The mechanism of the mixed inheritance of chloroplast genes in Pelargonium

Summary The distributions are given of gene frequencies among embryos after G X W and W X G plastid crosses within and between eight Pelargonium cultivars and some of their inbred or hybrid derivatives.Two distinct segregation patterns are recognized. Homozygous type I female parents (Pr₁Pr₁) have a high frequency of progeny with only maternal alleles, are intermediate for biparental and low for paternal offspring. Heterozygous type II female plants (Pr₁Pr₂) have an equally high frequency of maternal and paternal offspring and a generally low biparental frequency. These correspond to L-shaped and U-shaped gene frequency distributions respectively in which the only modes are at 0 per cent (maternal embryos) and 100 per cent (paternal embryos), with no mode corresponding to the population mean and no sign of a Gaussian distribution.The extremely variable plastid gene frequencies are strongly influenced by the maternal nuclear genotype and by the plastid genotype in which the wild-type allele is always more successful than the mutant in strict comparisons.The relative frequencies of maternal and paternal zygotes, and the mean gene frequency among all the zygotes in a cross, are explicable in terms of the input frequencies of genes from the two parents, their degree of mixing, and by some form of selective replication of plastids. This selection is controlled by nuclear and plastid genotypes which may act in the same direction, to increase the frequency of either the maternal or the paternal alleles, or in opposition. But selection alone is inadequate to explain the shapes of the gene frequency distributions. Instead, a model is proposed in which the segregation or replication of plastids appears to have a strong random element, which results in random drift of gene frequencies within a heteroplasmic zygote or embryo.     

Geographic distribution of alleles at the Ga2 locus for segregation distortion in barley

Summary A distorted segregation of esterase alleles at the complex loci, Est1, Est2 and Est4, was found in an F₂ population. This distortion is typical for cross combinations between the Ga2Ga2 and ga2ga2 genotypes responsible for segregation distortion, since the Ga2 locus is linked with the complex loci encoding the esterase isozymes. The segregation of esterase isozyme patterns in F₂ populations between 473 varieties of barley and a tester of ga2ga2 genotype was examined, and the genotypes inducing segregation distortion were detected. Varieties with a ga2ga2 genotype are widely distributed throughout the world, whereas Ga2Ga2 varieties are found only in eastern and southern regions of Asia, from Japan to North India, with a low frequency. In varieties collected from these regions, some associations were detected between alleles at the Ga2 locus and esterase isozyme patterns. Additionally, most of the Ga2 barley varieties are naked and possess a BtBtbt2bt2 genotype for a non-brittle rachis.     

The S-Distribution: Approximation of Discrete Distributions

The S-distribution is defined by the ordinary differential equation dF/dX = α(F^g — F^h F_o = F(X_o), where F is the cumulative distribution of the random variable X, and α, g, h, and F_o are parameters. The S-distribution was recently described in this journal as a tool for the approximation and classification of univariate, unimodal continuous probability distributions. This article shows that the S-distribution rather accurately models the commonly used univariate discrete distributions.     

Total and Regional Fat Distribution is Strongly Influenced by Genetic Factors in Young and Elderly Twins

Objective: Indirect estimates of obesity such as BMI seem to be strongly influenced by genetic factors in twins. Precise measurements of total and regional fat as determined by direct techniques such as DXA scan have only been applied in a few twin studies. The aim of the present study was to estimate the heritability (h²) of total and regional fat distribution in young and elderly Danish twins. Research Methods and Procedures: Monozygotic (108) and dizygotic (88) twins in two age groups (25 to 32 and 58 to 66 years) underwent anthropometric measurements and DXA scans. Intraclass correlations and etiologic components of variance were estimated for total and regional fat percentages using biometric modeling. Results: The intraclass correlations demonstrated higher correlations for all fat percentages among monozygotic twins as compared with dizygotic twins. The biometric modeling revealed a major genetic component (h²) of total (h²_young = 0.83, h²_elderly = 0.86) and regional fat percentages (trunk, h²_young = 0.82, h²_elderly = 0.85; lower body, h²_young = 0.83, h²_elderly = 0.81; and trunk/lower body, h²_young = 0.83, h²_elderly = 0.71) in both the young and elderly twins. Discussion: The h² estimates emphasize that body fat and distribution as determined by DXA scan are under extensive genetic control.     

High-resolution mapping, cloning and molecular characterization of the Pi-k h gene of rice, which confers resistance to Magnaporthe grisea

In order to understand the molecular mechanisms involved in the gene-for-gene type of pathogen resistance, high-resolution genetic and physical mapping of resistance loci is required to facilitate map-based cloning of resistance genes. Here, we report the molecular mapping and cloning of a dominant gene (Pi-k ^h ) present in the rice line Tetep, which is associated with resistance to rice blast disease caused by Magnaporthe grisea. This gene is effective against M. grisea populations prevalent in the Northwestern Himalayan region of India. Using 178 sequence tagged microsatellite, sequence-tagged site, expressed sequence tag and simple sequence repeat (SSR) markers to genotype a population of 208 F₂ individuals, we mapped the Pi-k ^h gene between two SSR markers (TRS26 and TRS33) which are 0.7 and 0.5 cM away, respectively, and can be used in marker-assisted-selection for blast-resistant rice cultivars. We used the markers to identify the homologous region in the genomic sequence of Oryza sativa cv. Nipponbare, and a physical map consisting of two overlapping bacterial artificial chromosome and P1 artificial chromosome clones was assembled, spanning a region of 143,537 bp on the long arm of chromosome 11. Using bioinformatic analyses, we then identified a candidate blast-resistance gene in the region, and cloned the homologous sequence from Tetep. The putative Pi-k ^h gene cloned from Tetep is 1.5 kbp long with a single ORF, and belongs to the nucleotide binding site-leucine rich repeat class of disease resistance genes. Structural and expression analysis of the Pi-k ^h gene revealed that its expression is pathogen inducible.     

Perchlorate reduction by a mixed culture in an up-flow anaerobic fixed bed reactor

Wolinella succinogenes HAP-1 is a Gram-negative microaerophile which reduces perchlorate to chloride by the proposed pathway ClO₄ to ClO₃ to ClO₂ to Cl + O₂. A cost-effective perchlorate treatment process has been established using a consortium of facultative anaerobic organisms and W. succinogenes HAP-1. The mixed anaerobic bacterial culture containing W. succinogenes HAP-1 was examined for the ability to form a biofilm capable of perchlorate reduction. An up-flow anaerobic fixed bed reactor (UAFBR) was packed with diatomaceous earth pellets and operated at residence times of 1.17 and 0.46 h to insure a viable biofilm had attached to the diatomaceous earth pellets. Reduction rates of perchlorate to chloride in the UAFBR could be maintained at 1 g of perchlorate reduced h⁻¹ L⁻¹. Studies with the same bacterial consortium in continuously stirred tank reactors (CSTR) generally reduced 0.5–0.7 g of perchlorate h⁻¹. Viable cell counts were performed periodically on the diatomaceous earth pellets and demonstrated that the W. succinogenes HAP-1 population was maintained at 28–47% of the total microbial population. Scanning electron micrographs demonstrated that the external and internal surfaces of the diatomaceous pellets were densely colonized with microbial cells of multiple cell types. This is the first report of an anaerobic mixed culture forming a biofilm capable of perchlorate reduction. Received 22 May 1997/ Accepted in revised form 07 January 1998     

松嫩平原苏打盐渍化旱田土壤表观电导率空间变异

在松嫩平原西部吉林省大安市乐胜乡,于2013年4月20日选择盐碱程度不均一的典型盐渍化旱田地块,面积为4.8 hm~2作为研究样地。利用EM38大地电导率仪测定结合田间定点采样,并通过经典统计和地统计相结合的方法研究了盐渍化旱田土壤表观电导率空间变异特征,分析了土壤表观电导率与土壤盐碱指标之间的关系。结果表明,盐渍化旱田土壤水平方向表观电导率(EC_h)经对数转换后具有强空间自相关,其变异特征主要是与地形地貌和水文状况等结构性因素有关。垂直方向表观电导率(EC_v)经对数转换后具有中等空间自相关性,其变异特征受结构性因素和随机因素共同作用。EC_h和EC_v半方差模拟的最优模型分别为球状模型和指数模型。Pearson分析表明土壤表观电导率(EC_h和EC_v)与土壤盐碱指标EC_(1∶5)、pH_(1∶5)、SAR、SC、Na~+、CO_3~(2-)、HCO_3~-呈正相关关系(P0.05),EC_h与土壤盐碱指标相关系数均大于EC_v。在实际应用中可以用EC_h来指示土壤的盐碱程度。回归分析表明土壤表观电导率(EC_h和EC_v)与土壤盐碱指标呈线性相关,且EC_h回归模型的决定系数均大于EC_v回归模型的决定系数,可用水平方向土壤表观电导率(EC_h)来计算土壤盐碱指标,进行土壤盐渍化的快速评估。     

Isoelectric focusing of red cell phosphoglucomutase (E.C.:2.7.5.1) at the PGM1 locus in a French-Canadian population

Summary Phosphoglucomutase₁ (PGM₁) polymorphism was studied in a French-Canadian population of Québec city, Canada by means of a low voltage (max 500 V) isoelectric focusing (IEF) procedure on vertical polyacrylamide gel slabs. Frequencies of the four common PGM₁ genes estimated from the phenotype distribution in 308 unrelated individuals were PGM ₁ ¹⁺ , 0.61 (±0.02); PGM ₁ ^1- , 0.13 (±0.01); PGM ₁ ¹⁺ , 0.61 (±0.02); PGM ₁ ^1- , 0.18 (±0.02); and PGM ₁ ¹⁺ , 0.61 (±0.02); PGM ₁ ^1- , 0.08 (±0.01). The segregation patterns observed in 154 families, which included 31 different mating types and 353 children, confirmed a Mendelian inheritance of four autosomal genes. The distribution of the PGM₁ phenotypes observed or expected in a Hardy-Weinberg equilibrium was compared with that of other populations. A significant (P<0.001) difference was found between the Québec population and a Black population from Keneba, Gambia, West-Africa.     

Behavior of potato gametoclonal plants against the necrotic strain of potato Y potyvirus

A total of 59 Solanum tuberosum androgenetic plants have been obtained through anther culture, 47 of which derived from a tetraploid clone, seven from a diploid hybrid, and five from an anther-derived clone. About two thirds of the anther-derived plants were dihaploids, a few were monohaploids (5.08%) or aneuploids (6.78%), whereas the tetraploid genotype generated about a third of tetraploids. Seven hundred twenty seven R₁ plants arisen from tubers of the androgenetic potatoes were mechanically inoculated with the necrotic strain of the potato Y potyvirus (PVY^N) and grown in a glasshouse. Fifty days after inoculation, the presence of PVY^N in R₁ plants was detected by DAS-ELISA (Double Autibody Sandwich). Only three plants (0.4%) of genotype H2-258 exhibited local necrotic symptoms (hypersensitivity reaction) suggesting the presence of the N _y gene, and this extreme resistance is epistatic to hypersensitive resistance. The immunity (R _y-gene) to PVY^N was retained through anther culturing and present at all levels of ploidy. The pattern of segregation for immunity was differentiated according to the ploidy level of the anther-derived plants. This changed segregation pattern may be due to a loss of resistance during the culturing, when an endoreduplication has taken place or to the possible regeneration from Second-division restituted unreduced microspores. Anyway, this segregation pattern must be taken into account when gametoclones are used in genetic studies. Published in Russian in Fiziologiya Rastenii, 2007, Vol. 54, No. 4, pp. 572–578. The text was submitted by the authors in English.     

The effect of trait type and strength of selection on heritability and evolvability in an island bird population

The heritability (h²) of fitness traits is often low. Although this has been attributed to directional selection having eroded genetic variation in direct proportion to the strength of selection, heritability does not necessarily reflect a trait's additive genetic variance and evolutionary potential (“evolvability”). Recent studies suggest that the low h² of fitness traits in wild populations is caused not by a paucity of additive genetic variance (V_A) but by greater environmental or nonadditive genetic variance (V_R). We examined the relationship between h² and variance‐standardized selection intensities (i or β_σ), and between evolvability (I_A:V_A divided by squared phenotypic trait mean) and mean‐standardized selection gradients (β_μ). Using 24 years of data from an island population of Savannah sparrows, we show that, across diverse traits, h² declines with the strength of selection, whereas I_A and I_R (V_R divided by squared trait mean) are independent of the strength of selection. Within trait types (morphological, reproductive, life‐history), h², I_A, and I_R are all independent of the strength of selection. This indicates that certain traits have low heritability because of increased residual variance due to the age at which they are expressed or the multiple factors influencing their expression, rather than their association with fitness.     

A statistical model of the reproduction of aphids

1. The logistic function has been generally used to describe the reproductive process of a “population” of animal. However, this model can not give us any information about the reproductive process of “individuals” in the population. In this study a statistical model on the basis of the reproduction of individuals of barley aphid is presented to find the proportion of the mature individuals, the heterogeneity in reproductive ability of the aphids, etc.
2. The model is constructed as follows:
3. The probability that j insects are found on a plant at time t₀ is represented as Q(j).
4. The probability that h individuals of j have reproductive ability, say, mature individuals, in the period t₀ to t₁ is represented as B(h/j)=_jC_hw^h(1−w)^j−h, where w is the proportion of mature individuals.
5. In a population with a homogeneous reproductive ability, the probability that each parent lays i offspring in the period t₀ to t₁ is represented as P(i/m)=e^−mmⁱ/i!, where m is mean. And, in a population, m changes according to the gamma distribution. Hence the probability that a parent lays i offspring between t₀ and t₁ is represented as , where p and k are parameters of negative binomial distribution. The probability that h parents on a plant lays s offspring is represented as .
6. From the assumptions mentioned above, the probability that s offspring are to be found at time t₁ on a plant with the original j individuals at time t₀ is represented by
7. The experimental populations were demonstrated to fit well to the model.

     

Modulation of inwardly rectifying Na+-K+ channels by serotonin and cyclic nucleotides in salivary gland cells of the leech,Haementeria

Summary The electrically excitable salivary cells of the giant Amazon leech, Haementeria, display a time-dependent inward rectification. Under voltage clamp, hyperpolarizing steps to membrane potentials negative to about –70 mV were associated with the activation of a slow inward current (I _h) which showed no inactivation with time. The time course of activation of I _hwas described by a single-exponential function and was strongly voltage dependent. The activation curve of_hranged from –72 to –118 mV, with half-activation occurring at –100 mV. Ion-substitution experiments indicated that I _his carried by both Na⁺ and K⁺ ions. 5-Hydroxytryptamine (5-HT) increased the amplitude of I _hand its rale of activation. It also produced a positive shift of the activation curve of the conductance underlying I _h G_hwithout altering the slope factor, thus indicating that the voltage dependence of I _hwas modulated by 5-HT. Cs⁺ blocked both I _hand the 5-HT-polentiated current in a voltage-independent manner, whereas Ba²⁺ had little effect. It is concluded that 5-HT increases I _hby modulating the inwardly rectifying Na⁺-K⁺ channels in the salivary cells. The effect of 5-HT may be mediated by an increase in adenylate cyclase activity since I _hwas increased by 8-bromocyclic AMP and by the phosphodiesterase inhibitor, 3-isobutyl-l-methylxanthine. In contrast, I _hwas reduced by 8-bromo-cyclic GMPand by zaprinast (an inhibitor of cyclic GMP-scnsitive phosphodieslerase). Cyclic GMP itself also reduced I _h, and the effect was specific to the 3,5 form; 2,3-cyclic GMP was inactive. The results suggest that the inward-rectifier channel may be modulated in opposite directions by cyclic AMP and cyclic GMPThis work was supported by a grant from the Science and Engineering Research Council (no. GR/F/17087). We are grateful to the SmithKline (1982) Foundation for provision of a pulse generator     

Molecular-marker-facilitated investigation on the ability to stimulate N2 fixation in the rhizosphere by irrigated rice plants

An F₂ population, consisting of 231 individuals derived from a cross between rice cultivars with a similar growing duration, Palawan and IR42, was utilized to investigate the genetic nature of rice varietal ability to stimulate N₂ fixation in the rice rhizosphere. To assess rhizospheric N₂ fixation, an isotope-enriched ¹⁵N dilution technique was employed, using ¹⁵N-stabilized soil in pots. IR42, an indica variety, had 23% higher N derived from fixation (Ndfa) than Palawan, a javanica genotype. Normal segregation of atom% ¹⁵N excess was obtained in the F₂ population, with an average of 0.218 with 8% of plants below IR42 (0.188) and 10% of plants above Palawan (0.248). One-hundred-and-four RFLP markers mapped on 12 chromosomes were tested for linkage to the putative QTLs. Significant (P<0.01) associations between markers and segregation of atom% ¹⁵N excess were observed for seven marker loci located on chromosomes 1, 3, 6 and 11. Four QTLs defined by the detected marker loci were identified by interval-mapping analysis. Additive gene action was found to be predominant, but for at least one locus, dominance and partial dominance effects were observed. Significant (P<0.01) epistatic effects were also identified. Individual marker loci detected between 8 and 16% of the total phenotypic variation. All four putative QTLs showed recessive gene action, and no phenotypic effects associated with heterozygosity of marker loci were observed. The results of this study suggest that rice genetic factors can be identified which affect levels of atom% ¹⁵N excess in the soil by interacting with diazotrophs in the rice rhizosphere.     

Effects of salinity on photosynthesis and respiration of the seagrass Zostera japonica: A comparison of two established populations in North America

Photosynthetic responses were quantified for two Zostera japonica Aschers. and Graebn. populations from the northern and southern limits of distribution exposed to a range of salinities along the Pacific Coast of North America. Plants were collected from Padilla Bay, Washington (northern) and Coos Bay, Oregon, USA (southern) and cultured together in experimental tanks at 3 salinities (5, 20 and 35) under saturating irradiance for 3 weeks. Subsequently, photosynthesis–irradiance (P vs. E curves) relationships for leaf segments from the two populations were assessed using an oxygen electrode system. We found no evidence for diel rhythms in either light saturated photosynthesis (P_max) or dark respiration (R_d). For the Padilla Bay population, P_max ranged from 192 to 390 μmol O₂ g DW⁻¹ h⁻¹; for the Coos Bay population P_max ranged from 226 to 774 μmol O₂ g DW⁻¹ h⁻¹. Photosynthetic maxima of the Coos Bay plants occurred at a salinity of 20, whereas salinity had no effect on the photosynthetic maxima of the Padilla Bay plants. There were significant differences in leaf tissue R_d among salinity treatments but the two populations responded similarly to salinity. North American populations of Z. japonica are best adapted to intermediate salinities, displaying minimum R_d rates, lower compensation irradiance, higher saturation irradiance, and greater P_max rates at a salinity of 20. Additionally, the southern population may be better adapted to southward expansion along the Pacific Coast and changes associated with global climate change.     

Microsatellites in Cassava (Manihot esculenta Crantz): discovery, inheritance and variability

 Fourteen microsatellites containing GA-repeats were isolated and characterized in cassava (Manihot esculenta Crantz, Euphorbiaceae). Microsatellite heterozygosity (h) was estimated in 48 accessions using (³²P)-end-labeled primers and in more than 500 accessions using fluorescence-based genotyping. Heterozygosity values ranged from 0.00 to 0.88 and the number of alleles detected varied from 1 to 15. The reproducibility of allele sizing was also assessed using fluorescence-based genotyping. The average inter-gel size difference was 1.03 nucleotides. Chi-square tests (χ²) were performed to analyse segregation distortion and the linkage between alleles segregating from either or both parents in an F₁ mapping population. Most microsatellite loci segregated in the expected 1 : 1, 1 : 2 : 1 or 1 : 1 : 1 : 1 ratio. Linkage was detected between loci segregating from either parent, and segregation distortion from the male parent was detected for locus GA-131. Approximately 80% of the microsatellites detected one or two alleles per accession, suggesting a low degree of microsatellite locus duplication, an unexpected finding for a putative allopolyploid, highly heterozygous species. The high h values of most microsatellites, their amplification in other Manihot taxa and their suitability for high-throughput, fluorescence-based genotyping, make microsatellites the marker of choice for germplasm characterization and saturation of the cassava map. Received: 4 September 1997 / Accepted 16 March 1998     

Anaerobic fermentation of fructose in a mixed culture of fermentative and methanogenic bacteria

Summary Two newly isolated strains of Methanosarcina, strains JKAD and DALS, were grown in monoculture and in mixed culture in combination with Acetobacterium woodii WB1. Methanosarcina strains convert acetate into methane and carbon dioxide while Acetobacterium woodii grows on fructose, producing acetate via homoacetate fermentation. Monocultures of A. woodii in continuous culture consumed up to 6 mmoles g^-1 dry weight (dw) h^-1 of fructose and produced up to 12.9 mmoles g^-1 dw h^-1 of acetate at a dilution rate (D) of 0.13 h^-1. In batch growth the methanogenic bacteria produced up to 12.1 mmoles g^-1 dw h^-1 of CH₄ at a specific growth rate of 0.043 h^-1. In continuous cultivation the specific growth rate and the specific methane production of Methanosarcina were lower than in batch cultures, with values of 0.031 h^-1 and 3.1 mmoles g^-1 dw h^-1 of methane, respectively. In combination, A. woodii and Methanosarcina strain DALS in batch cultures completely converted fructose to methane and carbon dioxide with a maximum specific methane production rate of 1.9 mmoles g^-1 dw h^-1 of methane. In continuous cultivation these mixed cultures produced between 1.2 and 2 mmoles g^-1 dw h^-1 of CH₄ at a dilution rate of up to 0.043 h^-1. The methanogens were washed out at D values higher than 0.043 h^-1 for A. woodii and Methanosarcina strain JKAD, and higher than 0.05 h^-1 for A. woodii and Methanosarcina strain DALS. Data obtained from defined mixed cultures allow one to follow interactions in a mixed population of two species with different growth constants.     

Estimation of Finite Population Variance Using Ratio and Product Methods of Estimation

For estimating finite population variance σ_y² of a character y under our study, estimators using auxiliary information on a character x in the form of ratio, product, ratio-type or product-type estimators have been suggested, and their comparative study with the conventional unbiased estimator s_y² of σ_y² has been made in simple random sampling with replacement. A generalized estimator representing a class of estimators for the finite populations variance, has also been studied.     

Density and depth variations of Daphnia multilocus genotypes during a summer period in Lake Maarsseveen

The genotype composition of a Daphnia population complex during a summer period in Lake Maarsseveen (The Netherlands) was determined by allozyme analysis. The depth distribution, diel vertical migration and several parameters of the total population were measured. Young-of-the-year (0⁺) perch (Perca fluviatilis) were caught and species and allozyme types of Daphnia in the perch gut were also analysed. During May 1997, the densities of D. hyalina, D. galeata, the back-cross D. g × h — hyalina and the multilocus allozyme genotypes of the hybrid D. g × h decreased, except one multilocus genotype (MMMF). Total population size decreased and the ratio of females with eggs to those without eggs decreased as well. Food limitation during this clear-water phase in the lake is considered responsible. All genotypes, except MMMF, gradually descended in the water column. This drift is thought to be a reaction to the abundantly present 0⁺ perch or to the kairomones of this fish, although predation on the daphnids was still absent. In June, diel vertical migration started, except again part of the MMMF subpopulation. The other part migrated over a short distance compared with the other taxa and allozyme types. Within two weeks, the upper 5 m of the epilimnion was devoid of Daphnia, and guts of perch were predominantly filled with MMMF. The daphnids in the gut and the lake did not differ in allozyme type composition. By the end of July, population density had increased again. The size and composition of the Daphnia population complex continuously changed during the study period, as did the depth distribution of the components. Different genotypes within the population complex seem to have developed different strategies to cope with starvation and predation and the state at a particular moment can be understood only if past and present factors are considered.     

Das Belichtungspotential der isolierten Retina des Einsiedlerkrebses (Eupagurus bernhardus L.) in Abhängigkeit von den extrazellulären Ionenkonzentrationen

Summary 1.The action potential of the isolated retina of the hermit crab Eupagurus bernhardus L. resulting from exposure to light has been measured with external electrodes under constant stimulus conditions.Three measurements of the retinal action potentials (RAP's) were taken to observe the changes of the RAP's quantitatively: a) The amplitude h _max of the maximum; b) the amplitude h _e of the plateau, measured at the end of the stimulus, for taking the shape quotient h _max /h _e ; c) the peak-amplitude-time t _max. 2.The RAP's of the retina in a standard physiological saline are compared with those of the retina in salines of different ionic composition while osmotic pressure and p _h were kept constant. 3.Increasing K⁺-concentration reduces the amplitude h _max of the RAP's gradually, which is zero at 500 mM K⁺/l. The peak-time t _max decreases with increasing K⁺-concentration up to 50 mM K⁺/l, whereas at higher concentrations it increases. In contrast to this fact h _max/h _e increases up to 50 mM K⁺/l and decreases above this concentration (Fig. 3). 4.Increasing Ca⁺⁺-concentration reduces h _max (zero above 350 mM Ca⁺⁺/l) and t _max. h _max/h _e rises up to a Ca⁺⁺-concentration of about 30 mM Ca⁺⁺/l; whereas at a higher Ca⁺⁺-concentration it decreases again (Fig. 6). When the Ca⁺⁺-concentration is very low the fall of the RAP is much slowed down and the plateau h _e extremly rises. In a Ca⁺⁺-free saline which contained 1 mM/l Ethylendiamintetraacetic acid (EDTA) the retina lost its irritability reversibly (Fig. 8). 5.The amplitude of the RAP's is augmented with increasing Mg⁺⁺-concentration up to 10–30 mM Mg⁺⁺/l and decreases above this concentration (Fig. 11). When the saline contains virtually no other cations but Mg⁺⁺ (367 mM/l) the amplitude of the RAP is small (20%) but not zero. 6.In a buffered isotonic NaCl-solution as well as in a saline in which all the Cl^--ions are substituted by SO₄ ^---ions the amplitude of the RAP's is higher but the shape of the RAP's is changed in the same way as in other solutions with very low concentrations of Ca⁺⁺. 7.All the changes of the RAP's described so far are reversible. 8.Even when the retina is kept in a salt solution containing sodium in a very low concentration (ca. 3–5 mM/l, the sodium substituted by choline⁺-ions) for 5 hours the amplitude h _max of the RAP does not change significantly but the shape: the peaktime t _max is longer, h _max/ h _e is much greater. Afterwards when the retina is brought into standard saline again, the amplitude h _max increases, t _max remains almost unchanged and h _max/h _e , decreases strongly (Fig. 17). 9.Substitution of all the Na⁺-, Ca⁺⁺- and Mg⁺⁺-ions by choline⁺-ions results in a decrease of the amplitude h _max, a lengthening of t _max and a small increase of h _max/h _e . 10.Substitution of all the NaCl by glucose decreases the amplitude h _max, lengthens t _max very much and decreases the value of h _max/h _e but little. Afterwards, when the retina is brought into standard saline again the effect of the glucose solution on the amplitude h _max is only little reversible: h _max increases very little, t _max decreases strongly and h _max/h _e increases (Fig. 21). 11.With increasing external K⁺-concentration the resting potential decreases. The changes of the resting potential cause the changes in the shape of the RAP's. 12.The presence of a small concentration of Ca⁺⁺-ions outside of the cell membrane is obviously necessary for the ability of the cell membrane of the photoreceptor to increase its ionic permeability consequent to stimulation by light. Above a Ca⁺⁺-concentration of about 1 mM/l the raise of permeability of the cell membrane during illumination is smaller with increasing Ca⁺⁺-concentration. The velocity of the changes in permeability is augmented, especially of those changes concerned with the fall of the RAP. The effect of Mg⁺⁺-ions is somewhat similar to that of Ca⁺⁺-ions, but much weaker. 13.The changes of the RAP are mainly determined by the low Ca⁺⁺-content when the retina stays in the NaCl- or sulfate saline. 14.Choline⁺-ions probably greatly increase the raise of permeability of the cell membrane for the divalent cations Ca⁺⁺ and Mg⁺⁺ during excitation. 15.It is suggested that under normal conditions in Eupagurus the amplitude of the RAP is determined primarily by the Na⁺-concentration gradient over the receptor cell membrane. But also the divalent cations Ca⁺⁺ and Mg⁺⁺ contribute to the amplitude of the RAP, especially after the retina has been treated with choline chloride.

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Herrn Professor Dr. C. Kosswig zum 60. Geburtstag überreicht.Der Deutschen Forschungsgemeinschaft danke ich für großzügige Unterstützung, Herrn Peter Thomsen und meiner Frau für technische Hilfe.     

Use of a large multiparent wheat mapping population in genomic dissection of coleoptile and seedling growth

Identification of alleles towards the selection for improved seedling vigour is a key objective of many wheat breeding programmes. A multiparent advanced generation intercross (MAGIC) population developed from four commercial spring wheat cultivars (cvv. Baxter, Chara, Westonia and Yitpi) and containing ca. 1000 F₂‐derived, F_6:7 RILs was assessed at two contrasting soil temperatures (12 and 20 °C) for shoot length and coleoptile characteristics length and thickness. Narrow‐sense heritabilities were high for coleoptile and shoot length (h² = 0.68–0.70), indicating a strong genetic basis for the differences among progeny. Genotypic variation was large, and distributions of genotype means were approximately Gaussian with evidence for transgressive segregation for all traits. A number of significant QTL were identified for all early growth traits, and these were commonly repeatable across the different soil temperatures. The largest negative effects on coleoptile lengths were associated with Rht‐B1b (?8.2%) and Rht‐D1b (?10.9%) dwarfing genes varying in the population. Reduction in coleoptile length with either gene was particularly large at the warmer soil temperature. Other large QTL for coleoptile length were identified on chromosomes 1A, 2B, 4A, 5A and 6B, but these were relatively smaller than allelic effects at the Rht‐B1 and Rht‐D1 loci. A large coleoptile length effect allele (a = 5.3 mm at 12 °C) was identified on chromosome 1AS despite the relatively shorter coleoptile length of the donor Yitpi. Strong, positive genetic correlations for coleoptile and shoot lengths (r_g = 0.85–0.90) support the co‐location of QTL for these traits and suggest a common physiological basis for both. The multiparent population has enabled the identification of promising shoot and coleoptile QTL despite the potential for the confounding of large effect dwarfing gene alleles present in the commercial parents. The incidence of these alleles in commercial wheat breeding programmes should facilitate their ready implementation in selection of varieties with improved establishment and early growth.