FLOWER-PROMOTING EFFECT OF GIBBERELLIN IN WINTER WHEAT AND BARLEY

1. Vernalized and unvernalized seeds of barley were sown in greenhouseunder short day or long day condition. At the second leaf stage,a half of the plants in each plot was sprayed with gibberellin.Plants grown from vernalized seeds headed at about the sametime under long day condition, whether they were treated withgibberellin or not. Under short day condition, however, gibberellinpromoted heading. With plants grown from the unvernalized seeds,gibberellin promoted heading under long day condition whereasit delayed heading under short day condition. Thus the substitutionof gibberellin for long day effect and for vernalization effectwas shown.
2. Immature embryos growing on developing ear of wheatand barleywere vernalized with low temperature combined withor withoutgibberellin application. Plants grown from the seedstreatedat their early ripening stage with low temperature combinedwith gibberellin gave earlier heading, associated with the decreasedleaf number, than the plants from seeds treated with low temperaturealone. This effect of gibberellin lasted for a half-year ofseed storage.
3. Gibberellin was applied to germinating seedsunder vernalizationtreatment. Gibberellin promoted floweringin varieties whichpossess high requirement for chilling vernalization,when thechilling was insufficient to satisfy the high requirement.However,the effect of gibberellin was obscure with varietiespossessingrelatively low requirement for vernalization.

(Received September 15, 1964; )     

Factors controlling Flowering in the Chrysanthemum: II. DAY-LENGTH EFFECTS ON THE FURTHER DEVELOPMENT OF INFLORESCENCE BUDS AND THEIR EXPERIMENTAL REVERSAL AND MODIFICATION

1. Inflorescence buds, produced by vernalized Chrysanthemum plantsin long day, cease to grow, and die at an early stage if maintainedin long day, but will produce open flowers if transferred toshort day. Dissection of such buds reveals that developmentdoes not proceed beyond the formation of the bare receptacleand no florets are initiated, while inflorescence buds producedin short day have almost completed floret initiation when theybecome macroscopically visible.
2. Inflorescence buds producedin long day can be induced to completetheir development inlong day by:
   1. removal of all lateral shoots, and
   2. by re-rootingthe inflorescenceitself, leaving only a numberof bracts onits axis.
3. Inflorescence buds produced in short day canbe inhibited fromdeveloping by
   1. transfer to long day,
   2. transferto low light intensity in shortday, and
   3. application of auxinpaste.
4. All three methods of inhibition become progressivelyless effectivewith the advancing development of the bud.
5. Thelatest stage at which development was found to have beenarrestedwas that of ovule formation.
6. Heights of plants were determinedat budding and when the flowershad started to open; markeddifferences due to length of daywere found.
7. Teratologicaleffects noted in buds, exposed for extended periodsto longday, included formation of bracts on the receptacle(the absenceof which distinguishes the subtribe Chrysantheminaeof the Compositaeto which the Chrysanthemum belongs) as wellas secondary inflorescences,petaloid stamens, &c.
8. The results are discussed in relationto known effects of auxinon vegetative growth and reproduction.

     

INHIBITORY EFFECT OF GROWTH RETARDANTS ON THE INDUCTION OF FLOWERING IN WINTER WHEAT

1. Growth retardants, CCC, Amo-1618, Phosfon-D and B-995, appliedduring seed vernalization inhibited the ear development of winterwheat. CCC applied during green plant vernalization inhibitedflowering,but it had no appreciable effect on the final stemlength. Theinhibition by CCC was reversed by foliar applicationof gibberellin.On the other hand, CCC applied after the vernalizationperiodaffected the final stem length but not flowering.
2. Theamount of endogenous gibberellin-like substance(s) was greaterin the vernalized plant than in the non-vernalized plant. Nogibberellin-like substance was detected in the CCC-treated plant.
3. Endogenous gibberellin-like substance(s), whose biosynthesisis inhibited by some growth retardants, may play a part in thevernalization process in winter wheat.

¹Present address: National Institute of Agricultural Sciences,Nishigahara, Kitaku, Tokyo     

Factors concerned in the Rooting Responses of Isolated Leaves

The rooting responses of isolated leaves of the dwarf Frenchbean and the ivy were studied by applying solutions of growthsubstances to the petiole: ß-indolyl-butyric acid(I.B.A.) for the former and -naphthyl-acetic acid (N.A.A.) forthe latter. The following factors were investigated:

1. The variation in response of successive leaves from the apextowards the base of the plant.
2. The optimal concentrationsof the growth substances and therelation between duration ofapplication and concentration.
3. The relation of age of theleaf and optimal concentration(ivy).
4. The nutritive factorsconcerned in the response were studied,(a) by varying periodsof contact between lamina and petiole,(b) by varying durationof light, (c) by varying the amountof light, and (d) by feedingwith sucrose and asparagine.

The most responsive leaf in the bean was the 2nd from the apex,in the ivy the 9th leaf. Very young leaves were killed. Withpetioles immersed for 24 hours the optimal concentrations wereI.B.A. at 2·5 parts per million (p.p.m.) for the bean,and N.A.A. 100 p.p.m. for the ivy. It was shown that the activesubstance entered mainly through the cut end in the transpirationstream; entry through the cuticle was much slower. Starvation of the cuttings whether by low light intensity, darkness,or separation of the lamina from the petiole reduced root formation.Feeding with sucrose and asparagine increased the response. Analysis of the leaves was carried out at regular intervalsfor total sugar, total and soluble nitrogen. In the bean solublenitrogen increased slightly in the petiole during the first5 days after treatment, after which insoluble nitrogen continuedto accumulate until the 7 day, when the roots first emerged.After this the total nitrogen decreased. Sugar content of thepetiole at first increased but rapidly fell before the rootsemerged and then again increased. In the ivy petiole the increasein soluble and total nitrogen was very slow, the former beinggreatest on the 15th day and the latter on the 20th day aftertreatment. The total sugar increased to the 10th day, but thendecreased until the emergence of roots, after which it againincreased. Treated leaves of the bean and ivy of different agesand the leaves starved for varying periods were also analysedfor total sugars and total nitrogen. Treated bean leaves receivingvarying periods of daily illumination were also analysed toelucidate their rooting response. Histological examination showed that in the bean the roots arosein the rays between the vascular bundles and in the ivy externalto the vascular bundles opposite the phloem. The growth of the rooted leaves was followed for more than amonth in the bean and over one year in the ivy. Some growthwas found in the immature bean leaves which survived treatment,but the final size was much below that of the control leavesattached to the plant. In the ivy very little further growthoccurred although the leaves produced a large root system andafter 2 years are still alive: the original differences in sizeof the successive leaves at the time of removal from the plantstill remain.     

Juvenility and flowering of Brunonia australis (Goodeniaceae) and Calandrinia sp. (Portulacaceae) in relation to vernalization and daylength

Background and Aims

The time at which plants are transferred to floral inductive conditions affects the onset of flowering and plant morphology, due to juvenility. Plants of Brunonia australis and Calandrinia sp. were used to investigate whether Australian native ephemeral species show a distinct juvenile phase that can be extended to increase vegetative growth and flowering.

Methods

The juvenile phase was quantified by transferring seedlings from less inductive (short day and 30/20°C) to inductive (vernalization or long day) conditions at six different plant ages ranging from 4 to 35 d after seed germination. An increase in days to first visible floral bud and leaf number were used to signify the end of juvenility.

Key Results

Brunonia australis was receptive to floral inductive long day conditions about 18–22 d after seed germination, whereas plants aged 4–35 d appeared vernalization sensitive. Overall, transferring plants of B. australis from short to long day conditions reduced the time to anthesis compared with vernalization or constant short day conditions. Calandrinia sp. showed a facultative requirement for vernalization and an insensitive phase was not detected. Floral bud and branch production increased favourably as plant age at time of transfer to inductive conditions increased. Younger plants showed the shortest crop production time.

Conclusions

Both species can perceive the vernalization floral stimulus from a very young age, whereas the photoperiodic stimulus is perceived by B. australis after a period of vegetative growth. However, extending the juvenile phase can promote foliage development and enhance flower production of both species.     

The Absorption of Ions by Excised Root Systems: III. OBSERVATIONS ON ROOTS OF PEA PLANTS GROWN IN SOLUTIONS DEFICIENT IN PHOSPHORUS, NITROGEN, OR POTASSIUM

1. Pea plants were grown in complete culture solution and in deficienciesof phosphorus, nitrogen, or potassium for a period of about5 weeks. Excised roots of these plants were treated with a complete,aerated culture solution for varying periods of time and thechanges in respiration rate, phosphorus, nitrogen, potassium,sugar, and starch contents measured.
2. There were changes infresh weight and dry weight of the excisedroots during treatment.The dry weight decreased with time butthe water content changeswere variable. Uptake of water wascorrelated with uptake ofpotassium and sucrose content in someinstances.
3. There wasno evidence of a ‘salt respiration’ inthose caseswhere active accumulation occurred.
4. The rates of gain or lossof phosphorus, nitrogen, or potassiumat 0 hours, 8 hours, and16 hours were calculated and it wasfound that the rate dependedboth on content of element in theroot and the sugar cotent.There was very little evidence thatone element affected therate of uptake of another. Simultaneousloss of one elementand gain of another occurred in some instances.
5. The observationsappear to be best explained on the assumptionthat the absorbedions are fixed in the cells in the form ofloosely bound compoundsand that these compounds are formedfrom sugars.

     

PROTEINS OF WHEAT EMBRYOS IN THE PERIOD OF VERNALIZATION

1. Soluble proteins prepared from non-vernalized and vernalizedwheat embryos were investigated by means of column chromatographyand disc electrophoresis. As vernalization proceeded, new proteinswere detectable as the fastest moving electrophoretic bandsor as the new peaks which were eluted with 0.025 M and 0.05M phosphate buffer (pH 7.0) from DEAE-cellulose. Plumule wasfound to be the part of embryo in which these proteins appear.After vernalization, protein pattern of winter wheat embryowas very similar to that of spring wheat embryo.
2. Histoneswere prepared from non-vernalized and vernalized wheatembryosand their chromatographic patterns were investigated.Winterwheat embryo showed more complicated pattern than didspringwheat embryo. Upon vernalization, histone pattern ofwinterwheat embryo became less complicated and similar to thatofspring wheat embryo.

(Received October 4, 1966; )     

The Peltier Effect and its Use in the Measurement of Suction Pressure

1. A method is described by means of which the suction pressureof living material may be measured by observations on its equilibriumvapour pressure.
2. It employs a very fine thermocouple whosetip is cooled by meansof the Peltier effect, below the dew-point.It collects a minuteamount of dew, and can thus be used asan exceedingly fine ‘wet-bulb’thermometer. As suchit is convenient to use, quick in action,and causes very littledisturbance to the system under observation.
3. The thermocoupleis calibrated by means of salt solutions ofknown strength.The scale is fairly linear.
4. The method possesses the advantagesof giving the suction pressureby direct observation ratherthan by interpolation; of speedin the actual measurement; ofnot subjecting the tissue to immersion;and of permitting organslike leaves, otherwise difficult tohandle, to be easily dealtwith. It also opens possibilitiesoutside the range of the conventionalmethods.

     

Studies in Abscission: I. FACTORS AFFECTING THE INHIBITION OF ABSCISSION BY SYNTHETIC GROWTH-SUBSTANCES

1. The general method is described for experimenting on applepedicelsor petioles from which the terminal organ has beenremoved.
2. Two quantitative techniques for applying growth-substancesaregiven in detail, one employing lanolin emulsion as the carrier,the other agar gel.
3. By these methods certain factors affectingthe inhibition ofabscission by the growth-substances -naphthylaceticacid (NAA)and 2:4-dichloro-phenoxyacetic acid (DPOA} have beeninvestigated. A relation between concentration of the growth-substanceandpersistence of the pedicel was established which was usuallylinear. In an experiment with NAA, for instance, the relationwas represented by— Persistence in days=6·52+0·0127xconcentrationin p.p.m.
4. The acid and the sodium salt of both NAA and DPOAgave similarresults when applied in lanolin emulsion.
5. Onboth young pedicels and young shoot internodes NAA was foundto exert a ‘formative’ influence resulting in increasein diameter which was not exhibited by DPOA to the same extent.
6. At least for concentrations of either growth-substance upto100 p.p.m., these were effective only when applied distallyto the abscission zone. At 1,000 p.p.m. there was an effectof application on the proximal side of the abscission region,but it was small compared with the effect of the same concentrationapplied distally.
7. The length of the path of the growth-substancefrom the pointof application to the abscission zone affectedthe degree ofinhibition inversely, the longer the path theless the effectof a given concentration in delaying abscission.The contrastbetween these findings for pedicels, and thoseof other authorsfor petioles, is briefly discussed.
8. A criticalperiod occurs shortly after removing the leaf-bladefrom itspetiole during which the abscission process is initiated,andto be effective in inhibiting this process growth-substancemust reach the abscission zone within this period. It is notat present established whether the pedicel shows a similar modeof behaviour.
9. A working hypothesis is given to account forthe control ofabscission by natural hormones, and extensionsare describedto embrace the results of experiments with syntheticgrowth-substances.

     

Studies on Plant Growth Hormones: I. BIOLOGICAL ACTIVITIES OF 3-INDOLYLACETALDEHYDE AND 3-INDOLYLACETONITRILE

1. Two neutral plant hormones, one isolated recently from plants(3-indolylacetonitrile) and the other (3-indolylacetaldehyde)reported to be present in plants, are avaible as pure syntheticcompounds for investigation of their biological activities.This paper is mainly concerned with their effects on cellelongationin the Avena coleoptile
2. 3-Indolylacetaldehyde is considerablyless active than 3-indolylaceticacid in the Avena straight-growthtest; for example, a 1.0 mg./l.solution of the aldehyde showsan activity equivalent to thatof a 0.1 mg./l. solution of theacid
3. An acidic substance is produced in solutions of the aldehydeduring the period of assay. In some experiments it accountsfor all of the activity shown by the aldehyde solutions, onthe assumption that it is 3-indoylacetic acid, and in otherexperiments it shows a greater activity than that of the aldehydesolutions from which it was obtained. Therefore, it is concludedthat 3-indolylacetaldehyde, itself is either inactive or inhibitory.Acid production in aldehyde solutions in vitro is much lower,a fact which suggests that there is enzymatic oxidation of aldehydeto acid in the presence of coleoptiles.
4. The activities of3-indolylacetaldehyde in the pea test andin root-inhibitionand of 3-indolylacetone in the straight-growthtest are brieflyreported.
5. 3-Indolylacetonitrile is considerably more activethan 3-indolylaceaticacid in the Avena straight-growth test;for erample, a 0.1 mg./l.solution of the nitrile shows an activityequivalent to a 1.0mg./l. solution of the acid. The inhibitoryeffect at concentrationsabove 1.0–10.0 mg./l. is lesswith the nitrile than withthe acid.
6. There is negligible productionof acid in solutions of the nitrileboth in vitro and in thepresence of Avena coleoptiles at temperaturesranging from –18?to 25? C. for varying lengths of time.The possibility of enzymaticconvesion of nitrile to acid insidethe cells of the coleoptileis discussed
7. The activities of 3-indolylacetamide and of 2:4-dichlorophenoxyaceticacid and the corresponding nitrile are considered in this connexion
8. The nitrile is destroyed by treatment with alkali but notbyacid. In the light of these results, it is desirable to re-examineprevious work on identification of auxins in plants by theiracid and alkali sensitivity. Evidence for the existence of thenitrile in a number of other plants is presented.

     

Observations on the Gaseous Exchanges which take place between Menyanthes trifoliata L. and its Environment: I. THE COMPOSITION OF THE INTERNAL GAS OF THE PLANT

1. As part of a general investigation into the exchange of gasesbetween the bogbean, Menyanthes trifoliata, and its environment,determinations have been made of the composition of the internalatmosphere of the plant at five different levels, viz. leafyshoot, three successive portions of stem, and roots.
2. Procedureis described for the analysis of small gas samplesusing a modificationof the Bonnier and Mangin apparatus.
3. In darkness with thelower part of the plant surrounded by anatmosphere of nitrogen,it has not been possible to show thepresence of a regular downwardsgradient of oxygen, such aswould be expected on a basis ofnormal gaseous diffusion.
4. Under these Air Top/Nitrogen Bottomconditions the roots areshown to contain between 12?5 and 17?5percent, of oxygen intheir intercellular gas system. The portionof stem immediatelyadjacent to the roots showed an oxygen levelof from 14?0 to18?0 per cent.
5. In plants kept under NitrogenTop/Air Bottom conditions in thedark for 48 hours, the concentrationof oxygen in the rootsfell to a level of 3?1 per cent, or belowin three plants andto 6?o per cent, in a fourth. The oxygenconcentration in theadjacent lowermost part of the stem wasas high as 18?0 percent., depending on the degree of aerationof the solution bathingthe stem. It is suggested that thisdistribution of oxygen canbe related to the relative impermeabilityof roots and of stemendodermis to gaseous diffusion from without,and it is thoughtthat the major part of the oxygen supply tothe roots is transportedto them through the stelar air passages.
6. Some evidence is presented to show that oxygen passes fromthelower parts of the plant into the medium surrounding it.

     

The Effect of Prolonged Chilling on Water Movement and Radial Growth in Trees

1. The woody shoots of young saplings of Fraxinus.excelsior andAcer Pseudo-platanus in pots were subjected to continuous coolingto about 2° C. during the growth season, with the resultthat radial growth was almost completely inhibited throughoutthe woody stem.
2. The chilling did not adversely affect extensiongrowth exceptthat it was later in commencement and proceededmore slowly.
3. If the temperature around the stem is loweredfrom 2° C.to 0° C., water conduction is cut down tosuch an extentas to cause wilting of the leafy shoots; turgidityis recoveredwhen the temperature is again raised to 2°C.
4. This wilting effect is discussed particularly in relationtothe part played by living cells in the upward movement ofwaterin the wood.

     

Studies on Plant Growth Hormones: II. FURTHER BIOLOGICAL PROPERTIES OF 3-INDOLYLACETONITRILE

1. 3-Indolylacetonitrile is more active than 3-indolylacetic acidin the Avena straight-growth test, but less active in the Avenacurvature test at comparable concentrations. Reasons for thisare discussed, and results of previous work on plant extractsusing the curvature test as a means of assay are considered.
2. Transport of both the acid and the nitrile is polar, fromapexto base of the coleoptile. The nitrile can reach the growingcells as easily, and possibly more easily, than the acid. Thesignificance of these findings for a theory on the mechanismof action of the nitrile is discussed.
3. The nitrile is inactivein the pea curvature test and straight-growthof pea stem sectionsexcept at high concentrations. It is alsoinactive or only slightlyactive in lateral bud inhibition,root initiation, and petioleabscission at the concentrationstested.
4. It is less activethan the acid in root inhibition in cress,but approximatelyas active in Avena. It is approximately asactive as the acidin parthenocarpic fruit development, andinitiation of cambialactivity.
5. The significance of these results is discussed.

     

The Water Permeability of Unplasmolysed Tissues2

1. The permeability of unplasmolysed cells of beetroot, v. ‘CrimsonGlobe’, was determined from the rate of water loss ofbeet slices on placing in sucrose solutions having O.P. greaterthan the suction pressure of the beet. The absolute values obtainedwere about 0?7µ³ water per µ² cell-surface per hourper atmosphere osmotic pressure difference, i.e. 0?7 µ/hr./atm.
2. The permeability of similar beet cells plasmolysed withintheircell walls was found to be about 13µ/hr./atm.
3. Thepermeability of beet cells which had been plasmolysed andallowedto recover was shown to be approximately the same asthat ofunplasmolysed cells.
4. The hypothesis is advanced that the increasein water permeabilityon plas-molysis is due to those partsof the plasma-membranewhich had formerly been pressed againstthe micelles of thecell wall becoming free and able to takepart in water transfer.
5. The energy requirement for the maintenanceof an excess hydrostaticpressure of five atmospheres withina cell by its vital activitywas shown to be about one-tenthof the total respiratory energyreleased in freshly cut beetslices.

     

Studies with Radioactive Tracers in Plant Nutrition: II. THE ESTIMATION OF RADIOACTIVE TRACERS

Part I Tracer methods can yield valid results only if the behaviourof the tracer within the plant is indistinguishable from thatof the normal element. The extent to which radioactive isotopessatisfy this requirement must be considered from the followingviewpoints:

1. their chemical and physical bahaviour before disintegration;
2. the effects and substances formed by their disintegration;
3. the effects of the radiation they emit.

Whereas, chemically and physically, isotopes with the exceptionof H¹ and H³ satisfy this requirement, they may cause significantradiation damage even when supplied in low concentration ifthey are accumulated metabolically. The investigation of possibleradiation effects is therefore an essential preliminary to allphysiological investigations. The value of tracer methods is considered. Part II Equipment and laboratory procedures for the electronic assayof P³² are described. For the assay of samples containing P³²a wet ashing method and the subsequent use of a liquid countingtube is preferred. Improvements of equipment to suit the requirementsof plant nutritional studies are considered. Sources of experimentalerror are examined. On account of the decay of radioactive isotopes,the time factor may be of special importance in tracer work.Its effect on both experimental design and on laboratory proceduresis considered. It is stressed that the scope and replicationof large experiments, particularly if they are of long duration,may be subject to serious limitations. The importance of simplifyingthe equipment used in tracer assay and increasing its reliabilityis emphasized.     

The Time Factor in Studies of Growth Inhibition in Excised Organ Sections

1. Apprehension over the adequncy of current techniques stimulateda detailed study of the time factor in the arsenate inhibitionof growth and respiration in excised stem and root sectionsof Pisum sativum.
2. Growth inhibition by arsenate sets in veryslowly, its rateof onset being related to the molar concentration(C) of arsenateate by the relation where T₅₀ is the time taken in hours to reduce the growthrateto 50 per cent of the control and K is a constant. An explanationof the physiological basis of this relationship is attempted.
3. Estimates were made of the final steady growth rate (relativeto control) in various arsenate concentrations. The inhibitionscalculated from this rate are held to approximate to the truearsenate effect and are shown to be very different from thosecalculated from ‘total growth’ measures.
4. Respirationof growing stem sections is not inhibited by thelow arsenateconcentrations that inhibit growth. Some inhibitionis indicatedat high concentrations (3 ? 10^–4M. and over)but onlyafter 15-20 hours of exposure.
5. Two per cent sucrose has noeffect on the arsenate inhibiitionof stem growth. Sucrose,however, markedly stimulates respirationin stem sections, butthis stimulation is prevented by arsenate.
6. The misinterpretationswhich may arise as a result of ignoringthe time factor in inhibitionstudies in excised organ sectionsare discussed and the desirabilityof constructing completegrowth curves in all such studies isstressed.

     

The Morphology and Anatomy of Pellia epiphylla considered in Relation to the Mechanism of Absorption and Conduction of Water

1. In Pellia epiphylla water travels in the form of capillary filmsbetween the rhizoids over the under surface, being partly absorbedthere. The remainder passes over the surface and is retainedin the region of the antheridia by the incurved and wavy marginsof the thallus.
2. The antheridia, oospheres, segmenting oospores,and sporogoniaare largely supplied with water from the exterior.This wateris retained in the narrow crevices between antheridialcavityand antheridium, between the flaps of the involucre,and betweenthese and the long necks of the archegonia. Travellingdownthe necks of the archegonia, it reaches the oospheres,and islater available for the developing sporophyte in theform offilms retained between the foot of the segmenting embryoandthe calyptra.
3. In the sporophyte, this water, absorbedby the foot largelyfrom external sources, travels up the seta,into the elaterophore,out to the elaten, and ultimately tothe spores.
4. The sporophyte, therefore, is much less dependenton the gametophytefor supplies of water and raw materials thanmight be expected.

The writer wishes to take this opportunity of thanking ProfessorF. A. Mockeridge for suggesting this work and for her valuableadvice and criticism during its progress.     

Effect of Photoperiod on the Regulation of Wheat Vernalization Genes VRN1 and VRN2

Wheat is usually classified as a long day (LD) plant because most varieties flower earlier when exposed to longer days. In addition to LD, winter wheats require a long exposure to low temperatures (vernalization) to become competent for flowering. Here we show that in some genotypes this vernalization requirement can be replaced by interrupting the LD treatment by 6 weeks of short day (SD), and that this replacement is associated with the SD down-regulation of the VRN2 flowering repressor. In addition, we found that SD down-regulation of VRN2 at room temperature is not followed by the up-regulation of the meristem identity gene VRN1 until plants are transferred to LD. This result contrasts with the VRN1 up-regulation observed after the VRN2 down-regulation by vernalization, suggesting the existence of a second VRN1 repressor. Analysis of natural VRN1 mutants indicated that a CArG-box located in the VRN1 promoter is the most likely regulatory site for the interaction with this second repressor. Up-regulation of VRN1 under SD in accessions carrying mutations in the CArG-box resulted in an earlier initiation of spike development, compared to other genotypes. However, even the genotypes with CArG box mutations required LD for a normal and timely spike development. The SD acceleration of flowering was observed in photoperiod sensitive winter varieties. Since vernalization requirement and photoperiod sensitivity are ancestral traits in Triticeae species we suggest that wheat was initially a SD–LD plant and that strong selection pressures during domestication and breeding resulted in the modification of this dual regulation. The down-regulation of the VRN2 repressor by SD is likely part of the mechanism associated with the SD–LD regulation of flowering in photoperiod sensitive winter wheat. These authors contributed equally to this work     

Studies on Plant-Growth Hormones: VI. THE NATURE OF INHIBITOR-{beta} IN POTATO

1. The chemical nature of a plant growth inhibitor in potato tuberpeel, the ‘Inhibitor-ß’ which commonlyoccurs on chromatograms of many plant extracts, has been examined.
2. The inhibition, as indicated by bioassays using wheat coleoptilesections, could not be associated with any particular compound,but was partly or entirely due to a complex mixture of aliphaticacids.
3. . Azelaic acid and the coumarin, acopoletin, were isolatedtogetherwith a new substance, Acid A; degradative evidenceis not sufficientto enable a complete structure to be proposedfor this acid,but it appears to be an unsaturated polyhydroxyfatty acid.
4. The growth of coleoptile sections in solutionsof ßat several concentrations was examined over thefirst 7 hoursof growth. Inhibition did not occur until 4 hours;visible damageto the cells of the tissues appeared after thisperiod. Whenß was examined in a mixture with 3-indolylaceticacid,inhibition was evident after 1 hour. These results areinterpretedand the chemical system in which ß mayoperate ingrowth is briefly considered.

     

The Effect of Day Length on the Response of Celery to Vernalization

Regimes of long photoperiods or long skotoperiods interruptedby night breaks during vernalization reduced bolting and floweringin celery (Apium graveolens L.) and decreased the stem length.However, after vernalization long photoperiods promote boltingand markedly enhance flower stalk elongation. The possibilitythat the developing inflorescence itself is the source of endogenousgibberellins which control stem elongation is discussed. It is concluded that the celery plant, in addition to its vernalizationrequirements, is a short-long day plant and not a day-neutralplant.