MODE OF COACTION OF PHYTOCHROME AND BLUE LIGHT PHOTORECEPTOR IN CONTROL OF HYPOCOTYL ELONGATION

Abstract The rate of hypocotyl longitudinal growth in seedlings of Sesamum indicum L. is strongly inhibited by continuous blue light (cBL)† and slightly by continuous far-red light while continuous red light (cRL) or red light pulses are hardly effective from 60 h after sowing onwards. Between 36 and 60 h after sowing the growth rate responds to red light pulses the effect of which is fully reversible by long wavelength far-red light. When seedlings are kept in cBL for 3 days and then treated with red light hypocotyl growth rate responds strongly. However, RL effectiveness decreases with time after transfer from BL to RL. BL → darkness transfer experiments with different levels of P_fr established at the beginning of darkness show that after a BL pretreatment phytochrome (P_fr) alone is capable of fully controlling growth rate. When white light (WL) is given no BL effect is detectable in weak WL. Only high light fluxes maintain a typical BL growth rate. At medium WL fluxes elongation rate returns gradually to the dark rate. The simplest explanation of the data is that light absorbed by a separate BL photoreceptor is necessary to maintain responsivity to P_fr. With increasing age of the seedlings the requirement for BL increases strongly. On the other hand, brief light pulses—given to demonstrate photoreversibility of phytochrome—remain equally effective provided that responsivity to P_fr exists.     

RELATIVE IMPORTANCE OF BLUE LIGHT AND LIGHT ABSORBED BY PHYTOCHROME IN GROWTH OF MUSTARD (Sinapis alba L.) SEEDLINGS*

Abstract— Hypocotyl straight growth in mustard (Sinapis alba L.) responds very strongly and in precisely the same way to low fluence rate red (RL) and white light (WL). The effect of weak light can be attributed fully to light absorption by phytochrome. Only with increasing fluence rate an effect of blue light (BL) comes into play which cannot be explained by the action of phytochrome. However, this specific action of BL can be demonstrated in hypocotyl growth of mustard seedlings only up to 5 days after sowing (25°C). With older seedlings control of hypocotyl growth seems to be exerted exclusively via phytochrome. Regarding the far-red light dependent “high irradiance reaction” (FR-HIR) it was found that it plays a dominant role in growth of mustard only during a relatively short period. It tends to disappear in favor of a RL-HIR between 3 and 4 days after sowing. It is concluded that the seedling exhibits a largely endogenous temporal pattern of responsiveness to light. Phototropism of the mustard seedling can be elicited by low fluence rates (< 1 mW m^?2) of unilateral BL. This same light has no effect on straight growth. It is concluded that BL-dependent phototropic growth response of a hypocotyl and the effect of BL on longitudinal growth of the hypocotyl are unrelated phenomena.     

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.     

THE MODE OF INTERACTION BETWEEN BLUE (UV) LIGHT PHOTORECEPTOR AND PHYTOCHROME IN ANTHOCYANIN FORMATION OF THE SORGHUM SEEDLING

Two non-photosynthetic photoreceptors (phytochrome and a blue light photoreceptor) are involved in light-mediated anthocyanin synthesis in the mesocotyl of Sorghum seedlings. The present study was undertaken to investigate the kind of interaction between phytochrome and the blue light photoreceptor. The data show that phytochrome (P_fr) can only act once a blue light effect has occurred. On the other hand, the blue light effect cannot express itself without P_fr. It is concluded that there is an obligatory dependency (or sequential interaction) between the blue light effect and the light effect occurring through phytochrome, although the blue light photoreaction per se is not affected by the presence or absence of phytochrome. The latter statement is based on the results of dichromatic experiments, i.e. simultaneous, high fluence rate irradiation with two kinds of light. Blue light can be replaced by UV light. It is not clarified yet whether the effect of blue and UV light is due to the same photoreceptor.     

INVOLVEMENT OF PHYTOCHROME IN LIGHT CONTROL OF STEM ELONGATION IN CUCUMBER (Cucumis sativus L.) SEEDLINGS

A series of polycondensed aromatic N-heterocycles (acridine, benzo-f-quinoline 1,2,7,8-dibenzacridine and 3,4,5,6-dibenzacridine) were adsorbed from the gas phase and from liquid solution on highly dispersed silica gels with very different specific surface areas and pore sizes. The translational mobility of the adsorbed species was quantified by the triplet decay and the delayed fluorescence following bimolecular triplet-triplet annihilation after pulsed laser irradiation. The decay kinetics were analyzed with conventional second order rate equations and with the fractal approach. The first method is reliable without limitations on adsorbents with large pore diameters. It yields second order annihilation constants of 4 times 10¹²-6 times 10¹¹ dm² mol^?1 s^?1 depending on the masses and sterical requirements of the adsorbates. For the second method a spectral dimension d_s= 4/3 was used. This method is quantitatively applicable to all heterocycles adsorbed on silica gel 60 that have very small pore sizes. An activation energy of 4.9 ± 0.5 kcal mol^?1 was obtained for the translational diffusion of acridine on hydroxylated silica gel.     

THE CONTROL OF METABOLISM BY BLUE LIGHT IN Acetabularia mediterranea—II. SELECTIVE TRANSLATIONAL CONTROL AND DIFFERENTIAL DEGRADATION OF ENZYMES

Abstract— During prolonged continuous irradiation with red light the specific activity of uridine 5'-diphosphoglucose (UDPG) pyrophosphorylase (uridine 5'-triphosphate: glucose 1-phosphate uridylyl-transferase EC 2.7.7.9) decreased in Acetabularia mediterranea Lamouroux (=A. acetabulum (L.) Silva). Subsequent blue light restored the original activity within a comparatively short period of 3 to 4 days. Computer-aided quantitative evaluation of density labelling experiments showed that the synthesis of the enzyme was accelerated about four-fold during the period of activation by blue light. A similar increase in the rate of synthesis was found for hydroxypyruvate reductase (EC 1.1.1.81), a control enzyme that showed no blue light-dependent changes in the specific activity under these conditions. The increase in the rate of enzyme synthesis was caused by an overall stimulation of the cytosolic translation. Degradation of UDPG pyrophosphorylase was unaffected by blue light, while the half life of hydroxypyruvate reductase was shortened about two-fold compared to continuous red light. Thus, degradation of proteins appears to be selectively light dependent in Acetabularia.
Model calculations for enzyme amount and enzyme synthesis were carried out using the measurements of enzyme activity, rates of cytosolic protein synthesis, and degradation constants of the enzymes. Assuming that activities represented amounts of the given enzymes, these calculations indicated a selective activation of UDPG pyrophosphorylase synthesis by blue light since it did not coincide with the overall stimulation of protein synthesis in the cytosol, in contrast to hydroxypyruvate reductase.     

ISOMERIZATION OF THE RETINYLIDENE CHROMOPHORE OF BACTERIORHODOPSIN IN LIGHT ADAPTATION: INTRINSIC ISOMERIZATION OF THE CHROMOPHORE AND ITS CONTROL BY THE APO-PROTEIN

Abstract— The dependence of the isomeric configuration of the retinylidene chromophore of bacteriorhodopsin on the pH value and on the wavelength of irradiation (in a photostationary state) were examined by high performance liquid chromatographic analyses of extracted retinal. The process of isomerization of the chromophore during light adaptation was also traced. More than 93% of all- trans and less than 5% of 13- cis retinal were extracted in the photostationary state for irradiation at 560 nm in the pH region of5–9 as well as for irradiation in the wavelength region of 400–650 nm at pH 7. Comparison of the above photostationary state composition with that of protonated n -butylamine Schiff base of retinal indicates that strong constraint is applied to the chromophore by the apo-protein. The constraint can be changed at low or high pH by a partial denaturation or transition of the apo-protein, which results in the generation of 11- cis retinal in the extract. At higher photon density, the isomerization process of the chromophore during light adaptation at pH 7 was characterized, as extracted isomeric retinal, by (1) the initial decrease in 13- cis and increase in all- trans , (2) a subsequent, transient toward the above photostationary state composition. The results are discussed in terms of both the photoisomerization pattern inherent in the retinylidene chromophore and the control by the apo-protein.     

ENHANCEMENT OF PHOTOREPAIR OF ULTRAVIOLET-INDUCED PYRIMIDINE DIMERS BY PREILLUMINATION WITH FLUORESCENT LIGHT IN THE GOLDFISH CELL LINE. THE RELATIONSHIP BETWEEN SURVIVAL AND YIELD OF PYRIMIDINE DIMERS

The enhancement of photorepair of UV-induced pyrimidine dimers by preillumination with fluorescent light, previously reported with RBCF-1 cells derived from caudal fin of a goldfish, was studied in terms of clonogenic ability and yields of dimers. In the logarithmic growth phase, the ability of photorepair increased with the time after preillumination, reached a maximum at 8 h, and gradually declined. At 8 h, the dose decrement with the photorepair-treatment for 20 min at 7.5 J/m2 UV increased by preillumination for 1 h from 1.6 to 3.1 J/m2 in terms of restoration of survival and from 1.2 to 4.3 J/m2 in terms of the disappearance of dimers. Incubation of the preilluminated cells in the medium containing cycloheximide (0.5 microgram/mL) after preillumination until UV-irradiation diminished their enhancement of photorepair. In the density-inhibited state, the ability of photorepair was higher than in the log phase, and it was hardly enhanced by preillumination.     

SOME RELATIONSHIPS BETWEEN ULTRAVIOLET LIGHT AND HEME-PROTEIN-INDUCED PEROXIDATIVE LIPID BREAKDOWN IN LIPOSOMES, AS REFLECTED BY FLUORESCENCE CHANGES: THE EFFECT OF NEGATIVE SURFACE CHARGE

Abstract— The water soluble, photolabile nitrene precursor,azidonaphthalene–2,7-disulfonic acid (ANDS) was encapsulated in small unilamellar, isoelectric (egg PC) or negatively charged (egg PC + dihexadecylphosphate) liposomes. The individual and combined effects of heme-proteins and UV irradiation on the fluorescence of these vesicles under aerobic conditions were studied. Consistent with the catalytic action of heme-proteins on lipid peroxidation and peroxide decomposition, addition of cytochrome c (positively charged) or catalase (negatively charged) to the vesicles elicited immediate formation of a fluorescence band at 470 nm, characteristic of Schiff bases that form from aldehyde byproducts of decomposing hydroperoxides. Ultraviolet irradiation of liposomes for 5 min caused no significant changes in the fluorescence spectrum, in spite of the radiolysis of ANDS inside the vesicles with consequent formation of nitrene radicals. When isoelectric vesicles were irradiated with UV light in the presence of cytochrome c or catalase, Schiff base formation was further increased by2–3 fold, which effect was not observed in the absence of internal ANDS, or in the presence of negative surface charge on the vesicles. These findings suggest that (a) UV irradiation, by itself, cannot trigger lipid decomposition even when it is assisted by photoproduced nitrene radicals, (b) there is a ternary synergism between UV light, heme-proteins and nitrene radicals in promoting peroxidative lipid breakdown, and (c) negative surface charge inhibits the above synergism, which effect is unlikely to be due to electrostatic interaction between the vesicles and the protein or the ANDS.     

CONTROL OF PHOTOSYNTHETIC REDUCTANT: THE ROLE OF LIGHT AND TEMPERATURE ON SUSTAINED HYDROGEN PHOTOEVOLUTION BY Chlamydomonas sp. IN AN ANOXIC,CARBON DIOXIDE-CONTAINING ATMOSPHERE*

–Sustained hydrogen photoevolution from Chlamy domonas reinhardtii and C. Moewusii was measured under an anoxic, CO₂-containing atmosphere. It has been discovered that light intensity and temperature influence the partitioning of reductant between the hydrogen photoevolution pathway and the Calvin cycle. Under low incident light intensity (1-3 W m^-2) or low temperature (approx. 0°C), the flow of photosynthetic reductant to the Calvin cycle was reduced, and reductant was partitioned to the hydrogen pathway as evidenced by sustained H₂ photoevolution. Under saturating light (25 W m^-2) and moderate temperature (20±5°C), the Calvin cycle became the absolute sink for reductant with the exception of a burst of H₂ occurring at light on. This burst of H₂ corresponded to the expression of about 450 electrons for each photosynthetic electron transport chain. These results suggest that the hydrogen pathway and the Calvin cycle compete for reductant under anoxic conditions and that partioning between the two pathways can, to a certain extent, be controlled by the appropriate choice of experimental conditions.     

ABSORPTION SPECTRA OF DEOXYRIBOSE, RIBOSEPHOSPHATE, ATP AND DNA BY DIRECT TRANSMISSION MEASUREMENTS IN THE VACUUM-UV (150—190 nm) AND FAR-UV (190—260 nm) REGIONS USING SYNCHROTRON RADIATION AS A LIGHT SOURCE

Transmission measurements of 2-deoxy-D-ribose, D-ribose-5-phosphate, ATP and DNA at 5 nm intervals were made with thin films in the wavelength region between 150 nm and 260 nm using synchrotron radiation. ATP and DNA exhibited two peaks in the absorption spectra around 260 nm and 190 nm, and a steep increase below 170 nm, while ribose phosphate and deoxyribose only exhibited the increase below 190 nm with no appreciable absorption above 190 nm. Since adenine does not exhibit the increase of absorption below 180 nm, these results indicate that the absorption of the sugar-phosphate group, rather than adenine, contributed to the increase below 170 nm in the absorption spectra of ATP and DNA.