APICAL GROWTH OF PROTONEMATA IN ADIANTUM CAPILLUSVENERIS. I. RED FAR-RED REVERSIBLE EFFECT ON GROWTH CESSATION IN THE DARK

Apical growth of individual protonemata in Adiantum capillus-veneris was microphotographically observed before, during and after light treatment. When single-celled protonemata precultured under continuous red light were transferred to darkness, the apical growth continued for the next 24 hr at a rate somewhat slower than that under continuous red light, but the rate significantly decreased thereafter and growth ceased within 72 hr in the dark. The growth in the dark was strongly inhibited by a brief irradiation with far-red light given immediately before the dark period, and the effect of far-red light was fully reversed by subsequent red light. This reversibility was repeatedly observed, suggesting the involvement of a phytochrome system.
The intracellular localization of the phytochrome system in the protonemata was studied, using a narrow-beam irradiator. The results showed that the photoreceptive sites of far-red light are not localized in any particular region of the cell.     

STUDIES ON THE FORMATION AND SPROUTING OF AERIAL TUBERS IN BEGONIA EVANSIANA ANDR. X. TUBERIZATION UNDER LONG-DAYS AND IN DARKNESS

1. Aerial tuber formation of Begonia evansiana Andr. known totake place usually in response to short-day conditions occurredalso under long-day conditions, provided a part of the photoperiodswas maintained at a lower temperature (chillng). Such a changeof the critical daylength was marked in degree when the chillingtemperature was from 9° to 13°. The effectiveness ofthe chilling was more pronounced when it was given during thelater part of photoperiods, namely, just before nyctoperiods,than when given during the early part. No promotion of the chillingeffect by sugar application was found. 2. If the plant was previously subjected to chilling under illumination,aerial tuber formation occurred in continuous darkness. Themagnitude of this dark tuberization increased with decreasingthe temperature and with prolonging the duration of the chilling. 3. If the plant was previously exposed to chilling, aerial tuberformation occurred in response to a single photoperiodic cycle,whose critical dark length was shorter than that in the standardcondition. The magnitude of the tuberization was increased withthe prolongation of the chilling period. The effectiveness ofthis previous chilling survived over one day even under illuminationand a temperature of 30°. In a plant unexposed to the chilling,tuber formation required at least two cycles of short-days. 4. The aged plant which is known to tuberize in darkness wasunable to respond to a single short-day. 5. Upon a modification of Gregory's scheme of the process ofshort-day response, the above findings were inclusively explained. (Received August 2, 1963; )     

The Mode of Flower-Inhibiting Action of Ethylene in Pharbitis nil

The inhibitory effect of ethylene on photoperiodic flower inductionin Pharbitis nil was investigated in relation to the time ofethylene application. Ethylene applied during an 18-h dark periodnot only made the dark period non-inductive, but also greatlyinhibited the flower-inducing effect of the 2nd 18-h dark periodgiven 6 h after the end of the first dark period. The seconddark period was inductive when it was given 30 h after the endof the first dark period, during which ethylene was applied.Ethylene applied during the light period prior to an inductivedark period had no inhibitory effect, suggesting that ethylenegiven during the dark period produces some flower-inhibitingentity. (Received April 17, 1987; Accepted June 17, 1987)     

SUCCESSIVE PROCESSES INVOLVED IN THE GERMINATION RESPONSE OF NASTURTIUM SEEDS

1. The seeds ofNasturtium palustreDC. do not germinate, eitherin the light or darkness, at various constant temperatures,but require for their full germination a certain period of alow temperature (5°) applied immediately after light irradiation.These results indicate the existance of at least two processes,a light-dependent process and a low temperature-requiring process,in the initiation of germination ofNasturtiumseeds. Experimentalevidence indicated further that the light exposure causes twodifferent processes in the seed germination. 2. When a dark period at 23° was inserted between the lightirradiation and the low temperature treatment the germinationwas suppressed. The inhibitory effect of the inserted dark periodat 23° was eliminated by a short irradiation during thedarkness (light-break). 3. Prolonged exposure ofNasturtium seeds to any concentrationof gibberellin brought about no germination when exposure wasgiven in complete darkness. The germination was promoted onlywhen light irradiation was applied to the seeds. A short applicationof gibberellin at a fairly high concentration was, however,remarkably effective for the germination even in the darkness,and the germination was inhibited as the gibberellin applicationwas lengthened. It was considered that gibberellin could substitutefor the combined effect of light irradiation and low temperaturetreatment to induce the germination of Nasturtium seeds, andthat gibberellin was inhibitive toward the reactions followingthe above treatments which induced the germination (Received October 31, 1996; )     

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; )     

Environmental factors controlling the time of flower-opening in Pharbitis nil

Pharbitis nil, strain Violet, subjected to various photoperiods(24-hr cycle at 24?C) bloomed about 10 hr after light-off whenthe light period was 10 hr or longer, and about 20 hr afterlight-on when the light period was shorter. The higher the temperature(20–30?C) during the dark period, the later the time offlower-opening, with the temperature during the last half ofthe dark period having a stronger effect than that during thefirst half. In continuous dark or light, flower buds of Pharbitis openedabout every 24 hr at all temperatures tested between 20 and28?C, which suggests the participation of a circadian rhythmin determining the time of flower-opening. A light pulse given6–12 or 28–36 hr after the onset of the dark periodgreatly advanced the phase of this rhythm (8–10 hr). Phasedelay of this rhythm could not be obtained by light pulses givenat any time. (Received September 29, 1979; )     

DE- AND RE-GENERATION OF CHLOROPLASTS IN THE CELLS OF CHLORELLA PROTOTHECOIDES: IV. EFFECTS OF 5-FLUOROURACIL, DIHYDROSTREPTOMYCIN, CHLORAMPHENICOL AND ACRIDINE ORANGE ON THE PROCESSES OF GREENING AND DIVISION OF "GLUCOSE-BLEACHED" ALGAL CELLS

1. The "glucose-bleached" cells of Chlorella protothecoides, whichwere obtained by the method described previously, were transferredto a glucose-free medium containing basal mineral nutrientsalone in the dark, and after a certain period of time, the cellsuspension was supplied with urea and light to induce the greeningof cells. At different times before and after the provisionof urea and light, the inhibitors were applied to the cultureto test their effects upon the process of greening.
2. Markedgreening of the glucose-bleached cells occurred aftera lagperiod in the control culture. 5-Fluorouracil inhibitedthecell greening strongly when it was applied at differenttimesbefore the provision of urea and light. When applied aftertheprovision of urea and light, the suppressive effect of 5-fluorouracilgradually decreased with the delay of its application. No inhibitiveeffect was observed when the uracil analogue was added laterthan the 12th hr after the provision of urea and light, thetime around which the chlorophyll formation started in the controlculture. On the other hand, the cell division was much morestrongly affected by 5-fluorouracil. Even when it was appliedat the 18th hr after the provision of urea and light, the celldivision was completely halted, indicating that the greeningand division of the glucose-bleached cells are separate processes.Different mechanisms of action of the uracil analogue towardsthese two processes were suggested.
3. Dihydrostreptomycin showedits strongest suppressive effectwhen added at the beginningof the dark incubation of algalcells in the glucose-free medium,and with the delay of application,its effect was progressivelyreduced, even during the periodof the dark incubation. Thesuppression, however, was stillmarked when it was applied atthe 15th hr.
4. Chloramphenicol was found to inhibit stronglythe chlorophyllformation and protein synthesis, but, to a muchlesser extent,RNA synthesis. Acridine orange suppressed thecell greeningand division at such a low concentration as 1.5µg/ml.
5. Based on these observations it was concludedthat synthesesof nucleic acid and protein are essential processesfor thegreening of the glucose-bleached algal cells. Successiveeventsoccurring in the greening process were discussed.

(Received March 9, 1965; )     

STUDIES ON THE FORMATION AND SPROUTING OF AERIAL TUBERS IN BEGONIA EVANSIANA ANDR. IX. EFFECTS OF TEMPERATURE ON TUBER INITIATION

The effects of temperature on the aerial tuber initiation ofBegonia evansiana Andr. in response to short-day condition wereinvestigated. Tuberization was inhibited by relatively low and high temperaturesduring the dark periods. The optimal nycto-temperature was 23°and hardly changed by not only photo-temperature but also daylength.There were two temperature-sensitive phases in the dark period;one came at its beginning, and the other later one came at varioustimes depending on the length of the light period. Low temperatureswere effective at both of these sensitive phases, but high temperatureshad an influence only at the later one. Photo-temperatures exerted little influence on tuberizationunder the sub-optimal daylength, but the lower temperatureswere promotive under longer daylengths. (Received August 2, 1963; )     

Effect of High-intensity Light Given Prior to Low-temperature Treatment on the Long-day Flowering of Pharbitis nil

Pharbitis nil, strain Violet which had been exposed to high-intensitylight (18,000 lux at 23?C) for 7 days followed by a low-temperaturetreatment (13–14?C) for 7 days initiated flower buds evenunder continuous light, but plants given these treatments inreverse order failed to bud. Three days of high-intensity lightat 23?C was most effective in promoting the flower-inducingeffect of the subsequent low-temperature period. Six days oflow temperature following the 3-day high-intensity light periodinduced near-maximum flowering response. DCMU (5?10^–6M) given during the high-intensity light period inhibited flowering,but when given during or after the low-temperature period itwas ineffective. DCMU at the same concentration given before,during or after an inductive 16-hr dark period at 26?C did notinhibit flowering. Sucrose, ATP, NADPH and some other reducingagents tested did not nullify the DCMU effect nor substitutefor the effect of high-intensity light. But, the high-intensitylight effect could be substituted, at least partly, by 5-chlorosalicylicacid, 3,4-dichlorobenzoic acid and some other benzoic acid derivatives,which are highly effective in inducing long-day flowering inthe short-day plant, Lemna paucicostata. (Received October 20, 1981; Accepted February 3, 1982)     

Studies on chloroplast development in Chlamydomonas reinhardtii I. Effect of brief illumination on chlorophyll synthesis

When dark grown cells of Chlamydomonas reinhardtii y-1 mutantwere exposed to continuous light, an immediate transformationof small amounts of protochlorophyll(ide), which had been presentin the dark grown cells, to chlorophyll was observed. Afterthis, there was a slow accumulation of chlorophyll lasting for2.5-3 hr before the start of exponential synthesis. Initialaccumulation of chlorophyll was distinctly slower at a highlight intensity (13,000 lux) than it was at moderate intensitiesof light (2,000–5,000 lux). However, the exponential synthesisof chlorophyll started after the same 2.5–3 hr of illumination. A brief pre-illumination of cells followed by incubation indarkness was effective in promoting chlorophyll synthesis undersubsequent continuous illumination at high, as well as moderatelight intensities. Pretreatment alleviated retardation of theinitial chlorophyll accumulation by light of high intensity.The promoting effect of preillumination on chlorophyll synthesiswas sufficient, even when a light impulse as short as 10 secwas given. However, the effect was dependent on length of thedark period after the short pre-illumination. The full extentof this effect was observed when the dark period was about 2.5–3hr long. Further dark incubation gradually decreased the effect. On the basis of these findings, it is assumed that a factor(s)responsible for promotion of chlorophyll (or chloroplast) synthesisin the process of greening of dark grown cells is produced duringthe dark period after a brief pre-illumination, and that thefactor is turned over at a relatively fast rate. The possiblenature of the presumed factor is discussed in relation to chloroplastdevelopment. ¹Present address: Department of Biology, Faculty of Science,Kobe University, Nada-ku, Kobe, Japan. (Received August 18, 1970; )     

Spectral Dependence of Night-break Effect on Photoperiodic Floral Induction in Lemna paucicostata 441

A single dark period of longer than 8 hr induced flowering inLemna paucicostata 441 cultured in E medium. Monochromatic lightsof 450, 550, 650 and 750 nm with a half-power bandwidth of 9nm given for 10 min at the 8th hour of a 14-hr dark period inhibitedflowering. The fluence rates required for 50% inhibition were10, 0.5, 0.1 and 3 µmol m^–2. sec^–1, respectively.When applied between the 4th and the 10th hour of the dark period,lights of 450, 550 and 650 nm were inhibitory showing a maximumeffect at the 8th hour. But 750-nm light completely inhibitedflowering when applied at any time during the first 8 hr ofthe dark period. The inhibitory effect of 750-nm light givenat the beginning of the dark period was totally reversed bya subsequent exposure to 650-nm light, and the fluence-responsecurves for the effect of 750-nm light given at the 0, 4th and8th hour were essentially the same. This suggests that the presenceof P_FR is crucial for the floral initiation throughout the first8 hr of the inductive dark period. The role of phytochrome inthe photoperiodic flower induction of L. paucicostata is discussed. (Received January 4, 1982; Accepted March 19, 1982)     

EFFECT OF TWILIGHT ON PHOTOPERIODIC INDUCTION IN SOME SHORT DAY PLANTS

Light-sensitivity of the first and the last processes in theinductive dark period, and the effect of twilight on photoperiodicinduction were investigated with four short day plants. In Oryza sativa (Akebono), the first and the last processesare relatively light-insensitive, and the photoperiodicallyeffective day length under natural conditions is consideredto be equal to the astronomical day length. In Biloxi soybean and Perilla frutescens, the first processis re latively light-insensitive, but the last process is moresensitive. Effective dark period seems to begin when twilightis 50200 lux in the evening and continue until it is about 10lux in the morning. In Xanthium saccharatum, both the first and the last processesare relatively light-sensitive, but the former is more sensitivethan the latter. Effective dark period seems to begin when twilightis 110 lux in the evening and continue until it is 1050 luxin the morning. ¹Present address: Laboratory of Genetics and Plant Breending,Faculty of Agriculture, University of Osaka Prefecture, Sakai-City,Osaka. (Received February 17, 1961; )     

Studies on the Photoreceptors for the Promotion and Inhibition of Flowering in Dark-Grown Seedlings of Pharbitis nil Choisy

Three-day-old etiolated seedlings of Pharbitis nil were exposedto red light for 10 min and sprayed with N⁶-benzyladenine beforetransfer to a 48-h inductive dark period, after which they weregrown under continuous white light. A second red irradiationpromoted flowering when given at the 5 and 24th hour of theinductive dark period but inhibited flowering at the 10 and15th hour. Far-red light inhibited flowering when given at anytime during the first 24 h of the dark period. Red/far-red reversibilitywas clearly observed at the 0, 5, 10 and 24th hour, but notat the 15th hour when both red and far-red lights completelyinhibited flowering. The action spectrum for the inhibition of flowering at the 15thhour of the inductive dark period had a sharply defined peakat 660 nm and closely resembled the absorption spectrum of theP_R form of phytochrome. The photoreceptors involved in thesephotoreactions are discussed. (Received June 10, 1983; Accepted July 6, 1983)     

Photoreversibility of flower initiation in Lemna perpusilla as affected by the light quality of the main light period

Reversible floral responses of Lemna perpusilla to red and far-redlights appeared only at the beginning of the inductive darkperiod when the 8 hr photoperiod consisted of white or red light.When blue or far-red light was given during the 8 hr photoperiod,the far-red given at the beginning of the dark period scarcelyinhibited flowering; red/far-red reversibility newly appearedat the middle of the dark period. This indicates that the photoregulationsystem in the flowering of L. perpusilla can be converted fromthe Pharbitis type to the Xanthium type by changing the lightquality of the main photoperiod from white or red to blue orto far-red, which is known to be effective for the so-calledhigh-energy photoreaction of photomorphogenesis. (Received July 2, 1975; )     

Perithecial formation in Gelasinospora reticulispora III. Inhibitory effects of near-UV and blue light during the inductive dark period

Growing hyphae of Gelasinospora reticulispora required a continuousdark period prior to photoinduction of perithecia. The inductivedark period was interrupted by brief exposure of the hyphaeto white light so that the formation of perithecia no longertook place. Photosensitivity of the hyphae in terms of the light-breakeffect gradually changed during the inductive dark period. Sensitivityreached its maximum at the 18th hr of the dark period when anirradiation of 1?10⁵ ergs cm^–2 of near-UV light or 4?10⁴ergs cm^–2 of blue-light was sufficient for the light-break.Red and far-red light had no effect at all. The light-breakeffect was limited to the irradiated portion of the hyphae anddid not affect any unirradiated portions. Inhibitory effecton perithecial formation of continuous white light could betotally replaced for several days with intermittent irradiationof near-UV or blue light if given for 5 min every 4 hr. (Received December 18, 1973; )     

EFFECT OF CHROMATIC LIGHTS ON PHYCOBILIN FORMATION IN A BLUE-GREEN ALGA, TOLYPOTHRIX TENUIS

1. The formation of phycobilin pigments in a blue-green alga Tolypothrixtenuis was investigated with special reference to the effectsof preillumination with colored lights.
2. It was discoveredthat the algal cells are capable of formingphycobilin pigmentsin the dark, if they have been previouslyilluminated for severalhours in the presence of CO₂.
3. The color of light applied inthe later period of preillumination(chromatic illumination)was found to affect the ratio of phycoerythrinto phycocyaninformed in the subsequent dark period. A greenlight acceleratesthe dark-formation of phycoerythrin, a redlight that of phycocyanin,and the two lights counteractingwith each other in their effects.
4. These directive effects of the "chromatic illumination" canbe accomplished within a very short period, for instance, in3 minutes if it is preceded by sufficient "preillumination"with an incandescent or day light fluorescent light. The reactionsoccurring during the period of chromatic illumination does notrequire the presence of CO₂ and the aerobic condition.
5. Thealga can be grown heterotrophically when supplied with casaminoacids and glucose. Under such a condition the alga forms phycocyanintogether with chlorophyll and carotenoids, but not phycoerythrin.
6. On the basis of the results obtained, a tentative scheme forthe biosynthesis of phycobilin pigments in the alga was proposed,assuming the light-induced formation of unknown precursors whichare converted into phycocyanin and phycoerythrin in the subsequentdark period.

(Received July 4, 1960; )     

Light Actions in the Germination of Cocklebur Seeds: III. EFFECTS OF PRE-TREATMENT TEMPERATURE ON GERMINATION RESPONSES TO FAR-RED LIGHT AND ON DARK GERMINATION IN THE RED LIGHT-REQUIRING UPPER SEEDS

Esashi, Y., Oota, H., Saitoh, H. and Kodama, H. 1985. Lightactions in the germination of cocklebur seeds. III. Effectsof pre-treatment temperature on germination responses to far-redlight and on dark germination in the red light-requiring upperseeds.—J. exp. Bot. 36: 1465-1477. Red light (R) responsiveness in R-requiring upper cocklebur(Xanthium pennsylvanicum Wallr.) seeds changed in differentpatterns during a soaking period at different temperatures.At temperatures above 23°C, the responsiveness increasedand then decreased. At lower temperatures (3–18°C),however, it continued to increase throughout an experimentalperiod. The lower temperatures caused germination in the subsequentdark at 33°C, regained the R responsiveness and acquiredthe dark germinability when subsequently exposed to 8°C,to an extent proportional to the duration of the chilling. Far-red (FR) was inhibitory to germination in an earlier soakingperiod at lower temperatures, but its effect gradually decresed,and finally turned promotive. The negative FR response was repeatedlycontrolled by the following R irradiation. However, the positiveFR response was enhanced by an immediate R irradiation, andFR/R reversibility occurred after the second FR. In contrastto the R responsiveness and dark germinability, the positivegermination response to FR was not induced by soaking at 3°C,in which the growth of the axial tissue as a photoreceptivesite did not occur at all. Similarly, it was not manifestedwhen the seeds soaked at 33°C were subsequently subjectedto 8°C. Key words: Cocklebur seeds, dark germination, far-red light, low temperature, red light, seed germination, Xanthium pennsylvanicum     

LEAF INITIATION CORRELATES WITH TIME OF MAXIMAL SENSITIVITY OF THE SDP XANTHIUM (ASTERACEAE) TO DARK INTERRUPTION

The hypothesis was tested that the well-known maximal sensitivity to a light break at or near the middle of the dark period of short-day plant Xanthium is correlated with a specific stage of leaf initiation. Samples were collected at various hours before and during noninductive 6-hr dark periods. Lengths of leaf primordia were calculated from serial transverse sections. The reproducible results confirmed that leaf initiation occurred at or near middark under the 18:6 hr light: dark growing conditions. The author suggests the working hypothesis that for a light break to be effective in nullifying the effect of a “long” night in photoperiodically sensitive plants, the light must react with a specific early stage of leaf initiation.     

Promotion and Inhibition of Inflorescence Growth by Long Days in Short-day Plants

Results of previous investigators have indicated that long periodsof light intercalated between inductive short-day cycles havean inhibitory effect on inflorescence growth in short-day plants.The present experiments show that such light periods can eitherpromote or inhibit inflorescence growth in Xanthium pemtsylvanicumand Chenopodium amaranticolor depending on their previous degreeof induction. Intercalated light exerts an inhibitory influence on the inductiveprocesses occurring during the dark period which follows itwhen unifoliate Xanthium plants have been previously exposedto not more than one short day and when fully foliated Chenopodiumplants have been previously exposed to not more than one ortwo short days. When plants are more strongly induced initially,an intercalated light period has a very marked promoting effecton the dark period succeeding it. In Xanthium this stimulatoryeffect increases with the duration of the light period up toan optimum of approximately 80 hours. It is suggested on the basis of available evidence that thepromotive effect of such intercalated light possibly affectsthe sensitivity of the apex to inductive stimuli and that itsinhibitory effect acts on the inductive processes occurringin the leaves.     

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.