Flowering in Pisum: Identification of a new ppd allele and its physiological action as revealed by grafting

The late flowering, quantitative long day habit of wild type pea ( Pisum sativum L.) is conferred by the joint presence of dominant genes Sn, Dne and Ppd. Grafting studies have shown that flowering in wild type plants is delayed under short days by formation of a graft-transmissible inhibitor and that the early flowering, day neutral mutants sn and dne are deficient in this inhibitor. However, the physiological action of the Ppd gene has not been examined by grafting and the possibility exists that the ppd mutation causes early flowering and a day neutral habit by blocking response to, rather than synthesis of, the inhibitor. We here identify a second, more severe (probably null) mutant allele ( ppd -2) at the Ppd locus and show that flowering was delayed by 4 nodes in a ppd -2 shoot grafted to a wild type stock, and promoted by 13 nodes in a wild type shoot grafted to a ppd -2 stock. Thus a ppd -2 shoot can respond to inhibitor donated by a wild type stock but a ppd -2 stock is unable to provide sufficient inhibitor to prevent early flower initiation in a wild type shoot. We conclude genes Sn, Dne and Ppd each control steps in the synthesis of the flower inhibitor. Grafts among the sn, dne and ppd mutants gave an indication that the three genes may act in the sequence Sn, Ppd, Dne , but possible cases of physiological complementation need to be tested using null mutants in the same genetic background.     

Association between genes controlling flowering time and shoot sodium accumulation in the Triticeae

Saline hydroponic studies of cytogenetic stocks of wheat have shown that near isogenic lines carrying contrasting alleles Vrn (vernalisation requirement) or Ppd (photoperiod requirement) genes accumulate less sodium when the dominant allele is present. These dominant alleles also confer early flowering. The genetic control of response to salt stress is discussed with respect to Vrn and Ppd genes. The data suggest that both these genes have pleiotropic effects on sodium accumulation. Salt treatment did not appear to switch on any genes which control sodium accumulation and it is concluded that the intrinsic genetic make-up of the plant determines fitness under salt stress conditions.     

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     

Histochemical Study of Photoperiodic and Low Temperature Effects on Floral Induction of Spinacia oleracea

Shoot apices of Spinacia oleracea plants have been induced toflower either by: (a) subjecting leaves to 24 h long day, or(b) exposure to a short photoperiod but displaced by 8 h (displacedshort day) in the usual 24 h short-day cycle, or (c) exposureto low temperature (5 °C) during the dark period of thenormal short day. A quantitative cytochemical assay of pentosephosphate pathway activity during floral induction indicatesan approximate doubling of the rate of activity when comparedto that of vegetative apices (short day) (21 °C). Exposure to either low temperature, or a displaced short photoperiodstimulates pentose phosphate pathway activity in the shoot apexin a manner similar to that seen by long-day induction. Thischange in metabolic activity is accompanied by changes in theshape of the shoot apex which resembles that seen at an earlystage during floral induction. Spinacia oleracea, pentose phosphate pathway, shoot apex, glucose-6-phosphate dehydrogenase, floral induction, chilling, displaced short day     

Effects of loci on chromosomes 2 (2H) and 7 (5H) on developmental patterns in barley (Hordeum vulgare L.) under different photoperiod regimes

 Heading-date in cereals is the final result of a number of interacting characters that include vernalization requirement, photoperiod sensitivity, and earliness per se. Progress in developing adapted varieties may be achieved by determining the chromosomal locations of genes controlling these characters. Nineteen doubled-haploid (DH) lines from the Dicktoo×Morex mapping population were phenotyped in controlled- environment photoperiod experiments to determine the role of two previously detected QTLs on the developmental patterns of barley. The QTLs are hypothesised to represent the effects of the Ppd and Sh2 loci on chromosomes 2 (2H) and 7 (5H), respectively. Alleles at the Ppd locus were found to be vary in response to photoperiod duration. Vernalization had some effect on alleles at both loci. The presence of early and late- flowering transgressive segregants in this mapping population can be explained by interactions between the Ppd and Sh2 loci. The Ppd and Sh2 loci are hypothesised to be homoeologous with the Ppd and Vrn1 loci of wheat. Received: 1 August 1996 / Accepted: 15 November 1996     

Photoperiod and Temperature Regulation of Floral Initiation and Anthesis in Soya Bean

Floral development includes initiation of floral primordia andsubsequent anthesis as discrete events, even though in manyinvestigations only anthesis is considered. For ‘Ransom’soya bean [Glycine max (L.) Merrill] grown at day/night temperaturesof 18/14, 22/18, 26/22, 30/26, and 34/30 °C and exposedto photoperiods of 10, 12, 14, 15, and 16 h, time of anthesisranged from less than 21 days after exposure at the shorterphotoperiods and warmer temperatures to more than 60 days atlonger photoperiods and cooler temperatures. For all temperatureregimes, however, floral primordia were initiated under shorterphotopenods within 3 to 5 days after exposure and after notmore than 7 to 10 days exposure to longer photoperiods. Onceinitiation had begun, time required for differentiation of individualfloral primordia and the duration of leaf initiation at shootapices increased with increasing length of photoperiod. Whileproduction of nodes ceased abruptly under photoperiods of 10and 12 h, new nodes continued to be formed concurrently withinitiation of axillary floral primordia under photoperiods of14, 15 and 16 h. The vegetative condition at the main stem shootapex was prolonged under the three longer photoperiods and issuggestive of the existence of an intermediate apex under theseconditions. The results indicate that initiation and anthesisare controlled independently rather than collectively by photoperiod,and that floral initiation consists of two independent steps—onefor the first-initiated flower in an axil of a main stem leafand a second for transformation of the terminal shoot apex fromthe vegetative to reproductive condition. Apical meristem, intermediate apex, floral initiation, anthesis, photoinduction, Glycine max(L.) Merrill, soya bean, photoperiod, temperature     

Osmotic stress at the barley root affects expression of circadian clock genes in the shoot

The circadian clock is an important timing system that controls physiological responses to abiotic stresses in plants. However, there is little information on the effects of the clock on stress adaptation in important crops, like barley. In addition, we do not know how osmotic stress perceived at the roots affect the shoot circadian clock. Barley genotypes, carrying natural variation at the photoperiod response and clock genes Ppd‐H1 and HvELF3, were grown under control and osmotic stress conditions to record changes in the diurnal expression of clock and stress‐response genes and in physiological traits. Variation at HvELF3 affected the expression phase and shape of clock and stress‐response genes, while variation at Ppd‐H1 only affected the expression levels of stress genes. Osmotic stress up‐regulated expression of clock and stress‐response genes and advanced their expression peaks. Clock genes controlled the expression of stress‐response genes, but had minor effects on gas exchange and leaf transpiration. This study demonstrated that osmotic stress at the barley root altered clock gene expression in the shoot and acted as a spatial input signal into the clock. Unlike in Arabidopsis, barley primary assimilation was less controlled by the clock and more responsive to environmental perturbations, such as osmotic stress.     

A <Emphasis Type="Italic">Pseudo-Response Regulator</Emphasis> is misexpressed in the photoperiod insensitive <Emphasis Type="Italic">Ppd-D1a</Emphasis> mutant of wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

Ppd-D1 on chromosome 2D is the major photoperiod response locus in hexaploid wheat (Triticum aestivum). A semi-dominant mutation widely used in the “green revolution” converts wheat from a long day (LD) to a photoperiod insensitive (day neutral) plant, providing adaptation to a broad range of environments. Comparative mapping shows Ppd-D1 to be colinear with the Ppd-H1 gene of barley (Hordeum vulgare) which is a member of the pseudo-response regulator (PRR) gene family. To investigate the relationship between wheat and barley photoperiod genes we isolated homologues of Ppd-H1 from a ‘Chinese Spring’ wheat BAC library and compared them to sequences from other wheat varieties with known Ppd alleles. Varieties with the photoperiod insensitive Ppd-D1a allele which causes early flowering in short (SD) or LDs had a 2 kb deletion upstream of the coding region. This was associated with misexpression of the 2D PRR gene and expression of the key floral regulator FT in SDs, showing that photoperiod insensitivity is due to activation of a known photoperiod pathway irrespective of day length. Five Ppd-D1 alleles were found but only the 2 kb deletion was associated with photoperiod insensitivity. Photoperiod insensitivity can also be conferred by mutation at a homoeologous locus on chromosome 2B (Ppd-B1). No candidate mutation was found in the 2B PRR gene but polymorphism within the 2B PRR gene cosegregated with the Ppd-B1 locus in a doubled haploid population, suggesting that insensitivity on 2B is due to a mutation outside the sequenced region or to a closely linked gene. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. J. Beales and A. Turner contributed equally to the work.     

Growth of Near-isogenic Wheat Lines Differing in Development--Spaced Plants

The relationship between phenological development in wheat (TriticumaestivumL.) and growth was studied to determine if the switchfrom a vegetative to a reproductive apex increases plant growthrate. Plant partitioning and relative growth rates during vegetativeand pre-flowering reproductive periods were determined in twosets of near-isogenic lines differing in phenological development.Spaced plants were grown in two photoperiods (15 and 10 h) toincrease the range of development rates. Lines within each isogenicset and photoperiod treatment did not differ in whole plantgrowth rate despite large differences in developmental rate.In addition, the partitioning of biomass between roots and shootswas also similar. The transition of the apex from vegetativeto reproductive mostly affected the partitioning of shoot biomassinto leaf (blades) and stems (rest of the shoot). A longer timeto reach floral initiation was associated with the productionof more, and larger, leaves as well as more tillers. This resultedin large differences in leaf area between isolines. However,at the whole plant level, all lines accumulated biomass at thesame rate with time. The early flowering lines compensated fortheir reduced leaf area by having a higher net assimilationrate and were thereby able to maintain the same relative growthrate as their later flowering counterparts.Copyright 1998 Annalsof Botany Company Development, growth, partitioning,Triticum aestivumL., wheat, isolines.     

Effects of Abscisic Acid on the Growth Pattern of the Shoot Apical Meristem and on Flowering in Chenopodium rubrum L.

Abscisic acid (ABA) at 1 x 10^–4 M or 3 x 10^–4 Mwas applied to the apical buds of Chenopodium rubrum plantsexposed to different photoperiodic treatments and showing differentpatterns of floral differentiation. Stimulation of growth inwidth of the apical meristem of the shoot and/or inhibitionof growth in length was obtained under all photoperiodic treatments.This change of growth pattern was followed by different effectson flowering. In non-induced plants grown under continuous light ABA stimulatedpericlinal divisions in the peripheral zone and the initiationof leaves as well as the growth in width of bud primordia. Inplants induced by two short days reduced growth of the meristemcoincided with ABA application. Longitudinal growth of the meristemwas inhibited in this case and only a temporary stimulationof inflorescence formation took place. In plants induced ata very early stage, ABA exerted a strong inhibitory effect onflowering. A permanent and reproducible stimulatory effect onflowering was obtained in plants induced by three sub-criticalphotoperiodic cycles if ABA was applied to apices released fromapical dominance. In this case formation of lateral organs andinternodes was promoted by ABA and was followed by stimulatedinflorescence formation. Gibberellic acid (GA2) at 1x 10^–4M or 3 x 10^–4 M brought about a similar effect on floweringas ABA, although the primary growth effect was different, i.e.GA₂ stimulated longitudinal growth. The effects of ABA and GA₂ on floral differentiation have beencompared with earlier results obtained from auxin and kinetinapplications. These growth hormones are believed to regulateflowering by changing cellular growth within the shoot apex.Depending on the actual state of the meristem identical growthresponses may result in different patterns of organogenesisand even in opposite effects on flowering. Shoot apex, flowering, photoperiodic induction, abscisic acid, gibberellic acid, Chenopodium rubrum L.     

The Influence of the Rht1 and Rht2 Alleles on the Growth of Wheat Stems and Ears

A field experiment was carried out with a set of near-isogenicspring wheat lines (cv. Triple Dirk) to determine the influenceof the Rht₁ and Rht₂ alleles on the partitioning of dry matterbetween the developing stem and the ear. Each line was sampledtwice weekly and dissected into its component above-ground parts.The rate of change of the dry mass of the individual plant organswas expressed as a proportion of the rate of change of the totalplant dry mass. This ratio was used to assess the relative sinkstrengths of the stem and ear during crop growth. The Rht₁ andRht₂ alleles reduced plant height, but increased grain yield.The greater yield was achieved through a greater grain numberper ear in the Rhtl line, a greater ear number per plant inthe Rht₂ line, and a greater allocation of assimilate to thedeveloping ear than to the developing stem in both Rht lines,particularly at the time of maximum stem growth (17 d beforeanthesis). From the earliest stages of detectable ear growthuntil anthesis, the ear masses per unit area of the Rht₁ andRht₂ lines exceeded that of Triple Dirk (Rht). It was not possibleto determine whether the Rht₁ and Rht₂ alleles were directlyresponsible for increasing grain number per ear and ear numberper plant, respectively, since the increase in these componentsof yield could equally be explained by a greater partitioningof assimilate to developing ears and tillers caused simply bya reduction in plant height. Triticum aestivum L., wheat Rht genes, stem and ear development, dry matter partitioning, allocation ratio     

The effect of day-neutral mutations in barley and wheat on the interaction between photoperiod and vernalization

Vernalization-2 (Vrn-2) is the major flowering repressor in temperate cereals. It is only expressed under long days in wild-type plants. We used two day-neutral (photoperiod insensitive) mutations that allow rapid flowering in short or long days to investigate the day length control of Vrn-2. The barley (Hordeum vulgare) early maturity8 (eam8) mutation affects the barley ELF3 gene. eam8 mutants disrupt the circadian clock resulting in elevated expression of Ppd-H1 and the floral activator HvFT1 under short or long days. When eam8 was crossed into a genetic background with a vernalization requirement Vrn-2 was expressed under all photoperiods and the early flowering phenotype was partially repressed in unvernalized (UV) plants, likely due to competition between the constitutively active photoperiod pathway and the repressing effect of Vrn-2. We also investigated the wheat (Triticum aestivum) Ppd-D1a mutation. This differs from eam8 in causing elevated levels of Ppd-1 and TaFT1 expression without affecting the circadian clock. We used genotypes that differed in “short-day vernalization”. Short days were effective in promoting flowering in individuals wild type at Ppd-D1, but not in individuals that carry the Ppd-D1a mutation. The latter showed Vrn-2 expression in short days. In summary, eam8 and Ppd-D1a mimic long days in terms of photoperiod response, causing Vrn-2 to become aberrantly expressed (in short days). As Ppd-D1a does not affect the circadian clock, this also shows that clock regulation of Vrn-2 operates indirectly through one or more downstream genes, one of which may be Ppd-1.     

The Growth of the Shoot Apex and the Apical Dome of Barley During Ear Initiation

The growth of the floral main shoot apex of spring barley wasstudied during the period of ear initiation (that is, from initiationof the collar primordium until maximum primordium number wasattained). While floral primordia were being initiated the relativelength growth rate of the shoot apex was low. After maximumprimordium number there was about a twofold increase in relativelength growth rate. Estimates of the volume, fresh and dry weightof the floral apex indicated that the relative weight growthrate was also low at first and increased after maximum primordiumnumber. The rates of growth and the size at initiation of thefloral primordia was affected by their position on the floralshoot apex. The relative volume growth rate increased acropetallyfrom the first initiated (collar) primordium. The collar wasthe smallest and each subsequently-initiated primordium increasedin length. The diameter of the newly-initiated primordium alsoincreased until more than half the primordia had been initiatedand then it declined. The apical dome increased in both lengthand diameter and both were at a maximum at the time of the double-ridgestage and then both measurements declined. Length and diameterwere at a minimum at maximum primordium number. Subsequentlythere was an increase in the length of the dome, after whichboth the dome and some of the last formed, distal primordiadied. The period of spikelet initiation therefore is a stage duringwhich the relative growth rate of the floral shoot apex is low,there are changes in the size of the dome and the primordiashow a progression of increasing relative growth rates acropetallyalong the shoot apex. These changes produce the embryo ear inwhich the most advanced spikelets are in the lower mid-partof the ear. Changes in size of the apical dome prior to maximumprimordium number may be related to the subsequent death ofspikelet primordia and therefore also to grain number in themature ear.     

Stimulation of the Flowering of Pharbitis nil Chois. by Gibberellin A3 : Time Dependent Action at the Apex

Gibberellin A₃ (GA₃) stimulated flowering when it was appliedto the shoot apex of seedlings of Pharbitis nil, dwarf strainKidachi; but, not when it was applied to the cotyledons. GA₃applied to the plumule before or shortly after the start ofan inductive dark period promoted both flowering and shoot elongation;but, the later the time of application during the dark periodless the promotion of flowering, although marked promotion ofshoot elongation always took place. The variation with time in the response of flowering to GA₃indicates that early floral processes at the apex are stimulatedby GA₃, but that subsequent processes are insensitive to it.The early processes of floral stimulus produced by a 16 hr inductivedark period probably are completed within 20 hr at 28°Cafter the end of the dark period. At low temperatures, suchas 15 and 20°C, early floral processes continued for morethan 40 hr. When cotyledons were removed at various times, the export ofthe floral stimulus to the shoot apex was apparent within hoursof the generation of the floral stimulus in the cotyledons,which started with the passage of the critical 9-hr dark period. (Received February 18, 1981; Accepted March 24, 1981)     

Gene-based high-density mapping of the gene rym7 conferring resistance to Barley mild mosaic virus (BaMMV)

For genetic analysis of Ppd-1 homoeologs controlling photoperiodic response of wheat (Triticum aestivum L.), bulk segregant analysis was performed using a doubled haploid (DH) population derived from a cross of Japanese wheat genotypes Winter-Abukumawase and Chihokukomugi. Based on the segregation of simple sequence repeat markers linked to the Ppd-1 homoeologs, Winter-Abukumawase carried insensitive alleles Ppd-B1a and Ppd-D1a and Chihokukomugi carried a single insensitive allele (Ppd-A1a) that was first found in common wheat. The genomic sequence of Ppd-1 homoeologs including the 5′ upstream region was determined and compared between the two genotypes. Ppd-D1a of Winter-Abukumawase had a deletion of 2,089 bp that was already reported for Ciano 67. Critical sequence polymorphism causing photoperiod insensitivity was not detected from the translation start codon to the 3′ untranslated region of Ppd-A1 and Ppd-B1. However, novel mutations were found in the 5′ upstream region. Ppd-A1a of Chihokukomugi had a deletion of 1,085 bp and Ppd-B1a of Winter-Abukumawase had an insertion of 308 bp. A total of 80 DH lines were classified into eight genotypes by PCR-based genotyping using specific primer sets to detect the In/Dels in the 5′ upstream region of three Ppd-1 genes. The heading dates of the DH lines differed significantly between the eight genotypes, showing that each of the three insensitive alleles accelerates heading by 7–9 days compared with the photoperiod-sensitive genotype. Interaction between the three genes was also significant.     

Flowering in Pisum: the Sites and Possible Mechanisms of the Vernalization Response

Grafting experiments with several genotypes provide evidencethat vernalization acts through at least two mechanisms. Vernalization of the stock promoted flowering by 26 nodes ingenotype If e Sn Hr and 5.5 nodes in genotype If e Sn hr buthad no detectable effect in genotype If e sn hr. Cold treatmentappears to cause a higher ratio of promoter to inhibitor, atleast in part, through low temperature repression of Sn activity.This mechanism is particularly evident in the cotyledons sincethey form a major area of Sn activity during vernalization.Continuous light was shown previously to prevent Sn forminginhibitor. It seems therefore that both photoperiod and vernalizationhave an effect through the Sn gene. Vernalization of the shoot promoted flowering by 19 nodes ingenotype If e Sn Hr, 3 nodes genotype If e Sn hr, and 1 nodein genotype If e sn hr1 grafted to an If e Sn hr stock. Theshoot effect may result from one or possibly two mechanisms.Firstly, vernalization may lower the threshold ratio of promoterto inhibitor required at the apex for floral initiation. Thesame change in threshold could result in changes in the floweringnode of quite different magnitude depending on the rate of changein the hormonal levels in the different genotypes. Secondly,vernalization may disturb the ageing process relative to theplastochronic age leading to an earlier (nodewise) decline ininhibitor level.     

Studies in Dormancy of Sycamore: II. THE EFFECT OF DAYLENGTH ON THE NATURAL GROWTH-INHIBITOR CONTENT OF THE SHOOT

1. An investigation was made into effect of daylength conditionsof the inhibition content of first-year seedlings of sycamore(Acer pseudoplatanus). 2. The shoot apical regions and mature leaves were extractedwith 80 per cent. Aqueous methanol, fractionated by paper chromatographyin isopropanol/ammonia and assayed by the wheat-coleptile growthtest. 3. A growth inhibitor was present in all extracts at R_f 0.7.Higher levels of inhibitor were present in both apices and matureleaves of plants transferred to short-day conditions than ofthose maintained under long-days throughout. 4. These difference in inhibitor level can be detected after2–5 days of short-day treatment, Preceding any markedeffect of daylength on growth. 5. Evidence is adduced in support of the hypothesis that theinhibitors is produced in the leaves during darkness and istransported to the apex during the photoperiod.     

Morpho-histogenic studies on tendrils of Passiflora

The ontogenetic development of the tendril and its associatedorgans is investigated in 17 species of Passiflora. The shootapex shows a single tunica layer though the second layer simulatestunica. The cytohistological zonation is not a constant feature.In P. caerulea Linn., it is distinct at leaf initiation butin P. pruinosa Mast., P. vespertilio Linn., and P. watsonianaMast., it is indistinct. The main axillary bud differentiatesfrom the peripheral meristem of the shoot apex. The differentiationof this bud into floral and tendril menstems occurs at a nodeimmediately below the shoot apex in P. minima Blanco. and Pracemosa Brot. In other species this differentiation generallyoccurs at the lower nodes. The floral meristem is initiatedas an accessory bud from this bud, thus forming a bud complex.The residuum of the bud complex develops as a tendril. The thirdaccessory bud which does not originate from this bud complex,develops into a vegetative branch. The fundamental nature ofthe vascular relationship between the flower, tendril, accessorybud, subtending leaf, and the axis is similar in most of theinvestigated species.