Presence Of Phytochrome Research Articles

Regulation of growth and development in phytochrome mutants of Arabidopsis thaliana by solar UV

Phytochrome mutants (phyA, phyB and phyAB) of Arabidopsis thaliana were grown under ambient and UV-excluded sunlight to understand their influence on growth and development by mutual exclusion. Phytochrome A and B played a complementary role in the regulation of germination. Suppression of hypocotyl length was predominantly under the control of phytochrome B; UV photoreceptors were active in suppression of hypocotyl growth only in phyB and phyAB mutants. Exclusion of UV promoted the number and the area of rosette leaves only in presence of phytochrome A and B. Phytochrome mutation reduced petiole length, whereas UV exclusion led to an increase. Requirement of long-day period for flowering was removed in the mutants. Under short-day conditions, flowering was predominantly under the control of phytochrome B, since phyB mutants flowered earlier than phyA mutants. Solar UV regulates the number of boltings and number of siliques per plant. Overall biomass of the plants is enhanced by the exclusion of UV only in the wild type. The interaction of phytochromes with UV photoreceptors is discussed in the paper.

Nucleoside diphosphate kinase isoforms regulated by phytochrome A isolated from oat coleoptiles.

Nucleoside diphosphate kinase (NDPK) (EC 2.7.4.6), the enzyme transferring the phosphate residue from ATP to nucleoside diphosphates, is localized mainly in the cytoplasm and mitochondria and in smaller amounts in cell nuclei and the microsomal fraction. Exposure of etiolated oat seedlings to red light causes an increase of the enzyme activity by about 42% in nuclear fraction, 7% in etioplastic and 14% in postetioplastic fraction. Endogenous phytochrome A, as visualized by an immunochemical method, translocates from the cytoplasm into the nucleus upon red, far-red or white light activation. Nuclei purified from oat seedlings contain two, and the postnuclear fraction four easily separated forms of NDPK. One of the nuclear isoforms (I(n)) and one isoform isolated from the postnuclear fraction (II(pn)) are activated by red light in the presence of phytochrome A purified from etiolated oat coleoptiles. Both phytochrome A-activated NDPKs purified to electrophoretic homogeneity have the same molecular mass (17-18 kDa) determined by SDS/PAGE. Both enzymes in the native form have similar molecular masses (71 and 63 kDa).

A phytochrome-mediated alteration from stem to rosette growth on chicory root explants in vitro

Chicory root explants (Cichorium intybus L. var. foliosum) of two cultivars, taken before and after hydroponic forcing, were cultured in vitro in complete darkness supplemented with red and far-red light treatments. Using 5 min red light per day, the strong stem elongation occurring in complete darkness was converted to rosette formation. This reaction was reversed to stem elongation (accompanied by leaf formation) adding 15 min far-red light after the red light. Fifteen min far-red light per day alone caused the same reaction as 5 min red/15 min far-red light. Far-red light followed by red light caused rosette formation. In stems, formed under complete darkness in vitro, the presence of phytochrome was shown. No phytochrome was detected in the root fragment itself.

Light‐induced, dark‐reversible colour shifts in petals of Phlox

Flowers of some Phlox (Phlox x paniculata L.) varieties undergo daily colour shifts, being blue in the early morning, turning red during the day, and returning to blue in the evening. The colour shift, which occurs only in the upper (adaxial) petal surfaces, is due to the daily changes in ambient light. In the laboratory, colour shifts could be induced by 2.5 h of ultraviolet, visible or far‐red light and recorded by reflectance spectrophotometry.There are indications that irradiations with different kinds of light cause qualitatively different colour shifts, and that thus more than one photoreceptor pigment and more than one primary light reaction may be involved. The presence of phytochrome was demonstrated in petals of white Phlox flowers by in vivo transmission spectrophotometry. It is therefore possible that colour shifts in coloured Phlox flowers are mediated by phytochrome. Possibly the movement of ions (e.g. hydrogen ions) into or out of the vacuole (where the visible pigments are located) is affected by light absorption in a pigment in the tonoplast.

The presence of phytochrome in purified barley etioplasts and its in vitro regulation of biologically-active gibberellin levels in etioplasts

Data are presented confirming that purified barley etioplasts contain, or have associated with them, consistently detectable amounts of photoreversible phytochrome. Etioplasts, separated from mitochondrial contamination by sucrose gradient centrifugation, respond in vitro to red light treatment by an increase in the level of extractable gibberellin-like substances. It is concluded that earlier reports of the substances. It is concluded that earlier reports of the phytochrome regulation of biologically-active gibberellin levels in crude plastid fractions represent responses of the etioplast alone.

PHYTOCHROME MEDIATED CAROTENOID SYNTHESIS IN THE FUNGUS VERTICILLIUM AGARZCZNUM

Abstract— Ten minutes of red irradiation (R) increased carotenogenesis in Verticillium agoricinum and this effect was reversed by 10min of far‐red (FR) irradiation indicating that phytochrome is involved. A far‐red minus red difference spectrum of a crude extract shows a peak at 670 nm and a dip at 750 nm wavelength, values slightly larger than higher plant phytochrome. indicating the presence of phytochrome.

In Vivo Measurement of Phytochrome in Tomato Fruit

Presence of phytochrome in two kinds of tomatoes (Lycopersicon esculentum Mill.), the yellow lutescent strain and cherry tomatoes (L. esculentum Mill. var. cerasiformecv. Red Cherry), was established by measuring the absorption difference spectra of the whole fruit after irradiation with red and with far red light. Phytochrome content was determined in yellow lutescent tomatoes and decreased gradually during the ripening period.

Regulation of enzyme levels by phytochrome in mustard cotyledons: Multiple mechanisms?

Phytochrome controls the appearance of many enzymes in the mustard (Sinapis alba L.) cotyledons. The problem has been whether the effect of phytochrome on the appearance of enzymes in this organ is due to a common initial action of Pfr, e.g. due to the liberation of a "second messenger". We have compared the modulation by light (phytochrome) of the appearance of phenylalanine ammonia lyase (PAL)(+) and ribulosebisphosphate carboxylase (Carboxylase)(+). PAL becomes detectable in the mustard cotyledons at 27 h after sowing while Carboxylase starts to appear only at 42 h after sowing (starting points, 25° C). The starting points cannot be shifted by light. As a major result, in the case of PAL the inductive effect of continuous red light (given from the time of sowing) remains fully reversible by 756 nm-light up to the starting point (27 h after sowing) while with Carboxylase full reversibility in continuous red light is lost at approximately 15 h after sowing. While the induction of Carboxylase is already saturated at a very low level of Pfr (e.g. continuous 756 nm-light saturates the response) and does not depend on irradiance (e.g. continuous 675 mW m(-2) red light and 67.5 mW m(-2) red light lead to the same time course), PAL induction is a graded response over a wide range of Pfr doses and depends strongly on the fluence rate (high irradiance response, HIR). It is concluded that PAL induction and Carboxylase induction are not only separated in time but differ in every regard except that both responses are mediated by phytochrome.The present data support the previous conclusion that the specification of the temporal and spatial pattern of development is independent of phytochrome even though the realization of the pattern of development can only occur in the presence of phytochrome (Pfr). It seems that there is no feedback from pattern realization to pattern specification.

Spectrophotometric evidence for the presence of phytochrome in the envelope membranes of barley etioplasts

PHYTOCHROME is a chromoprotein photoreceptor, existing in two photoconvertible forms (Pr and Pfr), and is responsible for various metabolic and developmental responses of higher plants to light1. The location of phytochrome in plant cells and its mechanism of action are matters of debate. Many physiological responses to light have been adduced as evidence for phytochrome either being a component of certain cellular membranes, or acting on them, bringing about rapid changes in cell metabolism which lead to developmental changes2. There have been claims that phytochrome, in the Pfr form only, binds specifically to as yet uncharacterised membranous fractions3–6 and the data have formed the basis for allosteric models of the action of phytochrome3–7. Further progress requires a demonstration of the precise location of phytochrome with relation to a well characterised membrane where it is known to direct a process in vitro. We demonstrated8,9 the specific association of a proportion of total cellular phytochrome with etioplasts isolated from 6-d-old etiolated barley leaves. Etioplast phytochrome, as a result of its interconversions, was shown to regulate, in vitro, the efflux of endogenous etioplast gibberellins across the envelope membranes into the surrounding medium. Confirmatory results have been obtained with etiolated wheat leaves10,11. Although phytochrome was detected spectrophotometrically in the purified etioplast preparations from barley, no data were obtained for the suborganellar location of the photoreceptor or for the amount present in the etioplasts. We report here that although only a small proportion of the total phytochrome is associated with etioplasts, it seems to be concentrated in the envelope membranes. These data support the view that phytochrome is located in specific cellular membranes where it regulates transmembrane transport12.

Floral Induction and the Effect of Red and Far-red Preillumination on the Light-Stimulated Bioelectric Response of Spinach Leaves

Summary It is found that under short day conditions, a low far-red bioelectric response of spinach leaves follows a daily rythm, increasing to a maximum at the end of the day and decreasing in the dark. The response is quickly reversible modified by red and far-red light treatments, and therefore appears to be associated with the presence of phytochrome (short term effect). The far-red response under short day conditions is strongly increased by acetylcholine; DCMU inhibits the photoreversibility of the response. Under long day conditions, we observe a high far-red bioelectric response partially irreversible (> 50%) that is characteristic of the induced state. Once acquired this response does not disappear if the plant is returned to SD conditions for 5 days. We have the same response in the few old plants which flower under SD conditions and in plants treated for 3 days with gibberellin or with acetylcholine. The LD irreversible response seems, therefore, to be in relation with flowering in spinach (long term effect). A spectral index can be used to determine immediately wether a leaf of Spinacia oleracea or Perilla nankinensis is induced. We propose the utilization by the plant of the specific-wavelength stimulated biopotential as electrical signals in coordinating the floral induction.

Leaflet movement of Mimosa pudica L. Indicative of phytochrome action

1. Closing movements of Mimosa pudica pinnae, upon change from light to darkness, depend upon the presence of phytochrome in the far-red-absorbing form. 2. The potentiated control of closing movements by phytochrome can be repeatedly established and reversed by repeated alternations of red and far-red radiation, respectively. 3. Action spectra were measured for the potentiation of closure and for its reversal. 4. The response to phytochrome action is evident in 5 minutes and is fully expressed in 30 minutes. 5. This rapid response and the more rapid potentiation with half times of less than 1 minute for several other responses to phytochrome action indicate that the primary action of phytochrome ist not gene activation, but rather metabolic control at the substrate level.