Influence of paclobutrazol on growth and development of fruit in Brassica juncea (L.) Czern and Coss

Foliar spraying of paclobutrazol(5, 10 and 20 g mL^–1) on Brassica juncea (cv. RLM 514) plants, at the green floral bud stage of the terminal inflorescence, exerted a profound effect on growth and metabolism of fruits (siliquae). Paclobutrazol caused a decrease in siliqua length but enhanced significantly siliqua width, seed size (diameter) and seed number per siliqua. Paclobutrazol increased dry matter production and also hastened the relative growth rate of the siliqua wall and seed. In paclobutrazol-treated plants the siliquae were darker green, and during active phases of growth both siliqua wall and seed exhibited higher total chlorophyll (Chl) content, decreased chl a/b ratios, greater hill reaction activity of chloroplasts and increased activities of -amylase, -amylase and invertase than controls. Paclobutrazol enhanced the levels of total soluble sugars, starch, protein and free amino acids in mature seeds. The seed oil content increased by 2 to 3 per cent with a treatment of 10 g mL^–1 pacolobutrazol.     

Indole-3-acetic acid concentration and ethylene evolution during early fruit development in peach

Ethylene evolution was measured from greenhouse-grown Jerseyglo peach fruits beginning 29 days after anthesis. Indole-3-acetic acid (IAA) levels were measured in the pericarp and seed tissues of individual fruits on a single shoot when variable ethylene evolution was noted. Despite hand-pollinating all flowers on the same day, variability within the shoot existed in fruit fresh weight, IAA levels, and ethylene evolution. Seed IAA concentration increased as fruit and seed fresh weight increased and ranged from 106 to 1572 ng. g^–1. As pericarp fresh weight increased, IAA levels in this tissue decreased. Ethylene evolution rates ranged from 0.21 to 1.07 nl. g.^–1 h^–1 and were not correlated with IAA concentration in seed, pericarp, or the whole fruit. High rates of ethylene evolution from the whole fruit occurred prior to increased IAA concentration in the seed.Fruits were excised from field-grown Redskin peach trees beginning 40 days after full bloom. Fruits from field sampled shoots appeared to be more physiologically advanced than the greenhouse-grown Jerseyglo fruits. Pericarp IAA concentration was low, ranging from 2.8 to 6.5 ng. g^–1. Seed concentrations accounted for 75% of the IAA found in the fruit and ranged from 239 to 1042 ng. g^–1. As with greenhouse-grown samples, whole fruit IAA concentration tended to decrease as fruits increased in fresh weight.     

Use of15N/14N rations to evaluate the food source of the mysid,Neomysis intermedia Czerniawsky,in a eutrophic lake in Japan

The stable isotope ratios of nitrogen were measured in the mysid,Neomysis intermedia, together with various biogenic materials in a eutrophic lake, Lake Kasumigaura, in Japan throughout a year of 1984/85. The mysid, particulate organic matter (POM, mostly phytoplankton), and zooplankton showed a clear seasonal change in ¹⁵N with high values in spring and fall, but the surface bottom mud did not. A year to year variation as well as seasonal change in ¹⁵N was found in the mysid. The annual averages of ¹⁵N of each material collected in 1984/85 are as follows: surface bottom mud, 6.3 (range: 5.7–6.9); POM, 7.9 (5.8–11.8); large sized mysid, 11.6 (7.7–14.3); zooplankton, 12.5 (10.0–16.4); prawn, 13.2 (9.9–15.4); goby, 15.1 (13.8–16.7). The degree of¹⁵N enrichment by the mysid was determined as 3.2 by the laboratory rearing experiments. The apparent parallel relationship between the POM and the mysid in the temporal patterns of ¹⁵N with about 3 difference suggests the POM (mostly phytoplankton) as a possible food source ofN. intermedia in this lake through the year.     

The “Bantu Clinic”: A Genealogy of the African Patient as Object and Effect of South African Clinical Medicine, 1930–1990

This paper is about power, medicine andthe identity of the African as a patient of westernmedicine. From a conventional perspective and asencoded in the current quest for wholeness thatcharacterises South African biomedical discourse, theAfrican patient – like any other patient – has alwaysexisted as an authentic and subjectified being, whosetrue attributes and experiences have been denied bythe mechanistic, reductionistic and ethnocentricpractices of clinical medicine. Against this liberalhumanist perspective on the body as ontologicallyindependent of power, this paper offers a Foucaultianreading of the African patient as – like any otherpatient – contingent upon the force relations immanentwithin and relayed through the clinical practices ofbiomedicine. A quintessential form of disciplinarymicro-power, these fabricate the most intimaterecesses of the human body as manageable objects ofmedical knowledge and social consciousness to makepossible the great control strategies of repression,segmentation and liberation that are the usual focusof conventional investigations into the place andfunction of medicine in society. Since the 1930s whenthe African body first emerged as a discrete object ofa secular clinical knowledge, these have repeatedlytransformed the attributes and identity of the Africanpatient, and the paper traces this archaeology ofSouth African clinical perception from then until the1990s to show how its quest for wholeness is not anend point of discovery or liberation, but merelyanother ephemeral crystallization of socio-medicalknowledge in a constantly changing force field ofdisciplinary power.     

Spectral position control of dye absorption band maximum in an orienting matrix

The continuous control of the maximum position of the dye absorption band (the zero of the derivative dD ()/d of the cell's optical density D ()) in a nematic matrix is demonstrated experimentally, as a result of changing the angle between the optical axis of a planar-oriented sample and the plane of polarization of absorbed light incident normal to the optical axis. The theory proposed describes quantitatively the experimental dependence (). The rotation of the polarizer with given frequency results in the spectral position modulation of the solute band maximum () within (=0°)–(90°)=700 cm^–1.     

The relation of proton motive force,adenylate energy charge and phosphorylation potential to the specific growth rate and efficiency of energy transduction inBacillus licheniformis under aerobic growth conditions

The magnitude of the proton motive force (p) and its constituents, the electrical () and chemical potential (-ZpH), were established for chemostat cultures of a protease-producing, relaxed (rel ^–) variant and a not protease-producing, stringent (rel ⁺) variant of an industrial strain ofBacillus licheniformis (respectively referred to as the A- and the B-type). For both types, an inverse relation of p with the specific growth rate was found. The calculated intracellular pH (pH_in) was not constant but inversely related to . This change in pH_in might be related to regulatory functions of metabolism but a regulatory role for pH_in itself could not be envisaged. Measurement of the adenylate energy charge (EC) showed a direct relation with for glucose-limited chemostat cultures; in nitrogen-limited chemostat cultures, the EC showed an approximately constant value at low and an increased value at higher . For both limitations, the ATP/ADP ratio was directly related to .The phosphorylation potential (G'p) was invariant with . From the values for G'p and p, a variable H⁺/ATP-stoichiometry was inferred: H⁺/ATP=1.83+0.52µ, so that at a given H⁺/O-ratio of four (4), the apparent P/O-ratio (inferred from regression analysis) showed a decline of 2.16 to 1.87 for =0 to _max (we discuss how more than half of this decline will be independent of any change in internal cell-volume). We propose that the constancy of G'p and the decrease in the efficiency of energy-conservation (P/O-value) with increasing are a way in which the cells try to cope with an apparent less than perfect coordination between anabolism and catabolism to keep up the highest possible with a minimum loss of growth-efficiency. Protease production in nitrogen-limited cultures as compared to glucose-limited cultures, and the difference between the A- and B-type, could not be explained by a different energy-status of the cells.Abbreviations CCCP carbonylcyanide-p-trichloromethoxyphenylhydrazone - DW dry weight of biomass - F Faraday's constant, 96.6 J/(mV × mol) - Fo chemostat outflow-rate (ml/h) - FCCP carbonylcyanide-p-trifluoromethoxyphenylhydrazone - G'p phosphorylation potential, the Gibbs energy change for ATP-synthesis from ADP and P_i - G'⁰p standard Gibbs energy change at specified conditions - H⁺/ATP number of protons translocated through - ATP synthase in synthesis of one ATP - H⁺/O protons translocated during transfer of 2 electrons from substrate to oxygen - specific growth rate (1/h) - _H+ transmembrane electrochemical proton potential, J/mol - M_b molar weight (147.6 g/mol) of bacteria with general cell formula C_6.0H_10.8O_3.0N_1.2 - pH_out,in extracellular, intracellular pH - P_i (intracellular) inorganic phosphate - p proton motive force, mV - pH transmembrane pH-difference - transmembrane electrical potential, mV - P/O number of ADP phosphorylated to ATP upon reduction of one O^2– to H₂O by two electrons transferred through the electron transfer chain - P/O (H⁺/O) × (H⁺/ATP)^–1 - P/O_F, P/O_N P/O with the two electrons donated by resp. (NADH + H⁺) and FADH - q specific rate of consumption or production (mol/g DW × h) - rel ⁺,rel ^– stringent, relaxed genotype - R universal gas constant, 8.36 J/(mol × degree) - T absolute temperature - TPMP⁺ triphenylmethylphosphonium ion - TPP⁺ tetraphenyl phosphonium ion - Y growth yield, g DW/mol - Z conversion constant=61.8 mV for 310 K (37 °C) - ZpH transmembrane proton potential or chemical potential, mV     

The Use of the [13C]/[12C] Ratio for the Assay of the Microbial Oxidation of Hydrocarbons

The study deals with a comparative analysis of the relative abundances of the carbon isotopes ¹²C and ¹³C in the metabolites and biomass of the Burkholderia sp. BS3702 and Pseudomonas putida BS202-p strains capable of utilizing aliphatic (n-hexadecane) and aromatic (naphthalene) hydrocarbons as sources of carbon and energy. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of Burkholderia sp. BS3702 on n-hexadecane (¹³C = –44.6 ± 0.2) were characterized by the values of ¹³C_{CO 2} = –50.2 ± 0.4, ¹³C_biom = –46.6 ± 0.4, and ¹³C_exo = –41.5 ± 0.4, respectively. The isotope compositions of the carbon dioxide, biomass, and exometabolites produced during the growth of the same bacterial strain on naphthalene (¹³C = –21 ± 0.4) were characterized by the isotope effects ¹³C_{CO 2} = –24.1 ± 0.4, ¹³C_biom = –19.2 ± 0.4, and ¹³C_exo = –19.1 ± 0.4, respectively. The possibility of using the isotope composition of metabolic carbon dioxide for the rapid monitoring of the microbial degradation of petroleum hydrocarbons in the environment is discussed.     

Normal and lysine-containing zeins are unstable in transgenic tobacco seeds

Chimeric genes composed of the -phaseolin promoter, an -zein coding sequence and its modified versions containing lysine codons, and a -zein polyadenylation signal were inserted into the genome of tobacco by Agrobacterium-mediated transformation. -Zein mRNA levels in the transgenic tobacco seeds 20 days after self-pollination varied between 1.0% and 2.5% of the total mRNA population. At 25 days after pollination the 19 kDa -zein was immunologically detected with a polyclonal antiserum in protein extracts from the seeds of transgenic plants. The transgenic plant with the highest level of zein gene expression had an -zein content that was approximately 0.003% of the total seed protein. The amount of -zein in other transgenic plants varied between 1 × 10^–4% and 1 × 10^–5% of the total seed protein. The differences in the amounts of mRNA and protein did not correlate with the lysine substitutions introduced into the -zein protein. Polysomes translating -zein mRNA isolated from tobacco seeds contained fewer ribosomes than those from maize endosperm, but this did not appear to be the cause of the inefficient protein synthesis. In vivo labelling and immunoprecipitation indicated that newly synthesized -zein was degraded in tobacco seeds with a half-life of less than 1 hour.     

A monoclonal antibody chromosome marker analysis used to locate a loose smut resistance gene in wheat chromosome 6A

Many genes have been located in wheat chromosomes, yet little is known about the location of genes for resistance to Ustilago tritici, which causes loose smut. Crosses were made between the loose smut susceptible alien substitution lines Cadet 6Ag(6A) and Rescue 6Ag(6A) (lines in which Agropyron chromosome 6 is substituted by wheat chromosome 6A) and four cultivars resistant to U. tritici race T19: Cadet, Kota, Thatcher and TD18. The segregating progeny were tested for reaction to race T19 and for the level of binding with a monoclonal antibody specific to a chromosome 6A-coded seed protein. The antibody, which does not bind to seed protein extracts in the absence of the 6A chromosome, was used as a chromosome marker. An association was established between resistance to race T19 and the presence of chromosome 6A for each of the cultivars tested, indicating that resistance to race T19 resides in chromosome 6A. Ustilago tritici race T19 resistance in Cadet appears to be located in the short arm of chromosome 6A, based on the evaluation of the Cadet 6A long ditelosomic stock, which was susceptible, and the Cadet 6A-short: 6-Agropyron- short alien translocation stock, which was resistant.     

Photoperiodism and thermoperiodism in the predatory mite Amblyseius potentillae are probably based on the same mechanism

Summary A comparative study was made of the photoperiodic and thermoperiodic induction of diapause in the phytoseiid mite Amblyseius potentillae. Sensitivity to thermoperiod was found to be highest during the protonymphal and deutonymphal stages, with some sensitivity still being present in the young adult. Summation of both photoperiodic and thermoperiodic cycles was shown to take place, which demonstrated the presence of a photoperiodic counter as well as a thermoperiodic counter in these mites. Vitamin A appeared to be necessary for some early step in the physiological mechanism of diapause induction and not just for the expression of the diapause response. The light sensitivity threshold for photoperiodic induction of diapause was found to be extremely low, viz. less than 0.02 W/cm². Moreover, the light sensitivity threshold appeared to be strongly temperature dependent in A. potentillae. Experiments in which the mites experienced various sequences of short-day photoperiods and short-day thermoperiods, applied either concurrently or in succession, showed that the information collected by the photoperiodic counter and the thermoperiodic counter is integrated into one induction sum. These results strongly suggest that photoperiodic and thermoperiodic induction of diapause in these mites is based on the same physiological mechanism.Abbreviations DD continuous darkness - LL continuous light - LD light-dark cycle (e.g. LD 16:8 is a cycle of 16 h of light and 8 h of darkness) - TC thermoperiodic cycle (e.g. TC 16:8 (27°: 15°) is a thermoperiod with a 16 h thermophase of 27 °C and an 18 h cryophase of 15°C)     

Effect of photoperiod on in vitro tuberization of potato (Solanum tuberosum L.)

Single-node cuttings of potato cultivars Jemseg, Katahdin, Russet Burbank and Superior were cultured on a multiplication medium containing MS salts and no growth regulators. Cultures were exposed to 8 h (SD) and 16 h (LD) photoperiodic regimes. The subsequent plantlets were excised and single node cuttings from each photoperiodic regime were placed under SD or LD on a second medium containing growth regulators which promoted tuberization. Production of microtubers was strongly influenced by genotype and by photoperiodic treatments. Superior produced stunted plantlets and some microtubers under SD conditions in the multiplication medium. The number of microtubers formed by Jemseg was not influenced by photoperiod. However, Katahdin and Russet Burbank formed fewer microtubers under LD-LD conditions compared to LD-SD, SD-SD and SD-LD regimes. Compared with the other regimes, LD-SD photoperiod generally promoted microtuber formation with larger diameters and significantly (p<0.05) greater fresh weight. The intensity of the tuberization stimulus was affected by daylength, and this was characterized by microtubers with secondary tubers, the growth of more than one axillary microtuber, and microtubers subtended by stolons. The maturity group of the potato cultivars and photoperiodic regime in vitro strongly influenced the production of microtubers. These results can be employed to adapt light regimes for multiplication and tuberization to the specific requirements for cultivars from different maturity groups, and thus increase the efficiency of potato multiplication protocols.     

Meiosis and fertility of F1 hybrids between hexaploid bread wheat and decaploid tall wheatgrass (Thinopyrum ponticum)

As the first step in the transfer of barely yellow dwarf virus resistance and salt tolerance from decaploid tall wheatgrass (Thinopyrum ponticum) into hexaploid bread wheat (Triticum aestivum L.), octoploid intergeneric hybrids (2n = 8x = 56) were synthesized by crossing the tall wheatgrass cultivar Alkar with wheat cvs. Fukuhokomugi (Fuko) and Chinese Spring. (Fuko x Alkar) F₁ hybrids were studied in detail. The F₁ hybrids were perennial and generally resembled the male wheatgrass parent with regard to morphological features and gliadin profile. Most hybrids were euploid with 56 chromosomes and showed high chromosome pairing. On an average, in 6 hybrids 83.6% of the complement showed chiasmatic association, some between wheat and wheatgrass chromosomes. Such a high homoeologous pairing would be obtained if Ph1, the major homoeologous pairing suppressor in wheat, was somehow inactivated. Some of the Fuko x Alkar hybrids had high pollen fertility (18.5–42.0% with a mean of 31.5%) and high seed fertility (3–29 seeds wtih a mean of 12.3 seeds per spike), offering excellent opportunities for their direct backcrossing onto the wheat parent.     

Patterns of direct and indirect embryogenesis from mesophyll protoplasts of Medicago sativa

Clones of three cultivars of Medicago sativa (Rambler, Regen S and Rangelander) were used as sources of mesophyll protoplasts. Although all three clones readily produced protoplasts, the subsequent development patterns in culture varied greatly among genotypes, with protoplasts from Regen S and Rambler forming calli which could be induced to form embryos, and protoplasts from Rangelander undergoing direct embryogenesis. Protoplasts of Regen S exhibited high rates of division while those of Rangelander tended to aggregate with only a few cells per aggregate surviving. The surviving cells gave rise to proembryos within the aggregates; these proembryos developed into differentiated embryos after 5–7 weeks of culture. Based on the initial protoplast population, the efficiency of embryo formation averaged 0.13% and ranged from 0.001–0.4%. Observations during the early stages of culture indicated that cell aggregation was a prerequisite for direct embryogenesis.     

Expression of enzymatically active,recombinant barley α-glucosidase in yeast and immunological detection of α-glucosidase from seed tissue

An -glucosidase cDNA clone derived from barley aleurone tissue was expressed in Pichia pastoris and Escherichia coli. The gene was fused with the N-terminal region of the Saccharomyces cerevisiae -factor secretory peptide and placed under control of the Pichia AOX1 promoter in the vector pPIC9. Enzymatically active, recombinant -glucosidase was synthesized and secreted from the yeast upon induction with methanol. The enzyme hydrolyzed maltose > trehalose > nigerose > isomaltose. Maltase activity occurred over the pH range 3.5–6.3 with an optimum at pH 4.3, classifying the enzyme as an acid -glucosidase. The enzyme had a K_m of 1.88 mM and V_max of 0.054 µmol/min on maltose. The recombinant -glucosidase expressed in E. coli was used to generate polyclonal antibodies. The antibodies detected 101 and 95 kDa forms of barley -glucosidase early in seed germination. Their levels declined sharply later in germination, as an 81 kDa -glucosidase became prominent. Synthesis of these proteins also occurred in isolated aleurones after treatment with gibberellin, and this was accompanied by a 14-fold increase in -glucosidase enzyme activity.Abbreviations: AGL, barley seed -glucosidase; rAGL, recombinant barley seed -glucosidase; BMGY, buffered glycerol-complex medium; BMMY, buffered methanol-complex medium; GA, gibberellic acid; UTR, untranslated region.     

Sources and inheritance of resistance to leaf curl virus in Lycopersicon

Summary One hundred and twenty-two varieties, lines and wild accessions of Lycopersicon were screened under three different regimes during the autumn/winter season of 1982–83 and 1983–84 for resistance to tomato leaf curl virus (TLCV). L. hirsutum f. glabratum (B6013) and L. hirsutum f. typicum (A1904) proved to be highly resistant to TLCV in all three environments. Various accessions of L. peruvianum were also highly resistant. L. pimpinellifolium (A1921) exhibited no TLCV symptoms within 90 days. Of the cultivated varieties, Acc 99 exhibited the minimim score for susceptibility; AC 142, Collection No. 2, Kalyanpur Angurlata and HS 101 had a low rating for virus incidence. The inheritance of resistance was studied in the interspecific crosses between a TLCV resistant line of L. pimpinellifolium (A1921) and five (HS 101, HS 102, HS 110, Pusa Ruby and Punjab Chhuhara) susceptible cultivars of L. esculentum. Parents, F₁, F₂ and backcross progenies were artificially inoculated with local strains of TLCV using vector the viruliferious whitefly, Bemisia tabaci (Genn.). Data indicated that the resistance of L. pimpinellifolium (A 1921) is monogenic and incompletely dominant over susceptibility.     

Sequence- and Regio-Selectivity in the Montmorillonite-Catalyzed Synthesis of RNA

The six binary montmorillonite clay-catalyzed reactions of the5-phosphorimidazolides of adenosine, cytidine, guanosine anduridine were performed and the eight dimers from each reactionwere separated and analyzed by HPLC. A 16–51-fold higher yieldof the 5-purine-pyrimidine dimers over that of the5-pyrimidine-purines was observed. The total yield of the5-purine-pyrimidine dimers was in the 50–70% range while thatof the 5-pyrimidine-purine dimers was 1.3–7.0%. Less sequenceselectivity was observed in the homodimers formed.Regioselectivity for the formation of 3, 5-phosphodiesterbonds over that found in the absence of clay was observed. The5-purine-pyrimidine, 5-pyrimidine-pyrimidine and5-purine-purine dimers had 3, 5-links in about half of theirphosphodiester bonds. The percent phosphodiester links in the5-pyrimidine-pyrimidine dimers was 18%, a value close to thatobserved in the absence of the montmorillonite catalyst. Themontmorillonite-catalyzed reaction of all four activatednucleotides was performed and the 24 products were separated andanalyzed. The trends observed in the binary reactions wereconfirmed and the results also showed that the relativereactivity of the activated monomers was A>G>C>U in theratio 8.2: 4.8: 1.3: 1 respectively. No 5-pyrimidine-purineswith a 5-U and pG³pU, pC³pAand pC³pG weredetected. These studies suggest that a limited population ofRNAs would have formed in catalyzed prebiotic reactions.     

O-Glycosidically linked oligosaccharides from peptidorhamnomannans ofSporothrix schenckii

-Elimination of peptidorhamnomannans purified from yeast-like and mycelial phases ofSporothrix schenckii released neutral and acidic reduced oligosaccharides that were O linked to serine and/or threonine. Man-(1–2)Man-ol, Rha(1–3)Man(1–2)Man-ol, Rha(1–4)GlcA(1–2)Man(1–2)Man-ol, and Rha(1–4)[Rha(1–2)] GlcA(1–2)Man(1–2)Man-ol were characterized based on methylation analysis, proton magnetic resonance and fast atom bombardment mass spectrometry.Abbreviations FAB fast atom bombardment - GLC gas liquid chromatography - GlcA d-glucopyranosyluronic acid - Man d-mannopyranose - Man-ol d-mannitol - MS mass spectrometry - NMR nuclear magnetic resonance - Rha l-rhamnopyranose     

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.     

Triple hybridization with cultivated barley (Hordeum vulgare L.)

Summary A crossing programme for trispecific hybridization including cultivated barley (Hordeum vulgare L.) as the third parent was carried out. The primary hybrids comprised 11 interspecific combinations, each of which had either H. jubatum or H. lechleri as one of the parents. The second parent represented species closely or distantly related to H. jubatum and H. lechleri. In trispecific crosses with diploid barley, the seed set was 5.7%. Crosses with tetraploid barley were highly unsuccessful (0.2% seed set). Three lines of diploid barley were used in the crosses, i.e. Gull, Golden Promise and Vada. Generally, cv Gull had high crossability in crosses with related species in the primary hybrid. It is suggested that Gull has a genetic factor for crossability not present in cv Vada and cv Golden Promise. One accession of H. brachyantherum used in the primary hybrid had a very high crossability (seed set 54.7%) in combination with cv Vada but no viable offspring was produced. In all, two trispecific hybrids were raised, viz. (H. lechleri x H. brevisubulatum) x Gull (2n=7–30) and (H. jubatum x H. lechleri) x Gull (2n=20–22). The first combination invariably had a full complement of seven barley chromosomes plus an additional chromosome no. 7, but a varying number of chromosomes (19–22) of the wild-species hybrid. The second combination had a full set of barley chromosomes. The meiotic pairing was low in both combinations.     

The influence of cation and gelling agent concentrations on vitrification of apple cultivars in vitro

Shoot tips of York and Vermont Spur Delicious apples (Malus domestica Borkh.) were cultured in vitro to test the influence of K⁺, Mg⁺⁺ and gelling agent concentrations on vitrification. These concentrations were 20.05, 14.05 and 8.05 mM K⁺, 1.5 and 3.0 mM Mg⁺⁺, 7.0 g/l Difco Bacto agar and 1.0, 1.5 and 2.0 g/l Gelrite. The lowest K⁺ level produced a higher percentage of vitrified shoots, affected tissue appearance, reduced shoot number and shoot elongation and apparently altered shoot metabolic activity. Gelrite consistently produced vitrified leaves and stems, even though media gelled with 1.5 g/l Gelrite presented the same apparent gel firmness as using 7 g/l Difco Bacto agar, which did not induce vitrification. Less shoot elongation, fewer total shoots, and more usable shoots of York were obtained on Bacto-agar, while similar but less noticeable effects were obtained with Vermont Spur Delicious. The results presented here show that vitrification can be studied in a standardized system in which the only change is substitution of one gelling agent for another.