Established cell lines from nonmammalian vertebrates: Models for DNA repair studies

Summary Several established cell lines from different classes of vertebrates were assayed for the presence of O⁶-methylguanine acceptor protein. This protein is instrumental in removing adducts from DNA caused by exposure to alkylating agents. Cultured cells had levels of acceptor protein activity within the range found in fresh tissues from animals in the same class. We suggest that cells from lower vertebrates are satisfactory in vitro models for studies of this DNA repair function.     

Comparison of glucokinase in C3H/He and C58 mice that differ in their hepatic activity

Partially purified preparations of the hepatic glucokinase from C3H/He and C58 inbred mice have been used to explore the molecular basis for the observed twofold difference in activity between the strains. The single codominant gene that appears to regulate activity, the alleles of which are designated Gk^a and Gk^b, respectively, for the two strains, could represent a structural gene change. This now seems unlikely because the mouse enzyme, although showing small differences from rat glucokinase, appeared to be identical in the two strains with respect to thermal stability, electrophoretic mobility in agarose gels, and kinetic properties such as the apparent K _m values for MgATP^2– and glucose and the unique cooperative interaction with the latter substrate. The enzymes also reacted identically in a range of immunological tests (double-diffusion, immunoelectrophoresis, immune precipitation and immune inhibition assays) and ELISA immune inhibition assays indicated that the twofold difference in activity was due to a similar difference in antigenically active enzyme. Genetic control over the physiologically significant regulation of enzyme amount is therefore probable.This work has been supported in part by a grant from the British Diabetic Association and a Training Studentship to PAJ from the Medical Research Council (U.K.).     

Crossing maize with sorghum,Tripsacum and millet: the products and their level of development following pollination

Summary Maize was crossed with sorghum, Tripsacum and millet with the aim of introgressing desirable alien characteristics into maize. The products of crosses were analyzed as to their level of differentiation following pollination; their further development on artificial culture medium was compared. In spite of a stimulation rate close to 5%, no evidence of hybridization between maize and sorghum or millet could be obtained. The plants recovered proved to be of maternal origin. However, with an appreciable frequency, stimulation leading to hypertrophic growth of nucellar tissue was observed. This phenomenon is bound to pollination, never occurring in non-pollinated ears. In crosses involving Tripsacum, more than 140 true hybrids were isolated. The influence of the genotypes used as well as factors such as climatic conditions or in vitro techniques are discussed. Except for one haploid maize plant, all the plants recovered proved to be classical hybrids, most of them showing the expected complement of chromosomes from each parent (10 + 36 chromosomes), a few others being slightly hyperploid (2n = 47 to 50 chromosomes). No non-classical hybrids constituted by a nonreduced female gamete and a reduced male gamete were obtained.     

Molecular analysis of the inheritance and stability of the mitochondrial genome of an inbred line of maize

Summary We have investigated the inheritance of the mitochondrial DNA (mtDNA) restriction endonuclease digestion patterns of maize inbred line B37N in individual plants and pooled siblings in lineages derived from five separate plants in the third generation following successive self-pollinations. The restriction fragment patterns of the different mtDNA samples were compared after digestion with five endonucleases. No differences were visible in the mobilities of the 199 fragments scored per sample. Hybridization analysis with two different cloned mtDNA probes, one of which contains homologies to a portion of the S2 plasmid characteristic of cms-S maize, failed to reveal cryptic variation. The apparent rate of genomic change in maize mtDNA from inbred plants appears to be very slow, compared with the faster rates of change seen in maize tissue cultures and with the documented rapid rate of inter- and intraspecific variation for mammalian mtDNA.     

Metabolism of polyamines in NaCl-resistant cell lines from Nicotiana sylvestris

The polyamine titers in three cell lines of Nicotiana sylvestris were compared: Type 1, rapidly adapting to NaCl; Type 2, constantly resistant to NaCl; Type 3, a saltsensitive wild strain. During short-term cultivation in MS medium in the presence of 170 mM NaCl (1 passage, 14 d) the changes in polyamine titer in cell suspensions of type 1 (in a slightly adapted state) and non-adapted wild strain (type 3) showed a considerable increase in spermidine and spermine and a decrease in putrescine. After prolonged adaptation to NaCl (20 passages) the putrescine content in the cells of type 1 and of type 2 was increased at the expense of the polyamines. This suggests that the pattern of polyamine titer varies under short- and long-term adaptation to NaCl. The inverse ratio between growth processes and changes in polyamine and proline level indicates that polyamines fulfil primarily a protective and osmorepulatory function in plant cells under NaCl stress.     

Knob heterochromatin homology in maize and its relatives

Summary We have characterised the major DNA sequence component of knob heterochromatin in maize, teosinte andTripsacum. Sequence analysis of this DNA gives strong support to the proposal that maize originated by selection of variants in teosinte. In situ hybridization has confirmed that this repeating DNA sequence, which is the major component of maize knob heterochromatin, is also the major component of knobs in teosinte,Zea diploperennis andTripsacum. In Southern blot hybridizations the repeat has a similar basic organization in all taxa;Tripsacum, however, is differentiated from maize and teosinte by a number of sequence features. Maize and teosinte knob heterochromatin are indistinguishable with regard to the distribution of mutations in the 180-bp repeat and the presence and organization of a 202-bp variant sequence. The knob DNA sequence was not detectable in three species ofCoix, an Old World genus of the Maydeae.Within the repeat unit is a 27-bp region that shows no sequence changes in maize, teosinte orTripsacum. The remainder of the repeat unit has randomly distributed nucleotide changes. The presence of the conserved sequence region suggests that knob DNA may have a functional role in the nucleus.     

玉米黄早4雄性不育系、保持系过氧化物酶同工酶的比较研究

在玉米黄早4雄性不育系、保持系的10个组织(叶、根、茎、芽鞘、胚轴、苞叶、穗轴、花丝、雌蕊、花药)中共检测出18种正、负极向过氧化物酶,其中有7个组织不育系与保持系间过氧化物酶没有差异,只有在3个组织中(叶、茎、花药)不育系与保持系间的过氧化物酶存在差异,说明玉米黄早4雄性不育系及保持系的过氧化物酶可能由细胞核基因编码。不育系与保持系个别组织内过氧化物酶存在差异,可能是由于核内编码过氧化物酶的基因表达异常所引起,而这种表达异常,可能是与不育系中不育细胞质基因调控核基因的表达有关。     

The relationship between carbon-dioxide-limited photosynthetic rate and ribulose-1,5-bisphosphate-carboxylase content in two nuclear-cytoplasm substitution lines of wheat,and the coordination of ribulose-bisphosphate-carboxylation and electron-transport capacities

Photosynthesis in two cultivars of Triticum aestivum was compared with photosynthesis in two lines having the same nuclear genomes but with cytoplasms derived from T. boeoticum. The in-vitro specific activity of ribulose-1,5-bisphosphate carboxylase (RuBPCase; EC 4.1.1.39) isolated from lines with T. boeoticum cytoplasm was only 71% of that of normal T. aestivum. By contrast, the RuBPCase activities calculated from the CO₂-assimilation rate at low partial pressures of CO₂, p(CO₂), were the same for all lines for a given RuBPCase content. This indicates that both types of RuBPCase have the same turnover numbers in-vivo of 27.5 mol CO₂·(mol enzyme)^–1·s^–1 (23°). The rate of CO₂ assimilation measured at normal p(CO₂), p _a =340 bar, and high irradiance could be quantitatively predicted from the amount of RuBPCase protein. The maximum rate of RuBP regeneration could also predict the rate of CO₂ assimilation at normal ambient conditions. Therefore, the maximum capacities for RuBP carboxylation and RuBP regeneration appear to be well-balanced for normal ambient conditions. As photosynthetic capacity declined with increasing leaf age, the capacities for RuBP carboxylation and RuBP regeneration declined in parallel.Abbreviations PAR photosynthetically active radiation - RuBP(Case) ribulose-1,5-bisphosphate (carboxylase)     

Genetic relationship between o6 and pro-1 mutants in maize

Summary This paper reports that the opaque-6 (o6) mutation of maize, which causes seedling lethality and interferes in the endosperm with the synthesis of zeins and b-32 protein, is a proline requiring mutant functionally allelic to proline-1 (pro-1). Furthermore, immunological studies on the b-32 content of ten independently originated o6 and pro-1 alleles demonstrated that four alleles contain an apparently normal b-32 protein while the others are either devoid of it or contain trace amounts of cross-reacting proteins of lower molecular weight.