A comparative analysis of the spin state distribution of in vitro and in vivo mutants of PsaC. A biochemical argument for the sequence of electron transfer in Photosystem I as FX → FA → FB → ferredoxin/flavodoxin

The EPR properties of in vivo and in vitro C14X–PS I and C51X–PS I (X = D, S, A or G) mutants of PsaC are compared in an attempt to extract information about electron transfer not contained in any one of these studies in isolation. This analysis indicates that 1) sulfur from an external 'rescue thiolate' is preferred over oxygen from an aspartate or serine replacement amino acid as a ligand to the F_A and F_B iron-sulfur clusters; 2) the inherent spectroscopic symmetry in the F_A and F_B clusters of unbound PsaC is lost when PsaC is docked to its site on the PsaA/PsaB heterodimer; 3) the bound 'rescue thiolate' ligand in the modified site of the F_A cluster, but not the F_B, cluster is displaced when PsaC is docked to its site on the PsaA/PsaB heterodimer; 4) the free energy of binding PsaC to the PsaA/PsaB heterodimer drives the otherwise-unfavorable ligand replacement in the F_A site. These and other findings argue that the substitute ligands support a [4Fe–4S] cluster at the modified site, but the cluster is in either a ground spin state of S 3/2 or S = 1/2 depending on the chemical identity of the ligand, on whether PsaC is unbound or bound, and on the reduction state of the cluster in the unmodified site. By a comparative analysis of the spin state distribution of the in vivo and in vitro C14X–PS I and C51X–PS I (X = D, S, A or G) mutants, and with knowledge from the X-ray crystal structure that PsaC is bound asymmetrically to the PS I reaction center, an independent case is made that PsaC is oriented so that the F_A cluster is proximal to F_X and the F_B cluster is distal to F_X. These results are compared and contrasted with the results of in vivo mutagenesis studies of PsaC in Anabaena variabilis ATCC 29413 and in Chlamydomonas reinhardtii. In all cases, the primary data can be interpreted to support the sequence of electron transfer as F_X F_A F_B ferredoxin.     

Clothing insulation as a biometeorological parameter during rest and exercise

A method of direct measurement of the heat and vapor transfer properties of clothing is described when worn in situ by human subjects during rest and exercise. Additional experimental observations were used to verify that a model for predicting F_pcl is reasonably accurate. From the thermal efficiency factor (F_cl), derived from _s and T_cl measurements, an effective value for I_clo can be determined and thus vapor permeation efficiency (F_pcl) can be predicted. A single coefficient () that characterizes the boundary environment over the skin surface is the ratio (hF_cl)/(h_eF_pcl) and is determined for any environment in terms of directly observed F_cl factor or clo value and relative air movement concerned. Ultimately,-factor may be used as a key biometeorological parameter to describe any heat balance condition graphically on a psychrometric chart. Its usefulness is also evident in prediction of the probable combination of operative temperature and humidity necessary for thermal acceptable zones, the limits for evaporative regulation, and the zone in which some degree of thermal regulatory failure can be expected.Presented at the Seventh International Biometeorological Congress, 17–23 August 1975, College Park, Maryland, USA.     

Reconstitution of iron-sulfur center FB results in complete restoration of NADP+ photoreduction in Hg-treated Photosystem I complexes from Synechococcus sp. PCC 6301

The F_B iron-sulfur cluster is destroyed preferentially by treating Photosystem I complexes with HgCl₂(Kojima Y, Niinomi Y, Tsuboi S, Hiyama T and Sakurai H (1987) Bot Mag 100: 243–53). When F_B is 95% depleted but F_Ais quantitatively retained in cyanobacterial PS I complexes, the reduction potential of F_A remains highly electronegative (E_m=–530 mV, n=1), the EPR spectral and spin relaxation properties of F_A and F_Xremain unchanged, but NADP⁺ photoreduction rates decline from 552 to 72 mol mg Chl^–1 h^–1.When F_B is reconstituted with FeCl₃, Na₂S and -mercaptoethanol, NADP⁺photoreduction rates recover to 528 mol mg Chl^–1 h^–1. The correlation between the presence of F_Band NADP⁺ photoreduction provides direct experimental evidence that this iron-sulfur cluster is required for electron throughput from cytochromec ₆ to flavodoxin or ferredoxin in Photosystem I.Abbreviations Chl chlorophyll - DPIP dichlorophenolindophenol - PS I Photosystem I Published as Journal Series #11091 of the University of Nebraska Agricultural Research Division. This paper is dedicated to the memory of the late Professor Daniel Arnon, who is remembered for his gracious and generous encouragement of the senior author's early career.     

Effects of selective destruction of iron-sulfur center B on electron transfer and charge recombination in Photosystem I

Incubation of spinach thylakoids with HgCl₂ selectively destroys Fe–S center B (F_B). The function of electron acceptors in F_B-less PS I particles was studied by following the decay kinetics of P700⁺ at room temperature after multiple flash excitation in the absence of a terminal electron acceptor. In untreated particles, the decay kinetics of the signal after the first and the second flashes were very similar (t _1/22.5 ms), and were principally determined by the concentration of the artificial electron donor added. The decay after the third flash was fast (t _1/20.25 ms). In F_B-less particles, although the decay after the first flash was slow, fast decay was observed already after the second flash. We conclude that in F_B-less particles, electron transfer can proceed normally at room temperature from F_X to F_A and that the charge recombination between P700⁺ and F_X ^-/A₁ ^- predominated after the second excitation. The rate of this recombination process is not significantly affected by the destruction of F_B. Even in the presence of 60% glycerol, F_B-less particles can transfer electrons to F_A at room temperature as efficiently as untreated particles.Abbreviations DCIP 2, 6-dichlorophenol indophenol - F_A, F_B, F_X iron-sulfur center A, B and X, respectively - PMS phenazine methosulfate     

Effects of stimulus timing on transmitter release and postsynaptic membrane potential at crayfish neuromuscular junctions

Summary Different synaptic terminals of the single excitor axon to the opener muscle of crayfish (Procambarus clarkii) often release transmitter in a very different manner when stimulated with the same equal-interval, doublet, or triplet patterns. Compared to synapses that show little facilitation (low F_e synapses), highly facilitating (high F_e) synapses show greater percentage increases in several measures of synaptic efficacy when stimulated with any of these patterns. Low F_e synapses usually show the greater absolute changes in these measures of synaptic efficacy. Changes in the span and pattern of doublets and triplets can independently affect both pre- and postsynaptic measures of synaptic efficacy at either low F_e or high F_e synapses.Abbreviations EJP excitatory junctional potential - MJP spontaneous miniature EJP - F _e ratio of EJP at 1 Hz to EJP amplitude at 10 Hz - F ₁ zero-time facilitation - A ₂,B ₂,C ₂ doubly corrected EJP amplitude of a particular pulse - average amplitude of doubly corrected EJPs in a train of equal-interval, doublets, and triplets, respectively - A_m, B_m, C_m maximum depolarization reached by a particular EJP - time constant of decay     

Genetic control of grain yield and its related traits in bread wheat

Summary Genetic control of tiller number, grain number, grain weight, harvest index and grain yield in six generations, along with the biparentals, F₃s, F₂xparental progeny, and F₂xF₁ progeny were investigated in an intervarietal cross of bread wheat involving two highly competitive varieties, WL711 and HD 2009. The performance of F₁, B₁, B₂, F₂, × p₁, F₂ × P₂ and F₂ × F₁ progeny was midway between the parents involved with respect to all the evaluated characters. The biparental progeny excelled the mean performance of their corresponding F₂ and F₃ progeny in tiller number, seed weight and grain yield. The estimates of variance components obtained from the two models deployed were almost similar. Considerable additive genetic variance was observed for grains per spike, seed weight and grain yield while dominance variance was more pronounced for harvest index. The additive-dominance model was adequate for grains per spike and harvest index. Epistatic effects of additive × additive and additive × dominance type for tiller number and grain yield, and of additive × dominance type for seed weight were observed. The digenic epistatic model was inadequate for explaining the nature of gene action for tiller number, seed weight and grain yield. The studies indicated that non-allelic interactions should not be ignored in formulating wheat breeding programmes and that a biparental approach could be adopted as an extremely useful tool for enhancing genetic variability and the creation of transgressive segregants. The usefulness of breeding methodologies utilising a biparental approach is discussed.     

Gene controlled selection of mitochondria in Paramecium.

Summary The slow growing mutant cl₁ of Paramecium, previously described (Sainsard, Claisse and Balmefrezol, 1974) differs from wild-type by a single recessive nuclear mutation and by a particular mitochondrial phenotype (M^cl) that gene cl ₁ distinguishes from the wild-type mitochondrial phenotype (M⁺). A further analysis of these nucleo-mitochondrial interactions was carried out by confronting the genes cl ₁ and cl ₁ ⁺ with mixed populations of M⁺ and M^cl mitochondria obtained after cytoplasmic exchange at conjugation. The following results were obtained: 1. M⁺ and M^cl mitochondria introduced respectively into mutant and wild-type cells do not multiply easily; 2. when a mixed population (M⁺+M^cl) is established, both mitochondrial types are maintained during the growth of the F₁ heterozygous cl ₁/cl ₁ ⁺ clones; 3. when the nuclear segregation occurs in F₂, the formation of homozygotes cl ₁/cl ₁ or cl ₁ ⁺ /cl ₁ ⁺ is soon followed by the segregation of the two mitochondrial types, M^cl or M⁺, reconstituting the two parental nucleo-mitochondrial associations.This paper is dedicated to Professor T.M. Sonneborn on the occasion of his 70th birthday     

Kinetic modeling of electron transfer reactions in photosystem I complexes of various structures with substituted quinone acceptors

The reduction kinetics of the photo-oxidized primary electron donor P₇₀₀ in photosystem I (PS I) complexes from cyanobacteria Synechocystis sp. PCC 6803 were analyzed within the kinetic model, which considers electron transfer (ET) reactions between P₇₀₀, secondary quinone acceptor A₁, iron-sulfur clusters and external electron donor and acceptors – methylviologen (MV), 2,3-dichloro-naphthoquinone (Cl₂NQ) and oxygen. PS I complexes containing various quinones in the A₁-binding site (phylloquinone PhQ, plastoquinone-9 PQ and Cl₂NQ) as well as F _X-core complexes, depleted of terminal iron–sulfur F _A/F _B clusters, were studied. The acceleration of charge recombination in F _X-core complexes by PhQ/PQ substitution indicates that backward ET from the iron–sulfur clusters involves quinone in the A₁-binding site. The kinetic parameters of ET reactions were obtained by global fitting of the P₇₀₀ ⁺ reduction with the kinetic model. The free energy gap ΔG ₀ between F _X and F _A/F _B clusters was estimated as ?130 meV. The driving force of ET from A₁ to F _X was determined as ?50 and ?220 meV for PhQ in the A and B cofactor branches, respectively. For PQ in A_1A-site, this reaction was found to be endergonic (ΔG ₀?=?+75 meV). The interaction of PS I with external acceptors was quantitatively described in terms of Michaelis–Menten kinetics. The second-order rate constants of ET from F _A/F _B, F _X and Cl₂NQ in the A₁-site of PS I to external acceptors were estimated. The side production of superoxide radical in the A₁-site by oxygen reduction via the Mehler reaction might comprise ≥0.3% of the total electron flow in PS I.     

Genetics of amylose content in rice (Oryza sativa L)

Inheritance of amylose content was studied in crosses involving very low-, intermediate-, and high-amylose parents. The single-grain analysis of parents, F₁, F₂, B₁F₁, and B₂F₁ seed from a single-season harvest, showed that the parental mean difference of 14–17 % in IR37307-8/BPI 121-407 or IR37307-8/IR24632-34 and about 20% in the cross IR37307-8/IR8 were controlled by a single gene with major effect, along with some minor genes and/or modifiers. The appearance of segregants inbetween the two parents was attributed to gene dosage effects in the endosperm. The results indicate that selection for amylose level can effectively be done in early segregating generations. Selection for intermediary segregants would be ineffective because the dosage effects would dissipate in further generations.     

Establishment of a gene tagging system in Arabidopsis thaliana based on the maize transposable element Ac

Summary An Ac-derived, two-component transposable element system has been developed and analyzed with respect to its use in Arabidopsis thaliana. This system consists of an immobilized Ac element (Ac clipped wing, Ac_cl) as the source of transactivating transposase and a nonautonomous Ds element, Ds_A, which is inserted into a chimaeric neomycinphosphotransferase gene used as excision marker. After separate introduction of Ac_c1 and Ds_A into Arabidopsis thaliana, progeny analysis of crosses between five different Ac_cl lines and seven different Ds_A lines shows that: (1) different Ac_cl lines differ greatly in their capacity to transactivate Ds_A; (2) different Ds_A lines do not differ significantly with respect to Ds_A transactivation by one Ac_cl line; (3) reintegration of excised Ds_A elements, both at (genetically) linked and unlinked sites, occurs in about 50% of the excision events; and (4) plants with a high rate of somatic excisions can be used as source of new Ds_A transpositions, allowing the creation of a large number of independent Ds_A insertions.     

Spectroscopic studies of bound cytochrome c and an iron-sulfur center in a purified reaction center complex from the green sulfur bacterium Chlorobium tepidum

Flash-induced optical kinetics at room temperature of cytochrome (Cyt) c ₅₅₁ and an Fe-S center (CF_A/CF_B) bound to a purified reaction center (RC) complex from the green sulfur photosynthetic bacterium Chlorobium tepidum were studied. At 551 nm, the flash-induced absorbance change decayed with a t _1/2 of several hundred ms, and the decay was accelerated by 1-methoxy-5-methylphenazinium methyl sulfate (mPMS). In the blue region, the absorbance change was composed of mPMS-dependent (Cyt) and mPMS-independent component (CF_A/CF_B) which decayed with a t _1/2 of 400–650 ms. Decay of the latter was effectively accelerated by benzyl viologen (Em –360 mV) and methyl viologen (–440 mV), and less effectively by triquat (–540 mV). The difference spectrum of Cyt c had negative peaks at 551, 520 and 420 nm, with a positive rise at 440 to 500 nm. The difference spectrum of CF_A/CF_B resembled P430 of PSI, and had a broad negative peak at 430435 nm.Abbreviations (B)Chl (bacterio)chlorophyll - Cyt cytochrome - F_A, F_B and F_X iron-sulfur center A, B and X of Photosystem I - CF_A, CF_B and CF_X F_A-,F_B- and F_X-like Fe-S center of Chlorobium - mPMS 1-methoxy-5-methylphenazinium methyl sulfate - PSI Photosystem I - RC reaction center     

Heliobacterial photosynthesis

Heliobacteria contain Type I reaction centers (RCs) and a homodimeric core, but unlike green sulfur bacteria, they do not contain an extended antenna system. Given their simplicity, the heliobacterial RC (HbRC) should be ideal for the study of a prototypical homodimeric RC. However, there exist enormous gaps in our knowledge, particularly with regard to the nature of the secondary and tertiary electron acceptors. To paraphrase S. Neerken and J. Amesz (2001 Biochim Biophys Acta 1507:278–290): with the sole exception of primary charge separation, little progress has been made in recent years on the HbRC, either with respect to the polypeptide composition, or the nature of the electron acceptor chain, or the kinetics of forward and backward electron transfer. This situation, however, has changed. First, the low molecular mass polypeptide that contains the terminal F_A and F_B iron-sulfur clusters has been identified. The change in the lifetime of the flash-induced kinetics from 75 ms to 15 ms on its removal shows that the former arises from the P798⁺ [F_A/F_B]^? recombination, and the latter from P798⁺ F_X ^? recombination. Second, F_X has been identified in HbRC cores by EPR and Mössbauer spectroscopy, and shown to be a [4Fe–4S]^1+,2+ cluster with a ground spin state of S = 3/2. Since all of the iron in HbRC cores is in the F_X cluster, a ratio of ～22 Bchl g/P798 could be calculated from chemical assays of non-heme iron and Bchl g. Third, the N-terminal amino acid sequence of the F_A/F_B-containing polypeptide led to the identification and cloning of its gene. The expressed protein can be rebound to isolated HbRC cores, thereby regaining both the 75 ms kinetic phase resulting from P798⁺ [F_A/F_B]^? recombination and the light-induced EPR resonances of F_A ^? and F_B ^?. The gene was named ‘pshB’ and the protein ‘PshB’ in keeping with the accepted nomenclature for Type I RCs. This article reviews the current state of knowledge on the structure and function of the HbRC.     

Linked epistasis for six quantitative traits in Indian mustard (Brassica juncea (L.) Czern & Coss)

Summary Gene effects, and interactions, and associations between days-to-flower initiation and maturity, number of secondary branches and siliquae per plant, and 1,000-seed weight and yield per plant were studied in a cross of Indian mustard (Brassica juncea (L.) Czern & Coss) using the parents and F₁, F₂, F₃, B₁, B₂, B₁₁, B₁₂, B₂₁, B₂₂, B_1S, B_2S, B₁F₁, B₂F₁, B_1bip, B_2bip, F₂P₁, F₂F₁, and F_2bip generations. A linked digenic model was adequate for all characters studied. According to this model, the main effects, additive and interactions between linked pairs of genes, were present in varying proportions for days-to-flower initiation and maturity and number of siliquae per plant. The contribution of linked epistatic effects, however, was much greater than that of additive effects. Dominance effects contributed significantly to the inheritance of days-to-flower initiation. Duplicate epistasis was observed for all traits except 1,000-seed weight where epistasis was of the complementary type. A complete association among the genes of similar effect (increasing or decreasing) was observed for number of secondary branches and siliquae, and yield per plant. Coupling phase linkage was observed for days-to-flower initiation whereas repulsion phase linkage was observed for daysto-maturity and 1,000-seed weight.     

Partial reproductive incompatibility between populations of spider mites (Acarina: Tetranychidae)

Partial reproductive incompatibility between spider mite populations of different origin is a common phenomenon. A comparative study was made of the characteristics of partial reproductive incompatibility both between various natural populations ofTetranychus urticae and between a laboratory strain and a number of chromosome mutation homozygous strains derived from it. Interpopulation crossing experiments were set up and percentages of nonviability assessed in the F₁, the haploid F₂, the B₁ obtained from hybrids that had been mated with males of the original male parent stock and the B₁ produced by hybrids that had been mated by males of the original female parent stock. In those cases where partial reproductive incompartibility between populations is due to different chromosome mutations similar degrees of nonviability were observed for the haploid F₂ and the B₁ generations belonging to it. With natural reproductive incompatibility the degree of lethality was highest in the haploid F₂; the percentage nonviability was usually less for fertilized eggs, and especially when the eggs were fertilized by a gamete of a male of the same origin as the female parent of the hybrid. Differences in hybrid sterility between reciprocal crosses were often found. It is assumed that, although chromosome mutations may play a role in speciation of tetranychids, partial reproductive incompatibility between natural populations is mainly due to lethal recombinations of genes and interactions between cytoplasmic factors and genes of alien male gametes.

---

Zusammenfassung Teilweise Fortpflanzungsunverträglichkeit zwischen Spinnmilbenpopulationen verschiedener Herkunft ist ein häufiges Phänomen. In einer vergleichenden Studie wurden die Eigenschaften solcher Inkombatibilität sowohl zwischen natürlichten Populationen vonTetranychus urticae als auch zwischen einem Laborstamm und einigen von diesem hergeleiteten Stämme mit homozygoter Chromosomenmutation untersucht. Kreuzungsexperimente zwischen den Populationen wurden durchgeführt und Prozentsätze der Nichtlebensfähigen (=nicht schlüpfenden Eiern) bestimmt u.zw. in der F₁, der haploiden F₂, der B₁, die von Hybriden erhalten wurde, die mit Männchen der ursprünglichen Elternzucht für Männchen gepaart waren und schließlich der B₁, von Hybriden erzeugt, die gepaart waren mit Männchen der ursprünglichen Elternzucht für Weibchen. In den Fällen, wo die Inkombatibilität zwischen den Populationen verursacht wird durch verschiedene Chromosomenmutationen, wurde ein ähnliches Ausmaß der Nichtlebensfähigkeit beobachtet für die haploide F₂ und die dazugehörigen B₁-Generationen. Bei natürlichen teilweiser Fortpflanzungsinkombatibilität war das Ausmaß der Lethalität am höchsten in der haploiden F₂; der Prozentsatz Nichtlebensfähigkeit war gewöhnlich für befruchtete Eier geringer, besonders wenn die Eier befruchtet waren durch einen Gameten von einem Männchen der gleichen Herkunft wie der weibliche Elternteil des Hybrids. Oft wurden Unterschiede in der Hybridsterilität zwischen reziproken Kreuzungen gefunden. Es wird angenommen, daß, obwohl Chromosomenmutationen eine Rolle spielen mögen in der Speciation der Tetranychiden, teilweise Fortspflanzungsinkombatibilität Zwischen natürlichen Populationen hauptsächlich verursacht wird durch lethale Rekombination von Genen und Wechselwirkungen zischen zytoplasmatischen Faktoren und Genen von fremden Männchengameten.

     

Genetics of gel consistency in rice (Oryza sativa L.)

Inheritance of gel consistency in rice was studied in crossés involving highamylose, low-gelatinizalion temperature parents with hard, medium, and soft gel consistency. The results of single-grain analysis of parents, F₁, F₂, B₁F₁, B₂F₂, and their reciprocal crosses from a single-season harvest showed that the differences between hard and soft, hard and medium, and medium and soft gel consistency are under monogenic control and that modifiers affect the expression of the trait. Multiple alleles at the same locus, hereby designated asgec ^a for medium gel consistency andgec ^b for soft gel consistency, were recessive to the wild type allele for hard gel consistency andgec ^a was dominant overgec ^b. The results indicate that selection for desired gel consistency can effectively be done in early segregating generations.     

Comparative Study of Thermal Degradation of Iron–Sulfur Proteins in Spinach Chloroplasts and Membranes of Thermophilic Cyanobacteria: Mössbauer Spectroscopy

Mössbauer spectra of chloroplasts isolated from spinach plants grown in a mineral medium enriched with ⁵⁷Fe and Mössbauer spectra of native membranes of the thermophilic cyanobacterium Synechococcus elongatus contain a broad asymmetric doublet typical of the iron–sulfur proteins of Photosystem (PS) I. Exposure of chloroplasts to temperatures of 20-70°C significantly modifies the central part of the spectra. This spectral change is evidence of decreased magnitude of the quadrupole splitting. However, the thermally induced doublet (Q = 3.10 mm/sec and = 1.28 mm/sec) typical of hydrated forms of reduced (divalent) inorganic iron is not observed in spinach chloroplasts. This doublet is usually associated with degradation of active centers of ferredoxin, a surface-exposed protein of PS I. The Mössbauer spectra of photosynthetic membranes of spinach chloroplasts and cyanobacteria were compared using the probability distribution function of quadrupole shift (1/2 quadrupole splitting Q) of trivalent iron. The results of calculation of these functions for the two preparations showed that upon increasing the heating temperature there was a decrease in the probability of the presence of native iron–sulfur centers F_X, F_A, and F_B (quadrupole shift range, 0.43-0.67 mm/sec) in heated preparations. This process was also accompanied by an increase in the probability of appearance of clusters of trivalent iron. This increase was found to be either gradual and continuous or abrupt and discrete in photosynthetic membranes of cyanobacteria or spinach chloroplasts, respectively. The probability of the presence of the iron–sulfur centers F_X, F_A, and F_B in chloroplasts abruptly decreases to virtually to zero within the temperature range critical for inhibition of electron transport through PS I to oxygen. In cyanobacteria, both thermal destruction of iron–sulfur centers of PS I and functional degradation of PS I are shifted toward a higher temperature. The results of this study suggest that the same mechanism of thermal destruction of the PS I core occurs in both thermophilic and mesophilic organisms: destruction of iron–sulfur centers F_X, F_A, and F_B, release of oxidized (trivalent) iron, and its accumulation in membrane-bound iron-oxo clusters.     

Quantitative genetics of growth and development in Populus. I. A three-generation comparison of tree architecture during the first 2 years of growth

One approach to gain an insight into the genetics of tree architecture is to make use of morphologically divergent parents and study their segregating progeny in the F₂ and backcross (B₁) generations. This approach was chosen in the present study in which material of a three-generation pedigree growing side by side in a replicated plantation, was analyzed. The pedigree included Populus trichocarpa (T) and P. deltoides (D) parents, their F₁ and F₂ hybrids and their B₁ hybrids to the D parent. The trees were grown in the environment of the T parent and measured for the first 2 years of growth. Nine quantitative traits were studied at the stem, branch and leaf levels of tree architecture, in which the original parents differed. Strong F₁ hybrid vigor relative to the better parent (T) was expressed in growth and its components. Most quantitative traits in the F₂ and B₁ hybrids were intermediate between the T and D parents but displayed a wide range of variation due to segregation. The results from the analysis of variance indicated that all morphometric traits were significantly different among F₂ and B₁ clones, but the B₁ hybrids were more sensitive to replicates than the F₂. Broad-sense heritabilities (H ²) based on clonal means ranged from moderately high to high (0.50–0.90) for the traits studied, with H ² values varying over age. The H ² estimates reflected greater environmental noise in the B₁ than in the F₂, presumably due to the greater proportion of maladaptive D alleles in those hybrids. In both families, sylleptic branch number and length, and leaf size on the terminal, showed strong genetic correlations with stem growth. The large divergence between the two original parents in the traits studied, combined with the high chromosome number in Populus (2n=38), makes this pedigree well suited for the estimation of the number of quantitative trait loci (QTLs) underlying quantitative variation by Wright's biometric method (1968). Variation in several traits was found to be under the control of surprisingly few major QTLs: 3–4 in 2nd-year height and diameter growth, a single QTL in stem diameter/height ratio.     

TheB locus (MHC) in the chicken: Association with the fate of RSV-induced tumors

The fate of tumors induced by Rous sarcoma virus (RSV) was determined in anF ₂ population segregating at three alloantigen loci. TheF ₁ resulted from crossing tumor-resistant RPRL line 6₁ (B ² B ² D ³ D ³ I ² I ²) with tumor-susceptible RPRL line 15₁ (B ⁵ B ⁵ D ⁴ D ⁴ I ⁸ I ⁸). Among theF ₂ segregantsB ² B ²,B ² B ⁵, andB ⁵ B ⁵, the percentage of chicks dying of terminal tumors (by 70 days post-inoculation) was 5, 26, and 93, respectively (P0.01). NeitherD orI genotypes nor sex significantly affected tumor growth. In chickens with terminal tumors, the incidence of metastatic lesions was also significantly associated withB genotypes. Thus, the MHC chromosomal region in the chicken appears to exert a crucial role in determining the outcome of RSV-induced tumors.     

Genetic mapping of a putative Thinopyrum intermedium-derived stripe rust resistance gene on wheat chromosome 1B

Key message

Stripe rust resistance transferred from Thinopyrum intermedium into common wheat was controlled by a single dominant gene, which mapped to chromosome 1B near Yr26 and was designated YrL693.

Abstract

Stripe rust caused by Puccinia striiformis f. sp. tritici (Pst) is a highly destructive disease of wheat (Triticum aestivum). Stripe rust resistance was transferred from Thinopyrum intermedium to common wheat, and the resulting introgression line (L693) exhibited all-stage resistance to the widely virulent and predominant Chinese pathotypes CYR32 and CYR33 and to the new virulent pathotype V26. There was no cytological evidence that L693 had alien chromosomal segments from Th. intermedium. Genetic analysis of stripe rust resistance was performed by crossing L693 with the susceptible line L661. F₁, F₂, and F_2:3 populations from reciprocal crosses showed that resistance was controlled by a single dominant gene. A total 479 F_2:3 lines and 781 pairs of genomic simple sequence repeat (SSR) primers were employed to determine the chromosomal location of the resistance gene. The gene was linked to six publicly available and three recently developed wheat genomic SSR markers. The linked markers were localized to wheat chromosome 1B using Chinese Spring nulli-tetrasomic lines, and the resistance gene was localized to chromosome 1B based on SSR and wheat genomic information. A high-density genetic map was also produced. The pedigree, molecular marker data, and resistance response indicated that the stripe rust resistance gene in L693 is a novel gene, which was temporarily designated YrL693. The SSR markers that co-segregate with this gene (Xbarc187-1B, Xbarc187-1B-1, Xgwm18-1B, and Xgwm11-1B) have potential application in marker-assisted breeding of wheat, and YrL693 will be useful for broadening the genetic basis of stripe rust resistance in wheat.