Hydrobiology and organic production in a marl lake of Kashmir Himalayan Valley

L. Naranbagh (alt. 1587 m) is a polymictic, shallow marl lake in the flood-plain valley of Kashmir, India. Macrofloral affinities resemble Potamogeton Type of Forsberg (1965) with alkaline waters, not rich in phosphorus. CaCO₃ precipitation coupled with decline in Ca²⁺ and alkalinity values are characteristic of the lake. Fluctuations in Mg²⁺, Na⁺, K⁺, and Cl^– were relatively conservative. The levels of PO _inf4 ^sup3– -P and NO _inf3 ^sup– -N indicate moderate fertility of the lake water.Persistence of a summer-autumn planktonic algal pulse is related to favourable irradiance, high water temperatures, and increased photosynthetic efficiency values. The most striking seasonality in photosynthetic rates (m^–2 h^–1) between winter minimum (3 mg C_assim) and summer maximum (75.4 mg C_assim) is determined by mainly climatic changes. Energy flow gave annual phytoplankton production of 51.95 × 10² KJ m^–2 for the ecosystem.The nutrient levels and productivity rates suggest mesotrophic status of L. Naranbagh in classic oligoeutrophic classification of lake types.     

Cloning and expression of a cDNA encoding a catalytically active fragment of calf thymus DNA polymerase alpha

A calf thymus cDNA expression library was constructed in the EcoRI site of lambda gt11 and probed with an antibody raised against calf thymus DNA polymerase alpha. Three classes of antibody-reactive clones were isolated. The largest class carried a 1.9 kilobase calf cDNA insert and expressed a 165-175 kilodalton beta-galactosidase:calf fusion protein which displayed DNA polymerase activity. The characteristic responses of the polymerase activity to alpha-specific inhibitors and antibodies identified the 1.9 kilobase cDNA as a sequence specifically derived from the structural gene encoding the pol alpha catalytic core.     

Peptide models of protein metastable binding sites: competitive kinetics of isomerization and hydrolysis

alpha 2-Macroglobulin and the complement components C3 and C4 each contain a metastable binding site that is essential for covalent attachment. Two cyclic peptides are useful models of these unusual protein sites. Five-membered lactam 1 (CH3CO-Gly-Cys-Gly-Glu-Glp-Asn-NH2) contains an internal residue of pyroglutamic acid (Glp). Fifteen-membered thiolactone 2 (CH3CO-Gly-Cys-Gly-Glu-Glu-Asn-NH2 15-thiolactone) contains a thiol ester bond between Cys-2 and Glu-5. These isomeric hexapeptides are spontaneously interconverted in water. Competing with the two isomerization reactions are three reactions involving hydrolysis of 1 and 2. These five processes were found to occur simultaneously under physiologic conditions (phosphate-buffered saline, pH 7.3, 37 degrees C). Best estimates of the five rate constants for these apparent first-order reactions were obtained by comparing the observed molar percentages of peptides 1-4 with those calculated from a set of exponential equations. Both isomerization reactions (ring expansion of 1 to 2, k1 = 6.4 X 10(-5) s-1; ring contraction of 2 to 1, k-1 = 69 X 10(-5) s-1) proceeded faster than any of the hydrolysis reactions: alpha-cleavage of 1 with fragmentation to form dipeptide 3 (k2 = 3.3 X 10(-5) s-1), gamma-cleavage of 1 with ring opening to yield mercapto acid 4 (k3 = 0.35 X 10(-5) s-1), and hydrolysis of 2 with ring opening to give 4 (k4 = 1.9 X 10(-5) s-1). The isomerization rate ratio (k1/k-1 = 10.9) agreed with the isomer ratio at equilibrium (1:2 = 11 starting from 1 and 10 starting from 2). The alpha/gamma regioselectivity ratio (k2/k3 = 9.7) for hydrolysis of the internal Glp residue of 1 was consistent with results for model tripeptides. Part of the chemistry of the protein metastable binding sites can be explained by similar isomerization and hydrolysis reactions.     

Regulatory effects of mast cells on lymphoid cells: the role of histamine type 1 receptors in the interaction between mast cells, helper T cells and natural suppressor cells

We have investigated the role of mast cells as modulators of lymphocyte function because the mast cells are concentrated in the areas of lymphoid storage; they are dependent upon T-cell growth factor for their proliferation; and they appear to be the principle if not sole storage site for histamine. We have tested the influence of mast cells on the proliferation of alloreactive cloned helper T cells, mixed leukocyte reactions, and the suppressive capacity of natural suppressor cells. We used an IL-3-dependent mast cell line that at high numbers (greater than 10(5)) suppressed and at low numbers (10(3) to 6 X 10(4)) augmented the proliferation of TH cells. Addition of histamine to cocultures enhanced the mast cell mediated proliferation of TH cells without directly affecting the helper cells. The action of histamine appeared to be mediated with H1 type receptors on these mast cells. Pretreatment of natural suppressor cells with supernatants from mast cell enhanced their suppressive capability. Here too, histamines enhanced suppression by the NS cell via histamine type 1 receptors on the natural suppressor cells. Our data suggest that mast cells may be a major modulator of the lymphoid cell immune function and demonstrate a role of histamine type 1 receptors in the interaction between mast cells, helper T cells, and natural suppressor cells.     

Specific hybridization probes demonstrate fewer xenotropic than mink cell focus-forming murine leukemia virus env-related sequences in DNAs from inbred laboratory mice.

We have derived hybridization probes from analogous 100-base-pair segments located within the N-terminal region of gp70 coding sequences which differentiate xenotropic from mink cell focus-forming (MCF)-related murine leukemia virus (MuLV) DNAs. The MCF probe annealed to the integrated proviruses of all six MCF MuLV isolates tested; the xenotropic probe hybridized to the DNAs of all four xenotropic proviral isolates examined. No cross-hybridization was observed, and neither probe reacted with the env segments of amphotropic or ecotropic MuLV DNAs. Southern blot analysis of HindIII- or EcoRI-digested genomic DNAs from a variety of inbred laboratory mice demonstrated the presence of more MCF- than xenotropic MuLV-related segments in every strain tested.     

Regulation of luteal cell 3-hydroxy-3-methylglutaryl coenzyme A reductase activity by estradiol

Recent studies have suggested that estradiol or androgen precursor may stimulate steroidogenesis in the luteal cell by modulating intracellular sterol availability and metabolism. This investigation was performed to examine the effect of estradiol on de novo synthesis of cholesterol. Pregnant rats hypophysectomized and hysterectomized on Day 12 were treated for 72 h with either estradiol or testosterone. De novo cholesterol synthesis was determined by measurement of the specific activity of the enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase, the rate limiting enzyme in cholesterol biosynthesis, in microsome-enriched preparations of luteal tissue and incorporation of [14C] acetate into cholesterol by corpora lutea incubated in vitro. Estradiol or testosterone treatment caused a 4- to 5-fold stimulation of luteal cholesterol biosynthesis, as measured by these techniques. NaF, an inhibitor of phosphatase which blocks the conversion of the inactive enzyme to the active form, reduced the HMG CoA reductase activity to 30% in corpora lutea obtained from either steroid or vehicle-treated rats. However, an increase in enzyme activity of comparable magnitude by steroids was observed whether microsomes were isolated with or without NaF. The effect of estradiol appears to be enzyme-specific, since it failed to affect the microsomal marker, NADPH-cytochrome c reductase. Since the cholesteryl ester content of corpora lutea falls in response to steroid treatment, rats were treated with 4-aminopyrazolo-[3,4d]pyrimidine (4-APP) to deplete cellular cholesterol content.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regulation of toxin biosynthesis by plasmids in Vibrio cholerae

Vibrio cholerae strain 569B Inaba harbouring P plasmid produced less toxin than the parent strain. To examine the effect of plasmid loss on toxin production, temperature-sensitive (ts) mutants of P, unable to replicate at 42 degrees C, were isolated. One ts plasmid was unstable at 42 degrees C and its loss yielded a cured strain that resumed a normal level of toxin biosynthesis characteristic of the plasmid-free parent strain. Toxin production was again suppressed in the cured strain after reacquisition of P plasmid. This suggested a role for plasmid-borne genes in the regulation of toxin biosynthesis. A mutant of strain 569B Inaba that produced mutant toxin was isolated by transfer of P and V plasmids. The mutant toxin was similar to choleragenoid because it did not give rise to symptoms of cholera but induced antitoxin immunity in rabbits.     

Caffeine tolerance: behavioral, electrophysiological and neurochemical evidence

The development of tolerance to the stimulatory action of caffeine upon mesencephalic reticular neurons and upon spontaneous locomotor activity was evaluated in rats after two weeks of chronic exposure to low doses of caffeine (5-10 mg/kg/day via their drinking water). These doses are achievable through dietary intake of caffeine-containing beverages in man. Concomitant measurement of [3H]-CHA binding in the mesencephalic reticular formation was also carried out in order to explore the neurochemical basis of the development of tolerance. Caffeine, 2.5 mg/kg i.v., markedly increased the firing rate of reticular neurons in caffeine naive rats but failed to modify the neuronal activity in a group exposed chronically to low doses of caffeine. In addition, in spontaneous locomotor activity studies, our data show a distinct shift to the right of the caffeine dose-response curve in caffeine pretreated rats. These results clearly indicate that tolerance develops to the stimulatory action of caffeine upon the reticular formation at the single neuronal activity level as well as upon spontaneous locomotor activity. Furthermore, in chronically caffeine exposed rats, an increase in the number of binding sites for [3H]-CHA was observed in reticular formation membranes without any change in receptor affinity. We propose, therefore, that up-regulation of adenosine receptors may underlie the development of tolerance to the CNS effects of caffeine.     

Effect of Light and Benzyladenine on Dark-Treated Growing Rice (Oryza sativa) Leaves II. Changes in Peroxidase Activity

Changes in peroxidase activity were studied in the attachedfirst leaf of dark-treated Oryza sativa L. cv. Bala seedlingsin response to benzyladenine and light treatments during laterperiods of leaf growth, prior to maturation. Darkness causeda mild decrease in peroxidase activity; but in illuminated leaves,the enzyme activity was stable at all times. There was a sharprise in peroxidase activity in dark-treated leaves upon lightor benzyladenine application, irrespective of the time of treatment.Benzyladenine treatment to illuminated leaves also caused arise in peroxidase activity. Exogenous hydrogen peroxide, glycolateand amizol resulted in a rise in peroxidase activity, whichwas further enhanced by benzyladenine treatment in both lightand dark incubated leaves. Proline maintained chlorophyll levels,whereas hydroxyproline caused chlorophyll degradation. Benzyladenineenhanced the proline effect and counteracted the hydroxyprolineeffect on chlorophyll. Both proline and hydroxyproline increasedperoxidase activity in the leaves of light and dark incubatedseedlings, and the enzyme activity further increased after benzyladeninetreatment. (Received December 7, 1984; Accepted May 8, 1985)     

Dual action of respiratory inhibitors: inhibition of germination and prevention of dormancy induction in lettuce seeds

`Grand Rapids' lettuce Lactuca sativa L. seeds germinate readily at 15°C but poorly at 25°C in darkness. When held in dark at 25°C for an extended period, the ungerminated seeds become dormant as shown by their inability to germinate or transfer to 15°C in darkness. Induction of dormancy at 25°C was prevented by exposure to CN<sup>−</sup>, azide, salicylhydroxamic acid (SHAM), dinitrophenol, and pure N<sub>2</sub> as determined by subsequent germination at 15°C on removal of inhibitors. The effectiveness of inhibitors to break dormancy declined as dormancy intensified. At relatively low levels, CN<sup>−</sup>, SHAM, and azide promoted dark germination at 25°C while at high levels they were inhibitory. Uptake of O<sub>2</sub> by seeds held at 25°C for 4 days in 1.0 millimolar KCN was inhibited by 67% but was promoted 61% when KCN was removed. Correspondingly greater inhibition (79%) and promotion (148%) occurred when 1.0 millimolar SHAM was added to KCN solution. When applied alone, SHAM had little effect on O<sub>2</sub> uptake. These data indicate that Cyt pathway of respiration plays a dominant role in the control of both dormancy induction and germination of lettuce seeds, and `alternative pathway' is effectively engaged in presence of CN⁻. The channeling of respiratory energy use for processes governing germination or dormancy is subject to control by physical and chemical factors.

A scheme is proposed that illustrates compensatory use of energy for processes controlling dormancy induction and germination. A block of germination, e.g. by low water potential polyethylene glycol solution or a supraoptimal temperature spares energy to be utilized for dormancy induction while a block of dormancy induction by low levels of CN⁻ (similar to GA and light effects) drives germination. Blocking both processes by inhibitors (e.g. CN⁻, CN⁻ + SHAM) presumably leads to accumulation of `reducing power' with consequent improvement in O₂ uptake and oxidation rates of processes controlling germination or dormancy induction upon removal of the inhibitors.