THE RELATIONSHIP BETWEEN THE PROMOTION OF ELONGATION OF FERN PROTONEMATA BY LIGHT AND GROWTH SUBSTANCES

Germinating spores of the fern Onoclea sensibilis L. were grown in darkness, so that they developed as filaments (protonemata). Brief daily exposure of the filaments to red, far-red or blue light increased the rate of filament elongation. Filament elongation was also promoted by indoleacetic acid. When filament elongation was promoted with both indoleacetic acid and exposure to light, the growth promotions caused by red and far-red light were additive to auxin-induced growth. Blue light promoted elongation only at sub-optimal concentrations of auxin. Elongation induced by guanine was additive to red- and far-red-induced elongation. Gibberellic acid had no effect on elongation under any condition. Blue-light-induced elongation resembled auxin-induced elongation in its requirement for exogenous sucrose and sensitivity to inhibition by parachlorophenoxyisobutyric acid. Red and far-red light were active regardless of the presence or absence of sucrose and promoted elongation at a concentration of parachlorophenoxyisobutyric acid which completely inhibited blue-light-induced elongation.     

PHOTOMORPHOGENESIS IN PTERIS VITTATA: I. PHYTOCHROME-MEDIATED SPORE GERMINATION AND BLUE LIGHT INTERACTION

1. Spores of the fern Pteris vittata did not germinate under totaldark conditions, while an exposure of the spores to continuouswhite light brought about germination. The germination was mosteffectively induced by red light and somewhat by green and far-red,but not at all by blue light. The sensitivity of spores to redlight increased and leveled off about 4 days after sowing at27–28. The promoting effect of red light could be broughtabout by a single exposure of low intensity. Far-red light givenimmediately after red light almost completely reversed the redlight effect, and the photoresponse to red and far-red lightwas repeatedly reversible. The photoreversibility was lost duringan intervening darkness between red and far-red irradiations,and 50% of the initial reversibility was lost after about 6hr of darkness at 27–28. These observations suggest thatthe phytochrome system controls the germination of the fernspore.
2. When the imbibed spores were briefly exposed to a low-energyblue light immediately before or after red irradiation, theirgermination was completely inhibited. The blue light-inducedinhibition was never reversed by brief red irradiation givenimmediately after the blue light. The escape reaction of redlight-induced germination as indicated by blue light given aftervarious periods of intervening darkness was also observed, andits rate was very similar to that determined by using far-redlight. Spores exposed to blue light required 3 days' incubationin darkness at 27–28 to recover their sensitivity tored light. The recovery in darkness of this red sensitivitywas temperature-dependent. It is thus suggested that an unknownbluelight absorbing pigment may be involved in the inhibitionof phytochrome-mediated spore germination.

(Received August 21, 1967; )     

Effects of Colchicine and Light on Cell Form in Fern Gametophytes. Implications for a Mechanism of Light-induced Cell Elongation

Spores of the fern, Onoclea sensihilis L., suffer a disruption of normal development when they are cultured on media containing colchicine. Cell division is inhibited, and the spores develop into giant spherical cells under continuous white fluorescent light. In darkness only slight cell expansion occurs. Spherical cell expansion in the light requires continuous irradiation. Photosynthesis does not seem to be involved, since variations in light intensity do not affect the final cell diameter; the addition of sucrose to the medium does not permit cell expansion in darkness; and the inhibitor DCMU does not block the light-induced cell expansion. Continuous irradiation of colchicine-treated spores with blue, red or far-red light produces different patterns of cell expansion. Blue light permits spherical growth, similar to that found under white light, whereas red and far-red light promote the reestablishment of polarized filamentous growth. Although ethylene is unable to induce polarized cell expansion in colchicine-treated spores in darkness or white and blue light, it enhances filamentous growth which already is established by red or far-red irradiation. Both red and far-red light increase the elongation of normal filaments (untreated with colchicine) above that of dark-grown plants, but under all 3 conditions the rates of volume growth are identical. Light, however, does cause a decrease in the cell diameters of irradiated filaments. These data are used to construct an hypothesis to explain the promotion of cell elongation in fern protonemata by red and far-red light. The model proposes light-mediated changes in microtubular orientation and cell wall structure which lead to restriction of lateral cell expansion and enhanced elongation growth.     

PHYTOCHROME ACTION IN ORYZA SATIVA L.: I. GROWTH RESPONSES OF ETIOLATED COLEOPTILES TO RED, FAR-RED AND BLUE LIGHT

1. Under continuous irradiation, the growth of intact rice coleoptilewas strongly inhibited by red light, and somewhat preventedby blue and far-red light. The inhibitory effect of red lighton coleoptile elongation was caused by a low-energy brief irradiation,and a single exposure of 1.5 kiloergs cm^–2 incidentenergy of red light brought about the 50% inhibition. This photoinhibitionof growth was observed only after the coleoptile had elongatedto about 10 mm or longer. The red light-induced effect was reversedby an immediately following brief exposure to far-red light,and the photoresponses to red and far-red light were repeatedlyreversible. The escape reaction of red lightinduced effect tookplace at a rate so that 50% of the initial reversibility waslost within 9 hr in darkness at 27. The inhibition by bluelight and reversal by far-red irradiation was also achievedrepeatedly with successive treatments of the coleoptiles. Theevidence for a low intensity red far-red reversible controlof coleoptile growth, indicative of control by phytochrome,seems clearly established in etiolated intact seedlings.
2. Incontrast, the elongation of apically excised rice coleoptilesegments was promoted by a brief exposure to red light in 0.02M phosphate buffer, pH 7, and the effect was almost completelynullified by an immediately subsequent exposure to far-red light.It becomes evident that the growth of intact coleoptiles wasinhibited by a exposure to red light, while that of excisedsegments in a buffer was rather promoted by red irradiation.The direction of red light induced responses, either promotiveor inhibitory, depends upon the method of bioassay using intactcoleoptiles or their excised segments.

(Received July 24, 1967; )     

STIMULATION OF NITRATE NET UPTAKE AND REDUCTION BY RED AND BLUE LIGHT AND REVERSION BY FAR-RED LIGHT IN THE GREEN ALGA ULVA RIGIDA1

The steady-state levels of nitrate, nitrite, and ammonium were estimated in the green alga Ulva rigida C. Agardh in darkness after addition of 0.5 mM KNO₃ and irradiation with red (R) and blue (B) light pulses of different duration (5 and 30 min). The net uptake of nitrate was very rapid. Seventy-five percent of the nitrate added was consumed after 60 min in darkness. Although uptake was stable after R or B, efflux of nitrate occurred within 3 h in the dark control and when R or B were followed by far-red (FR) irradiation. The internal nitrate concentration after 3 h in darkness was similar after R and B light pulses; however, the intracellular ammonium was higher after R than after B. The intracellular nitrate and ammonium decreased when FR tight pulses were applied immediately after R or B. Thus, the involvement of phytochrome in the transport of nitrate and ammonium is proposed. Nitrate reductase activity, measured by the in situ method, was increased by both R and B light pulses. The effect was partially reversed by FR light. Nitrate reductase activity was higher after 5 min of R light than after 5 min of B. However, after 30-min light pulses, the relative increase in activity was reversed for R and B. We propose that phytochrome and a blue-light photoreceptor are involved in regulation of nitrogen metabolism. Nitrate uptake and reduction correlates with previously detected light-regulated accumulation of protein in Ulva rigida under the same experimental conditions.     

THE EFFECT OF LIGHT ON THE CELLULAR COMPONENTS OF POLARIZED GROWTH IN BEAN INTERNODES

First internodes of light-grown bean seedlings exposed to supplementary red and far-red light and those of dark-grown seedlings were sectioned and studied to determine the effects of irradiation on the cellular components of polarized growth. Cell counts and measurements of epidermis, cortex, and pith are given. Increased length of internodes of far-red-treated plants was caused by both increased rate and increased duration of cell elongation. The effect of far-red light is interpreted as a reversal of the accelerating effect of light upon cell maturation. It is suggested that investigations of the mechanism of the red, far-red response of stems be concerned with the processes involved in cell elongation. In darkness, rate and duration of cell division as well as rate and duration of cell elongation were greater than in any of the irradiated plants, indicating that only part of the photocontrol of stem elongation is mediated through the red, far-red system.     

Photosensory mechanisms in the lettuce seedling hypocotyl

Summary A number of differences in the responses of Great Lakes lettuce seedlings to blue and far-red light indicate that more than one photo-sensitive pigment is involved in the photo-inhibition of hypocotyl elongation under highenergy conditions. In far-red light the inhibitory effect is restricted to young seedlings and is of limited duration; after 24 hours in far-red a rapid growth rate similar to that of plants maintained in darkness is resumed, despite continued irradiation. The onset of inhibition is relatively slow. Blue light, in contrast, exerts a strongly inhibitory effect on elongation at any age, and a slow rate of growth persists throughout the entire irradiation period. The onset of inhibition is very rapid. Furthermore, even when the inhibition in far-red had already been exhausted after prolonged exposure, transfer to blue light resulted in a prompt reduction in growth rate. Also the effect of far-red is almost completely lost after a pre-irradiation with red light which does not affect the response to blue. It is concluded that the responses to blue and far-red light in Great Lakes lettuce are not mediated by a single pigment system and that a distinct blue-sensitive pigment is present in addition to phytochrome. Red light has a number of different effects depending on conditions: (1) a pretreatment with red light almost completely prevents the inhibitory effect of a subsequent far-red irradiation, (2) a brief terminal treatment with red increases the inhibitory effect of either far-red or blue light; this is reversed by far-red, and (3) prolonged exposure to red light given alone increases the growth rate relative to darkness, because the more rapid elongation rate characteristic of young seedlings continues for longer with red light than in plants grown in darkness throughout.     

AN INTERPRETATION OF DOSE-RESPONSE CURVES FOR LIGHT-INDUCED CELL ELONGATION IN FERN PROTONEMATA

Protonemata of Onoclea sensibilis and Diyopteris filix-mas elongate in response to both red and far-red light. The promotion caused by far-red is larger than that caused by red light. This phenomenon differs from a typical response to phytochrome, the photoreceptor pigment immediately suggested by the activity of red and far-red light. The phenomenon has been explained by two different hypotheses, one of which holds that phytochrome is solely responsible for the response, whereas the other postulates an interaction between phytochrome and P₅₈₀, a yellow-green light absorbing pigment, to account for the response. The hypothesis that phytochrome is the sole photoreceptor leads to some specific predictions concerning the shapes of the dose-response curves for light-induced protonema elongation. These predictions were tested with both continuous and short-term irradiation. In all instances saturating far-red light caused greater elongation than did saturating red light, and no dose of red light duplicated the activity of saturating far-red light. Other experiments tested the interactions of red and far-red light and the effects of different doses of yellow-green light on protonema elongation. The results of many of the experiments were not in agreement with the hypothesis that phytochrome is the sole photoreceptor, whereas they were in agreement with the assumption that filament elongation is controlled by both phytochrome and P₅₈₀.     

Photomorphogenesis of the Gynophore, Pod and Embryo in Peanut, Arachis hypogaea L.

Darkened excized gynophores ceased to elongate after 8–10days in vitro and started to form a pod. Gynophore elongationwas inhibited to a greater extent in total darkness than underlow irradiance, while pod and embryo growth was stimulated indarkness only. Intact gynophores, enclosed in transparent vials containingglass beads, continued to elongate in both light and darkness.In light the elongating gynophores thickened as they penetratedbetween the glass beads, forming a seedless pod at the bottomof the vials. In the dark the elongating gynophores producedsmall pods in which the seeds had started to grow. Excized gynophores elongated in vitro under continuous whitelight at a rate similar to that of intact exposed gynophores.The rate of elongation in vitro, was lower under continuousblue or red-enriched light, than under white light, and wasfurther reduced under continuous far-red irradiation. Pods didnot form during any of the continuous irradiation treatmentsbut only after transfer to darkness, the largest pods formingafter continuous far-red irradiation. As little as 10 min daily exposure to red or far-red irradiancehad the same effect on gynophore elongation as continuous irradiation.Pods formed only when the daily periods of far-red irradiationwere 30 min or less. Reducing the daily exposures to 2 min decreasedthe time to onset of pod formation from 30 to 16 days. Far-redfollowing red irradiation was effective in inhibiting gynophoreelongation stimulated by red irradiation. Pod formation in red/far-redirradiation was only 50 per cent of that observed in far-redirradiation. The involvement of light in continual gynophoreelongation and in the concomitant inhibition of proembryo growthis discussed. Arachis hypogaea L., peanut, gynophore, photomorphogenesis, embryo development, pod development, proembryo     

EFFECTS OF VISIBLE AND ULTRAVIOLET RADIATION ON THE GERMINATION OF PHACELIA TANACETIFOLIA

Schulz , Sister M. Richardis , O.P., and Richard M. Klein . (N. Y. Bot. Gard., N. Y., N. Y.) Effects of visible and ultraviolet radiation on the germination of Phacelia tanacetifolia. Amer. Jour. Bot. 50(5): 430–434. Illus. 1963.—Germination of Phacelia tanacetifolia was suppressed by exposure to white light increasing with intensity and length of illumination. The light effect decayed during 24 hr of darkness. Seeds were most sensitive to the suppressive effects of light 13–17 hr after the beginning of imbibition. Light suppression was caused by a photocatalytic reaction. Wavelengths causing the suppression lie in the far-red, red, blue, near-ultraviolet and far-ultraviolet regions of the spectrum. At equal energies, blue light was less effective than far-red, red or ultraviolet radiation. There was no evidence for the existence of the phytochrome system. Simultaneous irradiation with red and blue light or simultaneous irradiation with red and far-red induced a synergistic repression of germination. The presentation of different wavelengths in various sequential patterns markedly altered the germination response. An interaction between elevated temperatures and visible radiation affecting germination response was also noted.     

EFFECTS OF RED AND FAR-RED ILLUMINATION ON THE ELONGATION OF FERN PROTONEMATA AND RHIZOIDS

The elongation of fern protonemata is controlled by red andfar-red light in an atypical fashion. Red light promotes theelongation of young plants but inhibits the elongation of olderplants. Far-red light promotes elongation regardless of filamentage, and the maximum promotion by far-red is greater than thepromotion which red light causes in young filaments. The elongationof rhizoids is under typical red, far-red control. Red lightpromotes elongation, and a period of far-red illumination followingred light treatment negates the promotive effects of red light. ¹ Present address of the authors: Dept. of Bacteriology andBotany, Syracuse University, Syracuse, New York, U. S. A. (Received November 5, 1962; )     

BLUE LIGHT, PHYTOCHROME AND THE FLOWERING OF LEMNA PERPUSILLA 6746

Lemna perpusilla 6746 was grown on HUTNER'S medium with sucroseunder light schedules combining red, blue and far-red light.As shown earlier, brief red exposures added to a continuousblue schedule inhibit flowering although either schedule alonepermits it; hence red and blue act together in establishinga long day (flower inhibiting) condition. However, the red exposurerequired to inhibit flowering is greater with high intensitythan with low intensity continuous blue, suggesting in additiona blue-red antagonism. Blue light reverses the effects of abrief red exposure closing a blue or far-red main photoperiod,but it also reverses the effects of a brief far-red exposureclosing a red photoperiod. Thus, blue can act either like redor like far-red, depending on the situation. All effects ofblue light on the flowering of L. perpusilla 6746 are consistentwith the notion that it establishes a Pfr level intermediatebetween those established by red and far-red light; the postulationof an additional photoreaction to explain the effects of blueseems unnecessary. ¹Research carried out at Brookhaven National Laboratory underthe auspices of the U. S. Atomic Energy Commission.     

Photocontrol of germination of cucumis anguria l

Germination ofCucumis anguria was inhibited by white, blue (B), and far-red (FR) irradiation and promoted by darkness and red (R) irradiation. The effect of white light was greater when supplied after rather than before the dark period. Darkness was more effective in reversing the effect of FR than FR in reversing the effect of darkness. FR was also more effective than B. When darkness followed B pretreatments, final germination percentage was higher than with FR pretreatment. R fully reversed the inhibitory effect of FR.     

Green light stimulates early stem elongation, antagonizing light-mediated growth inhibition

During the transition from darkness to light, the rate of hypocotyl elongation is determined from the integration of light signals sensed through the phototropin, cryptochrome, and phytochrome signaling pathways. In all light conditions studied, from UV to far-red, early hypocotyl growth is rapidly and robustly suppressed within minutes of illumination in a manner dependent upon light quality and quantity. In this study, it is shown that green light (GL) irradiation leads to a rapid increase in the growth rate of etiolated Arabidopsis seedlings. GL-mediated growth promotion was detected in response to constant irradiation or a short, single pulse of light with a similar time course. The response has a threshold between 10(-1) and 10(0) micromol m(-2), is saturated before 10(2) micromol m(-2) and obeys reciprocity. Genetic analyses indicate that the cryptochrome or phototropin photoreceptors do not participate in the response. The major phytochrome receptors influence the normal amplitude and timing of the GL response, yet the GL response is normal in seedlings grown for hours under constant dim-red light. Therefore, phytochrome activation enhances, but is not required for, the GL response. Seedlings grown under green, red, and blue light together are longer than those grown under red and blue alone. These data indicate that a novel GL-activated light sensor promotes early stem elongation that antagonizes growth inhibition.     

Light inhibition of internode elongation in green plants

The clongation of the first internode of fully greenVigna sinensis L. is inhibited by white light (W). This inhibition is fluence-rate dependent between 0 and 70 Wm^–2. The kinetics of elongation rate in the light after darkness were investigated with linear displacement transducers. The internode elongation rate does not exhibit any endogenous rhythm. A rapid inhibition occurs during the first 2 or 3 h after the onset of light, and a second type of inhibition (slow reaction) increases from the beginning to the 8th hour of light. The rapid inhibition is not fluence-rate dependent between 20 and 70 Wm^–2, but the slow reaction is. There is no rapid inhibition in a low fluence rate white light to high fluence rate white light transition, only the slow reaction is observed. The responses to different wavebands, i.e., blue light (B), yellow and green light (YG), and red light (R), are the same for the two inhibition reactions. Each waveband used separately does not reproduce the full effect observed in W. Results show a stimulation with B, a greater inhibition activity with YG than with R, and a synergistic action of B and R which when given together lead to an inhibition similar to that obtained in W. Plants returned from the light to darkness progressively recover a high elongation rate without any latent period. The W light regulating internode elongation rate is mainly perceived by the growing internode itself.Abbreviations B blue light - D darkness - F far-red light - HW high fluence rate white light - LW low fluence rate white light - R red light - W white light - YG yellow and green light     

Light germination ofAnthoceros miyabeanus spores

The effects of light on the spore germination of a hornwort species,Anthoceros miyabeanus Steph., were investigated. Spores of this species were photoblastic, but their sensitivities to light quality were different. Under either continuous white, red or diffused daylight, more than 80% of the spores germinated, but under blue light none or a few of them germinated. Under continuous far-red light or in total darkness, the spores did not germinate at all.Anthoceros spores required red light irradiation for a very long duration, i.e., over 12–24 hr of red light for saturated germination. However, the spore germination showed clear photo-reversibility by repeated irradiation of red and far-red light. The germination pattern clearly varied with the light quality. There were two fundamental patterns; (1) cell mass type in white or blue light: spores divide before germination, and the sporelings divide frequently and form 1–2 rhizoids soon after germination, and (2) germ tube type in red light: spores germinate without cell division, and the single-cell sporelings elongate without cell division and rhizoid formation.     

Growth and Dormancy in Lunularia cruciata (L.) Dum: VI. GROWTH REGULATION BY DAYLENGTH, BY RED, FAR-RED, AND BLUE LIGHT, AND BY APPLIED GROWTH REGULATORS AND CHELATING AGENTS

Experiments with photoperiods ranging from 2 to 24 h confirmthat 8 h light per day is optimal for Lunularia: there is nogrowth in the dark or in continuous light, which causes therapid onset of dormancy. Short-day cycles intercalated amonga series of continuous light cycles promote growth; in cycleslonger than 24 h very long dark periods are detrimental. Withvery short photoperiods (5 min) red light promotes growth moreeffectively than white light at higher intensity; far-red actsas dark. The growth effects of red and far-red light breaks(3 min) depended on the time of application; red light inhibitedin the middle but promoted at the beginning of the 16-h darkperiod of a short day; far-red light had the opposite effect;in each case red and far-red effects were reversible by theother wavelength. Blue light gave the same response as red includingthe reversibility of far-red effects and vice versa. Surprisingly,significant effects of 5 min red, blue, and far-red irradiationwere also found in the middle of the main high-intensity white-lightperiod, red and blue promoting growth, far-red reducing it;again there was ready reversibility of the effects. Growth promoters of higher plants are generally inhibitory toLunularia or have little effect; among growth retardants TIBA,Phosphon D, and CCC gave a slight promotion of growth. EDTApromoted growth (cell numbers) very significantly while 8-hydroxyquinolinewas initially inhibitory, but had a marked latent promotingeffect when subsequently washed from the thalli.     

EFFECT OF BLUE AND YELLOW LIGHT DURING THE LATER DEVELOPMENTAL STAGES OF SPHAEROBOLUS

When fruiting cultures of Sphaerobolus are transferred from continuous light to darkness the discharge of global masses continues for 1 day but then stops for the next few days. Experiments are reported in which this darkness is interrupted after 24 hr by brief (0.5-2 hr) treatment with light of different wavelengths and of equated low intensity (ca. 100 lux). Interruption by blue (ca. 448 mμ) or by green (ca. 500 mμ) light has no effect, but treatment with yellow (ca. 585 mμ) or red (ca. 650-700 mμ) leads to substantial discharge 24 hr later. If, however, the yellow treatment is followed immediately with blue there is little or no discharge; but if the order of this treatment is reversed, a high level of discharge results. This is somewhat greater than that resulting from treatment with yellow light alone. If, following a yellow treatment there is an interval of several hours before a blue treatment, the blue has less effect in negating the action of the yellow light. It is shown that, although in the final light-sensitive stages in development of the sporophore before it opens, yellow and red light are stimulatory but blue and green are not; in the phototropic response of the mature sporophores blue light is effective and yellow is not.     

Role of red light in hair-whorl formation induced by blue light in Acetabularia mediterranea

After a pre-treatment with red light, hair formation at the growing tip of the siphonaceous green alga Acetabularia mediterranea Lamour. (= A. acetabulum (L.) Silva) can be induced by a pulse of blue light. Red light is needed again after the inductive blue-light pulse if the new whorl of hairs is to develop within the next 24 h. In order to investigate the role of this red light, the duration of the red irradiation was varied and combined with periods of darkness. The response of hair-whorl formation was dependent on the total amount of red light, regardless of whether the red irradiation followed the blue pulse immediately or was separated from it by a period of darkness. Furthermore, periods of exposure to the photosynthesis inhibitor 3-(3,4-dichlorophenyl)-1-1dimethylurea had a similar effect to darkness. Both observations indicate that this red irradiation acts as a light source for photosynthesis. Whether or not the red light had an additional effect via phytochrome was tested in another type of experiment. The dependence of hair-whorl formation on red-light irradiance in the presence of simultaneous far-red irradiation was determined for the pre-irradiation period as well as for the irradiation period after the blue pulse. In both experiments, far-red light caused a small promotion of hair-whorl formation when low irradiances of red light were used. However, these differences were attributable to a low level of photosynthetic activity (which in fact was measurable) caused by red light reflected in the growth chamber. Furthermore, lowering the proportion of active phytochrome by far-red light would be expected to suppress hair-whorl formation. The influence of far-red light was also tested in a strain of Acetabularia mediterranea that developed hair whorls in about 20% of cells even when kept in complete darkness after the blue-light pulse. Far-red irradiation had no effect. These results strongly indicate that phytochrome is not involved in hair-whorl formation. Rather it is concluded that the effects of red light are caused by photosynthesis.Abbreviation DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

Action spectra for the inhibition of growth in radish hypocotyls

In etiolated seedlings of Raphanus sativus L. the inhibition of hypocotyl elongation by continuous light showed a major bimodal peak of action in the red and far-red, and two minor peaks in the blue regions of the spectrum. It is argued that, under conditions of prolonged irradiation, phytochrome is the pigment controlling the inhibition of hypocotyl elongation by red and far-red light, but that its mode of action in far-red is different from that in red. A distinct pigment is postulated for blue light.Abbreviations B blue - FR far red - G green - R red - HIR high irradiance reaction - P_r and P_fr red and far red absorbing forms of phytochrome - R red