Accumulation of heat shock proteins in field-grown cotton

Cotton (Gossypium hirsutum L.) plants grown under field water deficits exhibited an 80 to 85% reduction in leaf area index, plant height, and dry matter accumulation compared with irrigated controls. Midday photosynthetic rates of dryland plants decreased 2-fold, and canopy temperatures increased to 40°C at 80 days after planting compared with canopy temperatures of 30°C for irrigated plants. Leaves from dryland plants which had exhibited canopy temperatures of 40°C for several weeks accumulated stainable levels of polypeptides with apparent molecular weights of 100, 94, 89, 75, 60, 58, 37, and 21 kilodaltons. These polypeptides did not accumulate in leaves from irrigated plants.

Addition of [³⁵S]methionine to leaves of growth chamber-grown cotton plants and subsequent incubation at 40°C for 3 hours radiolabeled polypeptides with molecular weights similar to those that accumulate in dryland cotton leaves. These data suggest that the proteins which accumulate in water-stressed cotton leaves at elevated temperatures (40°C) are heat shock proteins and that these proteins can accumulate to substantial levels in field-stressed plants.

     

Effect of a zinc-deficient diet on lipid peroxidation in liver and tumor subcellular membranes

The effect of a zinc-deficient diet on lipid peroxidation in liver and tumor mitochondrial and microsomal membrane preparations from BALB/c mice was investigated. Mitochondrial and microsomal membranes from both tissues displayed increased rates of in vitro peroxidation, both enzymatic and nonenzymatic. Measurement of in vivo peroxidation, using diene conjugation as an index of measurement revealed slight increases in tissues from zinc-deficient animals that were not statistically significant. Serum lipoperoxides analyzed from all three groups revealed no significant differences. The results point to an alteration in the peroxidation potential of mitochondrial and microsomal membranes due to zinc deficiency which may be related to an alteration in fatty acid composition.     

Regulated expression of a Drosophila melanogaster heat shock locus after stable integration in a Drosophila hydei cell line.

DNA-mediated cotransformation has been used to transfer a Drosophila melanogaster heat shock locus into cultured Drosophila hydei cells by use of the copia-based selectable vector pCV2gpt and of pMH10A, a cloned 87A7 heat shock locus encoding a mutant heat shock protein (hsp). Transformed lines contain between 50 and 200 copies of both plasmids, each separately organized as a head-to-tail concatemer which is stably maintained in the transformed lines. Exposure of the cotransformants to heat shock temperatures induces the regulated expression of the hsp RNA and the mutant hsp in all the lines analyzed.     

Preservation of ischemic myocardial tissue with an antagonist of vasoconstrictor eicosanoids

A new antagonist of the vasoconstrictor eicosanoids, L-640,035, was studied in a standardized model of myocardial ischemia (MI) in anesthetized cats. This eicosanoid antagonist was not found to exert any overt hemodynamic action in cats subjected to a sham myocardial ischemia protocol. However, the antagonist markedly reduced the S-T segment of the electrocardiogram when administered 30 min after permanent occlusion of the left coronary artery. Moreover, circulating activities of the marker enzyme creatine kinase (CK) were markedly attenuated by L-640,035 3-5 h after the onset of MI. This was verified by cardiac biopsies 5 h post-MI since myocardial CK activities decreased much less in treated MI cats than in MI cats receiving only the vehicle for L-640,035 (i.e., ethanol). The active metabolite of the antagonist in biological fluids (i.e., L-636,499) markedly antagonized the vasoconstrictor actions of endoperoxide and thromboxane analogs, but not of noneicosanoids in isolated perfused coronary arteries.     

Interaction between the A2 and A19 amino acid residues is of critical importance for high biological activity in insulin: [19-leucine-A]insulin

The replacement of tyrosine at position A19 by leucine in the insulin molecule led to an analogue, [19-leucine-A]insulin [( Leu19-A]insulin), displaying insignificant receptor binding affinity and in vitro biological activity less than 0.1 and 0.05%, respectively, compared to the natural hormone. This analogue along with the previously reported [2-glycine-A]-, [2-alanine-A]-, and [2-norleucine-A]insulins is the least potent insulin analogue we have examined. Circular dichroic studies showed that all these analogues are monomeric at concentrations at which insulin is primarily dimeric. We conclude that an aromatic ring at position A19 and the presence of the side chain of isoleucine at position A2 are each of critical importance for high biological activity in insulin. It appears that the van der Waals interaction between the side chain of isoleucine A2 and tyrosine A19, present in crystalline insulin, is among the most important determinants for high biological activity in insulin.     

Chloroplast glutathione reductase: Purification and properties

Glutathione reductase was partially purified from isolated pea chloroplasts ( Pisum sativum L. cv. Progress #9). A 1600-fold purification was obtained and the purified enzyme had a specific activity of 26 μmol NADPH oxidized (mg protein)⁻¹ min⁻¹. The enzyme had a native molecular weight of approximately 156 kdalton and consisted of two each of two subunits of about 41 and 42 kdalton. The K_m for oxidized glutathione was 11 μ M and the K_m for NADPH was 1.7 μ M . Enzyme activity was affected by the ionic strength of the assay medium, and maximum activity was observed at an ionic strength of between 60 and 100 m M . The enzyme was inactivated by sulfhydryl modifying reagents and the presence of either oxidized glutathione or NADPH affected the extent of inactivation. Chloroplast glutathione reductase probably serves in the removal of photosynthetically derived H₂O₂ by reducing dehydroascorbate for ascorbate-linked reduction of H₂O₂. Intermediates of this reaction sequence, dehydroascorbate, ascorbate, reduced glutathione, and NADPH had no effect on enzymic activity.     

Regulation of prolactin and its role in gallinaceous bird reproduction

There are major changes in circulating luteinizing hormone (LH), prolactin (PRL), estrogens (E), and progesterone (P) in relation to the onset of reproduction, egg laying, incubation, and care of young. LH levels increase in the prelaying period, followed some days later by increased circulating levels of E, P, and PRL. Levels of these hormones tend to stabilize during egg laying with periodic ovulatory cycle changes. Around the onset of incubation PRL levels increase, while LH, E, and P levels fall. During incubation PRL reaches very high levels, falling sharply when incubation is terminated. Stimulatory effects of hypothalamic neurotransmitters, peptides, and ovarian steroids on PRL secretion have been shown. The prelaying increase is dependent on E and P and the high levels of incubation require a functional serotonergic system. The causal relationships and roles of PRL in incubation of gallinaceous birds are, however, still unclear.     

Membrane turnover in crab photoreceptors studied by high-resolution scanning electron microscopy and by a new technique of thick-section transmission electron microscopy

Summary Crab photoreceptors were examined after treatment by the osmium-DMSO-osmium method for high-resolution scanning electron microscopy. This technique of specimen preparation was also adapted for transmission electron microscopy, enabling sections up to 1 urn thick to be viewed in a conventional microscope at 75 kV. With appropriate pretreatment, some cytoskeletal elements can be visualised by both techniques. The methods were then used to investigate some of the daily changes known to occur in photoreceptor cell structure. Striking differences were found in the structure of Golgi bodies present in retinula cells during the synthesis and breakdown phases of the daily cycle of photoreceptor membrane turnover. Cyclic changes were also noticed in the mitochondria of retinula cells, and additional evidence was found for a previously proposed model of rhabdomeral microvillus formation.