A phytochrome-like protein AphC triggers the cAMP signaling induced by far-red light in the cyanobacterium Anabaena sp. strain PCC7120

In the filamentous, nitrogen-fixing cyanobacterium Anabaena sp. PCC7120, red light (630 nm) decreased, whereas far-red light (720 nm) increased cellular adenosine 3',5'-cyclic monophosphate (cAMP) content. To find a red and far-red light photoreceptor that triggers the cAMP signal cascade, we disrupted 10 open reading frame having putative chromophore-binding GAF domains. The response of the cellular cAMP concentration to red and far-red light in each open reading frame disruptant was determined. It was found that only the mutant of the gene all2699 failed to respond to far-red light. The open reading frame named as aphC encoded a protein with 920 amino acids including GAF domains similar to those involved in Cph2, a photoreceptor of Synechocystis sp. PCC6803. To determine which adenylate cyclase (AC) is responsible for far-red light signal, we disrupted all AC genes and found that CyaC was the candidate. The enzymatic activity of CyaC might be controlled by a far-red light photoreceptor through the phosphotransfer reaction. The site-specific mutant of the Asp59 residue of the receiver (R1) domain of CyaC lost its light-response capability. It was suggested that the far-red light signal was received by AphC and then transferred to the N-terminal response regulator domain of CyaC. Then its catalytic activity was stimulated, which increased the cellular cAMP concentration and drove the subsequent signal transduction cascade.     

Light regulation of cyclic-AMP levels in the red macroalga Porphyra leucosticta.

Total cyclic-3'-5'-adenosine monophosphate (cAMP) levels were measured in the gametophyte of the red macroalga Porphyra leucosticta under different light conditions in order to study its regulation by phytochrome or photosynthesis. cAMP levels were relatively low when samples were incubated in darkness, or exposed to red or far-red light. Irradiation with red+far-red light induced a moderate increase in cAMP levels, while white light induced a pronounced increase in cAMP levels. When incubated under increasing white light irradiance, cAMP levels closely followed the increase in photosynthetic oxygen evolution rate, suggesting a direct relationship between photosynthesis and cAMP accumulation. cAMP levels were not dependent on cellular ATP concentration, as inhibitors of ATP synthesis did not significantly affect cAMP levels in light. We conclude that cAMP depends on photosynthetic activity regardless of ATP synthesis and concentration or phytochrome activity.     

Cyclic-AMP levels in the lichen Evernia prunastri are modulated by light quantity and quality

Changes in the accumulation of cAMP levels were measured by the isotope dilution assay using protein kinase A in the lichen Evernia prunastri at varying light conditions. cAMP levels decreased following exposure to low irradiance (20 μmol quanta m⁻² s⁻¹, and below the compensation point for photosynthesis) of red light (600–710-nm wave length) and increased by 50% after far-red light illumination (15 μmol quanta m⁻² s⁻¹, 710–800-nm wavelength). Far-red partially reverted the effect of red light when the former was supplied after the latter. cAMP increased to its maximum level under high irradiance supplied by a non-photomorphogenic yellow light source (400 μmol quanta m⁻² s⁻¹, reaching photosynthetic saturation). The addition of small quantities of red and far-red light, however, had profound restricting effects on cAMP accumulation. The addition of inhibitors of electron transport chains did not promote any significant change in cAMP levels in any of the treatments, indicating that cAMP accumulation could not depend on ATP synthesis. We propose that the response of cAMP accumulation at low irradiance comprises the activation of a morphogenic pathway through a red/far-red photoreceptor. In addition, at high irradiance the response would occur most likely through photosystems II and I acting as sensors of light quantity, that can be strongly modified by the red/far-red photomorphogenic system. Thus, cAMP would be involved in sensing the overall light environment.     

Equal-quantum action spectra indicate fluence-rate-selective action of multiple photoreceptors for photomovement of the thermophilic cyanobacterium Synechococcus elongatus

Unicellular thermophilic cyanobacterium Synechococcus elongatus displayed phototaxis on agar plate at 55 degrees C. Equal-quantum action spectra for phototactic migration were determined at various fluence rates using the Okazaki Large Spectrograph as the light source. The shapes of the action spectra drastically changed depending on the fluence rate of the unilateral monochromatic irradiation: at a low fluence rate (3 mumol/m2/s), only lights in the red region had significant effect; at a medium fluence rate (10 mumol/m2/s), four major action peaks were observed at 530 nm (green), 570 nm (yellow), 640 nm (red) and 680 nm (red). At high fluence rates (30-90 mumol/m2/s), the former two peaks remained, while red peaks at 640 nm and 680 nm disappeared and, interestingly, an action peak around 700-740 nm (far-red) newly appeared. These results indicate that two or more distinct photoreceptors are involved in the phototaxis and that suitable photoreceptors are selectively active in response to the stimulus of light fluence rates. Far-red or red background lights irradiated vertically from above drastically inhibited phototaxis toward red light or far-red light, respectively. These results indicate involvement of some phytochrome(s).     

A POSSIBLE CONTROL BY A PHYTOCHROME-LIKE PHOTORECEPTOR OF CHLOROPHYLL SYNTHESIS IN THE GREEN ALGA Ulva rigida

Chlorophyll synthesis is stimulated by red light pulses in the green alga Ulva rigida C. Aghard. Chlorophyll synthesis in darkness is greater after longer red light pulses (30 min) than after shorter red light pulses (5 min). Chlorophyll synthesis was higher after red light pulses of 14 Wm_-2 fluence rate than after those of 7 Wm_-2. The effect of red light showed some far-red reversibility. The reversion by far-red light was higher after red light pulses of 4 min than after those of 30 min. These results indicate the existence of a rapid induction of chlorophyll synthesis during the red light pulses and a fast escape from photoreversibility. The percentage of reversion is also affected by the fluence rate of the light pulses. The reversion was reduced by about 15% when the photon fluence rate was increased from 7 to 14 Wm_-2. Reversion was also observed when red and far-red light pulses were applied successively. Thus, phytochrome or a phytochrome-like photoreceptor could be involved in the induction of chlorophyll synthesis in Ulva rigida.     

PHYTOCHROME AND EFFECTS OF SHADING ON GROWTH OF WOODLAND PLANTS

qrowth of Circaea lutetiaim plants was studied in various locations in or near a mixed deciduous woodland. Morphological changes resulting from increased shading included increases in leaf area ratio, specific leaf area and specific water content. Parallel measurements with a spectroradi-ometer confirmed that shading involved a reduction in both light fluence rate and light quality (e.g. red/far-red ratio). Phytochrome P_fr/P status was also studied by spectrophotometric measurements on Avena seedling test material and by biological (Lactuca seed germination) assay. Attempts were made to demonstrate phytochrome controlled changes in plant morphology under controlled environment, using both end-of-day far-red treatment and far-red enrichment of the main light period. Effects of natural shading were most clearly simulated by varying light fluence rate while maintaining a constant but high red/far-red ratio     

PHOTOREVERSIBLE CHANGES IN pH OF PEA PHYTOCHROME SOLUTIONS

Abstract— Photoinduced pH changes in unbuffered solutions of undegraded pea phytochrome were studied at 10_oC by using a glass electrode. Red light irradiation caused alkalinization of the solutions in the pH range 5.2–xs7.5 and acidification in pH 7.5–8.9. The pH changes were fully reversed by a subsequent irradiation with far-red light. The red and far-red light effects were repeatedly reversible. The solution of tryptic peptide of phytochrome (mol. wt 60000) showed similar photoreversible pH changes.     

PHYTOCHROME-MEDIATED PHOTOTROPISM IN PROTONEMATA OF THE MOSS Ceratodon purpureus BRID

Abstract— Protonemata of the moss Ceratodon purpureus cultured in white light were transferred to darkness for 3 days and then used for phototropic experiments. Irradiation of the apical region of vertically position protonemata with small beams (0.2 mm) of red light induced a growth response towards the irradiated side (positive phototropism). The phototropic response showed irradiance dependence. The effect of red light was completely reversed by far-red light following red light irradiations, demonstrating that phytochrome was the photoreceptor pigment. Far-red light or UV-blue light had no influence on either bulging or phototropism. Experiments with linearly polarized red or far-red light showed a different dichroic distribution of phytochrome in its different forms, the red-absorbing form, P_r and the far-red-absorbing form, P_fr. Red light with a vibration plane parallel to the long axis of the filaments was most effective. The effectiveness of far-red light was expressed best when its vibration plane was 90° to the electrical vector of the inductive red light.     

PHYTOCHROME-MEDIATED PHOTOTROPISM AND DIFFERENT DICHROIC ORIENTATION OF Pr AND Pfr IN PROTONEMATA OF THE FERN ADIANTUM CAPILLUS-VENERIS L.

Abstract— Single-celled protonemata of Adiantum capillus-veneris were cultured under continuous red light for 6 days and then in the dark for 15 h. Brief local exposure of a flank (5 times 20 /mi) of the subapical region of a protonema to a microbeam of red light effectively induced a phototropic response toward the irradiated side. The degree of the response was dependent upon the fluence of the red light. Red/far-red reversibility was typically observed in this photoreaction, showing that phytochrome was the photo-receptive pigment. When the flank was irradiated with a microbeam of linearly polarized red and far-red light, red light with an electrical vector parallel to the cell surface was most effective. However, the far-red light effect was most prominent when its electrical vector was normal to the cell surface. These polarized light effects indicate the different dichroic orientation of P_r (red-light-absorbing form of phytochrome) and P_r (far-red-light-absorbing form of phytochrome) at the cell flank.     

REGULATION OF PROTEIN PHOSPHORYLATION BY PHYTOCHROME IN Sorghum bicolor

Abstract— In vitro phosphorylation of some polypeptides was affected in extracts obtained from 5-and 6-day-old plants irradiated with 5 min of red light. The phosphorylation of 55 kDa polypeptide in both 5- and 6-day-old plants, a 60 kDa, and 76 kDa polypeptide in 6-day-old plants and 70 kDa, 67 kDa polypeptide in 5-day-old plants was stimulated by red light. This effect was reversible by far-red light. The extent of stimulation by red light and reversal by far-red light varied for different polypeptides. No differential effect of red and far-red light was seen on the phosphorylation of 94 and 40 kDa polypeptides. In fact, phosphorylation of 94 kDa polypeptide in 6-day-old plants decreased on red light irradiation. These results show that the phosphorylation or dephosphorylation of some proteins is affected by phytochrome and the effect of light is also dependent on the age of the plant.     

ANALYSIS OF LIGHT-CONTROLLED ANTHOCYANIN FORMATION IN COLEOPTILES OF Zea mays L.: THE ROLE OF UV-B, BLUE, RED AND FAR-RED LIGHT

Abstract— Light-induced anthocyanin formation in Zea mays L. coleoptiles was investigated in seven different varieties of this species. Under the test conditions, four varieties showed practically no response to any waveband used (UV, continuous red and continuous far-red), two responded strongly to both UV and far-red, and one showed a strong response only to far-red. The radiation-sensitive varieties showed, however, only a very weak response to continuous red light. In those varieties sensitive to far-red light, a pretreatment with continuous red light led to a greatly enhanced response to UV or in one case the manifestation of a response to UV that was previously lacking. Further investigations in one radiation-sensitive variety (INRA) showed that the UV response was to UV-B radiation below 350 nm. The UV response, as well as the far-red and blue responses in this variety, showed fluence-rate dependency. Red light was almost ineffective and showed only a very weak fluence-rate dependency.     

EVIDENCE FOR PHYTOCHROME CONTROLLED ENDOMITOSIS AND CELL ELONGATION IN PISUM SATIVUM EPICOTYLS

Elongation and endomitosis were studied in the epicotyl cortex cells of germinating seeds of Pisum sativum cv. Rondo. One min of red light per 24 h is sufficient to fully inhibit endomitosis. Terminal far-red irradiation can reverse the red effect to the level established by far-red light alone. This justifies the conclusion that phytochrome is involved in the regulation of endomitotic DNA replication. Since far-red light alone inhibits endomitosis to about 50%, we conclude that very low levels of Pfr are required to influence the endomitotic cycle.     

THE PHOTORECEPTORS INVOLVED IN ANTHOCYANIN SYNTHESIS

Abstract— Experiments with irradiation sequences where red precedes far-red lead to the conclusion that, in turnip, phytochrome is the only pigment mediating anthocyanin synthesis in red and far-red. Results from experiments where far-red precedes red, however, suggest that more than one reaction is involved. A possible interpretation is that the 'high-energy' reaction in far-red and the low energy red/far-red reversible reaction are mediated by two different forms of phytochrome.
The 'high-energy' reaction in blue light does not appear to depend on phytochrome.     

Manipulation of the Phytochemical Profile of Tenderstem® Broccoli Florets by Short Duration,Pre-Harvest LED Lighting

Light quality has been reported to influence the phytochemical profile of broccoli sprouts/microgreens; however, few studies have researched the influence on mature broccoli. This is the first study to investigate how exposing a mature glasshouse grown vegetable brassica, Tenderstem^® broccoli, to different light wavelengths before harvest influences the phytochemical content. Sixty broccoli plants were grown in a controlled environment glasshouse under ambient light until axial meristems reached >1 cm diameter, whereupon a third were placed under either green/red/far-red LED, blue LED, or remained in the original compartment. Primary and secondary spears were harvested after one and three weeks, respectively. Plant morphology, glucosinolate, carotenoid, tocopherol, and total polyphenol content were determined for each sample. Exposure to green/red/far-red light increased the total polyphenol content by up to 13% and maintained a comparable total glucosinolate content to the control. Blue light increased three of the four indole glucosinolates studied. The effect of light treatments on carotenoid and tocopherol content was inconclusive due to inconsistencies between trials, indicating that they are more sensitive to other environmental factors. These results have shown that by carefully selecting the wavelength, the nutritional content of mature broccoli prior to harvest could be manipulated according to demand.     

THE EFFECT OF RED AND FAR-RED LIGHT ON NUCLEIC ACID METABOLISM IN RYE SEEDLING SHOOTS

Abstract— The quantitative changes in the levels of RNA and DNA in shoots treated with red and/or far-red light are presented.
The results indicate that red light, but not far-red light, stimulated cell division. The changes in RNA are discussed in relation to the nature of the light treatment.     

PHYTOCHROME CONTROL OF EXTRACELLULAR PEROXIDASE ACTIVITY IN MUSTARD INTERNODES: CORRELATION WITH GROWTH, and COMPARISON WITH THE EFFECT OF WOUNDING

Abstract— The effects of phytochrome status on extracellular peroxidase activity were investigated in Sinapis alba L. seedlings grown for 12 days under continuous white light and transferred to darkness after a red light or a far-red light pulse. The rates of extension growth and dry matter accumulation in the first internode were increased by the far-red light pulse. Extracellular proteins, obtained by low speed centrifugation of intact internodes infiltrated with CaCl₂, were separated by isoelectrofocusing, and four extracellular acidic peroxidases were resolved, the most active being A3 and A4 (both ˜60 kD). The activity of A4 was reduced by the far-red light pulse perceived by phytochrome, while the activity of A3 was unaffected. The promotion of internode extension growth caused by far-red light is biphasic [Casal and Smith (1989) Plant, Cell Environ. 12 ,511–50]. Changes in peroxidase activity were detected prior to the second, but not to the first phase of the internode growth promotion. The effects on both growth and peroxidase activity were virtually restricted to the upper half of the internode and, once established, did not subsequently increase in magnitude.
In contrast to the effects mediated by phytochrome, blue light pretreatments affected growth but not extracellular peroxidase activity. Wounding the internode reduced extension growth, increased the activity of A3, but caused no significant effects on A4.
Other extracellular proteins, separated in sodium dodecyl sulphate polyacrylamide gels and stained with Coomassie blue, showed no significant differences. The concentration of extracellular proteins was higher in the upper than the lower half of the internode.
Results are discussed in terms of phytochrome effects in light grown plants, peroxidase activitv-arowth relationships, and extracellular peroxidase isoform functions.     

SOME EFFECTS OF LIGHT ON LEAF GROWTH IN PISUM SATIVUM AND TROPAEOLUM MAJUS

Abstract— The effect of wave-length of light on leaf expansion in Tropaeolum majus 'Double Orange Gleam' and Pisurn sativum 'Meteor' has been studied. In both species leaf growth is strongly promoted by light.
Increasing the daily duration of exposure to light increased leaf expansion in Tropueolum in both blue and red wave-bands over a range of light intensities. In Pisum a similar effect of ail increase in duration of irradiation was found over the whole range of intensities used for blue light but only at the highest intensity for red light: at the two lower intensities in red an increase in duration of the light treatment beyond 1 hr did not increase leaf expansion.
In both species a period of 4 hr of blue followed by 4 hr of red promoted leaf growth more than 4 hr of red followed by 4 hr of blue. The effect of a 4 hr period of red light was largely prevented when it was followed by far-red; the effect of 4 hr of blue light, on the other hand, was not affected by subsequent exposure to far-red.
It is concluded that leaf growth in Pisum and Tropaeolum is dependent not only on the 'low-energy' red/far-red reversible reaction but also on one or more 'high-enerFy' photo-reactions.     

PHYTOCHROME INDUCTION OF PHOTOREACTIVATING ENZYME IN Phaseolus vulgaris L. SEEDLINGS*

Abstract— Photoreactivating enzyme (PRE) activity was measured in hypocotyls of Phaseolus vulgaris L. seedlings using a radioimmunoassay for thymine dimers. In dark-grown seedlings a five-fold increase in PRE activity was observed after 6 h of irradiation with blue or far-red light. Short time irradiations with red light were also effective. Reversibility of this red-light-effect by a subsequent short term irradiation with far-red light and also the high effectiveness of continuous far-red light indicate that PRE activity is under phytochrome control. This observation points to PRE induction via gene activation.     

THE CONTROL BY PHYTOCHROME OF NITRATE REDUCTASE IN THE CURD OF LIGHT-GROWN CAULIFLOWER

Abstract— The activity of nitrate reductase from the curd of light-grown cauliflower ( Brassica oleracea (L) var botrytis (DC) 'St. Hilary') is modulated by nitrate and by light. Using broad-band sources of equal photosynthetically active radiation but with different proportions of red and far-red light, a linear relationship between nitrate reductase activity and ψ(Estimated phytochrome photoequilibrium) was obtained. This relationship, apparent after 8 h incubation, was maintained and little altered after 48 h incubation. The linearity was apparent between ψE 0.26 and ψE 0.69; ψE 0.26 being no more effective than a dark control. Far-red reversibility confirmed the involvement of phytochrome. Brief pulses of red light were also used to establish a range of phytochrome photoequilibria within the tissue. Again a linear relationship between ψ and nitrate reductase activity was obtained with a threshold for the response at ψ 0.3. With both monochromatic and broad-band sources it was seen that neither photon fluence rate nor duration of exposure affected the final activity of the enzyme and that phytochrome was acting solely through ψ (or [Pfr] since phytochrome is stable in this tissue) to bring about these responses.     

PHYTOCHROME ACTION AT HIGH PHOTON FLUENCE RATES: RAPID EXTENSION RATE RESPONSES OF LIGHT-GROWN MUSTARD TO VARIATIONS INFLUENCE RATE and RED: FAR-RED RATIO*

Abstract— Extension growth rate of light-grown mustard (Sinapis alba L.) seedlings was monitored continuously using a sensitive linear displacement transducer system. When high fluence rates (ca 2 mmol m^?2 s^_1) of mixed red and far-red light were presented to the growing internodes from fibre optic probes, fluctuations in extension rate occurred during the first 30 min. High red: far-red ratios (R: FR) caused growth deceleration, whilst low R: FR caused transitory growth acceleration. These changes in extension rate were not exactly as predicted from the proportions of Pr (the red-absorbing form of phytochrome) and Pfr (the far-red absorbing form of phytochrome) calculated to be established by the light sources. Nevertheless, the data demonstrate that phytochrome is able to control extension growth at fiuence rates approaching those of summer sunlight, thereby providing the capacity to sense the presence of neighbouring vegetation before shading seriously compromises photosynthesis. Varying fiuence rate over two orders of magnitude whilst maintaining R: FR constant evoked transient fluctuations in extension rate. At high R: FR, a 100-fold step down in fiuence rate led, after a lag of ca 10 min, to a transient (i.e. 20 min) deceleration of extension that was followed by a marked transient (i.e. 20 min) acceleration. After a 100-fold step up in fiuence rate, a transient (i.e. 20 min) acceleration only was observed, beginning after a lag of ca 10 min. When R: FR was low, neither a step-down nor a step-up in fluence rate resulted in appreciable fluctuations in extension rate. The data are discussed in relation to the possible role played by the accumulation of photoconversion intermediates using a simple computer model for simulating active phytochrome concentrations at high fluence rates. The possibility that the mechanism for the photoperception of light quality by phytochrome may be capable of rapid adaptation to fluence rate fluctuations is proposed.