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)     

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)     

Role of the Quality of Light in the Photoperiodic Flowering Response in Four Latitudinal Ecotypes of Chenopodium rubrum L.

The effect of the quality of light on the photoperiodic floweringresponse in four latitudinal ecotypes of Chenopodium rubrumwas examined. Two southern ecotypes, Sel-184 (50°10' N)and Sel-194 (34°20' N), displayed an obligate short-dayplant under white (W), red (R) and blue (B) light. Sel-372 (62°46'N),the most northern ecotype, was day-neutral in B and W lightand had an ambiphotoperiodic response in R light. Sel-374 (60°47'N) was an ambiphotoperiodic in B light and had a short-day responsein W and R light. In the B light regimens, the flowering ofSel-374 was modified from a typical ambiphotoperiodic to day-neutralresponse by changing the temperature from 20°C to 12°C. The photopriodic flowering response in the 8–16 hr photoperiodwas suppressed severely by the reducing light intensity from3,000 to 1,500 ergs.cm^–2.sec^–1, but that in continuousillumination was lowered only slightly by decreasing the lightintensity. The ambiphotoperiodic flowering response differedin its reaction to light; flowering in the 8-18 hr photoperiodrequired a high intensity light independent of the quality oflight, and flowering in the 24 hr photoperiod was promoted byB light. We considered the ambiphotoperiodic flowering responseto be a combination of the obligate short-day flowering responseand the flowering response for an extreme long-day condition,which is favored by B light. Therefore, this photoperiodic responseprobably is an intermediate step in the short-day and day-neutralresponses in day-neutralization. (Received December 8, 1980; Accepted February 20, 1981)     

Flowering Induced by Nitrogen Deficiency in Lemna paucicostata 151

Lemna paucicostata 151 is a weakly responsive short-day plantwhen grown in non-aseptic ten-fold diluted E medium supplementedwith 1 µM 6-benzyladenine, but it flowered even underlong-day conditions (continuous light) when grown in this mediumfor more than 14 days. On the 14th day of culture, the levelof endogenous nitrogen in the plants decreased to about 60%of that in the plants inoculated at the start of the culture.The flowering obtained under long-day conditions was suppressedby raising the concentration of nitrogen in the medium, whileit was induced more rapidly by lowering the concentration ofnitrogen in the medium. Benzyladenine did not cause floweringby itself, but it was required for the flowering that was inducedby a reduction in the level of nitrogen in the medium. Thus,the flowering observed under long-day conditions is due to nitrogendeficiency in the plants. Two inhibitors of proteases, bestatin and elastatinal, clearlyinhibited the flowering induced by nitrogen deficiency. It appears,therefore, that the induction or activation of some protease(s)is involved in the flowering that is induced by nitrogen deficiency. (Received March 19, 1991; Accepted August 16, 1991)     

Flowering of Cultivated Green and SAN 9789-Treated Chenopodium rubrum Plants Exposed to White,Blue, and Red Light

Green plants and plants devoid of photosynthetic pigments were compared with regard to their ability to flower under various growth conditions. Green plants of Chenopodium rubrum L. and plants treated with norflurazon SANDOZ-9789 (SAN) were grown on sucrose-containing media with or without hormones (GA₃, BA, IAA, ABA) under short-day photoperiodic or continuous illumination with white, blue, or red light. Green and SAN-treated albino plants produced flowers only under short-day conditions. The flowering of green plants was independent of the presence of sucrose and hormones in the medium as well as of the light quality. The albino plants produced flowers under white and blue light but did not flower in red light. The addition of GA₃ or BA to the medium induced flowering of albino plants exposed to red light. The functional interaction of photoreceptors in the flowering control is discussed.     

The Effects of Temperature and Light Integral on the Phases of Photoperiod Sensitivity inPetuniaxhybrida

Flowering in petunias is hastened by long days, but little isknown about when the plants are most sensitive to photoperiod,or how light integral or temperature affect such phases of sensitivity.The effects of these factors on time to flowering was investigatedusing reciprocal transfer experiments between long (16 h d^-1)and short days (8 h d^-1). The effect of light integral on thephases of photoperiod sensitivity was examined using two sowingdates and a shading treatment (53% transmission). The effectsof temperature were investigated by conducting reciprocal transferexperiments in glasshouse compartments at five temperature regimes(means of 13.7, 19.2, 22.3, 25.0 and 28.7 °C). The lengthof the photoperiod-insensitive juvenile phase of development,when flowering cannot be induced by any environmental stimulus,was sensitive to light integral; low light integrals prolongedthis phase, from 23 d at 2.6 MJ m^-2d^-1to 36 d at 1.6 MJ m^-2d^-1(totalsolar radiation). The length of this development phase was shortest(12.5 d) at 21 °C; it was longer under cooler (21 d at 13.5°C) and warmer temperatures (17.6 d at 28.3 °C). Afterthis phase, time to flowering was influenced greatly by photoperiod,with long days hastening flowering by between 28 and 137 d,compared with short days. Plants also showed some sensitivityto both temperature and light integral during this phase, butthe duration of the final phase of flower development, duringwhich plants were photoperiod-insensitive, was dependent primarilyon the temperature at which the plants were grown; at 14.5 °C,33.9 d were required to complete this phase compared with 11.4d at 25.5 °C. The experimental approach gave valuable informationon the phases of sensitivity to photothermal environment duringthe flowering process, and could provide the basis of a morephysiologically-based quantitative model of flowering than hashitherto been attempted. The information is also useful in thescheduling of lighting and temperature treatments to give optimalflowering times of high quality plants.Copyright 1999 Annalsof Botany Company Petunia,Petuniaxhybrida, juvenility, flowering, photoperiod, temperature, light integral, reciprocal transfer.     

Effects of Blue Light on the Vertical Colonization of Space by White Clover and their Consequences for Dry Matter Distribution

The morphology of white clover is very sensitive to the lightenvironment, especially to the ratio of red:far-red light andto photon irradiance. However, less is known about the effectsof blue light on clover morphogenesis. Cuttings of white cloverwere grown for 56 d in two controlled chambers receiving lightwith similar photosynthetic efficiency and phytochrome photoequilibriumstate but different levels of blue light: some plants were grownunder orange light (very low blue light, 0.02 µmol m^-2s^-1)or under white light containing blue light (83 µmol m^-2s^-1).Other plants were switched from white light to orange lightorvice versa,after 30 d. The absence of blue light modifiedthe growth habit of clover and raised the laminae in the upperlayer of the canopy by increasing petiole length, and petioleangle from the horizontal, and by raising stolons above theground surface. Moreover, the absence of blue light had no effecton total leaf area and total dry weight per plant, but increasedthe leaf area and biomass of petioles of the main axis. Largerpetioles and laminae were associated with the allocation ofmore dry weight to the petiole at the same petiole thicknessbut with thinner laminae. These results indicate that a decreasein blue light is involved in the perception of, and adaptationto, shading by the plant.Copyright 1997 Annals of Botany Company Biomass allocation; blue light; growth habit; leaf area; light quality; photomorphogenesis; Trifolium repensL.; white clover     

Growth Hormone Changes in Chrysanthemum morifolium: Effects of Environmental Factors Controlling Flowering

Simultaneous quantitative analyses have been made of the endogenouslevels of auxin- and gibberellin like substances, growth inhibitors,and auxin-oxidizing enzyme activity in the cold-requiring Chrysanthemummorifolium cv. Sunbeam subjected to different daylength, lightintensity and temperature regimes known to affect flowering.While little hormone or enzyme activity was found in extractsfrom unvernalized plants, a striking rise in auxin-oxidizingenzyme activity occurred rapidly after the end of cold treatment.Increased auxin activity was also recorded shortly after vernalization.At 28 °C both enzyme and auxin activity declined over aperiod of 3–4 weeks; at 20 °C this response was delayed.Gibberellin activity at 28 °C rose steeply about 2 weeksfrom vernalization and declined several weeks later; at 20 °Ca similar response was less marked. Low light intensity treatment,which may have increased endogenous auxin levels, or exogenousauxin application reduced gibberellin-like substance levelsand cause d devernalization.Phosphon D treatment also loweredgibberellin levels and prevented flowering. An extract fromvernalized plants containing gibberellin-like substances intensifiedthe flowering of partially vernalized test plants. Persistenceof high auxin activity in vernalized plants on long days wasassociated with failure to form normal flower buds. Stem elongationrates correlated in general with levels of endogenous auxin-and gibberellin-like substances. Significant amounts of an abscisin-likeinhibitor were found in extracts of flower buds. The mechanismof natural devernalization is discussed in relation to theseobservations.     

Light conditions of photoperiodic induction of flowering inChenopodium murale L. ecotype 197 - Early flowering long-day plant

A method of cultivation and effectiveness of different light sources and light regimes in photoperiodic induction of flowering in non-rosette long-day plantChenopodium murale L. ecotype 197 are described. Under the described conditions of cultivation 5 days, of continuous light produced by incandescent bulbs (TESLA 74 3x40 W, red 4.9 μWcm-²nn-¹, far-red 7.4 μWcn-2nm-¹, blue 0.25 μW cm-²nn-¹) induced flowering in the majority of plants.     

Effect of Low-intensity Red and Far-red Light and High-intensity White Light on the Flowering Response of the Long-day Plant Lemna gibba G3

The long-day plant Lemna gibba L., strain G3 exhibits a relatively low sensitivity to short, white-light interruptions given during the dark period of a short-day cycle. However, the plants are fairly sensitive to low-intensity red light treatments given during a 15-hour dark period on the third day of a 2LD-(9L:15D)-2LD-7SD schedule. Far-red light is almost as effective as red light, and attempts to reverse the red light response with subsequent far-red light treatments have not been successful. Blue light proved to be without effect. When plants were grown on a 48-hour cycle with 15 minutes of red light every 4 hours during the dark period, the critical daylength was reduced from about 32 hours to slightly less than 12 hours.

Continuous red light induced a fairly good flowering response. However, as little as 1 hour of white light each day gave a significant improvement in the flowering response over that of the continuous red light control. White light of 600 to 700 ft-c was more effective than white light of 60 to 70 ft-c. The white light was much more effective when divided into 2 equal exposures given 8 to 12 hours apart. These results suggest an increase in light sensitivity with regard to flower induction about 8 to 10 hours after the start of the light period.

     

Induction of flowering by nitrogen deficiency in Lemna paucicostata 441

Lemna paucicostata 441, a short-day plant, flowered even undercontinuous light in nitrogen-deficient, half-strength Hutner’smedium, when the endogenous level of nitrogen was decreasedto 1.4µg/mg fr wt or lower, but no flowering occurredin nitrogen-deficient, modified Hoagland medium when the endogenouslevel of nitrogen was similarly reduced. The failure to flowerin this medium can be ascribed to the presence of high concentrationsof calcium, the absence of EDTA, and low pH. Daylength-independent flowering induced by nitrogen deficiencywas greatly enhanced by the addition to the growth medium ofmicronutrients and EDTA at high concentrations. Among the micronutrients,zinc seemed to be the most important. (Received May 30, 1988; Accepted September 22, 1988)     

Effects of Light and Temperature on Flower-opening of Pharbitis nil

Flower buds of Pharbitis nil cut from plants growing in thefield opened rapidly when kept in darkness for 8 hr followedby continuous light at 20–25°C, but those kept indarkness for 4 hr opened promptly oniy when the temperatureduring the following light period was kept at 23°C or lower.Buds exposed to continuous light at 25°C did not open, butthose exposed to continuous light at 23°C opened slowly.At a lower temperature, the buds opened rapidly even in continuouslight. When the buds were placed in darkness at 25°C at13:30, 17:30 and 21:30 (artificial light from 17:30 to 21:30),they opened about 10 hr after the onset of darkness regardlessof the time of the onset of darkness, but when the buds werekept at 20°C in light from 13:30, 17:30 and 21:30, theyopened at 3:30–5:30 regardless of the time of transferto the lower temperature. The biological clock which controlsthe time of flower-opening is suggested to be easily reset bya light-off signal, but not by a shift from a normal to lowertemperature (20°C). At the lower temperature, the time offlower-opening probably is determined by the time of the latestpreceding light-off (or light-on) signal. ¹Dedicated to Professor Dr. Erwin Biinning on the occasion ofhis 75th birthday. (Received October 23, 1980; Accepted December 15, 1980)     

Inhibitory Action of Blue and Far-Red Light in the Flowering of Lemna paucicostata

In a new strain of short-day duckweed (Lemna paucicostata T-101), blue and far-red light-induced inhibition of flowering was investigated. Flowering of this strain failed to be induced under a short-day photoperiod of blue and far-red light, although it responded as a typical short-day plant in red and white light. When the short-day photoperiod of blue or far-red light was terminated by a 15 min red light pulse, flowering recovered completely. This inducing effect of red light was reversed by subsequent exposure to far-red light. Furthermore, it could be demonstrated that 30 min of blue light completely reversed the flowering inductive effect of 5 min red light and vice versa. Evidence is presented suggesting that the inhibitory action of blue and far red light may be due to the lowering of phytochrome P_fr levels below those required to start the dark reactions which lead to flowering. These results are discussed in relation to the time measurement system of photoperiodism.     

The Respiratory Costs of Nitrogen Fixation in Soyabean, Cowpea, and White Clover: II. COMPARISONS OF THE COST OF NITROGEN FIXATION AND THE UTILIZATION OF COMBINED NITROGEN

Plants of soyabean, cowpea, and white clover were grown singlyin pots in Saxcil growth cabinets at 23/18 °C, 30/24 °C,and 20/15 °C, respectively, until seed maturation or for85 d (white clover). Two populations were produced within eachspecies: one population effectively nodulated and wholly dependentfor nitrogen on fixation in the root nodules, and a second populationcompletely lacking nodules but receiving abundant nitrate nitrogen.In each species, the two populations were compared in termsof rate of gross photosynthesis, rate of shoot respiration,and rate of root respiration. Source of nitrogen had littleor no effect on rate of photosynthesis or shoot respiration.In contrast, the rate of respiration of the nodulated rootsof plants fixing their own nitrogen was greater, sometimes two-foldgreater, than that of equivalent plants lacking nodules andutilizing nitrate nitrogen. This superiority in terms of rateof root respiration was generally confined to the period ofintense nitrogen fixation. An analysis of the magnitude of thisrespiratory burden in terms of daily photosynthesis indicatesthat, in all three legumes, plants fixing their own nitrogenrespire 11–13% more of their fixed carbon each day thanequivalent plants lacking nodules and utilizing nitrate nitrogen.     

Some Effects of Light Intensity, Daylength and Temperature on Flowering and Pollen Tube Growth in the Watermelon (Citrullus lanatus)

The effects of light and temperature on flowering and pollentube growth were studied in watermelon [Citrullus lanatus(Thunb.)Matsum. and Nakai, cv. Early Yates] plants grown in controlledenvironment cabinets. All female flowers were pollinated inone group of plants; none was pollinated in the other group. Temperature increase from 25 ^°C to 35 ^°C with daylengthof 14 h and light intensity of 32 klx caused increase in flowernumber per plant, proportion of male flowers, ovary length anddiameter, ovule number per ovary, rate of pollen tube growthand percentage of penetrated ovules at 24 hand 48 h after pollination.Very few flowers were produced at 40 ^°C, but there was ahigh proportion of male flowers. Increase in daylength from14 h to 24 h at 25 ^°C with light intensity of 32 klx alsoincreased number of flowers per plant, ovary length and diameterand number of ovules per ovary but sex expression and rate ofpollen tube growth were unaffected. Reduction in daylength from14 h to 8 hat 25 °C and light intensity of 32 klx and reductionin light intensity from 32 klx to 8 klx at 25 ^°C and 14h daylength both produced an increase in the percentage of immatureovules. The presence of fruit on the vine resulted in fewerflowers per plant and in reduced ovary legnth and diameter underall conditions tested. The results are discussed in relation to the fruiting responseof the plant.     

Effects of Irradiance and Temperature on Flowering of Chrysanthemum morifolium Ramat. in Continuous Light

The short-day plant Chrysanthemum morifolium cv. Polaris initiatedflower buds in all irradiances of continuous light from 7.5to 120 W m^–2. As the irradiance increased, the transitionto reproductive development began earlier and the number ofleaves initiated before the flower bud was reduced. The autumn-floweringcultivars Polaris and Bright Golden Anne, and the summer-floweringGolden Stardust were also grown in continuous light at differenttemperatures; all initiated flower buds at temperatures from10 to 28 °C but only the buds of Golden Stardust developedto anthesis and then only at 10 and 16°C. Flower initiationbegan earliest at 16–22 °C, and the number of leavesformed before the flower bud was increased at 28°C. GoldenStardust was exceptional in that the number of leaves formedwas also increased at 10 °C. Axillary meristems adjacentto the terminal meristem initiated flower buds rapidly at 10°C but not at 28 °C in all three cultivars. These resultsare discussed in relation to the autonomous induction of flowerinitiation and the effects of the natural environment on floweringof chrysanthemum. Chrysanthemum morifolium Ramat, flowering, irradiance, temperature     

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)     

Different actions of red and blue or far-red lights in the photoperiodic tuberization of Begonia evansiana

The spectral dependence of Begonia evansiana in supplementarylight periods of photoperiodic tuberization and sprouting wasinvestigated. Supplementary application of red light inhibitedtuber development, thereby stimulating vegetative growth. Supplementaryblue or far-red light also suppressed tuber development, butbarely stimulated vegetative growth. However, both red and blue light, given at 6°C during themain light period or the supplementary light period, permittedthe tuberization under the subsequently given conditions ofeither long-days or darkness at 23°C. Blue light appliedafter 5-days of irradiation with white light at 10°C, showedalmost the same action as far-red light, which suppressed tuberizationin darkness. The nature and function of the pigments concernedin the photoperiodic responses are discussed. (Received October 11, 1968; )     

Thermomorphogenic and Photomorphogenic Control of Stem Elongation in Fuchsia Is Not Mediated by Changes in Responsiveness to Gibberellins

Stem elongation in Fuchsia × hybrida was influenced by cultivation at different day and night temperatures or in different light qualities. Internode elongation of plants grown at a day (25°C) to night (15°C) temperature difference (DIF+10) in white light was almost twofold that of plants grown at the opposite temperature regime (DIF−10). Orange light resulted in a threefold stimulation of internode elongation compared with white light DIF−10. Surprisingly, internode elongation in orange light was similar for plants grown at DIF−10 and DIF+10. Flower development was accelerated at DIF−10 compared with DIF+10 in both white and orange light. To examine whether the effects of DIF and light quality on shoot elongation were related to changes in gibberellin metabolism or plant sensitivity to gibberellins (GAs), the stem elongation responses of paclobutrazol-treated plants to applied gibberellins were determined. In the absence of applied gibberellins paclobutrazol (>0.32 μmol plant⁻¹) strongly retarded shoot elongation. This inhibition was nullified by the application of about 10–32 nmol of GA₁, GA₄, GA₉, GA₁₅, GA₁₉, GA₂₀, GA₂₄, or GA₄₄. The results are discussed in relation to possible effects of DIF and light quality on endogenous gibberellin levels and gibberellin sensitivity of fuchsia and their effects on stem elongation. Received October 4, 1997; accepted December 17, 1997     

The Effect of Cooling on Photosynthesis, Amounts of Carbohydrate and Assimilate Export in Sunflower

Sunflower plants (Helianthus annuus L.) grown at 30°C werecooled to 13°C in the light in atmospheric CO² or low CO²,or in darkness. Photosynthetic rate at 30°C after coolingwhole plants in atmospheric CO² for 12 h during a photoperiodwas significantly lower than at the start of the photoperiodcompared to plants cooled at low CO², those cooled in the darkand those maintained at 30°C. Amounts of sucrose, hexosesand starch in leaves at 13°C increased throughout a 14 hphotoperiod to levels higher than in leaves at 30°C, whereamounts of sucrose and hexoses were stable or falling after4 h. Carbohydrate accumulation at 13°C during this photoperiodwas more than twice that at 30°C. After three photoperiodsand two dark periods at 13°C carbohydrate levels in leaveswere still as high as at the end of the first photoperiod, butless carbohydrate accumulated during the photoperiods than duringthe first photoperiod, and more was partitioned as starch. Amountsof soluble carbohydrate in roots were greater after 14 h at13°C than in roots of plants at 30°C. Loss of ¹⁴C fromleaves at 30°C as a proportion of ¹⁴CO2 fixed by them at30°C, decreased after exposure of plants to 13°C inthe light for 30 min prior to ¹⁴CO²feeding. Results indicatean effect of cold on the transport process that was light-dependent.It is inferred that the reduction in the proportion of ¹⁴C lostfrom leaves after 10 h cooling was due to reduced sink demand,whereas the rise in the proportion of ¹⁴C lost from leaves after24 h reflects reduced photosynthetic rate. The coincidence ofreduced photosynthetic rate with raised carbohydrate levelsin leaves maintained at 30°C throughout, whilst the restof the plant was cooled to 13°C in the light implies feedbackinhibition of photosynthesis. This may reduce the imbalancebetween source and sink in sunflower during the first days oflong-term cooling. Key words: Temperature, carbon export, carbohydrates, photosynthesis, sunflower