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.     

Ethylene Production and 1-Aminocyclopropane-1-Carboxylic Acid Conjugation in Thermoinhibited Cicer arietinum L. Seeds

The effect of supraoptimal temperatures (30°C, 35°C) on germination and ethylene production of Cicer arietinum (chick-pea) seeds was measured. Compared with a 25°C control, these temperatures inhibited both germination and ethylene production. The effect of supraoptimal temperatures could be alleviated by treating the seeds with ethylene. It was concluded that one effect of high temperature on germination was due to its negative effect on ethylene production. This inhibitory effect of high temperature was due to increased conjugation of 1-aminocyclopropane-1-carboxylic acid to 1-(malonylamino)cyclopropane-1-carboxylic acid and to an inhibition of ethylene-forming enzyme activity.     

Biochemical properties of 1-aminocyclopropane-1-carboxylate N-malonyltransferase activity from early growing embryonic axes of chick-pea (Cicer arietinum L.) seeds

In the present work, certain biochemical characteristics ofthe enzyme 1-aminocyclopropane-1-carboxylate N-malonyltransferase(ACC N-MTase) which is responsible for the malonylation of 1-aminocyclopropane-1-carboxylate(ACC) in chickpea (Cicer arietinum) are described. Phosphatebuffer was the most appropriate buffer with regard to enzymestability and, therefore, ACC N-MTase was extracted, assayedand purified in the presence of this buffer. ACC N-MTase waspartially purified approximately 900-fold from embryonic axesof chick-pea seeds using ammonium sulphate precipitation, hydrophobicinteraction and molecular filtration chromatography. By gelfiltration chromatography on Superose-12, the molecular massof the enzyme was estimated to be 54 4 kDa. ACC N-MTase hadan optimal pH and temperature of 7.5 and 40C, respectively,as well as a K_m for ACC and malonyl-CoA of 400 M and 90 M,respectively. D-Phenylalanine was a competitive inhibitor ofACC N-MTase with respect to ACC (K_i of 720 M), whereas co-enzymeA was a competitive product inhibitor with respect to malonyl-CoA(K_i of 300 M) and a non-competitive inhibitor with respectto ACC (K_i of 600 M). Under optimal assay conditions, ACC N-MTasewas strongly inhibited by (a)divalent [Zn²⁺>Mg²⁺>>Co²⁺>Co²⁺>(NH₄)²⁺>Fe²⁺]and monovalent metal cations (Li⁺>Na⁺>K⁺), without activitybeing detected in the presence of Hg²⁺, and (b) PCMB or mersalicacid, suggesting that sulphydryl group(s) are involved at theactive site of the enzyme. Key words: ACC-N-malonyltransferase, Cicer arietinum, embryonic axes, ethylene, germination, seeds     

Pollen-ovule ratio,pollen size,and breeding system in Astragalus (Fabaceae) subgenus Epiglottis: a pollen and seed allocation approach

The correlation between pollen/ovule (P/O) ratio and breeding system has generally been accounted for either on the basis that P/O reflects pollination efficiency, or in terms of the sex allocation theory. The following were assessed for taxa belonging to genus Astragalus subgenus Epiglottis: 1) Degree of correlation between P/O and the breeding system, measured by means of autofertility; 2) The absence or existence of correlation between P/O and pollen grain size; and 3) The ability of various theories to account for the results obtained. Results showed a minimal correlation between P/O and autofertility, and between P/O and pollen grain size in the taxa studied. Analysis of these results in terms of the sex allocation theory enabled this correlation to be explained as a function of the variation existing between taxa with respect to the resources invested in each pollen grain and in each ovule. The predictive capacity of this theory, which has moreover proven valuable in explaining the structural peculiarities of the androecium in these taxa, was also highlighted. The type of self-pollination applicable was also discussed, as was the phenotypic model of selection of self-fertilization considered most plausible for these taxa.     

Water relations, gas exchange and abscisic acid content of Lupinus cosentinii leaves in response to drying different proportions of the root system

Soil columns in which the root system was divided into threeequal layers, each 24 cm in diameter and 33 cm high were usedto examine the influence of drying different proportions ofthe root system on the water relations, gas exchange and abscisicacid (ABA) concentration of lupin (Lupinus cosentinii Guss.cv. Eregulla) leaves. The treatments imposed were (i) all threelayers adequately watered (control), (ii) the upper layer unwateredwith the remaining layers kept adequately watered, (iii) thetwo upper layers unwatered with the basal layer kept adequatelywatered, (iv) all three layers unwatered. The treatments wereapplied at 56 d after sowing (DAS), and continued for 21 d inthe treatment in which the three layers were dried and for 36d in the other three treatments. After 21 d, the soil matricpotential in the layers that were unwatered had decreased toemdash 1.3MPa, compared to - 0.03 MPa in the adequately-wateredlayers. Within 8 d of cessation of watering, plants with the entireroot system in drying soil had significantly lower stomatalconductances, lower rates of net photosynthesis, and higherleaf ABA contents than did adequately-watered plants. Whilethe leaf osmotic potential decreased within 8 d of cessationof watering, the leaf water potential did not change for thefirst 15 d after water was withheld. After withholding waterfrom all layers, the shoot dry matter was 63% lower than thatin the adequately-watered plants. In the two partially-droughtedtreatments, 17% and 48% of the root length was subjected todrying. Compared to the adequately-watered plants, drying upto 50% of the root system for 36 d, in the two partially-droughtedtreatments, did not reduce stomatal conductance, net photosynthesis,or plant growth. Similarly, there was no significant effecton leaf water potential or osmotic potential. When either theupper or upper and middle layers of soil were dried, the ABAcontent of the leaves for most of the drying period was slightly,but not significantly, higher than in leaves of the adequately-wateredplants. The results suggest that lupins with a well-established rootsystem can utilize localized supplies of available soil waterto maintain leaf gas exchange despite appreciable portions ofthe root system being in dry soil. In contrast to other studies,the results also suggest that when only a portion of the soilvolume is dry and adequate water is available in the wet zone,root signals do not influence stomatal conductance and leafgas exchange of lupin. Key words: Abscisic acid, gas exchange, lupins, split-roots, water deficit     

Expression of ferredoxin-dependent glutamate synthase in dark-grown pine seedlings

Pine seedlings are able to accumulate chlorophylls and develop green plastids in a light-independent manner. In this work, we have characterized ferredoxin-dependent glutamate synthase (EC 1.4.7.1; Fd-GOGAT), a key enzyme in nitrogen interconversion during this process. Fd-GOGAT has been purified about 170-fold from cotyledons of maritime pine (Pinus pinaster). As occurs in angiosperms, the native enzyme is a single polypeptide with an apparent molecular mass of 163–168 kDa that is confined to the chloroplast stroma. Polyclonal antibodies generated against the purified enzyme were used to immunoscreen a gt11 expression library from Scots pine (Pinus sylvestris) seedlings and partial cDNA clones were isolated and characterized. The clone with the longest cDNA insert (pGOP44) contained the codification for the C-terminal (550 amino acids) of the pine Fd-GOGAT polypeptide. Immunological cross-reactivity and comparative amino sequence analysis revealed that Fd-GOGAT is a well conserved protein in higher plants. Western blot analyses showed that protein was expressed in chloroplast-containing pine tissues and this expression pattern was not affected by exogenously supplied nitrogen. Fd-GOGAT mRNA, polypeptide and enzyme activity accumulated in substantial amounts in dark-grown pine seedlings. The presence of a functional Fd-GOGAT may be important to provide the required glutamate for the biosynthesis of nitrogen compounds during chloroplast biogenesis in the dark.