Short Periods Of Illumination Research Articles

Photosynthetic reaction center of green sulfur bacteria studied by EPR

Membrane preparations of two species of the green sulfur bacteria Chlorobium have been studied by EPR. Three signals were detected which were attributed to iron-sulfur centers acting as electron acceptors in the photosynthetic reaction center. (1) A signal from a center designated FB, (gz = 2.07, gy = 1.91, gx = 1.86) was photoinduced at 4 K. (2) A similar signal, FA (gz = 2.05, gy = 1.94, gx = 1.88), was photoinduced in addition to the FB signal upon a short period of illumination at 200 K. (3) Further illumination at 200 K resulted in the appearance of a broad feature at g = 1.78. This is attributed to the gx component of an iron-sulfur center designated FX. The designations of these signals as FB, FA, and FX are based on their spectroscopic similarities to signals in photosystem I (PS I). The orientation dependence of these EPR signals in ordered Chlorobium membrane multilayers is remarkably similar to that of their PS I homologues. A magnetic interaction between the reduced forms of FB and FA occurs, which is also very similar to that seen in PS I. However, in contrast to the situation in PS I, FA and FB cannot be chemically reduced by sodium dithionite at pH 11. This indicates redox potentials for FA and FB which are lower by at least 150 mV than their PS I counterparts. The triplet state of P840, the primary electron donor, could be photoinduced at 4 K in samples which had been preincubated with sodium dithionite and methyl viologen and then preilluminated at 200 K.(ABSTRACT TRUNCATED AT 250 WORDS)

A method for analysis of fluorescence induction curve from DCMU-poisoned chloroplasts

The kinetic analysis of fluorescence induction curve from DCMU- poisoned chloroplasts involves the calculation of the growth of the complementary area above the curve with time. It has been shownthat extreme care must be taken in the estimation of the maximum fluorescence yield ( F m ), in order to obtain accurate values of the area and the rate constants. Prolonging illumination time to obtain more accurate F m value, however, met the problems of finding an adequate time of illumination and the presence of very slow fluorescence rise or quench, which was not related to the redox changes of Photosystem II acceptors. In this report, a mathematical analysis method is introduced. It enabled us to determine the F m value accurately from a fluorescence induction curve obtained after a relatively short period of illumination (2 s). Usingthe new method, we found that the rate constant of the slowest phase was much smaller than any previously estimated value. Moreover, we found that the fluorescence curve consisted of three instead of two phases. It appears that the existing hypotheses dealing with two phases may have to be re-examined.

Light‐induced release of Artemia dried embryos from diapause: Analysis of metabolic status

AbstractCommercially obtained Artemia cysts were hydrated and incubated for prolonged periods in aerobic conditions, but deprived from light. A part of these cysts refused to hatch and remained in diapause until they were activated by illumination. During a dark incubation period of 20 days, the light‐induced hatchability remained constant, while the respiration rate and the ATP concentrations slowly decreased to the very low values of 0.01 μl O2/hour mg WW and 0.3 nmol ATP/mg protein, respectively. The endogenous trehalose reserves did not measurably decrease and glycerol was not synthesized during this treatment.Furthermore, we have demonstrated that light, acting as a diapause breaker, induced, in an irreversible manner, an enhancement of respiration and a concomitant breakdown of trehalose. The fact that a very short period of illumination was sufficient to induce hatching and that the induction was irreversible demonstrated that we were definitely not dealing with an exogeneous dormancy, whereby the environment causes the arrest of development. Light acted as a transient signal suspending diapause and triggering development.

Photoinhibition and recovery of NH4+-oxidizing bacteria and NO2--oxidizing bacteria.

The effects of illumination on nitrifying bacteria were investigated with and without substrate. NH4+-oxidizing bacteria (strain H-1, probably Nitrosospira sp.) and NO2--oxidizing bacteria (strain O-1, probably Nitrobacter sp.), isolated from Lake Kizaki, were inhibited by light (about 75μEinsteins/m2/sec, 12-hr light: 12-hr dark). Photoinhibited H-1 and O-1 cells recovered after several to tens of days under dark conditions. However, H-1 cells, illuminated for 7 to 10 days in the absence of NH4+, did not produce NO2- significantly for 120 to 350 days in a medium containing 50uM NH4+. The substrate (NH4+) was found to protect H-1 from photoinhibition, while such an effect of NO2- on O-1 was not so clear. O-1 was more sensitive to light than H-1 in the short illumination period. However, the inhibitory effect of prolonged illumination was greater on H-1 than on O-1. It was indicated from growth kinetic analysis that the photoinhibitory effects on both NH4+-oxidizing bacteria and NO2--oxidizing bacteria were not only lethal but also bacteriostatic.

Changes of Time Courses of Delayed Fluorescence and Prompt Fluorescence during in vivo and in vitro Photoactivation of the Oxygen-evolving System in Dark-grown Spruce Seedlings

Photoactivation of the oxygen-evolving system in intact leaves and in isolated chloroplasts of dark-grown spruce (Picea abies) seedlings was studied by measuring the transient time courses of the delayed and prompt fluorescence of chlorophyll. The delayed fluorescence (measured between 0.5 and 12.5 msec after 15 msec illumination) as well as the prompt fluorescence of intact leaves increased in intensity when the oxygen-evolving system was activated by a short period of illumination. After illumination of chloroplasts isolated from the dark-grown seedlings, the long-lived component of delayed fluorescence (> 100 msec) was enhanced, but not that in the millisecond time range. An analysis of the ionic dependencies of the intensities of prompt and delayed fluorescence showed that the thylakoid membranes of chloroplasts isolated from dark-grown seedlings had almost the same electrostatic properties as those of mature angiosperm chloroplast membranes.

Light-induced spectral changes of carotenoids in chromatophores of Rhodopseudomonas sphaeroides

Carotenoid difference spectra were recorded of chromatophores of Rhodopseudomonas sphaeroides energized with low light intensities versus chromatophores under dark conditions. The amplitudes of the peaks and troughs were dependent on the light intensities and the duration of illumination, but the shape of the difference spectra remained constant. Sharp isosbestic points were found at 515, 500, 481, 465, and 452 mm. When potassium-valinomycin-induced diffusion potentials (inside negative) were imposed on the chromatophores “mirror images” of the light-induced difference spectra were recorded with the same isosbestic points and the same positions but different relative amplitudes of the peaks and troughs. The results are explained in terms of changes in the shape of the vibrational splittings of the carotenoid main electronic transition. This could be the result of changes in the fluidity of the environment of the carotenoids upon energization of the membrane. Prolonged periods of illumination with low or high light intensities resulted in irreversible changes of the difference spectra. Short periods of illumination with high light intensities resulted in reversible elevations of the baseline and red shifts of peaks, troughs, and baseline crossings.

A Light-dependent Protein Kinase Activity of Chloroplasts

A protein kinase activity from spinach chloroplasts, tightly associated with the thylakoid membranes, has been solubilized and partially characterized. This membrane-bound protein kinase is stimulated by light and electron transport activity through photosystem II appears to be required for stimulation.Electron transport inhibitors like 3,4-dichlorophenyl-1,1-dimethylurea, Tris, and NH(2)OH treatments, inhibit the light activation process. Furthermore, after Tris inhibition, the protein kinase activity is restored by washing the Tris-treated chloroplasts with dichlorophenol indophenol plus ascorbate. The protein kinase remains active in the dark after short illumination periods, suggesting that a product of electron transport may be involved in light activation.Two endogenous substrates of the protein kinase in thylakoid membranes are the N,N'-dicyclohexylcarbodiimide-reactive proteolipid and the light-harvesting chlorophyll-protein complex. The membrane-bound protein kinase also phosphorylates externally added histone.

A Possible Mechanism for a Light-Driven Regulation of the Fatty Acid Composition in Galactolipids of Chloroplasts

Abstract The occurrence of acylgalactosylglycerol (AGG) in spinach chloroplasts is proposed. In lipid se­parations of whole spinach leaves this fraction is hidden by variable amounts of extraplastidary steryl glucoside (SG) which depended on the physiological state of the leaf material. Beside the phospholipid fraction, this lipid mixture with unique chromatographic behavior, recently termed GL, exhibited the highest specific activity in the lipid extract of infiltrated leaf sections of spinach after short periods of illumination (2 min) under 14C-fixing conditions. The main source of label was found in the fatty acid residues of the lipids described. The decrease of specific activity in GL after a cold chase was accompanied by an increasing 14C-incorporation into the fatty acid moieties of the MGDG-as well as the phospholipid fraction. This effect was significantly reduced if the 14C-pulse was followed by a dark period. This incorporation behavior suggests, that AGG functions as an intermediary acyl acceptor in the light driven fatty acid transfer between the lipids decribed. SG-synthesis, on the contrary, is independent of additional illumination and seems to be localized outside the chloroplast. The last notion was derived from experiments involving the in­ corporation of [UDP-14C] glucose into SG by spinach leaf homogenates. With regard to the increasing level of trienoic fatty acids in AGG and MGDG during the regeneration of dark pretreated spinach leaves in the light, the data are interpreted in terms of a light regulated acylation of AGG with specific unsaturated fatty acids.

Electrophoretic mobility of membrane fragments on a sucrose gradient: Application to isolated purple membrane fragments from Halobacterium haloblum

A simple technique for electrophoresis of particles is presented. The technique is based on running charged particles in a vertical tube along a sucrose gradient (20–50%). Purple membrane fragments from Halobacterium halobium were used to demonstrate the method. The migration of the fragments was linear with time in the region of 20 to 40% sucrose. Electrophoresis of purple membrane fragments under illumination, darkness, or darkness interrupted by short periods of illumination showed that at pH 4.5 the dark-adapted form of bacteriorhodopsin is less negative than its light-adapted form. At pH 6.5 and 8.5 no difference between these forms could be detected.

Variation in Chloroplast Lipid Content and its Correlation to Photosynthetic Activities

Abstract During illumination infiltrated spinach leaf sections show after a short log a linearly increasing 14C-incorporation into membrane lipids from H14CO3 -. Isolated intact chloroplasts show this increase only for the neutral lipid fraction (NL). Glyco-and phospholipid accumulation declines in the light. In chloroplast suspensions the increase in content and also in its 14C-incorporation rate of the NL fraction is accompanied 1. by a proportional decrease of CO2-fixation capacity, 2. by a decrease of the P/2 e-quotient. From 14C-incorporation kinetics, this increase of neutral lipids in plastid suspensions even after short illumination periods appears to be a consequence of an inhibited glycolipid - and phospho­ lipid synthesis from diglycerides.

Different sensitivities of chloroplasts to uncouplers when ATP formation is induced by continuous illumination, by brief illumination, by pre-illumination, or by acid-base transitions.

All of the uncouplers tested are more effective in decreasing ATP formation at the beginning of the illumination period than they are during continuous illumination. The difference is quite small with the uncouplers methylamine and atebrin but very large with the uncouplers octylamine and carbonylcyanide p‐fluoromethoxyphenylhydrazone (FCCP). The illumination time required to initiate photophosphorylation in the absence of permeant ions is less than 5 ms at high light intensities and the short delay is not much affected by methylamine and atebrin. The delay on the onset of ATP formation is increased to about 40 ms by permeant ions such as K+ in the presence of valinomycin, although the same permeant ions have little or no effect on steady‐state phosphorylation [Ort and Dilley (1976) Biochim. Biophys. Acta, 449, 95–107]. Octylamine and FCCP also delay the onset of phosphorylation for about 40 ms and they do so at concentrations too low to cause significant inhibition of steady‐state phosphorylation. This may be the reason that they are much more inhibitory to phosphorylation during short illumination periods than during longer illumination periods. The delays in phosphorylation introduced by permeant ions and by low concentrations of the uncouplers octylamine and FCCP are not additive. Higher concentrations of all of the uncouplers which are capable of causing major inhibitions of steady‐state phosphorylation increase the delay in the onset of phosphorylation, whether or not permeant ions are present. The increase in delay caused by these higher concentrations is a function of the degree of uncoupling and of the extent of the delay already present at low uncoupler concentrations. For reasons which remain obscure, post‐illumination ATP formation is much more sensitive to the uncoupler methylamine than is ATP formation induced by either continuous illumination or acid‐base transitions. It is concluded that for the first 40 ms of illumination a transmembrane electric potential gradient is required for photophosphorylation and that permeant ions prevent the formation of such a potential by carrying charges across the lamellar membrane. Presumably the protonated form of octylamine, the octylammonium ion, is itself a permeant cation and therefore functions like K+ in the presence of valinomycin, whereas methylamine once protonated is probably trapped inside the lamellar vesicle, thus preserving the membrane potential. On the other hand, FCCP may destroy any developing membrane potential by carrying outside a small proportion of the hydrogen ions formed inside during electron transport. During the initial 40 ms of illumination, phosphorylation depends on the chemical potential of the hydrogen ions even though a transmembrane electric potential gradient seems also to be required.

Control of Diurnal Variations in Photosynthetic Products

Nitrate accumulates in the leaves of Capsicum annuum L. cv. California Wonder and the leaf content is dependent on the nitrate level supplied to the roots. There is no consistent diurnal periodicity in the leaf nitrate levels.Nitrate reductase activity exhibits three distinct peaks in the leaves. One in the dark period, a second at the time of the prevailing dawn, and a third 6 hours after the beginning of the photoperiod. The third peak of activity can be induced by a short period of illumination (20 minutes) which is also sufficient to induce the labeling of the amino acid fraction by (14)CO(2).

Effects of Kinetin, Gibberellins and (±) Abscisic acid on the Germination of Lettuce (Lactuca sativa)

AbstractGermination responses of achenes of lettuce (Lactuca sativa L, cv. Arctic King) to treatment with kinetin, gibbe‐rellins and abscisic acid were examined over a range of temperatures: in both light and dark.Kinetin (0.1–10 mg/l) strongly promoted germination at temperatures above 27±C in continuous light or after short periods of illumination during the early stages of imbibition. It also relieved the inhibitory affects of abscisic acid in these conditions. In total darkness however kinetin treatment resulted in only a minor promotive effect.Treatment with gibberellic acid (A3) or a mixture of gibberellins A4 and A7 were much less effective in promoting germination at higher temperatures of lettuce achenes exposed to light but were strongly promotive in the dark.

Sensitivity of the electron transport chain of pigmented and non-pigmented Sarcina membranes to photodynamic action.

Abstract— With malate as substrate, the respiratory system of Sarcina lutea is subject to photodynamic action when toluidine blue is added as a photosensitiser. Both whole cells and isolated cell membranes show similar photoinactivation. Cell and membrane suspensions of a carotenoid‐containing strain are significantly less sensitive than those from a non‐pigmented mutant prepared from the pigmented strain. Addition of histidine also provides photoprotection. Attempts to locate the site of photoinactivation within the respiratory system lead to the conclusion that several sites are affected. Short periods of illumination do not result in permanent damage since activity is recovered in these suspensions when incubated in the dark subsequent to illumination. The significance of these results and the possible mechanisms involved are discussed.

Phytochrome and Temperature Relations in Lactuca sativa L. Grand Rapids Seed Germination after Thermo-dormancy

THE phytochrome reaction involved in the response of seeds of the lettuce cultivar Grand Rapids to light is such that exposure to short periods of illumination with red light (660 nm) promotes its germination, but far red light (730 nm) inhibits it at all temperatures from 5° to 25° C1–8. There is, however, considerable variation between different seed stocks, which depends largely on the history of the parent plant9 and of the seeds after harvest10.

Germination characteristics ofDiamorpha cymosa seeds and an ecological interpretation.

Laboratory-stored seeds ofDiamorpha cymosa (Nutt.) Britton (Crassulaceae) were germinated at monthly intervals starting shortly after maturity in late May and ending at approximately the time germination is completed in the field (November). Seeds were placed at 5, 10, 15, 20, 25, 30, 15/6, 20/10, 30/15 and 35/20°C at a 14-hr photoperiod (12/12 hr thermoperiods at the alternating temperature regimes) and in constant darkness. In June, seeds were almost completely dormant and thus germinated poorly or not at all under all conditions. As seeds aged from late May to November 1. germination at the 14-hr photoperiod increased in rate and total percentage, 2. the maximum germination temperature increased from 15 to 25°C at constant temperatures and from 20/10 to 30/15°C at the alternating temperature regimes and 3. the optimum temperature for germination increased from 15 to 15-20°C at constant temperatures but remained at20/10°C at alternating temperature regimes throughout the study. During the same period germination in constant darkness was negligible at constant and alternating temperature regimes. This pattern of physiological after-ripening apparently is an adaptation to summer-dry,winter-wet habitats such as rock outcrops of southeastern United States.A short period of illumination with white light given after a 12-hr imbibition period in darkness promoted germination in the dark at 25/10°C but not at 15 or 25°C. A short period of illumination given during the imbibition period was much less effective in promoting germination in the dark. Drying up to 7 days did not cause light-stimulated seeds to lose their ability to germinate in darkness. The light requirement for seed germination probably does not play a role in restrictingD. cymosa to its well-lighted habitats on granite and sandstone outcrops.

THE EFFECT OF LIGHT ON THE SPAWNING OF CIONA INTESTINALIS.

1. The spawning of Ciona intestinalis with respect to light was studied, using both white light and monochromatic light. 2. A one-hour dark-adaption period followed by exposure to light resulted in spawning by 66.6% of the 884 animals tested. 3. Spawning occurs an average of 27.3 minutes after the onset of illumination. 4. Illumination need not be continuous until spawning occurs; the animals spawn when returned to the dark after a short illumination period, provided they have received enough energy. 5. The action spectrum for spawning suggests cytochrome c as a chromophore.

THE EFFECT OF LIGHT ON THE OCELLAR PIGMENT OF SPIROCODON, AN ANTHOMEDUSA

Abstract— The ocellar pigment of Spirocodon saltatrix was extracted with 2% mildly alkaline cetyltrimethylammonium bromide (CTAB) and 90% methanol acidified with HCl. In the case of CTAB‐extracted pigment, maximum changes in optical density upon illumination occurred in mildly alkaline media under aerobic conditions and in neutral media under anaerobic conditions. The density spectrum of the sample illuminated under anaerobic conditions closely resembled that of the reduced form of the pigment illuminated in the presence of air. When reduced in darkness, the pigment became photostable and its density spectrum differed from that of the pigment reduced after illumination. On aeration of the pigment solution illuminated under anaerobic conditions, its density spectrum in the visible range became similar to that of the pigment illuminated in the presence of air. A trace of air dissolved in experimental media caused auto‐oxidation of the reduced form, during the process of which a definite isosbestic point was observed at 480 mμ. Under anaerobic conditions, short period of illumination produced changes in spectral absorbance only in the visible range. Changes in the u.v. range required longer exposures. The pigment extracted with acidified methanol was readily auto‐oxidizable and it was the reduced form which showed photosensitivity, though the degree of sensitivity was extremely low. The density spectrum of illuminated pigment resembled that of the oxidized form. From these experiments, a tentative scheme involving an electron transfer system has been suggested for the chain of photic reaction of the anthomedusan ocellar pigment.

A Study of the Diatoms of the Ouse Estuary, Sussex II. The Ecology of the Mud-Flat Diatom Flora

By estimating samples of diatoms taken from 0.2 m contour lines, over a horizontal range of about 85 m in the months of July 1953 a nd February 1954 the ecological factors influencing the distribution of eleven species of mud-flat diatoms were investigated. The three important factors were considered to be: the resistance to desiccation near the M.H.W.L., the ability to live under short periods of illumination near to the M.L.W.L., and the ability to tolerate the organic materials present in the black sulphureous layer. Table 7 summarizes the results for the eleven species.

The photoreduction of chlorophyll in the presence of diphosphopyridine nucleotide in pyridine solutions

1. 1. Both in the presence and absence of DPN, illumination with red light of oxygen-free solutions of chlorophyll a and ascorbic acid in aqueous pyridine led to the conversion: chlorophyll a (438 m μ) → photredued chlorophyll (420 m μ) → photoreduced pheophytin (390 m μ) → unknown derivative (370 m μ). The wavelengths in the parentheses are the positions of the absorption maxima of the substances. 2. 2. The presence of DPN (0.001 M) greatly reduced the rate of photoreduction of chlorophyll and altered the relative amounts of the pigment derivatives present after short periods of illumination, but did not change the nature of the reactions. 3. 3. The accumulation of DPNH in illuminated solutions of chlorophyll, ascorbic acid, and DPN was not confirmed. 4. 4. Previously reported data, which were attributed to DPNH accumulation, were probably due to different extents of conversion of chlorophyll in the presence and absence of DPN.