Interspecific crosses inHordeum (Poaceae)

A crossing programme including 30 species and 40 cytotypes within the genusHordeum was undertaken. Viable hybrids were obtained in 302 combinations, 15 of which were intraspecific. Differences in seed set and in germination were observed in crosses between different groups of species. Obtaining crosses between different taxonomic groups was generally more difficult when diploid material was used. Some species, e.g.,H. lechleri, H. jubatum, andH. brachyantherum showed a higher crossability than others. The chromosome numbers of the hybrids were usually those expected from the parental numbers but aneuploid series around the expected numbers were rather frequent. Three cases of unreduced gametes were found. Selective chromosome elimination was restricted to combinations including eitherH. vulgare orH. bulbosum.—Despite a very diverse morphology, all South American diploid species together with the two North American diploidsH. intercedens andH. pusillum appear to be closely related. The hexaploid American speciesH. procerum, H. lechleri, andH. arizonicum are also related. The two North American tetraploid speciesH. jubatum andH. brachyantherum sometimes form semifertile hybrids. The Asiatic speciesH. roshevitzii appears to be related to both North and South American taxa.     

Pattern formation in fragmented eggs of the short germ insect Schistocerca gregaria

Summary The effect of transverse fragmentation on the segment pattern of the short germ embryo of the locust Schistocerca gregaria has been investigated at two stages subsequent to the formation of the germ anlage. Following fragmentation both anterior and posterior partial embryos were observed, although rarely in a single egg. Anterior partial patterns usually terminated with a segment visible at the time of fragmentation or with the next segment due to appear. Posterior partial patterns began with a wide range of segments depending on the level of fragmentation.Anterior and posterior partial patterns developing in a single egg were usually not complementary and the segments missing sometimes included some segments visible when the embryo was fragmented. Non-complementary patterns resulted following fragmentation in all regions, while complementary patterns only occurred after fragmentation in the visibly-segmented region.The results suggest that following fragmentation isolated posterior portions of the embryo continue to form segments, while isolated anterior regions usually do not. This effect could result from variable damage to an existing pattern of unequally-sized segment primordia, or from the disruption of a process of sequential segmentation in the elongating posterior region of the embryo. The results are broadly compatible with the progress zone model proposed by Summerbell et al. (1973).     

CELL ENLARGEMENT IN SKELETONEMA COSTATUM (BACILLARIOPHYCEAE)1

Skeletonema costatum (Grev.) Cl. exhibits an asexual means, of increasing cell size that is more common than auxosporulation. This phenomenon accounts for the genetic stability of S. costatum in culture and for the deficiency of heterozygotes in natural populations, and has important implications far the life history of this species.     

Sulfate influx across the rabbit ileal brush border membrane: Sodium and proton dependence,and substrate specificities

Summary In intact ileal mucosa, uptake of SO₄ across the brush border membrane requires the presence of Na and is saturable, withK1/2=1.3mm at 140mm Na (P.L. Smith, S.A. Orellana & M. Field, 1981.J. Membrane Biol. 63:199–206). The present study examines the substrate specificities and transport stoichiometry of the Na-dependent SO₄ uptake process. The effects of variations in medium anion and cation composition on lumen-to-epithelium influx of SO₄ (J _me ^SO4 ) were determined under short-circuit conditions.J _me ^SO4 is inhibited by thiosulfate, but not by phosphate, methylsulfate, vanadate or taurocholate. Cl is weakly inhibitory. Uptake of SO₄ is poorly supported by Li, and is unaffected by K, indicating a specific dependence on Na. At low SO₄ concentration (0.22mm),J _me ^SO4 is a hyperbolic function of medium Na concentration; the corresponding Hill plot is linear with a slope of 1.0, suggesting a transport stoichiometry of 1 Na: 1 SO₄. At high SO₄ concentration (6.7mm), the Na-dependent SO₄ velocity curve is sigmoidal and yields a Hill plot which is again linear but has a slope of 1.56, suggesting transport of more than 1 Na per SO₄. SO₄ uptake in presence of Na exhibits a dependence on medium pH. At 0.22mm SO₄ and 140mm Na,J _me ^SO4 was doubled by lowering pH from 7.4 to 6.8. However, at 6.7mm SO₄ and 140mm Na, changing pH had no effect onJ _me ^SO4 over the range 6.8 to 8.5. The pH dependence ofJ _me ^SO4 at 6.7mm SO₄ was restored when medium Na was lowered to 3mm, suggesting that pH sensitivity is a function of the concentration of preformed NaSO ₄ ^– ion pair. The results suggest that SO₄ influx across the ileal brush border occurs by electroneutral Na⁺/NaSO ₄ ^– or Na⁺/H⁺/SO ₄ ^2– cotransport, the former being favored by high concentrations of Na and SO₄.     

Thiolated nucleotides in yeast transfer RNA

By culturing Saccharomyces cerevisiae in growth medium containing Mg³⁵SO₄, we have determined the extent and variation of tRNA thiolation in this yeast. We find that 5-methoxycarbonylmethyl-2-thiouridine (mcm⁵s²U)¹ is the major, if not only, thiolated derivative in S. cerevisiae tRNA. In addition, a comparison of the chromatographic mobility of mcm⁵s²Up on cellulose thin layers with those reported for unknown uridine derivatives found in purified yeast tRNA digests, leads to the conclusion that at least two of these tRNAs contain this modification.     

Structural organization of the normal and anoxic heart of Scyllium stellare

Summary The general and ultrastructural organization of the heart of the elasmobranch, Scyllium stellare, was studied in normal and in anoxic animals. The rich coronary supply was revealed three-dimensionally by the use of corrosion casts, showing a thebesian system of coronary arterioles and capillaries in the thin, outer compact layer as well as in the predominant, inner spongy layer of trabeculae.Only the sinus venosus received a neuronal input of large bundles of granule-containing axons terminating at fenestrated regions of the endocardium and suggesting a neurohormonal function.A simple, tubular sarcoplasmic reticulum with flattened junctional cisternae was present in myocardial cells of 1–5 m diameter, which contained one or two bundles of myofibrils. The latter were closely apposed to the inner aspect of the plasmalemma. Mitochondria were located centrally in the cells, which were joined by unfolded desmosomes involving Z-band material.Long periods of anoxia were tolerated without loss of heart function, but at the expense of cytoplasmic glycogen. Lipid granules were abundant in all layers and chambers, notably in animals prepared in the summer. The lipid granules displayed a marked increase in electron density when the heart was incubated in a buffered oxalate solution prior to fixation. A glycogen-sparing effect of the lipids during anoxia was observed.     

Computer-aided Diagnosis of Acute Abdominal Pain

This paper reports a controlled prospective unselected real-time comparison of human and computer-aided diagnosis in a series of 304 patients suffering from abdominal pain of acute onset.The computing system''s overall diagnostic accuracy (91·8%) was significantly higher than that of the most senior member of the clinical team to see each case (79·6%). It is suggested as a result of these studies that the provision of such a system to aid the clinician is both feasible in a real-time clinical setting, and likely to be of practical value, albeit in a small percentage of cases.     

Biochemical studies of the chromaffin granule. II. Properties of membrane-bound and water-soluble forms of chromogranin A and dopamine-β-hydroxylase activity

1. Chromogranin A has been isolated from the washed membrane fraction of highly purified chromaffin granules after solubilization in Triton X-100. A hydrated molecular weight of 2.9·10⁵ has been obtained for chromogranin A_M which in its electrophoretic mobility and molecular volume appears very similar to chromogranin A_I of the water-soluble fraction.     

Further observations on the effect of ethionine on the synthesis of β-galactosidase inEscherichia coli: Formation of an immunologically cross-reacting protein

It was found that ethionine partially inhibits the transport of the inducer (TMG) of β-galactosidase into the cells ofEscherichia coli ML-30. The synthesis of β-galactosidase-specific messenger RNA is not inhibited. Ethionine appears to be incorporated into proteins synthesized by the strains used. The incorporation of ethionine into the molecule of β-galactosidase results in the synthesis of an enzymically inactive, immunologically cross-reacting protein.