Phytochrome Control Research Articles

Effect of light and exogenously applied precursors on amaranthin synthesis in Amaranthus caudatus

Light stimulates the synthesis of amaranthin in Amaranthus caudatus var. viridis. Evidence suggests that this stimulation is markedly dependent on seedling age. Synthesis is controlled by both a “low-energy” red/far-red reversible phytochrome system and an HER at least partially under phytochrome control. In seedlings exposed to light, synthesis is promoted by exogenously applied DOPA and tyrosine. It is suggested that at least two light-promoted reactions occur in the biosynthetic pathway; one between tyrosine and DOPA and a second between DOPA and amaranthin.

Quantitative studies on ferredoxin in greening bean leaves.

Two methods of measuring small amounts of the iron-sulphur protein ferredoxin are described. One involves measurements of the signal at g=1.96 produced by reduced ferredoxin in an e.p.r. (electron-paramagnetic-resonance) spectrometer; the other depends on the rate of ferredoxin-dependent electron transport in a chloroplast bioassay measured in an O(2) electrode. These methods of measurement were used to examine the development of ferredoxin during the greening of etiolated bean leaves. Ferredoxin is present in low concentrations in the leaves and cotyledons of 14-day-old etiolated beans (Phaseolus vulgaris L. var. Canadian Wonder), and develops in a linear manner with time when the leaves are illuminated. This synthesis appears to be independent of chlorophyll synthesis during the early stages of greening. However, the chlorophyll/ferredoxin ratio reaches a final value of approx. 360 irrespective of the light intensity, indicating the existence of a control mechanism operative in deciding the stoicheiometry of these components in the mature chloroplast. The ferredoxin synthesis appears to be light-dependent, and red light is the most effective in its promotion. The effect of red illumination is not reversed by far-red light, indicating the absence of a phytochrome control of ferredoxin synthesis. From experiments using specific inhibitors of chloroplast protein synthesis, it is concluded that ferredoxin is synthesized on cytoplasmic ribosomes.

Phytochrome action inOryza sativa L. VI. Red far-red reversible effect on early development of coleoptiles

When 3–4 mm long coleoptiles of etiolated rice seedlings (cv. Koshijiwase) were irradiated with continuous red light their growth was seriously inhibited. If a brief exposure of red light (4×103 ergs cm−2) was given to the short coleoptiles, the growth rate dropped immediately after the irradiation, but the growth did not stop till the coleoptile reached some calculated length. If another brief red irradaition of the same order was given 24 hr after the first, the growth rate and the final length dropped further. The effect of red light was reversed by successively given far-red light, and this response was repeatedly red and far-red reversible. The escape reaction was rather slow so that photoreversibility was not lost at all by 8th hr, and 50% of the initial reversibility was lost within ca. 16 hr at 25±0.5 C. Blue light also induced the inhibition of coleoptile elongation, the effect was reversed by subsequent far-red irradiation, and this could be obtained repeatedly. Thus, the photoinhibition of the young coleoptile can be concluded to be under the control of phytochrome, and the mode of action appeared quite different from the previously reported results with longer coleoptiles.

Endogenous rhythmicity and energy transduction. II. Phytochrome action and the conditioning of rhythmicity of adenylate kinase, NAD- and NADP-linked glyceraldehyde-3-phosphate dehydrogenase in Chenopodium rubrum by temperature and light intensity cycles during germination

Endogenous rhythmicity in NADP- and NAD-linked glyceraldehyde-3-phosphate dehydrogenase (NADP- and NAD-GPD) as well as in adenylate kinase (AK) activity is initiated or synchronized during cyclic germination conditions of light and temperature, and is free-running in a dark period interrupting continuous light.There is phytochrome control of the amplitude in NADP-GPD and AK oscillations during the first hours of darkness if the beginning of the dark period is in phase with the beginning of the germination period. The endogenous rhythm acts like an "on-off" switch for potential phytochrome action. The results are discussed in relation to daily photoperiodic cycles.

Regulation of senescence in detached rice leaves by light, benzimidazole and kinetin

The senescence of excised leaves of Oryza sativa Var. BBS 873 was followed by measuring the net breakdown of chlorophyll and protein with respect to the time of detachment. Kinetin was relatively ineffective but benzimidazole was effective in retarding the senescence. Red light was also effective in senescence retardation but on the other hand, far-red light speeded the senescence. Benzimidazole was the most effective treatment under red light in retarding leaf senescence. The red light induced retardation and the far-red enhancement of senescence is suggested to be under phytochrome control and dependent on photosynthesis.

Blue Light Interference in the Phytochrome-controlled Germination of the Spores of Cheilanthes farinosa

Short exposure of the spores of Cheilanthes farinosa to low intensity red light promotes their germination, which is not reversed by a subsequent exposure to far red light. Germination is, however, inhibited by blue light administered before or after red light. Inhibition of germination by blue light is annulled by exposure to a higher intensity of red light, and germination of the repromoted spores is inhibited by far red light. Mutual photoreversibility of germination is also observed in repromoted spores irradiated successively with far red and red light. Although germination appears to be basically under phytochrome control, it is postulated that the presence of a blue light-absorbing pigment interferes with phytochrome transformations in the spores.

INDUCTION OF RAPID CHLOROPHYLL ACCUMULATION IN DARK GROWN SEEDLINGS. II. PHOTOREVERSIBILITY

SUMMARY A short pre-irradiation with red light some hours before the start of continuous illumination with white light eliminates the lag phase in chlorophyll-a (Chl-a) accumulation. In seedlings of several cultivars of bean, pea, and maize, grown in complete darkness, this inductive action of red light is hardly reversible by far red. Most cases of low reversal can be explained by the considerable inductive capacity of far red light itself. However, far red reversibility of the effect induced by red increased considerably with increasing duration of the period of dark incubation between pre-irradiation and continuous white light. On the other hand, more or less complete red-far red reversal was observed in plants de-etiolated by a pre-irradiation given some hours prior to the normal inductive treatment. Even relatively short exposures to a green safelight caused a significant degree of de-etiolation with concomitant increase in subsequent red-far red antagonism. It is concluded that the biosynthetic pathway leading to protochlorophyll (Pchl) and Chl-a is not directly under phytochrome control. In excised leaf material the rate of Chl-a accumulation in continuous light proved strongly depressed and completely insensitive to irradiations that were inductive in intact plants.

Phytochrome Control of Germination of Rumex crispus L. Seeds Induced by Temperature Shifts

High germination of curly dock (Rumex crispus L.) seeds is evident after suitable imbibition and temperature shift treatment, but germination at constant temperatures fails without an input of far red-absorbing form of phytochrome. Preliminary imbibitions at high temperatures (30 C) sharply reduce germination induced by temperature shifts. High germination may be restored by low energies of red radiation, or by brief far red adequate for the photosteady state. Prolonged far red during imbibition also nullifies temperature shift-induced germination. After prolonged far red, high germination may be restored by red radiation of an energy dependent upon the duration of the far red treatment. The evidence supports the conclusion that dark germination induced by temperature shifts arises from the interaction of pre-existent far red-absorbing form of phytochrome in the mature seeds with the temperature shift.

Phytochrome Control of Growth Cessation and Initiation of Cold Acclimation in Selected Woody Plants

Short day enhancement of cold acclimation in twigs of Cornus (red-osier dogwood), Weigela, and Pyracantha (firethorn) was studied using dark interruptions with red or with red-far red radiation. Hardiness was estimated by freezing stem tissues to preselected temperatures and evaluating injury electrolytically. Dark-period interruptions with red radiation suppressed cold acclimation in Cornus and Weigela. When red light was followed by far red light, suppression was relieved. No radiation control of acclimation was found with Pyracantha. The short day enhancement of cold acclimation in Cornus and Weigela appears to be phytochrome-mediated.

Phytochrome-controlled Nyctinasty in Albizzia julibrissin

Indole-3-acetic acid, alpha-naphthylacetic acid, and 2,4-dichlorophenoxyacetic acid (0.001 to 1.0 mm) inhibit the nyctinastic closure of excised Albizzia leaflet pairs; antiauxins and auxin analogs are ineffective, and the auxin effects seem not to be mediated by ethylene. Indoleacetic acid (0.001 to 0.1 mm) also promotes rhythmic opening in the dark, but is ineffective during that phase of rhythmic closure ("leaky phase") which is insensitive to azide. At these concentrations, all of the indoleacetic acid effects are reversible upon transfer of the tissue to water and are linked to alteration of potassium flux in pulvinule motor cells.A supraoptimal concentration of indoleacetic acid (1 mm) inhibits rhythmic opening as well as nyctinastic closure, although it has little or no effect on potassium flux in motor cells. These inhibitions cannot be completely reversed by transferring the leaflets to water.Although indoleacetic acid (0.01 to 1.0 mm) inhibits leaflet opening and potassium flux in dorsal and ventral motor cells when leaflets are transferred from darkness to light, it has no effect during other portions of the light period, implying that changes in endogenous auxin do not control leaflet angle in the light. Neither does auxin seem to be involved in the phytochrome-regulated process, since it does not alter phytochrome control of leaflet movement or potassium flux. However, endogenous auxin probably plays an important role in controlling potassium flux into ventral motor cells during the opening phase of rhythmic leaflet movement in the dark.

The effect of light on endogenous cytokinin levels in seeds of Rumex obtusifolius

Exposure of Rumex obtusifolius seed to red light resulted in a rapid increase in extractable cytokinins. This increase can be reversed if the red light treatment is immediately followed by far-red irradiation. In germinating seed hardly any cytokinin activity could be detected in the butanol and aqueous extracts. An increase in the amount of activity present in the petroleum ether extracts of these seeds was, however, observed.The present findings suggest that cytokinin activity in light-sensitive seeds could be under the control of phytochrome.

Phytochrome Control of Another Phytochrome-mediated Process

The phytochrome-mediated attachment of root tips of mung bean (Phaseolus aureus) and barley (Hordeum vulgare) to glass is affected by the prior exposure of hydrated seeds or seedlings to red or far red radiation. Prior irradiation of seeds or seedlings of mung bean with red light promotes attachment, while far red light promotes detachment of root tips. Similar exposure of barley seeds and seedlings to red light accentuates detachment, while far red light accentuates attachment of root tips. Red-far red light reversibility of the pretreatments indicates phytochrome control.Indoleacetic acid concentrations of 10 nM or higher appear to mimic the effects of far red light pretreatments in both mung bean and barley roots tips.

Phytochrome Control of the Level of Extractable Ribonuclease Activity in Etiolated Hypocotyls

AN increase in RNA degrading activity of hypocotyl homo-genates can be detected 6–10 h after transferring 5 day old, dark-grown seedlings of Lupinus albus L. to continuous white light1. This increase is concomitant with the onset of inhibition of hypocotyl extension1, 2. The ribonuclease component whose level of activity is affected by light treatment (tentatively identified as a ribonucleate nucleotido-2′-transferase (cyclizing) (EC 2.7.7.17)) is associated with the ribosomes (and polysomes)1 in hypocotyl homogenates. This is in contrast to the bulk of RNA degrading activity in homogenates which is associated with the soluble fraction1. Isolation of the ribosomal fraction therefore makes it possible to follow changes in the level of activity of this ribonuclease which would be too small to detect in unfractionated cell homogenates. The results reported here indicate that the photoconversion of the red-absorbing form of phytochrome (Pr) to the physiologically-active far-red-absorbing form (Pfr) leads to a specific increase in ribosome-bound ribonuclease activity.

Ion Relations, Chlorophyll Synthesis and the Question of ‘Bulk’ Phytochrome in Pisum sativum

AbstractLack of correlation between spectrophotometric phytochrome assays and physiological experiments has led to the concept of a ‘bulk’ phytochrome that is measurable but inactive, in contrast to an active form that is not measured in the standard assay. Because of suggestions that phytochrome action involves changes in membrane permeability, particularly to potassium ions, we investigated potassium and sodium uptake and efflux in Pisum sativum epicotyl sections which were equally de‐etiolated yet differed three‐fold in their phytochrome contents. Although dependent on the metabolic integrity of cell membranes (as shown by respiratory inhibitors) the selective uptake of potassium in this tissue is not under phytochrome control. Experiments were also conducted to see whether a three‐fold difference in phytochrome content affects chlorophyll synthesis in Pisum. Differences in chlorophyll synthesis observed can be related to the effectiveness of the pretreatments in eliminating the lag phase, not to their differences in phytochrome; Pfr decay rate has no effect on chlorophyll synthesis. The failure to find any correlation with the amount or state of ‘bulk’ phytochrome in these and previous experiments indicates that no function of this material is yet known.

Photocontrol of Anthocyanin Synthesis

Red far red reversibility (phytochrome control) of anthocyanin synthesis can be easily demonstrated for the response induced by short (5 minutes) and relatively short (4 hours) irradiation. Red far red reversibility of the response induced by longer irradiations can be demonstrated by the use of cyclic irradiations alternating short exposures to red and far red light.The level of anthocyanin formed during the dark incubation period following exposure to light depends upon the duration of the irradiation and becomes proportionally smaller as the length of the irradiation increases.Production of anthocyanins under cyclic irradiations depends upon the total energy applied and upon the length of the dark interval between successive irradiations.The relative efficiencies of radiations in various spectral ranges change with changes in the length of the irradiations.

Phytochrome-controlled rapid contraction and recovery of contractile vacuoles in the motor cells of Mimosa pudica as an intracellular correlate of nyctinasty

Using living thin sections (ca. 70-80 μ thick) of tertiary pulvini of Mimosa pudica, we have quantitatively determined that the bahavior of the contractile tannin vacuoles in the motor cells is under phytochrome control. Using material in which these vacuoles were in their most expanded state in white light, contraction was observable 3 min after the material was placed in continuous darkness. No contraction occurred if the cells were irradiated with 90 sec of far-red light; red light reversed this effect. Futhermore, the kinetics of change of the vacuolar conformation was closely paralled by that of the nyctinastic changes of the pinnule closure during the different treatments. When the section of pulvinus was irradiated with a microbeam of far red light in one part of the section, and the motor cell vacuoles in another area were monitored for contraction, they almost always responded.We therefore conclude that the contractile vacuole of the motor cell is an excellent cellular correlate of phytochrome-mediated nyctinasty in M. pudica, and discuss its possible causal role in regulating the phenomenon. It is further concluded that functional phytochrome is present in all parts of the pulvinus and that, upon absorption of the stimulus energy, an intercellular messenger is released which stimulates all the motor cells in the pulvinus.

Phytochrome Control of Germination of the Spores of Asplenium nidus

Phytochrome Control of Germination of the Spores of <i>Asplenium nidus</i>

Die Phenylalaninammoniumlyase (PAL, EC 4.3.1.5) des Senfkeimlings (Sinapis alba L.), ein elektrophoretisch einheitliches Enzym

Improved techniques in localization of phenylalanine ammonia-lyase (PAL) on polyacrylamide disk electrophoresis columns indicate that the enzyme synthesized under the control of phytochrome is electrophoretically indistinguishable from the enzyme present in dark grown mustard seedlings. Furthermore, no heterogeneity of PAL with respect to molecular size has been detected. However, the formation of high molecular weight aggregates with PAL activity in tris buffer of low concentration has been demonstrated. The data lead to the conclusion that phytochrome does not induce the synthesis of a novel PAL enzyme differing in its structural properties from the PAL in dark grown seedlings. The observations of other investigators on separable forms of PAL are critically discussed.

Deoxyribonucleic Acid-dependent Ribonucleic Acid Polymerase Activity of Nuclei and Plastids from Etiolated Peas and their Response to Red and Far Red Light in Vivo

DNA-dependent RNA polymerase activity has been found in both the nuclei and etioplasts of dark-grown pea seedlings (Pisum sativum). Although these enzymes had similar over-all characteristics with respect to substrate, pH, and inhibitor responses, they could be distinguished by their different sensitivities to sonication.Brief irradiation of the seedlings with red light resulted in an increase in the activity of both the nuclear and plastid enzymes, but the time course of this response showed it to be too slow to be considered an early result of phytochrome control of metabolism. Far red light following red treatment largely prevented the increase in the activity of the nuclear enzyme. The plastid enzyme responded to far red light in a manner similar to its response to red light so that no reversal was observed when far red treatment followed red.

Photocontrol of C-glycosylflavones in barley seedlings

The sole flavonoid of etiolated barley plumules is saponarin, a C-glycosylflavone restricted to the primary leaves. Increased saponarin synthesis is under a typical low-energy phytochrome control in both etiolated plumules and in those grown in white light. Prolonged illumination with white light, or high levels of blue light followed by red light, greatly increases saponarin and initiates the synthesis of lutonarin; this response is characteristic of high-energy photoresponses (HER). Kinetic studies show a typical lag of about 4 hr for phytochrome control of saponarin in etiolated plumules. Surprisingly, during this lag-phase and within 2 min following a red-light (132 Kerg cm −2) treatment, there is a 25 per cent decrease in saponarin recovered from whole plumules. Within 1 hr the light-treated plants yield only about half as much saponarin as do the dark controls. After 1 hr apparent saponarin content increases and by the fourth hour the flavonoid content of the light-treated and dark-control plants is similar. The fate of this “lost” saponarin is not known; it may be in part translocated into other parts of the seedling as the apical 1 cm of the plumule shows a more rapid recovery under these conditions, a part may be complexed into forms not recoverable by our techniques. Mediatory aspects of changes in saponarin localization within the tissues are considered.