Cytokinins in Tobacco and Wheat Chloroplasts. Occurrence and Changes Due to Light/Dark Treatment

Although cytokinins (CKs) affect a number of processes connected with chloroplasts, it has never been rigorously proven that chloroplasts contain CKs. We isolated intact chloroplasts from tobacco (Nicotiana tabacum L. cv SR1) and wheat (Triticum aestivum L. cv Ritmo) leaves and determined their CKs by liquid chromatography/tandem mass spectroscopy. Chloroplasts from both species contained a whole spectrum of CKs, including free bases (zeatin and isopentenyladenine), ribosides (zeatin riboside, and isopentenyladenosine), ribotides (isopentenyladenosine-5'-monophosphate, zeatin riboside-5'-monophosphate, and dihydrozeatin riboside-5'-monophosphate), and N-glucosides (zeatin-N(9)-glucoside, dihydrozeatin-N(9)-glucoside, zeatin-N(7)-glucoside, and isopentenyladenine-N-glucosides). In chloroplasts there was a moderately higher relative amount of bases, ribosides, and ribotides than in leaves, and a significantly increased level of N(9)-glucosides of zeatin and dihydrozeatin. Tobacco and wheat chloroplasts were prepared from leaves at the end of either a dark or light period. After a dark period, chloroplasts accumulated more CKs than after a light period. The differences were moderate for free bases and ribosides, but highly significant for glucosides. Tobacco chloroplasts from dark-treated leaves contained zeatin riboside-O-glucoside and dihydrozeatin riboside-O-glucoside, as well as a relatively high CK oxidase activity. These data show that chloroplasts contain a whole spectrum of CKs and the enzymatic activity necessary for their metabolism.     

Control of Retinal Sensitivity : I. Light and Dark Adaptation of Vertebrate Rods and Cones

Rods and cones in Necturus respond with graded hyperpolarization to test flashes spanning about 3.5 log units of intensity. Steady background levels hyperpolarize the rods, and the rod responses become progressively smaller as background level is increased. In cones, higher background levels reduce the effectiveness of test flashes, so higher ranges of test intensities are required to elicit the full range of graded responses. When backgrounds are terminated, cones return rapidly, but rods return slowly to the dark potential level. The effects of backgrounds on both rods and cones can be observed at intensities that cause negligible bleaching as determined by retinal densitometry. During dark adaptation, changes are observed in the rods and cones that are similar to those produced by backgrounds. Receptor sensitivities, derived from these results, show that rods saturate, cones obey Weber's law, and sensitization during dark adaptation follows a two-phase time-course.     

Phosphorylation and Dephosphorylation of Guard-Cell Proteins from Vicia faba L. in Response to Light and Dark

Phosphorylation and dephosphorylation of proteins were investigated in guard-cell protoplasts from Vicia faba L. When guard-cell protoplasts were incubated with 32Pi in the dark for 80 min, several proteins, with molecular masses of 42, 40, 34, 32, 26, and 19 kD, were phosphorylated. Illumination of the dark-adapted protoplasts with red light caused dephosphorylation of the 26-kD protein, but there was no detectable change in levels of phosphorylation in other proteins. In the dephosphorylation of the 26-kD protein, far-red light of 730 nm was most effective, but when the light was turned off, the protein was phosphorylated to the original level within 10 min. Subcellular fractionation of guard-cell protoplasts indicated that the 26-kD protein was located in the chloroplast. The migration pattern of the 26-kD protein was exactly the same as the light-harvesting Chl a/b protein complex of photosystem II (LHCPII) from Vicia mesophyll cells on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The dephosphorylated 26-kD protein was phosphorylated by adding sodium hydrosulfite, a strong reducing agent, under the far-red illumination of guard-cell protoplasts. The magnitude of dephosphorylation by red light (660 nm) was increased by 3-(3,4-dichlorophenyl)-1,1-dimethylurea, an electron transfer inhibitor of photosystem II (PSII). Light-induced dephosphorylation was inhibited by 1 nM okadaic acid, an inhibitor of serine/threonine protein phosphatase. From these results, it is concluded that the 26-kD protein is LHCPII and that LHCPII is present mostly in the phosphorylated form in the dark and is dephosphorylated by type 2A protein phosphatase under the light absorbed by photosystem I in Vicia guard-cell protoplasts.     

A BIN2-GLK1 Signaling Module Integrates Brassinosteroid and Light Signaling to Repress Chloroplast Development in the Dark

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Acute Toxicity of TiO2 Nanoparticles to Ceriodaphnia dubia under Visible Light and Dark Conditions in a Freshwater System

The ever increasing industrial and consumer applications of titanium dioxide nanoparticles (TiO₂ NPs) raise concern over the possible risk associated with their environmental exposure. Still, the knowledge regarding nanoparticle behavior in a freshwater ecosystem is lacking. The current study focuses on the toxicity of TiO₂ NPs towards Ceriodaphnia dubia (a dominant daphnid isolated from the freshwater) under two different conditions; (1) light and dark photoperiod (16:8 h) and (2) continuous dark conditions, for a period of 48 h. An increase in toxicity was observed with an increase in the concentration, until a certain threshold level (under both photoperiod and dark conditions), and beyond which, reduction was noted. The decrease in toxicity would have resulted from the aggregation and settling of NPs, making them less bioavailable. The oxidative stress was one of the major contributors towards cytotoxicity under both photoperiod and dark conditions. The slow depuration of TiO₂ NPs under the photoperiod conditions confirmed a higher NP bioaccumulation and thus a higher bioconcentration factor (BCF) compared to dark conditions. The transmission electron micrographs confirmed the bioaccumulation of NPs and damage of tissues in the gut lining.     

The Synthesis of Amino-acids in Chlorella in Light and Dark: I. PHOTOSYNTHETIC PRODUCTS IN CHLORELLA

Experiments with Chlorella show that glycine and serine bothbecome radioactive during photosynthetic incorporation of radioactivecarbon dioxide. By contrast, when radioactive glucose is fedto Chlorella in the dark, alanine, glutamate, and aspartateare the major products. These are not produced in significantamount during photosynthesis at low concentrations of carbondioxide but their formation may be stimulated by the additionof ammonium ions.     

Fermentative Metabolism of Chlamydomonas reinhardtii: I. Analysis of Fermentative Products from Starch in Dark and Light

The anaerobic starch breakdown into end-products in the green alga Chlamydomonas reinhardtii F-60 has been investigated in the dark and in the light. The effects of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and carbonyl cyanide-p-trifluoromethoxyphenyl hydrazone (FCCP) on the fermentation in the light have also been investigated.     

On the Problem of Cooperation of the Reaction of Hands: I. Cooperation of Hand Reaction to Sound and Light Stimuli in Healthy Subjects

Coordinated reaction of hands was analyzed during examination of healthy subjects and patients with focal lesions of the central nervous system in order to find the morphological structures responsible for such cooperation. Results of investigation of coordinated hand reaction in healthy subjects to sound and light stimuli with a warning signal are presented. The degree of cooperation was estimated by the correlation coefficient between the values of the reaction time of the right and left hands under conditions of their simultaneous response. In healthy subjects, there exists a strong positive correlation, whose variability in repeated examinations is determined by constitutional features of the subject.     

Light versus Dark Carbon Metabolism in Cherry Tomato Fruits: II. Relationship Between Malate Metabolism and Photosynthetic Activity

The possible relationship between malate metabolism and photosynthetic activity in green tomato fruit tissues (Lycopersicum esculentum var. cerasiforme Dun A. Gray) was investigated. Initial experiments consisted of vacuum-infiltrating ¹⁴C-3 or ¹⁴C-4-malate into isolated tissues in darkness and then incubating the tissues under photosynthetic conditions. Other experiments involved a short pulse with ¹⁴C-bicarbonate in darkness to label the malate pool(s), followed by a chase in the light in the presence of nonradioactive bicarbonate. Both series of experiments were followed by the separation and identification of labeled metabolic intermediates.     

Photochemical Electron Transport in Photosynthetic Reaction Centers from Rhodopseudomonas spheroides: III. Effects of Orthophenanthroline and Other Chemicals

Reaction centers from Rhodopseudomonas spheroides mediate the photochemical oxidation of cytochrome c (cyt c), and show a time-varying fluorescence of P870. Analyses of these effects indicate that the reaction centers contain a primary photochemical electron acceptor capable of holding one electron. Native or added ubiquinone (UQ) can act as a secondary electron acceptor. Orthophenanthroline (o-phen) blocks electron transfer from primary to secondary acceptors, and allows the primary acceptor to be exhibited in the foregoing experiments. Other chelators (with the possible exception of 8-hydroxyquinoline) and dichlorophenyldimethylurea (DCMU) are without apparent effect on reaction centers. o-Phen also inhibits the primary photochemical act in reaction centers; this effect is prevented by the presence of UQ. 2-n-Nonyl-4-hydroxyquinoline-N-oxide (NQNO) inhibits the primary photochemistry in reaction centers but does not affect secondary electron transfer.     

Behavioral Responses of Adult Deathwatch Beetles,Xestobium rufovillosum de Geer (Coleoptera: Anobiidae), to Light and Dark

Video tracking equipment was used to quantify the behavior of adult deathwatch beetles, Xestobium rufovillosum in a light/dark choice chamber. Effects of insect age, sex, and mating status on this behavior were analysed. The behavior recorded included the initial direction of movement, the time taken to reach the light or dark zone, the time spent in each zone, the time spent moving in each zone and the distance moved in each zone. The results show that both male and female insects 1–12 days old prefer the light zone. Insects more than 12 days old demonstrate sexually differential photoresponsive behavior. Males show a preference for the light. Females show an increasing preference for the dark, mated females more so than unmated females. The implications of these differences in behavior are discussed in relation to control programmes.     

Conformations of Cyclobut-A and Cyclobut-G: structural resemblance to nucleosides and incorporation into double helical DNA.

Conformational energy calculations have been carried out on two modified nucleosides Cyclobut-A and Cyclobut-G using the methods of molecular mechanics (MM2) obtainable in the computational software MacroModel. Conformations were generated as a function of the torsion angles equivalent to the glycosidic and backbone torsions in deoxyribonucleotides. The structural resemblance of the energy minimized models of the modified nucleosides to their corresponding deoxyribonucleosides has been investigated. It is found that conformations which lie within 3 kcal/mole of the global minimum do resemble the overall shape and volume of the B-DNA nucleoside. Following this result, two deoxypentanucleotides d(GCGCG).d(CGCGC) and d(ATATA).d(TATAT) were model built incorporating cyclobut-G and cyclobut-A, respectively. These were then energy refined using the molecular mechanics package AMBER. The resultant structures demonstrate that cyclobut-A and cyclobut-G can be easily accommodated in double helical polynucleotides with minimal overall distortions.     

Stomata of Micropropagated DelphiniumPlants Respond to ABA, CO2, Light and Water Potential, but Fail to Close Fully

Morphological and physiological characteristics of micropropagatedplants of Delphinium cv. Princess Caroline were studied. Leavesproduced in vitro showed poor control of water loss which appearsto result from restricted responses by stomata and not frompoor cuticular development. Stomata of leaves produced in vitrowere larger and more frequent than those produced during acclimatization.Despite the fact that stomata from isolated epidermis of leavesproduced in vitro reduced their apertures when exposed to turgor-reducingtreatments, they did not close fully. This, together with highstomatal frequencies might explain the poor control of waterloss shown by intact leaves produced in culture when exposedto dry air. While leaves from acclimatized plants showed almostcomplete closure with ABA, low water potentials, darkness andCO₂, stomata from leaves produced in vitro reduced their apertureswhen exposed to those factors, but only to a limit. Therefore,stomata from leaves cultured in vitro seem to be partially functional,but some physiological or anatomical alteration prevents themfrom closing fully. Stomata from leaves produced in vitro wereparticularly insensitive to ABA which appears to be partly associatedwith the high cytokinin concentration in the culture medium.In the long-term, this stomatal insensitivity to ABA might contributeto plant losses when micropropagated plantlets are transferredto soil. Key words: Micropropagation, stomatal physiology, dehydration, PEG, ABA, BAP, darkness, CO₂, Delphinium     

Light chain germ-line genes and the immune response to 2-phenyloxazolone.

Direct sequencing of mRNA has shown that the early primary response of the BALB/c mouse to the hapten 2-phenyloxazolone is dominated by antibodies with a particular light chain, V kappa-Ox1. Although the V kappa-Ox1 sequence is still commonly expressed later in the response it now includes a number of nucleotide changes. From two independent BALB/c germ-line DNA libraries 13 different genes hybridizing to a V kappa-Ox1 probe were isolated and characterized. Two are identical to mRNA sequences found in the early primary response, one of which is the V kappa-Ox1 sequence. None of the germ-line clones show the characteristic nucleotide changes contained in the late anti-phenyloxazolone light chain mRNAs. These results demonstrate that the V kappa-Ox1 sequence used in the early primary response is entirely encoded by the germ-line and further substantiate the importance of somatic mutations in the maturation of the anti-phenyloxazolone response. The statistical analysis of the data shows that the V kappa-Ox1 related germ-line gene family contains greater than 20 and probably less than 50 genes.     

Reef-Building Corals—Symbiotic Autotrophic Organisms: 2. Pathways and Mechanisms of Adaptation to Light

Ways, mechanisms, and responses of ontogenetic adaptation of reef-building corals to light are discussed on the basis of original and literature data. The possible ways of photoacclimation of corals within the range of tolerance to light are shown: (1) adaptation to bright light (>70% incident photosynthetic active radiation, PAR_s), (2) adaptation to moderate shade (50–10% PAR_s), and (3) adaptation to extremely low light (<5% PAR_s). In each of the ways, general and specific mechanisms and reactions are involved in photoacclimation of corals. Adaptive changes take place in plant (zooxanthellae) and animal (polyps) components of the symbiotic organism. They involve morphology, physiology, and biochemistry of colonial polyps and their zooxanthellae. During changes of the light regime, some adaptive reactions last several months and others occur within a few days. Some physiological and biochemical alterations occur as early as the next day after the light regime changes. The wide range of light tolerance of corals and a great number of mechanisms and reactions of photoacclimation allowing corals to adapt to bright and low light with minimum losses in their metabolic activity give grounds to classify them as a single ecological group of light- and shade-tolerant organisms.     

The Potential for Photoinhibition of Pinus sylvestris L. Seedlings Exposed to High Light and Low Soil Temperature

The effect of high light and root chilling on gas exchange,chlorophyll fluorescence, and bulk shoot water potential (_shoot)was examined for Pinus sylvestris seedlings. Transferring plantsfrom low light (200 µmol m^–2s^–1, PAR) anda soil temperature of 15 °C to high light (850 µmolm^–2 s^–1) and 1 °C caused >90% decrease innet photosynthesis and leaf conductance measured at 350 mm³dm^-3 CO₂, and a decrease in the ratio of variable to maximumfluorescence (F_v/F_m) from 0.83 to 0.63. The decrease in Fv/Fmwas, however, only marginally greater than when seedlings weretransferred from low to high light but kept at a soil temperatureof 15 °C. Thus, photoinhibition was a minor component ofthe substantial decrease observed for net photosynthesis at1 °C soil temperature. The decrease in net photosynthesisand _shoot at 1 °C was associated with an increase in calculatedintracellular CO₂ concentration, suggesting that non-stomatalfactors related to water stress were involved in inhibitingcarbon assimilation. Measurements at saturating external CO₂concentration, however, indicate that stomatal closure was thedominant factor limiting net photosynthesis at low soil temperature.This interpretation was confirmed with additional experimentsusing Pinus taeda and Picea engelmannii seedlings. Decreasesin gas-exchange variables at 5 °C soil temperature werenot associated with changes in _shoot Thus, hormonal factors,localized decreases in _needles or changes in xylem flux maymediate the response to moderate root chilling.