EFFECT OF BLUE/UV LIGHT ON ANTHOCYANIN SYNTHESIS IN TOMATO SEEDLINGS IN THE ABSENCE OF BULK CAROTENOIDS

Abstract Anthocyanin synthesis in the hypocotyl of tomato ( Lycopersicon esculentum ) seedlings responds strongly and specifically to blue/UV light while the response to red and far-red light, operating through phytochrome, is weak. The herbicide Norflurazon (SAN 9789) was used to inhibit synthesis of colored carotenoids almost completely without affecting growth and development measurably. Even though carotenoid content was reduced to less than 2% of normal and the fluence rate response function for blue and UV light was linear within the experimental range, Norflurazon treatment did not reduce seedling sensitivity toward blue/UV light. It was concluded that at least'bulk'carotenoids are not the photoreceptor chromophore of the blue/UV photoreceptor pigment.     

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.     

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.     

ACTION SPECTRUM FOR PHOTOREVERSION OF THE ACTIVE Pfr-FRACTION OF Mougeotia in vivo

Abstract— The dichroic oriented fraction of the far-red light absorbing form of phytochrome (Pfr) in the green alga Mougeotia was characterized by action spectroscopy. Microbeam irradiations had to be used for the induction of chloroplast movement in Pfr-containing cells, because of the special dichroic absorption characteristics of the red light absorbing form of phytochrome (Pr) and Pfr in the alga. Fluence-response curves were elaborated especially in the far-red spectral region by reverting Pfr to Pr at the flanks of the cells and thus generating Pfr-gradients. Linearly polarized light vibrating perpendicularly to the cell axis was used, thus corresponding to the S,-transition moments of Pfr at the flanks of the cells. The action spectrum is characterized by a peak at approximately 715 nm and a very pronounced decrease towards 728 and 734 nm. The data indicate that the spectral absorption of the active Pfr-fraction in green Mougeotia is shifted towards shorter wavelengths as compared to extracted phytochrome from etiolated or even green higher plants. This "blue shift" seems to be typical for Pfr from green lower plants.     

PHYTOCHROME REGULATION OF STEM GROWTH AND INDOLE-3-ACETIC ACID LEVELS IN THE lv AND Lv GENOTYPES OF Pisum

Phytochrome influences stem elongation and the mechanism for this is not understood. The levels of indole-3-acetic acid (IAA) were analyzed in an leLv genotype of Pisum sativum L. which responded to end-of-day far-red light by doubling growth rate. The IAA levels in epidermal peels increased 40% after far-red light whereas IAA levels of the entire stem tissue changed insignificantly. This increase was reversible by red light. Under light-grown conditions, the lv mutation increases stem elongation rates by 2–3-fold and is thought to block the transduction of a phytochrome signal. Analysis of the short-term stem elongation kinetics of dark- and light-grown Lv and lv seedlings suggests that lv blocks the action of the light-stable form of phytochrome. The higher growth rate of lv plants was found to be associated with abnormally high epidermal IAA levels typical of far-red treated Lv plants. End-of-day far-red treatments did not substantially increase epidermal IAA levels in lv plants. These observations support the view that phytochrome regulation of stem elongation may occur in part through modulation of epidermal IAA levels. The lv mutation may result in increased internode growth in part by blocking the ability of phytochrome to decrease epidermal IAA levels.     

PHYTOCHROME CONTROL OF ITS OWN SYNTHESIS IN Sorghum vulgare AND Avena sativa

The accumulation of phytochrome in the dark was measured for Avena sativa seedlings after a white light pretreatment and for Sorghum vulgare seedlings after continuous red or far-red light treatments, using the herbicide Norflurazon to prevent greening under continuous irradiation. In both cases the accumulation of phytochrome depends on the state of the phytochrome at the light-dark transition: high P_fr levels (red light pulse) led to a slower rate of phytochrome accumulation than lower P_fr levels (long wavelength far-red (RG 9) light pulse). Poly-(A⁺)-RNA was isolated fromA. sativa seedlings grown for 48 h in darkness + 24 h WL + light pulse (5 min) (red, RG 9 light, red followed by RG 9 light or RG 9 followed by red light pulse) + 19 h darkness. The poly-(A⁺)-RNA was translated in a rabbit reticulocyte lysate system and the translation products were immunoprecipitated by specific anti-phytochrome antibodies. It was demonstrated that the activity of mRNA coding for phytochrome was under phytochrome control.     

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     

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.     

RESPONSE OF LIGHT-GROWN WILD-TYPE and LONG HYPOCOTYL MUTANT CUCUMBER PLANTS TO END-OF-DAY FAR-RED LIGHT

Abstract— A long-hypocotyl mutant ( lh ) of cucumber ( Cucumis sativus L.) has been studied which has previously been shown to lack phytochrome control of growth in de-etiolated seedlings and thought to be modified with respect to the light-stable type of phytochrome. We have analyzed the response of lh mutant and isogenic wild-type (WT) plants to daily treatment with end-of-day far-red light (EODFR). Only the WT responded to this treatment resulting in a large increase in internode length; an increase in petiole length; changes in leaf development (increased area, decreased thickness and reduction in indentation); redistribution of dry matter from leaf blades to stem; increased apical dominance and promotion of tendril formation. There were only small or no significant effects on chlorophyll and total carotenoid content, chlorophyll alb ratio, soluble protein levels and net photosyn-thetic rates. The lh mutant failed to respond to EODFR treatment, and had the appearance of a shade-avoiding plant growing in extreme shade. The lh mutant appears to completely lack the phytochrome responses attributable to the type of phytochrome that is active in shade detection. A discussion of the possible roles of the stable and labile types of phytochrome in light grown plants follows.     

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-dependent photomovement responses mediated by phototropin family proteins in cryptogam plants

In this review, we describe the regulation of photomovement responses by phototropin and phytochrome photoreceptors. The blue light receptor phototropin mediates various photomovement responses such as phototropism, chloroplast movement and stomatal opening. In cryptogamic plants including ferns, mosses and green alga, red as well as blue light mediates phototropism and chloroplast movement. The red/far-red light reversibility suggests the involvement of phytochrome in these responses. Thereby, plant growth is presumably promoted by coordinating these photomovements to capture efficiently light for photosynthesis.     

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.     

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.     

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.     

Light Regulation of Phytochrome Content in Wild-type and Aphototropic Mutants of the Moss Ceratodon purpureus

In filaments of the moss Ceratodon purpureus , phototropism is controlled by the photoreceptor phytochrome. Thirty-three aphototropic mutants with a proposed defect in phytochrome-chromophore biosynthesis were isolated and analyzed. The phototropic response of those mutants was rescued with the precursor of the phytochrome chromophore, biliverdin. Phytochrome spectral activity was measured in 19 arbitrarily chosen mutants. All contained low but still measurable quantities of photoactive phytochrome; the highest level was around 15% of the wild-type. The level of total phytochrome (apophytochrome and holophytochrome) as assayed by immunoblotting was indistinguishable from wild-type. The content of photoactive phytochrome in Ceratodon is light-regulated. Phytochrome of wild-type kept for 24 h in red light was reduced to 50% as compared to dark controls but was unaffected by blue. The red-light-induced decrease was partially reversible by far-red light, indicating that phytochrome itself is the photoreceptor for this response. This regulation was further analyzed with the mutant ptr114 , which contains 15% photoactive phytochrome as compared to the wild-type. In this mutant, continuous red light given for 6 days decreased the level of spectrally active phytochrome down to 25% of dark controls, whereas the amount of phytochrome found on immunoblots was hardly reduced. This indicates that the loss of phytochrome affects only the holoprotein and implies that Ceratodon phytochrome is specifically degraded as a far-red-absorbing phytochrome.     

PHYTOCHROME-MEDIATED THRESHOLD CONTROL OF HYPOCOTYL GROWTH IN PARTLY DE-ETIOLATED MUSTARD (Sinapis alba L.) SEEDLINGS

Abstract— Hypocotyl elongation in etiolated mustard ( Sinapis alba L.) seedlings is known to be controlled by phytochrome (Pfr) through a threshold mechanism. The Pfr threshold value required to suppress hypocotyl growth was low (3 times 10⁻²% Pfr, based on total phytochrome in the hypocotyl at 36 h after sowing = 100%). In the present study the question was addressed whether the threshold control by Pfr of hypocotyl elongation also operates in light-pretreated, partly de-etiolated seedlings after transfer to darkness. The experimental results show that this is the case. Calculation of the threshold level in far-red light pretreated seedlings led to a very low value (3 times 10⁻⁷%) compared to etiolated seedlings (3 times 10⁻²%). In red light pretreated seedlings the threshold level was calculated to be 9 times 10⁻⁷%. Since the light pretreatment affected the rate of degradation of phytochrome strongly (half-life of Ptot in continuous red light was found to be 35 min in far-red pretreated instead of 47 min in etiolated material), the difference in threshold level between far-red and red pretreated material cannot be interpreted unambiguously. However, the conclusion can be drawn that light nretreatment strongly increases the degradation rate of Pfr and decreases the threshold level.     

PHYTOCHROME-MEDIATED CONTROL OF PROLAMELLAR BODY REORGANIZATION AND PLASTID SIZE IN MUSTARD COTYLEDONS

Abstract— The development of plastids in the palisade parenchyma cells of the cotyledons of mustard seedlings ( Sinapis alba L.) was studied by electron microscopy. In darkness the etioplasts undergo a sequence of morphogenic changes previously recognized in principle in bean and barley leaves, as summarized by Rosinski, J. and W. G. Rosen (1972) Quart. Rev. Biol. 47 , 160–190. From 12 to 36 h after sowing, an increase in the percentage of etioplast profiles with paracrystalline prolamellar bodies can be observed. Thereafter, the degree of organization and size of the prolamellar bodies decrease. 60 h after sowing, the etioplasts show only remnants of prolamellar bodies with irregularly spaced tubules. Continuous far-red light, which is considered to operate via phytochrome, counteracts the decay of organization of the prolamellar body and strongly increases the size of the plastids. The effect of continuous far-red light (onset of light 36 h after sowing) can be substituted by 12 h of far-red light given between 36 and 48 h after sowing. It is shown with red and far-red light pulses that the morphogenic effect of long-term far-red light on plastid size and appearance of the prolamellar body is exclusively due to phytochrome (P_fr). Changes by light in the amounts of protochlorophyll(ide) or chlorophyll(ide) do not affect these results. The action of P_fr on the structure of the prolamellar body is a relatively fast process, occurring within 3 h. Formation of thylakoids does not seem to be under phytochrome control. Rather, this response seems to be related to the protochlorophyll(ide)→ chlorophyll(ide) a transformation.     

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.     

STIMULATION OF THE SHIBATA SHIFT BY PHOTOCHROME IN THE COTYLEDONS OF THE MUSTARD SEEDLING SINAPIS ALBA L.

Abstract— In the cotyledons of the mustard seedling Sinapis alba L. the duration of the Shibata shift can be greatly shortened by a pretreatment with light pulses prior to the protochlorophyllide– chloro-phyllide a photoconversion. It was shown that the light pulses act through photochrome (P _fr ). Since reversibility of a red light pulse induction by a far-red light pulse is rapidly lost (within 2 min) it is concluded that at least the initial action of P_fr occurs rapidly in this response. On the other hand, the effect of a red light pulse on the rate of protochlorophyll regeneration in the mustard seedling cotyledons is fully reversible by a far-red light pulse for more than 5 min. It is concluded that control of protochlorophyll regeneration and control of the Shibata shift by phytochrome cannot be consequences of the same initial action of P_fr Apparently P_fr controls both phenomena independently.     

PHOTOREGULATION OF ROOT: SHOOT RATIO IN SOYBEAN SEEDLINGS*

Abstract— The partitioning of plant growth between shoot and root has the potential to affect diverse physiological processes including water and nutrient uptake, nitrogen fixation, light interception, and interactions between plant and soil microorganisms. Root: shoot ratio is determined both by genetics and developmental status as well as by availability of water, nutrients and light. It is shown here that relative root growth was modulated by photomorphogenetic treatments designed to affect phytochrome (supplemental far-red radiation given either as an end-of-day treatment or continuously during the photoperiod) or blue light photoreceptors (blue light-deficient low pressure sodium lamps ± low irradiances of supplemental blue [i.e. 5% of total photon flux: 25 μ.mol m^?2 s^?1]). Photomorphogenetic control of root: shoot ratio was apparent within1–2 days when light treatments were initiated at emergence, and did not necessarily involve changes in net seedling growth. On the other hand, shortened daylength inhibited early seedling growth but had little effect on partitioning. Changes in relative root dry matter induced by supplemental far red radiation or blue light deficiency were similar to those caused by low irradiances, suggesting that phytochrome or blue light photoreceptors may be involved in regulating the partitioning of growth between shoot and root as a part of adaptation to vegetation shade. The influence of spectral quality on root: shoot ratio should be considered when comparing plants grown under different types of lighting or with different spacing.