Stimulation of ethylene production in citrus leaf discs by mannitol

Wound ethylene formation induced in leaf tissue of citrus (Citrus sinensis [L.] Osbeck cv. “Washington Navel”) by excision was significantly stimulated by mannitol after a lag period of about 6 hours. The extent of stimulation was dependent upon the concentration of mannitol (10 to 100 millimolar). This increased ethylene production was not simply due to osmotic effect or water stress as other osmoticums tested failed to exert such an effect. The stimulatory effect of mannitol resulted from both the enhancement of 1-aminocyclopropane-1-carboxylic acid (ACC) formation and the conversion of ACC to ethylene. The effect on the latter step was particularly pronounced in aged discs. The use of labeled mannitol showed that it was taken up by the leaf discs, utilized for respiration, and metabolized to sucrose, but no radioactivity was detected in the ethylene.     

Dark metabolism of carbon monoxide in lettuce leaf discs

In the dark, leaf tissue of crisphead lettuce (Lactuca sativa L.) metabolized ¹⁴CO to ¹⁴CO₂ and acid-stable products. Tissue incubated at 2.5°C for 3.5 hours and 48 hours converted about 1% and 17%, respectively, of the applied ¹⁴CO to ¹⁴CO₂, and incorporated about 0.04% and 0.6% of the ¹⁴C in acid-stable products. Examination of soluble acid-stable products from ¹⁴CO and ¹⁴CO₂-treated leaf tissue revealed that the labeling patterns of both treatments were identical during the 3.5-hour and the 48-hour incubation periods. Malate, citrate, and aspartate together comprised 70% or more of the soluble radioactivity from both treatments. Incorporation of radioactivity from CO into soluble acid-stable products during a 3-hour incubation period at 2.5°C was inhibited 90% by adding 3% nonradioactive CO₂. These results indicate that in head lettuce in the dark ¹⁴CO is metabolized primarily to ¹⁴CO₂ which is the precursor of acid-stable products. In leaf discs at 2.5°C, the apparent K_m for CO oxidation to CO₂ was 5.3 microliters per liter and the V_max was 9.7 nanoliters per gram per hour. The mitochondrial fraction of the leaf homogenate was the most active fraction to oxidize CO to CO₂, and this activity was heat-labile and cyanide-sensitive.     

Evidence for Ascending and Descending Intraspinal as Well as Primary Sensory Somatostatin Projections in the Rat Spinal Cord

Somatostatin distribution was measured quantitatively in the rat spinal cord by radioimmunoassay. Rostro-caudally, somatostatin content was about 50% higher in lumbar-sacral cord than in cervical or thoracic levels. The dorso-ventral distribution is more uneven: somatostatin is highest in the dorsal horn, where the peptide is 15 times as concentrated as it is in the ventral white matter, the region of lowest concentration. However, measurable amounts of the peptide were found in all regions studied. Dorsal root ganglionectomy decreased somatostatin levels in the dorsal cord, supporting the previously proposed role for this peptide as a primary sensory neurotransmitter or modulator; but somatostatin content also was decreased both rostral and caudal to spinal transection, indicating the presence of ascending and descending somatostatin pathways within the spinal cord. Brain levels did not change. Met-enkephalin and substance P were also measured after the above surgical manipulations. Met-enkephalin content was not altered and substance P content was lowered significantly only after ganglionectomy. Although this study confirms the primary sensory neuron as the origin of a part of spinal cord somatostatin, it further indicates the presence of ascending and descending somatostatin pathways within the rat spinal cord.     

Sex Differences in the Content of β-Endorphin and Enkephalin-Like Peptides in the Pituitary of Obese (ob/ob) Mice

Abstract: The β-endorphin content in pituitary extracts of male and female obese (ob/ob) and lean (+/?) mice was determined by radioimmunoassay. The amount of β-endorphin-like material contained in the pituitary of 3-month-old ob/ob male mice is similar to that of lean male mice. In contrast, the pituitary glands of female ob/ob mice have a greater amount of β-endorphin-like material than lean female mice. To determine with greater precision the molecular nature of the polypeptide that accounts for the increase in β-endorphin immunoreactivity, the various molecular forms of β-endorphin immunoreactivity were resolved by Biogel P-30 column chromatography. At least four peaks of immunoreactive material were detected. The first peak elutes in the void volume, and the second and the third peaks appear in the elution volumes of β-lipotropin and β-endorphin, respectively. That the material present in the void volume might be proopiocortin is supported by adrenocorticotropic hormone radioimmunoassay. The increased total β-endorphin immunoreactivity in pituitary glands of ob/ob mice is accounted for mainly by β-endorphin. The β-endorphin content of various brain structures of ob/ob mice is similar to that of lean littermates.     

Structures of cytokinins influence synergistic production of ethylene

Twenty-five naturally occurring cytokinins and structurally related compounds were tested for their ability to promote ethylene production synergistica     

Covalently closed circular DNAs of murine type C retrovirus: depressed formation in cells treated with cycloheximide early after infection.

Formation of viral closed circular supercoiled DNA duplexes and production of progeny virus were both inhibited in cultured mouse cells treated with cycloheximide in the first 4 h of type C retrovirus infection. With different doses of cycloheximide to cause different degrees of inhibition, the number of viral supercoiled DNA duplexes detected in the cells at 11 h showed an apparent correlation with the amount of progeny virus produced in the 12- to 22-h period of infection. A slight accumulation of the full-genome linear duplex and an open circular duplex of viral DNA intermediate was observed in the cycloheximide-treated cells. Cycloheximide given to the cells during the time of conversion of viral DNA from linear to supercoiled duplex forms (6 to 11 h after virus inoculation) did not inhibit the conversion. These kinetic data suggest that a cycloheximide-sensitive metabolic process, probably early viral protein synthesis, is required for retrovirus replication and supercoiled viral DNA formation in the cell.     

Biochemical characterization of enkephalin-like immunoreactive peptides of adrenal glands

The total enkephalin-like immunoreactive peptide content of adrenal glands from dog, cattle, guinea pig and rat was investigated by radioimmunoassay using a (met⁵)-enkephalin antiserum. Dog adrenals contain the highest amount of peptides, cattle and guinea pig adrenals contain lesser amounts, and the rat adrenals had the least amount (0.05% that of the dog). Comparison of the (met⁵)-enkephalin content of the adrenal cortex and medulla with that of whole bovine adrenal gland indicates that the peptides are concentrated in the medulla. Analysis of the chromaffin granules from bovine adrenal medulla indicates this to be the primary storage site for (met⁵)-enkephalin-like peptides. Gel chromatography reveals a molecular heterogeneity of the immunoreactive peptides in all species tested; high molecular weight peptides account for a larger proportion of the immunoreactivity when compared with the low molecular weight peptides.     

Plant tumor reversal associated with the loss of foreign DNA

Summary Transformation of plant tissues into crown gall tumors has been associated with the transfer of a portion of a tumor-inducing plasmid (Ti-plasmid) into plant DNA. Various laboratories have regenerated normal-appearing plants from a number of crown gall tumors. This study investigates the fate of the foreign DNA in a series of tissues derived from various parts of a plant regenerated from the tumor BT-37 by Braun and his coworkers. It was found that all the foreign DNA sequences were lost from tissues that had lost all their tumorous traits; whereas the plasmid DNA sequences were still present in tissues that appeared normal but still exhibited tumorous traits when returned to tissue culture media. From these studies it would appear that the presence of the Ti-plasmid sequences in the plant DNA is required for the maintenance of the transformed state. Presented in the Symposium on Gene Transfer, Differentiation and Neoplasia in Plant and Animal Cells at the 30th Annual Meeting of the Tissue Culture Association, Seattle, Washington, June 10–14, 1979. This symposium was supported in part by Grant CA 26748 from the National Cancer Institute, DHEW, and Grant RD-67 from the American Cancer Society.     

Primary culture of mouse mammary tumor epithelial cells embedded in collagen gels

Summary Mammary tumor epithelial cells from BALB/cfC3H mice were dispersely embedded inside the collagen gels in Ham's F-12 medium containing horse serum. A sustained cell growth leading to a 5- to 10-fold increase in cell number over initial level was observed in less than 2 weeks. The extent of this growth was found to be dependent on serum concentration. However, addition of various protein and steroid hormones, both singly and in combination, to low-serum-containing medium failed to achieve a comparable level of growth to that promoted by higher serum concentration. Mammary tumor cells can now be consistently propagated in primary culture. This investigation was supported by Grants CA05388 and CA09041 awarded by the National Cancer Institute, Department of Health, Education and Welfare, and by cancer research funds of the University of California.     

Ordered conformation of polypeptides and proteins in acidic dodecyl sulfate solution

The conformation of some polypeptides and proteins in sodium dodecyl sulfate (NaDodSO4) solutions was studied by circular dichroism. The type and extent of induced structure depend on their helix- and beta-forming potential. Anionic side groups in segments of helix or beta form tend to destabilize the ordered structure unless they are protonated. beta-Endorphin has one Glu inside a predicted helical segment; its helicity in a NaDodSO4 solution is enhanced at pH below 4. alpha-Melanocyte-stimulating hormone having a Glu in a beta segment undergoes a pH-induced coil to beta transition in 1.25 mM NaDodSO4 (excess surfactant will disrupt the beta form). Reduced somatostatin assumes a beta form in 2 mM NaDodSO4 and a partial helix in 25 mM NaDodSO4, both of which are unchanged in acidic pH because it lacks -COOH groups. The unordered gastrin with five consecutive Glu's becomes helical in a NaDodSO4 solution at pH 4. Neurotensin with one Glu has no structure-forming potential and is unordered in both neutral and acidic NaDodSO4 solutions. This charge effect also manifests in segments of ordered structure for polypeptides and proteins such as glucagon, cytochrome c, parvalbumin, ribonuclease A, and lysozyme. The effect is especially predominant in tropomyosin that is rich in clusters of anionic side groups. Its more than 90% helicity is reduced to about one-half in a neutral NaDodSO4 solution, but most of it can be restored by lowering the pH to 2.4.