The prickly-pears (Opuntia spp., Cactaceae): A source of human and animal food in semiarid regions

The Cactaceae contain many economically promising species primarily in the genus Opuntia. This genus appears to have its center of genetic diversity in Mexico where it is widely used as fodder, forage, fruit, and a green vegetable. In southwestern United States, the prickly-pears have been considered as both weeds and valuable forage plants. During the frequent, unpredictable droughts, propane torches known as “pear burners” are used to singe the spines off cactus pads so that they can be eaten by livestock. Although spineless varieties of Opuntia can be consumed directly by domestic livestock, they are extremely susceptible to herbivory by wildlife. The Cactaceae possess Crassulacean Acid Metabolism, which can be four- to five-fold more efficient in converting water to dry matter than the most efficient grasses. Some Opuntia strains grow rapidly with fresh-fruit yields of 8,000–12,000 kg/ha/ yr or more and dry-matter vegetative production of 20,000–50,000 kg/ha/yr.     

Proposed Mechanism of Inheritance and Expression of the Human Fragile-X Syndrome of Mental Retardation

A mechanism is proposed for the inheritance and expression of the fragile-X-linked syndrome of mental retardation in humans. Two independent events are required for expression of the syndrome: the fragile-X mutation, and X chromosome inactivation in pre-oogonial cells. The fragile-X mutation at site Xq27 has little or no effect until the chromosome is inactivated in a female as part of the process of dosage compensation. At a stage where the inactivated X chromosome would normally be reactivated in preparation for oogenesis, the mutation results in a local block to the reactivation process. This block to reactivation leads to mental retardation in progeny by reducing the level of products from the unreactivated Xq27 region in male cells, and, for a heterozygous female, in somatic cells in which the normal X chromosome has been inactivated. Published data relevant to this proposed mechanism are discussed.     

Transformation ofAspergillus flavus to study aflatoxin biosynthesis

Aflatoxin contamination of agricultural commodities continues to be a serious problem in the United States. Breeding for resistant genotypes has been unsuccessful and detoxification of food sources is not economically feasible. New strategies for control may become apparent once more is known about the biosynthesis and regulation of aflatoxin. Although the biosynthetic pathway of aflatoxin has been extensively studied, little is known about the regulation of the individual steps in the pathway. We have developed a genetic transformation system forAspergillus flavus that provides a new and expedient approach to studying the biosynthesis of aflatoxin and its regulation. Through the use of this genetic transformation system, genes for aflatoxin biosynthesis can be identified and isolated by the complementation of aflatoxin negative mutants. In this paper we discuss molecular strategies for studying the regulation and biosynthesis of aflatoxin.     

Mn2+ reduces Yz + in manganese-depleted Photosystem II preparations

Manganese in the oxygen-evolving complex is a physiological electron donor to Photosystem II. PS II depleted of manganese may oxidize exogenous reductants including benzidine and Mn²⁺. Using flash photolysis with electron spin resonance detection, we examined the room-temperature reaction kinetics of these reductants with Y_z ⁺, the tyrosine radical formed in PS II membranes under illumination. Kinetics were measured with membranes that did or did not contain the 33 kDa extrinsic polypeptide of PS II, whose presence had no effect on the reaction kinetics with either reductant. The rate of Y_z ⁺ reduction by benzidine was a linear function of benzidine concentration. The rate of Y_z ⁺ reduction by Mn²⁺ at pH 6 increased linearly at low Mn²⁺ concentrations and reached a maximum at the Mn²⁺ concentrations equal to several times the reaction center concentration. The rate was inhibited by K⁺, Ca²⁺ and Mg²⁺. These data are described by a model in which negative charge on the membrane causes a local increase in the cation concentration. The rate of Y_z ⁺ reduction at pH 7.5 was biphasic with a fast 400 s phase that suggests binding of Mn²⁺ near Y_z ⁺ at a site that may be one of the native manganese binding sites.Abbreviations PS II Photosystem II - Y_D tyrosine residue in Photosystem II that gives rise to the stable Signal II EPR spectrum - Y_z tyrosine residue in Photosystem II that mediates electron transfer between the reaction center chlorophyll and the site of water oxidation - ESR electron spin resonance - DPC diphenylcarbazide - DCIP dichlorophenolindophenol     

Melanin as a natural germ cell marker for intraspecific transplantation experiments in Ambystoma mexicanum (Urodela,Amphibia)

Summary In urodele amphibians, the lack of a reliable germ cell marker restricts the experimental study of the germ lineage. In the present work, we conducted genetic and histological analyses in order to demonstrate that melanin from oocytes constitutes a germ cell marker available for intraspecific experiments in Ambystoma mexicanum. Then, using this marker, we implanted germ cells from undifferentiated gonads (stage 48) into the blastocoel of host embryos and investigated their fate and determined state. Our results show that, from this stage on, the donor cells do not differentiate into other cell types; therefore, they are restricted in developmental capacity and irreversibly determined as germ cells. On the other hand, exogenous germ cells were found in an isotopic position until the young tail-bud stage, and then were found in an ectopic position; these results suggest that, from the middle tail-bud stage on, an active process contributes to migration of primordial germ cells to the gonadal territory.     

Developmental expression of 44-kDa bone phosphoprotein (osteopontin) and bone γ-carboxyglutamic acid (Gla)-containing protein (osteocalcin) in calcifying tissues of rat

New aspects of the distribution and developmental appearance of the 44-kDa bone phosphoprotein (44K BPP, also called sialoprotein I or osteopontin) and bone gamma-carboxyglutamic acid (Gla)-containing protein (BGP, also called osteocalcin) during osteogenesis and dentinogenesis were investigated with immunocytochemical techniques using monospecific, affinity-purified polyclonal antibodies. Sections from newborn rat incisors and from various bone anlagen of newborn animals and fetuses were processed for detection of 44K BPP or BGP antigenicity. In addition, histochemical reactions for detection of alkaline phosphatase or calcium salts were performed on a number of the sections. The 44K BPP appears to be synthesized and secreted by chondrocytes only in the areas of cartilage-to-bone transition; these cells could participate indirectly in the process of bone formation by providing a suitable scaffold onto which primary marrow osteoblasts attach and spread. During osteogenesis, 44K BPP is found in bone-forming cells almost concomitantly with the appearance of alkaline phosphatase and before osteoid deposition, whereas BGP is still absent during early stages of mineralization. We hypothesize that this dramatic difference between the developmental appearance of 44K BPP and BGP reflects the delayed expression of the BGP gene relative to that of 44K BPP. In long-term cultures of bone marrow from adult mice, some fibroblastic cells expressed the 44K BPP phenotype; these cells could represent early osteogenic progenitor cells. Some experiments also suggested that, as with BGP, 44K BPP or an immunologically related protein is synthesized by some odontoblasts and secreted into predentin, prior to the onset of mineralization.     

Recognition of a genus-wide antigen ofLegionella by a monoclonal antibody

A monoclonal antibody was produced against a cytoplasmic membrane protein that appears to be common to all species of the genusLegionella. The antibody was positive in polyacrylamide gel electrophoresis and Western blotting with extracts of all of 22 species type strains ofLegionella that were tested. The apparent molecular mass of the protein varied from 57.2 to 62.1 kilodaltons for the 23 species type strains ofLegionella. An enzyme-linked immunosorbent assay (ELISA) was developed with the monoclonal antibody to enable rapid screening of clinical and environmental isolates forLegionella. All of 23 species type strains ofLegionella that were tested were strongly positive with the monoclonal antibody in the ELISA. Among 27 other bacterial species and 84 strains that were tested, onlyBordetella ssp. andAcinetobacter lwoffii were cross-reactive in the ELISA. These two cross-reactive species are readily distinguishable fromLegionella by culture characteristics. The monoclonal antibody may also be useful in tests to detect the genus-wide antigen in body fluids of patients with legionellosis.     

Modified inoculum for radiometric susceptibility testing ofMycobacterium tuberculosis

Two-hundred and fifteen isolates ofMycobacterium tuberculosis were evaluated with the BACTEC 460 radiometric method for susceptibility to isoniazid, rifampin, ethambutol, and streptomycin (SM); a revised protocol for inoculum preparation was used. Fresh clinical isolates were subcultured into 7H9 broth and then photometrically adjusted to the equivalent of a 0.5 McFarland standard, one-half the recommended inoculum density. This method produced an overall 98.3% correlation with a conventional agar method. The sensitivity of this procedure was good for all drugs tested except for the lowest concentration of SM (2 g/ml). Specificity was excellent for all drugs tested. After repeat testing, only four discrepancies were found, yielding a 99.8% correlation between the two systems. The time required for susceptibility tests averaged 4.6 days. This method for inoculum preparation effectively minimized the number of susceptibility tests exceeding the threshold value before the fourth day of incubation. This allowed for definite trends of the growth index values to become established before interpretation of results.     

Action of a cell wall proteinase (PI) from Streptococcus cremoris HP on bovine β-casein

Summary The specificity of a cell wall proteinase (P_I) from Streptococcus cremoris strain HP in its action on bovine -casein was determined. To this end an enzymic digest (pH 6.2; 15° C) of -casein was brought to pH 4.6 and the soluble fraction separated by semi-preparative reversed-phase HPLC. Purified peptides were analyzed by amino acid and end-group analysis. Ten chromatographic components were identified, which together accounted for at least seven cleavage sites all being located in the C-terminal fifty-residue part of -casein. In five cases it concerned a Gln-X or X-Gln peptide linkage. The specificity of this proteinase from S. cremoris HP shows similarity to that reported for a cell wall proteinase from S. lactis NCDO 763 in its action on -casein.Presented at the second FEMS Symposium on Lactic Acid Bacteria held in 1987 at Wageningen, Netherlands