The Effects of Red, Far-red, and Blue Light on the Geotropic Response of Coleoptiles of Zea mays

The effects of red, far-red, and blue light on the geotropicresponse of excised coleoptiles of Zea mays have been investigated.Seedlings were grown in darkness for 5 or 6 days, exposed tovarious light treatments, and then returned to darkness fordetermination of the geotropic response. The rate of response of the coleoptiles is decreased after theyhave been exposed to red light (620–700 mµ, 560ergs cm^–2sec^–1 for the 24 hrs, but not for the 4hrs, preceding stimulation by gravity. Furthermore, their rateof response is greatly reduced if they are exposed to red lightfor 10 min and then returned to darkness for 20 hrs before geotropicstimulation. At 25° C an interval of 6 to 8 hrs elapses between a 10-minexposure to red light and the first detectable decrease in thegeotropic response of the coleoptile. This interval can be lengthenedby exposing the seedlings to low temperatures (0° to 2°C) after the light treatment but cannot be greatly shortenedby increasing the duration of exposure to red light. Using a standard procedure of exposing 5-day-old etiolated seedlingsto light for various times, replacing them in darkness for 20hrs and then determining the response of the coleoptiles to4 hrs geotropic stimulation, it has been found that: (a) Exposureto red light for 15 sec significantly decreases the geotropiccurvature of the coleoptiles and that further reduction occurson increasing the length of the light treatment to 2 and 5 min.(b) Far-red light has no effect on the geotropic response ofthe coleoptiles but it can completely reverse the effect ofred light. After repeated alternate exposure to red and far-redlight the geotropic response of the coleoptile is determinedby the nature of the last exposure, (c) Complete reversal ofthe effect of red light by far-red radiation only occurs whenexposure to far-red follows immediately after exposure to red.The reversing effect of far-red radiation is reduced if a periodof darkness intervenes between the red and far-red light treatments,and is lost after a dark interval of approximately 2 hrs. The effect of red light on the rate of geotropic response ofthe coleoptiles is independent of their age and length at thetime of excision. Blue light acts in a similar way to red light, but the seedlingsare less sensitive to blue than to red light. Coleoptiles grown throughout in a mixture of continuous, weak,red, and far-red light have a lower rate of geotropic responsethan etiolated coleoptiles.     

Flowering of the long-day plant, Lemna gibba, under short-day schedules composed of red and far-red light

Flowering in Lemna gibba, a long-day duckweed, can be inducedunder a short-day condition when the photoperiodic regimes areR₇FR₃ (7 hr red followed by 3 hr far-red), R₅FR₅ and R₃FR₇.This indicates the necessity of a proper balance between redand far-red effects for flowering. The flowering induced bythese regimes is inhibited by a brief exposure to red givenat the start of darkness and this inhibition is reversed bysubsequent exposure to far-red. Thus, the red/far-red reversibleeffect is found only at the beginning of darkness for floweringof L. gibba. However, flowering of L. gibba is promoted by a red light breakgiven near the middle of a 14 hr dark period. The promotiveeffect is not reversed by subsequent exposure to far-red, i.e.,the effect of the red break converts from inhibition to promotionas when given later in the dark period, which suggests the involvementof a timing mechanism. (Received July 21, 1973; )     

PHOTOCONTROL AND TEMPERATURE DEPENDENCE OF GERMINATION OF RUMEX SEEDS

1. Light is not obligatory for the germination of the seed ofRumex obtusifolius L. subsp.agrestis DANSER, which has beenregarded as being a typical light sensitive seed. Even in continuousdarkness, a short period of high (30°) or low temperature(5°) treatment evokes germination very readily. 2. Germination is markedly promoted by 1 min exposure to a redlight and this red light effect is completely removed by 1-hrexposure to a far-red light. Alternations of the red and far-redradiation bring about an alternate promotion and inhihibitionof germination. 3. When a dark interval is inserted between the red and thefar-red treatments, inhibition of germination becomes less distinctas the duration of darkness increases. When the seeds are irradiatedwith far-red prior to red, with an inserted darkness, germinationpromotion due to the red light also decreases with the durationof inserted darkness. 4. Complicated interdependence between the light and temperatureeffects are demonstrated. This suggests a participation of somereactants besides pigments in the photoreaction. 5. The observed interdependence between the light and temperatureeffects on the germination of Rumex seeds implies that, if,as BORTHWICK has assumed, two forms of pigment, viz., a far-red-absorbingform and a red-absorbing one, are participating in the photoreaction,they should be presumed to coexist from the start of imbibition. (Received September 27, 1960; )     

Effect of far-red light pulse on induction and production of flowers in Lemna paucicostata 6746 in darkness

A short-day duckweed, Lemna paucicostata 6746, was exposed tocontinuous darkness at 26^?C, and the changes in the floral parameters(3) due to far-red and/or red light pulse given at various timesof the dark period were studied. Parameters a (vegetative growth rate) and (flowering ratio)were respectively decreased and increased with a far-red lightpulse given at the outset of the dark period. The decreaseda and the increased remained almost unchanged until the 7thhour, but returned to their initial levels thereafter. The far-redlight actions on a and were reversed by subsequent exposureto red light. Parameter P₁ (pre-flower induction period) wasextended by 1 day when far-red and/or red pulse was given atabout the 7th hour of the dark period. A far-jed pulse givenat the outset of the dark period only affected parameter P₂(flower induction period). Although the sensitivity of P₂ tored light increased with time, its sensitivity to far-red lightremained constant and at about the 7th hour was equally sensitiveto far-red and red lights. Both red and far-red pulses givenlater than the 7th hour were increasingly ineffective on P₂.The red/far-red reversibility occurred only for the action onP₂ of the far-red pulse applied during the early dark period.Parameter P₄ (flower production period) varied rhythmicallyin length with a far-red puke, the maximum shortening and extensionbeing induced by the pulse given at about the 7th and 19th hours,respectively. The sensitivity of P₄ to red light also changedrhythmically with an inverse phase angle to the rhythmic responseto farred light, and the far-red and red light actions werereversed respectively by subsequent red and far-red lights. These findings suggested that multiple timing devices includingan hourglass-type clock and a circadian clock are involved induckweed flowering. (Received October 25, 1978; )     

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     

The Influence of Light on Geotropism in Cress Roots

Light affects the growth and orientation of roots of cress seedlings(Lepidium sativum L. cv. Curled). The effects are manifest eitheras increased rates of geotropic curvature or, if the roots arehorizontal, as distorted and crinkled forms of growth. Blue,red, and far-red irradiation can bring about these effects,but with differences of detail: at equal fluence rates duringthe period of geostimulus, blue is more effective than red atincreasing the rate of geocurvature; however, with irradiationprior to a geostimulus, only the stimulatory effects of redirradiation persist for 2–4 h of darkness. Short periods(5 min) of radiation, if given at the time of geostimulus, enhancegeocurvature, again with blue most, and far-red least, effective,but there are no clear indications of red/far-red reversibility.The possibility of there being more than one photosystem responsiblefor the effects of white light on the geotropic responsivenessof roots is discussed.     

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 Light, pH, Temperature, and Crowding on Megaspore Germination and Sporophyte Formation in Marsilea

Megaspore germination and sporophyte formation of Marsilea vestitaH. and G. was studied under different light, pH, temperature,and crowding conditions during a 6 d experimental period. Maximumgermination and sporophyte development occurs under relativelylow light intensity. Darkness and high light intensity inhibitsporophyte development. Selected wavelengths of light (red,far-red, green, blue) and darkness reduce both megaspore germinationand sporophyte development as compared to white light. Megasporesand sporophytes show maximum development at 25 ?C in light,whereas their development is reduced at all temperatures indarkness. The optimum pH range for megaspore germination ispH 7–8 and that for sporophyte development is pH 7. Sporocarpcontents alter the pH of unbuffered acidic and basic media towarda more optimal growth condition (pH 6–8) for megasporegermination. Megaspore germination and sporophyte developmentvary inversely with conditions of crowding. Root and leaf growthon developed sporophytes is very similar in most treatments.     

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; )     

Control of Flowering of Xanthium pensylvanicum by Red and Far-red Light

A study was made of the effects of various durations, intensities and combinations of red and far-red light interruptions on the flowering responses of Xanthium pensylvanicum Wallr. A dual response to treatments of far-red light was observed. In short dark periods, far-red light alone did not greatly affect flowering but was able to overcome the inhibition of flowering caused by red light. In dark periods longer than 15 hours, far-red inhibited flowering and added to rather than overcame the inhibition by red light. The dark period length required for far-red inhibition remained the same whether far-red was given at the start or at the eighth hour of darkness.

In 48-hour dark periods Xanthium showed 3 responses to additions of red and far-red light breaks: A) response to red light; B) response to far-red light; and C) response to red followed by far-red light. Red light given any time in the first 30 hours of darkness overcame the inhibitory effect of far-red light given at either the start or the eighth hour of darkness. Red light given later than the thirtieth hour did not overcome the far-red effect.

Approximately the same energy of red light was required to overcome the inhibitory effect of far-red at the second hour of darkness as was required to produce maximum red light inhibition at the eighth hour. Although far-red light was most inhibitory when given early in a long dark period, approximately the same energy of far-red light was required to saturate the far-red response at the fourth, eighth and sixteenth hours.

The results are discussed in relation to other reports of far-red inhibition of flowering in short-day plants.

     

The relationship between red and far-red light on flowering of the long-day plant, Lemna gibba

Lemna gibba, a long-day duckweed, can be induced to flower whenthe 10 hr white photoperiod is extended with red or far-redlight. The 10 hr red photoperiod is also effective in inducingflowering when followed by a far-red extension, but a red extensionis ineffective. When 2 hr of far-red light are given immediately after the 10hr red photoperiod, the following red as well as the far-redextension can induce flowering, indicating that the 2 hr far-redlight plays an important role as a starting factor for induction.This red or far-red extension is effectively replaced by a redbreak given at a proper time in the darkness which follows the2 hr far-red light as the starting factor. The effect of thered break in not cancelled by subsequent exposure to far-red,which synergistically promotes flowering. However, a red break given immediately after a proper periodof far-red extension further promotes flowering. The phase sensitiveto the red break coincides with that sensitive to the red breakgiven in darkness. The effect of the red break is reversed bysubsequent exposure to far-red, contrary to the effect of thered break in darkness. Using these results, relation between red and far-red lighton flowering in L. gibba is discussed. (Received July 17, 1971; )     

Growth and Dormancy in Lunularia cruciata (L.) Dum.: IV. LIGHT AND TEMPERATURE CONTROL OF RHIZOID FORMATION IN GEMMAE

The first sign of initiation of growth in dormant gemmae ofL. cruciata is the formation of rhizoids. Gemmae in the cupcannot ‘germinate‘ until exposed to substrate conditionsallowing the outward diffusion of a growth inhibitor. Rhizoidproduction depends on temperature and light. With long lightperiods rhizoids are formed over a wide range of temperatures.Transference to darkness after 2 h white light causes about50 per cent of gemmae to produce rhizoids, and these are formedonly between 20 and 25 °C. Outside these temperature limitsthe percentage of gemmae with rhizoids soon drops to zero. Althoughrhizoid production is prevented in total darkness, gemmae remainalive for well over 6 months. Red light for as little as 5 spromoted, and far-red light inhibited, rhizoid formation inthe dark. Coumarin and indol-3yl-acetic acid can substitutefor light and partly reverse the effect of far-red irradiation.     

Measurement of the Critical Nyctoperiod by Lemna paucicostata 6746 Grown in Continuous Light

The short-day duckweed Lemna paucicostata 6746 could be inducedto flower in two days at 26C when continuous illumination forentrainment was followed by continuous darkness. This 48-h darkperiod or the minimum darkness requirement for floral inductionwas called the induction period. The length of the inductionperiod (IP) was routinely computed as the number of 24-h cyclesusing the equation of regression of flower number in logarithmon culture time. A light pulse given about 7 h after the startof the induction period increased the apparent IP value fromtwo to three, suggesting that the interrupted first day hadfunctioned as a noninductive day. A pulse given at any otherpart of the induction period did not modify the IP value. Thelight-sensitive part is probably the inducible phase, and thefirst 7-h period of darkness terminated by it seems to be thecritical nyctoperiod. These and relevant facts suggest thatthe light-off oscillator measures the critical night length,7 h. Either red or far-red irradiation at the inducible phase extendedthe IP value by one. No red/far-red photoreversibility was detected.As expected, however, red or far-red irradiation of any otherpart of the critical nyctoperiod could not modify the IP value. (Received February 8, 1985; Accepted May 14, 1985)     

Effect of Plant Growth Regulators on Flower-Opening of Pharbitis nil

Flower buds of Pharbitis nil (due to open the next morning)cut from plants in the field before noon open very slowly bothin darkness and at a low temperature (20°C), unlike thebuds cut in the evening. On cool cloudy days, even the budscut in the evening open very slowly. Addition of sucrose, mineralnutrients or plant growth regulators other than ABA to the waterin which the cut buds were placed did not promote flower-openingunder such conditions, but addition of ABA (10–100 µM)greatly promoted it. IAA (100 µM) given alone or in combinationwith ABA suppressed floweropening completely. Mature flowerbuds placed in an ABA solution opened even under continuouslight at 25°C just as those kept in darkness without ABA;flower-opening occurred about 12 h after the application ofABA. ABA given to the buds in darkness at 25°C and thatgiven in continuous light at 20°C also advanced the timeof flower-opening. The action mechanism of ABA is discussed. ¹ This paper is dedicated to the memory of Dr. Joji Ashida,the first president of the Japanese Society of Plant Physiologist. (Received October 28, 1982; Accepted January 7, 1983)     

Germination of seeds in Jussiaea suffruticosa

Seeds of Jussiaea suffruticosa reach high germination percentagesonly when exposed to long periods of continuous illumination.The light reaction may be repeatedly reversed by short exposuresto red and far red light, thus being mediated by the phytochromesystem. Seeds also germinate at high percentages if exposedto various cycles of 1 hr light and 24 hr of darkness at 20°C.If the temperature in the periods of darkness is raised up to30°C or lowered to 10°C the promotive effect of lightis inhibited. High temperatures (35°C) during imbibitionhave a promotive effect, whereas a pure O₂ atmosphere decreasesthe response to light. KNO₃ and kinetin enhance the responseto light but do not provoke germination in the dark. Only ifseed coats are punctured or removed does germination in thedark occur. (Received January 14, 1969; )     

Periodical growth response of Lemna gibba G3 to light-break

Brief exposure to light promotes frond multiplication in Lemnagibba G3 in darkness. Extent of promotion changes periodicallywith the time of the light-break. Response curves are interpretedin terms of a superposition of two modes of growth responseto light-break, which are, respectively, under the control ofdifferent physiological timing devices; circadian oscillationand the hourglass-type clock. Circadian oscillation, which consistsof a half-cycle of increasing photophily followed by anotherhalf-cycle of declining photophily, starts at a light-on signaland continues for a few days with rapid damping. The 24-hr periodof oscillation is the same at temperatures ranging from 16 to26°C. The hourglass is released by a light-off signal to‘accumulate sand’ or to increase photophily in asigmoidal way with time and is temperature-sensitive; the tempoof‘sand accumulation’ being quicker at 21°Cthan at 16 or 26°C. Oscillation is hastened to fade-outat 21°C, most likely due to the accelerated pace of thehourglass. Red and far-red reversibility is disclosed in bothmodes of growth response. (Received December 31, 1969; )     

Variations in Tiller Dynamics and Morphology in Lolium multiflorum Lam.Vegetative and Reproductive Plants as affected by Differences in Red/Far-Red Irradiation

Lolium multiflorum Lam, plants were grown in a growth room undertwo light sources with red/far-red ratios of 1·62 and0·84 but similar photosynthetically active radiation.In both situations the capacity to produce new tillers and thelight available per tiller decreased with canopy growth. Tilleringwas further reduced by the low red/far-red ratio while lightinterception and plant dry weight were unaffected by this treatment.In both reproductive and vegetative plants under the lower red/far-redratio the time between leaf expansion and the appearance ofa tiller in its axil was increased and the proportion of ‘maturebuds’ that developed was reduced. Irradiation with lowred/far-red advanced the reproductive development and increasedthe number of fertile tillers per plant. It also caused longerleaf sheaths, blades and reproductive shoots. The results suggestthat as canopy density increases the lower light interceptionper tiller and the photomorphogenic effect of low red/far-redratios may reduce the capacity to produce new tillers. Lolium multiflorum, Lam., annual ryegrass, tillering, tiller growth, leaf growth, flowering, light quality.     

Phytochrome Control of Chlorophyll and Carotenoid Accumulation in Sorghum bicolor

Etiolated Sorghum bicolor seedlings manifested a significantmorphological response to short term irradiations by red andfar-red light and to a continuous far-red light. Accumulationof chlorophylls in white light and carotenoids in darkness isunder red/far-red reversible control as well as along with theeffectiveness of ‘High Irradiance Reaction’. Phytochromeis also found to eliminate the lag phase during the accumulationof chlorophylls and carotenoids in white light. (Received March 11, 1981; Accepted May 2, 1981)     

Effects of Blue Light Pretreatments on Internode Extension Growth in Mustard Seedlings after the Transition to Darkness: Analysis of the Interaction with Phytochrome

The effects of blue light (B) pretreatments on internode extensiongrowth and their possible interaction with phytochrome mediatedresponses were examined in Sinapis alba seedlings grown for11 d under 280 µmol m^–2 s^–1 of continuousblue-deficient light from low pressure sodium lamps (SOX). SupplementaryB (16 µmol m^–2 s^–1) caused no detectable inhibitionof the first internode growth rate under continuous SOX, butgrowth rate was inhibited after transfer to darkness. This effect,and the growth promotion caused by far-red bend-of-day' lightpulses were additive. The addition of B at 16 µmol m^–2s^–1 during 11 d, or only during the first 9 or 10 d orthe latest 0.75, 1 or 2 d of the SOX pretreatment caused approximatelythe same extent of inhibition after the transition to darkness.A single hour of supplementary B before darkness caused morethan 50% of the maximum inhibition. However, 24 h of lower fluencerates of B (4 or 7 µmol m^–2 s^–1) were ineffective.Covering the internode during the supplementary B period didnot prevent the response to B after the transition to darkness.Far-red light given simultaneously with B (instead of the SOXbackground) reduced the inhibitory effect of B. Above a given threshold fluence rate, B perceived mainly inthe leaves inhibits extension growth in subsequent darkness,provided that high phytochrome photo-equilibria are presentduring the irradiation with B. Once triggered, this effect doesnot interact significantly with the ‘end-of-day’phytochrome effect. Key words: Blue light, extension growth, phytochrome     

Influence of Environmental Stress on the Germination of Anabaena vaginicola Akinetes

Germination of akinetes of Anabeana vaginicola v. fertilissimaPrasad in response to environmental stress was studied. Additionof nitrate to the medium induced early and maximum germination(96 per cent), whereas less than half of the akinetes germinatedwhen either nitrate or phosphate was omitted from the medium.The pH range over which germination occurred was 7.0–9.0.The desiccated akinetes after rehydration germinated after acertain lag period, depending upon the dehydration state. Thetemperature optimum for germination and vegetative growth wasthe same (25 °C) and germination did not occur at 5 °Cor above 35 °C. The limit of heat shock tolerated was 55°C for 4 min. In addition to white light, only the red partof the visible spectrum induced germination. Ultraviolet radiationreduced germination rate presumably by inducing thymine dimersin DNA. The photoreactivating system (s) in akinetes is certainlynon-photosynthetic. LD₅₀ photon flux densities were 300 Jm^–2for akinetes and 240 Jm^–2 for vegetative cells. Anabaena vaginicola, blue-green alga, akinete, germination, environmental stress