Photosystem 2 Efficiency and Thylakoid Protein Pattern in DCMU-Treated Wheat Seedlings during Senescence

Changes in various components of photosynthetic apparatus during the 6-d dark incubation at 25 °C of detached control and DCMU-treated Triticum aestivum L. leaves were examined. The rate of photosystem 2 (PS2) activity was decreased with increase of the time of dark incubation in control leaves. In contrast to this, DCMU-treated leaves demonstrated high stability by slowing down the inactivation processes. Diphenyl carbazide and NH₂OH restored the PS2 activity more in control leaves than in DCMU-treated leaves. Mn²⁺ failed to restore the PS2 activity in both control and DCMU-treated samples. Similar results were obtained when F_v/F_m was evaluated by chlorophyll fluorescence measurements. The marked loss of PS2 activity in dark incubated control leaves was primarily due to the loss of D1, 33, and 23 kDa extrinsic polypeptides and 28-25 kDa LHCP2 polypeptides.     

Changes in photosynthetic apparatus during dark incubation of detached leaves from control and ultraviolet-B treatedVigna seedlings

Changes in various components of photosynthetic apparatus during the 4 d dark incubation at 25°C of detached control and ultraviolet-B (UV-B) treatedVigna unguiculata L. leaves were examined. The photosynthetic apparatus was more degraded in younger control seedlings and for a longer time UV-B treated seedlings than in the older or for a shorter time UV-B treated seedlings. This was shown by determining the losses in chlorophyll (Chl) and protein contents, variable fluorescence yield, photosystem (PS) 2, PS1 and ribulose-1,5-bisphosphate carboxylase (RuBPC) activities, and photosynthetic¹⁴CO₂ fixation. In contrast, the Car/Chl ratio increased during the dark incubation due to less expressed degradation of Car.     

Changes in photosynthetic apparatus during dark incubation of detached leaves from control and ultraviolet-B treatedVigna seedlings

Changes in various components of photosynthetic apparatus during the 4 d dark incubation at 25°C of detached control and ultraviolet-B (UV-B) treatedVigna unguiculata L. leaves were examined. The photosynthetic apparatus was more degraded in younger control seedlings and for a longer time UV-B treated seedlings than in the older or for a shorter time UV-B treated seedlings. This was shown by determining the losses in chlorophyll (Chl) and protein contents, variable fluorescence yield, photosystem (PS) 2, PS1 and ribulose-1,5-bisphosphate carboxylase (RuBPC) activities, and photosynthetic¹⁴CO₂ fixation. In contrast, the Car/Chl ratio increased during the dark incubation due to less expressed degradation of Car.     

Effects of Photoperiod and Plant Developmental Stage on NADH Dehydrogenase and Photosystem Activities of Isolated Chloroplasts

Barley (Hordeum vulgare L. cv. Hassan) leaves were used to study the effects of developmental stage and photoperiod on the NAD(P)H-ferricyanide oxidoreductase (NAD(P)H-FeCNR) and on the photosystem (PS) 1 and 2 activities of isolated chloroplasts. From day 6 to day 12, both the PS 1 and NADH-FeCNR activities decreased while NADPH-FeCNR activity remained almost unchanged. Methyl jasmonate had no significant effect on the NAD(P)H-FeCNR activity changes. In 6- to 7- and 14- to 15-d-old plants, the NADH-FeCNR activity was higher during the photoperiod than during the dark period and, in the 14- to 15-d-old plants, the PS 1 activity increased during photoperiod in the same way, but to a lesser extent. The PS 1 activity of plants during a dark-accelerated senescence was low. The simultaneous changes in chloroplast PS 1 and NADH-FeCNR activities support the role proposed for the chloroplast NADH dehydrogenase complex in the cyclic electron transport.     

Formation of Chlorophyll-Protein Complexes during Greening. 2. Redistribution of Chlorophyll among Apoproteins

The formation of Chl-protein complexes (CPs) in cucumber cotyledonsduring a dark period after a brief illumination was studied.SDS-PAGE analysis showed that the P700-Chl a-protein complex(CP1) and Chl a-protein complex of the PS II core (CPa) increased,with a concomitant decrease in the light-harvesting Chl a/6-proteincomplex of PS II (LHCII), during 24-h dark incubation of cotyledonsafter 6h of continuous illumination. In agreement with theseresults, curve analysis revealed that spectral components characteristicof CP1 and CPa increased while those of Chi b decreased duringthe dark incubation. Since Chl is not synthesized in the dark,Chl must be released from LHCII and re-incorporated into CP1and CPa. The amounts of apoproteins of CP1 and 43 kDa protein(one of the apoproteins of CPa) increased during the dark incubation,and the increase could be inhibited by chloramphenicol (CAP).CP1 did not increase in the dark when tissues were incubatedwith CAP which inhibited the synthesis of apoproteins of CP1,indicating that CP formation by Chl redistribution needs newlysynthesized apoproteins. The decrease in LHCII apoproteins duringdark incubation was inhibited by CAP probably because Chl wasnot removed from LHCII by apoproteins of CP1 and CPa, whosesynthesis was blocked by the presence of CAP. When intermittently-illuminatedcotyledons containing a little LHCII were incubated with CaCl₂in the dark, Chl b and LHCII apoproteins accumulated with thedisappearance of 43 kDa protein; Chl of 43 kDa protein may beutilized for LHCII formation. We concluded that Chl moleculesonce bound with their apoproteins are redistributed among theapoproteins. (Received October 17, 1990; Accepted December 6, 1990)     

Spectral properties of soluble and pelletable phytochrome from epicotyls of etiolated pea seedlings

The red-light(R)-absorbing form of phytochrome (Pr) was detected spectrophotometrically in a 20,000 g particulate fraction prepared from a 1,000 g supernatant fraction from epicotyl tissue of pea (Pisum sativum L.) seedlings grown in the dark and only briefly exposed to dim green light. The difference spectrum of phytochrome in this fraction was essentially the same as that of soluble phytochrome from the same tissue. When the non-irradiated 20,000 g particulate fraction was incubated in the dark at 25° C, an absorbance change (decrease) of Pr after actinic red irradiation was found only in the far-red (FR) region. When the 20,000 g particulate fraction was irradiated with R and then incubated in the dark, the FR-absorbing form of phytochrome (Pfr) disappeared spectrally at a rate about half that in the soluble fraction, and the difference spectrum of the Pr which became detectable after dark incubation of the 20,000 g particulate fraction was markedly distorted. In contrast, Pfr in a 20,000 g particulate fraction prepared from tissues irradiated with R did not change optically during dark incubation at 25° C for 60 min, while Pfr in the soluble fraction from the same tissue disappeared in the dark. No dissociation of either Pr or Pfr from the 20,000 g particulate fraction was indicated during a 60-min dark incubation at 25° C, but Pfr in a 20,000 g particulate fraction prepared in vitro from R-irradiated 1,000 g supernatant fraction in the presence of CaCl₂ disappeared spectrally and the difference spectrum of Pr in the 20,000 g particulate fraction became quite distorted during the dark incubation.Abbreviations Pr red-light-absorbing form of phytochrome - Pfr far-red-light-absorbing form of phytochrome - FR far-red light - FR1 first actinic far-red light - FR2 second actinic far-red light - R red light - R1 first actinic red light - 1kS 1,000 g supernatant fraction - 20kS 20,000 g supernatant fraction - 20kP 20,000 g particulate fraction     

Hydrolytic enzyme activities in germinating spores ofAdiantum capillus-veneris L.

Changes in hydrolytic enzyme activities were investigated during spore germination ofAdiantum capillus-veneris L. The spores were incubated for 3 days in the dark at 25 C for imbibition, and then germination of the spores was induced by continuous irradiation with red light. At day 2 after onset of the red light irradiation, rhizoids appeared out of spore coats and protonemal cells became visible on the following day. Lipase occurred in dry spores and its activity decreased during 3 days of dark incubation. The activity started to increase when the spore germination was induced by red light irradiation. On the other hand, amylolytic and aminopeptidase activities which were also detected in dry spores decreased continuously during the dark incubation and following the germination process. RNase activity also decreased during 3 days of dark incubation but the activity was retained thereafter at a constant level with or without red light irradiation. Developmental patterns of these hydrolytic enzymes were classified into two groups: One decreased during imbibition and dark incubation but increased after red light irradiation and the other continuously decreased during dark incubation and germination. These results are discussed in relation to compositional changes of cell constitutions such as lipid, sugars, proteins and amino acids during spore germination.     

Dark calcification and the daily rhythm of calcification in the scleractinian coral, <Emphasis Type="Italic">Galaxea fascicularis</Emphasis>

The rate of calcification in the scleractinian coral Galaxea fascicularis was followed during the daytime using ⁴⁵Ca tracer. The coral began the day with a low calcification rate, which increased over time to a maximum in the afternoon. Since the experiments were carried out under a fixed light intensity, these results suggest that an intrinsic rhythm exists in the coral such that the calcification rate is regulated during the daytime. When corals were incubated for an extended period in the dark, the calcification rate was constant for the first 4 h of incubation and then declined, until after one day of dark incubation, calcification ceased, possibly as a result of the depletion of coral energy reserves. The addition of glucose and Artemia reduced the dark calcification rate for the short duration of the experiment, indicating an expenditure of oxygen in respiration. Artificial hypoxia reduced the rate of dark calcification to about 25% compared to aerated coral samples. It is suggested that G. fascicularis obtains its oxygen needs from the surrounding seawater during the nighttime, whereas during the day time the coral exports oxygen to the seawater.     

Nonlineal relationship between g=2 doublet and multiline signals in Ca(2+)-depleted Photosystem II

Illuminating of the Ca(2+)-depleted PS II in the S(2) state for a short period induced the doublet signal at g=2 with concomitant diminution of the multiline signal, both in the presence and absence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). In the absence of DCMU, the doublet signal decayed (t(1/2) approximately 7 min) during subsequent dark incubation at 273 K and the multiline signal was regenerated to the original amplitude with the same kinetics of the doublet decay. In the presence of DCMU, the doublet signal decayed much faster (t(1/2) approximately 1 min) by charge recombination with Q(A)(-), while the time course of the multiline recovery was inherently identical with that observed in the absence of DCMU. A simple theoretical consideration indicates the direct conversion from the doublet-signal state to the multiline state with no intermediate state between them. Lengthy dark storage at 77 K led to disappearance of the DCMU-affected doublet signal and a Fe(2+)/Q(A)(-) electron spin resonance (ESR) signal, but no recovery of the multiline signal. Notably, the multiline signal was restored by subsequent dark incubation at 273 K. The charge recombination between Q(A)(-) and the doublet signal species led to a thermoluminescence band at 7 degrees C in a medium at pH 5.5. The peak position shifted to 17 degrees C at pH 7.0, presumably due to a pH-dependent change in the redox property of a donor-side radical species responsible for the doublet signal. Based on these results, redox events in the Ca(2+)-depleted PS II are discussed in contradistinction with the normal processes in oxygen-evolving PS II.     

The density-dependency of dark- and low-background radiation effects on water and water solution properties

The effects of dark -(Ev=0 lux) and low-background radiation (BGR), where R<1μRongen/h, on physicochemical properties (specific electrical conductivity, heat fusion, hydrogen peroxide (H2O2), and oxygen contents) of distilled water (DW) and physiological solution (PS) at 4°C and 18°C were studied. The incubation of DW and PS samples in dark and in low BGR (under dark) medium at 4°C and 18°C brings to changes of their physicochemical properties compared with DW and PS samples incubated in light and normal BGR condition (Ev=500-550 lux and R=17 μRoentgen/h). The observed changes of DW and PS properties depended on their initial temperature, density and ionic composition. It is suggested that water molecules dissociation and ions hydration are sensitive to illumination and BGR. Therefore, the cell-bathing medium can be considered as a messenger through which direct and non direct (by modulating of others factors-induced effects) influences of illumination and BGR on cell metabolism are realized.     

Induction of the Photosystem 2 Dark Formation in Etiolated Leaves with the Involvement of Exogenous Chlorophyllides

The delayed luminescence (DL) of photosystem 2 (PS2) after infiltration of 7-d-old etiolated barley leaves with chlorophyllides (Chlide) a or b followed by 2.5 h dark incubation was studied. Chlide a caused a very weak DL of PS2 just at the beginning of irradiation and the intensity of this DL was not higher when the infiltration medium contained 2 mM of NADPH. Chlide b was a somewhat more efficient inducer of PS2 formation in the dark and NADPH enhanced this efficiency 4.5 times though it did not affect the amount of esterified Chlides. The photoconversion of endogenous Pchlide led to a much higher intensity of the DL in comparison with the infiltration of Chlides, while the total amount of chlorophyll (Chl) formed was almost unchanged. The use of Chlide b together with the acetone extract from green leaves, devoid of pigments, resulted in the DL intensity comparable with that observed after Pchlide photoconversion followed by 2.5 h incubation in the dark. Dark formation of active PS2 in etiolated leaves was shown for the first time. Thus the dark formation of active PS2 may require Chl b, NADPH, and some unidentified water-soluble factor(s), synthesized in the dark after a short irradiation of etiolated leaves and inherent in green leaves. This revised version was published online in September 2006 with corrections to the Cover Date.     

Synthesis,storage and degradation of polyglucose in chlorobium thiosulfatophilum

Cultures of Chlorobium thiosulfatophilum form polyglucose during growth. The polyglucose is laid down within the cells as rosette-like granules, which are made up from smaller grains. The size of each granule appears to be limited to less than 30 nm, since an increase in polyglucose content leads to more granules being formed rather than an increase in granule size.The polyglucose in washed cells is fermented in the dark to acetate, propionate, caproate and succinate, of which acetate by far comprises the largest fraction (68%). During incubation of washed cells without hydrogen donor, the level of polyglucose decreases regardless of whether the cells are incubated in the dark or in the light. Since the products formed from polyglucose under the two different conditions are not the same, it is suggested that polyglucose in the dark serves as an energy source, whereas when in the light the role of polyglucose is mainly to provide the cell with reducing power.     

Experimental studies on egg production by Convoluta roscoffensis: Graff, 1882 (Turbellaria,Acoela)

Convoluta roscoffensis collected from the natural habitat in reproductive condition laid egg capsules for up to 16 weeks under laboratory conditions. However, both the number of capsules laid and number of embryos per capsule decreased with time in culture. When animals were maintained in an alternating light and dark regime, the capsules were laid during the dark period. Animals ceased to deposit egg capsules within five days of incubation in the photosynthetic inhibitor, DCMU. This suggests that metabolism of the algal symbionts of C. roscoffensis contributes to egg production.     

Photosystem 1 preparations from dark-and light-grown cells of the cyanobacterium,Chlorogloea fritschii

Photosystem 1 (PS1) enriched preparations have been extracted from the cyanobacterium Chlorogloea fritschii grown either in darkness or in the light. Absorption spectra show that the main chlorophyll peak has shifted from 678 nm in PS1 from light grown cells to 675 nm in PS1 from dark grown cells. Fluorescence spectra show a similar blue shift in wavelength maximum from 690 nm to 678 nm and the fluorescence intensity is higher in PS1 from dark grown cells. Allophycocyanin is present in PS1 from light grown cells, but absent from preparations from C. fritschii grown in the dark. P700: chlorophyll a ratios of the preparations from light and dark grown cells are 1:35 and 1:80 respectively, all P700 being photoactive. The results are interpreted to suggest that allophycocyanin is not attached to PS1 in dark grown C. fritschii, neither is all chlorophyll arranged in such a way as to ensure efficient energy transfer to P700.     

PHOSPHOLIPID METABOLISM IN LIGHT AND DARK ADAPTED EXCISED RETINA

Abstract— The phospholipid composition of, and the incorporation of labelled phosphorus into the different phospholipids of rat and calf retina have been studied. The influence of various conditions, such as dark and light adaptation, during the preparation of retina, lipid extraction and incubation of retina with radioactive phosphorus was investigated.
The phospholipid composition of rat retina did not differ significantly from that of calf retina and the different conditions of preparation and incubation did not modify the distributions.
The specific radioactivities of the different phospholipids of calf and rat retina, incubated in the presence of ³²P, distinguished in both species two groups of components characterized by the rate of labelling. Phosphatidic acid (PA) and inositol glycerophospholipids (PI) belonged to the first group and showed the highest uptake of labelled phosphorus; the second group, comprising choline glycerophospholipids (PC), serine glycerophospholipids (PS), sphingomyelin (SP), ethanolamine glycerophospholipids (PE) and cardiolipin (CL) showed low incorporation activities. Only SP was labelled differently in rat and calf retina. With the exception of PS, there was no evidence for the influence of light on the turnover of individual phospholipids. The finding that PS showed higher specific radioactivities when adaptation and incubation proceeded in the dark, seems to be of interest and needs further study.     

Production of RNA by a marine photosynthetic bacterium, Rhodovulum sp.

The marine photosynthetic bacterium, Rhodovulum sp. PS88, produces RNA not only in cells but also as an extracellular polymeric substance during aerobic continuous cultivation in the dark. At a dilution rate of 0.32–0.5 h^–1, the maximum RNA production was 460 mg RNA l^–1 broth (200 mg RNA g^–1 suspended solids) which is a value about 2–3 times more than that of yeast cells.     

The density-dependency of dark- and low-background radiation effects on water and water solution properties

The effects of dark -(Ev = 0 lux) and low-background radiation (BGR), where R < 1μRongen/h, on physicochemical properties (specific electrical conductivity, heat fusion, hydrogen peroxide (H₂O₂), and oxygen contents) of distilled water (DW) and physiological solution (PS) at 4°C and 18°C were studied. The incubation of DW and PS samples in dark and in low BGR (under dark) medium at 4°C and 18°C brings to changes of their physicochemical properties compared with DW and PS samples incubated in light and normal BGR condition (Ev = 500–550 lux and R = 17 μRoentgen/h). The observed changes of DW and PS properties depended on their initial temperature, density and ionic composition. It is suggested that water molecules dissociation and ions hydration are sensitive to illumination and BGR. Therefore, the cell-bathing medium can be considered as a messenger through which direct and non direct (by modulating of others factors-induced effects) influences of illumination and BGR on cell metabolism are realized.     

Sleep dependent effect of dark pulses on sleep in albino and pigmented rats

Light-to-dark transitions have been found to enhance paradoxical sleep (PS) in albino rats but not pigmented rats. Furthermore, PS inducing effect of dark pulses in albino rats depends on sleep states. This study examined whether the relationship between PS and preceding non-rapid-eye-movement sleep (NREMS) in pigmented Brown Norway rats was different from that in albino F344 rats and whether such a difference was associated with different responses to dark pulses in the two rat strains. Both rat strains showed a positive relationship between PS and preceding NREMS. However, only the albino F344 rats exhibited the PS inducing effect of dark pulses. Dark pulses did not alter the relationship between PS and preceding NREMS in either rat strain, and, reciprocally, nor did duration of preceding NREMS affect dark pulse-induced PS enhancement. Furthermore, this study verified that dark pulses given during NREMS in albino F344 rats specifically induced the suppression of NREMS concomitant with the enhancement of PS. This study proposed that dark pulses might inhibit NREMS and facilitate PS regulating areas concurrently in albino rats.     

Luminescence decay kinetics in relation to quenching and stimulation of dark fluorescence from high and low CO2 adapted cells of Scenedesmus obliquus and Chlamydomonas reinhardtii

Two green algal species, Chlamydomonas reinhardtii and Scenedesmus obliquus, exhibited a relative maximum during the decay of luminescence, when adapted to low CO₂ conditions that was not observed in high CO₂ adapted cells.From the kinetics of transient changes in the level of dark fluorescence, after illumination and parallel to the luminescence maxima, it was concluded that the maximum in Scenedesmus was mainly related to a decrease in nonphotochemical quenching, whereas in Chlamydomonas the maximum was mainly related to a dark reduction of the primary PS II acceptor Q_A.ATP/ADP ratios from low CO₂ adapted Scenedesmus showed transient high levels after a dark/light transition that was not observed in high CO₂ adapted cells. After 30 s of illumination the ATP/ADP ratios however stabilized at the same steady state level as in high CO₂ adapted cells.Dark addition of HCO₃ ^- to low CO₂ adapted cells of Chlamydomonas resulted in a rapid transient quenching of luminescence that was not observed in low CO₂ adapted cells of neither species.It is concluded that the luminescence maxima present in both low CO₂ adapted Scenedesmus and Chlamydomonas reflect adaptation of the cells to low CO₂ conditions. It is further suggested that the difference in mechanistic origin of luminescence maxima in the two species reflects differences in adaptation.Abbreviations ADP adenosine-diphosphate - ATP adenosine-triphosphate - C_i inorganic carbon - F_D dark fluorescence recorded under dark adapted conditions - F₀ fluorescence with all reaction centers open - FV variable fluorescence - PS I photosystem I - PS II photosystem II - Q_A the first quinone acceptor of PS II     

Interaction of cycloheximide and light on chlorophyll content and chloroplast ultrastructure inBrassica campestris

Cycloheximide retarded the loss of chlorophyll from detached komatsuna (Brassica campestris cv. Komatsuna) leaves during incubation in the dark but promoted its loss in light. Cycloheximide-induced chlorophyll bleaching in light was prevented by some active oxygen scavengers. Chloroplast envelopes of cycloheximide-treated leaves incubated in both the dark and light were destroyed within 48 h. The grana of cycloheximide-treated leaves incubated in light were dilated.