The Growth and Development of the Wheat Apex: The Effects of Photoperiod on Spikelet Production and Sucrose Concentration in the Apex

Spring wheat (Triticum aestivum cv. Warimba) plants were grownin a controlled environment (20°C) in two photoperiods (8or 16 h). In the first instance, plants were maintained in eachof the photoperiods from germination onwards at the same irradiance(375 µE m^–2 s^–1). In the second case, allplants were grown in a long photoperiod until 4 days after double-ridgeinitiation when half the plants were transferred to a shortphotoperiod with double the irradiance (16 h photoperiod at225 or 8 h at 475 µE ^–2 s^–1). The rates of growth and development of the apices were promotedby the longer photoperiod in both experiments. Shoot dry weightgain was proportional to the total light energy received perday whereas the dry weight of the shoot apex increased withincreasing photoperiod even when the total daily irradiancewas constant. The principal soluble carbohydrate present in the shoot apexwas sucrose, although low concentrations of glucose and fructosewere found in the apices of long photoperiod plants late indevelopment. Sucrose concentration was invariably greater inthe slow-growing apices of short photoperiod plants, but roseto approach this level in the long photoperiod plants when theterminal spikelet had been initiated. Triticum aestivum, wheat, apex, spikelet initiation, photoperiod, flower initiation     

The Relationship between Sugar and Amino Acid Export to the Phloem in Young Wheat Plants

The relationship between amino acid and sugar export to thephloem was studied in young wheat plants (Triticum aestivumL. ‘Pro-INTA, Isla Verde’) using the EDTA-phloemcollection technique. Plants grown with a 16 h photoperiod showeda rapid decrease in the concentration of sugars and amino acidsin the phloem exudate from the beginning of the dark period.When plants grown with a 16 h photoperiod were kept in the darkfor longer than 8 h the free amino acid content in leaves andexudate (on a dry weight basis) increased continually throughoutthe 72 h of darkness. During the first 24 h of darkness thesugars in the phloem exudate decreased to 30% of the initialvalue, and returned to the control level when plants were returnedto light. When plants grown under low light intensity for 10d were transferred to high light intensity, they showed an increasein leaf sugar content (dry weight basis) after 3 d but therewere no differences in leaf free amino acid content (dry weightbasis) compared to low-light plants. The sugar concentrationin the phloem exudate was increased by higher light intensities,but there was no difference in the amino acid concentrationof the phloem exudate, and thus the amino acid:sugar ratio inthe phloem decreased in the high-light plants. The present resultssuggest that amino acids can be exported to the phloem independentlyof the export of sugars. Copyright 1999 Annals of Botany Company Sugar exudation, amino acid transport, nitrogen, phloem, transport, wheat, Triticum aestivum L.     

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     

Leaf Emergence of Spring Wheat Receiving Varying Nitrogen Supply at Different Stages of Development

We examined effects of nitrogen (N) supply on leaf emergenceof spring wheat (Triticum aestivum L.) grown in sand with nutrientsolution containing different N concentrations (9NO₃: 1NH₄).In expt 1, the cultivar 'Gamenya' received nutrient solutiontwice weekly containing a constant N supply ranging from 50to 2400 µM N. In expts 2 and 3, cultivars 'Aroona' and'Gamenya' were irrigated hourly with nutrient solution containingeither low (L = 50 µM N) or high (H = 2000 µM N)N supply. In expt 2, the N supply to half of the plants receivingL and H was changed at the double ridge stage of apical development,producing plants receiving LL, LH, HL and HH. In expt 3, N supplywas changed firstly when the main stem apex was vegetative (oneto two leaves) and secondly when the main stem apex was at doubleridge stage (four to five leaves), producing plants receivingLLL, LHL, HLH and HHH. Leaves on the main stem and primary tillerswere counted. Rate of leaf emergence was estimated from regressionof number of leaves against thermal time; the phyllochron wascalculated as 1/ rate of emergence. Severely N-deficient plants (which had at least a 60% reductionin shoot dry weight) had slower rates of leaf emergence (expt1). Fluctuating N supply sometimes, but not always, changedthe rate of leaf emergence (expts 2 and 3). The N supply beforedouble ridge stage had bigger effects on the phyllochron thanthat afterwards (expt 3). The phyllocrons of the main stemswere generally lower than those of tillers, with a greater differencebetween stems in N-deficient plants. Low N supply at the vegetativeapex stage decreased the total number of leaves on the mainstem, while low N supply after double ridge did not.Copyright1994, 1999 Academic Press Nitrogen, stress, spring wheat, Triticum aestivum, leaf emergence, phyllochron, apical development     

Responses of Leaf and Tiller Emergence and Primordium Initiation in Wheat and Barley to Interchanged Photoperiod

The influence of constant (9, 13 and 19 h) and reciprocally-interchangedphotoperiods [at terminal spikelet (TS) or triple mound (TM)]on leaf, tiller and primordium development were examined usingphotoperiod-responsive cultivars of spring wheat, ‘UQ189’ and spring barley, ‘Arapiles’. In bothspecies, constant longer photoperiod reduced the duration fromsowing (S) to double ridge (DR), as expected. However, photoperiodsensitivity was not restricted to this mainly vegetative phase.There was also a marked increase or reduction in the durationof reproductive phases between TS/TM and heading (H) when plantswere transferred to shorter or longer photoperiods respectively,compared with controls. These responses were largely independentof the photoperiod during previous phases although minor effectsof the previous photoperiod were observed. For both species,the time course of leaf emergence was linear, or bi-linear,depending on the final leaf number on the main stem. The rateof leaf emergence was faster for the first six to eight leavesthan for the leaves appearing subsequently. The rate of emergenceof early-formed leaves was independent of photoperiod whereasthe rate of emergence of later leaves varied with photoperiod.Photoperiod also affected the dynamics of tillering. The rateof leaf primordium initiation was little affected by variationin photoperiod, but the rate of spikelet initiation increasedwith increases in photoperiod. The rates of leaf and spikeletprimordium initiation were both substantially higher in barleythan in wheat. The fact that the reproductive phase from TS/TMto H was largely independent of the duration of the previousphase provides evidence that this phase might be geneticallymanipulated to increase the time for floret development andhence grain number. Copyright 2000 Annals of Botany Company Photoperiod, rate of development and leaf emergence, tillering, wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.)     

Expression of Vernalization Requirement and Spikelet Number in Synthetic Hexaploid Wheats and their Triticum tauschii and Tetraploid Wheat Parents

Vernalization requirement, as measured by days from sowing toear emergence (plants grown under an 18-h photoperiod), andspikelet number per ear were recorded for 17 synthetic hexaploidwheats and the six tetraploid (Triticum durum) and the ninediploid T. tauschii parents used to synthesize them. The tetraploid parents and the synthetic hexaploids had springphenotypes (little or no vernalization requirement) whereasthe T. tauschii parents were all winter types (strong vernalizationrequirement). The tetraploid wheats and the synthetic hexaploidsreached ear emergence 50·3 to 63·8 d and 58·2to 75·3 d after sowing, respectively, while the T. tauschiilines reached ear emergence 114·3 to 179·5 d aftersowing. The spring habit of the synthetic hexaploids demonstrates theepistasis of spring over winter habit. It is considered thatwith a presumed single vrn locus in the diploid species T. tauschiithe range of ear emergence in these lines is consistent withthe action of multiple alleles at that locus. Although there was no general epistasis for spikelet number,the tetraploid parents appear to be exerting more influenceover spikelet number in the synthetic hexaploids than T. tauschii.The well established association between the duration from sowingto ear emergence and spikelet number was not evident eitherwithin each ploidy group or when the 32 lines were consideredtogether. Triticum tauschii, Triticum durum, hexaploid wheat, spikelet number, vernalization requirement     

Development Rate in Wheat as Affected by Duration and Rate of Change of Photoperiod

A field study was conducted to test the hypothesis that wheatdevelopment rate responds to the rate of change of photoperiod.Two wheat cultivars (Condor and Thatcher) were sown on 18 Aug.1992 at Melbourne (38° S). Photoperiod was extended artificiallyto give five treatments up to terminal spikelet initiation (TS)viz.: natural photoperiod (rate of change of photoperiod, 2·3mind d^-1), two faster rates of change (9·8 and 13·1min d^-1) and two constant photoperiods of 14·0 and 15·5h. After TS, the two constant photoperiods were extended to15·0 and 16·5 h, respectively and treatments wererandomly re-allocated, i.e. some plots received different photoperiodregimes before and after TS. There were no significant differences among treatments in thelength of the period from sowing (S) to seedling emergence (E)phase, ranging from 15 to 16·3 d. The rate of developmentfrom E to TS responded to increases in photoperiod in both cultivars,increasing with average photoperiod across all treatments butthere was no effect of rate of change of photoperiod independentof its average photoperiod. The rate of development from TSto anthesis (A) did not show any trend with average photoperiod.This lack of effect of photoperiod on the period from TS toA contrasts with other results from the literature and possiblereasons for this conflicting result are discussed. Rate of changeof photoperiod did not affect the duration of the phase fromTS to A either. Therefore, the effect of photoperiod on theduration of the S-A period was strongly and positively correlatedto that of the length of the E-TS phase.Copyright 1994, 1999Academic Press Triticum aestivum L., wheat, phasic development, photoperiod, rate of change     

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     

Influence of Photoperiod on Culm Elongation and Apical Development in Semi-dwarf and Standard-height Wheats

Flower initiation (FI) coincided with the commencement of culmelongation under both long (18 h) and normal (104–144h) photoperiod in eight spring wheats, including both gibberellicacid-sensitive and -insensitive types, which differed widelyin photoperiod sensitivity At FI the apex was significantly (P = 005) higher (above ground)in three of the wheats under long, compared with normal photoperiod;with no difference between the remaining five. Differences inresponse were not related to photoperiod response or gibberellicacid-sensitivity/insensitivity differences between the wheats. Long photoperiod prolonged the phase from terminal spikeletinitiation (TSI) to anthesis (A) in all the wheats, except Sunset(with the greatest photoperiod insensitivity), with no cleardifferences in response between semi-dwarf and standard-heightwheats. Respective rates of culm elongation from FI to TSI were lowerunder normal, compared with long, photoperiod in all varieties.That from TSI to A was unaffected by photoperiod, except inSunset when it was significantly (P = 001) slower under long,compared with normal photoperiod. Rate of culm elongation from FI to TSI across cultivars andphotoperiods was inversely related to spikelet number per head(r = –053, P = 005) but not to rate of spikelet initiation(r = –014 n.s.). Gibberellin-sensitivity, spikelet number, flower initiation, terminal spikelet initiation     

Rate of Leaf Appearance and Final Number of Leaves in Wheat: Effects of Duration and Rate of Change of Photoperiod

This study was conducted to test the hypothesis that photoperiodor its rate of change significantly affects the rate of leafappearance (RLA) and final number of leaves (FNL) in wheat,as suggested from several time-of-sowing experiments. Two wheatcultivars (Condor and Thatcher) were sown in the field on 2Sep. 1992 at Melbourne (38°S). Photoperiod was extendedartificially to give five treatments up to terminal spikeletinitiation (TS) viz.: natural photoperiod (rate of change ofphotoperiod = 2 min d^-1), two faster rates of change (8·5and 13·3 min d^-1) and two constant photoperiods of 14·0and 15·5 h. After TS, the two constant photoperiods wereextended to 15·0 and 16·5 h, respectively, andtreatments were re-randomised, i.e. some plots received differentphotoperiod regimes before and after TS. The rate of leaf appearance maintained strong linear relationshipswith thermal time. It was greater for Condor [0·012-0·013(°C d)^-1] than for Thatcher [0·011-0·012 (°Cd)^-1] and did not alter during plant development or in responseto the change in photoperiod at TS. Rate of leaf appearanceon the main culm was not influenced by the rate of change ofphotoperiod nor by the average photoperiod. Cultivar and photoperiod significantly affected FNL on the mainculm. Condor produced more leaves than Thatcher under long butnot under short photoperiods. The rate of change of photoperioddid not affect FNL independently of the effect of average photoperiod.Most of the variation in FNL due to photoperiod resulted fromdifferences in duration of leaf initiation. The lack of effects of the photoperiod treatments on RLA contrastwith previous reports of its effects on the rate of phasic developmentfrom seedling emergence to double ridge. Therefore, the numberof visible leaves on the main culm (NL) at double ridge andat TS were not constant. However, NL on the main culm at doubleridge was closely correlated with FNL.Copyright 1994, 1999 AcademicPress Triticum aestivum L., wheat, leaf appearance, phyllochron, photoperiod     

Effect of Water Deficit on Sporogenesis in Wheat (Triticum aestivum L.)

Plants of Triticum aestivum L., cv. Gabo, were grown in a glasshousefor 4 weeks and then transferred to a controlled environmentwith 20±1 °C temperature and 16 h photoperiod. Theywere subjected to water deficit by withholding the water supplyduring various stages of floral development, including thoseimmediately before meiosis and all stages until just after anthesis. The proportion of apparently normal florets which produced grainwas reduced when water deficit occurred during and immediatelyafter meiosis in the generative tissues. The effect of thisreduced grain set on total grain yield was partially compensatedby an increase in the weight of the remaining grains. Cross-pollinationbetween stressed and well-watered plants showed that grain setwas reduced as a direct consequence of the induction of malesterility by water stress, whereas female fertility was unaffected.A large proportion of the anthers on water-stressed plants weresmall and shrivelled, did not dehisce normally and containedpollen which was devoid of normal cytoplasmic constituents andshowed no staining reaction with triphenyl tetrazolium chloride.This effect on male fertility was not a result of desiccationof the sporogenous tissue, but an indirect outcome of the decreasein water potential elsewhere in the plant. Water stress, Triticum aestivum L., wheat, pollen, sporogenesis, grain set, male sterility     

Abnormal Sporogenesis in Wheat (Triticum aestivum L.) Induced by Short Periods of High Temperature

Plants of Triticum aestivum L. cv. Gabo, grown at 20 °C,were exposed to 30 °C for short periods during the timebetween the beginning of meiosis in the pollen mother cellsand anthesis. Plant water deficit at this temperature was avoidedby maintaining a high atmospheric relative humidity and tissuewater potential did not change. This temperature treatment appliedfor 3 days, at the time of reduction division and tetrad breakup in the male tissue, lowered grain yield through a drasticreduction in grain set, but was without effect at other stagesof development. Grain set was also reduced by exposing plantsto 30 °C for 1 day only or to a 30 °C day, 20 °Cnight (16 h photoperiod) regime for 3 days during the sensitiveperiod. A reduction in grain set did not result in a compensatoryincrease in the weight of remaining grains. The female fertility of previously heat-stressed plants wasassessed by pollinating with pollen from plants grown at a lowertemperature (20 °C). Grain set in such plants was less thanthat in plants grown at the lower temperature and hand pollinatedwith similar pollen, indicating that female fertility was reducedby high temperature. This was not the sole reason for reducedgrain set, however, as some anthers on heat-stressed plantswere small and neither extruded nor dehisced normally. Suchanthers contained pollen grains that were mostly shrivelled,had abnormal cytoplasm and showed no reaction to 2, 3, 5-triphenyltetrazolium chloride. Similar effects were also noted in pollenfrom apparently normal anthers on heat-stressed plants. Triticum aestivum, wheat, heat stress, pollen, sporogenesis, grain set, male sterility, female sterility     

Expression of Vernalization Genes in Near-lsogenic Wheat Lines: Duration of Vernalization Period

Vernalization periods ranging from 0 to 11 weeks at 4 °Cwere used to study the reproductive development of four near-isogeniclines of wheat (Triticum aestivum L. em. Thell). From the resultsfor days to anthesis two types of gene action were identified,a threshold (all-or-nothing) response (vrn3 and/or vrn4) anda cumulative (graded) response (vrn1). The action of anothergene (vrn2) intensified these two responses. Based on the actionof genes, a model relating days to anthesis to genotype wasderived. Final leaf number and days to anthesis were shown tobe closely related after adjusting for differences due to theduration of vernalization treatment. No relationship betweendays to anthesis and spikelet number was observed. This studyemphasises the need to understand vernalization at the levelof the gene in terms of responses and interactions. Such knowledgeshould enable the plant breeder to predict and more preciselycontrol reproductive development. Triticum aestivum L., wheat, vernalization, gene action, isogenic lines     

Nitrogen Deficiency Slows Leaf Development and Delays Flowering in Narrow-leafed Lupin

Effects of nitrogen (N) supply on leaf and flower developmentinLupinus angustifolius L. cv Merrit were examined in a temperature-controlledglasshouse. Low N supply (0.05 or 0.4 mM N) had little effecton leaf initiation but slowed leaf emergence on the main stemcompared with plants receiving high N supply (6.0 or 6.4 mMN), or with symbiotic N₂-fixation. Plants experiencing transientN deficiency had slower leaf emergence than plants with a continuoussupply of 6.4 mM N. Nitrogen supply did not affect the timeof floral initiation, which occurred within 4 weeks of sowing,by which time nine to ten leaves had emerged. However, the floweringof low-N plants was delayed by 68 to 220 °C d (i.e. 4–14d) even though they had fewer leaves. The effect of N deficiencyon flowering time was largely a result of slower leaf emergence. Lupinus angustifolius L.; nitrogen; leaf; flower initiation; thermal time; plastochron; phyllochron     

Temperature Effects on Cytokinin Accumulation and Kernel Mass in a Dwarf Wheat

The objectives of this study were: (1) to quantify post-anthesiskernel cytokinin levels in ‘Tibet Dwarf’, a dwarfwheat (Triticum aestivumL.) that accumulates elevated quantitiesof leaf cytokinins; and (2) to measure the effects of temperatureon kernel cytokinin accumulation and mature kernel mass in thiswheat. Post-anthesis kernel cytokinin accumulation was measuredin control plants maintained at 25/12 °C (day/night) andtreated plants which received a 7 d exposure to 35/25 °Cbeginning at anthesis and grown to maturity at 25/15 °C.Zeatin (Z), dihydrozeatin (diHZ) and their respective ribosideswere the predominant cytokinins detected in control and treatedplants. Minimal quantities of isopentenyl adenine-type cytokininswere detected. Kernel cytokinin content peaked within 3 d afteranthesis in both groups and returned to baseline levels within1–2 d. Relative to controls, exposure to high temperaturereduced kernel cytokinin content approx. 80% within 1 d afteranthesis. Because kernel cytokinin in control Tibet Dwarf plantsexceeded that previously measured in other varieties by over100-fold, the reduced content of treated plants still exceededthat of untreated plants of other varieties. The increased cytokinincontent did not enhance thermotolerance. The temperature treatmentreduced mature kernel weights approx. 27%, similar to reductionsmeasured in other wheat varieties.Copyright 1999 Annals of BotanyCompany Triticum aestivum, endosperm development, heat stress, kernel mass, cytokinins.     

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     

Effects of the Reversal of Day and Night Temperatures on Tillering and on the Elongation of Stems and Leaf Blades of Wheat

Different cultivars of wheat (Triticum aestivum L.) were grownin cabinets, under a 12 h photoperiod, at constant temperatures,and high day/low night and low day/high night temperatures.Plants were also transferred at different ages, between 18/10°C and 10/18 °C regimes. Application of the growth regulatorsCCC and TIBA was tested at 18/10 °C and GA₃ and IAA at 10/18°C. The reversal of day and night temperatures did not affect spikedifferentiation or the numbers of leaves and elongating internodes.However, tillering and tiller development were markedly promotedby the low day/high night temperature regimes whereas the elongationof leaf blades and stem internodes were suppressed under theseregimes. These effects were attributed to the effects of thetemperature regimes on the endogenous hormone balance of theplants. Considering the results of the transfer and growth regulatortreatments it was concluded that there were no obligatory associationsamong the number of tillers appearing, their subsequent development,leaf blade length, and stem elongation. It is suggested thatthe study of the physiological mechanisms controlling thesecharacters may benefit from experimentation under reciprocallydiffering day night temperature regimes.     

Floret Initiation and Development in Spring Wheat (Triticum aestivum L.)

The number and developmental stages of florets were determinedin each spikelet of the spike in the main shoots of spring wheat.Samples were taken frequently from plants grown in a phytotronand in a nitrogen application field-test. Ten stages of development,from floret initiation until anthesis, were recognized and described. Inter-spikelet variation in the total number of initiated floretswas rather small. However, the number of florets at advancedstages of development, as well as the number of grains, washighest in the central spikelets in which florets initiatedfirst. Floret initiation did not proceed beyond spike emergence,whereafter the distal florets and the spikelet apex degenerated.Grain-set was restricted to florets which had developed at leastto the stage of visible anther lobes at spike emergence. Thenumber of these florets was increased significantly by nitrogenapplication. Wheat, Triticum aestivum L., spikelet, floret, grain set, nitrogen     

Photoperiod Sensitivity during Flower Development of Opium Poppy (Papaver somniferum L.)

Photoperiod is a major factor in flower development of the opiumpoppy (Papaver somniferum L. ‘album DC’) which isa long-day plant. Predicting time to flower in field-grown opiumpoppy requires knowledge of which stages of growth are sensitiveto photoperiod and how the rate of flower development is influencedby photoperiod. The objective of this work was to determinewhen poppy plants first become sensitive to photoperiod andhow long photoperiod continues to influence the time to firstflower under consistent temperature conditions. Plants weregrown in artificially-lit growth chambers with either a 16-hphotoperiod (highly flower inductive) or a 9-h photoperiod (non-inductive).Plants were transferred at 1 to 3-d intervals from a 16- toa 9-h photoperiod andvice versa . All chambers were maintainedat a 12-h thermoperiod of 25/20 °C. Poppy plants becamesensitive to photoperiod 4 d after emergence and required aminimum of four inductive cycles (short dark periods) beforethe plant flowered. Additional inductive cycles, up to a maximumof nine, hastened flowering. After 13 inductive cycles, floweringtime was no longer influenced by photoperiod. These resultsindicate that the interval between emergence and first flowercan be divided into four phases: (1) a photoperiod-insensitivejuvenile phase (JP); (2) a photoperiod-sensitive inductive phase(PSP); (3) a photoperiod-sensitive post-inductive phase (PSPP);and (4) a photoperiod-insensitive post-inductive phase (PIPP).The minimum durations of these phases forPapaver somniferum‘album DC’ under the conditions of our experimentwere determined as 4 d, 4 d, 9 d, and 14 d, respectively. Anthesis; days to flowering; flower bud; opium poppy; Papaver somniferum L.; photoperiod; photoperiod sensitivity; predicting time to flowering; transfer     

A Study of Floret Development in Wheat (Triticum aestivum L.)

Plants of wheat (Triticum aestlvum L.) cv. Aotea were grownat high or low nitrogen levels and in a natural photoperiodor continuous light. Starting 17–21 days from the double-ridgestage, eight plants from each treatment were sampled every 3days until anthesis, and the two basal, the sixth, and the terminalspikelets were sectioned longitudinally. A developmental scorewas assigned to each floret and rates of development calculated.Continuous light hastened development but reduced the numberof spikelets per ear, while high nitrogen delayed developmentbut increased spikelet numbers. The number of florets initiatedin each spikelet varied within narrow limits, but grain settingdepended strongly on spikelet position and on treatment. Althoughflorets were initiated in acropetal succession, the rate ofdevelopment tended to increase up to floret 4 but then declinedmarkedly. As a result grain setting was confined to basal floretpositions, although the two basal spikelets developed so slowlythat they contributed relatively little to grain yield. Distalflorets degenerated almost simultaneously at or before ear emergence,but those in intermediate positions continued to develop untilafter fertilization in the lower florets. It is argued thatthe spikelet is an integrated system in which correlative mechanismsplay a part throughout the development of the florets.