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; )     

The Role of Benzoic Acid and Plant Hormones in Flowering of Lemna gibba G3

The level of benzoic acid was measured in Lemna gibba G3 grownon M and E media under inductive and non-inductive daylengths.Benzoic acid was slightly higher in plants grown on M mediumbut there was no difference in the benzoic acid levels in floweringand vegetative plants. When L. gibba G3 was grown under continuouslight on 1/10 M medium or 1/2 H medium there was virtually noflowering, but addition of benzoic acid to either medium ledto a substantial flowering response. In both cases this floweringresponse was inhibited by the plant hormones IAA, GA₃, ABA andzeatin, with IAA and GA₃ being the least inhibitory and ABAbeing the most inhibitory. This same pattern of inhibition wasseen when L. gibba G3 was grown on M medium under continuouslight, conditions that lead to photoinduction of flowering.These results leave open the possibility that endogenous benzoicacid may interact with other factors to influence the floweringresponse in L. gibba G3. (Received November 13, 1984; Accepted February 27, 1985)     

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     

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; )     

The Use of Chemical and Infra-red Spectral Analyses to Verify the Identification of Two Species of Duckweed, Lemna minor L. and Lemna gibba L. Grown Under Defined Conditions

Flat forms of the fronds of Lemna gibba L., used widely in laboratoryexperiments, can be easily confused with Lemna minor Chemicalanalyses of the two species, grown under defined laboratoryconditions, showed clear distinctions between the two speciesin relation to total protein content and the content of individualmonosaccharides. Infra-red spectral analysis confirmed the chemicaldata for protein content and also revealed differences in thetypes of proteins present in the two species. Chemical and infra-redspectral analyses, particularly the amide I: carbohydrate absorbanceratio, provide a rapid and reliable means of verifying betweenthe two species, which are often difficult to identify withcertainty from morphological differences. Key words: Gibbosity, infra-red spectroscopy, Lemna gibba, Lemna minor, monosaccharides, proteins     

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; )     

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; )     

Comparison of the flowering behavior of the long-day plant Lemna gibba G3 from different laboratories

In an effort to determine the cause for the wide discrepanciesin the level of flowering response reported for the long-dayplant Lemna gibba L., strain G3, cultures of L. gibba G3 wereobtained from the laboratories of W. S. Hillman (G3-H), R. Kandeler(G3-K), Y. Oota (G3-O) and and A. Pieterse (G3-P) and comparedto the L. gibba G3 (G3-C) from this laboratory. Under continuouslight all cultures gave FL% values of 77 or above, and on a9L:15D short-day treatment, all cultures were completely vegetative.However, on daylengths of 10 to 12 hr, small but statisticallysignificant differences were obtained for the different cultures.The critical daylength curves for G3-G, which showed the shortestcritical daylength, and G3-K, which showed the longest criticaldaylength, differed by approximately one hour. Salicylic acidtreatment caused flower promotion in each culture, but statisticallysignificant differences were obtained between some of the culturesin their response to salicylic acid. It is concluded that the large discrepancies in the floweringresponses of L. gibba G3 that have been reported are due primarilyto differences in culturing methods and counting proceduresin the different laboratories. However, the results also indicatethat there may be distinct cultures of L. gibba G3 that exhibitsmall physiological and/or genetic differences that would makeprecise quantitative comparison between different laboratoriesvery difficult. (Received January 23, 1979; )     

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)     

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     

The Influence of Nicotinic Acid and Plant Hormones on Flowering in Lemna

Nicotinic acid induces flowering in Lemna paucicostata 151 and381 and Lemna gibba G3 when they are grown in one tenth-strengthM medium under continuous light. For L. paucicostata 151 and381, the simultaneous addition of IAA, GA₃ or ABA to the mediumleads to an inhibition of the flower-inducing effect of nicotinicacid, while zeatin leads to a further stimulation of floweringabove that obtained by nicotinic acid alone. By contrast, inL. gibba G3 all four plant hormones inhibit the nicotinic acid-inducedstimulation of flowering. The effect of nicotinic acid on flowering in all three plantsis strongly daylength dependent when the plants are grown inhalf-strength Hutner's medium. Thus, nicotinic acid causes floweringin L. gibba G3 on continuous light but not on 9L:15D or 10L:14Dregimes. In L. paucicostata 381 nicotinic acid has a small effecton 12L:12D regime, a large effect on a 13L:11D regime and noeffect with daylengths longer than 14 hours, and in L. paucicostata151 nicotinic acid is only effective on daylengths shorter thanabout 11 hours. However, in L. paucicostata 151 and 381 treatmentwith both nicotinic acid and zeatin results in flowering undercontinuous light on half-strength Hutner's medium. Nicotinic acid is present in different Lemna but its concentrationdoes not appear to be influenced by changes in daylength. Thus,flowering clearly cannot be controlled by nicotinic acid actingalone, but the results of this study indicate that nicotinicacid could interact with other factors, possibly including oneor more of the known plant hormones, to influence the floweringprocess in Lemna. (Received August 28, 1985; Accepted October 29, 1985)     

Induction of flowering in Lemna gibba G 3 by Fe-EDDHA

Fe-EDDHA (iron salt of ethylenediamine-di-o-hydroxyphenylaceticacid) induced profuse flowering in Lemna gibba G 3 culturedin HUTNER'S medium. The maximum number of flowering plants wasobserved in a medium supplemented with 5 ppm of this chelate. (Received April 20, 1970; )     

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)     

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; )     

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; )     

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; )     

A possible mechanism for sugar inhibition of duckweed flowering

Sugar (ca. 1%) reduced the floral index in Lemna gibba G3 byca. 50%, and supplemental addition of cyclic AMP (ca. 10^–5M)removed nearly all of this sugar action. Inhibition by sugarof duckweed flowering may be explained in terms of cataboliterepression. (Received October 9, 1971; )     

Experimental control of flowering in Pistia stratiotes L.

GA₃, salicylic acid and EDDHA induced flowering in Pistia stratiotesin vitro under short days and conditions of continuous light.It has been hypothesized that EDDHA and salicylic acid bringabout the same effect on flowering in Pistia and the duckweedspecies Lemma gibba G3 whereas the effect of GA₃ on the floweringmechanism of these species is basically different. (Received March 14, 1978; )     

Effect of L-Pipecolic Acid on Flowering in Lemna paucicostata and Lemna gibba

L-Pipecolic acid was found to be effective in inducing floweringof Lemna paucicostata 151, 381, 441 and 6746, and of Lemna gibbaG3. When the plants were grown on half-strength Hutner's medium,L-pipecolic acid caused profuse flowering of L. paucicostata151 maintained under 9 and 10 h of light daily. In L. paucicostata441 and 6746, L-pipecolic acid had a strong flower-promotingeffect under a near critical photoperiod. In L. paucicostata381, by contrast, L-pipecolic acid had only a very small effecton flowering. In L. gibba G3 substantial promotion of floweringwas observed under continuous light. When one-twentieth-strengthHutner's medium was used as the basic medium, L-pipecolic acidstimulated flowering in all strains of Lemna examined, evenunder continuous light. When L. paucicostata 151 was grown on one-tenth-strength M mediumor one-twentieth-strength Hutner's medium, the flower-inducingactivity of L-pipecolic acid was greatly enhanced by cytokininunder continuous light. However, when this strain was grownwith 9 h of illumination daily, this synergistic effect of cytokininwas only slight. A short-term (even 1-h) treatment with L-pipecolicacid resulted in flowering, suggesting that L-pipecolic acidis involved in the induction of flowering, rather than its evocation.D-Pipecolic acid also had flower-inducing activity, but itsactivity was 50 times lower than that of the L-isomer. (Received January 23, 1992; Accepted March 9, 1992)