Cs. Koncz

Location of nodulation and nitrogen fixation genes on a high molecular weight plasmid of R. meliloti

SummaryR. meliloti strain 41 (Rm41) was shown to harbour two indigenous plasmids with molecular weights of 140 Mdal (pRmc41a) and more than 300 Mdal (pRme41b), respectively. Using a heat-treatment procedure, derivatives of Rm41 defective in nodulation (Nod-) or nitrogen fixation (Fix-) have been readily obtained. In some Nod- mutants the deletion of a segment of plasmid pRme41b was found.Based on the demonstrated homology between the nitrogen fixation (nif) genes of Klebsiella pneumoniae and of R. meliloti the Rhizobium nif region has been cloned into the cosmid vector pHC79, then recloned into pBR322 and the restriction map of the nif region has been determined. 32P-labelled nick-translated probe prepared from the cloned nif DNA fragment hybridized to pRme41b of Rm41 but for most Nod- mutants this hybridization was not detected. Hybridization of a cosmid containing Rm41 DNA to total DNA digests from the wild-type bacterium and from a series of Nod- mutants revealed that at least a 24 kb DNA fragment including the nif structural genes was missing from most of the Nod- mutants. These results, together with the genetic analyses of these symbiotic mutations suggest that some nod and fix genes are located on pRme41b.

Plant regeneration from intergeneric cell hybrids

Protoplasts isolated from cell suspension culture of an albino mutant of Daucus carota and from leaves of Aegopodium podagraria were fused by polyethylene glycol treatment. Plants have been regenerated from green calli developed after this intergeneric protoplast fusion. The degree of hybridization of RNA synthesized in nuclei of selected plants to Ae. podagraria DNA was significantly higher than that obtained using nuclear RNA from the albino mutant. Restoration of normal chloroplast ultrastructure and of synthesis of photosynthetic pigments, as well as expression of Ae. podagraria markers for root development and for root carotenoids, indicated the presence of Ae. podagraria genes in the genome of selected plants, which possessed only D. carota chromosomes. Intergeneric gene transfer by fusion of protoplasts from dividing and mitotically inactive somatic cells is discussed as a possible method in genetic manipulation of higher plants.

Megacinogenic plasmid from Bacillus megaterium 216.

SummaryAbility to produce megacin A, a bacteriocin of b. megaterium, was transferred from the strain B. megaterium 216 into auxotrophic derivatives of the strain B. megaterium KM via protoplast fusion and polyethylene-glycol-induced protoplast transformation by plasmid DNA, respectively. A 30.9 megadalton plasmid was detected in cells with MegA phenotype, and the loss of this phenotype was accompanied in each case with the elimination of that plasmid. The megacinogenic plasmid pBM309 has a single site for both BamIII and XhoI. It is cleaved by the endonucleases SalI, BglII, PstI, PvuII, and EcoRI into 3, 3, 4, 4, and 9 fragments, respectively. The physical map of this plasmid is presented.

Homology between rRNA of Escherichia coli and mitochondrial DNA of maize

Chloroplast and mitochondria of higher plants possess their own DNA coding for organelle-specific RNAs and proteins. The similarity between the translation systems of chloroplast and mitochondria and those of bacteria may serve as a proof of the evolutionary relationship between these semiautonomous cell organelles and procaryotic organisms [l-3], Recently, compa~son of 16 S rRNA sequences of Escherichia coZi and maize chloroplast has revealed a 76% homology between the two rRNAs [4]. A similar result was obtained from sequencing data of 16 S rRNA of E~g~e~~ ~acili~ chloroplast [S]. We demonstrate here the homology between rRNA of E. coli and mitochondrial DNA of maize based on Southern hybridization experiments.

Fermi-shuttle acceleration of electrons in ion–matter interaction

Abstract Large electron yields, compared to theoretical predictions, have often been observed in the high-energy part of the electron spectra in collisions of energetic ions with atomic, molecular or solid targets. The relative enhancement of the electron emission yield at high energies can be especially strong in ion–solid collisions. In this work, following a brief overview, recent experimental evidences are presented for Fermi-shuttle type accelerating electron scattering sequences in ion–atom collisions. Signatures for double (projectile–target, P–T), triple (projectile–target–projectile, P–T–P) and quadruple (P–T–P–T) scattering sequences have been found in different collision systems. Our new results indicate the presence of even higher-order scattering contributions in the collisions of few keV energy N + ions with inert gas atoms. The observations support that high-energy electrons produced by accelerating scattering sequences may play a significant role in ion–solid collisions.

Key for classification of cytoplasmic male sterile types in maize

Abstract Male-sterile cytoplasms in maize were classified by using restriction endonuclease fragment analysis of mitochondrial DNAs and by investigation of the process and products of microsporogenesis. The groups constructed with both procedures were identical with those of Beckett obtained from a fertility restoration pattern. A general classification key by combining the biochemical and cytological methods is proposed.

Continuous electron spectra from 150 keV/u C+ + He, Ne, Ar collisions at electron emission angles from 0° to 180°

Electron spectra in the 20–550 eV energy range and in the full angular range of 0–180° were measured by the impact of 150 keV/u C+ ions on He, Ne and Ar atoms. Double differential cross sections for electron emission have been determined. We observed an unexpected, broad structure around 300 eV electron energy at backward emission angles relative to the beam direction. Our calculations support the hypothesis that the new structure is due to double scattering of the target electrons on the screened fields of the projectile and the target. The calculations also show that both electron-emitting partners are multiply ionized in the collision.

Double scattering of ejected electrons in ion-atom collisions

A simple quantum-mechanical model for the ionization process in ion-atom collisions is constructed. A second-order Born approximation based on this model which uses plane waves in the final and intermediate states provides a qualitative description of the double-scattering process (events which can be conceived as two consecutive collisions of the active electron with the projectile and target cores). We draw attention to the fact that the usual first-order Born calculation with realistic target eigenfunctions in both the initial and final states also takes account of this process.

Plasma diagnostics measurements on the new ECR heavy ion source of ATOMKI

Abstract Between 1993 and 1996 a new 14.5 GHz electron cyclotron resonance (ECR) ion source was designed and built at ATOMKI for atomic and plasma physics research. In 1996 the assembling of the ion source has been finished and the first plasma diagnostic (visible and X-ray) measurements were carried out. In this work we started an investigation of the spectral distribution of the visible range of the electromagnetic spectrum. We studied the change of relative line intensities and the Xe 2 to Xe 1 ratio depending on the pressure inside the plasma. We were able to find spectral lines of Xe 2 which are good candidates for plasma diagnostic tools in future investigations.

Calculated cross sections for the single ionization of fullerenes by electron impact

Abstract A spherically symmetric model is constructed in order to obtain one-electron wavefunctions for the valence electrons of the Buckminsterfullerene. Using these wavefunctions, the cross sections for the ionization of the fullerene ion and of the neutral fullerene by electron impact are calculated within the distorted-wave Born approximation. The obtained results are compared with the experimental data.