Organization of inputs to motoneurons during fictive respiration in the isolated lamprey brain

Summary The intracellular activity of motoneurons during fictive respiration in the isolated lamprey brain was investigated. In association with each respiratory cycle three distinct PSP phases were observed: an early, low amplitude EPSP phase; a large, brief EPSP phase that drove action potentials; and a subsequent IPSP phase (Fig. 1). Selective midline and trigeminal lesions, and trigeminal stimulation, demonstrated that the large excitatory and inhibitory phases were generated by a previously described pair of central pattern generators located in the trigeminal region of the medulla (V) (Figs. 3, 4). Lesion studies further showed that the low amplitude excitatory input could be produced independently of the trigeminal pacemakers (Figs. 3, 5), near the region of the medulla that contains the respiratory motoneurons (VII, IX, and X).In addition to normal fictive respiration, the isolated brain was found to produce several variations of the respiratory pattern. These motor programs, coughs, arousal breathing, and weak breathing, were distinguished from the normal respiratory pattern by their much longer burst durations, distinctive underlying synaptic input, and separate coordinating mechanism (Figs. 6–8). Activity similar to these motor programs could be independently produced by the caudal medulla after both trigeminal central pattern generators had been removed (Figs. 5, 6). Lesion studies, and the observation that respiratory-related neural activity ceased in the trigeminal region during the production of these long-duration programs, suggest that the caudal medulla also contains paired central pattern generators involved in lamprey respiration (Figs. 5, 9, 10).Abbreviations CPG central pattern generator - HRP horseradish peroxidase     

The CySF-L2 factor from dialysable human leucocyte extract activates natural killer cytotoxicity by induction of interferon γ

Summary The mechanism of natural killer (NK) cytotoxicity activation of human peripheral blood mononuclear cells (PBMC) by CySF-L2 was elucidated. CySF-L2 is a cytotoxicity-stimulating factor isolated from dialysable human leucocyte extract, which activates NK cytotoxicity against NK-sensitive and insensitive tumour cells (K562; Daudi; Raji; MOLT4) when preincubated with effector cells for 72 h. CySF-L2-mediated activation was synergistic to interleukin-2(IL-2)-mediated activation of NK cytotoxicity. Induction of interferon (IFN) release was the crucial step during CySF-L2-mediated NK cytotoxicity activation since enhancement of NK activity was completely blocked when anti-IFN antibodies were present during treatment of PBMC. Anti-IFN, anti-TNF (tumour necrosis factor ) anti-IL-1 and anti-IL-2 antibodies showed no blocking effect. Analysis of the supernatant culture medium after 72 h incubation of PBMC and their highly purified subpopulations demonstrated that CySF-L2 induced release of IFN from CD3⁺T cells and CD56⁺CD3^– NK cells and of TNF and prostaglandin E₂ from monocytes. CySF-L2 was also capable of activating NK cytotoxicity of highly purified (98%) CD56⁺CD3^– NK cells as well as of monocytes (94% pure). Cell cooperation studies connected with analysis of cytokine release and enhancement of NK cytotoxicity indicated that CySF-L2 might play an essential role in the up and down regulation of NK cytotoxicity by the cytokine network.     

Observations on phase-locking within the response of primary muscle spindle afferents to pseudo-random stretch

In order to uncover encoder properties of primary muscle spindle afferent fibers, time coupling (phase-locking) of action potentials on cyclic muscle stretch was studied by means of pseudo-random noise. In cats Ia action potentials were recorded from dorsal root filaments and the gastrocnemius muscles of one hind leg were stretched. The stimulus time course was a determined sequence of randomly varying muscle length which could be applied repeatedly (sequence duration 0.6 or 20 s). The noise amplitude (standard deviation of displacements) was varied between 5 and 300 m, the upper cut-off frequency of noise f _c was varied between 20 and 100 Hz. The responses to the consecutive pseudo-random noise cycles were displayed as raster diagrams and cycle histograms. Phaselocking characterized the responses at all noise amplitudes outside the near threshold range (>10 m). The higher and f _c , the stronger was the phase-locking of impulses on the stretch. When and f _c were selected to achieve high mean stretch velocities of about 500 mm/s, phase-locking was as precise as 0.15 ms, measured as the variability of spike occurrences with respect to stretch. The rasters obtained with low noise amplitudes (<40 m) showed a loose phase-locking and this gave insight into underlying mechanisms: The elicitation of action potentials caused by dynamic stretch can be prevented by a post-spike depression of excitability. This disfacilitation was very effective in counteracting weak stretch components within the random sequence and less effective or even missing when relatively strong stretch components could force the spike elicitation. This led to the reestablishment of phase-locked patterns. The results were discussed in relation to the known encoder models.     

Cloning bacterial genes with plasmid λdv

Summary Fragments ofEscherichia coli DNA carrying genes for -galactosidase, or for biosynthesis of guanine or biotin were recombined in vitro with dv DNA. The cloned recombinant molecules recovered from transformedE. coli cells consisted of a biologically functional bacterial DNA fragment and, except for dv-bio30-7, two dv monomer units: one of the dv units was used as the insertion site for the bacterial DNA, whereas the other was intact, and seemed to be responsible for the replication of the recombinant plasmid. The process which gives rise to these recombinant molecules at high frequency from mixtures of monomeric dv DNA's and bacterial DNA fragments is discussed.     

The Mutation Spectrum of the CFTR Gene in Cystic Fibrosis Patients from Bashkortostan

Mutations of CFTR were studied in patients with cystic fibrosis (CF) from Bashkortostan. In total, 15 mutations were observed and 51% of all mutant alleles identified. The most diagnostically significant mutations were delF508 (33.8%), 394delTT (3.52%), CFTRdele2,3(21kb) (1.41%), R334W (1.41%), 3849 + 10kbC T (1.41%), and N1303K (1.41%). Mutations G542X, 2184insA, S1196X, and W1282X were each found in less than 1% patients. Five new mutations and two neutral substitutions were revealed. These were I488M (exon 10), 1811 + 12A C (intron 11), T663S (exon 13), I1226R (exon 19), 4005 + 9A C (intron 20), 2097A C (A655A, exon 13), and 3996G C (V1288V, exon 20). Bashkortostan was shown to differ in the CFTR mutation spectrum from other regions of Russia. The results will allow direct DNA diagnostics of CF in far more families. Molecular screening of probands" relatives will contribute to identification and medical genetic counseling of heterozygous carriers, which is essential for CF prevention.     

Plant regeneration from Citrus protoplasts: Variability in methodological requirements among cultivars and species

Summary Nucellar callus lines were established from two orange cultivars (Nucellar Shamouti, Shamouti Landau), three mandarin cultivars (Murcott, Dancy, Ponkan) one grapefruit cultivar (Duncan) and sour orange (Citrus aurantium). These callus lines were initiated from in vitro cultured ovules of young fruits and maintained an embryogenic capacity. The plating efficiencies of protoplasts derived from these calli, as well as those of protoplasts from lemon (cv. Villafranca) nucellar callus were differentially affected by the maceration enzymes and by the sugars used as osmotic stabilizers. Plants with normal morphological features were regenerated from cultured protoplasts derived from each of the nucellar callus lines. The establishment of eight new protoplast systems in Citrus paves the way for cell genetics studies and for novel breeding approaches in these economically important orchard trees.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. E-290, 1981 series     

Somatic embryogenesis,plant regeneration and somaclonal variation in barley

In vitro culture of immature embryo and young leaf tissues was carried out with five cultivars of barley, Hordeum vulgare. Two cultivars (Albacete and Porthos) responded poorly from both types of explants, while the three others (Dissa, Golden Promise and Ingrid) produced a high frequency of embryogenic callus from these explants (25–60%). For Dissa and Ingrid, young leaf explants were slightly better than immature embryo explants for embryogenic callus induction, while immature embryo cultures of Golden Promise responded better than young leaf explants. Thus, there appears to be a significant genotype × explant interaction in the initiation of embryogenic callus in barley.Some phenotypic variants were detected among the regenerated plants of Golden Promise and Ingrid, most originating by epigenetic changes. Only in one case was the variant phenotype heritable, probably due to a mutation in the chloroplast DNA. Mitotic alteractions were not detected. Consequently, somaclonal variation did not appear to be a very frequent event in plants regenerated from 1- to 6- month-old cultures of barley.     

Centrophobism inDrosophila melanogaster

Summary The term centrophobism is introduced to describe a newly discovered modification of search behavior in the walking fruitfly,Drosophila melanogaster: the avoidance of the center of an arena after diethylether narcosis. Evidence for the effect is obtained by comparison of the tracks of etherized and non-etherized flies under the influence of olfactory attractant around the center of the arena (Fig. 3). The tracks can be distinguished by their mean radial distance from the central district of the arena. Centrophobia denotes the relative difference of the distances of etherized flies and non-etherized controls (Fig. 4).Etherized flies avoid the center of the arena in spite of the attraction of olfactory, thermal or visual cues. The avoidance is significant even in the absence of conspicuous sensory cues for the discrimination of center and surround. The centrophobia obtained in the arena can be used to estimate the efficacy of attractants in the non-etherized control flies (Figs. 6, 7).The lowest possible dose of ether sufficient to elicit narcosis is sufficient to induce centrophobia. None of the other prevalent insect anaesthetics, CO₂, N₂ and cold, substitutes ether in the present experiments (Figs. 8, 9).Centrophobia arises immediately after ether narcosis. Once induced the effect lasts apparently undiminished for the life time of the flies (Fig. 9).Centrophobia has been found in either sex of the 9 strains tested so far (Fig. 5). Four strains including mutants deficient in wing formation (vestigial) or learning (dunce) show either temporal decline or partial suppression of centrophobia. The anomalous properties are actually due to enhanced spontaneous centrophobism in the non-etherized control groups of these strains (Fig. 10).     

Bacterial regeneration of ammonium and phosphate as affected by the carbon:nitrogen:phosphorus ratio of organic substrates

The effect of carbonnitrogenphosphorus (CNP) ratio of organic substrates on the regeneration of ammonium and phosphate was investigated by growing natural assemblages of freshwater bacteria in mineral media supplemented with the simple organic C, N, and P sources (glucose, asparagine, and sodium glycerophosphate, respectively) to give 25 different substrate CNP ratios. Both ammonium and phosphate were regenerated when CN and NP atomic ratios of organic substrates were 101 and 161, respectively. Only ammonium was regenerated when CN and NP ratios were 101 and 10–201, respectively. On the other hand, neither ammonium nor phosphate was regenerated when CN and NP ratios were 151 and 51, respectively. In no case was phosphate alone regenerated. As bacteria were able to alter widely the CNP ratio of their biomass, the growth yield of bacteria appeared primarily dependent on the substrate carbon concentration, irrespective of a wide variation in the substrate CNP ratio.     

Transformation of Atriplex gmelini plants from callus lines using Agrobacterium tumefaciens

Atriplex gmelini plants were regenerated via organogensis from hypocotyl explants. Callus lines were induced from the hypocotyl explants on Linsmaier and Skoog (LS) medium supplemented with 1 M benzyladenine and 5 M -naphthaleneacetic acid in the dark. Shoots were regenerated from the callus lines on LS medium supplemented with 20 M thidiazuron and 0.1 M -naphthaleneacetic acid under a high-intensity light condition (450 mol m^–2 s^–1). The regenerated shoots were rooted on LS medium without growth regulators to obtain fully developed plants. We succeeded in transforming Atriplex gmelini from callus lines using Agrobacterium tumefaciens.     

Crcadian pacemaker in theBursatella eye: Properties of the rhythm and its effect on locomotor behavior

Summary The eye of the frilled sea hare,Bursatella leachi plei, expresses a circadian rhythm in the frequency of spontaneously occurring optic nerve impulses. The rhythm will free-run for at least 3 cycles in vitro (Fig. 2) and can be entrained by light cycles provided in vivo (Fig. 4 A). While bothBursatella andAplysia eyes contain circadian pacemakers the two rhythms differ in several respects: (1) the peak impulse frequency forBursatella eyes is only 96/h (±36 SD) compared with 247/h (±61 SD) forAplysia. (2) The ocular waveform of theBursatella rhythm exhibits a steep rise and fall from peak frequencies and lacks the delayed falling phase which creates a shoulder on the ocular waveform inAplysia (Fig. 2). (3) The in vitro free-running period of theBursatella ocular rhythm is 21.2 h (±0.6 SD) compared with 24.3 h (±0.9 SD) for theAplysia rhythm (Fig. 2). (4) The steady state phase angle for entrainment differs withBursatella eyes showing a median activity peak at +3 Z.T. compared with a medianAplysia peak at –1 Z.T. (Fig. 4).We also investigated the locomotor rhythm.Bursatella were found to be predominantly diurnal when exposed to LD, 1212 (Fig. 5A) and to exhibit anticipatory locomotor activity when maintained on LD), 915 (Fig. 6). The eyes appear to play a minor role, if any, in timing the locomotor rhythm. EyelessBursatella remained diurnal on LD, 915 and most animals continued to exhibit anticipatory behavior (Fig. 6). These results suggest that theBursatella eye plays a less prominent role than theAplysia eye in controlling locomotor behavior.Abbreviations DD constant darkness - LD 1212 24 h light cycles 12 h light, 12 h dark - EST Eastern Standard Time - Z.T. Zeitgeber Time We would like to thank L. Baird, W. Kilmartin and S. Wallace for help with animal maintenance, data presentation and photography. We also thank T. Breeden for our computer programs. This work was supported by NIH grant NS-15264 to G. Block.     

Discrimination of objects through electrolocation in the weakly electric fish,Gnathonemus petersii

Summary Three weakly electric fish (Gnathonemus petersii) were force-choice trained in a two-alternative procedure to discriminate between objects differing in their electrical characteristics. The objects were carbon dipoles in plexiglass tubing (length 2.5 cm, diameter 0.6 cm). Their electrical characteristics could be changed by varying the impedance of an external circuit to which they were connected (Fig. 1). In one (the capacitance dipole) the resistance was very low(< 3 ) and the capcitance variable. In the other (the resistance dipole) the resistance was variable and the capacitance low (<50 pF).Capacitances from several hundred pF (lower thresholds, Fig. 2) to several hundred nF (upper thresholds, Fig. 3) could be discriminated from both insulators and good conductors. In all cases the reward-negative stimulus was the capacitance dipole, which was avoided by all fish spontaneously. Thresholds were defined at 70% correct choices.The fish were then tested for their ability to discriminate between one object with a given capacitance and another with resistances varying from 3 to 200 k. The capacitance dipole continued to be the negative stimulus throughout. All 3 fish avoided it in at least 80% of the trials at each stimulus combination (Fig. 4). This result suggests that Gnathonemus perceives the capacitance and the resistance of objects differentially.The effect of the dipole-objects as well as some natural objects on the local EOD was recorded differentially very close to the fish's skin (Fig. 5). The amplitude of the local EODs was affected by all types of objects as they approached the skin. However, the waveform was changed only by capacitance dipoles and some natural objects (Figs. 6 and 7). It appears that the fish perceive not only intensity changes in the local EOD but wave-form deformations as well and can thus distinguish objects of different complex impedances.Abbreviations EOD electric organ discharge - f _max maximal spectral frequency - GP Gnathonemus petersii - LFS local filtered signal - PMA probing motor act - S+ positive stimulus - S negative stimulus     

Agrobacterium tumefaciens-mediated transformation of safflower (Carthamus tinctorius L.) cv. ‘Centennial’

Efficient callus formation was achieved from cotyledon, stem, and leaf expiants of the domestic safflower cultivar Centennial on MS salts medium containing 1 mg/L BAP and 1 mg/L NAA. Shoot buds were regenerated from 26% of leaf-derived calli on callus induction medium, although attempts to root regenerated shoots were not successful. Centennial expiants inoculated with Agrobacterium tumefaciens containing NPT II and GUS genes produced kanamycin-resistant calli from which buds were regenerated. Transformation and stable integration of transgenes was confirmed by GUS assay and DNA hybridization in kanamycin-resistant calli, and GUS assay in regenerated shoots.Abbreviations BAP 6-benzylaminopurine - NAA 1-naphthaleneacetic acid - 2,4-D 2,4-dichlorophenoxyacetic acid - MS Murashige and Skoog (1962) - GUS -glucuronidase - IAA indole-3-acetic acid - NPT II neomycin phosphotransferase II     

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 .

     

Multi-loop representation of the segmental muscle stretch reflex

Bees were trained to react to differences both in the size and in the degree of greyness of discs. To measure the differential sensitivity on these parameters, differences in size and shade of grey (-intervals) were established such as lead to a specific choice reaction (Fig. 3). The -intervals may be described for both parameters by Weber's rule (Fig. 4). The main result is the following relationship between the differential sensitivity and the equivalence curve as defined by cross modality matching. The bee treats two discs, which differ from a reference disc in diameter or in degree of greyness, as equivalent when both differ from the reference disc by an equal number of -intervals (Fig. 6). The choice reactions between the reference disc and the discs of the equivalent pair are the same for these parameters. This does not hold for another parameter (Fig. 7A and B). Problems of infering from the -intervals to the differential sensitivity are then discussed.     

Adoptions expérimentales de larves entre des fourmis de genres différents:Leptothorax nylanderi Förster etSolenopsis fugax Latreille

Résumé En l'absence de son propre couvain,Solenopsis fugax a élevé des larves deLeptothorax nylanderi, à la température de 22°C. Les ouvrières deSolenopsis détruisirent une partie de ces larves mais nourrirent celles qu'elles épargnèrent; ces dernières grossirent lentement pendant cinq à six mois, sans atteindre le stade prénymphe. Lorsque les ouvrières deS. fugax et les larves deL. nylanderi furent soumises ensemble à un hivernage préalable, elles donnèrent les mêmes résultats que sans hivernage. La présence d'une jeune reine deSolenopsis fut défavorable aux larves deLeptothorax.Inversement,L. nylanderi fut capable d'élever, à la température de 22°C, des larves deS. fugax et de les amener jusqu'au stade adulte. En présence de leurs propres larves, les ouvrières deL. nylanderi détruisirent tapidement toutes les larves deS. fugax introduites dans leur nid. D'autre part, un jeune couvain deLeptothorax remplaçait plus ou moins rapidement les larves deLeptothorax enlevées au préalable; sa présence était alors défavorable au développement des larves deSolenopsis. Un hivernage en début d'expérience fut plutôt favorable auxS. fugax, de même que la présence d'une reine féconde deLeptothorax. LesSolenopsis ainsi obtenus n'ont pas vécu plus de sept semaines. Ils étaient tous de caste ouvrière et de taille très petite.

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Summary When its own eggs and larvae missed,Solenopsis fugax bred larvae ofLeptothorax nylanderi, at a temperature of 22°C. TheSolenopsis workers killed some of this larvae and fed the others; these slowly grew bigger during five or six months but never reached the pre-pupa stage. The result was the same if the workers ofS. fugax and the larvae ofL. nylanderi overwintered together or not at all. A youngSolenopsis queen being there was noxious to the larvae ofLeptothorax.On the contrary,L. nylanderi has been able to breed larvae ofS. fugax up to the imago stage, at a temperature of 22°C. When its own larvae were in the nest, together with larvae ofS. fugax, the workers ofL. nylanderi killed the larvae ofS. fugax. On the other hand, new eggs and young larvae ofLeptothorax had to replace, more or less quickly, the larvae which had been taken away, and that was noxious to the growth ofSolenopsis larvae. An overwintering at the beginning of the experiment was rather favourable toS. fugax as was the presence of a fecundLeptothorax queen. TheSolenopsis thus obtained lived no longer than seven weeks. They all were workers and very small.

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S. Fugax L. Nylanderi 22° . Leptothorax , , , , . . S. Fugax Leptothorax.,L. Nylanderi 22° S. Fugax . L. Nylanderi ( )Leptothorax ; S. Fugax Solenopsis, Leptothorax. S. Fugax . .

     

Structural diversity of O-polysaccharides and serological classification of <Emphasis Type="Italic">Pseudomonas syringae</Emphasis> pv. <Emphasis Type="Italic">garcae</Emphasis> and other strains of genomospecies 4

Novel O-serotypes were revealed among Pseudomonas syringae pv. garcae strains by using a set of mouse monoclonal antibodies specific to the lipopolysaccharide O-polysaccharide. Structural studies showed that the O-polysaccharide of P. syringae pv. garcae NCPPB 2708 is a hitherto unknown linear L-rhamnan lacking strict regularity and having two oligosaccharide repeating units I and II, which differ in the position of substitution in one of the rhamnose residues and have the following structures: I:3)--L Rha (12)-- L Rha (12)--L-Rha-(13)--L Rha (1;II: 2)--L-Rha-(13) -L-Rha-(12)--L-Rha-(13)--L Rha (1.The branched O-polysaccharides of P. syringae pv. garcae ICMP 8047 and NCPPB 588^T have the same L-rhamnan backbone with repeating units I and II and a lateral chain of 14)- or 13)-linked residues of 3-acetamido-3,6-dideoxy-D-galactose (D-Fuc3NAc). Several monoclonal antibody epitopes associated with the L-rhamnan backbone or the lateral -D-Fuc3NAc residues were characterized.Translated from Mikrobiologiya, Vol. 73, No. 6, 2004, pp. 777–789.Original Russian Text Copyright © 2004 by Ovod, Zdorovenko, Shashkov, Kocharova, Knirel.     

The mechanism of object fixation and its relation to spontaneous pattern preferences in Drosophila melanogaster

The orientation behavior of walking flies, Drosophila melanogaster, towards a single 6° wide black vertical stripe (elementary stripe) can be explained by use of the turning tendency function H(). This function is characterized by maximal values at an angular distance of =25° from the stable zero position (=orienting direction), a sharp decline from this maximum to =60°, and a very slow approach to the unstable zero position (Horn and Wehner, 1975). The shape of this function is influenced by both translatory and rotatory components of movement. If the translatory component is minimized by measuring the turning function W() (see 2.3) at a distance of 10 mm (C1) from the center of the arena, a change in the strength of this decline is caused. But with increasing translatory component, i.e. at a greater distance from the center of the arena, W() approximates the heuristical function H() (Fig. 12). The turning functions W() are pattern-specific; the angular positions of the maximum responses shift to greater angles with increasing width of the patterns (Fig. 2). In the twopattern configuration with double or single stripes, there is always a coincidence between the stable zero positions of W (), the mean of the frequency distributions P() of the flies' positions and n _g() of the straight courses, and the stable zero positions of H () obtained from an additive superposition of two or more angular shifted turning tendency functions H() (Fig. 5, 7). Therefore, the mean positions of the flies in a multi-stripe experiment composed of elementary stripes can be predicted from the addition of many angular shifted turning tendency functions H(). Between H() and the frequency distribution P() of the flies' positions , the following formula holds: P() =C·H()d (Fig. 13). With this equation, the spontaneous preference of the broader of two double stripes can be explained presuming lateral interactions between the components of the patterns (Fig. 8, 10). The strength x _i ^* of this lateral interaction depends on the width of the double stripes. The greater , the smaller is x _i ^* . x _i ^* is a pattern-specific value (Table 1, 2).Supported by the Deutsche Forschungsgemeinschaft, Ho 664/2     

The effect of leaf source and developmental stage on shoot organogenic potential of sweetgum (Liquidambar styraciflua L.) leaf explants

Leaf explants harvested from shoot proliferating cultures and intact plants of Liquidambar styraciflua Variegata were placed on solidified Woody Plant medium supplemented with 0.1 mgl^-1 (0.5 M) naphthaleneacetic acid and 2.5 mgl^-1 (11.1 M) benzyladenine to initiate shoot meristems directly. Leaves from intact plants produced over 4 times more adventitious shoots than leaves from in vitro shoots and had a greater tendency to form shoots on the lamina. The relative developmental age of leaf tissue used dramatically influenced the shoot organogenic response observed for leaf explants from intact plants of L. styraciflua Variegata and Moraine.-Leaves that were either 20% or 50% of full size and still actively expanding were superior to other developmental stages for shoot organogenesis. As developmental leaf age increased throughout the period of leaf expansion, the number of shoots forming on the petiole stub remained constant, whereas shoot formation on the lamina increased 8 fold. Shoots derived from Variegata leaves rooted well and grew normally as plants. Differences in rooting ability and plant size could be detected between groups that had been separated according to explant source (in vitro vs. intact plant) and the location of shoot formation (petiole vs. lamina).     

Linkage mapping of the cystathionine β-synthase (CBS) gene on human chromosome 21 using a DNA polymorphism in the 3′ untranslated region

We used single-strand conformation polymorphism (SSCP) to detect DNA polymorphisms in the 3 untranslated (3UT) region of the gene for cystathionine -synthase (CBS). A polymorphism due to a T-to-C substitution at nucleotide 549 of the 3UT region with heterozygosity of 46% has been identified. Genotypes for this polymorphism have been obtained in all of the informative CEPH families, and CBS has been placed in the linkage map of human chromosome 21.