD. Thus the formation ofa strong tuber sink was consistently associated with more rapidleaf starch accumulation. Potato, Solanum tuberosum L., cv. Norchip, photoperiod, temperature, genotype, starch accumulation, partitionin     

Modelling Temperature Effects in Breaking Rest in Red-osier Dogwood (Cornus sericea L.)

Temperature requirements for bud development after a rest period(breaking rest) from maximum rest to end of rest were determinedto develop an empirical model for predicting rest developmentin terminal vegetative buds of red-osier dogwood (Cornus sericeaL.). One-year-old plants at maximum rest were exposed to temperaturesfrom 5 to 20 °C a 12 h photoperiod (SD) in growth chambers.Depth of rest was measured by days to bud break in either 16h photoperiod (LD) or natural daylength at 20/15 °C/nighttemperature. Developmental stages during rest development wereexpressed by degree growth stage (°GS). Chilling was effective breaking rest after plants attained maximumrest (270 °GS). Development during rest (breaking rest)increased with decreasing temperature. No significant developmentoccurred at 20 °C. Rate of rest development (°GS h^–1)at all temperatures varied during the breaking rest period anddepended on developmental stage (°GS). A °GS model describedand quantified rest development (°GS). Using temperatureand developmental stage, the model predicted end of rest (315°GS)within 3 days and daily rest development (°GS) in both years. Cornus sericea L, Cornus stolonifera Michx, dogwood, bud development, dormancy, temperature effects, chilling, degree growth stage     

Developmental regulation of metabolites and low temperature tolerance in lines of crosses between spring and winter wheat

Low temperature (LT) tolerance in cereals needs developmental regulation of metabolites, a process which is associated with vernalization requirement. This study was initiated to investigate the relationships among stage of phenological development, final leaf number (FLN), the activities superoxide dismutase, catalase, guaiacol peroxidase, ascorbate peroxidase and polyphenol oxidase, the contents of proline, photosynthetic pigments, and hydrogen peroxide (H₂O₂) during vernalization and LT acclimation in spring and winter wheat. Six genotypes with different vernalization requirements were grown under greenhouse and field conditions. The spring-habit parent, “Pishtaz” and line 4021, rapidly entered the reproductive phase and had a limited capacities to LT acclimate. They also had the lowest antioxidative activities and accumulation of proline among genotypes. Lines 4002 and 4014, with a short vernalization requirement and higher FLN, remained in the early stages of phenological development longer and developed a higher level of LT tolerance and metabolites compared to spring habit genotypes. In contrast, the winter habit “Norstar” and line 4023 spent a longer time in the vegetative stage and accumulated higher levels of metabolites. Maximum LT tolerance and metabolite accumulations occurred near the vegetative/reproductive transition in all genotypes. The longer periods of vernalization and increased FLN that happened along with increased defense mechanisms and decreased damage indices (H₂O₂ content and LT₅₀) ensured LT tolerance in wheat. These results demonstrate that both genetic and environmental factors via developmental regulation of metabolites play important roles in creating LT tolerance in long mild winters of Iran. Significant correlations coefficients for many of the metabolites considered in this study and Lethal temperature 50 (LT₅₀) also suggest that they could be useful as indirect measures of plant LT tolerance potential in wheat breeding programs.     

Dual Floral Induction Requirements in Phleum alpinum

Flowering requirements of four Norwegian populations of Phleumalpinum were studied in controlled environments. A dual inductionrequirement was demonstrated in all populations. Inflorescenceinitiation had an obligatory requirement for short days (SD)and/or low temperature, while culm elongation and heading wereenhanced by long days (LD) and higher temperatures. At 3 and6 °C primary induction was almost independent of photoperiod,whereas SD was more effective than LD at higher temperatures.The critical temperature for primary induction was about 15°C in SD and 12 °C in LD. Saturation of induction required12 weeks of exposure to inductive conditions, although someheading and flowering took place with 6 weeks exposure to optimalconditions (9 °C/SD). Inflorescence development also tookplace in 8 h SD although it was delayed and culm elongationwas strongly inhibited compared with LD conditions. Only smalldifferences in flowering response were found between the populations. Phleum alpinum L., alpine timothy, dual floral induction, flowering, photoperiod, temperature     

Some Effects of Daylength, Temperature and Exogenous Growth Regulator Application on the Growth of Actinidia chinensis Planch

The growth responses of Actinidia chinensis raised from cuttingswere compared in 8 h short days (SD) and 16 h long days (LD)at 15, 20 and 25 °C, as well as under varying day and nighttemperatures The data obtained reveal effects on stem elongation,apparent plastochrons, leaf area and shape, as well as dry matteraccumulation and water contents of different plant parts Theseinvestigations were supplemented by studies on the effects ofapplied GA₃ and ethephon Alternating day/night temperatures(thermoperiodicity) increased leaf area and d wt accumulationin LD Effects on sugar and starch contents, are described anddiscussed Unexpected effects such as very high petiole watercontents and their continuous growth, increased twisting ofthe climbing stem in SD and other findings are also reportedand discussed Actinidia chinensis, Kiwi fruit, gibberellic acid, ethephon, temperature, photoperiod, themoperiodicity     

Genetic and Photoperiodic Control of the Relative Rates of Reproductive and Vegetative Development in Peas

The rates of leaf and flower production were determined in peas(Pisum sativum L.) of genotypes e sn hr (line 13), E Sn hr (line60), and E Sn Hr (line G2), to assess the role of the interactionof alleles Sn and Hr with photoperiod in development. The ratesat which flowers at successive nodes opened (AR) and leavesat successive nodes unfolded (PR) were constant. The AR wasfaster than the PR so that successive flowers opened at nodescloser to the apical bud. The rate at which this occurred wasindependent of photoperiod in line 13 but was slightly or markedlyslower in short days (SD) than long days (LD) in lines 60 andG2, respectively. The opening of flowers closer to the apicalbud of G2 peas in SD was so slow as to not be visually apparentduring the time of this study. The number of nodes between thefirst open flower and the apical bud was unaffected by photoperiodin line 13 but was greater in SD than LD in lines 60 and G2.The daylength effects are photoperiodic, since development ofG2 peas in LD with respect to the parameters measured was unaffectedby light intensity. It is concluded that photoperiod and theE Sn allele combination control the rate of reproductive developmentrelative to vegetative development in peas. The effects of ESn are magnified by the presence of the Hr allele. The constantrates of development measured are not consistent with declineof Sn allele expression with age. Delay of the rate of reproductivedevelopment relative to vegetative development correlated withdelay of apical senescence, suggesting that these processesare related. Pisum sativum, genotypes, photoperiod, flowering, reproductive development, vegetative development, senescence     

Variation in the Durations of the Photoperiod-sensitive and Photoperiod-insensitive Phases of Post-first Flowering Development in Maturity Isolines of Soyabean [Glycine max(L.) Merrill] 'Clark'

Plants of eight isolines of soyabean [Glycine max(L.) Merrill],comprising all combinations of two alleles at the three lociE₁/e₁,E₂/e₂andE₃/e₃inthe cultivar ‘Clark’ background, were transferredafter different periods following first flowering from longdays (LD, 14 h d^-1) to short days (SD, 12 h d^-1) andvice versaina reciprocal-transfer experiment in a plastic house maintainedat 30/24 °C (day/night). Photoperiod (0.10>P>0.05),transfer time (P<0.001),>isoline (P<0.001), and theirinteractions (P<0.001) all affected flowering duration, i.e.the period from first flowering until the appearance of thelast flower. The flowering duration comprised two distinct phases:a photoperiod-sensitive phase beginning at first flowering,and a subsequent photoperiod-insensitive phase. The durationof the photoperiod-sensitive phase varied much more among theisolines in LD than in SD. Only the dominant alleleE₁increasedthe sensitivity of the photoperiod-sensitive phase of floweringduration to photoperiod singly, but positive epistatic effectswere detected betweenE₁andE₂,E₁andE₃, and especially among allthree dominant alleles. The increases in flowering durationresulting from the combined effects of gene and environment(i.e. photoperiod) were associated with considerable increasesin biomass and seed yield at harvest maturity.Copyright 1998Annals of Botany Company. Glycine max(L.) Merrill, soyabean, maturity genes, flowering, photoperiod, reciprocal transfer, yield.     

Cell Cycle Changes in the Shoot Apex of Silene coeli-rosa During the Second and Third Days of Floral Induction

The cell cycle in Silene coeli-rosa shoot apices was measuredto test whether or not early components of the floral stimulus,produced during the 2nd and 3rd long days (LD) of an inductiveLD treatment, resulted in an increase in the duration of G₂phase in constant 20–24 h cell cycles. Plants were grownat 20°C in short days (SD) of 8 h light and 16 h darknessfor 28 d (day 0). Starting on day 0, plants were given SD or3 LD each comprising an identical 8 h day and 16 h photo-extension,or 3 dark-interrupted (d.i.) non-inductive LD, interrupted at1700 h of each day with 1 h of darkness. The cell cycle (percentagelabelled mitoses method) and changes in cell number were determinedin the shoot apical meristem. During days 1–2 of the SDtreatment, the cell cycle and mean cell generation time (MCGT)was 18 and 32 h, respectively, giving a growth fraction of 56%.During days 2–3, the cell cycle and MCGT shortened to15 and 23 h, respectively (growth fraction = 65%). During days1–2 of the LD and d.i. LD treatments, cell cycles andMCGTs were 9–10 and 27–29 h, respectively, resultingin smaller growth fractions (about 33%). Thus, shortened cellcycles and altered growth fractions occurred regardless of whetheror not the treatment was inductive. The LD treatment resultedin a marked shortening of G₁ and, to a lesser extent, S-phase,whilst G₂ remained constant. These changes were consistent withincreases in the proportion of cells in G₂ during the photoextensionof each LD which were suppressed during the comparable periodsof the d.i. LD treatment. The latter treatment resulted in eachphase occupying virtually identical proportions of the cellcycle as in the SD treatment. Thus, the unique cell cycle responsesto the initial part of the inductive LD treatment were increasesin the proportion of cells in G₂ coupled with G₁ and G₂ beingof similar duration. Cell cycle, mean cell generation time, shoot apex, Silene coeli-rosa     

Reanalysis of Vernalization Data of Wheat and Carrot

Vernalization is an important determinant of the growth, development,and yield of biennial and perennial crops. Accurate simulationof its response to temperature is thus an important componentof successful crop systems modelling. Vernalization has a lowoptimum temperature compared to other temperature responsesof plants, and thus may be difficult to treat using expressionsthat are appropriate for other plant processes. This paper examinesthe application of a simple equation that has been used forother processes. It reads as v=V_max(T_max-T_{Tmax- Topt} ) (T_Topt)^{T_optTmax-T_opt}, where v is thedaily rate of vernalization progress at temperature T, T_optandT_maxare the optimum and maximum temperatures for vernalization,respectively, andV_max is the maximum daily rate of vernalization(the inverse of the minimum number of days required to completevernalization), which occurs at T_opt. The model was appliedto published vernalization data for wheat and carrot. The fitsto data were good (adjusted R²for wheat of 0.94, for carrot0.98), with estimatedT_opt and T_maxbeing 5.7±0.5 and 21.3±1.4°C, respectively, for wheat ‘Norin 27’ and 6.6±0.2and 14.1±0.3 °C for carrot ‘ Chantenay RedCored’. The estimated parameters, in particular the highT_maxfor wheat, were close to those reported using differentanalytical approaches. It was suggested that the function wouldbe useful for summarizing vernalization data, and that its usewould avoid the abrupt changes that are inevitable when differentlinear relationships are used for part of the overall response.It was also suggested the high T_maxshould be taken into accountwhen interpreting data obtained with wheat grown under warmconditions. Copyright 1999 Annals of Botany Company Plant, vernalization, temperature response, modelling, wheat (Triticum aestivum L.), carrot (Daucus carota L.).