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     

Flowering in Pisum: the Effect of Age on the Gene Sn and the Site of Action of Gene Hr

Late cultivars of peas behave as quantitative long day plants.The reason that they flower between nodes 20 and 35 under an8 h photoperiod is shown to be because the leaves and maturestem produce a more promotory ratio of the flowering hormonesas they age. Later formed leaves may also start with a slightlymore promotory ratio than the leaves produced at a lower node.The gene Sn controls the production of a flower inhibitor andit is suggested that the activity of this gene in a leaf isgradually reduced as the leaf ages. From grafting experiments,the site of action of the gene Hr is shown to be in the leavesor mature stem and not at the shoot apex. This supports a previoussuggestion that the gene Hr is a specific inhibitor of the ageingresponse of gene Sn. Gene Hr is shown to cause a substantial delay in the floweringnode of decotyledonized plants of genotype If e sn hr undershort day conditions, suggesting that Hr has little effect inthe cotyledons. It is argued that the gene sn is a leaky mutantand that gene Hr does not control a photoperiod response inits own right but has its effect through the Sn locus. From a comparison of intact plants and self-grafts of the lategenotype If e Sn hr it is shown that under the conditions usedphysiological age may be of more importance than chronologicalage in determining flowering in peas. Reasons for the smalleffect of defoliation treatments on flowering are discussedas well as possible reasons for the promotory effect of decotyledonizationon the flowering node of late lines. Pisum sativum L, flowering, ageing, genetic control     

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.     

Apical Senescence in Pisum: A Direct or Indirect Role for the Flowering Genes ?

Apical senescence was examined in a range of intact and defloweredflowering genotypes under both long and short photoperiods.The flower inhibitor produced by the gene Sn, appears to havea direct effect on apical senescence since it can delay apicalsenescence under short day conditions in the absence of flowerand fruit development or where the rate of such developmentis the same in different treatments. Gene Hr can magnify thiseffect. Gene E, on the other hand, appears to influence apicalsenescence only indirectly through the effect it has on flowerand fruit development. The flowering genes at the If, sn andhr loci are also thought to have indirect effects on apicalsenescence. Even in deflowered plants apical senescence appearsto occur eventually in continuous light in all genotypes testedindicating that the presence of developing fruits, althoughpromotory, is not essential for apical senescence. Pisum sativum L., garden pea, flowering, senescence     

Flowering in Pisum: A Sixth Locus, Dne

A sixth major flowering gene, dne, is identified in the gardenpea (Pisum salivum L.). Linkage tests show dne is located onchromosome 3 near locus st. The ability to respond to photoperioddepends on the joint presence of the dominant genes Sn and Dnewhich together confer a long day habit. Genotypes Sn dne, snDne and sn dne are all essentially day-neutral although by examiningseveral flowering criteria under strictly controlled conditionssome small responses could be demonstrated. Like sn, dne reducedthe response to vernalization when substituted into genotypeSn Dne. It is suggested genes Sn and Dne both control steps in a biosyntheticpathway which leads to the production of a graft-transmissibleinhibitor of flowering and apical senescence. Stocks of genotypeSn dne and sn Dne promoted flowering in Sn Dne scions whileSn Dne stocks delayed flowering in Sn dne (and sn Dne) scions.However, reciprocal grafting between genotypes Sn dne and snDne gave no evidence of physiological complementarity correspondingto the genetic complementarity ofSn and Dne. Initial resultssuggest dne may be less effective than sn at blocking inhibitorproduction but this requires confirmation.     

Flowering in Pisum: the Effect of Genotype, Plant Age, Photoperiod, and Number of Inductive Cycles

The genotypes If e Sn hr, Lf e Sn hr, and If e Sn Hr requirefewer inductive cycles as they age. It is suggested that thisresults from a decrease in the activity of the Sn gene in theleaves as they age, resulting in a higher ratio of promoterto inhibitor. Gene Lf does not affect the rate of this agingbut it does increase the number of inductive cycles requiredfor flower induction over the first 5 weeks of growth. The geneHr has no effect until week 4 but thereafter causes a reductionin the effect of age on the Sn gene. The genotype If e Sn Hrcan be induced by a single inductive cycle (32 h of light) fora relatively long period. The length of dark period required for the expression of theSn gene is shown to be less than 4 h providing a relativelylong photoperiod precedes the dark period. It appears that noper manent induction of tissue by photoperiods favourable toflowering occurs in peas. The critical photoperiod for plantsof genotype if e Sn Hr is shown to be between 12 and 14 h atl7·5 °C and the usefulness of the term ‘criticalphotoperiod’ is discussed with respect to quantitativelong-day plants.     

Flowering in Pisum: the Effect of Light Quality on the Genotype If e Sn Hr

Far-red light, when given as a 16 h photoperiod extension, iamore effective than red light in reducing the flowering nodeof genotype Pisum. In contrast, when a 16 h dark period is interruptedby a 2 h light break red light is more effective than far-redlight. In addition, the stimulatory effect of a red interruptionis partially reversed by a subsequent period of far-red. However,a light interruption is not effective until over 12 h have elapsedsince the start of the previous photoperiod, regardless of whetherthe photoperiod was of 4 or 8 h duration. The results suggest that there are two light-dependent reactionscontrolling flowering in peas, one operating through the phytochromesystem with high levels of Pfr suppressing production of flowerinhibitor by the sn gene and a second requiring continuous illuminationwith wavelengths above 700 nm. The role of time measurementin the photoperiod response in peas is suggested to be filledby the proportion of time the Sn gene is effectively producinginhibitor. The photoperiod response in peas is not independentof temperature or plant age since the activity of gene Sn isalso varied by these factors.     

Genetic Regulation of Flowering in Grafts on Pisum sativum L

Lf, E, Sn, and Hr are major loci that condition the flowering and photoperiod responses of Pisum sativum L. Genetic lines containing the dominant alleles of these loci are characterized by flowering in long days, but having a prolonged (>50 node) vegetative phase in short days. A representative of this class, response type G, was used as a receptor in short days for donors of other flowering response types. The qualitative and quantitative flowering response of G receptors depended on the genotype of the donor. Donors containing sn hr induced the earliest development, followed by sn Hr and Sn hr donors. The Lf and E loci in foliar donors apparently did not affect flowering of G. Five-leaved > single-leaved > cotyledonary donors in effecting a flowering response in G, in part due to the longer life of the foliar donors. The responses of G to the various donors were generally consistent with the proposed roles of Lf, E, and Sn, but the role of Hr in these grafts was unclear.     

Photoperiodic and genetic control of carbon partitioning in peas and its relationship to apical senescence

Apical senescence but not flower initiation is delayed by short days (SD) compared to long days (LD) in pea plants (Pisum sativum L.) of genotype E Sn Hr. We recently reported that delay of senescence correlated with slower reproductive development, suggesting that fruits are weaker sinks for assimilates under delayed senescence conditions. Thus, we have examined assimilate partitioning in peas to determine if genotype and photoperiod regulate relative sink strength. Assimilate diversion by developing fruit has been implicated in senescence induction. A greater percentage of leaf-exported ¹⁴C was transported to fruits and a smaller percentage to the apical bud of G2 peas (genotype E Sn Hr) in LD than in SD. Relatively more of the ¹⁴C delivered to the apical bud of G2 peas was transported to flower buds than to young leaves in LD as compared to SD. There was no striking photoperiodic difference in carbon partitioning in genetic lines without the Sn Hr allele combination. The Sn Hr allele combination and photoperiod may regulate the relative strength of reproductive and vegetative sinks. Photoperiodic differences in sink strength early in reproduction suggest that these genes regulate sink strength by affecting the physiology of the whole plant. High vegetative sink strength in SD may maintain assimilate supply to the apical bud, delaying senescence.     

The Control of Apical Bud Growth and Senescence by Auxin and Gibberellin in Genetic Lines of Peas

Pea (Pisum sativum L.) lines G2 (dwarf) and NGB1769 (tall) (Sn Hr) produce flowers and fruit under long (LD) or short (SD) days, but senesce only under LD. Endogenous gibberellin (GA) levels were inversely correlated with photoperiod (over 9-18 h) and senescence: GA20 was 3-fold and GA1 was 10- to 11-fold higher in flowering SD G2 shoots, and the vegetative tissues within the SD apical bud contained 4-fold higher levels of GA20, as compared with the LD tissues. Prefloral G2 plants under both photoperiods had GA1 and GA20 levels similar to the flowering plants under LD. Levels of indole-3-acetic acid (IAA) were similar in G2 shoots in LD or SD; SD apical bud vegetative tissues had a slightly higher IAA content. Young floral buds from LD plants had twice as much IAA as under SD. In NGB1769 shoots GA1 decreased after flower initiation only under LD, which correlated with the decreased growth potential. We suggest that the higher GA1 content of G2 and NGB1769 plants under SD conditions is responsible for the extended vegetative growth and continued meristematic activity in the shoot apex. This and the increased IAA level of LD floral buds may play a role in the regulation of nutrient partitioning, since more photosynthate partitions of reproductive tissue under LD conditions, and the rate of reproductive development in LD peas is faster than under SD.     

The Influence of Genes ar and n on Senescence in Pisum sativum L.

The effect of genes ar (violet flowers, small hilum) and n (thick,fleshy pod wall) on whole plant in senescence peas was examinedby comparing Ar- with arar and N- with nn plants in segregatingprogenies. Homozygosity for ar or n significantly delayed the time whenthe plants were ready for harvest of their entire seed crop.These genes did not delay either the onset of reproduction orthe onset of apical arrest in the first instance. However, whereasAr- N- plants almost invariably senesced and died as the firstseed crop matured, the majority of arar and/or nn plants entereda period of secondary growth and a further fruiting cycle. Comparedwith Ar- plants, arar plants had over twice as many pods andseeds but individual seeds were 58 per cent lighter and totalseed yield (wt) was 19 per cent less. Pod length was unaffected.Compared with N-plants, nn plants had shorter pods (16 per cent),fewer seeds per pod (21 per cent), smaller seeds (20 per cent)and a lower total seed yield (wt 14 per cent less). It appearsthat ar and n impose a lower metabolic drain per reproductivenode as a consequence of their effects on hilum anatomy andpod morphology, respectively. These mutants disrupt the normalpattern of monocarpic senescence by breaking the coordinationbetween apical arrest and subsequent events. The developingseed crop delimited by the first arrest fails to cause plantdeath, possibly because sink size is less than in normal counterparts. Pisum sativum L, garden pea, senescence, hilum, pod, seed size, genetics     

Development of Floral Apex After Floral Induction in Stylo (Stylosanthes guianensis (Aubl.) Sw. var. guianensis)

The apex morphology of stylo (Stylosanthes guianensis var. guianensis)is described in four developmental phases (vegetative, transitional,initiated and floral) further subdivided into a total of tenstages. The apical dome broadens and flattens as induction proceedsuntil the initiation phase when apical diameter within 0.05mm of the dome apex is 55 per cent greater than in the vegetativeapex. Changes in vegetative morphology during induction aredescribed. Stylosanthes guianensis var. guianensis, stylo, flowering, reproductive anatomy, developmental stages     

Effects of Abscisic Acid on Growth of Wheat (Triticum aestivum L)

Daily application of abscisic acid (ABA) to growing wheat plants,although initially inhibiting growth, resulted, after a shortlag, in an increase in the number of leaves and tillers. Thismay have been due to reduced apical dominance. At 84 days thetotal dry weight and area of all leaves produced up to thistime was less for the plants treated with ABA than for the controlplants. However, the area of green, living leaves and the dryweight were not significantly affected by the ABA treatment.Further effects of the daily ABA treatment were the inhibitionof transpiration, especially on the abaxial surface, the reductionof leaf size, the promotion of flowering and the stimulationof trichome formation on the leaf surfaces. ABA did not promoteleaf senescence in whole plants and actually increased leaflongevity. Triticum aestivum L., wheat, leaf senescence, transpiration, growth, flowering, abscisic acid     

Hormone physiology of pea mutants prevented from flowering by mutations gi or veg1

The veg1 ( vegetative ) mutant in pea ( Pisum sativum L.) does not flower under any circumstances and gi ( gigas ) mutants remain vegetative under certain conditions. gi plants are deficient in production of floral stimulus, whereas veg1 plants lack a response to floral stimulus. During long days in particular, these non-flowering mutant plants eventually enter a stable compact phase characterised by a large reduction in internode length, small leaves and growth of lateral shoots from the upper-stem (aerial) nodes. The first-order laterals in turn produce second-order laterals and so on in a reiterative pattern. The apical bud is reduced in size but continues active growth. Endogenous hormone measurements and gibberellin application studies with gi-1 , gi-2 and veg1 plants indicate that a reduction in gibberellin and perhaps indole-3-acetic acid level may account, at least partially, for the compact aerial shoot phenotype. In the gi-1 mutant, the compact phenotype is rescued by transfer from a 24- to an 8-h photoperiod. We propose that in plants where flowering is prevented by a lack of floral stimulus or an inability to respond, the large reduction in photoperiod gene activity during long days may lead to a reduction in apical sink strength that is manifest in an altered hormone profile and weak apical dominance.     

Apical Growth and Modification of the Development of Primordia During Re-flowering of Reverted Plants of Impatiens balsamina L

Impatiens balsamina L. was induced to flower by exposure to5 short days and then made to revert to vegetative growth byreturn to long days. After 9 long days reverted plants wereinduced to re-flower by returning them to short days. Petalinitiation began immediately and seven primordia already presentdeveloped into petals instead of into predominantly leaf-likeorgans. However, the arrangement of primordia at the shoot apex,their rate of initiation and size at initiation remained unchangedfrom the reverted apex, as did apical growth rate and the lengthof stem frusta at initiation. The more rapid flowering of thereverted plants than of plants when first induced, and the lackof change in apical growth pattern, imply that the revertedapices remain partially evoked, and that the apical growth patternand phyllotaxis typical of the flower, and already present inthe reverted plants, facilitate the transition to flower formation. Impatiens balsamina, flower reversion, partial evocation, shoot meristem, determination, leaf development     

Profiles of Leaf Senescence During Reproductive Growth of Sunflower and Maize

We investigated the effect of reproductive growth on the profilesof leaf senescence in maize (Zea mays L.) and sunflower (Helianthusannuus L.). Leaf senescence after flowering was assessed usingboth structural (leaf chlorophyll, nitrogen and dry matter)and functional (photosynthesis) variables in undisturbed plants(+G) and in plants in which grain set was prevented (-G). Twoweeks after flowering, lack of grain accelerated senescencein maize and delayed senescence in sunflower as indicated byleaf chlorophyll; leaf nitrogen and dry matter were less sensitiveresponse variables. Lack of interaction between reproductivetreatment and leaf position indicates that the senescence signal,whatever its nature, was equally effective throughout the plantin both species. In both species, feedback inhibition of photosynthesiswas first detected 30–35 d after flowering; excess carbohydratein the leaves was therefore an unlikely trigger of acceleratedsenescence in maize. As reproductive development progressed,differences between +G and -G plants were more marked in sunflower,and tended to disappear or reverse in maize. In sunflower, interactionsbetween leaf position and reproductive treatment—attributableto the local effect of grain—were detected around 20–27d after flowering. Copyright 2000 Annals of Botany Company Helianthus annuus, Zea mays, chlorophyll, light, nitrogen, photosynthesis, reproductive growth, senescence, source-sink, SPAD.     

Mechanisms of Developmental Integration of Aster novae-angliae L. and Hieracium murorum L.

This paper is an inquiry into the regulatory features of developmentof Aster novae-angliae and Hieracium murorum. Computer-generatedplant models are compared with real plants to analyze branching,conver sion from vegetative to flowering development, stem elongation,and flowering.     

A yeast mitotic activator sensitises the shoot apical meristem to become floral in day-neutral tobacco

True day-neutral (DN) plants flower regardless of day-length and yet they flower at characteristic stages. DN Nicotiana tabacum cv. Samsun, makes about forty nodes before flowering. The question still persists whether flowering starts because leaves become physiologically able to export sufficient floral stimulus or the shoot apical meristem (SAM) acquires developmental competence to interpret its arrival. This question was addressed using tobacco expressing the Schizosaccharomyces pombe cell cycle gene, Spcdc25, as a tool. Spcdc25 expression induces early flowering and we tested a hypothesis that this phenotype arises because of premature floral competence of the SAM. Scions of vegetative Spcdc25 plants were grafted onto stocks of vegetative WT together with converse grafts and flowering onset followed (as the time since sowing and number of leaves formed till flowering). Spcdc25 plants flowered significantly earlier with fewer leaves, and, unlike WT, also formed flowers from axillary buds. Scions from vegetative Spcdc25 plants also flowered precociously when grafted to vegetative WT stocks. However, in a WT scion to Spcdc25 stock, the plants flowered at the same time as WT. SAMs from young vegetative Spcdc25 plants were elongated (increase in SAM convexity determined by tracing a circumference of SAM sections) with a pronounced meristem surface cell layers compared with WT. Presumably, Spcdc25 SAMs were competent for flowering earlier than WT and responded to florigenic signal produced even in young vegetative WT plants. Precocious reproductive competence in Spcdc25 SAMs comprised a pronounced mantle, a trait of prefloral SAMs. Hence, we propose that true DN plants export florigenic signal since early developmental stages but the SAM has to acquire competence to respond to the floral stimulus.     

Characterization of waldmeister, a novel developmental mutant in Arabidopsis thaliana

A novel Arabidopsis thaliana (L.) Heynh. developmental mutant,waldmeister (wam), is described. This mutant was found in theprogeny arising from an Ac-Ds tagging experiment, but does notappear to be tagged by an introduced transposon. This recessivenuclear mutation maps between GAPB and ap1 on chromosome 1 andshows extreme morphological and physiological changes in bothfloral and vegetative tissues. Changes to the vegetative phenotypeinclude altered leaf morphology, multiple rosettes, stem fasciation,retarded senescence and disturbed geotropic growth. Changesto the floral phenotype include delayed flowering, increasednumber of inflorescences, determinate inflorescences, alterednumber and morphology of floral organs, chimeric floral organs,and ectopic ovules . wam was crossed to a number of previouslydescribed floral mutants: apetela 2, apetela 3, pistillata,agamous, and leafy. The phenotype of the double mutant was ineach case additive. In the case of agamous, however, the indeterminaterepetitive floral structure of agamous was lacking, emphasizingthe determinate inflorescence growth of wam. The extreme phenotypeof the wam mutant is suggestive of a disturbance to a gene ofglobal importance in the regulation of plant growth and development. Key words: Arabidopsis thaliana, waldmeister, developmental mutant, flower mutant     

A Model of Flowering in Chrysanthemum

A mathematical model of flowering in Chrysanthemum morifoliumRamat. is described which may be used to predict quantitiessuch as the number of primordia initiated by the apex, plastochronduration and apical dome mass before, during and after the transformationof the apical meristem from vegetative to reproductive development.The model assumes that primordial initiation is regulated byan inhibitor present in the apical dome. Within each plastochronthe apical dome grows exponentially, and the inhibitor concentrationdeclines through chemical decay and dilution. When the inhibitorconcentration falls to a critical level a new primordium isinitiated. There is instantaneous production of inhibitor, anda decrease in dome mass corresponding to the mass of the newprimordium. The process continues until the apical dome attainsa particular mass when the first bract primordium is produced.Subsequent primordia compete with the apical dome for substrates,and the specific growth rate of the dome declines with successiveplastochrons. Eventually, the net mass of the dome starts todecline until it is entirely consumed in the production of floralprimordia. Chrysanthemum morifoliumRamat, flowering, primordial initiation