Optimizing purebred selection for crossbred performance using QTL with different degrees of dominance

A method was developed to optimize simultaneous selection for a quantitative trait with a known QTL within a male and a female line to maximize crossbred performance from a two-way cross. Strategies to maximize cumulative discounted response in crossbred performance over ten generations were derived by optimizing weights in an index of a QTL and phenotype. Strategies were compared to selection on purebred phenotype. Extra responses were limited for QTL with additive and partial dominance effects, but substantial for QTL with over-dominance, for which optimal QTL selection resulted in differential selection in male and female lines to increase the frequency of heterozygotes and polygenic responses. For over-dominant QTL, maximization of crossbred performance one generation at a time resulted in similar responses as optimization across all generations and simultaneous optimal selection in a male and female line resulted in greater response than optimal selection within a single line without crossbreeding. Results show that strategic use of information on over-dominant QTL can enhance crossbred performance without crossbred testing.     

Effect of postnatal development on calcium currents and slow charge movement in mammalian skeletal muscle

Single- (whole-cell patch) and two-electrode voltage-clamp techniques were used to measure transient (Ifast) and sustained (Islow) calcium currents, linear capacitance, and slow, voltage-dependent charge movements in freshly dissociated fibers of the flexor digitorum brevis (FDB) muscle of rats of various postnatal ages. Peak Ifast was largest in FDB fibers of neonatal (1-5 d) rats, having a magnitude in 10 mM external Ca of 1.4 +/- 0.9 pA/pF (mean +/- SD; current normalized by linear fiber capacitance). Peak Ifast was smaller in FDB fibers of older animals, and by approximately 3 wk postnatal, it was so small as to be unmeasurable. By contrast, the magnitudes of Islow and charge movement increased substantially during postnatal development. Peak Islow was 3.6 +/- 2.5 pA/pF in FDB fibers of 1-5-d rats and increased to 16.4 +/- 6.5 pA/pF in 45-50-d-old rats; for these same two age groups, Qmax, the total mobile charge measurable as charge movement, was 6.0 +/- 1.7 and 23.8 +/- 4.0 nC/microF, respectively. As both Islow and charge movement are thought to arise in the transverse-tubular system, linear capacitance normalized by the area of fiber surface was determined as an indirect measure of the membrane area of the t-system relative to that of the fiber surface. This parameter increased from 1.5 +/- 0.2 microF/cm2 in 2-d fibers to 2.9 +/- 0.4 microF/cm2 in 44-d fibers. The increases in peak Islow, Qmax, and normalized linear capacitance all had similar time courses. Although the function of Islow is unknown, the substantial postnatal increase in its magnitude suggests that it plays an important role in the physiology of skeletal muscle.     

Chemical modification of spinach ferredoxin with diethylpyrocarbonate: evidence for the essential nature of the histidyl residue

Spinach ferredoxin contains a single ferredoxin which can be chemically modified with diethylpyrocarbonate. By varying the concentration of diethylpyrocarbonate modified ferredoxins could be prepared which had only one or both of the imidazole nitrogens of the histidine modified. A small amount of tyrosine was also modified. Ferredoxin with only one of the imidazole nitrogens modified was fully active in NADP photoreduction by chloroplast membranes. This activity was lost as the second imidazole nitrogen was modified. The results suggest an essential role for the single histidine of ferredoxin.     

Effect of temperature on drought resistance and growth of cotton plants

In cotton plants ( Gossypium hirsutum L. cv. B.J.A.) the temperature of the roots affected both root and shoot growth, as did the temperature of the shoot. Drought resistance increased when the temperature imposed on roots (27°C) was lower than that imposed on shoots (17°C); the result was a decrease in both transpiration and flow of root sap. Stomatal characteristics as measured by density, index and resistance, depended only on shoot temperature. Differences in drought resistance, depended only on shoot temperature. Differences in drought resistance seem to be a result of changes in transpiration flow modulated by the amount of absorbed water.     

Muscle development in the tambaqui, an important Amazonian food fish

Eggs of the tambaqui Colossoma macropomum were incubated at 28 and 31) C. Somitogenesis started shortly after the formation of the neural plate and notochord. New somites were added at the rate of one every 13 min at 28) C and one every 11 min at 31) C. Myogenesis started in the most rostral myotomes at the 9-somite stage and proceeded in a caudal direction. Mononuclear myotubes with the morphological characteristic of muscle pioneer cells were observed lateral to the notochord. The majority of myotubes were formed from the fusion of 3–6 spindle-shaped myoblasts. Myofibril synthesis started soon after cell fusion at the periphery of myotubes. Close membrane contacts and 'gap'-type junctions were observed between myotubes, immature muscle fibres and at the inter-somite boundary, suggesting that the cells were electrically coupled. Embryos exhibited rhythmic movements at the 20-somite stage, and hatched at the 29–30-somite stage 15–18 h post-fertilisation (PFT) at 28° C and 11 h PFT at 31° C. Larvae hatched at a comparatively early stage of development prior to the completion of somitogenesis and the formation of eye pigment, pectoral fins and jaws. The myotomes comprised a single superficial layer of well-differentiated muscle fibres which contained abundant mitochondria, overlying an inner core of myotubes (presumptive white muscle layer). Differentiation and growth during the larval stages was extremely rapid, and the juvenile stage was reached after little more than 6 days at 28° C.     

Responses of seed of Stylosanthes humilis to germination regulators

Seed of Stlosanthes humilis both have hard integuments and display physiological dormancy, the latter being lost during post-harvest ageing. Ethrel and l-aminocyclopropane-1-carboxylic acid (ACC) partially released scarified young seed from physiological dormancy. Cobalt and silver ions and abscisic acid inhibited germination of scarified non-dormant seed. Abscisic acid also inhibited germination of voung seed promoted by ACC. Thiourea and ethrel plus benzyladenine showed the greatest efficacy in breaking seed dormancy.