Effects of Kinetin on Growth of the Apical Meristem and Floral Differentiation in Chenopodium rubrum L.

Kinetin (1•10^–4 M and 1•10^–3 M) was appliedto the plumules of 6-day-old Chenopodium rubrum plants. Effectson growth, anatomical structure and organogenesis in the apicalmeristem were followed. Floral differentiation as affected bykinetin was also investigated in plants induced to flower byshort-day treatment. Kinetin increased mitotic activity in the apical meristems inboth induced and non-induced plants. The effect was most pronouncedin the peripheral and subcentral zone. An increase in nucleolussize and a higher degree of pyroninophilia in the peripheralzone was also observed, indicating a localized promotion ofRNA synthesis. A higher rate of leaf initiation and a stimulationof leaf and stem growth was subse quentiy recorded. The growthof axillary meristems and of bud primordia was promoted onlyat the lower concentration of kinetin (1•^10–4 M),in both photoperiodically-induced and non-induced plants. However,the pattern of lateral bud growth differed from that found innormal floral differentiation. In kinetintreated plants, thebud primordia are isolated from the summit of the shoot apexby a succession of rapidly growing leaves. The enhancement ofleaf growth leads to correlative inhibition of axillary budpriniordia and results, finally, in a suppression of floraldifferentiation. The inhibitory effect of kinetin on floweringwas compared with that of auxin. Inhibition of flowering occurredin both cases but is achieved in two different ways.     

The Negative Response of Photoperiodic Floral Induction in Chenopodium rubrum L. to Preceding Growth

In Chenopodium rubrum there exists a correlation between theage of the seedlings and the effectiveness of photoperiodicinduction. The younger the plants the more effective was photoperiodictreatment. In three-day-old seedlings one short day was sufficientto promote incomplete flowering, while two short days broughtabout 100 per cent flowering. With six-, eight-, and ten-day-oldplants exposed to two or three short days quantitative differenceswere observed in the earliness of flowering and the percentageof flowering plants. The effects of continuous light and ofshort days with a light break preceding the inductive treatmentwere compared. The results obtained indicate that the inhibitoryeffect of plant age cannot be attributed solely to the appearanceof inhibitors under continuous light but changes of growth patternin plants of different age should also be taken into consideration. The inhibition of RNA synthesis in shoot apices brought aboutby 6-azauridine resulted also in a flowering stimulation, providedthat the inhibitor was applied one or two days prior to inductionand the inductive process itself remained undisturbed. Thisstimulation was accompanied by inhibition of vegetative growthand by a decrease of RNA concentration in the cytoplasm as estimatedcytophotometrically. The competition between growth of vegetative organs and floraldifferentiation affects the response to inductive treatment.The suppression of growth can result in enhancement of flowering.     

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 Role of Hypocotyl and Roots in Photoperiodic Floral Induction of Chenopodium rubrum

Abstract: Hypocotyls and roots of Chenopodium rubrum were tested as possible receptors of photoperiodic signals inducing flowering. The hypocotyl was found to be responsive to such a signal. Its role as the locus of synthesis andjor the transport sys tem of a florigenic stimulus is discussed. The roots respond to light/dark conditions solely by changing their growth rate but they do not seem to be involved in induction of flowering.     

Floral and growth responses in Chenopodium rubrum L. to an extract from flowering Nicotiana tabacum L.

Flowering of Chenopodium rubrum seedling plants was obtained in continuous light after application of fractions of a partially purified extract from leaves of flowering Maryland Mammoth tobacco (Nicotiana tabacum). The stage of flowal differentiation was dependent on the age of the Chenopodium plants used for the bioassay. Apices of plants treated with the extract at the age of four or seven days showed an advanced branching of the meristem or the beginning of formation of a terminal flower; treatment with the extract of plants 12 d old resulted in rapid formation of flower buds in all assay plants. Non-treated control plants kept in continuous light remained fully vegetative. The effects of the extract on flowering were associated with pronounced growth effects. Floral differentiation was preceeded by elongation of the shoot apex. Extension of all axial organs occurred, while growth of leaves, including leaf primordia, was inhibited. The pattern of growth after application of the flower-inducing substance(s) did not resemble the effects of the known phytohormones, but showed some similarities to growth changes resulting from photoperiodic induction of flowering.     

Effects of Indol-3yl Acetic Acid on the Citrate-Condensing Reaction by Preparations of Root and Shoot Tissue

Preparations of citrate condensing enzyme (citrate oxaloacetate-lyase(CoA-acetylating) E. C. 4. 1. 3. 7) from root and shoot tissueof 5-day-old bean seedlings (Phaseolus vulgaris L., var. Burpee'sStringless Greenpod) had different activities, expressed asreaction rate per unit of fresh tissue. Activity per mg proteinwas increased when protein concentrations of the preparationswere reduced by dilution. Addition of indol-3yl acetic acid(IAA) enhanced activity of both root and shoot preparations.The effect was optimal at a concentration of 1.25x10^-4 M andthe enzyme was inhibited at 1.25x10^-3 M. Enhanement was greaterin root than in shoot preparations and in mixtures of equalamounts of each prepartion activity was intermediate betweenthose of the separte enzymes in absence of IAA but in its presenceapproached that of the shoot preparation. Apparent citrate synthesis in vivi was increased in shoots by application of IAA but therewas no such effect in roots.     

The Pattern of Reproductive Development in Chenopodium rubrum L.

Individual plants of Chenopodium rubrum were given differentnumbers of inductive cycles in a 12 h photoperiod and the patternof reproductive development was analysed after 40 d of growth.At least 2 inductive cycles are required to form any determinatereproductive organs and at least 12 cycles are required fornormal reproductive development. Individuals given a singleinductive cycle display a loss of apical dominance at thosenodes formed immediately after the treatment without the subsequentformation of any floral structures. Plants given between 2 and12 mductive cycles display both determinate reproductive organsand indeter minate vegetative shoots. The pattern of reproductivedevelopment on such plants depends upon the number of cyclesrelative to the developmental age of newly initiated primordia.It is suggested that the early events of floral induction mayinvolve a radical decrease in the ratio of auxin to cytokinin.     

Production of betalains by suspension cultures of Chenopodium rubrum L.

Red-violet cell suspension cultures of Chenopodium rubrum were found to accumulate the betacyanins amaranthin, celosianin and betanin and the betaxanthins vulgaxanthin I and vulgaxanthin II. Under a 16-h daylight regime the cells accumulated 0.3–0.4% betacyanins on a dry mass basis after 2–3 weeks of cultivation on the growth medium. Experiments to define a production medium for betacyanins failed with this habituated line. The accumulation could however be increased up to 1% or 100 mg betacyanins/1 by feeding tyrosine and by adaptation of the inoculum size to the nutrient concentration.     

Photoperiod and the Determination of Potential Seed Number in Chenopodium rubrum L.

Individuals from two latitudinal populations of Chenopodiumrubrum, a short-day annual, were induced in two inductive photoperiods,15 h and 12 h, to examine the dynamics of reproductive developmentthat determine the potential number of seeds produced. The northernpopulation (50° N) is induced in both photoperiods, whilethe southern population (34° N) is induced only in the 12h photoperiod. Individuals were given either 2, 6, 10 or continuousinductive cycles and dissected at intervals after the startof inductive treatments to determine the rates of initiationand differentiation of primordia on the main axis and selectedaxillary buds. Initial reproductive data indicated that the duration of reproductivedevelopment among individuals of the northern population, whengrown in the longer photoperiod, was 25 per cent greater, butthe number of seeds was increased by a factor of 46. Likewisethe duration of reproductive development among individuals ofthe southern population, when grown in the same photoperiodas the northern population, was 50 per cent longer and the numberof seeds was increased by a factor of 66. Dissection of reproductively-developing individuals revealedthat induction leads to a stimulation in the rate of initiationof primordia followed by a complete inhibition coincident withthe differentiation of terminal floral structures. The timingof this stimulation-inhibition process on each axillary buddepends upon its age relative to the timing of induction. Thuscertain primordia on individuals prematurely removed from inductivetreatments escape floral differentiation and remain vegetative.The total number of floral primordia (potential number of seeds)is determined early in reproductive development by (1) the numberof axillary buds at the start of induction, (2) the stimulatedrate of initiation of primordia after induction, and (3) therate of differentiation of induced primordia. Among individuals of the northern population, the longer inductivephotoperiod leads to a greater stimulation in the rate of primordialinitiation and a decrease in the rate of floral differentiation,which together lead to the production of more primordia. Likewiseamong individuals of the southern population in the shorterphotoperiod, the rate of organ initiation is similar to thatof the northern population in the same photoperiod, but therate of floral differentiation is lower, leading to the initiationof many more primordia. The effects of photoperiod on seed number are discussed in termsof physiological and ecological criteria of optimality. Sincenatural induction occurs in the longest, physiologically-'sub-optimarphotoperiods possible, and this leads to the greatest productionof seeds, it is suggested that the critical photoperiod is amore meaningful focus of interpretation than the physiologically‘optimal’ photoperiod. Of the factors influencing potential seed number, the most significantdifference between the two latitudinal populations is the responseof the rate of floral differentiation to the photoperiod ofinduction. Thus potential seed number in natural populationsis intimately related to the prevailing photoperiods throughthe rates of developmental events. Selection for changes inor maintenance of a particular reproductive ecology must bemediated through developmental responses. Limitations on the potential growth rate of plants are discussedin terms of the ratio of meristematic cells to the total cellpopulation in the plant. Thus the number of growing axillarybuds greatly contributes to the potential growth rate, and thedegree of correlative inhibition is interpreted as a cost ofselection for vertical growth among terrestrial plants competingfor light. By means of a simple model the cost of correlativeinhibition is also discussed in terms of potential seed number.Reproduction is seen as a release from the developmental constraintsrequired by plant form and a stimulation of growth that leadsto a very high production of potential seeds.     

Some Effects of Indol-3-yl Acetic Acid on Lateral Root Development in Attached and Excised Roots of Pisum sativum L.

The effect of continuous exposure to indol-3-yl acetic acid(IAA) on primordium initiation and their subsequent emergenceas lateral roots was determined in excised and attached rootsof Pisum sativum. IAA was found to stimulate the number of primordiainitiated per centimetre of attached or excised primary. Similarly,lateral emergence in terms of the number produced per centimetreof primary was promoted in the presence of IAA. This stimulationof lateral emergence even took place in excised roots whichwere 1 cm in length at the onset of culture and which neverproduced secondary roots over a 6-d culture period when grownin the absence of auxin. These effects of IAA on lateral rootdevelopment have been considered in relation to the concurrentchanges which take place in proliferative activity in the apicalmeristem of the primary root during exposure to auxin. Pisum sativum, garden pea, anlage, primordium, emerged lateral, cell proliferation, indol-3-yl acetic acid     

风信子花被外植体年龄对花器官分化的影响

离体培养风信子(Hyacinthus orientalis L．)不同年龄的花被外植体诱导花器官直接再生的实验表明;1．在MS附加6-BA 2 mg／L,2,4-D 0.1 mg／L的培养基上,年龄V的外植体大量衰老,基本丧失器官再生能力,处于年龄段Ⅱ～Ⅳ的外植体可发生玻璃化反应。2．玻璃化反应的外植体转移至MS附加6-BA 0.2 mg／L、NAA 0.005 mg／L的培养基上继续培养30 d后可再生正常的花被片,表明降低培养基中外源激素浓度能够阻止玻璃化反应继续发生。3．在MS附加6-BA 2 mg／L．2,4-D 0.1 mg／L的培养基上,外植体形态学下部可再生雌蕊状早期结构。平均每块外植体分化雌蕊状早期结构数以年龄Ⅲ的外植体最多。     

Electrical membrane potential and resistance in photoautotrophic suspension cells of Chenopodium rubrum L.

On photoautotrophically grown, suspension-cultured cells of Chenopodium rubrum L. the electrical potential difference V _mand the electrical resistance across plasmalemma and tonoplast have been measured using one or two intracellular micro-electrodes. In a mineral test-medium of 5.8 mM ionic strength V _mvalues between 100 and 250 mV, 40% thereof between 170 and 200 mV, and a mean value (±S.E.M.) of 180.6±3.4 mV have been recorded. The average membrane input resistance R _mwas 269±36 M, corresponding to an average membrane resistivity r _mof 3.0 m². V _mand r _mare sensitive to light, temperature, and addition of cyanide, suggesting the presence of an electrogenic hyperpolarizing ion pump, and are ascribed essentially to the plasmalemma. A hexose-specific saturable electrogenic membrane channel is identified through a decrease of V _mand r _mupon addition of hexoses. The hexoseconcentration-dependent depolarization V _msaturates at 92 mV and returns half-saturating concentrations (apparent k _mvalues) of 0.16 mM galactose, 0.28 mM glucose, and 0.48 mM fructose. The magnitude of V _mand r _mwell agrees with pertinent data from mesophyll cells in situ (where only V _mdata are available) and from photoautotrophic lower plant cells. However, V _mis markedly higher than reported for heterotrophically grown suspension cells of different higher plants (with which r _mdata have not been reported so far). It is concluded from the present study and a companion paper on water transport (Büchner et al., Planta, in press) that photoautotrophically grown Chenopodium suspension cells closely resemble mesophyll cells as to cell membrane transport properties.Abbreviations V _m membrane potential(mV) - R _o input resistance () - R _m membrane input resistance () - r _m specific resistance (resistivity) of the membrane (m²)     

Rhythms as photoperiodic timers in the control of flowring in Chenopodium rubrum L.

Summary In C. rubrum, the amount of flowering that is induced by a single dark period interrupting continuous light depends upon the duration of darkness. A rhythmic oscillation in sensitivity to the time that light terminates darkness regulates the level of flowering. The period length of this oscillation is close to 30 hours, peaks of the rhythm occurring at about 13, 43 and 73 h of darkness.Phasing of the rhythm by 6-, 12- and 18-h photoperiods was studied by exposing plants to a given photoperiod at different phases of the free-running oscillation in darkness. The shift in phase of the rhythm was then determined by varying the length of the dark period following the photoperiod; this dark period was terminated by continuous light.With a 6-h photoperiod the timing of both the light-on and light-off signals is shown to control rhythm phasing. However, when the photoperiod is increased to 12 or 18 h, only the light-off signal determines phasing of the rhythm. In prolonged periods of irradiation-12 to 62 h light—a durational response to light overrides any interaction between the timing of the light period and the position of the oscillation at which light is administered. Such prolonged periods of irradiation apparently suspend or otherwise interact with the rhythm so that, in a following dark period, it is reinitiated at a fixed phase relative to the time of the light-off signal to give a peak of the rhythm 13 h after the dusk signal.In daily photoperiodic cycles rhythm phasing by a 6-h photocycle was also estimated by progressively increasing the number of cycles given prior to a single dark period of varied duration.In confirmation of Bünning's (1936) hypothesis, calculated and observed phasing of the rhythm controlling flowering in c. rubrum accounts for the photoperiodic response of this species. Evidence is also discussed which indicates that the timing of disappearance of phytochrome P_fr may limit flowering over the early hours of darkness.     

Turgor pressure and water transport properties of suspension-cultured cells of Chenopodium rubrum L.

The turgor pressure and water relation parameters were determined in single photoautotrophically grown suspension cells and in individual cells of intact leaves of Chenopodium rubrum using the miniaturized pressure probe. The stationary turgor pressure in suspension-cultured cells was in the range of betwen 3 and 5 bar. From the turgor pressure relaxation process, induced either hydrostatically (by means of the pressure probe) or osmotically, the halftime of water exchange was estimated to be 20±10 s. No polarity was observed for both ex- and endosmotic water flow. The volumetric elastic modulus, , determined from measurements of turgor pressure changes, and the corresponding changes in the fractional cell volume was determined to be in the range of between 20 and 50 bar. increases with increasing turgor pressure as observed for other higher plant and algal cells. The hydraulic conductivity, Lp, is calculated to be about 0,5–2·10^–6 cm s^–1 bar^–1. Similar results were obtained for individual leaf cells of Ch. rubrum. Suspension cells immobilized in a cross-linked matrix of alginate (6 to 8% w/w) revealed the same values for the half-time of water exchange and for the hydraulic conductivity, Lp, provided that the turgor pressure relaxation process was generated hydrostatically by means of the pressure probe. Thus, it can be concluded that the unstirred layer from the immobilized matrix has no effect on the calculation of Lp from the turgor pressure relaxation process, using the water transport equation derived for a single cell surrounded by a large external volume. By analogy, this also holds true for Lp-values derived from turgor pressure changes generated by the pressure probe in a single cell within the leaf tissue. The fair similarity between the Lp-values measured in mesophyll cells in situ and mesophyll-like suspension cells suggests that the water transport relations of a cell within a leaf are not fundamentally different from those measured in a single cell.     

风信子花被外植体年龄对花器官分化的影响

离体培养风信子（ＨｙａｃｉｎｔｈｕｓｏｒｉｅｎｔａｌｉｓＬ．）不同年龄的花被外植体诱导花器官直接再生的实验表明：１．在ＭＳ附加６ＢＡ２ｍｇ／Ｌ、２,４Ｄ０．１ｍｇ／Ｌ的培养基上,年龄Ｖ的外植体大量衰老,基本丧失器官再生能力,处于年龄段ＩＩ～ＩＶ的外植体可发生玻璃化反应。２．玻璃化反应的外植体转移至ＭＳ附加６ＢＡ０．２ｍｇ／Ｌ、ＮＡＡ０．００５ｍｇ／Ｌ的培养基上继续培养３０ｄ后可再生正常的花被片,表明降低培养基中外源激素浓度能够阻止玻璃化反应继续发生。３．在ＭＳ附加６ＢＡ２ｍｇ／Ｌ、２,４Ｄ０．１ｍｇ／Ｌ的培养基上,外植体形态学下部可再生雌蕊状早期结构。平均每块外植体分化雌蕊状早期结构数以年龄Ⅲ的外植体最多     

Ultrastructure of Chenopodium rubrum L. apices during the effect of fusicoccin and photoperiodic induction

Plant transition from vegetative to reproductive development is associated with ultrastructural changes in stem apices. Those seen in Chenopodium rubrum L. under the influence of fusicoccin in many ways resemble those induced by a short-day treatment favourable to flowering. This suggests that fusicoccin can play a definite (physiological) role in plant development.     

Auxin Physiology of Decapitated Stems of Phaseolus vulgaris L. Treated with Indol-3yl-acetic Acid

Physiological amounts of indol-3yl-acetic acid (IAA) were accumulatedby decapitated stems of Phaseolus vulgaris L. seedlings fromlanolin pastes, containing 0.1 per cent IAA, applied to thecut surfaces of the stumps. Both the levels and gradients ofextractable and diffusable IAA detected in the treated stumpscompared favourably with those reported for the whole plants.A considerable portion of IAA that entered the tissue was metabolizedto a compound that had chromatographic properties similar toindol-3yl-acetylaspartic acid. Two other metabolities were tentativelyidentified as indol-3yl-acetylaspartic acid indol-3yl-acetylglucose.The accumulated IAA appears to be transported as indol-3yl-aceticacid at an apparent velocity of 28 mm/h down the decapitatedinternodes.     

Charybdotoxin blocks cation-channels in the vacuolar membrane of suspension cells of Chenopodium rubrum L.

Using the patch-clamp technique, we studied the action of charybdotoxin which blocks Ca(2+)-activated large-conductance K+ channels in animal tissue on the slow-activating (SV), Ca(2+)-activated cation channel in the vacuolar membrane of suspension-cells of Chenopodium rubrum L. The toxin reversibly reduced the vacuolar current with EC50 approximately 20 nM suggesting structural similarities between ion channels in animal and plant membranes.     

Diurnal Modulation of Arginine Decarboxylase Activity of Chenopodium rubrum L. by Temperature and Light

Arginine decarboxylase (ADC), one of the key enzymes of polyaminemetabolism in plants, was investigated in Chenopodium rubrumL. seedlings under constant and alternating temperature andlighting conditions. With seedlings grown at constant temperature,ADC activity of the whole seedling increased rapidly betweenthe second and the third day after sowing. This effect was alwayshigher under continuous light than in continuous darkness. Fromthe third to the seventh day after sowing, there was a markeddecrease in ADC activity of the whole seedling almost down tothe level of the second day. Under "normal" lighting and temperatureconditions (32.5?C/10?C, light/dark) there was a marked increasein ADC activity when plants were transferred to 10?C and a rapiddecrease when they were transferred to 32.5?C. The same timecourse was observed when an "inverse" light-temperature program(32.5?C/10?C; dark/light) was applied. This means that the timecourse of ADC activity in the seedlings is slightly light-dependent,but strongly temperature-dependent. The data are discussed withrespect to the chronopathological effects of the "inverse" light-temperatureprogram. (Received March 5, 1985; Accepted October 2, 1985)