Involvement of phytochrome and a blue light photoreceptor in UV-B induced flavonoid synthesis in parsley (Petroselinum hortense Hoffm.) cell suspension cultures

Flavonoid synthesis in cell suspension cultures of parsley (Petroselinum hortense Hoffm.) occurs only after irradiation with ultraviolet light (UV), mainly from the UV-B (280–320 nm) spectral range. However, it is also controlled by phytochrome. A P_fr/P_tot ratio of approximately 20% is sufficient for a maximum phytochrome response as induced by pulse irradiation. Continuous red and far red light, as well as blue light, given after UV, are more effective than pulse irradiations. The response to blue light is considerably greater than that to red and far red light. Continuous red and blue light treatments can be substituted for by multiple pulses and can thus probably be ascribed to a multible induction effect. Continuous irradiations with red, far red and blue light also increase the UV-induced flavonoid synthesis if given before UV. The data indicate that besides phytochrome a separate blue light photoreceptor is involved in the regulation of the UV-induced flavonoid synthesis. This blue light receptor seems to require the presence of P_fr in order to be fully effective.Abbreviations HIR high irradiance response - P_fr far red absorhing form of phytochrome - P_tet total phytochrome - UV ultraviolet light     

Further support for the involvement of phytoehrome in stomatal movement

The involvement of phytochrome in stomatal movement in Commelina communis L. is indicated by the following observations: 1) Short irradiation with red or blue light causes opening, of isolated stomata and swelling of guard cell protoplasts. This is reversed by subsequent far red irradiation. 2) In a similar way, stomatal response to prolonged irradiation with red or blue light is decreased by concomitant far red irradiation. 3) Pretreatment with filipin, which interferes with phytochrome binding to membranes, decreases stomatal opening in red and blue light. The stomatal responses to blue and red light are modified by DCMU, N₂, CO_2-enriched atmosphere, and CO_2-free air, which are known to affect, among other processes, chlorophyll fluorescence. Increased chlorophyll fluorescence by DCMU, N₂ and CO₂-enriched atmosphere enhanced stomatal opening in blue light and inhibited it in red light. CO₂-free air, which decreases chlorophyll fluorescence, had the opposite effect.     

Visualization of a rapid,red/far-red light-dependent reaction by centrifuge microscopy

Summary Using a centrifuge microscope with stroboscopic illumination, we examined the effects of light irradiation on the passive movement of chloroplasts in dark-adapted mesophyll cells ofVallisneria gigantea. While irradiation with red light accelerates the passive gliding of chloroplasts produced by centrifugal force, irradiation with far-red light negates this effect. Irradiation with blue light does not accelerate the passive gliding, while red light is completely effective even in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea, an inhibitor of photosynthesis. An apparently active movement of chloroplasts can be induced by irradiation with red or blue light only in the presence of the far-red light-absorbing form of phytochrome. The significance of the reaction in the light with respect to the regulation of cytoplasmic streaming is discussed.Abbreviations APW artificial pond water - CMS centrifuge microscope of the stroboscopic type - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - Pfr phytochrome, far-red light-absorbing form - Pr phytochrome, red light-absorbing form     

Reorientation of microtubules at the outer epidermal wall of maize coleoptiles by phytochrome,blue-light photoreceptor,and auxin

Summary The effects of red and blue light on the orientation of cortical microtubules (MTs) underneath the outer epidermal wall of maize (Zea mays L.) coleoptiles were investigated with immunofluorescent techniques. The epidermal cells of dark-grown coleoptiles demonstrated an irregular pattern of regions of parallel MTs with a random distribution of orientations. This pattern could be changed into a uniformly transverse MT alignment with respect to the long cell axis by 1 h of irradiation with red light. This response was transient as the MTs spontaneously shifted into a longitudinal orientation after 1–2 h of continued irradiation. Induction/reversion experiments with short red and far-red light pulses demonstrated the involvement of phytochrome in this response. In contrast to red light, irradiation with blue light induced a stable longitudinal MT alignment which was established within 10 min. The blue-light response could not be affected by subsequent irradiations with red or far-red light indicating the involvement of a separate blue-light photoreceptor which antagonizes the effect of phytochrome. In mixed light treatments with red and blue light, the blue-light photoreceptor always dominated over phytochrome which exhibited an apparently less stable influence on MT orientation. Long-term irradiations with red or blue light up to 6 h did not reveal any rhythmic changes of MT orientation that could be related to the rhythmicity of helicoidal cell-wall structure. Subapical segments isolated from dark-grown coleoptiles maintained a longitudinal MT arrangement even in red light indicating that the responsiveness to phytochrome was lost upon isolation. Conversely auxin induced a transverse MT arrangement in isolated segments even in blue light, indicating that the responsiveness to blue-light photoreceptor was eliminated by the hormone. These complex interactions are discussed in the context of current hypotheses on the functional significance of MT reorientations for cell development.Abbreviations MT cortical microtubule - P_r, P_fr red and far-red absorbing form of phytochrome     

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     

Amaranthin accumulation in continuous red and blue light by seedlings ofAmaranthus caudatus L.

Four days oldAmaranthus seedlings responded to light treatment with an increase of amaranthin accumulation. With increasing irradiation time, red light caused a saturation effect. Blue light induced a high irradiation response. The blue light effect was reversible to a certain extent by far-red irradiation given at the end of the treatment with blue light. Intermittent red light (3 h red light, 3 h dark, …) caused a higher amaranthin accumulation than 24 h continuous red light. Results obtained with red and blue light are discussed on the basis of the phytochrome system.     

Growth control by phytochrome of de-etiolated bean hypocotyls mediated by chlorophyll fluorescence

The elongation of hypocotyls excised from de-etiolated seedlings of beans (Phaseolus vulgaris L. cv. British Wax) is inhibited by light, blue and red irradiations being equally effective. Conditions which decrease chlorophyll fluorescence, such as CO₂-free air, abolish the inhibitory effect of blue irradiation and enhance the inhibition by red light. Conversely, conditions which increase chlorophyll fluorescence, such as a N₂ atmosphere or irradiation through a chlorophyll filter, abolish the inhibitory effect of red light and enhance the inhibition by blue irradiation. The inhibitory effect of blue light is reversible by red irradiation under increased fluorescence as well as by far red. We propose that the chlorophyll fluorescence excited by blue and red irradiations in λ_F > 660 nm and λ_F > 720 nm, respectively, is responsible for the inhibitory effect of blue light and the reduction of the inhibitory effect of non fluorescing red light. Both red and blue wavelengths seem, therefore, to control hypocotyl elongation through phytochrome.     

Light-stimulated respiration in the green algaDunaliella tertiolecta: Involvement of the ultraviolet/blue-light photoreceptor(s) and phytochrome?

Starch breakdown and respiratory O₂ uptake in the green algaDunaliella tertiolecta (Butcher) are stimulated not only by blue, but also by red light. In the present study, attempts are described to identify the photoreceptor(s) involved. Fluence rate-response curves with different slopes in the ultraviolet (UV)/blue and in the red spectral region as well as differences in the kinetics and in the unfluence of dark pre-incubation on the stimulation of respiratory O₂ uptake by blue and red light strongly indicate the action of two photoreceptors. Since the effect of red light shows some far-red reversibility, and since simultaneous irradiation with red and far-red light decreases the effectiveness of red light, the involvement of phytochrome — in addition to the UV/blue photoreceptor(s) — is suggested in the light-stimulated respiration inDunaliella.Abbreviation UV ultraviolet     

Photostimulation of Hydroxypyruvate Reductase Activity in Peroxisomes of Pharbitis nil Seedlings: II. Photoreceptors in Blue Light

The action spectrum for stimulation of hydroxypyruvate reductase(HPR) activity in etiolated cotyledons of Pharbitis nil showsthe three effective regions of blue (B), red (R), and far red(FR), with high B efficiency. Light duration response curvesand kinetics of stimulation in continuous light were comparedat 455 nm, 660 nm and 710 nm. Before 10 h, the efficienciesat 455 and 660 nm were higher than that at 710 nm. After 10h, lengthening of the 660 nm irradiation was ineffective whilelengthening of the 710 and 455 nm irradiation caused linearincreases in HPR activity. These results together with the effectof pre-R-irradiation on FR or B stimulation suggest that twopigments are simultaneously involved in the B light effect:phytochrome and a specific blue-absorbing pigment. Phytochromemay be the main effective pigment up to 10 h in blue light whilethe blue-absorbing pigment may be more effective for longerexposures. (Received November 22, 1983; Accepted June 20, 1984)     

Control of chlorophyll a synthesis by phytochrome and cryptochrome in the red alga Corallina elongata Ellis et Soland

Chlorophyll a synthesis in the red alga Corallina elongata is controlled by phytochrome and by a specific blue light photoreceptor. Although the estimated photoequilibrium of phytochrome is similar in blue and red light, the amount of chlorophyll accumulated is greater in blue light, which implies the action of cryptochrome, according to the criteria for the specific blue light photoreceptor involvement. The amount of chlorophyll synthesized is greater when the level of photoequilibrium approaches 65% (in blue and red light) than with higher levels (72.7% in white light and 70.8% in green light). The action of phytochrome is demonstrated by the induction of chlorophyll synthesis after red pulses and the reversion after far red pulses. The reversion is not complete but the percentage of reversibility is high (85-90%). The amount of chlorophyll accumulated is greater in darkness after the application of red light pulses than in white light after the same light pulses. The induction of chlorophyll synthesis is greater after red pulses than after continuous red light. The existence of a fast destruction of chlorophyll in continuous light is observed. This destruction is greater in the high photoequilibrium of phytochrome (70-72%). The turnover times and the induction mechanism of chlorophyll synthesis must be very fast. This indicates the existence of a possible rapid adaptation to the change in light quality and intensity in the marine system.     

Phytochrome action on the timing of cell division in adiantum gametophytes

When filamentous protonemata of Adiantum capillus-veneris L. precultured under continuous red light were transferred to the dark, the apical cell divided about 24 to 36 hours thereafter. The time of the cell division was delayed for several hours by a brief exposure to far red light given before the dark incubation. The effect of far red light was reversed by a small dose of red light given immediately after the preceding far red light. The effects of red and far red light were repeatedly reversible, indicating that the timing of cell division was regulated by a phytochrome system. When a brief irradiation with blue light was given before the dark incubation, the cell division occurred after 17 to 26 hours in darkness. A similar red far red reversible effect was also observed in the timing of the blue light-induced cell division. Thus, the timing of cell division appeared to be controlled by phytochrome and a blue light-absorbing pigment.     

Red-light and blue-light photoreceptors controlling chlorophyll a synthesis in the red alga Porphyra umbilicalis and in the green alga Ulva rigida

Chlorophyll synthesis is stimulated by red light in the green alga Ulva rigida C. Ag. and in the red alga Porphyra umbilicalis (L.) Kützing. Because the effect of red light showed some far-red reversibility in successive red and far-red light treatments, the involvement of phytochrome or a phytochrome-like photoreceptor is suggested. The extent of the response is dependent on exposure and photon fluence rate of red-light pulses. In addition to the effect of red light, a strong stimulation of chlorophyll synthesis by blue light was only observed in Ulva rigida. The effect of blue light shows also some far-red reversibility. In the green alga the accumulated chlorophyll is higher after blue light pulses than after red light pulses. In Porphyra umbilicalis , however, the contrary is observed. In Ulva rigida the involvement of a blue light photoreceptor in addition to phytochrome or a phytochrome-like photoreceptor is proposed. The different responses to red and blue light in both algae are explained in terms of their adaptation to the natural light environment.     

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     

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.     

Phytochrome Modifies Blue-light-induced Electrical Changes in Corn Coleoptiles

Unilateral blue light administered to corn coleoptile segments produces no alteration of transmembrane potential on the light side, and only a small and slow hyperpolarization on the dark side. Red light causes a 5-15 millivolt depolarization in cells on the light side causes and somewhat smaller effects on the dark side. Blue given after red causes a rapid hyperpolarization on both sides of the coleoptile. The effect of the potentiating red preirradiation is probably due to phytochrome, being largely abolished by far-red given after red, but before the blue light. The effect of prior red irradiation decays in the dark, showing a half-time of about 45 minutes at room temperature. This rapid cooperativity between phytochrome and the phototropic pigment may indicate a common locale, possibly in a membrane.     

In Vivo Properties of Membrane-bound Phytochrome

After a 3-minute irradiation with red light, which saturates the phototransformation from the red light-absorbing form of phytochrome to the far red light absorbing form of phytochrome, about 40% of the phytochrome extractable from hooks of etiolated squash seedlings (Cucurbita pepo L. cv. Black Beauty) can be pelleted as Pfr at 17,000g after 30 minutes. Dark controls yield only 2 to 4% pelletable phytochrome in the form Pr. If a dark period intervenes between red irradiation and extraction, the bound Pfr gradually loses its photoreversibility. The time course for this destruction parallels the time course for phytochrome destruction in vivo following saturating red irradiation. The soluble fraction of phytochrome remains constant. These results suggest that in squash seedlings phytochrome destruction is related exclusively to the fraction which becomes membrane-bound. The induction of phytochrome binding by red light is not completely reversible by far red. In plants given saturating red followed immediately by saturating far red light, 12% of the phytochrome is found in the bound fraction as Pr if the phytochrome extraction is immediate. If a dark period intervenes between red-far red treatment and extraction, the bound phytochrome is released within 2 hours. A model of the binding properties of phytochrome, based on molecular interaction at the membrane is proposed, and possible consequences for the mechanism of action of phytochrome are discussed.     

An action spectrum in the blue for inhibition of germination of lettuce seed

Summary Using a 2-h irradiation period at constant quantum irradiance, a complete action spectrum for inhibition of germination of lettuce seed has been obtained. Action maxima were near 470 and 720 nm, the latter being the most active wavelength. It was also shown, under conditions where light inhibition cannot occur, that phytochrome potentiation of germination is maximal at all wavelengths below 700 nm, including the highly active blue region. Evidence was presented for promotion of germination by a 2-h irradiation in the red which cannot be explained on the basis of conversion of phytochrome to the active form.Abbreviations Bl blue - FR far-red, P_FR far-red-absorbing form of phytochrome - R red Supported in part by funds provided for biological and medical research by the State of Washington Initiative Measure No. 171 and the Graduate School Research Funds.     

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.     

Evidence of Phytochrome Mediation in the Low-pH-Induced Root Hair Formation Process in Lettuce (Lactuca sativa L. cv. Grand Rapids) Seedlings

−2 . The inductive effect of 100 Jm⁻² red light could be partially reversed by subsequent far-red light only one time. On the other hand, the inductive effect of 1,000 Jm⁻² red light was partially reversed by subsequent far-red light irradiation at least twice. These results indicate the involvement of phytochrome in this response. The inductive effect of blue light was repeatedly reversed by subsequent far-red light irradiation, suggesting that the blue-light induction was mainly mediated by phytochrome. Received 13 August 1999/ Accepted in revised form 22 December 1999     

Photoregulation of asymmetric cell division followed by rhizoid development in the fern Ceratopteris prothalli

Strap-shaped prothalli of CERATOPTERIS: richardii grown in the dark have an apical meristem, a subapical elongation zone and a basal growth cessation zone [Murata et al. (1997) Plant Cell Physiol. 38: 201]. When the dark-grown prothalli were irradiated with continuous white light, marginal cells of the elongation zone divided asymmetrically, and the resulting smaller cells developed into rhizoids. The asymmetric division was also induced by brief irradiation of red light. The effect of red light was cancelled by subsequent irradiation of far-red light, indicating that the asymmetric division was regulated by phytochrome. Since the response to red light was not observed at 10(1) J m(-2) and saturated at 10(2) J m(-2) and the response is photoreversible by far-red light, the photoresponse was classified as a low-fluence response of phytochrome. Although the asymmetric division was induced by brief irradiation of red light, continuous irradiation of white, blue or red light was necessary to induce rhizoid growth. These results indicate that asymmetric division and subsequent cell growth are independently regulated by light in CERATOPTERIS: prothalli.