EFFECTS OF RED AND FAR-RED RADIATION ON CELL DIVISION AND ELONGATION IN THE STEM OF PINTO BEAN SEEDLINGS

Nine-day-old Pinto bean seedlings, Phaseolus vulgaris L., were treated daily for 12 days with supplementary red or far-red radiation following daily exposure to 8 hr of daylight. Stem elongation was nearly exponential from the 4th to the 12th day of treatment and was about 2.9 times greater under far-red radiation. Cell division and cell elongation were promoted essentially equally by far-red radiation. There was virtually no difference in either the rate of leaf initiation or the duration of growth of internodes under the supplementary radiation.     

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; )     

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.     

BLUE LIGHT IN THE DEVELOPMENT OF FERN GAMETOPHYTES AND ITS INTERACTION WITH FAR-RED AND RED LIGHT

Two effects of blue light on the development of Onoclea sensibilis spores are demonstrated. Brief irradiation promotes the protonemal or filamentous type of growth, and the rate of filament elongation is greater than in darkness. Longer periods of irradiation induce the formation of 2-dimensional prothallia. Blue-light treatments which promote filament elongation interact with elongation-promoting far-red light. Far-red irradiation alone promotes filament elongation to a greater extent than blue light, but a blue-light irradiation, either following or preceding far-red treatment, strongly inhibits the far-red promotion. In darkness, a slow recovery from the blue-light-induced loss of sensitivity to far-red takes place. The recovery may be greatly accelerated by interposing a red-light treatment between blue and far-red irradiation.     

ROLE OF GROWTH SUBSTANCES IN THE FILAMENT GROWTH OF FUCHSIA HYBRIDA CV “BRILLIANT”

Filaments of Fuchsia hybrida cv “Brilliant” double in length within 24 hr after bud opening. Filament growth characterized by fresh wt increase and cell elongation was significantly inhibited in vitro by l-aminocyclopropane-l-carboxylic acid (ACC) but was not promoted by any growth regulator tested. Ions of Co²⁺ blocked the inhibitive effects of ACC in vitro suggesting that ethylene produced from ACC is the growth inhibiting substance. Ethylene levels surrounding the filaments within the closed bud decreased during development, and premature opening of the sepals which released the ethylene into the atmosphere resulted in rapid filament growth. The ACC levels were found to be much higher in the anthers than the filaments. This suggests that ethylene produced from floral organs other than filaments regulates filament elongation in Fuchsia. This is the first report of filament growth which cannot be promoted by application of growth regulators but which is inhibited by ethylene.     

THE ROLES OF AUXIN,ETHYLENE, AND ACID GROWTH IN FILAMENT ELONGATION IN GAILLARDIA GRANDIFLORA (ASTERACEAE)

Filament elongation and the role of auxin in this process in Gaillardia grandiflora was investigated. Filament elongation in vivo occurred just prior to anthesis and was accompanied by cell elongation and fresh weight increase. Filaments isolated and exposed to auxin in vitro grew more rapidly than controls and their growth was comparable to that of filaments in vivo. Furthermore, the natural auxin content of disc flowers (determined by double-standard isotope dilution analyses) increased just prior to anthesis and filament elongation. These results imply that auxin controls filament elongation. Applied ethylene slightly promoted filament elongation in vitro, and ethylene production of the flowers (determined by gas chromatography) slightly increased prior to filament growth. Fusicoccin and acidic buffers also stimulated elongation of isolated filaments. Thus, the role of auxin in controlling filament elongation in Gaillardia may involve stimulation of ethylene biosynthesis and acid growth.     

Light Dependence of Chloroplast Replication and Starch Metabolism in the Moss Polytrichum commune

Spores of Polytrichum conwtuine were grown on a mineral salt solution with or without sucrose and exposed to continuous white light, continuous darkness, red light and/or far-red light. With sucrose, germination and filament growth occurred in all conditions, Without sucrose, germination and filament growth occurred only in light. Two phytochrome mediated responses of the chloroplasts were demonstrated. Chloroplast replication occurred in continuous white light and red light of 15 min/6 hours. In continuous darkness and in far red light of 15 min/6 hours, the size of the chloroplasts increased; but no replication occurred. Both the chloroplast replication and chloroplast size were red, far-red light reversible. When changed from one continuous light environment to another, a lag period occurred before the chloroplasts responded to the new environment. Electron micrographs of sections and in vivo staining of the chloroplasts with iodine solution demonstrated that the change in size of the chloroplasts was at least partially due to the synthesis and degradation of starch.     

Response of excised Avena coleoptile segments to red and far-red light

Summary In seeking a simple, red light-promoted straight growth test in which phytochrome assays may be conducted without interference by protochlorophyll, the response of excised Avena coleoptile segments to red and far-red light was re-examined. The elongation of apical (non-decapitated) segments is promoted by a brief exposure to red light, and this effect is almost completely nullified by an immediately subsequent exposure to far-red light. Although growth promotion by red light occurs in distilled water alone, the effect is greater on a medium consisting of 0.02 M phosphate buffer, pH 6.2 to 6.4, with 1 to 2% sucrose. Over the pH range 4.5 to 7.4, dark-growth decreases with increasing pH, but the absolute increment brought about by red light is nearly constant. Elongation appears to be entirely the result of increased cell size.Contrary to previous reports, similar results can be obtained with subapical (decapitated) coleoptile segments, although the absolute magnitude of the response is reduced.Research carried out at Brookhaven National Laboratory under the auspices of the U.S. Atomic Energy Commision.     

Action Spectra for Light-induced Elongation in Fern Protonemata

The action spectrum for promotion of elongation of protonemata of Onoclea sensibilis has peaks at 400–420, 580–600 and 640–660 nm. The largest growth increments at saturating light doses are produced by yellow and far-red light. Elongation induced by yellow and far-red irradiation persists in old as well as young filaments, while red-light promotion is found only in young filaments. The growth promotion caused by yellow light is partially reversed by red light down to the level of growth produced by red irradiation alone. Elongation of rhizoids is under reversible red, far-red control, while yellow light is inactive. A model is proposed and discussed in which the light-sensitive elongation of filaments is accounted for by the presence of three distinct photoreceptors: phytochrome; a pigment absorbing yellow light. P₅₈₀; and a pigment absorbing blue light, P₄₂₀.     

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; )     

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.     

The Photobiology of Fern Gametophytes: I. THE PHENOMENON OF RED/FAR-RED AND YELLOW/F AR-RED PHOTOREVERSIBILITY

This paper shows that the hypothetical yellow-light-absorbingpigment P₅₈₀ is an unnecessary postulate for describing thephotobiology of fern filaments. The existence of P₅₈₀ was originallypredicted on the basis of action and response spectra that assumedthat filament elongation is the growth parameter subject todirect photocontrol. The present work supports an alternativeconcept, that the cross-sectional area at the base of the apicaldome is the photocontrolled parameter. Far-red irradiation reversesthe effects of both red and yellow light, and dose-responsecurves for yellow light parallel but lag behind the curves forred light. These observations indicate that the responses offern filaments to the entire long wavelength spectral region(yellow to far-red) can be attributed to absorption of lightby phytochrome alone.     

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.     

Photocontrol of stem elongation in light-grown plants of Fuchsia hybrida

Stems of the caulescent long-day plant, Fuchsia hybrida cv Lord Byron, showed 2 types of response to light. In one, internode length was increased by far-red irradiation given at the end of an 8 h photoperiod: the response was no greater with prolonged exposure and was less when the start of far-red was delayed. The effect of far-red was reversible by a subsequent exposure to red light. Internode length was inversely proportional to the P_fr/P ratio established before entry to darkness and there was no evidence for loss of P_fr during a 16 h dark period. The inhibitory effect of P_fr acted at a relatively late stage of internode growth. With the development of successive internodes a second response appeared in which stems lengthened following prolonged daily exposures to red or far-red light, or mixtures of the two, or to brief breaks with red or white light. In these later internodes, a short exposure to far-red near the middle of the night was not reversible by red because red alone promoted elongation at this time. Internode length increased with increase in the daily duration of light and, when light was given throughout an otherwise dark period of 16 h, with increase in illuminance to a saturation value of 200 lx from tungsten lamps. Elongation increased as a linear function of decrease in photostationary state of phytochrome down to P_fr/P0.3; however, internodes were shorter in far-red light than in 25% red/red+far-red. It was concluded that stem length is a net response to two modes of phytochrome action. An inductive effect of P_fr inhibits a late stage in internode expansion, and a phytochrome reaction which operates only in light (and may involve pigment cycling) promotes an early stage of internode development. Stem elongation is thus a function both of the daily duration of light and its red/red+far-red content. The outgrowth of axillary buds was controlled by the first type of phytochrome action only.Abbreviations and symbols FR far red light - R red light - P phytochrome - P_fr phytochrome in the far-red light absorbing form - SD 8 h short days - LDP long-day plant - SDP short-day plant     

Effects of red and far-red light on cell division in the shoot apex ofSilene coeli-rosa L.

Summary 28-day-old plant ofSilene coeli-rosa were exposed at 1,700 hours to 5 or 10 minutes red light, 5 or 10 minutes far-red light, red followed by far-red, far-red followed by red or maintained in darkness. Measurements of the proportions of cells with the 2 C and 4 C amounts of DNA in the shoot apex of the plants, sampled at 2,000 hours, showed that far-red light promoted an increase in the G2 proportion whereas red light resulted in an increase in the G1 proportion of the cell cycle, relative to the dark controls. Moreover these changes were red, far-red reversible. All light treatments resulted in increases in the mitotic index in the apex compared with the dark controls, suggesting increases in the growth rate. The data implicate phytochrome in a low energy response and suggest that, in the shoot apex, G1 is shortened markedly following exposure to farred light, whilst G2 is shortened the most following exposure to red light. The results are discussed in relation to flower-initiation.     

PHOTOMORPHOGENESIS OF THE GAMETOPHYTES OF LYGODIUM JAPONICUM

Protonemata of Lygodium japonicum turn biplanar in both red and blue light regimes and remain filamentous in far-red light. Biplanar gametophytes formed in red light are longer than broad with long, rectangular cells, whereas in blue light they appear broader than long with short, isodiametric cells. Transfer of protonemata of all ages from far-red regime to red or blue light induces a morphological type of growth characteristic of the new light regime. However, only relatively young biplanar forms transferred from red or blue light are able to resume filamentous type of growth in a subsequent regime of far-red light.     

Photocontrol of petiole elongation in light-grown strawberry plants

Summary The mode of phytochrome control of elongation growth was studied in fully-green strawberry (Fragaria x Ananassa Duch.) plants. Petiole growth showed two distinct types of response to light. In one, the end-of-day response, petioles were lengthened by low-intensity far-red irradiation for 1 h immediately following the 8 h photoperiod. The response was little or no greater with prolonged exposure and less when the start of far-red was delayed. It was already evident in the first leaf to emerge after treatment began. With the development of successive leaves a second, photoperiodic, type of response appeared, in which petioles lengthened following only prolonged exposure to red, far-red, mixtures of the two, or tungsten lighting, all at low levels of intensity. As with the inhibition of flowering in previous experiments, irradiation with red light during the second half of the otherwise long dark period gave the greatest response.Abbreviations and Symbols FR far-red light - HIR high irradiance response - R red light - P_r phytochrome in the red light absorbing form - P_fr phytochrome in the far-red light absorbing form - SDP short-day plant - LDP long-day plant - PAR photosynthetically active radiation     

Ethylene and the Responses to Light of Rice Seedlings

The growth of rice seedlings (Oryza satira L.) in the presence of ethylene caused a change in the response to light of coleoptile elongation. In plants grown in air without added ethylene coleoptile elongation was promoted by red, far-red and yellow-green light only in very young seedlings; in older plants irradiation inhibited the growth of the coleoptile. The effect of growing plants in the presence of ethylene was to prolong the period during which light promoted coleoptile growth. Elongation of the first internode was inhibited by light whether or not the seedlings were grown in the presence of ethylene. A correlation existed between the growth effect of an irradiation and the initial decay rate of phytochrome which was established by the treatment. Regardless of wave length, light sources whose intensities were adjusted to produce a decay rate of about 10% per hour or less induced a moderate rate of coleoptile elongation which persisted for a relatively long period. Irradiation with red or yellow-green light of higher intensity which produced a higher rate of phytochrome decay induced a higher rate of coleoptile elongation, but growth stopped after several hours. Other observations, however, showed that one cannot establish a general simple correlation between the rate of elongation of rice coleoptiles under light and the status of measurable phytochrome in the plant.     

THE DEVELOPMENT OF ISOLATED ROOTS OF COMPTONIA PEREGRINA (MYRICACEAE) IN CULTURE

Seedling roots of the sweet fern Comptonia peregrina (L.) Coult. were excised aseptically and cultured in a modified Bonner-Devirian liquid nutrient medium. Root elongation was very slow in the basic medium which contained inorganic salts, B-vitamins, trace elements and 4 % sucrose. The addition of plant hormones including gibberellic acid, indoleacetic acid, and zeatin, alone or in combinations, had little effect on growth. Myoinositol at 10 or 100 ppm doubled the rate of elongation. The effect of this sugar alcohol could not be replaced by scyllitol, D-sorbitol, D-mannitol or by increasing the sucrose concentration. Subcultured root tips showed progressively less elongation in successive transfers. Secondary thickening of the roots, especially in the basal half, occurred in initial passages and in subcultured roots without added hormones. Root buds also occurred spontaneously especially in the basal portions of cultured roots, both in first and in successive passages. An anatomical analysis showed that these buds were endogenous, arising from a secondary cortex of pericyclic origin.     

A phytochrome-mediated alteration from stem to rosette growth on chicory root explants in vitro

Chicory root explants (Cichorium intybus L. var. foliosum) of two cultivars, taken before and after hydroponic forcing, were cultured in vitro in complete darkness supplemented with red and far-red light treatments. Using 5 min red light per day, the strong stem elongation occurring in complete darkness was converted to rosette formation. This reaction was reversed to stem elongation (accompanied by leaf formation) adding 15 min far-red light after the red light. Fifteen min far-red light per day alone caused the same reaction as 5 min red/15 min far-red light. Far-red light followed by red light caused rosette formation. In stems, formed under complete darkness in vitro, the presence of phytochrome was shown. No phytochrome was detected in the root fragment itself.Abbreviations R red light - FR far-red light - GA gibberellinic acid - A absorbance - FW fresh weight