Metabolism of H-Gibberellin A(1) and H-Gibberellin A(4) by Phaseolus coccineus Seedlings

[³H]-Gibberellin A₁ (GA₁) and ³H-GA₄ were applied separately to Phaseolus coccineus seedlings grown under red light. ³H-GA₁ was converted to a compound with gas-liquid radiochromatography retention times identical to those of GA₈. ³H-GA₄ underwent conversion to at least three metabolites, none of which corresponded to GA_1-38. The rate of metabolism of ³H-GA₄ was significantly higher than that of ³H-GA₁.     

Metabolism of [1,2-3H]gibberellin A4 by epicotyls and cell-free preparations from Phaseolus coccineus L. seedlings

Cell-free systems were prepared from germinating seed and seedlings of Phaseolus coccineus. Gibberellin A₄ (GA₄)-metabolising activity was detected in vitro using preparations from roots, shoots and cotyledons of germinating seed, but only up to 24 h after imbibition. Cell-free preparations from cotyledons converted [³H]GA₄ to GA₁, GA₃₄, GA₄-glucosyl ester and a putative O-glucoside of GA₃₄, and, in addition converted [³H]GA₁ to GA₈. Preparations from embryo tissues contained 2-hydroxylase activity, converting [³H]GA₄ to GA₃₄ and [³H]GA₁ to GA₈.The presence of GA-metabolising enzymes was also indicated by in-vivo feeds of [³H]GA₄ to epicotyls of intact 4-d-old seedlings, which resulted in the accumulation of GA₁, GA₈, GA₃-3-O-glucoside, GA₄-glucosyl ester, GA₈-2-O-glucoside and a putative O-glucoside of GA₃₄. Gibberellin A₁ was the first metabolite detected, 15 min after application of [³H]GA₄, but after 24 h most of the label was associated with GA₈-2-O-glucoside. Over 90% of the recovered radioactivity was found in the shoot. Within the shoot, movement was preferentially acropetal, and was not dependent upon metabolism of the applied [³H]GA₄.Abbreviations DEAE diethylaminoethyl - GA_n gibberellin A_n - GPC gel permeation chromatography - HPLC-RC high performance liquid chromatography-radio counting - S-1 1000·g supernatant - UDP uridine 5-diphosphate     

Uptake and metabolism of radioactive gibberellins by barley aleurone layers

Summary When aleurone layers were treated with labeled gibberellin A₁ (³H-GA₁), gibberellin A₅ (³H-GA₅) and the methyl ester of ³H-GA₅ (³H-GA₅-ME), radioactivity was accumulated by the tissue for a period of 20–30 h. After this time, radioactivity was released into the medium. Concomitantly, ribonuclease was also liberated by the tissue. The radioactivity accumulated by aleurone layers was associated with polar metabolites of the respective GAs, and the extent of extent of accumulation was a function of the degree of GA metabolism (GA₅-ME>GA₅>GA₁). Accumulation of radioactivity was inhibited in the cold and by the metabolic poisons NaF and dinitrophenol. This was thought to be due to inbition of GA metabolism. The accumulation of ³H-GA₁ in aleurone tissue did not reach saturation when unlabeled GA₃ up to 10^-2 M was added to the incubation medium.Abbreviations GA gibberellin - GA₅ ME, gibberellin A₅ methyl ester - RNase ribonuclease     

Transport and metabolism of h-gibberellin a(1) in dioecious cucumber seedlings

The transport of ³H-GA₁ through hypocotyl segments of cucumber (Cucumis sativus L.) was found to be nonpolar. The transport of ³H-GA₁ was increased by pretreatment with relatively high concentrations of either IAA or Ethephon (2-chloroethylphosphonic acid). Hypocotyl segments from plants of a gynoecious genotype transported more ³H-GA₁ than those of an androecious. The metabolism of ³H-GA₁ in hypocotyl segments was neither related to the sex genotype of the cucumber plant nor influenced by pretreatment with Ethephon. The primary metabolite of GA₁ was suggested to be GA₈. Two other suspected metabolites were not identified. Differences in the endogenous GA of gynoecious and androecious plants could not be accounted for by transport differences.     

Preparation of radioactive gibberellin a(1) and its metabolism in dwarf peas

Gibberellin A₁-3,4-³H was prepared by selective catalytic reduction of gibberellic acid with a mixture of tritium and hydrogen. ³H-GA₁ was applied at physiological concentrations to dwarf peas and the metabolism of the hormone was investigated. ³H-GA₁ was converted to an acidic, biologically active compound. Radioactive but biologically inactive compounds were also found in the neutral fraction and could not be converted to acidic gibberellins by hydrolysis. No attachment of gibberellin to any macromolecular fraction was evident.     

Some properties of 2-5A binding/nucleolytic activities in gel filtered rabbit reticulocyte lysates

Rabbit reticulocyte lysates, gel filtered on Sephadex G-25 with or without ATP (or its analogs), were preincubated at 37°C and their subsequent binding to p₃A₄,3-[³²P]pCp was studied. Lysates filtered without ATP or in the presence of 0.1 mM 8-bromo-ATP, 1,N⁶-etheno-ATP, or ITP showed a time-dependent decrease in binding activity. This decrease was completely prevented when lysates were filtered with 0.1 mM ATP, 2-deoxy-ATP, --methylene-ATP, or ATP--S. The stability of binding provided by ATP or 2-deoxy-ATP analogs corresponds to a more active 2–5A dependent endonucleolytic (RNAase L) activity based on studies using [³H] viral mRNA. Chromatography on heparin-agarose showed that ATP-supplemented gel-filtered reticulocyte lysates had a different p₃A₄,3-[³²P]pCp binding activity elution-profile than lysates gel-filtered in the absence of ATP. Covalent cross-linking of periodate-oxidized p₃A₄,3-[³²P]pC to gelfiltered lysates, preincubated at 0°C or 37°C for 30 min, showed the following results: (1) all lysates gave a major cross-linking of the radioactive ligand to an 80 000 dalton polypeptide, regardless of the temperature of preincubation, (2) Iysates gel-filtered without ATP, with 0.1 mM ITP, or --methylene-ATP, showed a significant reduction in the cross-linking of the 80 000 dalton protein, after preincubation at 37°C for 30 min. This decrease was accompanied by an increase in the labeling of two smaller polypeptides.Abbreviations used 2 5-oligoadenylates oligonucleotides consisting of 5-adenylic acid residues joined by a 2 5-phosphodiester linkage     

In-vivo binding of radioactive gibberellins in dwarf pea shoots

Summary When shoots of 6-day-old, dark-grown peas were excised 30 mm below the apex and floated on a solution of radioactive gibberellin A ₁ (³H-GA₁) or radioactive gibberellin A₅ (³H-GA₅), more radioactivity accumulated in the apical part of the stem which responds to GA than in the basal, unresponsive region. The accumulation of ³H-GA₁ was, however, less pronounced than the accumulation of ³H-GA₅. GA derivatives of very low biological activity were not taken up preferentially by the apical region of the stem. Light, which lowers the responsiveness of dwarf peas to GA₁ and particularly to GA₅, also reduced the accumulation of these GAs in the apical part of the stem. Sections from the GA-responsive region were able to retain a higher level of GA₅ than sections from the non-responsive, basal region. The accumulation and retention of GA in the hormone-responsive tissue may be due to binding of the hormone to specific GA receptors.This work was supported by the United States Atomic Energy Commission under Contract AT (11-1)-1338.     

Interaction of environment and ABA and GA treatments on the maize anther culture response

Treatments designed to influence abscisic acid (ABA) or gibberellin (GA) concentrations were applied to developing tassels of maize (Zea mays L.) plants in different environments or to anthers in culture to determine the effect on formation of embryo-like structures (ELS). Production of ELS was significantly affected in certain environments when ABA, GA₃, ancymidol, or fluridone solutions were pipetted into whorls of field-grown plants approximately 3 days before tassel harvest. In 1996 anthers from 10 M ancymidol-treated plants were most responsive, producing 35 ELS/100 anthers and 50 M GA₃-treated plants were least responsive, producing 12 ELS/100 anthers. In 1997 under hotter, drier conditions, anthers from 50 M GA₃-treated plants were most responsive, producing 20 ELS/100 anthers and those from 50 M ABA-treated plants were least responsive, producing 2.4 ELS/100 anthers. Anthers from growth chamber plants were significantly more responsive when grown in a 16-h than a 12-h photoperiod. With the 16-h photoperiod the response was significantly greater with a 250 M ABA whorl treatment. With the 12-h photoperiod there was no significant effect from whorl treatments. Modification of the culture medium with added ABA, GA₃, ancymidol, or fluridone was generally ineffective, except in 1997 when the response was significantly higher with 1 M ABA added to the culture medium. The results suggest that the maize anther culture response may be influenced by environmental conditions that interact with ABA and GA treatments to donor plants during tassel development.     

Fate of radioactive gibberellin a(1) in maturing and germinating seeds of peas and Japanese morning glory

Radioactive gibberellin A₁ (³H-GA₁) was injected into excised fruits of peas and Japanese morning glory. These were then grown in sterile culture to maturity and the label was followed in the seeds during further development and subsequent germination. During development of both pea and morning-glory seeds a large part of the radioactivity became associated with the aqueous fraction, while another part of the ³H-GA₁ was converted into 2 new, acidic, biologically active compounds, designated X₁ and X₂. A relatively small part of the neutral compounds could be converted back to ³H-GA₁, X₁, and X₂ by means of mild acid hydrolysis. During germination of pea and morning-glory seeds, part of the bound compounds was released in the form of ³H-GA₁, X₁ and X₂ while, particularly during rapid seedling growth, a further conversion of ³H-GA₁, mainly to X₁, took place. In pea seedlings, growth during the first 2 to 3 days after imbibition was not affected by Amo-1618, an inhibitor of gibberellin biosynthesis. This, in conjunction with the findings on the interconversions between free and bound ³H-GA₁ suggests that, at least in peas, early seedling growth may at least partly be regulated by gibberellins released from a bound form which was formed during seed development.     

Effects of gibberellins on abscission in cotton seedling explants

Summary Gibberellic acid (GA₃) accelerated abscission when applied, in a wide concentration range, to excised abscission zones of cotton. Abscission was promoted equally by distal or proximal applications of from 10^-3 to 100 g. A slight, but inconsistent, abscission retardation was obtained with distal applications of 10^-6 and 10^-7 g.Seven different gibberellins accelerated abscission equally when applied distally at amounts of 5×10^-4 to 5×10^-1 g per abscission zone. At 5×10^-5 g there were great differences in effectiveness; their activities can be ranked: A₃>A₅A₄>A₇=A₈>A₁=A₉.The ready translocatability of GA₃ was suggested when 1.0 or 0.01 g was applied to one petiole, and the opposite untreated petiole abscised at the same time as the treated one. However, 0.001 g was not effective in moving across the stem and inducing abscission of the untreated petiole.The rate of abscission of petioles treated with 1.0 g GA₃ was not affected by increasing the length of the petiole from 3 to 9 mm. However, abscission of petioles treated with smaller amounts is inversely proportional to petiole length.The rate of abscission of petioles treated with GA₃ decreased with increasing seedling age; there was a simultaneous increase in abscission rate of the controls.Part of this research was based on a portion of a thesis submitted by the senior author to the Graduate Division, University of California, Davis, in partial fulfillment of the requirements for the M.S. degree.     

Further Characterization of 5-HT1A Receptors in the Goldfish Retina: Role of Cyclic AMP in the Regulation of the In Vitro Outgrowth of Retinal Explants

The presence of serotonin 5-HT_1A receptors and their physiological role were further characterized in the goldfish retina. The effects of the 5-HT_6/7 receptor antagonists pimozide, fluphenazine and amoxapine, the 5-HT_1A receptor antagonist WAY-100,135, and the alkylating agent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline, on the 5-HT_1A receptor agonist [³H]8-hydroxy-2-(di-n-propylamino)tetralin binding to retinal membranes, were evaluated. In addition, the effects of serotonin, 8-hydroxy-2-(di-n-propylamino)tetralin, WAY-100,135, the adenylate cyclase inhibitors SQ22536 and MDL12330A, and the cyclic AMP analog 8-bromoadenosine-3:5 cyclic monophosphate were also studied on neuritic outgrowth from retinal explants. WAY-100,135 but not 5-HT_6/7receptor antagonists inhibited [³H]8-hydroxy-2-(di-n-propylamino)tetralin binding to retinal membranes N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline decreased [³H]8-hydroxy-2-(di-n-propylamino)tetralin binding sites up to 70%, while receptor turnover was similar to that reported in other tissues. Serotonin and 8-hydroxy-2-(di-n-propylamino)tetralin stimulated cyclic AMP production, both ex vivo and in vitro, and these increases were related to inhibition of neuritic outgrowth. The inhibitory effect was reduced by SQ22536 and by WAY-100,135, and was mimicked by 8-bromoadenosine-3:5cyclic monophosphate. This study supports previous findings about the role of serotonin as a regulator of axonal outgrowth during in vitro regeneration of the goldfish retina and demonstrates that this effect is mediated, at least in part, by 5-HT_1A receptors through a mechanism which involves an increase of cyclic AMP levels.     

Metabolism of Tritiated Gibberellin A(9) by Shoots of Dark-grown Dwarf Pea, cv. Meteor

Tritium-labeled gibberellin A₉ (³H-GA₉) was metabolized by etiolated shoots of dwarf pea (Pisum sativum cv. Meteor) to GA₂₀, GA₁₀, 2,3-dihydro-GA₃₁, and a number of highly polar, acidic GA-like substances. Identifications were made by gasliquid radiochromatography and combined gas chromatography-mass spectrometry. Kinetic studies showed that GA₃₀ and 2,3-dihydro-GA₃₁ were produced within 5 hours following ³H-GA₉ application to pea shoots. The polar GA-like substances were produced between 5 and 10 hours after ³H-GA₉ application. Levels of GA₁₀ increased with time, and since no GA₁₀ was produced during the purification procedures, GA₁₀ was, in all probability, produced from ³H-GA₉ within the plant tissue. The radioactive interconversion products produced by pea from ³H-GA₉ have chromatographic properties similar to biologically active GA-like substances present in etiolated shoots of dwarf pea. Large scale applications of ³H-GA₉ with very low specific activity to etiolated pea shoots showed that the radioactivity of the interconversion products was correlated exactly with biological activity as assayed by dwarf rice (Oryza sativa cv. Tan-ginbozu).     

MEK1/2 and p38-like MAP kinase successively mediate H2O2 signaling in Vicia guard cell

As a second messenger, H₂O₂ generation and signal transduction is subtly controlled and involves various signal elements, among which are the members of MAP kinase family. The increasing evidences indicate that both MEK1/2 and p38-like MAP protein kinase mediate ABA-induced H₂O₂ signaling in plant cells. Here we analyze the mechanisms of similarity and difference between MEK1/2 and p38-like MAP protein kinase in mediating ABA-induced H₂O₂ generation, inhibition of inward K⁺ currents, and stomatal closure. These data suggest that activation of MEK1/2 is prior to p38-like protein kinase in Vicia guard cells.Key words: H₂O₂ signaling, ABA, p38-like MAP kinase, MEK1/2, guard cellAn increasing number of literatures elucidate that reactive oxygen species (ROS), especially H₂O₂, is essential to plant growth and development in response to stresses,^1–4 and involves activation of various signaling events, among which are the MAP kinase cascades.^1–3,5 Typically, activation of MEK1/2 mediates NADPH oxidase-dependent ROS generation in response to stresses,^4,6–8 and the facts that MEK1/2 inhibits the expression and activation of antioxidant enzymes reveal how PD98059, the specific inhibitor of MEK1/2, abolishes abscisic acid (ABA)-induced H₂O₂ generation.^6,8,9 It has been indicated that PD98059 does not to intervene on salicylic acid (SA)-stimulated H₂O₂ signaling regardless of SA mimicking ABA in regulating stomatal closure.^2,6,8,10 Generally, activation of MEK1/2 promotes ABA-induced stomatal closure by elevating H₂O₂ generation in conjunction with inactivating anti-oxidases.Moreover, activation of plant p38-like protein kinase, the putative counterpart of yeast or mammalian p38 MAP kinase, has been reported to participate in various stress responses and ROS signaling. It has been well documented that p38 MAP kinase is involved in stress-triggered ROS signaling in yeast or mammalian cells.^11–13 Similar to those of yeast and mammals, many studies showed the activation of p38-like protein kinase in response to stresses in various plants, including Arabidopsis thaliana,^14–16 Pisum sativum,¹⁷ Medicago sativa¹⁸ and tobacco.¹⁹ The specific p38 kinase inhibitor SB203580 was found to modulate physiological processes in plant tissues or cells, such as wheat root cells,²⁰ tobacco tissue²¹ and suspension-cultured Oryza sativa cells.²² Recently, we investigate how activation of p38-like MAP kinase is involved in ABA-induced H₂O₂ signaling in guard cells. Our results show that SB203580 blocks ABA-induced stomatal closure by inhibiting ABA-induced H₂O₂ generation and decreasing K⁺ influx across the plasma membrane of Vicia guard cells, contrasting greatly with its analog SB202474, which has no effect on these events.^23,24 This suggests that ABA integrate activation of p38-like MAP kinase and H₂O₂ signaling to regulate stomatal behavior. In conjunction with SB203580 mimicking PD98059 not to mediate SA-induced H₂O₂ signaling,^23,24 these results generally reveal that the activation of p38-like MAP kinase and MEK1/2 is similar in guard cells.On the other hand, activation of p38-like MAP kinase^23,24 is not always identical to that of MEK1/2^8,25 in ABA-induced H₂O₂ signaling of Vicia guard cells. For example, H₂O₂^- and ABA-induced stomatal closure was partially reversed by SB203580. The maximum inhibition of both regent-induced stomatal closure were observed at 2 h after treatment with SB203580, under which conditions the stomatal apertures were 89% and 70% of the control values, respectively. By contrast, when PD98059 was applied together with ABA or H₂O₂, the effects of both ABA- and H₂O₂-induced stomatal closure were completely abolished (Fig. 1). These data imply that the two members of MAP kinase family are efficient in H₂O₂-stimulated stomatal closure, but p38-like MAP kinase is less susceptive than MEK1/2 to ABA stimuli.Open in a separate windowFigure 1Effects of SB203580 and PD98059 on ABA- and H₂O₂-induced stomatal closure. The experimental procedure and data analysis are according to the previous publication.^8,23,24It has been reported that ABA or NaCl activate p38 MAP kinase in the chloronema cells of the moss Funaria hygrometrica in 2∼10 min.²⁶ Similar to this, SB203580 improves H₂O₂-inhibited inward K⁺ currents after 4 min and leads it to the control level (100%) during the following 8 min (Fig. 2). However, the activation of p38-like MAP kinase in response to ABA need more time, and only recovered to 75% of the control at 8 min of treatment (Fig. 2). These results suggest that control of H₂O₂ signaling is required for the various protein kinases including p38-like MAP kinase and MEK1/2 in guard cells,^1,2,8,23,24 and the ABA and H₂O₂ pathways diverge further downstream in their actions on the K⁺ channels and, thus, on stomatal control. Other differences in action between ABA and H₂O₂ are known. For example, Köhler et al. (2001) reported that H₂O₂ inhibited the K⁺ outward rectifier in guard cells shows that H₂O₂ does not mimic ABA action on guard cell ion channels as it acts on the K⁺ outward rectifier in a manner entirely contrary to that of ABA.²⁷Open in a separate windowFigure 2Effect of SB203580 on ABA- and H₂O₂-inhibited inward K⁺ currents. The experimental procedure and data analysis are according to the previous publication.²⁴ SB203580 directs ABA- and H₂O₂-inactivated inward K⁺ currents across plasma membrane of Vicia guard cells. Here the inward K⁺ currents value is stimulated by −190 mV voltage.Based on the similarity and difference between PD98059 and SB203580 in interceding ABA and H₂O₂ signaling, we speculate the possible mechanism is that the member of MAP kinase family specially regulate signal event in ABA-triggered ROS signaling network,^1–4 and the signaling model as follows (Fig. 3).Open in a separate windowFigure 3Schematic illustration of MAP kinase-mediated H₂O₂ signaling of guard cells. The arrows indicate activation. The line indicates enhancement and the bar denotes inhibition.     

The GABAA receptor family in the mammalian brain

The GABA_A-benzodiazepine receptor protein from bovine brain was purified by affinity chromatography and the subunit composition examined by gel electrophoresis in sodium dodecyl sulfate. Protein staining revealed a doublet at 51–53 kDa, a band at 55 kDa, and a broad band at 57–59 kDa. The 51 and 53 kDa bands co-migrated with the ₁ and ₂ gene products identified by Western blotting with subtype-specific antibodies. These two bands were also photoaffinity labeled by [³H]flunitrazepam, as was a breakdown product at 44 kDa. Partial sequencing of proteolytic fragments of these polypeptides yielded sequences found in all clones, and identified the benzodiazepine binding site within residues 8–297 and probably between 106–297 of ₁; the 44 kDa and 31 kDa bands yielded fragments containing ₃ sequence. The native ₃ polypeptide was identified with subtype-specific antibody at 57 kDa overlapping with the two major bands photolabeled with [³H]muscimol at 55 and 58 kDa. Antisera to a -selective peptide recognized four bands at 60, 58, 57 and 55 kDa. Thus, one can identify 6–8 distinct polypeptides with the possibility of another 4–6 in purified GABA_A receptor proteins, depending on brain region, consistent with the family of gene products suggested by molecular cloning.Special issues dedicated to Dr. Eugene Roberts     

Determination of plant growth substances in liquid endosperm of immature walnut (Juglans nigra) nuts by an ELISA technique

Plant growth substances (PGSs) were analysed in liquid endosperm of black walnut using HPLC and an ELISA procedure. Of all the PGSs studied, we show no GA₃, low levels of cytokinins (io⁶A, i⁶Ade, i⁶Ado) and ABA, and very high level of IAAAbbreviations ABA Abscisic acid: - Ade Adenine: - GA₃ Gibberellic acid: - IAA Indole-3-acetic acid: - i⁶Ade N⁶(²-1) adenine: - i⁶Ado N⁶(²-isopentenyl adenosine: - io⁶A Zeatin riboside:     

Reaction center light harvesting B875 complexes from Rhodocyclus gelatinosus: characterization and identification of quinones

Reaction center-B875 pigment-protein complexes were purified from Rhodocyclus gelatinosus. The proteic components consist of 7–8 polypeptides among which some were identified by their apparent molecular weights: the light harvesting B875 polypeptides and of 8 and 6 kDa, reaction center L (23 kDa), M (28 kDa) and H (34 kDa), cytochrome c (43 kDa). Four c-type hemes were found per reaction center. Flash-induced absorbance changes showed the presence of both Q_A and Q_B in the complex. Charge recombination times were determined to be: 1.16±0.2 (n=30) for P⁺Q_AQ_B ^- and 7–10 ms for P⁺Q_A ^- in presence of herbicides. From quinone analysis on one hand and kinetics of charge recombination on the other hand, we proposed that in the reaction center of Rhodocyclus gelatinosus Q_A is menaquinone 8 and Q_B is ubiquinone 8.     

Movement of Abscisic Acid Across the Plasmalemma and the Tonoplast of Guard Cells of Valerianella locusta

Uptake experiments and efflux compartmental analyses of abscisic acid (ABA) with acid treated epidermal peels of Valerianella locusta were performed to elucidate the mechanisms of transport of ABA across the plasmalemma and tonoplast of guard cells. ABA uptake across the plasmalemma is linearly correlated with external ABA concentration in the incubation medium. Under alkaline conditions ABA-uptake was not significantly above background, indicating that ABA uptake occurs mainly by diffusion of undissociated ABAH as the most permeable species, which is trapped afterwards in the alkaline cytosol as impermeable ABA^?. Efflux analysis of ABA revealed a saturable component of ABA transfer across the tonoplast. A Woolf-Augustinsson-Hofstee analysis suggested the existence of two transport systems for ABA at the tonoplast. The high affinity transport system had a K_M of 0.21 mol m^?3 and a V_max 85.8 amol ABA cell^?1 h^?1. Using the data of the uptake and efflux experiments we calculated the permeability coefficients of ABA for the plasmalemma and the tonoplast of guard cells, which are 2.46 10^?7 m s–¹ and 1.26 10^?8m s^?1, respectively. The distribution of the pH-probe (¹⁴C)-DMO between medium, cytosol and vacuole was investigated and used to calculate cytosolic and vacuolar pH. The vacuolar pH is too low to explain the high vacuolar ABA concentration by trapping of ABA^?, whereas the cytosol is sufficiently alkaline to act as an efficient anion trap. Therefore we conclude that ABA transport across the guard cell tonoplast is catalyzed by a saturable uptake component.     

Subchronic Treatment with Methamphetamine and Phencyclidine Differentially Alters the Adenosine A1 and A2A Receptors in the Prefrontal Cortex,Hippocampus, and Striatum of the Rat

Subchronic treatment with MAP (4.6 mg/kg, i.p., once daily for 11 days) significantly decreased the K_d, but not B_max, values of [³H]1,3-dipropyl-8-cyclopentylxanthine ([³H]DPCPX) binding to adenosine A₁ receptors in the prefrontal cortex and hippocampus, but not striatum, of rat brain. However, subchronic treatment with PCP (10 mg/kg, i.p., once daily for 11 days) did not alter the K_d and B_max values of [³H]DPCPX binding to adenosine A₁ receptors in these three regions. Subchronic treatment with MAP or PCP did not alter the B_max and K_d values of [³H]2-p-(2-carboxyehyl)phenethylamino-5-N-ethylcarboxyamidoadenosine ([³H]CGS21680) binding to adenosine A_2A receptors in the striatum. Furthermore, subchronic treatment with MAP or PCP significantly decreased the specific binding of [³H]CGS21680 to adenosine A_2A receptors in the hippocampus, but not in the prefrontal cortex. Thus, these results suggest that MAP and PCP may produce differential effects on the adenosine A_2A receptors, but not adenosine A₁ receptors in rat brain.     

Recombination in the lambda repressor gene: evidence that very short patch (VSP) mismatch correction restores a specific sequence

Summary The mutation am6 in the cI gene of bacteriophage is identified as a CT transition in a 5CC _T ^A GG sequence. In four-factor crosses of am6 with nearby mutations in cI, the frequencies of cI⁺ recombinants are much higher than expected from the physical distances. A very short patch (VSP) mismatch repair system is presumed to recognize am6/am ⁺ mispairs in the heteroduplexes that accompany recombination between the outside markers. Mutation am6 is corrected to am ⁺; correction of am ⁺ to am6 was not detected. Clear-plaque mutation 1-1 in cI is a TC transition in a 5CTTGG sequence, resulting in the sequence 5CC _T ^A GG. When 1-1 was crossed with nearby mutations in gene cI, there were no excess cI⁺ recombinants, which would result from repair of CCTGG (1-1) to CTTGG (cI⁺). However, in crosses of cI⁺ phages with mutation 1-1, there was an excess of cI^- recombinants, indicating that cI⁺ was repaired to 1-1. Preferential repair does not require adenine or cytosine methylation: when repairing a mismatch, the VSP repair system apparently identifies specific mispaired bases by sequence alone.