Rhythm in potassium uptake by a duckweed, Lemna gibba G3

The potassium uptake activity of the "flow-medium culture" ofa long-day duckweed, Lemna gibba G3, followed a circadian rhythmwhich persisted for more than 5 days under continuous light.The period of the rhythm was about 25 hr under 3000 lux at 26?Cand was slightly over-compensated against temperature, Q₁₀ beinga little less than 1.0. The amplitude of the rhythm was dependenton light intensity, and there was no potassium uptake in thedark. Magnesium uptake was affected by the potassium movementand showed circadian rhythmicity with a small amplitude underconditions where the potassium uptake was already saturated.Calcium uptake did not show any obvious rhythm. In Contrastto L. gibba, a short-day duckweed L. perpusilla 6746 displayedcircadian rhythm of potassium uptake only in the dark and notin the light. This rhythm did not persist beyond the secondcycle. (Received June 13, 1978; )     

Flowering of the long-day plant, Lemna gibba, under short-day schedules composed of red and far-red light

Flowering in Lemna gibba, a long-day duckweed, can be inducedunder a short-day condition when the photoperiodic regimes areR₇FR₃ (7 hr red followed by 3 hr far-red), R₅FR₅ and R₃FR₇.This indicates the necessity of a proper balance between redand far-red effects for flowering. The flowering induced bythese regimes is inhibited by a brief exposure to red givenat the start of darkness and this inhibition is reversed bysubsequent exposure to far-red. Thus, the red/far-red reversibleeffect is found only at the beginning of darkness for floweringof L. gibba. However, flowering of L. gibba is promoted by a red light breakgiven near the middle of a 14 hr dark period. The promotiveeffect is not reversed by subsequent exposure to far-red, i.e.,the effect of the red break converts from inhibition to promotionas when given later in the dark period, which suggests the involvementof a timing mechanism. (Received July 21, 1973; )     

Characterization of Senescence in Lemna gibba G3: A Determinate Growth System

Frond senescence in Lemna gibba G3 was characterized, and itscontrol by light, ABA and kinetin investigated. The plant exhibitsa determinate growth pattern with a frond producing a set numberof daughter fronds before undergoing senescence and death regardlessof whether or not it flowers. When a frond was cut in half,the distal half (half frond) which lacks any meristem underwentrapid senescence as compared with intact fronds. In both intactand half fronds, the onset of senescence was accelerated byABA and retarded by kinetin. Continuous white light acceleratedsenescence in both intact and half fronds over the dark controls.Under different photoperiodic light regime, the pace of daughterfrond production is accelerated in proportion to the lengthof light period. In half fronds, however, very short photoperiodiclight treatments (e.g. 1L: 23D or 3L: 21D) rather delayed senescenceover the dark controls. Two separate light control systems operatingin opposite directions in Lemana senescence appear to exist. ¹Present address: Department of Biology, Yonsei University,Seoul 120-749, Korea ²Present address: U.S. Department of Agriculture, Aero SpaceBuilding, Rm. 323, 901 D Street, S.W., Washington, D.C. 20251-2200, U.S.A. (Received July 13, 1989; Accepted May 8, 1990)     

Flowering responses of Lemna perpusilla and L. gibba in relation to nitrate concentration in the culture medium

Flowering responses of Lemna perpusilla strain 6746, a short-dayplant, and L. gibba strain G3, a long-day plant, to nitrateconcentration in Hoagland's type medium with or without EDTA,were compared. Maximum flowering of L. perpusilla under SD occurredat higher nitrate concentrations than did colony proliferation.Even under CL, L. perpusilla grown at sub-optimal nitrate concentrationsfor colony proliferation, flowered irrespective of the presenceof EDTA which reduces flowering. Unlike L. perpusilla, L. gibba failed to flower under SD atany nitrate concentration whether or not EDTA was added. UnderCL, however, L. gibba flowered at almost any nitrate concentrationwith or without EDTA. Double optima for nitrate concentrationwas exhibited in the presence of EDTA; optimal concentrationfor colony proliferation came between the two optima for flowering. We concluded that the nitrogen level of the medium is importantin regulating flowering of duckweeds, and that the effect ofEDTA, if any, may primarily be on colony proliferation and onlysecondarily or antagonistically on flowering. ¹ Present address: Institute for Agricultural Research, TohokuUniversity, Sendai 980, Japan. (Received September 25, 1971; )     

DNA synthesis as related to the reappearance of "light interruption rhythm" in a long-day duckweed, Lemna gibba G3

DNA synthesis in the light perturbation period and its relationto the reappearance, due to light perturbation, of once faded-out"light interruption rhythm" in a long-day duckweed, Lemna gibbaG 3, were studied. After long continuous darkness, the duckweedincorporated ³H-thymidine into both nuclear and satellite DNA_sunder a light condition, but into satellite DNA alone undera dark condition. The number of dividing cells in frond epidermisincreased in proportion to the length of the light perturbationperiod. This increase was inhibited by 5-fluorodeoxyuridine.From these and previous results we conclude that nuclear DNAnewly synthesized in the light is intimately related with thereappearance of the rhythm. (Received June 15, 1970; )     

Maintenance of high Pfr-level in the dark period in relation to flowering in Lemna gibba G3

The relative Pfr-level in a long-day duckweed, Lemna gibba G3,was estimated by the null response method. The null % R value(% R in a R/FR-mixture that provides a null flowering response.This value was assumed to indicate the endogenous Pfr-levelof the duckweed.) remained high during the initial hours ofthe 15 hr nyctoperiod then decreased rapidly, if a 12 or 33hr photoperiod preceded the nyctoperiod. The null % R valuedropped immediately after the start of the 15 hr nyctoperiodsubsequent to a 1 or 24 hr photoperiod. Thus, the duration ofthe maintenance of a high Pfr-level changed rhythmically dependingon the length of the preceding photoperiod. Nyctoperiods ofup to 9 hr following a 12 hr photoperiod hardly affected flowering,but nyctoperiods given after a 24 hr photoperiod suppressedflowering in proportion to the length of the period. The Pfr-levelin the nyctoperiod, therefore, seems to be important for flowering,and phytochrome change, as a function of the length of photoperiod,may serve as a photoperiodic timer. Although floral responseto interruption with R or FR changed with the application period,the difference in response between R-treated and FR-treatedplants was relatively constant during a 15 hr nyctoperiod combinedwith a photoperiod of any length other than 1 hr. Apparently,the floral response to the R or FR pulse was regulated by ashift in the Pfr-level caused by the light pulse. (Received April 2, 1979; )     

EFFECTS OF NUCLEIC ACID- AND PROTEIN-ANTIMETABOLITES ON FROND AND FLOWER PRODUCTION IN LEMNA GIBBA G3

Frond and flower production in a long-day duckweed, Lemna gibbaG3, grown under continuous illumination in the presence or absenceof varied concentrations of 5-fluorodeoxyuridine, 5-fluorouracill,2- thiouracil, 8-azaguanine or ethionine and/or correspondingmetabolite, i.e., thymidine, orotic acid, uracil, guanine ormethionine, have been investigated. From the results obtained,the presumptive flows of vegetative and reproductive informationfrom gene DNA to protein have been associated with frond andflower initiation in the duckweed meristem, respectively. (Received September 3, 1964; )     

Evidence against involvement of circadian floral rhythm in the critical daylength measurement in Lemna gibba G3

Using the min-LD method, light requirements of the L1- and L2-phasesof L. gibba G3 were found to be satisfied by only 5 min illuminationgiven respectively from CT 0:00 to 0:05 and from CT 11:55 to12:00. This rigorous time sense was displayed without any alterationeven in the presence of iron reagents, e.g., 10^–5 M o-phenanthroline,10^–5M,'-dipyridyl and 10–6 M kinetin, which completely eliminatedcircadian rhythmicity in reproductive (flower production) aswell as vegetative (frond production) response to a light pulsescanning a continuous dark period. Circadian rhythms of metabolicactivities, e.g., active K⁺ ion uptake and respiratory CO₂ output,were not changed at all by the iron reagents. These and relevantresults suggested that in this long-day duckweed, the circadianoscillator, probably located in the meristem and sensitive toiron deficiency, only modulates the frond and flower productionin the meristem and is not related to the critical daylengthmeasurement. (Received December 18, 1978; )     

EXPERIMENTAL CONTROL OF FLOWERING IN LEMNA. III. A RELATIONSHIP BETWEEN MEDIUM COMPOSITION AND THE OPPOSITE PHOTOPERIODIC RESPONSES OF L. PERPUSILLA 6746 AND L. GIBBA G3

Hillman , William S. (Yale U., New Haven, Conn.) Experimental control of flowering in Lemna. III. A relationship between medium composition and the opposite photoperiodic responses of L. perpusilla 6746 and L. gibba G3. Amer. Jour. Bot. 48(5): 413–419. Illus. 1961.—In a simple Hoagland-type medium, L. perpusilla 6746 flowers, irrespective of daylength; L. gibba G3 does not flower under any daylength, as long as the medium is changed frequently. Ethylenediaminetetraacetic acid (EDTA) prevents the flowering of L. perpusilla in long days but not in short, and brings about the flowering of L. gibba in long days but not in short. The same results are obtained with medium “aged” by the growth in it of L. gibba for several weeks (in any photoperiod) as well as with tartaric acid. The effectiveness of both EDTA and “aged” medium is greater at pH levels near 5 than at 4 or below, probably reflecting action through metal-chelation. These results are most easily interpreted as effects on photoperiodic sensitivity, and suggest a central role of metals in photoperiodism.     

Disappearance of rhythmicity in growth response to dark- and light-breaks in Lemna gibba G3 due to iron deficiency

Inhibition of flower initiation in light culture of a long-dayduckweed, Lemna gibba G3 by an inserted period of brief darknesschanges its magnitude with the application time of the dark-break.‘Response vs. time of the dark-break’ curve consistsof superimposed thermo-insensitive oscillatory and thermo-sensitivehourglass components. Oscillation is diurnal and damps in afew days. The situation is very similar to what has previouslybeen revealed concerning the non-photosynthetic light-requirementof the same strain of duckweed for frond multiplication. Increasingphotophily for flower production is likely accompanied by decreasingphotophily for frond production, and vice versa. The presenceof iron chelators such as o-phenanthroline and ,'-dipyridylor reduced iron concentration in culture medium abolishes theoscillatory change, without modifying the hourglass change,in either vegetative or reproductive photophily. Ferrous, butnot ferric, ions likely mediate between the basic clock andthe photophily. Critical daylength for flower induction is notaffected by exogenous chelators. (Received November 17, 1970; )     

Effects of some metabolic inhibitors on flowering of Lemna gibba G3, a long-day duckweed

Flowering of Lemna gibba G₃, a long-day duckweed, was inhibitedby adding CuSO₄, AgNO₃, HgCl₂, Na₂WO₄ or iodoacetamide to themedium at the concentrations inducing long-day flowering inLemna paucicostata 6746, a short-day duckweed. This suggeststhat these metabolic inhibitors affected the photoperiodic sensitivityrather than directly affecting flower initiation. Ferricyanidepromoted flowering in both of these short-day and long-day duckweeds. (Received July 7, 1977; )     

EFFECTS OF EXOGENOUS AMINO ACIDS ON THE FLOWER AND FROND PRODUCTION IN DUCKWEED, LEMNA GIBBA G3

1. Twenty usual amino acids examined were shown to be dividedinto two groups with respect to their actions on the flowerformation (A) and frond multiplication (B) in a long-day duckweed,L. gibba G3. Amino acids of the first group (e.g., arginine)inhibited A without preventing B, and those of the second group(e.g., lysine) inhibited both A and B. The inhibition of flowerformation was always the greatest when amino acid was appliedat the induction period. 2. The floral inhibition by arginine applied at the inductionperiod was partially or wholly reversed by the simultaneousaddition of other amino acid (especially lysine) or by one additionallong day. The inhibitions by lysine, however, were not reversedby arginine. 3. It was discussed that the terminal step(s) of photoperiodicinduction process might depend largely on the relative in vivoconcentrations of amino acids. (Received January 28, 1964; )     

EXPERIMENTAL CONTROL OF FLOWERING IN LEMNA. IV. INHIBITION OF PHOTOPERIODIC SENSITIVITY BY COPPER

Hillman , William S. (Brookhaven Nat'l. Lab., Upton, N. Y.) Experimental control of flowering in Lemna. IV. Inhibition of photoperiodic sensitivity by copper. Amer. Jour. Bot. 49(8): 892–897. Illus. 1962.—Lemna perpusilla 6746 and L. gibba G3 are both photoperiodi c in a purified Hoaglandtype medium; purification thus imitates the effects of high levels of chelating agents previously reported. On the addition of 0.5–10.0μM/liter cupric ion (optimum about 2.0μM/liter) L. perpusilla, instead of responding as a short-day plant, flowers in both long and short days, while L. gibba, formerly a long-day plant, loses its ability to flower. A similar, but less distinct, effect of Hg can be attributed to a “copper-sparing” action. No other ion tested, including Cd, Co, Cr, Mn, Ni, Pb or Zn, had a similar effect. Certain macronutrient ions, probably Ca and phosphate, modify but do not obscure the effects of copper. The action of copper can be interpreted as an inhibition of photoperiodic sensitivity, since it makes both plants respond as if under short days regardless of the actual conditions. Some possible mechanisms, including disturbance of the photoperiodic pigment system, are discussed.     

Seed and Embryo Germination in Syringa vulgaris and S. reflexa as Affected by Temperature during Seed Development

A nitrogen source was needed for the flowering of Lemna gibba L., a long-day plant, and L. perpusilla Torr., a shortday plant. The level of endogenous amino acids analyzed by an Amino Acid Analyzer, rose during the first few inductive cycles, but was reduced during later stages of the flowering process. Serine and threonine levels increased during the light period and decreased during the dark period in L. perpusilla. Exogenous serine and threonine added to the culture medium at 10^?6M increased the rate of flowering by more than 35% over the controls. Cysteine inhibited flowering, while other amino acids had little or no promotive effect on flowering. Serine and threonine increased flowering rate in L. perpusilla only when added during a dark period of the inductive cycle. The addition of amino acids during a light period not followed by a dark period had no effect on flowering.     

Endogenous light-on rhythm in respiration of a long-day duckweed, Lemna gibba G3 III. Relationship to frond production

Relationship between the C>2-uptake rhythm and frond productionin a long-day duckweed, Lemna gibba G3, was investigated. The rate of frond production and the amplitude of the rhythmwere dependent on light intensity. Photosynthetic inhibitors,CMU and DCMU, at concentrations effective in stopping frondproduction, abolished the O₂-uptake rhythm after a lag of 1day. In the presence of inhibitors of protein and RNA syntheses,ETH, CH and TU, at concentrations which brought about completeinhibition of frond production, the O₂-uptake rhythm disappeared.FUdR, an inhibitor of DNA synthesis, did not eliminate the rhythmalthough it suppressed frond production. This indicates a ratherindirect correlation between the rhythm and the rate of frondproduction which, in turn, is probably related to photosynthesis.The rhythm may be more directly correlated with the cell expansion. (Received July 27, 1971; )     

Influence of nutrients on the development of gibbosity in fronds of the duckweed Lemna gibba L.

The duckweeds Lemna gibba L. and Lemna minor L. only grew wellin undisturbed culture under axenic conditions in low lightintensity when provided with a suitable energy source such asglucose. In media containing N0₃-N gibbosity (a convex ventralsurface) was induced in the presence of the chelating agentethylene-diamine-di-o-hydroxyphenylacetic acid (EDDHA). In nutrientsolutions containing NO₃-N as the only N source, but withoutEDDHA, L. gibba occasionally exhibited gibbosity in culturesolutions of 40 cm³ volumes. More fronds were induced to exhibitgibbosity when the volume of the culture medium was increasedfrom 40 cm³ to 200 cm³. Gibbosity was never induced in L. minor,neither was it induced in L. gibba in media containing NH₄-N,even in the presence of NO₃-N. There was no direct correlationbetween the occurrence of gibbosity and frond growth rate, butgibbosity occurred only when there was good frond growth. In the absence of a sugar, frond growth was enhanced by bubblingair through the culture solution in the light. Increasing theCO₂ concentration in the air up to 1% enhanced growth and inducedgibbosity. Carbon dioxide did not induce gibbosity in mediacontaining NH₄-N. Key words: Ammonium-N, carbon dioxide, gibbosity, Lemna, nitrate-N     

Effect of interruption of the nyctoperiod with an R/FR-mixture of various ratios of red and far-red light on flowering in Lemna gibba G3

A brief R pulse inserted in the 15-hr nyctoperiod of the 9L15D regime almost always promoted flower formation of a long-dayduckweed, Lemna gibba G3. This R effect was partially reversedby subsequent FR, which suggests that phytochrome is involvedin the floral processes occurring in the nyctoperiod. The null% R value (% of R in the R/FR-mixture that exerts no effecton flowering) was high during the initial 7.5 hr of the nyctoperiod,then rapidly decreased. The starting time of the rapid decreasein the null % R value was hardly affected by a change in temperaturein the nyctoperiod. A similarly high initial level of the null% R value followed by a rapid decrease was observed when thenyctoperiod was extended to 39 hr. At hour 15 of the 39-hr nyctoperiod,flower promotion by the R puke was not reversed by subsequentFR, although the spectral dependence of the light pulse effectdid not exclude the possible involvement of phytochrome. Atabout hour 21 of the 39-hr nyctoperiod, the null % R value beganto increase rapidly, and almost reached the initial high levelat hour 24 when R-FR reversibility was also restored. These results suggest that the Pfr-level remained high duringthe initial hours of the nyctoperiod, followed by a rapid decreaseirrespective of the temperature of the nyctoperiod. This rapiddecrease in the Pfr-level may play a role in the time measurementof the photoperiodic floral induction of L. gibba G3. (Received February 13, 1979; )     

Photoreversibility of flower initiation in Lemna perpusilla as affected by the light quality of the main light period

Reversible floral responses of Lemna perpusilla to red and far-redlights appeared only at the beginning of the inductive darkperiod when the 8 hr photoperiod consisted of white or red light.When blue or far-red light was given during the 8 hr photoperiod,the far-red given at the beginning of the dark period scarcelyinhibited flowering; red/far-red reversibility newly appearedat the middle of the dark period. This indicates that the photoregulationsystem in the flowering of L. perpusilla can be converted fromthe Pharbitis type to the Xanthium type by changing the lightquality of the main photoperiod from white or red to blue orto far-red, which is known to be effective for the so-calledhigh-energy photoreaction of photomorphogenesis. (Received July 2, 1975; )     

EFFECTS OF GROWTH SUBSTANCES ON FROND AND FLOWER PRODUCTION IN LEMNA GIBBA G3

Frond and flower production in a long-day duckweed, Lemna gibbaG3, growing under different photoperiodic conditions in presenceand absence of varied concentrations of applied IAA, KIN andGA was investigated. The predominant actions of IAA, KIN and GA were revealed tobe respectively the depression of flowering, the promotion offrond multiplication and the enhancement of flowering. The rateof increase in FL % as an index of the concentration of floralstimulus in the tissues was curtailed greatly by IAA, to a lesserextent by KIN and little by GA. GA at 10^–5 M apparentlyreduced the critical day length (12 hr) and the induction period(48 hr) by 2 and 4 hr, respectively. No vegetative growth waspromoted by KIN in the light. On the basis of these and relevant findings the sites of actionof the growth substances examined in the flowering process ofthe duckweed were suggested. (Received May 30, 1965; )     

The Comparative Biology of Closely Related Species Living in the Same Area: V. INTER- AND INTRASPECIFIC INTERFERENCE WITHIN CULTURES OF LEMNA spp. AND SALVINIA NATANS

Studies were made of the growth of populations of Lemna minor,L. polyrrhiza, L. gibba, and Salvinia natans under controlledlaboratory conditions. The intrinsic exponential growth-ratesof the clones were determined in un-crowded cultures, and thechanges in growth-rate of self-crowding cultures were measuredand interpreted in terms of an initial exponential growth-ratefollowed by a phase of arithmetic increase in weight and followedin turn by a phase in which the death of submerged and shadedfronds caused a decline from the arithmetic rate of growth.Mean frond weight declined in self-crowding cultures (exceptof L. gibba). Mixed cultures of two species were examined under self-crowdingconditions and changes in the proportions of the species werefollowed. Whereas the total weight of mixed cultures remainedvery constant between replicates, there was wide variation inthe proportions of components. The variation in the two componentswas most closely correlated (negatively) when the struggle forexistence was most evenly balanced. The mean frond weight ofthe losing component declined during the experiments. The order of decreasing vigour of species measured by variousparameters was as follows: Relative (intrinsic) growth-rate: L. minor > S. natans > L. gibba > L. polyrrhiza Arithmetic growth-rate when crowded: S. natans > L. polyrrhiza > L. gibba > L. minor Asymptotic yield per culture: L. polyrrhiza > L. minor > S. natans > L. gibba Success in mixed cultures: The success of a species in mixture could not be predicted fromthe parameters of growth in pure culture. Morphologic featuressuch as the gibbosity of L. gibba