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.     

Chemical control of flowering in the long-day plantLemna gibba G3

Lemna gibba G3 is an ideal system for studying the chemical control of flowering in a photoperiodic plant due to its small size and aquatic growth habit which allow substances to be taken up continuously and rapidly distributed throughout the plant. Each of the known plant growth regulators has been tested onL. gibba G3 and only the gibberellins appear to be important for flowering, although they are not the limiting factor for flowering on short days. Salicylic acid (SA) and ferricyanide will both induce flowering inL. gibba G3 with ferricyanide being most effective on short days where flowering is daylength limited and SA most effective where flowering is limited by factors other than daylength. The ferricyanide action is probably due to HCN and it may act during photoperception or photoinduction. SA is most effective when reversing the inhibition caused by various parameters including copper and agar, and its effect is always strongly daylength dependent. It is postulated that SA may interact with the flowering stimulus to promote flowering and thus that SA acts at some point following photoinduction and the formation of the flowering stimulus.     

Die Wirkung von Lithium und ADP auf die Phytochromsteuerung der Blütenbildung

Summary Lithium seems to diminish the action of phytochrome on the flower induction: under long-day conditions 10^-3 M LiCl inhibits flower production in the long-day plant Lemna gibba Gl. However, under the same conditions flowering in the short-day plant Lemna perpusilla 6746 is stimulated by 10^-3 M LiCl.ADP seems to enhance the action of phytochrome on flower induction: under long-day conditions 10^-4 M ADP promotes the flowering in Lemna gibba G1 (Kandeler, 1969a, b). However, it inhibits flowering in Lemna perpusilla 6746.It is assumed that Li⁺ acts as antagonist to K⁺ (see Eberius). Since K⁺ and ADP are also cofactors for the phytochrome regulation of membrane potential (Tanada, 1968b), it is assumed that the regulation of membrane properties is the general physiological primary reaction of phytochrome.     

TWO LIGHT REACTIONS IN THE PHOTOPERIODIC CONTROL OF FLOWERING OF LEMNA PERPUSILLA AND L. GIBBA

The effects of light quality on the photoperiodic control inthe flowering of a SD duckweed, Lemna perpusilla strain 6746,and a LD duckweed, L. gibba strain G3, were investigated withspecial reference to the interaction between R and B or FR lights. In the diurnal alternation of R or G light and dark periods,L. perpusilla responded as a SDP, but in that of B or FR lightit was almost daylength-indifferent. On the other hand, L. gibbaresponded as a LDP under B, R or FR light, although the criticallight length was altered by the light quality. In the diurnal alternation of R and B or FR light periods containingno dark period, L. perpusilla flowered with the shortening ofthe optimal and critical R light lengths, compared with theplant exposed to that of R light and dark period. The floweringresponse of L. gibba to the R light length showed double peaks,that is, the first peak at the R duration less than 9 hours,and the second at the R duration longer than 9 hours. The firstpeak corresponds to the optimal R light length in L. perpusilla. Under the CL with a mixture of R and B or FR lights, the floweringand frond production were influenced by the intensity ratioof two light given. In both plants, the optimal ratio of B toR or FR to R for the flowering was always greater than thatfor the frond production. It is suggested that the B or FR light interacts with the Rlight in the photoperiodic process in the plants and this interactionbetween the R and B or FR lights should be of importance forobtaining a better understanding of photoperiodism. (Received August 28, 1965; )     

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.     

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; )     

Absorption of Copper by Lemna as Influenced by Some Factors Which Nullify the Copper Effect on Flowering and Growth

The effect of copper on flowering and growth of Lemna paucicostata6746 and Lemna gibba G3 in a copper-containing medium is nullifiedby the addition of EDTA, ammonium ions or salicylic acid tothe medium or a decrease in its nitrate concentration. Thesefactors were examined for their effects on the absorption ofcopper by the plants. The addition of EDTA to the medium completelyinhibited the absorption of copper in both species, thus eliminatingthe copper effect. Ammonium ions also inhibited copper absorption,their effectiveness rising with their concentration. Loweringthe nitrate concentration in the medium nullified the coppereffect on flowering in L. paucicostata 6746, and the additionof salicylic acid to the medium also nullified the copper effectin L. gibba G3, both without affecting the absorption of copper. (Received June 7, 1982; Accepted August 27, 1982)     

EXPERIMENTAL CONTROL OF FLOWERING IN LEMNA. II. SOME EFFECTS OF MEDIUM COMPOSITION,CHELATING AGENTS AND HIGH TEMPERATURES ON FLOWERING IN L. PERPUSILLA 6746

Hillman , William S. (Yale U., New Haven, Conn.) Experimental control of flowering in Lemna. II. Some effects of medium composition, chelating agents and high temperatures on flowering in L. perpusilla 6746. Amer. Jour. Bot. 46(7): 489–495. Illus. 1959.—-L. perpusilla 6746 flowers as a short-day plant on Hutner's medium (containing ethylenediaminetetraacetic acid [EDTA]) at constant temperatures from 25 to 30°C., but eventually flowers also in old cultures under 16 or 24 hr. of light. This old-culture flowering is more pronounced in dilute medium. Flowering is rapid under both long and short days at constant temperatures from 25 to 28°C. in media not containing EDTA; the addition of 10^-5 M EDTA or of similar or higher concentrations of numerous other chelating agents suppresses flowering under long days but not under short (8 hr. light). This effect does not depend on promotion or inhibition of vegetative growth. At 29 to 30°C., a short-day requirement is manifested even in media permitting flowering under long days at the lower temperatures. Temperatures above 31°C. completely inhibit flowering under all conditions. Brief periods of high temperature given to plants under short-day conditions inhibit flowering when given during the dark period but not during the light period. The implications of these observations for the further study of flowering are discussed.     

Influence of timing and number of consecutive inductive photoperiodic cycles on the flowering of lemna

Requirements for flowering of the short day plant Lemna perpusilla Torr. strain 6746 can be studied by interposition of varying numbers of consecutive short days during 7 days of continuous light. A single inductive cycle can cause the formation of few flowers if it comes during the middle of a 7-day period of continuous light. Three inductive cycles cause 30% or more of the fronds to flower if the cycles are properly spaced in the 7-day period. The fact that timing of the inductive photoperiodic cycles is critical indicates the importance of development time and abortion of evoked floral primordia in the flowering response. These results are particularly useful in studies of processes occurring during induction.     

Inhibition of Flower Induction by Some Inhibitors of Protease in the Short-day Plant Lemna paucicostata 6746 and the Long-day Plant Lemna gibba G3

Four inhibitors of proteases, namely, bestatin, diisopropylfluorophosphate, elastatinal and p-toluenesulfonyl-L-lysinechloromethyl ketone hydrochloride, were examined for their effectson flowering of a short-day plant Lemna paucicostata 6746 anda long-day plant Lemna gibba G3. Each of the inhibitors greatlyinhibited the flowering of Lemna paucicostata 6746 that is normallyinduced by nitrogen deficiency. Bestatin or elastatinal givenonly during the first half of the culture period inhibited theflowering more clearly than when each was given during the latterhalf, suggesting that they inhibited the inductive process(es)involved in flowering rather than development of flower buds.Bestatin or elastatinal greatly inhibited the flowering of Lemnapaucicostata 6746 induced by photoperiodic stimulus, ferricyanideand continuous far-red light. Simultaneous application of thesetwo inhibitors was more effective in the inhibition of photoperiodicallyinduced and ferricyanide-induced flowering than was each inhibitoralone. They also completely inhibited the photoperiodic floweringof Lemna gibba G3. These results suggest that the inductionor activation of some proteases, probably followed by the degradationof some protein(s), is necessary for the induction of floweringin both these plants. (Received November 21, 1989; Accepted February 19, 1990)     

The accumulation of arsenic,uranium, and boron in Lemna gibba L. exposed to secondary effluents

Aquatic plants are used as a practical and effective method to remove toxic elements from secondary-treated municipal wastewater. In this study, Lemna gibba was investigated for its capacity to remove uranium, arsenic, and boron from secondary effluents. L. gibba was collected from a natural lake in Elaz??, Turkey, then acclimatized to the effluent in situ. The concentration of toxic elements in the plant material was monitored as a function of time for 7 days. L. gibba significantly accumulated the toxic elements, particularly in the first 2 days. Arsenic, uranium, and boron were accumulated in the highest concentrations (133%, 122%, and 40%, respectively). However, in the following days, accumulation levels showed both increases and decreases, most probably due to L. gibba reaching saturation levels.     

Spectral dependences of flowering in Lemna perpusilla and L. gibba

Floral induction in Lemna perpusilla and L. gibba was determinedunder continuous irradiation with monochromatic light in spectralranges from 396 to 765 nm. In the former it was induced underwavelengths from about 400 to 550 nm and longer than 700 nm,while in the latter with wavelengths near 400 nm and from about550 to 650 nm. The patterns of these spectral dependences werenearly mirror images and corresponded to the P_fr level in thephotostationary states of phytochrome. (Received December 3, 1974; )     

Comparison of the Ability of Salicylic Acid and Ferricyanide to Induce Flowering in the Long-day Plant, Lemna Gibba G3

Both salicylic acid and ferricyanide induce flowering in the long-day plant Lemna gibba L., strain G3 under 8- and 9-hour short days. In both cases the effect is daylength-dependent. Salicylic acid is ineffective on daylengths less than 8 hours and ferricyanide is ineffective on daylengths less than 5 hours. When both substances are given together a striking synergistic interaction is observed, and some flowering is obtained on daylengths as short as 3 hours. However, even with the optimal combinations the flower-inducing effect remains daylength-dependent.     

Replacement by ionophores of the photoperiodic light requirement in Lemna gibba G3

Light requirement during the phytochrome-mediated L1-phase ofLemna gibba G3 can be replaced by 10 µg/liter of valinomycinor gramicidin, supporting the idea (5) that a promoted K⁺-iontransport across membranes would be involved in the photoperiodiclight action on the L1-phase. (Received June 6, 1977; )     

Isolation of Flower-inducing and Flower-inhibitory Factors from Aphid Honeydew

The aphid Dactynotus ambrosiae Thomas has been allowed to feed on vegetative or flowering plants of the short-day plant Xanthium strumarium L., and the honeydew which they produce is extracted and tested for an effect on flowering using the long-day plant Lemna gibba L., strain G3 for the bioassay. One zone of flower-inducing activity and at least two zones of flower-inhibitory activity are consistently obtained from the honeydew extracts. The levels of flower-inducing and flower-inhibitory activity are not demonstrably different in vegetative and flowering honeydew. The honeydew extracts are inactive on Xanthium but do give some flower induction with the short-day plant Lemna perpusilla Torr., strain 6746. The flower-inducing activity is clearly of plant origin and is present in the phloem since the same active material can be obtained from vegetative or flowering Xanthium by methanol extraction, and honeydew produced by aphids feeding on a chemically defined synthetic diet is completely without flower-inducing activity. This is the first report of successful flower induction in the long-day plant L. gibba G3 by some means other than long-day treatment.     

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; )     

Poly- und Metaphosphate in höheren Pflanzen (Lemnaceae)

Summary After pulse-labelling with [³²P]orthophosphate of higher plants (Lemna perpusilla (Torrey) and Lemna gibba (L.)) which were previously grown in a P-free medium for 24 h, the [³²P]-radioactivity is partially incorporated into condensed inorganic phosphates. The isolation of the latter was achieved by joint extraction with the nucleic acids and fractionation on methylated serum albumin and Kieselgur (MAK). Two-dimensional thin layer chromatography on a mixture of cellulose and microcrystalline cellulose revealed that ³²P-radioactivity was present in linear oligophosphates with 2 to 7 residues as well as in cyclic tri-, tetra-, penta- and hexametaphosphates. Among the low-molecular condensed inorganic phosphates the trimetaphosphate contained significantly more radioactivity than the other compounds. It is supposeded that the condensed phosphates are involved in the regulation of the ATP-ADP-P_i-system.     

Chromium and cadmium removal from wastewater using duckweed - Lemna gibba L. and ultrastructural deformation due to metal toxicity

Phytoremediation potential of Lemna gibba was evaluated for chromium (Cr) and cadmium (Cd) under laboratory conditions for variable metal load of 1?mg/l, 3?mg/l, 5mgl, 7?mg/l and 9?mg/l, respectively, for 7 and 15?days of treatment period. Effects of both metals on structural attributes of L. gibba were also analyzed by Scanning Electron Microscopic (SEM) study. The metal removal percentage by L. gibba for Cr metal was found in the range of 37.3% to 98.6% and for cadmium it was found within the range of 81.6% to 94.6%. Bio concentration factor (BCF) of L .gibba was observed within the range of 37 to 295 for Cr metal and for Cd metal it ranged from 237 to 1144, which shows that the plant is a hyper accumulator for Cd metal and moderate accumulator for Cr metal. Statistical analysis (Two-way ANOVA) was performed on experimental results to confirm the individual effect of metal concentration and treatment period as well as cumulative effect of both factors together on percentage metal removal and on BCF. Research studies indicated that with the progress of treatment period metal removal percentage increases but increasing metal load during experiment negatively co-relates the metal removal percentage and BCF.     

Flower initiation of Lemna perpusilla under continuous low-intensity light

Lemna perpusilla 6746, a short-day plant, flowered under low-intensitywhite light (10 lux)irrespective of the photoperiod. Red lightof about 20 ergs/cm²/sec also permitted flowering under continuousillumination. The effect of the low-intensity light employedwas not equivalentto that of darkness but similar to that ofblue or far-red light in photoperiodic system. (Received June 15, 1973; )     

Investigations on the effects of metal ions and chelating agents on growth and flowering of Lemna gibba G 3

The effect of different chelating agents on growth and floweringof Lemna gibba G 3 was studied in M and HUTNER'S media. Theincorporation of EDDHA and Fe-EDDHA in the media resulted inprofuse flowering and gibbous character of the fronds. However,EDTA was relatively less effective. It was demonstrated thatthe metal which influenced flowering in L. gibba G 3 was mostlikely copper. (Received August 19, 1970; )