Cadmium bioavailability

Cadmium slowly accumulates in the liver and kidney and has a long biological half-life, estimated to be 2-3 decades in the kidney. If the kidney cadmium concentration reaches a critically high level, proximal tubular damage results, which can be followed by severe bone mineral loss. There are only a few measurements of cadmium bioavailability in foods; however, the data are indicative of lower utilization from foods than from inorganic salts. In animal tissues cadmium is bound primarily to a heat-resistant small protein with a high cysteine content (metallothionein), whereas little is known about the form in which cadmium occurs in the edible parts of plants. Low intakes of many nutrients exacerbate the effects of cadmium and supplemental intakes are protective. Newborn and young animals absorb much higher quantities of cadmium than adults. There is some evidence in animals that females may be more adversely affected than males. Itai-itai disease, a painful disease with kidney damage and bone demineralization, occurred in elderly Japanese women who had borne several children and who were exposed to cadmium via food and drinking water. Inasmuch as cadmium in the U.S. food supply affords an estimated safety factor of only 4- to 15-fold, it is important to establish factors that affect the bioavailability of cadmium from foods.     

Changes in the Expression of the αα Form of Enolase During Neuroblastoma Differentiation

Abstract: The relative amounts of the different enolase isozymes present in neuroblastoma cells change during differentiation. When differentiation is induced by low serum in the presence of DMSO (dimethyl sulfoxide), there is a 50% decrease in the concentration of enolase activity associated with the form αα, and an increase in the activity associated with the γ-containing isozymes (αγ plus γγ); in the absence of DMSO, there is no decrease in αα or in total enolase activity. In order to study the mechanism of the changes in αα, cells differentiated with low serum with and without DMSO were compared. Measurements of the concentration of the α antigen by microcomplement fixation and by immunotitration demonstrate that the decreased enolase activity in DMSO cells is due to a decreased concentration of the α antigen. Measurements of the relative rate of synthesis of the antigen show that the decreased concentration of the α antigen is due to a decreased rate of synthesis. Enolase in differentiated cells is sufficiently stable (t_1/2 > 100 h) that a comparison of the relative rates of degradation has not been possible. The decreased synthesis of the α subunit of enolase that occurs under these conditions appears to be a useful model system for studying the de-expression of the α gene that occurs in vivo during neuronal differentiation.     

Sources of sucrose translocated from illuminated sugar beet source leaves

A search for source leaf sucrose pools that differed in their relation to export was carried out in photosynthesizing leaves of Beta vulgaris L. The time course of depletion of [¹⁴C]sucrose in a leaf in unlabeled CO₂ following steady state labeling provided evidence for two distinct sucrose pools. After the start of the light period, leaf blade sucrose remained constant although it exchanged between the two pools. Newly synthesized sucrose destined for export passed through one pool more rapidly than through the other. All of the leaf blade sucrose appeared to exchange with export sucrose. Modeling and regression analysis of [¹⁴C]sucrose data provided a means for estimating the size of the two pools. From 20 to 40% of the sucrose was calculated to be present in the pool that provided the less direct path to export; this was likely vacuolar sucrose. The remainder of the sucrose in the blade was probably in the cytoplasm and veins. Added amounts of leaf blade sucrose, produced in response to elevated CO₂, appeared to be stored mainly in the vacuolar compartment.     

Gene mapping and determination of the structure of chloroplast transfer RNA from various photosynthetic organisms

The review sums up data on gene mapping studies of tRNAs of chloroplasts from maize, beans, Euglena, Cyanophora. The mechanisms of splicing of tRNA2Ile from maize chloroplasts and coded for by a gene of unusual length was investigated.     

Role of basidiospores as inocula of mycorrhizal fungi of birch

Summary Fruitbodies of sheathing mycorrhizal fungi collected under birch (Betula pendula andB. pubescens) were suspended over pots of soil and the resulting spore-supplemented soils were planted with sedlings ofB. pendula. Inocybe lacera, I. lanuginella, Hebeloma sacchariolens andH. leucosarx formed mycorrhizas readily.Lactarius pubescens andLeccinum roseofracta did not form mycorrhizas from basidiospore inocula, even after prolonged periods of seedling growth.Paxillus involutus gave equivocal results, perhaps because the soil was unsuitable for this species. Storage of the basidiospore-supplemented soils for 6 months in outdoor conditions or in a growth room at 18°C did not materially alter the results.The results are discussed in relation to the concept of mycorrhizal succession.     

Studies of protoplast fusion in Streptomyces chrysomallus

Conditions for the regeneration of cells from protoplasts of Streptomyces chrysomallus, a producer of the peptide antibiotic actinomycin, are described. Regeneration of fusion products was most efficient at 27-30 degrees C on regeneration R2 medium (Okanishi et al., 1974) containing 0.25 M-sucrose. The addition of phosphate (150-300 mg 1(-1) to the medium and incubation at 23 degrees C proved to be optimal for the regeneration of individual strains. Highest recombination frequencies after protoplast fusion were obtained by fusing protoplasts in the presence of 45% (w/v) polyethylene glycol 6000. With strains that produce no, or little antibiotic, protoplasts must be present in excess in fusion mixtures in order to overcome inhibition of regeneration by the antibiotic-producing partner.     

Germline integration of moloney murine leukemia virus at the Mov13 locus leads to recessive lethal mutation and early embryonic death

Thirteen mouse substrains genetically transmitting the exogenous Moloney murine leukemia virus (M-MuLV) at a single locus (Mov locus) have been derived previously. Experiments were performed to investigate whether homozygosity at the Mov loci would be compatible with normal development. Animals heterozygous at an Mov locus were mated, and the genotype of the offspring was analyzed. From parents heterozygous at the loci Mov1 to Mov12, respectively, homozygous offspring were obtained with the expected Mendelian frequency. In contrast, no homozygous offspring or embryos older than day 15 of gestation were obtained from parents heterozygous at the Mov13 locus. When pregnant Mov13 females at day 13 and day 14 of gestation were analyzed, approximately 25% of the embryos were degenerated. Genotyping revealed that these degenerated embryos were invariably homozygous and the normal appearing embryos were either heterozygous or negative for M-MuLV. These results suggest that integration of M-MuLV at the Mov13 locus leads to insertion mutagenesis, resulting in embryonic arrest between day 12 and day 13 of gestation. It is possible that the Mov13 locus represents a gene or gene complex involved in the early embryonic development of the mouse.