Experimental study of the influence of errors of genetic correlation estimates on unrestricted,optimum, and desired gains selection indices

Summary Effects of errors in estimates of the genetic correlation on the accuracy of unrestricted, optimum, and desired gains selection indices were examined experimentally in Tribolium castaneum. Three lines were selected for three generations for pupal weight at 21 days and adult weight at 31 days, using unrestricted (I9), optimum (O9), and desired gains (G9) index selection methods. The genetic correlation between pupal and adult weights in the base population was 0.95. The optimum index was designed to set the response of pupal weight by a fixed amount, while in the desired gains index the responses of pupal and adult weights were specified as being equal to 31. Three other indices were constructed using a deliberately incorrect genetic correlation (0.25), i.e., unrestricted (I2), optimum (O2), and desired gains (G2). Responses observed in unrestricted index lines (I9 versus I2) and optimum index lines (O9 versus O2) did not differ significantly, even though lines I9 and I2 differed in a practical sense. Responses in desired gains index lines (G9 versus G2) differed significantly. Responses obtained for aggregate genotype (pupal weight + adult weight) and for the component traits were greater in line I9 than those obtained in line I2. Responses obtained in the O9 and O2 lines for pupal and adult weights were similar, while those obtained in the G9 and G2 lines were similar for pupal weight but not (P<0.05) for adult weight. Therefore, underestimation of the genetic correlation seems to affect the efficiency of a desired gains index more than that of unrestricted or optimum indices.     

Factor and principal component analyses as alternatives to index selection

Summary Selections from factor and principal component analyses were compared with those from the Smith-Hazel index when selecting for several switchgrass (Panicum virgatum L.) traits. The objective of this study was to examine several alternatives to index selection. Such procedures would potentially eliminate problems of selection associated with Smith-Hazel indices, including errors in genetic parameter estimates and difficulty in assigning relative economic weights to traits. Selection was performed on 1,280 plants that were evaluated over 2 years at 1 location, in a randomized complete block design with 4 replicates. The plants were evaluated for forage yield and several forage quality traits. The comparisons of index selection with principal factor analysis, maximum-likelihood factor analysis and principal component analysis were made for three sets of traits (five traits per set) to estimate repeatability for the comparisons. Multivariate analyses were performed on both simple and genotypic correlation matrices. Comparisons were made by computing Spearman's rank correlations between selection index plant scores and scores computed from multivariate analysis and by determining the number of plants selected in common for the selection methods. Among the three multivariate analysis methods evaluated in this study, principal component analysis had the highest correlation with index selection. The high correlation for principal component analysis of simple correlation matrices indicates the potential for using this statistical method for selection purposes. This would permit the breeder to reduce field costs (e.g., time, labor, equipment) required to obtain the genetic parameter estimates necessary to construct selection indices.     

Multitrait index based on factor analysis and ideotype‐design: proposal and application on elephant grass breeding for bioenergy

This study proposes a new multitrait index based on factor analysis and ideotype‐design (FAI‐BLUP index), and validates its potential on the selection of elephant grass genotypes for energy cogeneration. Factor analysis was carried out, and afterwards, factorial scores of each ideotype were designed according to the desirable and undesirable factors, and the spatial probability was estimated based on genotype‐ideotype distance, enabling genotype ranking. In order to quantify the potential of the FAI‐BLUP index, genetic gains were predicted and compared with the Smith‐Hazel classical index. The FAI‐BLUP index allows ranking the genotypes based on multitrait, free from multicollinearity, and it does not require assigning weights, as in the case of the Smith‐Hazel classical index and its derived indices. Furthermore, the genetic correlation ‐ positive or negative ‐ within each factor was taken into account, preserving their traits relationship, and giving biological meaning to the ideotypes. The FAI‐BLUP index indicated the 15 elephant grass with the highest performance for conversion to bioenergy via combustion, and predicted balanced and desirable genetic gains for all traits. In addition, the FAI‐BLUP index predicted gains of approximately 62% of direct selection, simultaneously for all traits that are desired to be increased, and approximately 33% for traits which are desired to be decreased. The genotypes selected by the FAI‐BLUP index have potential to improve all traits simultaneously, while the Smith‐Hazel classical index predicted gains of 66% for traits that are desired to be increased, and ?32% for traits that are desired to be decreased, and it does not have potential to improve all traits simultaneously. The FAI‐BLUP index provides an undoubtable selection process and can be used in any breeding programme aiming at selection based on multitrait.     

Selection strategies for developing smooth bromegrass cell wall ideotypes

Summary A random sample of 80 families of the B8HD smooth bromegrass (Bromus inermis Leyss.) population were tested in three environments for forage yield and cell wall constituents. Expected progress from one cycle of family selection was computed for single-trait selection and multiple-trait restricted selection. Expected gains were compared to desired goals and actual results from one cycle of phenotypic selection. Desired goals were: Model I = reduced lignin and cellulose, with increased hemicellulose, resulting in no change in cell wall content; Model II = reduced lignin and cellulose with no change in hemicellulose; or Model III = reduced lignin, cellulose, and hemicellulose. Single-trait selection for high hemicellulose in first harvest or low cellulose in second harvest had the best expected responses, of any single trait, for Model I. Possible undesirable effects of selection for low cellulose would be a reduction in forage yield potential. Multiple-trait restricted selection was judged to be more effective, with responses all in the desired direction, by specifying increased hemicellulose in index development. Selection in second harvest was expected to have similar responses as first harvest, except for a greater increase in forage yield. Development of Models II or III is expected to be difficult due to a negative correlation estimate between first and second harvest cell wall concentration.     

不同酸度酸雨对小麦花后氮硫代谢和籽粒蛋白组分的影响

酸雨是中国重要的环境问题,为研究酸雨对小麦籽粒品质的可能影响,以小麦品种扬麦15和汶农17为材料开展盆栽试验,研究了不同酸度(pH2.5、p H4.0和p H5.6)酸雨对小麦花后氮硫代谢关键酶活性和籽粒蛋白质含量及组分的影响。结果显示:酸雨处理抑制叶片硝酸还原酶(NR)活性,提高了扬麦15整个灌浆期及汶农17灌浆中后期叶片谷氨酰胺合成酶(GS)活性,促进了叶片蛋白的降解,降低了叶片可溶性蛋白含量。不同酸度酸雨提高了成熟期籽粒中蛋白质含量,酸度越强,增加幅度越大,籽粒中各蛋白组分含量和大部分氨基酸含量也有明显提高。酸雨提高了扬麦15叶片丝氨酸乙酰转移酶(SAT)和O-乙酰丝氨酸硫裂解酶(OAS-TL)活性,但对汶农17硫代谢关键酶活性影响较小,酸雨处理还提高了籽粒中二硫键和含硫氨基酸含量。可见酸雨对小麦氮硫代谢有不同程度影响,进而影响了小麦籽粒蛋白质含量和组成,酸度越强影响越大,但不同品种对酸雨响应有一定差异。     

Potential gain from selection for yield stability in two grain sorghum populations

Summary Maximum yield under highly unpredictable environments should be associated with selection of genotypes with superior performance across good and poor environments. Several stability parameters have been proposed to identify superior genotypes over a wide range of environments. None of these has been used as selection criteria, however, because of their low heritability. The objective of the study presented here was to compare the relative efficiency of predicted gain from indirect selection among three stability parameters: the coefficient of regression (b), deviation from regression (S _d ² ), and principal components scores (PC) from the AMMI model; two indices including mean yield and a stability parameter; and three indices involving yield at the best, the worst, and an intermediate environment. Two hundred S₁ families from each of two sorghum populations (TP24D and KP9B) were evaluated at four dry-land evironments over 2 years. The low heritability estimates and the low genetic correlation between the various stability parameters and mean yield resulted in their low relative efficiency as indirect selection criteria for high yield across environments. However, when the parameters were combined with mean yield over all to create indices, the relative efficiency increased for all the environments. In terms of resource allocation, these indices were not as efficient as mean productivity, rank summation, and selection index that involved fewer environments in their estimation.Contribution no. 9820 of Agricultural Research Division, Univ. of Neb. and no. 92-203-J of Kansas Exp. Stn.     

Chemical and optical changes in freshwater dissolved organic matter exposed to solar radiation

We studied the chemical and optical changes inthe dissolved organic matter (DOM) from twofreshwater lakes and a Sphagnum bog afterexposure to solar radiation. Stable carbonisotopes and solid-state ¹³C-NMR spectraof DOM were used together with optical andchemical data to interpret results fromexperimental exposures of DOM to sunlight andfrom seasonal observations of two lakes innortheastern Pennsylvania. Solar photochemicaloxidation of humic-rich bog DOM to smaller LMWcompounds and to DIC was inferred from lossesof UV absorbance, optical indices of molecularweight and changes in DOM chemistry. Experimentally, we observed a 1.2 enrichment in ¹³$C and a 47% loss in aromaticC functionality in bog DOM samples exposed tosolar UVR. Similar results were observed inthe surface waters of both lakes. In latesummer hypolimnetic water in humic LakeLacawac, we observed 3 to 4.5enrichments in ¹³C and a 30% increase inaromatic C relative to early spring valuesduring spring mixing. These changes coincidedwith increases in molecular weight and UVabsorbance. Anaerobic conditions of thehypolimnion in Lake Lacawac suggest thatmicrobial metabolism may be turning overallochthonous C introduced during springmixing, as well as autochthonous C. Thismetabolic activity produces HMW DOM during thesummer, which is photochemically labile andisotopically distinct from allochthonous DOM orautochthonous DOM. These results suggest bothphotooxidation of allochthonous DOM in theepilimnion and autotrophic production of DOM bybacteria in the hypolimnion cause seasonaltrends in the UV absorbance of lakes.     

Are economic selection indices always superior to a desired gains index?

Conclusions The comparison of different selection indices is justified only if the indices are constrated to achieve the same profit function, even when each index is not optimized with respect to that profit function.When a profit function is known and is non-linear, the desired gains index may be more efficient than the economic index. The optimum desired gains index should be determined by iterative techniques over several generations to compare the genetic progress with the economic index, because gains by the economic index are not linear and the changes observed in the initial generations of selection are not the same rates in future generations, although those changes are linear in the case of the desired gains index.     

Long-term effects of selection based on the animal model BLUP in a finite population

Monte Carlo simulation was used to assess the long-term effects of truncation selection within small populations using indices (I=f+m) combining mid-parent [f=(a _i+a _d)/2] and Mendelian-sampling (m=a-f) evaluations provided by an animal model BLUP (a=f+m). Phenotypic values of panmictic populations were generated for 30 discrete generations. Assuming a purely additive polygenic model, heritability (h ₂) values were 0.10, 0.25 or 0.50. Two population sizes were considered: five males and 25 females selected out of 50 candidates of each sex (small populations, S) and 50 males and 250 females selected out of 500 candidates in each sex (large populations, L). Selection was carried out on the index defined above with = 1 (animal model BLUP), =1/2, or =0 (selection on within-family deviations). Mass selection was also considered. Selection based on the animal model BLUP (=1) maximized the cumulative genetic gain in L populations. In S populations, selection using = 1/2 and mass selection were more efficient than selection under an animal model (+ 3 to + 7% and + 1 to + 4% respectively, depending on h ²). Selection on within-family deviations always led to the lowest gains. In most cases, the variance of response to selection between replicates did not depend on the selection method. The within-replicate genetic variance and the average coefficient of inbreeding (F) were highly affected by selection with =1 or 1/2, especially in populations of size S. As expected, selection based on within-family deviations was less detrimental in that respect. The number of copies of founder neutral genes at a separate locus, and the probability vector of origin of the genes in reference to the founder animals, were also observed in addition to F values. The conclusion was that selection procedures placing less emphasis on family information might be interesting alternatives to selection based on animal model BLUP, especially for small populations with long-term selection objectives.     

Inheritance of legumin and albumin contents in a cross between round and wrinkled peas

Summary Legumin and albumin are the fractions of pea seed proteins preferred to vicilin because of their high sulfur amino acid contents. The joint inheritance of legumin and albumin contents was studied in a cross between to contrasting lines of peas — one with high legumin and low albumin, and the other with low legumin and medium to high albumin. Single seed determinations were made in the parental, F₁; F₂ and backcross generations using rocket immunoelectrophoresis. In the non-segregating generations (P₁, P₂ and F₁), legumin and albumin contents were negatively correlated (r=–0.50). The estimates of correlation coefficients in the segregating generations (F₂, BC₁ and BC₂) were also about –0.5. However, the two estimates based on the round and on the wrinkled seeds separately in the F₂ generation were not significantly different from zero. At least four individual round F₂ seeds showed the desired recombination of high legumin with high albumin indicating that the unfavorable correlation can be broken. In this cross legumin content showed predominantly additive genetic variation whereas the dominance variance was the largest component for albumin content. A combined relative sulfur index, proposed as a convenient measure for selection, showed a narrow sense heritability of 47%. In general these results support the view that sulfur amino acid content of peas can be improved by breeding, but that the required selection regime must take both legumin and albumin content into account.     

Widespread Adaptive Evolution in the Human Immunodeficiency Virus Type 1 Genome

We investigated variable selective pressures among amino acid sites in HIV-1 genes. Selective pressure at the amino acid level was measured by using the nonsynonymous/synonymous substitution rate ratio ( = d_N/d_S). To identify amino acid sites under positive selection with > 1, we applied maximum likelihood models that allow variable ratios among sites to analyze genomic sequences of 26 HIV-1 lineages including subtypes A, B, and C. Likelihood ratio tests detected sites under positive selection in each of the major genes in the genome: env, gag, pol, vif, and vpr. Positive selection was also detected in nef, tat, and vpu, although those genes are very small. The majority of positive selection sites is located in gp160. Positive selection was not detected if was estimated as an average across all sites, indicating the lack of power of the averaging approach. Candidate positive selection sites were mapped onto the available protein tertiary structures and immunogenic epitopes. We measured the physiochemical properties of amino acids and found that those at positive selection sites were more diverse than those at variable sites. Furthermore, amino acid residues at exposed positive selection sites were more physiochemically diverse than at buried positive selection sites. Our results demonstrate genomewide diversifying selection acting on the HIV-1.     

Estimation of genetic variability and heritability for biofuel feedstock yield in several populations of switchgrass

Information on heritability and predicted gains from selection for increased biomass yield for ethanol production in switchgrass is limited and may vary among breeding populations. The purpose of this study was to estimate heritability and predicted gains from selection for higher biomass yield within a lowland ecotype switchgrass population, Southern Lowland 93 (SL‐93), and two upland ecotype switchgrass populations, Southern Upland Northern Upland Early Maturing (SNU‐EM) and Southern Upland Northern Upland Late Maturing (SNU‐LM). Narrow‐sense heritabilities (h_n²) for biomass yield in each of the three populations were estimated via progeny–parent regression analysis. Half‐sib (HS) progeny families from 130 randomly selected plants from the SL‐93 population were evaluated for biomass yield in replicated trials in 2002 and 2003. Clonal parent plants were evaluated for biomass yield in separate environments to provide unbiased h_n² estimates from progeny–parent regression. Yield differences were highly significant among SL‐93 HS progenies within and over years. For the SL‐93 population, h_n² estimates were 0.13 and 0.12 based on individual plant and phenotypic family mean (PFM) selection, respectively. Predicted genetic gains (ΔG) per selection cycle were 0.15 kg dry matter (dm) plant^?1 and 0.10 kg dm plant^?1 for PFM and individual plant selection methods, respectively. For the SNU‐EM and SNU‐LM populations, year and year × HS family effects were highly significant (P < 0.01) and the HS family effect over years was nonsignificant (P < 0.05). However, HS family effects were highly significant within respective years (P < 0.01). Estimates of h_n² for the SNU‐EM and SNU‐LM populations based on PFM and individual plant selection were similar, ranging from 0.44 to 0.47; ΔG per selection cycle ranged from 0.22 to 0.33 kg dm plant^?1. The magnitudes of the estimates of additive genetic variation suggest that selection for higher biomass yield should be possible. The substantial effect of environment on biomass yields in the upland populations and the failure of families to respond similarly over years stress the importance of adequately testing biomass yield over years to assess yield.     

Efficiency of physiological trait-based and empirical selection approaches for drought tolerance in groundnut

Drought is the major abiotic constraint affecting groundnut productivity and quality worldwide. Most breeding programmes in groundnut follow an empirical approach to drought resistance breeding, largely based on kernel yield and traits of local adaptation, resulting in slow progress. Recent advances in the use of easily measurable surrogates for complex physiological traits associated with drought tolerance encouraged breeders to integrate these in their selection schemes. However, there has been no direct comparison of the relative efficiency of a physiological trait‐based selection approach (Tr) vis‐à‐vis an empirical approach (E) to ascertain the benefits of the former. The genetic material used in the present study originated from three common crosses and one institute‐specific cross from four collaborating institutes in India (total seven crosses). Each institute contributed six genotypes and each followed both the Tr and E selection approaches in each cross. The field trial of all selections, consisting of 192 genotypes (96 each Tr and E selections), was grown in 2000/2001 in a 4 × 48 alpha design in 12 season × location environments in India. The selection efficiency of Tr relative to E, RE_Tr, was estimated using the genetic concept of response to selection. Based on all the 12 environments, the two selection methods performed more or less similarly (RE_Tr= 1.045). When the 12 environments were grouped into rainy season and post‐rainy season, the relative response to selection in Tr method was higher in the rainy than in the post‐rainy season (RE_Tr= 1.220 vs 0.657) due to a higher genetic variance, lower G × E, and high h². When the 12 environments were classified into four clusters based on plant extractable soil‐water availability, the selection method Tr was superior to E in three of the four clusters (RE_Tr= 1.495, 0.612, 1.308, and 1.144) due to an increase in genetic variance and h² under Tr in clustered environments. Although the crosses exhibited significant differences for kernel yield, the two methods of selection did not interact significantly with crosses. Both methods contributed more or less equally to the 10 highest‐yielding selections (six for E and four for Tr). The six E selections had a higher kernel yield, higher transpiration (T), and nearly equal transpiration efficiency (TE) and harvest index (HI) relative to four Tr selections. The yield advantage in E selections came largely from greater T, which would likely not be an advantage in water‐deficient environments. From the results of these multi‐environment studies, it is evident that Tr method did not show a consistent superiority over E method of drought resistance breeding in producing a higher kernel yield in groundnut. Nonetheless, the integration of physiological traits (or their surrogates) in the selection scheme would be advantageous in selecting genotypes which are more efficient water utilisers or partitioners of photosynthates into economic yield. New biotechnological tools are being explored to increase efficiency of physiological trait‐based drought resistance breeding in groundnut.     

MACROALGAL RESPONSES TO NITROGEN SOURCE AND AVAILABILITY: AMINO ACID METABOLIC PROFILING AS A BIOINDICATOR USING GRACILARIA EDULIS (RHODOPHYTA)1

The use of macroalgae as biological indicators of dissolved nutrient source and availability in the water column was investigated. Total tissue nitrogen (N) content, pigments, and amino acids of the red alga Gracilaria edulis (Gmelin) Silva were compared to N source and availability in laboratory and field incubations to identify responses that would serve as bioindicators of N. Field-collected algae were preincubated (6–8 wk) in low-nutrient seawater to deplete their luxury reserves ofN. Incubations were then conducted for periods of 3 d in laboratory aquaria (N-spiked seawater) and in the field using macroalgal incubation chambers. After incubation in different N sources (NH₄⁺, NO₃^?, and urea) in laboratory aquaria, photosynthetic pigments (phycoerythrin and chlorophyll a) and total tissue N increased, in response to increasing [NH₄⁺] but not to [NO₃^?] or [urea]. Incubation in two ranges of [NH₄⁺], one from 0 to 80 μM and the other from 0 to 800 μM, in laboratory aquaria increased the total amino acid pool. Citrulline concentrations were the most responsive to [NH₄⁺] (r²= 0. 84). NH₄⁺ source treatments produced increases in citrulline, phenylalanine, serine, and free NH₄⁺ and decreases in alanine; NO₃^? treatments produced increases in glutamic acid, citrulline, and alanine; and urea treatments produced increases in free NH₄⁺ and decreases in phenylalanine and serine. The observed variations in amino acid content facilitated the development of an index for each N source based on relative concentrations of various amino acids (i. e. metabolic profiling). Gracilaria edulis was incubated along a field N gradient in the Brisbane River (three sites) and Moreton Bay (four sites), Queensland, Australia. Both phycoerythrin and tissue N appeared to respond equally to NH₄⁺ and NO₃^? availability in the field. N source indices, based on amino acid concentration, were effective predictors of both [NH₄⁺] and [NO₃^?] over a wide range of concentrations along the field gradient. Macroalgal physiological responses, particularly amino acid content, to changes in source and availability of N appear to be useful as sensitive bioindicators of N.     

镉胁迫对姬松茸生长和镉吸收累积的影响

利用外源镉添加的袋栽试验,系统研究了镉对姬松茸J37和J1两菌株农艺性状、子实体产量、氨基酸和镉含量的影响,以求为低富集镉的姬松茸品种选育和安全栽培提供科学依据。结果表明外源镉添加对姬松茸J37和J1品种子实体的农艺性状的影响各异,两菌株单个子实体重量、子实体高度、菌盖直径、菌盖厚度和菌柄直径等均与外源镉浓度具有显著的负相关性,其中子实体重量与外源镉浓度间的相关性最大;15 mg/kg镉水平是两菌株农艺性状发生显著变化的敏感点。不同镉水平下J37菌株单个子实体重量比J1菌株高10.9%—36.6%,表现为较强镉耐受性。姬松茸J37与J1菌株子实体产量、氨基酸和镉含量均随着潮次的增加而降低,子实体产量和氨基酸含量随着外源镉水平增加而降低,而镉含量随外源镉水平增加而增加。与外源镉0mg/kg处理相比,当外源镉水平达15 mg/kg时,J1和J37子实体总产量分别下降23.4%和13.4%以上,J1和J37子实体镉含量分别提高51.5%、13.7%以上,且J1子实体镉含量已达到食品卫生标准的临界值。当外源镉水平达到35 mg/kg时,J1和J37子实体产量分别下降45%、32%以上,J1和J...     

Comparing measures of breeding inequality and opportunity for selection with sexual selection on a quantitative character in bighorn rams

The reliability and consistency of the many measures proposed to quantify sexual selection have been questioned for decades. Realized selection on quantitative characters measured by the selection differential i was approximated by metrics based on variance in breeding success, using either the opportunity for sexual selection I_s or indices of inequality. There is no consensus about which metric best approximates realized selection on sexual characters. Recently, the opportunity for selection on character mean OSM was proposed to quantify the maximum potential selection on characters. Using 21 years of data on bighorn sheep (Ovis canadensis), we investigated the correlations between seven indices of inequality, I_s, OSM and i on horn length of males. Bighorn sheep are ideal for this comparison because they are highly polygynous and sexually dimorphic, ram horn length is under strong sexual selection, and we have detailed knowledge of individual breeding success. Different metrics provided conflicting information, potentially leading to spurious conclusions about selection patterns. I_δ, an index of breeding inequality, and, to a lesser extent, I_s showed the highest correlation with i on horn length, suggesting that these indices document breeding inequality in a selection context. OSM on horn length was strongly correlated with i, I_s and indices of inequality. By integrating information on both realized sexual selection and breeding inequality, OSM appeared to be the best proxy of sexual selection and may be best suited to explore its ecological bases.     

Simultaneous improvement of grain yield and protein content in durum wheat by different phenotypic indices and genomic selection

Key message

Simultaneous improvement of protein content and grain yield by index selection is possible but its efficiency largely depends on the weighting of the single traits. The genetic architecture of these indices is similar to that of the primary traits.

Abstract

Grain yield and protein content are of major importance in durum wheat breeding, but their negative correlation has hampered their simultaneous improvement. To account for this in wheat breeding, the grain protein deviation (GPD) and the protein yield were proposed as targets for selection. The aim of this work was to investigate the potential of different indices to simultaneously improve grain yield and protein content in durum wheat and to evaluate their genetic architecture towards genomics-assisted breeding. To this end, we investigated two different durum wheat panels comprising 159 and 189 genotypes, which were tested in multiple field locations across Europe and genotyped by a genotyping-by-sequencing approach. The phenotypic analyses revealed significant genetic variances for all traits and heritabilities of the phenotypic indices that were in a similar range as those of grain yield and protein content. The GPD showed a high and positive correlation with protein content, whereas protein yield was highly and positively correlated with grain yield. Thus, selecting for a high GPD would mainly increase the protein content whereas a selection based on protein yield would mainly improve grain yield, but a combination of both indices allows to balance this selection. The genome-wide association mapping revealed a complex genetic architecture for all traits with most QTL having small effects and being detected only in one germplasm set, thus limiting the potential of marker-assisted selection for trait improvement. By contrast, genome-wide prediction appeared promising but its performance strongly depends on the relatedness between training and prediction sets.

     

The release of glutamate and aspartate from rat brain synaptosomes in response to domoic acid (amnesic shellfish toxin) and kainic acid

Kainic acid is known to stimulate the release of glutamate (GLU) and aspartate (ASP) from presynaptic neurons. It has been suggested that the enhanced release of these endogenous EAA's plays a significant role in the excitotoxic effects of KA. Domoic acid (DOM), a shellfish toxin, is structurally similar to KA, and has been shown to be 3–8 times more toxic than KA. In this study, effects of KA and DOM on the release of GLU and ASP from rat brain synaptosomes were investigated. Amino acid analysis was performed by the reversed phase HPLC, following derivatization with 9-fluorenylmethyl chloroformate (FMOC). Potassium chloride (40 mM) was used as a positive control, and stimulated GLU release from rat brain synaptosomes in presence or absence of Ca²⁺. DOM enhanced the release of GLU, whereas KA stimulated the release of both GLU and ASP from synaptosomes in the presence of Ca²⁺. However, their potency to stimulate GLU and ASP release was enhanced in absence of Ca²⁺. These results indicate that diferent mechanisms may be involved in the release of GLU and ASP in response to DOM and KA, and that neurotransmitter release appeared to be highly specific for these agonists. It would appear that DOM and KA may interact with different receptors on the presynaptic nerve terminal, and/or activate different subtypes of voltage-dependent Ca²⁺ channels to promote influx of Ca²⁺ which is targeted for different pools of neurotransmitters.Abbreviations ANOVA analysis of variance - ASP aspartate - DOM domoic acid - DHKA dihydrokainic acid - EAA excitatory amino acid - FMOC 9-fluorenylmethyl chloroformate - GLU glutamate - KA kainic acid     

Changes in free amino acid content and activities of amination and transamination enzymes in yeasts grown on different inorganic nitrogen sources,including hydroxylamine

This study concerns inter- and intraspecific differences between yeasts at assimilation of different nitrogen sources. Alterations in the content of free amino acids in cells and media as well as in the related enzyme activities during growth were studied. The hydroxylamine (HA)-tolerant Endomycopsis lipolytica was examined and compared with the nitrate-reducing Cryptococcus albidus, and Saccharomyces cerevisiae, requiring fully reduced nitrogen for growth. Special attention was paid to alanine, aspartic acid, and glutamic acid, the amino acids closely related to the Krebs cycle keto acids. The amino acids were analyzed as their n-propyl N-acetyl esters by gas-liquid chromatography (GLC).The composition of the amino acid pool was similar for the three yeasts. Glutamic acid was predominant; in early log-phase cells of E. lipolytica contents of 200–234 mol·g^-1 dry weight were found. A positive correlation between the specific growth rate and the size of the amino acid pool was observed.The assimilation of ammonia was mediated by glutamate dehydrogenase (GDH). The NADP-GDH was the dominating enzyme in all three yeasts showing the highest specific activity in Cr. albidus grown on nitrate (6980 nmol· (min^-1)·(mg protein^-1). Glutamine synthetase (GS) displayed a high specific activity in S. cerevisiae, which also had a high amount of glutamine. The assimilation of HA did not differ greatly from the assimilation of ammonium in E. lipolytica. The existing differences could rather be explained as provoked by the concentration of available nitrogen.     

Degradation of surface-water dissolved organic matter: influences of DOM chemical characteristics and microbial populations

The degree to which biodegradation of dissolved organic matter (DOM) depends on microbial community structure and source remains unknown. In this study, we concentrated the microbial biomass from two streams in northern Michigan and a dystrophic bog lake in northern Wisconsin with varying initial DOM concentration (6.7–78.8 mg C l^–1) and DOM chemical characteristics (e.g. DOM average molecular weights from 808–1887 Da). Each of the three microbial inocula was added to each of the three DOM sources at in situ population levels for a total of nine treatments. Changes in DOM concentration and bacterial productivity, along with chemical characteristics, were examined over 308 h. The [³H]-leucine incorporation method was used to measure microbial production. In two of three sampling sites, bacterial communities were most productive when metabolizing DOM in their native waters. A variable peak in productivity was seen between 16–48 h after inoculation, followed by a drop in productivity in most treatments, with periods of DOM production most likely due to microbial turnover. These data suggest that microbial communities are better able to degrade the DOM of their native habitats, suggesting that biodegradation of DOM is influenced by source-specific microbial species and DOM chemical characteristics.