Ganglioside-cholera toxin interactions: a binding and lipid monolayer study

Summary On t.l.c. plates ¹²⁵I-cholera toxin binds to a disialoganglioside tentatively identified as GD_lb with about 10 times less capacity than to ganglioside GM₁. Binding of labeled toxin to both gangliosides was abolished in presence of excess amounts of unlabeled B subunit. Ganglioside extracts from human or pig intestinal mucosa showed toxin binding to gangliosides GM₁ and GD_1b. In ganglioside-containing lipid monolayers the penetration of the toxin was independent of the ganglioside binding capacity.Abbreviations GM₂ Gal-NAc14Gal(3-2NeuAc)14G1c1Cer - GM₁ Gal3Ga1-NAc14Gal(32NeuAc)14G1c11Cer - GD_1a NeuAc23Ga113Gal-NAc14Gal(32NeuAc)14G1c11Cer - GD1b Gall3Gal-NAcl4Gal(32NeuAc82NeuAc)14Glc11Cer - GT_1b NeuAc23Ga113Ga1-NAcal4Gal(3-2NeuAc82NeuAc)14G1c11Cer - dpPC 1,2-hexadecanoyl-sn-glycero-3-phosphocholine - dpPE 1,2-hexadecanoyl-sn-glycero-3-phosphoethanolamine     

Use of hydrogen cyanamide for apple and plum thinning

Effects of various concentrations of Dormex (a.i. 49% hydrogen cyanamide) on fruit thinning of Rome Beauty apple (Malus domestica Borkh.), Friar and Simka plums (Prunus salicina Lindley) were studied. A full bloom application of Dormex at all tested concentrations decreased Rome Beauty apple fruit set and yield, and increased fruit weight. Dormex at 0.25% (v/v) resulted in adequate apple thinning, indicated by production of an optimum fruit weight (320 g). Prebloom and full bloom applications of Dormex at greater than 0.75% reduced plum fruit set and yield in Friar. Full bloom application of Dormex at 0.50% showed a satisfactory fruit set, yield, and fruit weight in Friar plum. Prebloom Dormex application had no significant effect on `Simka' plum fruit set or yield, but full bloom application decreased fruit set and yield.     

Adoptions expérimentales de larves entre des fourmis de genres différents (II):Myrmica laevinodis Nylander etAnergates atratulus Schenck

Résumé Nous avons fait élever des larves d'Anergates atratulus par des ouvrières deMyrmica laevinodis à 22°C. Pour y parvenir, il n'est pas utile de faire hivernerensemble les larves d'Anergates et les ouvrières deMyrmica. La présence de larves autochtones n'empêche pas lesMyrmica d'élever des larves d'Anergates. Dans toutes les expériences lesMyrmica ont été soumises au fridavant de recevoir des larves d'Anergates. Aucune reine deMyrmica n'a été utilisée dans ces expériences.Sur les 64 larves d'Anergates que nous avons utilisées, 38 se sont transformées en imagos. C'est au début de l'adoption et au moment des métamorphoses que périrent la plupart des 26Anergates perdus. Les femelles vécurent en général 2 ou 3 jours et cherchèrent très tôt à quitter le nid natal. Les mâles vécurent 2 à 3 semaines.

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Summary Larvae ofAnergates atratulus were experimentally reared by workers ofMyrmica laevinodis, at 22°C. An overwintering of both larvae ofAnergates and workers ofMyrmica is not necessary for the success of that experiment. The presence of larvae ofMyrmica does not keep theMyrmica from rearing larvae ofAnergates. The workers ofMyrmica have been cooled, in all the experiments, before receiving larvae ofAnergates. No queen ofMyrmica have been used in that experiments.38 of the 64 larvae ofAnergates used became imagos. Most of the 26 lostAnergates died at the beginning of the adoption and during the metamorphosis. The females lived generally 2 or 3 days and tried, very early, to leave their native nest. The males lived 2 or 3 weeks.

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Anergates atratulus Myrmica laevinodis, 22 . bmecme Anergates Myrmica. Myrmica Anergates. Myrmica Anergates. Myrmica . 64 Anergates , 38 . 26 Anergates 2 3 . 2 3 .

     

Development of alfalfa strains with differential tolerance to aluminum toxicity

Summary Aluminum toxicity limits root growth in acid subsoils that are difficult to lime. An alternative to subsoil liming is the development of plants having greater tolerance to Al. Alfalfa (Medicago sativa L.) is considered an Al-susceptible species. Preliminary studies indicated that alfalfa cultivars differ in Al tolerance, but the extreme plant-to-plant variation within cultivars prevented the establishment of clearcut cultivar differences.Tolerant and susceptible plants were selected from each of six cultivars (DuPuits, Atlantic, Team, Buffalo, Grimm, and Sirsa 9) grown on an Al-toxic Bladen soil at pH 4.1 to 4.3. The tolerant selections were repotted and interpollinated to form one population of polycross seed. Susceptible selections were treated similarly to form a second population. These two populations, tolerant and susceptible, were subjected to an additional cycle of recurrent phenotypic selection for tolerance and susceptibility, respectively, to Al-toxic Bladen soil at pH 4.6.Plants from the population selected for tolerance to the acid Bladen soil were significantly higher in both root and top vigor on Al-toxic Tatum soil than plants from the population selected for susceptibility. The results indicated that Al tolerance is a heritable trait in these alfalfa populations and that recurrent selection can be used effectively to develop strains having differential tolerance to Al-toxic soils. The observation that only 2% of the plants from the tolerant population were in the most tolerant class suggests a good opportunity for more progress in selecting toward Al tolerance.     

PEG-enhanced,electric field-induced fusion of tonoplast and plasmalemma of grape protoplasts

Cultured grape cells accumulate anthocyanins in vacuoles rather than secreting them into the nutrient medium. Therefore, grape cells that contain tonoplast segments in their plasmalemma should be capable of excreting anthocyanins rather than sequestering them in their vacuoles. In initial attempts to construct such novel cells, small vacuoles were fused with the plasmalemma of cultured plant cells. Protoplasts were isolated from grape calluses that produce and accumulate anthocyanins. Small vacuoles were formed by gently rupturing vacuoles isolated from grape protoplasts. Although small vacuoles and protoplasts became aligned in an AC field, the tonoplast and plasmalemma did not readily fuse when subjected to 3 DC pulses of 1200 V cm^–1 for 50 s each. Changes in the intensity, number and/or duration of the DC pulses had no effect on the fusion process. When 1.0% polyethylene glycol was added to the electrofusion buffer, however, small vacuoles and protoplasts fused within a few minutes after the DC pulses were applied. These novel grape cells remained viable for several hours.Abbreviations BSA bovine serum albumin - 2,4-D 2,4-dichloro-phenoxyacetic acid - DTT dithiothreitol - EGTA ethyleneglycol-bis-(-amino-ethyl ether)-N,N,N,N - MES 2-[N-Morpholino]ethanesulfonic acid - MOPS 3-[N-Morpholino]propanesulfonic acid - PVP polyvinylpyrrolidone     

Synthesis of the acceptor analog αFuc(1→2)αGal-O(CH2)7 CH3: A probe for the kinetic mechanism of recombinant human blood group B glycosyltransferase

We report the chemical synthesis of Fuc(12)Gal-O(CH₂)₇CH₃ (1) an analog of the natural blood group (O)H disaccharide Fuc(12)Gal-OR. Compound 1 was a good substrate for recombinant blood group B glycosyltransferase (GTB) and was used as a precursor for the enzymatic synthesis of the blood group B analog Gal(3)[Fuc(12)]Gal-O(CH₂)₇CH₃ (2). To probe the mechanism of the GTB reaction, kinetic evaluations were carried out employing compound 1 or the natural acceptor disaccharide Fuc(12)Gal-O(CH₂)₇CH₃ (3) with UDP-Gal and UDP-GalNAc donors. Comparisons of the kinetic constants for alternative donor and acceptor pairs suggest that the GTB mechanism is Theorell-Chance where donor binding precedes acceptor binding. GTB operates with retention of configuration at the anomeric center of the donor. Retaining reactions are thought to occur via a double-displacement mechanism with formation of a glycosyl-enzyme intermediate consistent with the proposed Theorell-Chance mechanism.     

Purification and characterization of (1→3, 1→4)-β-glucan endohydrolases from germinated wheat (Triticum aestivum)

A (13, 14)--glucan 4-glucanohydrolase [(13, 14)--glucanase, EC 3.2.1.73] was purified to homogeneity from extracts of germinated wheat grain. The enzyme, which was identified as an endohydrolase on the basis of oligosaccharide products released from a (13, 14)--glucan substrate, has an apparent pI of 8.2 and an apparent molecular mass of 30 kDa. Western blot analyses with specific monoclonal antibodies indicated that the enzyme is related to (13, 14)--glucanase isoenzyme EI from barley. The complete primary structure of the wheat (13, 14)--glucanase has been deduced from nucleotide sequence analysis of cDNAs isolated from a library prepared using poly(A)⁺ RNA from gibberellic acid-treated wheat aleurone layers. One cDNA, designated LW2, is 1426 nucleotide pairs in length and encodes a 306 amino acid enzyme, together with a NH₂-terminal signal peptide of 28 amino acid residues. The mature polypeptide encoded by this cDNA has a molecular mass of 32085 and a predicted pI of 8.1. The other cDNA, designated LW1, carries a 109 nucleotide pair sequence at its 5 end that is characteristic of plant introns and therefore appears to have been synthesized from an incompletely processed mRNA. Comparison of the coding and 3-untranslated regions of the two cDNAs reveals 31 nucleotide substitutions, but none of these result in amino acid substitutions. Thus, the cDNAs encode enzymes with identical primary structures, but their corresponding mRNAs may have originated from homeologous chromosomes in the hexaploid wheat genome.     

Differential expression of enzyme activities initiating anoxic metabolism of various aromatic compounds via benzoyl-CoA

The regulation of the expression of enzyme activities catalyzing initial reactions in the anoxic metabolism of various aromatic compounds was studied at the whole cell level in the denitrifying Pseudomonas strain K 172. The specific enzyme activities were determined after growth on six different aromatic substrates (phenol, 4-hydroxybenzoate, benzoate, p-cresol, phenylacetate, 4-hydroxyphenylacetate) all being proposed to be metabolized anaerobically via benzoyl-CoA. As a control cells were grown on acetate, or aerobically on benzoate. The expression of the following enzyme activities was determined.Phenol carboxylase, as studied by the isotope exchange between ¹⁴CO₂ and the carboxyl group of 4-hydroxybenzoate; 4-hydroxybenzoyl-CoA reductase (dehydroxylating); p-cresol methylhydroxylase; 4-hydroxybenzyl alcohol dehydrogenase; 4-hydroxybenzaldehyde dehydrogenase; coenzymeA ligases for the aromatic acids benzoate, 4-hydroxybenzoate, phenylacetate, and 4-hydroxyphenylacetate; phenylglyoxylate: acceptor oxidoreductase and 4-hydroxyphenylglyoxylate: acceptor oxidoreductase; aromatic alcohol and aldehyde dehydrogenases.The formation of most active enzymes is strictly regulated; they were only induced when required, the basic activities being almost zero. The observed whole cell regulation pattern supports the postulate that the enzyme activities play a role in anoxic aromatic metabolism and that the compounds are degraded via the following intermediates: Phenol 4-hydroxybenzoate 4-hydroxybenzoyl-CoA benzoyl-CoA; 4-hydroxybenzoate 4-hydroxybenzoyl-CoA benzoyl-CoA; benzoate benzoyl-CoA; p-cresol 4-hydroxybenzaldehyde 4-hydroxybenzoate 4-hydroxybenzoyl-CoA benzoyl-CoA; phenylacetate phenylacetyl-CoA phenylglyoxylate benzoyl-CoA plus CO₂; 4-hydroxyphenylacetate 4-hydroxyphenylacetyl-CoA 4-hydroxyphenylglyoxylate 4-hydroxybenzoyl-CoA plus CO₂ benzoyl-CoA.     

A quantitative method for separating reaction components of CMP-sialic acid: Lactosylceramide sialyltransferase using Sep Pak C18 cartridges

A rapid procedure is described for the separation of CMP-sialic acid:lactosylceramide sialyltransferase reaction components using Sep Pak C₁₈ cartridges. The quantitative separation of the more polar nucleotide sugar, CMP-sialic acid, and its free acid from the less polar G_M3-ganglioside is simple and rapid relative to previously described methods. Recovery of G_M3 is optimized by the addition of phosphatidylcholine to the reaction mixture prior to the chromatographic step. Using rat liver Golgi membranes as a source of CMP-sialic acid: lactosylceramide sialyltransferase activity (G_M3 synthase; ST-1), the transfer of [¹⁴C] sialic acid from CMP-[¹⁴C] sialic acid to lactosylceramide can be quantified by this assay. The procedure is reliable and may be applicable to the isolation of ganglioside products in otherin vitro glycosyltransferase assays.Abbreviations G_M3 G_M3-ganglioside - II³NeuAc-LacCer NeuAc2-3Gal1-4Glc1-1Cer - G_D1a G_D1a-ganglioside, IV³NeuAc, II³NeuAc-GgOse₄Cer, NeuAc2-3Gal1-3GalNac1-4(NeuAc2-3)Gal1-4Glc1-1Cer - G_D3 G_D3-ganglioside, II³(NeuAc)₂LacCer, NeuAc2-8NeuAc2-3Gal1-4Glc1-1Cer - GgOse₄Cer asialo-G_M1 Gal1-3GalNAc1-4Gal1-4Glc1-1Cer - FucG_MI fucosyl-G_MI-ganglioside, Fuc1-2Gal1-3GalNAc1-4Gal1-4 Glc1-1Cer - ST-1 G_M3 synthase, CMP-sialic acid:lactosylceramide sialyltransferase - LacCer lactosylceramide, Gal1-4Glc1-1Cer - CMP-NeuAc cytidine 5-monophospho-N-acetylneuraminic acid - PC phosphatidylcholine - PMSF phenylmethylsulfonyl fluoride     

The ability of acidic pH,growth inhibitors,and glucose to increase the proton motive force and energy spilling of amino acid-fermenting <Emphasis Type="Italic">Clostridium sporogenes</Emphasis> MD1 cultures

Clostridium sporogenes MD1 grew rapidly with peptides and amino acids as an energy source at pH 6.7. However, the proton motive force (p) was only –25 mV, and protonophores did not inhibit growth. When extracellular pH was decreased with HCl, the chemical gradient of protons (ZpH) and the electrical membrane potential () increased. The p was –125 mV at pH 4.7, even though growth was not observed. At pH 6.7, glucose addition did not cause an increase in growth rate, but increased to –70 mV. Protein synthesis inhibitors also significantly increased . Non-growing, arginine-energized cells had a of –80 mV at pH 6.7 or pH 4.7, but was not detected if the F₁F₀ ATPase was inhibited. Arginine-energized cells initiated growth if other amino acids were added at pH 6.7, and and ATP declined. At pH 4.7, ATP production remained high. However, growth could not be initiated, and neither nor the intracellular ATP concentration declined. Based on these results, it appears that C. sporogenes MD1 does not need a large p to grow, and p appears to serve as a mechanism of ATP dissipation or energy spilling.Mandatory disclaimer: Proprietary or brand names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product, and exclusion of others that may be suitable.     

Alpha-tocopherol in the retinal outer segment of bovine eyes

Summary -Tocopherol was identified in lipid extracts of bovine retinal outer segment (ROS) preparations. Positive identification was obtained by the thin layer chromatographic characteristics of the tocopherol form and its oxidation product -tocopherylquinone, and by the ultraviolet spectrum of the oxidized and KBH₄-reduced form of the tocopherylquinone. In the ROS preparations used, -tocopherol chromanol was the predominant species, the quinone form accounting for 25% or less of the total. The concentration of -tocopherol in the ROS preparations was about 0.1 mole -tocopherol per mole rhodopsin, or about 1 nmole/mg, protein. Mitochondria from bovine retina contained about 0.4 nmole -tocopherol per mg protein.     

Localization of a gene for human α-galactosidase B (=N-Acetyl-α-D-Galactosaminidase) on chromosome 22

Summary The localization of the structural gene for human -galactosidase B (=N-acetyl--galactosaminidase) was investigated by means of man-Chinese hamster and man-mouse somatic cell hybrids. The hybrid clones were analyzed for chromosomes and for a large number of known enzyme markers. The lysates of the hybrid cells were treated with Sepharose-coupled antihuman -galactosidase B and the activity of the adsorbed enzyme was measured on the Sepharose beads as N-acetyl--galactosominidase. The results show that the structural gene for human -galactosidase B is situated on chromosome 22, and that there is no structural relationship between human -galactosidase A and human -galactosidase B.     

The effect of some macronutrients on adventitious root development on scion apple cultivars in vitro

The influence of some macronutrients, especially NH₄NO₃ and KNO₃, on root development of microcuttings from 3 apple scion cultivars is discussed. A reduction of the level of NH₄NO₃ in the medium from full strength to 1/4 strength significantly increased the percentage rooting of Gala and Royal Gala, but not Jonagold. Further reduction of NH₄NO₃ level from 1/4 strength to zero significantly reduced the percentage of rooting in Gala but not Royal Gala. Jonagold rooted best at zero concentration NH₄NO₃. Without NH₄NO₃, rooting percentages were as high as 100% for all 3 cultivars when KNO₃ was provided at full strength. The results show that adventitious roots can be induced on apple scion cultivars by media manipulation.     

Mechanisms for controlling balance between light input and utilisation in the salt tolerant alga Dunaliella C9AA

The yield of photosynthetic O₂ evolution was measured in cultures of Dunaliella C9AA over a range of light intensities, and a range of low temperatures at constant light intensity. Changes in the rate of charge separation at Photosystem I (PS I) and Photosystem II (PS II) were estimated by the parameters _{PS I} and _{PS II} . _{PS I} is calculated on the basis of the proportion of centres in the correct redox state for charge separation to occur, as measured spectrophotometrically. _{PS II} is calculated using chlorophyll fluorescence to estimate the proportion of centres in the correct redox state, and also to estimate limitations in excitation delivery to reaction centres. With both increasing light intensity and decreasing temperature it was found that O₂ evolution decreased more than predicted by either _{PS I} or _{PS II}. The results are interpreted as evidence of non-assimilatory electron flow; either linear whole chain, or cyclic around each photosystem.Abbreviations F₀ dark level of chlorophyll fluorescence yield (PS II centres open) - F_m maximum level of chlorophyll fluorescence yield (PS II centres closed) - F_v variable fluorescence (F_m-F₀) - PS I Photosystem I - PS II Photosystem II - P₇₀₀ reaction centre chlorophyll(s) of PS I - q_N coefficient of non-photochemical quenching of chlorophyll fluorescence - q_P coefficient of photochemical quenching of fluorescence yield - q_E high-energy-state quenching coefficient - _{PS I} yield of PS I - _{PS II} yield of PS II - _S yield of photosynthetic O₂ evolution - _P intrinsic yield of open PS II centres     

Organization of α-chain genes among Hb G-Philadelphia heterozygotes in association with Hb S, β-thalassemia,and α-thalassemia-2

The percentages of the -chain variant Hb G-Philadelphia (Hb G) or ₂ 68 AsnLys₂ were evaluated in 84 adult and 18 newborn heterozygotes. These included members of three families who were studied in more detail by nucleic acid hybridization techniques. The adult heterozygotes fell in two categories, one with a higher proportion of Hb G [46.5±1.0% (SD), N=21] and another with lower values (33.9±3.4%, N=63). Among the newborn heterozygotes, two babies fell in the category with the higher proportion of Hb G while 16 babies gave values between 25 and 34%. Studies of -chain gene organization on the parents of one neonate with a Hb G level of 27% at birth and 37% at 8 months excluded the presence of chromosomes with triplicated -chain genes which could lead to the ^0G/ genotype. Rather, these studies on five Hb G heterozygotes from three families confirmed the linkage between Hb G and a specific type of -thalassemia-2 associated with the presence of a 16-kbp Bgl II fragment which most probably carries the ^G locus since it has been found in 19 Hb G heterozygotes studied to date. The presence of an -thal-2 heterozygosity and three -chain genes (^0G/) was confirmed among Hb G heterozygotes with lower proportions of this variant. It is likely that the even lower values found in some newborn could arise through defective assembly of ^G- dimers. The presence of an -thal-2 homozygosity and two active -chain genes, one on each chromosome (^0G/⁰), was confirmed among heterozygotes with the higher proportion of Hb G. One of each of these categories was present in each of the three families investigated. This type of variability in the number of active -chain genes due to a heterozygosity or a homozygosity for -thalassemia-2 explains the trimodality of Hb S percentages among heterozygotes and the atypical hematological or biosynthetic features among patients with -thalassemia and sickle-cell syndromes.This research was supported by USPHS Research Grants HLB-05168 and HLB-15158 and by designated research funds of the Veterans Administration. This is Contribution No. 0693 of the Department of Cell and Molecular Biology, Medical College of Georgia, Augusta.     

An elongated segment of DNA observed between two human α globin genes

Summary Detailed restriction enzyme analysis of the DNA from a Chinese female showed that one of her chromosomes had a >17.5 kb deletion of DNA, including the , 2, and 1 globin genes, which is present in many Southeast Asians with an -thalassemia-1 chromosome. Her normal chromosome had the expected cluster of -like globin genes (5----2-1-3), but the segment of DNA between the two globin genes was elongated by some 0.5–0.7 kb. Analyses of various restriction sites suggested that this normal variant of the human globin gene complex is due to a crossover between a normal chromosome with () and a chromosome with an -thalassemia-2 (–^3.7) and an -21-hybrid gene.     

Selection studies in sugarcane (Saccharum sp. hybrids)

Summary An approximate method to determine sample size for the estimation of population variance, ², is given. The estimate of ² is denoted as s² . Based on the assumption of a normal distribution for (s²/²–1), the sample size is approximately equal to 20,000 z² _p,/k²; where z is a standard normal deviate, p is the probability that s² ( 100¦s² – ²¦/²) is less than, or equal to, a critical value k, and k (measured as gDs²) is the desired precision of s² .The expected value of s², with respect to sample size, and the expected cumulative frequencies of s² over sample size for various k values are given. Their goodness of fit to the observed results was satisfactory except for populations that were different from normal. The observed values were taken from a study on four yield components in five sugarcane polycross progenies, grown in two contrasting environments over 2 years in three selection stages.The expected s² was found to be independent of the population coefficient of variance.Research suppoted in part by USDA, ARS, grant #12-14-5001-34. Published with the approval of the Director as Paper No. 412 in the Journal Series of the Experiment Station, Hawaiian Sugar Planters' Association.     

Physiological relationship between the temperate phages lambda and phi80

Summary This work deals with the ability of phage 80 to provide defective mutants of with their missing functions. Functions Involved in Recombination. As shown by others, the Int mechanism of 80 cannot excise prophage . However, 80 efficiently excises recombinants from tandem dilysogens, using its Ter mechanism. Likewise, the nonspecific mechanism Red is interchangeable between 80 and . Maturation of DNA by 80. The Ter recombinants excised by 80 from tandem dilysogens are packaged into a 80 protein coat. This contrasts with the fact, already mentionned by Dove, that 80 is extremely inefficient for packaging phage superinfecting a -lysogen. The latter result is also found when the helper phage is a hybrid with the left arm of (80hy4 or 80hy41 — see Fig. 1). However, the maturation of the superinfecting is much more efficient if the 80hy used as a helper has the att-N region of (like 80hy1). Conversely a with the att-N region of 80 (hy6 — see Fig. 1) is packaged more efficiently by 80 or 80hy4 than by 80hy1. It is suggested that the maturation of chromosome superinfecting an immune cell requires a recombination with the helper phage. Vegetative Functions. Among the replicative functoons O and P, the latter only can be supplied by 80. That N mutants are efficiently helped by 80 does not tell that 80 provides the defective with an active N product; the chromosomes are simply packaged into a 80 coat. This shows that 80 is unable to switch on the late genes of . That neither 80 nor any of the 80hy tested can provide an active N product is shown in a more direct way by their complete failure to help N ^-r₁₄; this phage carries a polar mutation which makes the expression of genes O and P entirely N-dependant. The maturation of a N ^- by 80 contrasts with the fact that mutants affected in late genes (A, F or H) are not efficiently helped by 80. This suggests that the products coded by these genes are not interchangeable between 80 and , and that packaging of DNA into 80 coats is possible but inhibited when late proteins are present in the cell. Activation of the Late Genes. Among the im ₈₀ h ⁺ hybrids tested, only 80hy41 is able to switch on the late genes of a N defective mutant. This hybrid differs from the other hybrids studied here, by the fact that it has the Q-S-R region of (see Fig. 1). The results are consistant with the view that the product of Q gene is sufficient for activating the late genes of a DNA. N would thus control the expression of late genes only indirectly by controlling the expression of gene Q (Couturier & Dambly have independantly reached the same conclusion, 1970). Furthermore the failure of 80 and of the 80hy1 and 80hy4 to activate the late genes of would imply that these phages are unable to provide an Q product active on the chromosome Reciprocally, switches on the late genes of prophage 80hy41, but not of prophages 80hy1 and 80hy4. This suggests that the initiation of late genes expression takes place at a main specific site located in the Q-S-R region of the chromosome. The expression of the late genes would thus be sequential, and proceed through the left arm only when steaky ends cohere. Similar conclusions were reached independantly by Toussaint (1969) and by Herskowitz and Signer (1970).

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Ce travail a été réalisé dans le cadre du contrat d'association Euratom-U. L. B. 007-61-10 ABIB et avec l'aide du Fonds de la Recherche Fondamentale Collective.     

Bioassembly of acyl lipids in microspore-derived embryos of Brassica campestris L.

The native lipid composition and the capacity of cell-free extracts to biosynthesize acyl lipids in vitro were determined for the first time using the recently reported microspore-derived (MD) embryo system from the Brassica campestris low erucic acid line BC-2 (Baillie et al. 1992). The total lipid fraction isolated from midcotyledonary stage MD embryos (21 days in culture) was composed primarily of triacylglycerol (76%) with an acyl composition quite similar to that of mature BC-2 seed. When incubated in the presence of glycerol-3-phosphate, ¹⁴C 181-CoA, and reducing equivalents, homogenates prepared from 21-day cultured MD embryos were able to biosynthesize glycerolipids via the Kennedy pathway. The maximum in vitro rate of triacylglycerol biosynthesis could more than account for the known rate of lipid accumulation in vivo. The homogenate catalyzed the desaturation of 181 to 182 and to a lesser extent, 183. The newly-synthesized polyunsaturated fatty acids initially accumulated in the polar lipid fraction (primarily phosphatidic acid and phosphatidylcholine) but began to appear in the triacylglycerol fraction after longer incubation periods. As expected for a low erucic acid cultivar, homogenates of MD embryos from the BC-2 line were incapable of biosynthesizing very long chain monounsaturated fatty acyl moieties (201 and 221) from 181-CoA in vitro. Nonetheless, embryo extracts were still capable of incorporating these fatty acyl moieties into triacylglycerols when supplied with ¹⁴C 201-CoA or ¹⁴C 221-CoA. Collectively, the data suggest that developing BC-2 MD embryos constitute an excellent experimental system for studying pathways for glycerolipid bioassembly and the manipulation of this process in B. campestris.Abbreviations CPT sn-1,2-diacylglycerol cholinephosphotransferase - DAG diacylglycerol - DGAT diacylglycerol acyltransferase - DGDG digalactosyldiacylglycerol - G-3-P glycerol-3-phosphate - G-3-PAT glycerol-3-phosphate acyltransferase - LPA lyso-phosphatidic acid - LPAT lyso-phosphatidic acid acyltransferase - LPC lyso-phosphatidylcholine - LPCAT acyl-CoA: lyso-phosphatidylcholine acyltransferase - LPE lyso-phosphatidylethanolamine - MGDG monogalactosyldiacylglycerol - PA phosphatidic acid - PA Phosphatase, phosphatidic acid phosphatase - PC phosphatidylcholine - PE phosphatidylethanolamine - PG phosphatidylglycerol - TAG triacylglycerol - 181-CoA oleoyl-Coenzyme A - 181 oleic acid, cis-9-octadecenoic acid - 182 linoleic acid, cis-9,12-octadecadienoic acid - 183 -linolenic acid, cis-9,12,15-octadecatrienoic acid - 201 cis-11-eicosenoic acid - 221 erucic acid, cis-13-docosenoic acid; all other fatty acids are designated by number of carbon atoms: number of double bonds National Research Council of Canada Publication No. 35896     

Identification of restriction fragment length polymorphisms linked to genes controlling soluble solids content in tomato fruit

Summary Gene(s) conferring high soluble solids (SS) in tomato fruit had been backcrossed previously from a wild tomato species, Lycopersicon chmielewskii LA1028 ( 10% SS), into a L. esculentum cultivar, VF36 ( 5% SS), to derive a BC₅S₅ line, LA1563, similar to VF 36 but with 7–8% SS. DNAs from these lines and a tomato breeding line, H2038, were screened for restriction fragment length polymorphisms (RFLPs) using four restriction endonucleases and sixty clones chosen at random from a tomato cDNA library. Most of the cDNA clones (56) identified the same RFLP in VF 36 and LA1563 and a different RFLP in LA1028. However, two cDNA clones identified the same RFLP in LA1563 and LA1028 and a different RFLP in VF36. To determine whether RFLPs identified by these two cDNA clones were linked to SS genes, a H2038 x LA1563 F₂ population was screened for segregation of the RFLPs and for SS content. The segregation ratios of these RFLPs were consistent with ratios expected for codominant alleles at unlinked loci. Analysis of variance of SS content for different RFLP genotypic classes indicated that RFLP alleles at one of the loci were linked to genes controlling SS content. The RFLP allele from the high SS tomato line, LA1563, was associated with significantly higher SS content and, therefore, could be useful in selecting for high SS gene(s) in a tomato breeding program.