Onset Of Illumination Research Articles

Formula omitted] synthesis of photosynthetic membranes: I. Development of photosystem I activity and cyclic photophosphorylation

First successful in vitro synthesis of functional photosynthetic phosphorylating membrane is reported. Etioplasts, highly enriched in cytoplasmic and plastid proteins, isolated from etiolated Cucumber cotyledons pretreated with kinetin and gibberellic acid, and illuminated in a cofactor fortified medium showed commencement of chlorophyll (Chl) synthesis immediately after illumination from exogenous δ-aminolevulinic acid, while photosystem I (PS I) activity commenced 15 min after the onset of illumination. When cotyledons pretreated with kinetin and gibberellic acid were illuminated directly, there was a lag phase of 30 min before the commencement of Chl synthesis and PS I activity developed after 1 h of illumination. In plastids developed both in vivo and in vitro , the electron flow from dichlorophenolindophenol to methyl-viologen was coupled to phosphorylation as observed by an increase in the electron transport rate on the addition of uncouplers. Analysis of polypeptide profiles of the greening plastids in vitro showed the disappearance of many higher molecular weight proteins during greening. Polypeptides of molecular weight 32, 20.5, 19.5 K absent in etioplasts appeared as distinct bands after 4 h of greening in vitro .

Three light-evoked responses of the retinal pigment epithelium

This paper summarizes our findings on light-evoked changes in retinal pigment epithelial cell (RPE) membrane potentials. Experiments were performed on the eye of the anesthetized or decerebrate cat and on isolated tissues from the eyes of a lizard, Gekko gekko, and a frog. Rana calesbeiana. In cat. as was previously shown, the RPE apical membrane potential responds to changes in [K +] 0 in the subretinal space. At the onset of illumination it hyperpolarizes to a peak at 4.0 sec as [K +] 0 decreases. The next RPE response is a hyperpolarization of the basal membrane that peaks at 20 sec and is also dependent on the decrease in subretinal [K +] 0. The last and slowest response is a depolarization of the basal membrane that peaks at 300 sec, and is not obviously associated with K + changes. The same responses also appear in gecko at a slower time-course, but only the apical-membrane K − -response is present in frog. The three responses also are associated with changes of the opposite polarity at the offset of illumination. These changes in membrane potential are the origin, respectively, of the RPE component of the ERG c-wave, the fast oscillation, and the light peak (slow oscillation).

The effect of alpha terthienyl on photosynthesis

Alpha terthienyl (α-T), an allelopathic polyacetylene derivative occurring in the Asteraceae, was examined for its photosensitizing effect on respiration in Chlorella and photosynthesis in Chlorella and isolated spinach chloroplasts. In experiments with the Clark electrode, O2 evolution in saturating light with Chlorella was much more sensitive to α-T plus near ultraviolet (UV) treatments than respiration. O2 transients at the onset of illumination as measured with the modulated O2 polarograph were also inhibited by α-T plus near UV. The Hill reaction in uncoupled spinach chloroplasts using ferricyanide as electron acceptor is sensitive to photosensitization with α-T, but electron transport through photosystem I operating on its own showed no decrease in activity. The results are interpreted as an indication of a site of inhibition near photosystem II and possibly in CO2 fixation as well.

Electrical activities of a type of electroretinogram recorded from the ocellus of a jellyfish, Polyorchis penicillatus (Hydromedusae).

An electroretinogram (ERG), evoked by light stimuli, was recorded from ocelli of Polyorchis penicillatus (Hydromedusae). The ERG is a polyphasic response with a positive potential change at the onset of illumination followed by a slower biphasic pulse, and a positive deflection at the cessation of illumination which is followed by a series of high-frequency pulses. The most striking features of the initial pulse are its latency-log intensity relation and the gradation of pulse amplitude with respect to the intensity of the light stimulus and to different wavelengths. Maximum spectral sensitivity lies around 530 nm. Response patterns induced by shadowing and repeated stimulation of light- and dark-adapted ocelli are described. Morphological structures which could give rise to the mass response of the ocellus are discussed.

Induction of Flavonoid Synthesizing Enzymes by Light in Etiolated Pea (Pisum sativum cv. Midfreezer) Seedlings

Etiolated pea (Pisum sativum cv. Midfreezer) seedlings respond to illumination with white light by changes in the activity of phenylpropanoid and flavonoid synthesizing enzymes. Unlike in cell cultures, changes in enzyme activity in pea seedlings are not concerted. Phenylalanine ammonia-lyase (EC 4.3.1.5) activity peaked approximately 18 hours after onset of illumination. The phenylacetate path did not interfere with the measurement of phenylalanine ammonia-lyase activity. Activity of cinnamic acid 4-hydroxylase (EC 1.14.13.11) showed an early peak after 8 hours illumination, declined thereafter sharply, then gradually increased during the remainder of the experiment. Activities of chalcone synthase and UDP glucose:flavonol 3-O-glucosyltransferase (EC 2.4.1.91) increased steadily and reached a plateau after approximately 70 hours illumination time. Activity of 4-hydroxycinnamate:coenzyme A ligase (EC 6.2.1.12) remained relatively unchanged, whereas that of chalcone isomerase (EC 5.5.1.6) declined steadily during the course of the experiment. The relative in vitro enzyme activities suggest that the rate-limiting step for the phenylpropanoid path is the cinnamic acid 4-hydroxylase, that of the flavonoid pathway is the chalcone synthase. Integration of enzyme activity curves, however, show that only the curve deriving from phenylanine ammonia-lyase activity matches closely the production of the flavonol glycosides.

ELECTRICAL ACTIVITY IN RESPONSE TO LIGHT OF THE OCELLUS OF THE HYDROMEDUSAN,SARSIA TUBULOSA

The electroretinogram (ERG) recorded from the ocellus of Sarsia tubulosa has a characteristic positive potential change at the onset of illumination, followed by a slower biphasic pulse and a positive deflection at the cessation of illumination succeeded by high-frequency pulses. The amplitude of initial pulse is graded with respect to changes in intensity and wavelength of the light stimulus. The maximum spectral sensitivity lies around 540 nm. Responses to light with opposite polarity were recorded from the optic ganglion which surrounds the ocellus. Differences in response patterns inside and outside the receptive field of the ocellus were mapped. Morphological structures which could give rise to component responses of the ERG and its neuronal pathway are discussed.

Diurnal Fluctuation of Quinolizidine Alkaloid Accumulation in Legume Plants and Photomixotrophic Cell Suspension Cultures

Abstract Fluctuations of quinolizidine alkaloid content in leaflets of Lupinus polyphyllus, L. hartwegii, Baptisia australis, and Sarothamnus scoparius were studied over a 36 h period. The alkaloid contents reached their maximum at noon or early afternoon, and their minimum during the night. The amplitudes of diurnal variations in alkaloid levels lay within a range of 60 to 470% of the early morning contents of alkaloids (= 100%) in leaves. In photomixotrophic cell suspension cultures of L. polyphyllus and S. scoparius cultured under day-night regime, a similar increase of the alkaloid levels was observed within 5 to 8 h after onset of illumination. A subsequent excretion of the alkaloids produced, which also followed a diurnal rhythm, was found. S. scoparius cells excreted lupanine, L. polyphyllus cells 13-cinnamoyloxylupanine. From the cell culture and plant experiments it can be assumed that the alkaloids which are formed during illumination are translocated to some degree afterwards. In cell suspension cultures the alkaloids are subjected to rapid and rhythmic turnover. Exogenous alkaloids, fed to the cultures, are taken up by the cells and disappear usually within the first 72 h. A possible mechanism for a light-mediated regulation of quinolizidine alkaloid biosynthesis which was found to be localized in leaf chloroplast, is discussed.

Influence of calcium on guanosine 3',5'-cyclic monophosphate levels in frog rod outer segments.

In the presence of 10(-9) M calcium, rod outer segments freshly detached from dark-adapted frog retinas contain between 0.01 and 0.02 moles of guanosine 3',5'-cyclic monophosphate (cyclic GMP) per mole of rhodopsin. The dark level of cyclic GMP is reduced approximately 50% by illumination that bleaches 5 x 10(5) rhodopsin molecules/outer segments. The dark levels of cyclic GMP also can be suppressed to approximately 0.007 mol/mol of rhodopsin by increasing the concentration of calcium from 10(-9) M to 2 x 10(-9) M, and they remain at this level as calcium concentration is raised to 10(-3) M. The final level to which illumination reduces cyclic GMP in unaffected by the calcium concentration between 10(-9) and 10(-3) M. The maximal light-induced decrease in cyclic GMP occurs within 1 s from the onset of illumination at all calcium concentrations. The magnitude and time-course of the light-induced decrease in cyclic GMP measured in these experiments are comparable to values obtained previously (Woodruff et al. 1977. J. Gen. Physiol. 69:677-679; Woodruff and Bownds. 1979. J. Gen. Physiol. 73:629-653). The data are consistent with a role for cyclic GMP in visual transduction irrespective of the calcium concentration.

Circadian rhythmicity in Adesmia cancellata L. (Coleoptera: Tenebrionidae) from Kuwait

The rhythmic onset of locomotory activity in A. cancellata, a day-active desert beetle, is advanced in darkness and retarded by constant light, in contradiction to the ‘circadian rule’. In alternating light and darkness, activity takes place progressively earlier during the light period when this is being decreased, and even starts before the onset of illumination if the photoperiod is very short. The endogenous clock continues to free-run at temperatures below 10 °C although locomotory activity has been suppressed. The significance of these findings to the ecology of the insect are discussed.

Contribution of Membrane Potentials to Energy Conversion in Photosynthetic Membranes

AbstractThe conversion of the energy of light into the chemical energy of ATP occurs at the photosynthetic membrane with the transmembrane electrochemical gradient of protons as intermediate. The electric portion, i.e. the light‐induced change of the electric potential difference (photopotential), quickly attains a maximum of 200 mV after the onset of illumination and decreases toward the steady state for the benefit of the H+‐concentration gradient. The resulting stationary photopotential is determined by two different methods, on the one hand directly through the electrochromic absorption change of membrane pigments, on the other hand by calculating the change of the surface potential at the inner side of the membrane from the surface charge densities. The charge density in the dark state is derived from the kinetics of an electron transfer reaction in the membrane (reduction of oxidized chlorophyll‐aI) sensitive to the pH of the inner surface. Its dependence on pH is characterized by an isoelectric point of 4.8. The light‐induced change of the charges is determined from the amount of protons additionally bound to the inner membrane surface. For the calculation of surface potentials from the charge densities the conventional Gouy‐Chapman theory is modified by assuming a transverse spreading of surface charges over a layer of 20 A thickness. — The results of both the methods are similar. The stationary transmembrane photopotential is dependent on the concentration of electrolyte and exhibits a maximal value of 60–70 mV at 6 mM KCl. Under physiological conditions the contribution of the photopotential is below 20 mV and can be neglected compared to the light‐induced difference in proton concentration with respect to energetic and kinetic considerations.

Physiological changes observed in the goldfish ( Carassius auratus) during behavioral arousal and fright

Goldfish were placed in a controlled environment and their behavioral and physiological responses to stimuli observed. Various stimuli presented caused behavioral arousal, but in some cases fright behavior was observed. During arousal, cardiac and ventilatory decelerations occurred and there was a decrease in ventilatory amplitude. When fright responses were observed, a brief cardiac deceleration was followed by an acceleration, the ventilatory rate and amplitude increased, and there was an increase in the electromyogram. Three stimuli, the onset of illumination, the passage of a moving black edge across the light source, and the operation of a plunger, were more effective in eliciting physiological arousal responses than a moving spot past the light source, 500 Hz noise, and a small paddle in the aquarium. The physiological changes which occurred on arousal habituated on regular, repeated presentation of the stimulus, habituation not being affected by the interval between stimulus presentations. A close correlation exists between the magnitude of the arousal response of a fish to a novel stimulus and the number of presentations of that stimulus required for habituation of the response. Cardiac and ventilatory changes, associated with behavioral arousal, are considered to be variables, the use of which may aid the study of the phenomenon itself.

Electroencephalographic studies on arousal in the goldfish (Carassius auratus).

Goldfish with implanted intracranial electroencephalographic (EEG) electrodes showed high-voltage slow activity of 6-9 Hz and a low-voltage fast activity of 16-24 Hz when resting in the dark. The former frequency was prevalent in the telencephalon, diencephalon, and midbrain but remained only in parts of the midbrain and cerebellum when the fish was left resting in an illuminated environment. In this latter condition the 16-24 Hz activity became predominant. Presentation of two stimuli, the onset of illumination and the passage of a moving edge across the source of illumination, caused bradycardia and a reduction in ventilatory rate, associated with behavioral arousal in this animal. An increase in the amplitude of 16-24 Hz activity in the EEG also occurred, most evident in the anterior and posterior tectum and dorsomedial and posterior telencephalon. Anterior tectal EEGs, on arousal, had the shortest latency and longest duration and were most resistant to habituation on repeated presentation of the moving-edge stimulus, the dorsomedial telencephalon showing similar characteristics to a lesser degree. It is suggested that these areas may be intimately concerned with the arousal response in teleosts.

Bacteriorhodopsin in liposomes. II. Experimental evidence in support of a theoretical model

In the preceding article equations describing relevant ion flows in illuminated suspensions of bacteriorhodopsin liposomes have been derived. Here these equations are subjected to experimental tests. Changes in permeability characteristics of the liposomal membrane are brought about by addition of specific ionophores and change of medium composition. Using light-driven proton uptake and electrochemical potential differences for protons across the membrane as observation parameters, ridig attempts to falsify the derived equations are unsuccessful. Agreement between equations and experimental results is established on the point of: (i) the antagonistic effect of valinomycin and nigericin on the two components of the proton-motive force, (ii) the time dependence of the changes in transmembrane electrical and chemical potential differences after the onset of illumination. In three independent experimental systems evidence was obtained for the correctness of the postulated dependence of the turnover rate of the photochemical cycle on back pressure by the transmembrane electrochemical potential difference for protons.

Galactolipid and chlorophyll synthesis and changes in fatty acid composition during the greening of etiolated maize leaf segments of different ages

The pattern of net chlorophyll synthesis, the changes in the fatty acid composition of both total and individual acyl lipids and the increase in the mono- and digalactosyldiglyceride have been determined during the greening of each of three sequential 2-cm segments cut from the shoots of 5-day old etiolated maize seedlings. The youngest tissue failed to ‘green’ while progressively older tissues green at progressively faster rates; however the final chlorophyll concentration in these different tissues are very similar. The major changes in the fatty acid composition during ‘greening’ were the increase in linolenic acid (18 : 3) and the appearance in the older tissues of the trans Δ 3 hexadecenoic acid. In both the total lipid and the individual lipids the increases in the proportions of 18 : 3 during illumination decreased with increasing age of the etiolated tissue used, although the actual quantitative increases were similar. The results confirm the thesis that the development status of the etioplast at the onset of illumination will influence the subsequent pattern of etioplast-chloroplast transformation.

The rates of onset of photophosphorylation and of the protonic electrochemical potential difference in bacterial chromatophores

We have studied the kinetic and thermodynamic parameters of photophosphorylation in bacterial chromatophores of Rhodopseudomonas capsulata under steady state experimental conditions, as related to the protonic potential difference (Ap) across the membrane [l-4]. The main conclusions of these studies were that under ‘state 4’ conditions, i.e., under conditions of static head for both Ap and phosphorylation, a general agreement exists between the affinity of the reaction of ATP synthesis (A,& and the extent of Ap [ 1,3]. We observed, however, that the steady state rate of ATP synthesis was markedly affected by the rate of electron flow, when this was decreased by antimycin A or by limiting the intensity of actinic light, in spite of the fact that the value of Ap was not largely diminished under these conditions [3,4]. These observations led us to consider the possibility of short range interactions between the ATP synthetase complexes and the electron transport chains, involving the mechanism of energy transduction itself or alternatively only a control of the turnover rate of ATP synthetase. It is clear that more detailed informations on this point would be obtained if the transient rates of ATP synthesis and of Ap formation, upon the onset of illumination, were compared. This approach requires fast and sensitive techniques for the measure of ApH, A$ and ATP concentration. The spectroscopic methods in use in our laboratory for the measurement of ApH and of A$ in chromatophores [3] are fast enough to allow a quantitative evaluation of Ap after a flash, before the relaxation of the protonic gradient reaches a significant extent (in preparation). The luciferine-luciferase assay, recently adapted for the continuous monitoring of photophosphorylation in bacterial chromatophores [S], offers the technical possibility for a comparative study of the transient rates of phosphorylation versus the onset of &. This paper describes some preliminary results of experiments relating Ap and ATP synthesis induced by flashes of light of variable time length.

Characterization of the Inhibition of Photosynthetic Electron Transport in Pea Chloroplasts by the Herbicide 4,6-Dinitro-o-cresol by Comparative Studies with 3-(3,4-Dichlorophenyl)-1,1- dimethylurea

An attempt to characterize the mechanism of inhibition of photosynthetic electron transport in isolated pea chloroplasts by the herbicide 4,6-dinitro-o-cresol (DNOC) by a comparison with the effects of 3-(3,4-dichlorophenyl)-1.1-dimethylurea (DCMU) revealed the following: 1.The percent inhibition of oxygen evolution by a given herbicide concentration is the same at various light intensities except at very low intensities where the percent inhibition becomes larger. The same results are obtained with the herbicide DCMU. 2.The concentration of DCMU causing 50% inhibition of oxygen evolution decreases with de­creasing chloroplast (and thus of chlorophyll) concentration. With DNOC, the relative decrease is much less than with DCMU. At the inhibited molecule, there appears to be a cooperative binding of DCMU with two binding sites and a noncooperative binding of DNOC with only one binding site. 3.The chlorophyll a fluorescence induction is influenced by DNOC in the same characteristic way as it is by DCMU: both herbicides cause a faster rise in fluorescence yield than in control chloroplasts, although a higher concentration of the former is required for the same effect. 4.The chlorophyll fluorescence emission spectra at 77 CK show a slight decrease in the bands at 685 and 735 nm, and no or only a very slight decrease at 695 nm upon addition of high con­centrations of either DCMU or DNOC before the onset of illumination. 5.The degree of polarization of chlorophyll a fluorescence is lower after addition of DCMU or DNOC upon excitation by 460 or 660 nm light. It is concluded that, although the chemical structure of DNOC is completely different from that of DCMU, its site and mechanism of inhibition is similar to that of DCMU. Both herbicides inhibit electron transport between the primary electron acceptor of photosystem II and the plastoquinone pool. This causes a closing of the reaction centers of photosystem II. However, the interaction with the inhibited molecule is different for the two herbicides.

Taurine fluxes in isolated cat and rat retinas: Effects of illumination

Taurine is taken up by isolated cat retinas incubated in an oxygenated medium in the light or in the dark. Onset and cessation of illumination are associated with a prompt transient release followed by reuptake of taurine; in contrast, glycine is gradually released only with onset of illumination. The uptake of taurine and the light evoked release of taurine followed by reuptake are inhibited by reduction in temperature, iodoacetate, ouabain, and absence of glucose. Similar light-evoked taurine fluxes are observed in the isolated retinas from normal rats and 30-day-old RCS rats but cannot be demonstrated in the photoreceptorless retinas from 180-day-old RCS rats. These findings support the idea that the effects of illumination on taurine fluxes depend on the viability of photoreceptor cells.

Temperature dependencies of the rate of electron flow and of the formation of the high energy state in spinach chloroplasts and leaves

The relationship between the rate of electron transport and the rate of formation of the high energy state during illumination was studied by measuring temperature dependencies of oxygen uptake and of the induction of millisecond delayed fluorescence of chlorophyll in isolated spinach chloroplasts and in spinach leaves. Measurements in chloroplasts with and widiout added electron acceptors showed that the decrease in the rate of formation of the high energy state caused by cooling was due to the decrease in the rate of electron transport linked to the Mehler reaction. Measurement of the induction of delayed fluorescence in leaves suggested the existence of a similar temperature-sensitive step in the electron transport system. Delayed fluorescence of chlorophyll in green plants is known to be generated by reversal of the photosynthetic reactions (6~, 11). Recent studies (4, 13) on the phenomenon showed that the intensity of delayed fluorescence emitted within a few milliseconds after illumination of chloroplasts sensitively reflects formation of the high energy state for photophosphorylation. In the previous study (5) it was found that the induction in the intensity of delayed fluorescence during illumination (a transient time course of the intensity of delayed fluorescence at the onset of illumination) is highly sensitive to temperature. By decreasing temperature the increase in the intensity during illumination, which reflects formation of the high energy state, became quite slow in the absence of added electron acceptors (5). In isolated chloroplasts molecular oxygen is known to serve as an electron acceptor at room temperature (2, 7, 8). It seefns likely that the rate of electron transport supported by the reduction of oxygen molecules, the Mehler reaction (7), is temperature dependent when no external electron acceptor is added. At lower temperatures, the lower rate of electron transport may result in slow formation of the high energy state. In-this study temperature dependencies of the rates of formation of the high energy state and of the Mehler reaction were studied by measuring the induction of delayed fluorescence and the oxygen uptake in isolated chloroplasts. The temperature dependencies were analyzed in order to examine the above assumption. Temperature dependency of the induction of delayed fluorescence was also studied in intact leaves.

Photoreactivation of DNA-containing cauliflower mosaic virus and tobacco mosaic virus RNA on Datura.

Abstract— Datura stramonium L. is a local lesion host for TMV‐RNA and DNA‐containing cauliflower mosaic virus (CAMV). Datura can photorepair UV‐damaged TMV‐RNA and CAMV, giving photoreac‐tivation sectors of 0.40 and 0.33, respectively. Dose response curves for photoreactivation of TMV‐RNA and CAMV show that 4540 min of cool white light (15 W.m‐2) is required for maximum photoreactivation. Blue light and near UV are equally effective in photoreactivating UV‐irradiated TMV‐RNA, whereas near UV is initially more effective than blue light for the photorepair of UV‐inactivated CAMV. Higher doses of near UV apparently inactivate the CAMV photorepair system. In the case of CAMV, photoreactivating light must be applied immediately after inoculation with the virus. Two to three hours of incubation in the dark after inoculation results in complete loss of response to photoreactivating irradiation. In contrast, limited photoreactivation of TMV‐RNA occurs even after 4 h of dark incubation after inoculation, although photoreactivating irradiation is most effective when applied immediately after inoculation. Light is required for the maintenance of photoreactivation for both TMV‐RNA and CAMV. Daturas placed in the dark for six days lose their ability to photoreacti‐vate. Recovery of the TMV‐RNA photorepair system is rapid; complete recovery attained with 90 or more min of white light (15 W m‐'). Recovery of CAMV photorepair system is slow; 90% recovery attained after only 20 h of light. However, full recovery can be induced by as little as 6h of light when CAMV is inoculated 24 h after the onset of illumination. These results suggest two photorepair systems are present in Datura.

Decarboxylierung von Indolylessigs�ure im Zusammenhang mit dem Phototropismus inAvena-Koleoptilen

3-Indolyl[1-14C]acetic acid (IAA) or 1-naphthyl[1-14C]acetic acid (NAA) was applied toAvena coleoptiles and the output of14CO2 was measured afterwards. In the dark the applied IAA was decarboxylated by the coleoptiles. The decarboxylation rate increased for 3h after addition of IAA. Under the same conditions NAA was not decarboxylated by the coleoptiles. When the coleoptiles were illuminated before application of IAA, the kinetics of14CO2-output did not change, a finding which shows that the IAA decarboxylating enzyme system is not induced or activated by light. In order to study decarboxylation of IAA in relation to phototropism coleoptiles were illuminated unilaterally during the measurement of14CO2-output. Blue light and white light within the range of phototropically active intensities do not cause any increase of the IAA decarboxylated rate after the onset of illumination. There is a difference between NAA and IAA concerning the behaviour in vivo and in vitro. NAA is decarboxylatedin vitro as well asin vivo. IAA, however, is found to be photosensitive invitro but seems to be protected against light destruction invivo.