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.     

TEMPORAL COMPARTMENTATION IN LEMNA PAUCICOSTATA: PHOTOPERIODISM,RESPIRATION, NITROGEN NUTRITION AND HETEROTROPHIC GROWTH OF DIFFERENT STRAINS

In previous work with strain 6746 of Lemna paucicostata Hegelm. in heterotrophic culture, changes in the light schedule affected certain features of the daily respiratory pattern, on some but not all nitrogen sources, in a manner parallelling their effects on timing in the photoperiodic flowering response. Seeking further guidance on which metabolic processes should be investigated to understand this relationship, twelve additional strains were compared with 6746 in regard to 1) heterotrophic flowering under short-day skeleton photoperiods, and 2) daily respiratory patterns under 0.25 hr daily of dim red light. Heterotrophic flowering occurred in eight strains; among these, several differed sharply from 6746 in the character of their respiratory patterns and the probable relation of those patterns to photoperiodic timing. For example, in 6746, the second daily peak on NO₃, NH₄ and probably on glutamine reflects photoperiodic timing; the patterns on N-deficient, aspartate and glutamate media do not. In strains 6609 and 381, in contrast, glutamate also elicits a second peak probably reflective of photoperiodic timing; in strain 421, neither the NO₃ nor NH₄ patterns resemble those reflecting photoperiodic timing in 6746. Other strain differences in flowering, respiratory patterns and heterotrophic growth provide useful material for studying phytochrome action, N assimilation and respiration, and they confirm the view that strain identity may be crucial in biochemical investigations on Lemnaceae. These results also reinforce the concept that the “temporal compartmentation” of systems entrained to light/dark cycles can provide important insights, and should be more widely used, in work on regulation of plant metabolism.     

Induction of flowering in the duckweed Lemna paucicostata under non-inductive photoperiods by tannic acid

Flowering in Lemna paucicostata 6746 could be induced by tannic acid under strictly non-inductive photoperiods. This polyphenol completely abolished the photoperiodic sensitivity of strain 6746 as flowering could also be obtained under continuous light (nearly 80% flowering was recorded in the plants supplied with 10⁻⁵ tannic acid). Though its mode of action is unknown, tannic acid is unlikely to act as a gibberellin-antagonist in its effect on flowering in strain 6746.     

Flower-inducing Activity of Vitamin K in Lemna paucicostata

Vitamins K₁ K₃ and K₅ induced flowering in Lemna paucicostata151, a short-day plant, cultured in 1/10 strength M medium (1/10M medium) under continuous light, and their activity was greatlyintensified by simultaneous application of benzyladenine. Themost active of these was vitamin K₅ L. paucicostata 6746 ismore sensitive to vitamin K₅ than strain 151, but the effectof vitamin K₅ on strain 6746 was not intensified by benzyladenine.The flower-inducing activity of vitamin K₅ was intensified bythe addition of benzoic acid in both strains and by the additionof copper or ferricyanide in Strain 6746, when these chemicalswere added at such low concentrations that they would scarcelyinduce flowering. In strain 6746, vitamin K₅ added to 1/10 M had little effecton flowering under a subcritical photoperiod, while it clearlyinduced flowering under continuous light. In this strain, vitaminK₅ added to full strength M medium, in which this plant wasmore sensitive to short photoperiods than in 1/10 M medium,did not induce flowering even under continuous light, and wasrather inhibitory under short photoperiods. (Received August 14, 1984; Accepted October 16, 1984)     

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.     

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.     

Influence of Temperature on the Flowering of Lemna perpusilla 6746 Grown under Skeleton Photoperiods

The flowering of Lemna perpusilla Torr. strain 6746 grown under 24-hour skeleton photoperiods consisting of 13- and 10.5-hour dark periods separated by 0.25-hr light pulses is strongly dependent on temperature. When plants are cultured in 50-ml Erlenmeyer flasks containing 20 ml of half-strength Hutner's medium supplemented with 1% (w/v) sucrose maximum, per cent, flowering occurs at 23 C. At temperatures above and below 23 C a marked decline in per cent flowering is seen.     

Role of Adenosine 3'5'-Cyclic Monophosphate in Flowering of a Short-Day Duckweed Lemna paucicostata 6746

The well-known second messenger in animal systems, adenosine3',5'-cyclic monophosphate (cAMP), stimulated flowering in theshort-day plant, Lemna paucicostata 6746, under both inductiveand non-inductive photoperiods, when grown on modified Bonnerand Devirian medium. Flowering could be achieved even in continuouslight in the presence of cAMP, although the intensity of theresponse was still daylength-dependent. Besides flower induction,cAMP also enhanced their development. 5'-AMP and 5'-ATP alsoinduced some flowering under non-inductive long days, but theresponse was weak as compared to that of cAMP. 5'-ADP, in contrast,had no effect whatsoever on flowering under long days, whereasa small effect was observed under inductive short days. Whatcould be the probable mechanism of action of cAMP and whetherits effect on flowering is mediated through the cAMP-adenylcyclasesystem, has been discussed. (Received May 11, 1988; Accepted June 23, 1988)     

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)     

Flower Induction by Nitrogen Deficiency in Lemna paucicostata 6746

Lemna paucicostata 6746, a short-day plant, produced flowerbuds even under continuous light when cultured in nitrogen-deficientmodified Hoagland medium with 1% sucrose for 3 days or morefollowed by culture on nitrogen-rich medium (either nitrateor ammonium). Flowering was also induced by culture on mediumcontaining 20–100 µM nitrate as the sole nitrogensource for 10 days or more, but not on medium with a low ammoniumconcentration. However, if plants cultured on medium containing5–20 µM ammonium as the sole nitrogen source for10 days were grown in a nitrogen-rich medium for a further 4days, they produced flower buds. Thus, nitrogen deficiency caninduce day length-independent flowering in Lemna paucicoslata6746, but nitrogen is required for the manifestation of flowering. (Received January 31, 1986; Accepted April 24, 1986)     

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.     

Promotion of Flowering in Lemna paucicostata 6746 (a Short-Day Duckweed) by Cytokinins

Lemna paucicostata 6746 is a short-day plant and flowers inresponse to a single photoinductive cycle. Flowering in thisduckweed could be promoted, under short days, in the presenceof a cytokinin in the nutrient medium. 6-Benzyladenine (BA)was the most effective for promotion of flowering, followedby zeatin and kinetin. Since EDTA itself is promotive for floweringin this plant, the cytokinin effect is best observed in mediumdevoid of EDTA. Nevertheless, in their combined presence floweringwas more as compared to when either of these was individuallypresent. This additive effect on flowering was especially prominentwhen the plants were kept in near-critical photoperiods. Besidesthe increase in percentage of the flowering fronds, floweringis also sustained a little longer in the cytokinin-treated plants.BA, however, did not alter the critical dark period requirement,either in the presence or absence of EDTA. (Received March 26, 1983; Accepted May 6, 1983)     

Floral Induction in Short-Day Lemna paucicostata 6746 by 8-Hydroxyquinoline, under Long Days

Lemna paucicostata 6746 is a short-day duckweed and flowersin response to a single photoinductive cycle. Its critical darkperiod requirement is ca. 10 h. Flowering in this duckweed couldbe induced by 8-hydroxyquinoline (8-HQ) under an otherwise non-inductivelong-day regime of 16 h light and 8 h darkness; the criticaldark period requirement for initiation of flowering was thusreduced by at least 2 h. However, 8-HQ was ineffective in initiatingflowering in strain 6746 under continuous illumination. Atomicabsorption analysis of the plant material revealed that thecontent of both iron and copper is markedly higher in the plantstreated with 8-HQ. A comparison of the effects of 8-HQ and thoseof EDTA and ethylenediamine-di(o-hydroxyphenylacetic acid),on flowering of strain 6746, has also been made. (Received August 23, 1983; Accepted October 18, 1983)     

Influence of Ammonium on the Ability of Salicylic Acid to Induce Flowering in the Short-Day Plant Lemna paucicostata 6746

When the short-day plant Lemna paucicostata 6746 is grown inhalf-strength Hutner's medium, which contains 1.25 mM NH4NO3,salicylic acid does not induce flowering on daylengths of 16hr or longer. By contrast, in M (Hoagland-type medium), Pirson-Seidelor ammonium-free half-strength Hutner's media, none of whichcontain ammonium, salicylic acid is able to induce some floweringeven under continuous light. Neverthless, in each of these threemedia the effect of salicylic acid is strongly daylength dependentbecause there is a sharp drop in the flowering response to salicylicacid between the 12 and 16 hr daylengths, and the floweringresponse is nearly constant from the 16 hr daylength to continuouslight. Ammonium has the opposite effect and at 50 to 75 µMis able to overcome the salicylic acid effect completely andprevent any flowering on daylength of 16 hr or longer. (Received December 3, 1980; Accepted March 5, 1981)     

EFFECTS OF PHOTOPERIOD AND KIND OF SUPPLEMENTAL LIGHT ON GROWTH,FLOWERING, AND STEM FASCIATION OF CELOSIA

Piringer , A. A., and H. A. Borthwick . (U.S.D.A., Beltsville, Md.) Effects of photoperiod and kind of supplemental light on growth, flowering and stem fasciation of Celosia. Amer. Jour. Bot. 48(7): 588–592. Illus. 1961.—Four cultivars of Celosia argentea L. var. cristata were grown on photoperiods ranging from 8 hr to continuous light. Supplemental low-intensity incandescent light was used to extend 8 hr of natural light and provide the given photoperiod. In all cultivars, short main stems occurred on photoperiods of 12 or fewer hours and long main stems, due to more nodes, on photoperiods of 16 or more hours. Flowering was a nonobligate short-day response in all cultivars. Plants of certain cultivars tended to have shorter stems and flower later when 8 hr of fluorescent instead of incandescent light was used to provide the 16-hr photoperiod. In 3 of the cultivars studied, photoperiods of 16 or more hours induced marked stem fasciation.     

The action of skeleton photoperiods on flowering in Lemna perpusilla

The effects of 24 hr cycle skeleton photoperiodic schedulesinvolving two short light pulses on flowering in Lemna perpusillahave been studied. Simulation of complete photoperiods by correspondingskeletal ones is nearly perfect for all photoperiods up to 8hr and is unstable for periods of 9 to 13 hr. A jump in theresponse phase appears when skeleton photoperiods ranging from12 to 13hr are given. For all skeleton photoperiods longer than14 hr the phase is entrained so that it agrees with that givenby skeleton photoperiods of complemental lengths. That is, askeleton photoperiod of 18 hr is equivalent to that of 6 (=24–18) hr. Simulation is largely related to whether thesecond pulse is locked on to "dawn" or to "sunset" dependingon when it falls during the dark period following the firstpulse. The inductive action of skeleton photoperiods that gives unstableentrainment depends on the length of a preliminary dark periodgiven before the plant receives the first pulse, since in theseskeleton schedules the sensitive zone to the second pulse shiftswith the length of the preliminary darkness. Thus, we tentatively conclude that the circadian oscillationin L. perpusilla involves an entrainment mechanism and thatphotoperiodic induction is contingent on the coincidence oflight and a specific inductive phase in oscillation. (Received September 18, 1968; )     

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; )     

多胺及其合成抑制剂MGBC对稀脉萍成花反应的影响

腐胺、亚精胺和精胺对稀脉萍的成花均有一定的抑制作用,这种作用随多肢的浓度增加而增强。多胺合成抑制剂MGBG强烈抑制稀脉萍群体的增殖速率,并使稀脉萍群体在非诱导光周期下开花。这种由MGBG引起的增殖速率的降低及成花诱导作用均可被多胺逆转。稀脉萍成花诱导过程中,内源腐胺含量显著升高,亚精胺则下降。     

Comparison between Induction of Flowering by Nitrogen Deficiency and that by Short Days or Continuous Irradiation with Blue or Low-Intensity White Light in Lemna paucicostata 6746

Flowering of Lemna paucicostata 6746, a short-day plant, isinduced by nitrogen deficiency or by the suppression of nitratereductase activity under continuous light. The plant also flowersunder continuous blue or low-intensity white light. However,the nitrate reductase activity and levels of endogenous nitrogenof the plants did not decrease under these conditions. Glutaminesynthetase activity decreased slightly in darkness, but daylength-independentflowering was not induced by the suppression of the enzymaticactivity by methionine sulfoximine. Endogenous nitrogen levels of plants grown on nitrogen-deficientmedium at 30°C fell more rapidly than those of plants grownat 25°C, and thus difference was expressed as an enhancementof flowering at 30°C. Photoperiodic flowering was greatlysuppressed by exposure of plants to a high temperature (30°C)during the dark period, whereas the flowering induced undercontinuous blue or low-intensity white light was enhanced onlyslightly by high temperature during culture. (Received April 24, 1989; Accepted September 20, 1989)     

Flower-Inducing Activity of Lysine in Lemna paucicostata 6746

Flowering of Lemna paucicostata 6746, a typical short-day plant,was induced by culture for 96 or 120 h in nitrogen-free mediumunder continuous illumination. To examine the effects of lysine,we homogenized entire plants of L. paucicostata 151 in a solutionof lysine and the supernatant obtained after centrifugationof the homogenate was added to the medium to give various concentrationsof lysine in the medium. Flowering of strain 6746 in nitrogen-freeor nitrogen-deficient culture medium was effectively promotedby the addition of a lysine-containing supernatant to the medium.The suppressive effect of elastatinal, a protease inhibitor,on the induction of flowering was almost completely reversedby the simultaneous application of a lysine-containing supernatantto the medium. During nitrogen-free culture, the level of endogenousfree lysine, expressed on the basis of the amount of total freeamino acids, increased. Lysine-containing supernatants alsoinduced flowering of plants in nitrogen-rich medium under continuousillumination. These findings suggest that endogenous lysineis involved in the induction of flowering in L. paucicostata6746 on nitrogen-free or nitrogen-deficient medium, as it isin the induction of flowering in L. paucicostata 151 (Received July 29, 1996; Accepted November 18, 1996)