INTERACTION OF IONIZING AND VISIBLE RADIATION IN MUTATION INDUCTION IN NEUROSPORA CRASSA

Klein , Richard M. (New York Bot. Gdn., New York, N.Y.), and Deana T. Klein. Interaction of ionizing and visible radiation in mutation induction in Neurospora crassa. Amer. Jour. Bot. 49(8): 870–874. 1962.—Conidia of the purple adenineless strain of N. crassa were irradiated with 25 kr of X rays and then exposed to far-red or red radiations or to far-red followed by red radiation. Far-red light, without effect on un-irradiated conidia, augmented the genetic damage caused by X rays as measured by survival (colony count), back mutation to adenine prototrophy, and the induction of mutants affecting colony morphology. Post-X-irradiation with red light ameliorated the severity of X-radiation as measured by survival and back mutation. The potentiation of X-ray-induced genetic damage by far-red light could be completely negated by subsequent exposure to red light.     

THE PHOTOINHIBITION OF GROWTH IN ETIOLATED STEM SEGMENTS. III. FAR-RED REVERSIBILITY OF BLUE LIGHT EFFECTS IN PISUM

Bertsch , Walter F. (Yale U., New Haven, Conn.) The photoinhibition of growth in etiolated stem segments. III. Far-red reversibility of blue light effects in Pisum. Amer. Jour. Bot. 50(8):754–760. Illus. 1963.—Etiolated pea stem segments were used to study the relationship between blue light effects and the red, far-red reversible photoinhibition of growth. The irradiation periods were too short to give an appreciable effect of high-energy, nonreversible photoreactions. Filters which were used to isolate blue light are specified, contaminations by other wavelengths being extremely small. It was found that photoinhibitions due to uncontaminated blue light were reversible by subsequent far-red irradiation, regardless of whether a broad band of blue wavelengths, or the 4358-A emission line of mercury, was used. Blue light (4800 A) was about 0.3-1% as effective as red (6600 A) light. Changes in the incubation medium caused the same changes in photosensitivity to blue as to red irradiations. These observations are presented as evidence supporting the hypothesis that the pigment moiety of phytochrome absorbs blue light.     

SOME FACTORS AFFECTING THE GERMINATION OF SEED OF THE SAGUARO CACTUS (CARNEGIEA GIGANTEA)

Alcorn , Stanley M. (U. S. Dept. of Agric., Tucson, Ariz.), and Edwin B. Kurtz , Jr . Some factors affecting the germination of seed of the saguaro cactus (Carnegiea gigantea). Amer. Jour. Bot. 46(7): 526–529. 1959.—Germination of saguaro cactus seeds is stimulated by red light (approx. 6550 A) or daylight and far-red light (approx. 7350 A) counteracts this effect. About 0.1% germinate in continuous darkness. A single exposure to red light was most effective when the seeds were imbibed 24 hr., but maximum germination resulted from multiple exposures to red light during a 72-hr. imbibition period. The optimum temperature for germination was 25°C.; no germination occurred at 15°C. and only slight germination at 35°C. Imbibition of light-treated seeds in 0.05 to 0.2% KNO₃ increased germination. Germination of seeds in either light or dark was increased by imbibing the seeds in 500 to 1000 p.p.m. gibberellic acid.     

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.     

Blue light induced inhibition of seed germination: The necessity of the fruit coats for the blue light response

The seeds (achenes) of Laportea bulbifera require a chilling to break their dormancy and are negatively photoblastic. Their germination is inhibited by both continuous blue light and continuous or prolonged far-red radiation. The germination of de-coated seeds, prepared by removing the fruit coats, however, was strongly inhibited by continuous far-red, but not by continuous blue light. Photoreversible germination by a brief irradiation with red light occurred when the chilled seeds were exposed to prolonged far-red light. These results suggest that far-red light may regulate the germination of L. bulbifera seeds through the phytochrome system which exists in the regions other than fruit coats and that the blue light reaction may be governed by other photoreceptor system(s).     

Photocontrol of spore germination in the fern Thelypteris kunthii

The light requirement for germination in spores of the fern Thelypteris kunthii (Desv.) Morton was fully satisfied by a long period of continuous red light or partially by intermittent, short periods of red light. Red light-potentiated spore germination was inhibited by brief far-red light irradiation, indicating phytochrome involvement. Repeated exposure of spores to prolonged red and short far-red irradiations, or exposure of red-potentiated spores to far-red light after an extended period in darkness, led to their escape from inhibition of germination by far-red light. Prolonged irradiation of spores with blue light before or after red light treatment partially antagonized the effect of red light.     

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; )     

SPECTRAL SENSITIVITY OF SEED GERMINATION IN ARTEMISIA MONOSPERMA

The absolute requirement for light in the germination of achenesof Artemisia monosperma is as satisfied by radiant energy inthe blue, green, yellow, red and far-red regions of the visiblespectrum, as by unfiltered white light. The same stimulationwas obtained by a short irradiation as by an uninterrupted one.Phytochrome seems to be either absent, or masked by a differentpigment which absorbs light in the entire visible spectrum andthus initiates germination. ¹ This study was supported by grant FG-Is-115 from the UnitedStates Department of Agriculture.     

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     

Light Actions in the Germination of Cocklebur Seeds: IV. DISAPPEARANCE OF RED LIGHT-REQUIREMENT FOR THE GERMINATION OF UPPER SEEDS SUBJECT TO ANOXIA, CHILLING, CYANIDE OR AZIDEPRETREATMENT

Esashi, Y., Fuwa, Nn Kojima, K. and Hase, S. 1986. Light actionsin the germination of cocklebur seeds. IV. Disappearance ofred light-requirement for the germination of upper seeds subjectto anoxia, chilling, cyanide or azide pretreatmenL—J.exp. Bot. 37: 1652–1662. The effects on the germination of positively photoblastic uppercocklebur (X anthium pennsylvanicum Wallr.) seeds by pretreatingwith anoxia, chilling, cyanide or azide, which stimulates theirdark germination, were examined in relation to light actions.Prior to experiments, seeds were pre-soaked at 23 °C inthe dark for 1 or 2 weeks to remove the pre-existing Pfr. Whenthe prctreatment conditions were suboptimal for germinationinduction, the stimulating effects of the pretreatments on germinationduring a subsequent dark period at 23 °C were manifest onlywhen seeds were irradiated with red light before or after thepretreatment Red light promotion was reversed by blue or far-redlight treatment. However, both prc-chilling for 6 d at 8 °Cand prctreatment with 1· 5 mol m ^{– 3} NaN³ for 2d could induce full germination without red light exposure.On the other hand, both pre-exposure to anoxia for 8 d and pretreatmentwith 30 mol m^–3 KCN could induce the dark germinationonly when germination occurred at 33 °C which is known toaugment the ratio of an alternative respiration flux to a cytochromeone. Moreover, the dark germination in response to these inductionswere strongly inhibited by the inhibitors of alternative respiration,propyl gallate and benzohydroxamic acid, applied during a subsequentdark period. It was thus suggested that Pfr has some relationto the operation of two respiration systems of cocklebur seeds,but it is not indispensable to germination of this positivelyphotoblastic seed. Key words: Anoxia, azide, blue light, chilling cyanide, dark germination, far-red light, red light, seed germination, X anthium pennsylvanicum     

Control of Mitosis by Phytochrome and a Blue-Light Receptor in Fern Spores

The first mitosis in spores of the fern A. capillus-veneris was observed under a microscope equipped with Nomarski optics with irradiation from a safelight at 900 nm, and under a fluorescent microscope after staining with 4[prime],6-diamidino-2-phenylindole. During imbibition the nucleus remained near one corner of each tetrahedron-shaped dormant spore, and asymmetric cell division occurred upon brief irradiation with red light. This red light-induced mitosis was photoreversibly prevented by subsequent brief exposure to far-red light and was photo-irreversibly prevented by brief irradiation with blue light. However, neither far-red nor blue light affected the germination rate when spores were irradiated after the first mitosis. Therefore, the first mitosis in the spores appears to be the crucial step for photoinduction of spore germination. Furthermore, experiments using a microbeam of red or blue light demonstrated that blue light was effective only when exposed to the nucleus, and no specific intracellular photoreceptive site for red light was found in the spores. Therefore, phytochrome in the far-red absorbing form induces the first mitosis in germinating spores but prevents the subsequent mitosis in protonemata, whereas a blue-light receptor prevents the former but induces the latter.     

ON THE MECHANISMS OF LIGHT-INDUCED GERMINATION INHIBITION OF PHACELIA TANACETIFOLLV

Germination of seed of Phacelia tanacetifolia is inhibited by several mechanisms. In addition to physical restraints imposed by the seed coats, the seed contains a water-soluble inhibitor which is independent of light or temperature for its activity. Available evidence also points to the presence of 1 or more light-activated inhibitors which are not easily leached from the seed. The blue-light-activated inhibition can be negated by high oxygen tensions or mechanical abrasion of the micropylar end of the seed. The suppression of germination by far-red or red light can be negated by abrasion but is only partially reversed by oxygen. Combinations of abrasion and high oxygen tensions negate both light-induced and temperature-induced inhibitions of germination.     

GROWTH REGULATION BY ETHYLENE IN FERN GAMETOPHYTES. IV. INVOLVEMENT OF PHOTOSYNTHESIS IN OVERCOMING ETHYLENE INHIBITION OF SPORE GERMINATION

The inhibitory effects of ethylene on spore germination were investigated. In darkness spore germination was completely inhibited by 10 μ1 · 1⁻¹ ethylene. Light partially overcame this inhibition, and the effect of continuous irradiation with white fluorescent light saturated at about 450 μW · cm⁻². Monochromatic red, blue and far-red light were effective in overcoming ethylene inhibition, whereas green was not. Short periodic exposures to red or far-red light were not sufficient to overcome ethylene inhibition. This suggested that phytochrome was not involved. The photosynthetic inhibitor DCMU blocked the effect of light. Infrared gas analysis showed that photosynthesis saturated at about 450 μW · cm⁻² in white light. Red, blue and far-red light were more efficient photosynthetically than green light; DCMU blocked photosynthesis. Normalized curves of photosynthesis and germination vs. light intensity showed a similar dependence on light energy. It was concluded that light appears to overcome the inhibitory effects of ethylene through some process dependent on photosynthesis.     

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; )     

Phytochrome-mediated effects of near-ultraviolet radiation in the induction of flowering in etiolated Lemna paucicostata T-101, a short-day plant

Induction of flowering of etiolated Lemna paucicostata Hegelm. T-101, a short-day plant, was inhibited by far-red (FR) or blue light (BL) applied at the beginning of a 72-h inductive dark period which was followed by two short days. In either case the inhibition was reversed by a subsequent exposure of the plants to near-ultraviolet radiation (NUV), with a peak of effectiveness near 380 nm. Inhibition by BL or FR and its reversion by NUV are repeatable, i.e., NUV is acting in these photoresponses like red light although with much lower effectiveness. Thus, it is considered that NUV acts through phytochrome and no specific BL and NUV photoreceptor is involved in photocontrol of floral induction on this plant.Abbreviations BL blue light - FR far-red light - NUV near ultraviolet radiation - P red-absorbing form of phytochrome - P_fr far-red absorbing form of phytochrome - R red light     

THE EFFECTS OF TEMPERATURE ON THE GERMINATION AND RADICLE GROWTH OF PHOTOSENSITIVE LETTUCE SEED

1. The time course of germination of Grand Rapids lettuce seedshas heen followed with different combinations of temperature(3°–35°) and irradiation (red or far-red light).For each set of conditions the following three parameters weredetermined: (i) the time required for half maximum germination,(ii) the rate of germination during the actively germinatingphase, and (iii) the maximum germination attained. In general,as the temperature was lowered, with dark-imbibed seeds, (i)became longer, (ii) became lower, but (iii) became progressivelyhigher. The effect of red light at any temperature was to shorten(i) and increase (ii) and (iii) over the values dark controls.Far-red light exerted an effect opposite to that of red light.Temperatures higher than 25° inhibited (ii) and (iii) underany light conditions. The optimum temperature to the actionof red and far-red light is 25°, at which the stimulatoryeffect of red light and the inhibition of this effect by far-redlight are both maximal. 2. The growth of the radicles of de-coated seeds of Grand Rapidslettuce shows two phases at all temperatures studied. PhaseI is characterized by slow but linear growth which continuesuntil shortly after visible differentiation of the radicle intothe hypocotyl and the root. Phase II is a phase of active growthin which the total length reflects mainly the length of theroot. The optimum temperature for Phase I is 25°-35°,and that, for Phase II is 25°. In neither phase, and atnone of the temperatures studied, is there any effect of redor far-red radiation on the growth of the radicle. The firstvisible sign of radicle elongation in red light induced seeds,however, takes place at exactly the same time as that of germination. 3. Similarities and dissimilarities between the germinationand the growth are pointed out, and it is concluded that thetwo phenomena are different, but proceed at sites closely associatedin the embryo. ¹Present address: Johnson Foundation for Medical Physics, Universityof Pennsylvania, Philadelphia, Pa., U.S.A.     

Blue- and red-light action in photoorientation of chloroplasts in Adiantum protonemata

An action spectrum for the low-fluencerate response of chloroplast movement in protonemata of the fern Adiantum capillus-veneris L. was determined using polarized light vibrating perpendicularly to the protonema axis. The spectrum had several peaks in the blue region around 450 nm and one in the red region at 680 nm, the blue peaks being higher than the red one. The red-light action was suppressed by nonpolarized far-red light given simultaneously or alternately, whereas the bluelight action was not. Chloroplast movement was also induced by a local irradiation with a narrow beam of monochromatic light. A beam of blue light at low energy fluence rates (7.3·10^-3-1.0 W m^-2) caused movement of the chloroplasts to the beam area (positive response), while one at high fluence rates (10 W m^-2 and higher) caused movement to outside of the beam area (negative response). A red beam caused a positive response at fluence rates up to 100 W m^-2, but a negative response at very high fluence rates (230 and 470 W m^-2). When a far-red beam was combined with total background irradiation with red light at fluence rates causing a low-fluence-rate response in whole cells, chloroplasts moved out of the beam area. When blue light was used as background irradiation, however, a narrow far-red beam had no effect on chloroplast distribution. These results indicate that the light-oriented movement of Adiantum chloroplasts is caused by red and blue light, mediated by phytochrome and another, unidentified photoreceptor(s), respectively. This movement depends on a local gradient of the far-red-absorbing form of phytochrome or of a photoexcited blue-light photoreceptor, and it includes positive and negative responses for both red and blue light.Abbreviations BL blue light - FR far-red light - Pfr far-red-absorbing form of phytochrome - Pr red-absorbing form of phytochrome - R red light - UV ultraviolet     

Action spectra for polarotropism and phototropism in protonemata of the fern Adiantum capillus-veneris

The action spectrum for polarotropism was determined, using the Okazaki large spectrograph, by brief irradiation with light between 260 nm and 850 nm in single-celled protonemata of the fern Adiantum capillus-veneris L., which had been cultured for 6 days in red light and then in the dark for 15 h. The action spectrum had a peak at around 680 nm. This effect was nullified by subsequent irradiaton with far-red light, and typical red/far-red reversibility was observed, indicating the involvement of phytochrome. Polarized ultraviolet or blue light had no effect on the direction of apical growth. The action spectrum for phototropism was also determined in the red light region by means of brief microbeam irradiation of a flank of the subapical region of the protonema. This spectrum showed a peak at 662 nm which was consistent with the absorption peak of phytochrome, but not with the peak of the action spectrum for polarotropism.     

Phytochrome involvement in stomatal movement in Pisum sativum, Vicia faba and Pelargonium sp.

Red and blue light triggered the opening of isolated stomata of Pisum sativum L. cv. Peleg Alvador, Vicia faba L. (unknown cultivar) and Pelargonium sp. The stimulatory effect of short irradiation with red or blue light was reversed by a subsequent short irradiation with far-red light. In Pisum the stimulatory effect of a continuous irradiation with red or blue light was also abolished by a concomitant far-red light. In leaf pieces of P. sativum blue light was more effective than red, but not in isolated guard cells. In the presence of mesophyll, DCMU inhibited stomatal opening in red light more than in blue, and thus increased the relative response to blue light. This was less evident in isolated guard cells.     

PHOTOCONTROL OF GROWTH AND FLOWERING OF CARYOPTERIS

Piringer , A. A., R. J. Downs , and H. A. Borthwick . (U. S. Dept. of Agriculture, ARS, Belts ville, Md.) Photocontrol of growth and flowering of Caryopteris . Amer. Jour. Bot. 50(1): 86–90. Illus. 1963.—Flower buds were initiated on plants of Caryopteris × clandonensis A. Simmonds (C. incana [Houtt.] Miq. × C. mongholica Bunge) on all photopcriods but developed to anthesis only when daily dark periods exceeded 8 hr. Anthesis occurred in not less than 22 days after the beginning of 11 or more short photoperiods. Treatments with short days could be interrupted by as many as 30 non-inductive long days without significant increase in the minimum number of short days required for anthesis. Anthesis, like floral initiation of many plants, was reversibly controlled by red and far-red radiation acting through phytochrome. The inductive effectiveness of long dark periods was nullified by 1 min of red light or about 1 hr of far red. It was modified by night temperature in the range 45–70.F and filament lengths of stamens were shorter at night temperatures of 60 than at 70 F.