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 Role of Plant Hormones and Benzoic Acid in Flowering of Lemna paucicostata 151 and 381

The effects of plant hormones on flowering of Lemna paucicostata151 and 381 were investigated when exogenously applied in combinationwith benzoic acid. These strains are very sensitive to benzoicacid and flower readily on application of benzoic acid. Theflower-inducing effect of benzoic acid was strongly modifiedby plant hormones: gibberellins, indole-3-acetic acid and abscisicacid were inhibitory, while cytokinins were promotive (synergistic),suggesting that the balance between endogenous levels of benzoicacid and plant hormones contributes to the regulation of floweringin Lemna. (Received October 6, 1982; Accepted December 23, 1982)     

Flowering and Endogenous Levels of Plant Hormones in Lemna Species

The occurrence and endogenous level of various plant hormoneswere measured for the short-day plants Lemna paucicostata 151and 381 and the long-day plant Lemna gibba G3 to determine whetherany of them are involved in the photoperiodic control of flowering.ABA, IAA, GA₁, GA₂₉, GA₃₄, GA₅₃, trans- and cis-zeatin, trans-and cis-ribosyl zeatin, N⁶-(²-isopentenyl) adenine and N⁶-(²-isopentenyl)adenosine were definitely detected in each species, while GA₄was only detected in L. gibba G3 and GA₂₀ was only detectedin L. paucicostata 151. The endogenous levels of ABA and IAAwere in the range of 1–7 ng/g fr wt and were not significantlydifferent in vegetative and flowering plants. The endogenousgibberellin levels were generally higher in Lemna grown underlong-day rather than short-day conditions. The endogenous cytokininlevels were almost the same in both flowering and vegetativeplants of L. paucicostata 151 and 381. In L. gibba G3, however,the level of cis-ribosyl zeatin, N⁶-(²-isopentenyl) adenineand N⁶-(²-sopentenyl) adenosine were higher in vegetative thanin flowering plants. These results indicate that there is not necessarily a directrelation between endogenous plant hormone levels and flowering,and that the chemical basis for the photoperiodic control offlowering cannot be explained solely by changes in hormone levels.The possibility remains, however, that one or more of the planthormones has some influence of secondary importance on the floweringprocess in Lemna. (Received January 29, 1986; Accepted July 12, 1986)     

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)     

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)     

Influence of Giving Salicylic Acid for Different Time Periods on Flowering and Growth in the Long-Day Plant Lemna gibba G3

When the long-day plant Lemna gibba L., strain G3 is grown under continuous light on ammonium-free half-strength Hutner's medium (NH₄⁺-free 0.5 H medium) growth is excellent, but flowering is severely inhibited and often is zero. Addition of 10 micromolar salicylic acid (SA) to NH₄⁺-free 0.5 H medium quickly reverses this inhibition and leads to optimal flowering. The SA treatment also leads to a considerable reduction in the growth rate and increase in frond gibbosity. Removal of SA from the medium quickly leads to an increase in the growth rate and a large decrease in flowering. Thus, for maximal effectiveness SA must be present in the medium for the entire experiment, and the effect of SA is clearly not inductive.     

Flowering and Endogenous Levels of Benzoic Acid in Lemna Species

The occurrence of benzoic acid, a flower-inducing factor inLemna species, in L. paucicostata strains 151, 381, 321 andL. gibba G3 was established by several purification steps andfinal use of gas liquid chromatography-selected ion monitoring.Quantitative analyses of benzoic acid were made in non-floweringand flowering Lemna to determine differences in levels. Theendogenous level of benzoic acid was shown to vary dependingon culture conditions, but no positive correlation could befound between the endogenous level of benzoic acid and floweringof Lemna. (Received October 6, 1982; Accepted December 23, 1982)     

Isolation and Identification of Nicotinic Acid as a Flower-Inducing Factor in Lemna

Extracts of flowering plants of the long-day plant Lemna gibbaG3 and the short-day plants Lemna paucicostata 151 and 381 weretested on L. paucicostata 151 for flower-inducing activity.Crude extracts failed to show any activity but after severalpurification steps three fractions with flower-inducing activitywere obtained. One fraction obtained from all three plants wasshown to contain nicotinic acid by mass spectroscopic and NMRspectroscopic analyses. These results raise the possibilitythat nicotinic acid may act to influence the flowering processin Lemna. (Received August 28, 1985; Accepted October 29, 1985)     

脱落酸在植物花发育过程中的作用

植物激素脱落酸(ABA)对植物的生长发育具有多方面的调节作用,比如种子休眠、萌发,营养生长,环境胁迫反应等。大量研究显示,ABA也参与了植物的成花调控。影响植物成花调控的环境因子,包括光周期变化、春化作用、干旱等均会导致植物体内ABA代谢的变化。本文从调控植物开花的4条主要途径与植物体内ABA代谢变化之间的相互关系,花芽分化时期ABA在植物叶芽和花芽中的动态分布以及离体培养条件下ABA对花芽分化的影响等方面总结了ABA与植物花发育这一领域的最新研究进展。对ABA在植物成花诱导和花发育中的作用进行了综合分析。     

The Mode of Action of Benzoic Acid and Some Related Compounds on Flowering in Lemna paucicostata

Benzoic acid (BA) (10 µM) added to the medium during onlythe first 24 h of culture induced flowering in Lemna paucicostata151 even under continuous light at 24.5?C when 1/10 M medium(pH 4.0) containing 1 µM benzyladenine (BAd) was usedas the basic medium. Flower buds were produced on the 4th–5thday and almost all the fronds that developed during the subsequent3–4 days had flower buds. Even a 4-h treatment with BA(50 µM) followed by culture in the basic medium inducedflowering. This suggests that the effect of BA is inductive.A similar effect of BA was observed in strain 381, a sensitiveshort-day plant, but not in strain 441 or 6746. Even in the absence of BAd in the medium, a 24-h treatment withBA induced flowering, but the induced state disappeared rapidlyafter the 5th-6th day. BAd was effective when given after theBA treatment and had no significant effect when added duringthe BA treatment. BA given after a single inductive dark periodalso promoted flowering in strains 441 and 381. BAd seems towork to sustain the induced state or to promote the developmentof flower buds rather than inducing flowering. A short-term treatment with nicotinic acid (NA) at 200–500µM was as effective as 10µM BA, but that with salicylicacid (SA) was ineffective at all concentrations tested. 5-C1-SAand EDDHA were also effective, although not as effective asBA. (Received April 10, 1986; Accepted July 12, 1986)     

Conversion of Lysine to L-Pipecolic Acid Induces Flowering in Lemna paucicostata 151

The natural occurrence of L-pipecolic acid and conversion oflysine to L-pipecolic acid in Lemna paucicostata 151 were demonstrateddefinitively by GC-MS. The strong flower-inducing activity ofL-pipecolic acid has already been demonstrated. Thus, the presentstudy indicates that the effect of lysine on flowering is mediatedby L-pipecolic acid. (Received June 30, 1997; Accepted August 22, 1997)     

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.     

Effect of Heat-Treated Noradrenaline on Flowering in Lemna

In a previous study, heat-treated noradrenaline induced flowering of the short-day plant Lemna paucicostata Hegelmaier 151. In the present study, we found that heat-treated noradrenaline also had flower-inducing activity in short-day L. paucicostata strains 441 and 6746 and in long-day L. gibba strain G3. The flower-inducing activity in these plants was enhanced by water homogenates of eggplant (Solanum melongena L.).     

Gibberellin and CCC Effects on Flowering and Growth in the Long-day Plant Lemna gibba G3

The application of gibberellic acid (GA₃) to the non-rosette long-day plant Lemna gibba G3 at concentrations from 0.1 to 100 mg/l did not induce flowering on short days and inhibited flowering on long days at concentrations of 1 mg/l and higher. On both short and long days GA₃ concentrations above 1 mg/l caused a decrease in frond size and fresh and dry weight, but an increase in the rate of frond production and thus an increase in the # VF (number of vegetative fronds). Identical results were obtained when gibberellin A₇ was used instead of GA₃.     

Role of Salicylic Acid and Benzoic Acid in Flowering of a Photoperiod-Insensitive Strain, Lemna paucicostata LP6

Lemna paucicostata LP6 does not normally flower when grown on basal Bonner-Devirian medium, but substantial flowering is obtained when 10 μm salicylic acid (SA) or benzoic acid is added to the medium. Benzoic acid is somewhat more effective than SA, and the threshold level of both SA and benzoic acid required for flower initiation is reduced as the pH of the medium is lowered to 4.0. SA- or benzoic acid-induced flowering is enhanced in the simultaneous presence of 6-benzylaminopurine (BAP), although BAP per se does not influence flowering in strain LP6. Continuous presence of SA or benzoic acid in the culture medium is essential to obtain maximal flowering. A short-term treatment of the plants (for first 24 h) with 10 μm SA or benzoic acid, followed by culture in the basal medium containing 1 μm BAP can, however, stimulate profuse flowering. Benzoic acid is more effective than SA, and the effect is more pronounced at pH 4 than at 5.5. Thus, under these conditions, flowering is of an inductive nature. Experiments with [¹⁴C]SA and [¹⁴C]benzoic acid have provided evidence that at pH 4 there is relatively more uptake of benzoic acid than SA, thus leading to an increased flowering response. The data obtained from the experiments designed to study the mobility of [¹⁴C]SA and [¹⁴C]-benzoic acid from mother to daughter fronds indicate that there is virtually no mobility of SA or benzoic acid between fronds.     

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)     

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.     

Factors Affecting the Water-sensitive Phase of Flowering in the Short Day Plant Lemna perpusilla

The flowering of Lemna perpusilla strain 6746 is inhibited by daily transfers to water for short periods during a sensitive phase. Supplementing the water with Ca(NO₃)₂ partially reverses the inhibition of flowering while MgSO₄ increases the inhibition. The inhibition by MgSO₄ is overcome by low concentrations of Ca(NO₃)₂. Flower-promoting activity was detected in water and in MgSO₄ solutions that had been incubated with plants under dark but not light conditions. The prevention of this effect by light appears to be photosynthetic rather than to depend on phytochrome. The activity is destroyed by autoclaving but not by brief boiling. This loss of a flower-promoting material may explain the inhibiting effect on flowering by transfers to water.     

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)