TRIDENS X OKLAHOMENSIS (T. FLAVUS X T. STRICTUS), AN INTERSPECIFIC STERILE HYBRID IN THE ERAGROSTEAE (GRAMINEAE)

The incidence of Tridens oklahomensis Feath. with T. flavus (L.) Hitchc. and T. strictus (Nutt.) Nash together with its morphological intermediacy between the latter two species suggests a hybrid origin. Field and laboratory studies conducted over several years provide substantial evidence of an interspecific cross. Tridens oklahomensis appears in generally disturbed habitats, such as roadsides and cleared areas, where the adventive (for this region) T. strictus occurs as overlapping populations with the ubiquitous T. flavus. At no time has the supposed hybrid been recorded solely with one or the other of the two species. On a moisture gradient, T. strictus is found mainly in swales and ditches while T. flavus occurs on the drier and more general upland. The hybrid occurs toward the moist end of gradient, near T. strictus. On this basis it is reasoned that the latter is the pistillate parent. The hybrid is sterile and has no vegetative means of spreading. Under these conditions its presence is limited to chance fertilization in those situations where T. strictus has invaded the range of the more widespread T. flavus.     

Comparison of four routinely used vitamin D automated immunoassays

BackgroundTo compare four automated immunoassays for the measurement of 25(OH)-vitamin D (25-OHD) and to assess the impact on the results obtained from a healthy population.MethodsWe analysed 100 serum samples on Unicel DxI 800 (Beckman Coulter), Architect i1000 (Abbott), Cobas e411 (Roche) and Liaison XL (DiaSorin). Passing-Bablok regression and Bland-Altman plots were used for method comparison. In order to categorise the obtained values, results were categorised into the following groups: 0-25 nmol/L, 25-50 nmol/L, 50-75 nmol/L and above 75 nmol/L and compared. The percentage of samples below 75 nmol/L, and below 50 nmol/L was then calculated for every method.ResultsAccording to paired comparisons, each method differs from others (p<0.0001) except Cobas vs Architect, which do not show a statistically significant difference (p=0.39). The strongest correlation was found between Liaison and Architect (ρ=0.94, p<0.0001). The percentage of samples below the recommended value of 75 nmol/L were: 70% (Architect), 92% (Liaison), 71% (Cobas) and 89% (Unicel). The percentage of samples below the value of 50 nmol/L were: 17% (Architect), 55% (Liaison), 28% (Cobas) and 47% (Unicel).ConclusionsThe observed differences stem from the use of different analytical systems for 25-OHD concentration analysis and can result in different outcomes. The recommended values should be established for each assay in accordance with the data provided by the manufacturer or in the laboratory, in accordance with proper standardisation.     

Classical bile acids in animals, beta-phocaecholic acid in ducks

1. Bile samples of different animals were analysed and the percentage content of classical bile acids was determined. 2. Herbivorous birds mostly excreted a large proportion of chenodeoxycholic acid. 3. The anteater (Myrmecophaga tridactyla) excreted deoxycholic acid most probably as a primary bile acid. 4. In the bile of ducks (Anas platyrhynchos) a large amount of (23R)3 alpha, 7 alpha, 23-trihydroxy-5 beta-cholan-24-oic acid (beta-phocaecholic acid) was found.     

Histochemical study of an unusual cat intrafusal muscle fiber

A cat tenuissimus muscle spindle that contained two long chain intrafusal fibers in its distal pole is described. One of the fibers (lc1) had a histochemical profile (ATPase, NADH-TR, ChE reactions) of the kind which is characteristic for long chain fibers. The other fiber (lc2) consisted of two separate segments. The inner lc2 segment included the sensory equatorial region and was histochemically normal. The outer lc2 segment carried a motor plate, and did not stain for NADH-TR in the same way as the inner lc2 segment and the lc1 fiber. It is suggested that the unusual enzyme staining properties of the outer lc2 segment stemmed from its lack of sensory innervation, a situation which may have permitted the full expression of influences mediated by its motor nerve supply.     

Steady-state kinetics of horse-liver alcohol dehydrogenase with a covalently bound coenzyme analogue

The steady-state kinetics of the enzyme modified by affinity labelling with NAD analogue, nicotinamide-N6-[N-(6-aminohexyl)carbamoylmethyl]-adenine dinucleotide, has been investigated using a recycling reaction with p-nitrosodimethylaniline and n-butanol as substrates and compared to the kinetics of native alcohol dehydrogenase. The modified enzyme obeys a ping-pong mechanism involving two inactive enzyme forms (enzyme-NAD and enzyme-NADH complexes in the 'open' conformations, the nicotinamide moieties of the coenzymes being out of the active center). The rate of p-nitrosodimethylaniline reduction in the reaction catalyzed by the modified enzyme is comparable to that observed in the presence of the native enzyme. On the other hand, the oxidation of butanol by the modified enzyme is essentially slower under our experimental conditions (pH 8.5). The measurements in the presence of specific alcohol dehydrogenase inhibitors competing with substrates and coenzymes (isobutyramide, pyrazole and AMP) revealed that the relative portion of the inactive 'open' form of the enzyme-NADH complex is negligible, whereas the 'open' form of the enzyme-NAD complex seems to represent a more significant portion (about 30%) under the conditions used.     

Origin of intrafusal muscle fibers in the rat

The expression of several isoforms of myosin heavy chain (MHC) by intrafusal and extrafusal fibers of the rat soleus muscle at different stages of development was compared by immunocytochemistry. The first intrafusal myotube to form, the bag2 fiber, expressed a slow-twitch MHC isoform identical to that expressed by the primary extrafusal myotubes. The second intrafusal myotube to form, the bag1 fiber, expressed a fast-twitch MHC similar to that initially expressed by the secondary extrafusal myotubes. At subsequent stages of development, the equatorial and juxtaequatorial regions of bag2 and bag1 intrafusal myofibers began to express a slow-tonic myosin isoform not expressed by extrafusal fibers, and ceased to express some of the MHC isoforms present initially. Myotubes which eventually matured into chain fibers expressed initially both the slow-twitch and fast-twitch MHC isoforms similar to some secondary extrafusal myotubes. In contrast, adult chain fibers expressed the fast-twitch MHC isoform only. Hence intrafusal myotubes initially expressed no unique MHCs, but rather expressed MHCs similar to those expressed by extrafusal myotubes at the same chronological stage of muscle development. These observations suggest that both intrafusal and extrafusal fibers develop from common pools of bipotential myotubes. Differences in MHC expression observed between intrafusal and extrafusal fibers of rat muscle might then result from a morphogenetic effect of afferent innervation on intrafusal myotubes.