Promotion by phloroglucinol of micropropagation of Minuartia valentina, an endangered and endemic Spanish plant

Tissue culture techniques for the propagation and conservation of endemic or threatened plants can be used to complement the methods usually applied in ex situ conservation. Thus, Minuartia valentina (Caryophyllaceae), an endangered plant species endemic to the Valencia Community (Eastern Spain), was successfully regenerated through shoot proliferation from wild plants growing in their natural area. Nodal segments, 10~mm long, were cut from rametes of adult material, sterilised and established in vitro. Equally successful shoot multiplication was achieved on Murashige and Skoog (MS) medium with 80 mg l-1 phloroglucinol in combination with either 1 mg l-1 6-benzylaminopurine or 1 mg l-1 kinetin. Excised shoots were rooted in MS medium supplemented with an auxin (indole acetic acid, indole-3-butyric acid, or napththalene acetic acid). Shoots rooted well (96–100%) within three weeks in all auxin treatments. However, the use of napththalene acetic acid was discarded because this auxin delayed root differentiation, and induced adventitious root malformation. Rooted plantlets were transferred to pots and 85% of them acclimatized successfully four weeks after transfer to greenhouse conditions, where they exhibited normal morphology and growth.     

Bats of the Gulf of Guinea islands: faunal composition and origins

The present study compares the bat faunas of the islands of the Gulf of Guinea. Species composition. endemism and hypothetical origins are discussed. All families present in the mainland region are found in Bioko, a typical landbridge island. Foliage gleaning guild species (Nycteridae) show limited colonization abilities. This is also true of the family Rhinolophidae, but not for the closely related family Hipposideridae. The majority of the oceanic island species are African bats which show a widespread distribution and, therefore, have a high ecological plasticity. The continental relatives of the two endemic species Myonycteris brachycephala and Chaerephon tomensis are restricted to relatively small forested areas. Bioko's bat fauna is the result of the recent isolation from a formerly land-connected community. The oceanic bat faunas originated from the establishment of incomers from other areas. Nevertheless, extinction appears in both vicariant and dispersal processes, as an important factor in modelling the current bat communities of the Gulf of Guinea islands.     

Functional analysis of the γ-glutamylcysteine synthetase of Escherichia coli B: effect of substitution of His-150 to Ala

A high expression system of the -glutamylcysteine synthetase gene (gshl) of Escherichia coli B was constructed, and rapid purification of GSH-I was performed. The active site of GSH-I was analysed by chemical modification, and Lys, Arg and His residues seemed to be involved in the active site of the enzyme. Among them, His residues were substituted to Ala by site-directed mutagenesis, and His-150 was found to be essential for the activity of GSH-I. Correspondence to: A. Kimura     

Severe hypoxia decreases oxygen uptake relative to intensity during submaximal graded exercise

The effect of severe acute hypoxia (fractional concentration of inspired oxygen equalled 0.104) was studied in nine male subjects performing an incremental exercise test. For power outputs over 125 W, all the subjects in a state of hypoxia showed a decrease in oxygen consumption ( O₂) relative to exercise intensity compared with normoxia (P < 0.05). This would suggest an increased anaerobic metabolism as an energy source during hypoxic exercise. During submaximal exercise, for a given O₂, higher blood lactate concentrations were found in hypoxia than in normoxia (P < 0.05). In consequence, the onset of blood lactate accumulation (OBLA) was shifted to a lower O₂ ( O₂ 1.77 l·min^–1 in hypoxia vs 3.10 l·min^–1 in normoxia). Lactate concentration increases relative to minute ventilation ( _E) responses were significantly higher during hypoxia than in normoxia (P < 0.05). At OBLA, _E during hypoxia was 25% lower than in the normoxic test. This study would suggest that in hypoxia subjects are able to use an increased anaerobic metabolism to maintain exercise performance.     

Formation of functionally active chloroplasts is determined at a limited stage of leaf development in virescent mutants of rice

The ability to form functionally active chloroplasts is determined at a certain early stage of leaf development in three non-allelic temperature-sensitive virescent mutants of rice. Temperature-shift analysis, together with anatomical observations, indicates that the intrinsic developmental signals of the virescent genes are expressed at the stage immediately following the formation of basic leaf structure, but just before the onset of leaf elongation. These signals control the expression of chloroplast-encoded genes but do not affect the subsequent morphological development of the leaf or the photo-regulation of the expression of nuclear genes encoding chloroplast proteins.     

Chromosome segregation in an asymmetrically dividing bacterium,Caulobacter crescentus

The mode of chromosome segregation in an asymmetrically dividing bacterium, Caulobacter crescentus, was studied by examining the fate of labeled DNA strands. Swarmer cells (one type of Caulobacter daughter cell), in which single strands of DNA had been labeled with [³H]thymidine during the previous round of chromosome replication, were grown synchronously in a non-radioactive medium for two generations. The distribution of radioactivity among the cells was visualized by autoradiography under a phase-contrast microscope. The labeled DNA strands in each cell were found to consist of two conserved units. From this, we propose a model in which the swarmer cell has two identical chromosomes, which are segregated into the progeny swarmer cell and the progeny stalked cell after chromosome replication.     

Differential effect of UV irradiation on induction of intragenic and intergenic recombination during commitment to meiosis in Saccharomyces cerevisiae

A comparison was made between the induction of intragenic and intergenic recombinations during meiosis in a wild-type diploid of Saccharomyces cerevisiae. Under non-irradiated normal conditions, production of both intragenic and intergenic recombinants greatly increased in the cells with commitment to meiosis. The susceptibility of cells to the induction of both the spontaneous intra- and intergenic recombinations in meiotic cells was similar. However, under condition of UV irradiation, there were striking differences between intra- and intergenic recombinations. Susceptibility to induction of intragenic recombination by UV irradiation was not enhanced at meiosis compared with mitosis, and was not altered through commitment to meiotic processes. In contrast, however, susceptibility to the induction of intergenic recombination by UV irradiation was enhanced markedly during commitment to meiosis compared with mitosis. Genetic analysis suggested that the enhanced susceptibility to recombination during meiosis is specifically concerned with reciprocal-type recombination (crossing-over) but not non-reciprocal-type recombination (gene conversion). Hence it is concluded that the meiotic process appears to be intimately concerned with the mechanism(s) of induction of recombination, especially reciprocal-type recombination.