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)     

Flower-Inducing Activity of Exogenous Lysine in Lemna paucicostata 151 Cultured on Nitrogen-Rich Medium

Flower-inducing activity of lysine was examined in Lemna paucicostata151, a weakly responsive short-day plant, cultured on nitrogen-richmedium under long-day conditions (continuous light). Lemna paucicostata151 was homogenized in a solution of lysine and the homogenatewas centrifuged. The supernatant (lysine-containing extract)was added to nitrogen-rich medium after passage through a membranefilter to give various concentrations of lysine in the medium.Flowering was induced in plants grown for six days on mediumthat contained lysine at concentrations above 0.25 µM.In plants grown on medium that contained 1 µM lysine,a significant flowering response was observed on the fourthday of culture. However, the flower-inducing activity of lysinedisappeared when the lysine-containing extract was added tothe medium and the medium was then autoclaved, suggesting thatthe active principle is unstable to autoclaving. Among derivativesof lysine tested, lysine hydroxamate had the highest flower-inducingactivity and lysyl lysine had almost same activity as that oflysine. When added to the medium without homogenization withplant material, lysine and lysyl lysine had flower-inducingactivity but lysine hydroxamate did not induce flowering. (Received April 26, 1993; Accepted November 8, 1993)     

Inhibition of Flowering in the Long-Day Plant Lemna gibba G3 by Hutner's Medium and its Reversal by Medium Modification

The long-day plant Lemna gibba G3 flowers normally in E medium(Hoagland-type medium plus 30 µM EDTA) but in 0.5 H mediumthere is no flowering. Ammonium is present in 0.5 H medium andis known to inhibit flowering in L. gibba G3, but even in NH₄⁺-free0.5 H medium there is virtually no flowering under continuouslight. Increasing the phosphate concentration of the NH₄⁺-free0.5 H medium from 1.15 ITIM to 12 or 16 mM results in substantialflowering. Decreasing the EDTA concentration from 850 µIMto 250 µM, or raising the nitrate concentration from 4mM to 12 mM, results in only a small increase in flowering.If the decrease in EDTA and increase in nitrate are combinedwith the increase in phosphate, however, the flowering responseis nearly as good as that obtained using E medium. Thus, withthese three changes the inhibitory effect of NH₄⁺free 0.5 Hmedium for flowering in L. gibba G3 is almost completely reversed In the above studies flowering was not limited by daylength.When plants were grown on E medium under an 11 hour daylengthwhere flowering is limited by daylength, decreasing the phosphateconcentration in the medium reduced flowering, but increasingthe phosphate concentration in the medium did not stimulateflowering. Thus, when flowering is limited by daylength, highphosphate will not cause flowering, but a certain level of phosphateappears to be necessary for the expression of photoinductionunder long days. (Received January 14, 1986; Accepted June 24, 1986)     

Flower Induction by Daily 17-h Culture on Nitrogen-Free Medium in Lemna paucicostata 6746

Daylength-independent flowering in Lemna paucicostata 6746,a short-day plant, was induced by daily treatment with nitrogendeficiency for 17 hours, which inhibited nitrate reductase activity.The endogenous nitrogen level in plants treated daily with 17-hnitrogen deficiency was much higher than in plants culturedon medium containing 50–200 and 1,000µM nitratefor 10 and 14 days, respectively, which were induced to flower.These results suggest that suppression of nitrogen metabolismfor more than a certain number of hours can induce floweringeven in plants with a high nitrogen level. (Received January 16, 1987; Accepted August 28, 1987)     

Reproductive Development and Nitrogen Fixation in Soybean (Glycine max [L.] Merril)

Gomes, M. A. F. and Sodek, L. 1987. Reproductive developmentand nitrogen fixation in soybean (Glycine max (L.) Merril).—J.exp. Bot. 38: 1982–1987. Nitrogenase activity (acetylene reduction) was measured duringthe growth cycle of soybean plants induced to flower at twodifferent ages. The decline in nitrogenase activity towardsthe end of the cycle was clearly associated with pod-fillingfor both flowering dates when plants were cultivated under lowerlight and temperature conditions (out of season). Under higherlight and temperature conditions (normal growing season) thedecline was independent of the flowering date. Furthermore,the timing of the decline was not altered when plants were maintainedunder long-day (vegetative) conditions nor when flowers wereremoved. It is suggested that under more favourable growth conditionsthe diversion of assimilates by the fruits is not the primarycause of the decline in nodule activity, but competition bythe fruits may be important when the production of photo-assimilatesis more limited. Key words: Glycine max, nitrogenase, source-sink     

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)     

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-Inducing Activity of Phloem Exudate in Cultured Apices from Pharbitis Seedlings

Phloem exudate from cotyledons of photoperiodically inducedPharbitis plants induced flowering in apices excised from non-inducedseedlings and cultured in vitro. The exudate also stimulatedflowering in apices excised from photo-induced seedlings andcultured under long-day conditions. The application of benzoicacid had similar effects. Both the exudate from non-inducedplants and gallic acid suppressed flowering in apices from photo-inducedseedlings. It appears that the phloem exudate contains flower-inducingor flower-suppressing substance(s), depending on the plant materialsfrom which it was collected. (Received August 15, 1989; Accepted May 14, 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; )     

Effect of Ferricyanide, Ferrocyanide and KCN on Growth and Flowering in the Short-Day Plant Lemna paucicostata 6746

Flowering in the short-day plant Lemna paucicostata 6746 canbe induced under continuous light by the addition of ferricyanie,ferrocyanide or KCN to M-sucrose medium. Each substance is nearly10 times more effective when the flasks are covered by glassbeakers than when cotton plugs are used. By contrast, when floweringis induced under continuous light by copper or by short-daytreatment, neither flowering nor growth are affected by whetherglass beakers or cotton plugs are used. Ferricyanide, ferrocyanideand KCN are also able to induce long-day flowering when theplants are grown on Msucrose medium in small beakers that areplaced in a covered storage dish that also contains a solutionof one of these compounds. Addition of a KOH trap to the storagedish completely blocks the flowering induced by these compounds.If [¹⁴C]ferrocyanide is added to the storage dish both the M-sucrosemedium and the plants contain significant amounts of radioactivity,the amount of radioactivity being proportional to the floweringresponse. These results indicate that ferricyanide, ferrocyanideand KCN break down to release HCN and that it is the HCN whichis responsible for inducing flowering in L. paucicostata 6746under continuous light. ¹Present address: Department of Biology, Osaka Kyoiku University,Ikeda, Osaka 563, Japan. ²Present address: Institute of Horticulture, The Volcani Center,P. O. B. 6, Bet-Dagan, Israel. (Received January 17, 1983; Accepted March 24, 1983)     

Suppression of long-day flowering by nitrogenous compounds in Lemna perpusilla 6746

The long-day flowering of Lemna perpusilla 6746 on an SH inhibitor-containingmedium was inhibited by the application of ammonium ion to themedium. Ammonium ion not only suppressed long-day flowering,but relieved the inhibition of vegetative growth caused by theinhibitors. Nitrite, casamino acids, glutamine and asparaginehad a similar effect, suggesting that the inhibition of long-dayflowering by ammonium ion is not a direct effect of the ion.Most amino acids, with the exception of glutamate and aspartate,also prevented long-day flowering, but their effects on vegetativegrowth varied. No qualitative differences in amino acid compositionwere observed among plants cultured on media containing nitrate,nitrite or NH4₄NO₃as the sole nitrogen source. However, theamounts of free and total amino acids werehigher in plants fedwith nitrite or NH₄NO₃ than in those fed with nitrate. Thissuggests that the inhibition of long-day flowering by ammoniumand nitrite can be ascribed to increased nitrogen metabolism. Though decreased activity by SH inhibitors of nitrate reductase(SH enzyme) is assumed to result in long-day flowering by loweringthe nitrogen metabolism, lowering the nitrogen level in M mediumdid not bring about floral initiation in the absence of SH inhibitors. (Received January 7, 1975; )     

Correlation between Long-Day Flowering and Root Elongation in Pharbitis nil, Sfrain Kidachi

Long-day flowering of Pharbitis nil, dwarf strain Kidachi, at20?C was greatly influenced by the size of the culture vesseland the number of plants per vessel. The smaller the vessel,the greater the flowering response. The volume of nutrient solutionper plant was not decisive for long-day flowering. For instance,plants cultured singly in 200-ml beakers flowered, but thosecultured in 5,000-ml vessels (33?26?11.5 cm, 48 plants per vessel)did not, even though there was only about 100 ml of nutrientsolution per plant. Long-day flowering was always accompaniedby the suppression of root elongation, but not by a decreasein the dry weight of roots or shoots, or in the rate at whichthe leaf primordia appeared (plastochrone). Aeration of thenutrient solution or culture in vermiculite promoted root elongationeven in small vessels, thereby inhibiting long-day flowering.Thus the suppression of root elongation seems to be necessaryfor long-day flowering. Removal of the roots or cotyledons;however, suppressed long-day flowering even when root elongationwas inhibited by culture in small vessels. When plants werecultured at 24?C, suppression of root elongation (culture ina small vessel) did not induce long-day flowering; but, short-daytreatment induced flowering without suppressing root elongation. (Received April 19, 1982; Accepted June 24, 1982)     

Effect of different photoperiodic regimes on growth, flowering and essential oil in Mentha species

Three major cultivated Mentha spp. (M. arvensis, M. citrata and M. cardiaca) were grown under short-days, normal-days or long-days for 60 cycles. Subsequent to photoperiodic treatment, the plants were assessed for growth behaviour, essential oil content, oil composition and essential oil biosynthesis. The species grew better under long-day conditions. The long-day treatment resulted in flowering in M. citrata, which normally does not flower under our conditions. The oil concentration and biogenesis was maximal in short-day plants. The photoperiodic treatment also affected the oil composition. The observations are discussed in relation to physiology of the oil biogenesis.     

Induction of flowering by cytokinins in a short-day plant, Lemna paucicostata

Lemna paucicostata, normally a short-day plant, can be inducedto flower under long-day conditions by providing a cytokininin a medium containing a high level of ferric citrate (5 x 10^–4M).Interestingly, when a cytokinin and EDDHA are present togetherin the medium, flowering is induced even at low levels of iron(10^–5 and 5 x 10^–5M ferric citrate). However, inthe absence of a cytokinin, flowering takes place only undershort days. (Received September 30, 1968; )     

Flower-Inducing Activity of Lysine in Lemna paucicostata 151 Cultured on Nitrogen-Deficient Medium

Lemna paucicostata 151, a weakly responsive short-day plant,flowers even under continuous illumination when cultured onnitrogen-free medium for more than 72 hours with subsequentculture on nitrogen-rich medium. During the nitrogen-free culture,the protease activity and protein content of the plant increasedand decreased, respectively. The plant contained a protein(s)that induced flowering of the plant when added to the medium.The level of this protein(s) also decreased during the nitrogen-freeculture. The total amount of free amino acids in plants culturedon nitrogen-free medium for 96 hours decreased to about 15%of that in plants at the start of nitrogen-free culture, butlevels of some amino acids increased. These amino acids wereexamined for their effects on flowering of plants cultured onnitrogen-deficient or nitrogen-free medium. Most of the aminoacids had no effect on flowering. However, profuse floweringwas induced when lysine was added to the medium. Lysine promotedthe flower-inductive process(es) rather than the developmentof flower buds. These results suggest that nitrogen deficiency-induced floweringof the plants is induced by lysine, which is generated froma specific protein(s) by proteolysis. (Received May 11, 1992; Accepted July 30, 1992)     

Measurement of Endogenous Phosphorus Levels in Relation Flowering in the Long-Day Plant Lemna gibba G3

When Lemna gibba G3 was grown on E medium, a decrease in thephosphate concentration caused a suppression of flowering andlead to a decrease in the phosphorus concentration in the plants.Addition of salicylic acid reversed this inhibition withoutcausing an increase in the phosphorus concentration, while additionof copper or ammonium to Hoagland-type medium inhibited flowering,also without affecting the phosphorus concentration. Plantsgrown under 8 h or 24 h daylengths exhibited a FL% of 0 or about50, respectively, but showed no difference in their phosphorusconcentrations. These results indicate that a high phosphorusconcentration is not always required for flowering in Lemnagibba G3. When plants were grown on a modified E medium in which 1/50strength Hutner’s medium micronutrients were substitutedfor the normal E medium micronutrients, the suppression of floweringcaused by reduced phosphate was completely eliminated. Addingeach micronutrient individually at the normal concentrationto the modified E medium demonstrated that manganese inhibitedflowering in modified E medium with a low phosphate concentration. (Received January 31, 1986; Accepted July 4, 1986)     

Long-Day Flowering of Perilla Plants Cultured in Nitrogen-Poor Media

Green-leaved and red-leaved Perilla plants (short-day plants)cultured aseptically on diluted modified White's medium or onfull strength White's medium (W) containing reduced concentrationsof nitrogen sources, initiated flower buds under continuouslight (2,000–2,200 lux fluorescent lamps) at 24–26?C.The addition of sucrose to the medium promoted flower formation;the optimum concentration was 2% in 1/10?W medium. The plantscultured on unfertilized vermiculite also developed flower budsreadily, unlike those on fertilized vermiculite. High-intensity light (8,000 lux fluorescent lamps) given duringthe first 30 days of culture promoted flowering. This effectwas also produced to a lesser degree by the addition of sucroseto the medium, instead. On the other hand, high-intensity lightgiven during the second 30 days or throughout the culture periodinhibited flowering, irrespective of the presence of sucrosein the medium. (Received February 4, 1982; Accepted June 14, 1982)     

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)     

pH Dependence of the Copper Effect on Flowering, Growth and Chlorophyll Content in Lemna paucicostata 6746

The short-day plant Lemna paucicostata 6746 took up the sameamount of copper from the medium whether the pH of the mediumwas 4.1 or 5.1. At pH 4.1, an addition of copper to the mediumresulted in an unchanged chlorophyll content, a somewhat reducedgrowth rate and a substantial induction of long-day flowering.By contrast, at pH 5.1 the same copper concentration causeda reduction in the chlorophyll content and strong inhibitionof growth, but it did not induce any long-day flowering. (Received June 14, 1982; Accepted October 14, 1982)     

Flower-Inducing Activity of Water Extract of Lemna

Flowering of Lemna paucicostata 441 (P441), a sensitive short-dayplant (SDP), was promoted under a near critical photoperiodby the crude water extract of the same plant added to the medium.The extract induced flowering in L. paucicostata 151 (P151),a weakly responsive SDP, under continuous light. The activityfor P151 was greatly promoted by simultaneous application ofbenzyladenine, and the extract of only 0.3 mg fr wt plant addedto 10 ml of assay medium with 1 µM benzyladenine was active.Active substance(s) was similarly obtained from both flower-inducedand non-induced plants, and more or less from all species andstrains of Lemna tested, including P151. However, the extractof short-day strains was more active than that of L. gibba G3(G3), a long-day strain. G3 responded only slightly to the extractof either P441 or G3, whereas P151 responded far more stronglyto the extract of P441 than to that of G3. (Received April 17, 1989; Accepted August 10, 1989)