Significance of temperature fluctuation and oxygen concentration for germination of the rice field weeds Fimbristylis littoralis and Scirpus juncoides

Summary A diurnally fluctuating temperature was found to be almost an absolute requirement for the germination of Fimbristylis littoralis and Scirpus juncoides. It is demonstrated that in f. littoralis sensitivity to the amplitude of temperature fluctuation can functuation as a depth sensing mechanism under water. This species did not germinate at all in the absence of oxygen. S. juncoides germinated best in anaerobic conditions and at low oxygen concentrations, but normal atmospheric concentrations inhibited germination. It is shown that this requirement for little or no oxygen together with the requirement for a fluctuating temperature cause the germination of S. juncoides to be restricted to the upper layers of waterlogged soil.     

Influence of glyoxylic acid on properties of isolated mitochondria]

Glyoxalate is an effector of oxidative phosphorylation in isolated mitochondria : it slows down State 3 but does not affect State 4 respiration. This report presents the findings of our study on the mechanism of action of glyoxalate ; these findings are listed below. The inhibition of Stage 3 respiration by glyoxalate does not set in immediately, can be reversed in part by the addition of an uncoupling agent or a dithiol, is non-competitive against succinate and can be demonstrated with substrates requiring the involvement of other membrane transport systems. Glyoxalate prevents the increased oxygen uptake stimulated by 2,4-DNP or Sr++. Glyoxalate also inhibits phosphate transport and this inhibition can account for most of the effect observed. The inhibition of State 3 respiration is paralleled by a decrease in the mitochondrial accumulation of succinate : this decrease could arise from a direct effect of glyoxalate on dicarboxylic acid transport or could be the result of an inhibiton of the phosphate transport system, which is connected with the former. The decrease in the respiratory rate of uncoupled mitochondria placed in a phosphate free medium demonstrates that the effector acts directly at the substrate transport or/and electron transfer level. Phosphate, by delaying the respiratory inhibiton due to glyoxalate, has a protecting effect on mitochondrial functions. Glyoxalate is thus acting at several mitochondrial sites. It acts presumably by forming hemimercaptals, blocking sulfhydryl groups. Its effects can be accounted for by the unfolding of such (hemicercaptal) groups under the influence of ADP, Pi, uncoupling or others agents which bring about conformational changes in the internal mitochondrial membrane.     

Formation of pure and mixed clones of c mutants in serratiaphage sigma after treatment of the free virion with UV or hydroxylamine

The clone composition of c mutants of phage σ induced by UV irradiation of the free virion was studied, using Hcr⁺, Hcr^? and UV-irradiated Hcr⁺ cells as hosts and 2, 3 and 4 different UV doses, respectively. Most of the c plaques contained only mutant phages, and the distribution of mosaics was asymmetrical, i.e. most mixed clones contained >80% mutant type. The frequency of mosaics decreased with increasing UV dose in all three host systems; however, the decrease was significant only with the UV-irradiated Hcr⁺ host. Propagation of UV-irradiated σ in Hcr⁺ and Hcr^? hosts, respectively, did not lead to a significant difference in the frequency of mosaics, but, using UV-irradiated Hcr⁺ host significantly increased the percentage of mixed clones.The composition of plaques containing c mutants, after UV irradiation and treatment with hydroxylamine, was also studied by picking and testing all plaques (mutant and wild-type) of the survivors of a single UV dose and a single incubation time, respectively. In both experiments, besides pure and nearly pure (visible) c mutant plaques, many cryptic mutants containing predominantly >20% mutant type were found. The distribution of mosaics was of an almost “inverse symmetrical” type, the class of clones with about 50% mutant and 50% wild-type being the rarest.From these results incomplete recombinational repair is suggested to be responsible for the formation of pure mutant clones in mutation induction.     

Metabolism of glycerate-2,3-P2--II. Enzymes involved in the glycerate-2,3-P2 metabolism in chicken skeletal muscle

1. Four enzyme fractions which may be involved in the synthesis and breakdown of glycerate-2,3-P2 have been isolated from extracted skeletal muscle by gel-filtration and ion-exchange chromatography. 2. One of the fractions, corresponding to the glycerate-2,3-P2 dependent phosphoglycerate mutase, has been purified to homogeneity. In addition to the main enzymatic activity, it shows intrinsic glycerate-2,3-P2 synthase activity and glycerate-2,3-P2 phosphatase activity stimulable by glycolate-2-P. Its synthase activity represents about 10% of the total synthase activity of the tissue, and its phosphatase activity corresponds to about 60% of the total phosphatase activity. 3. Two of the fractions have glycerate-2,3-P2 synthase, glycerate-2,3-P2 phosphatase and phosphoglycerate mutase activities in a ratio similar to that of the glycerate-2,3-P2 synthase described in mammalian skeletal muscle. Their synthase activity corresponds to about 90% of the total synthase activity, and their phosphatase activity represents about 1% of the total phosphatase activity of the tissue. 4. The fourth fraction shows only glycerate-2,3-P2 phosphatase activity and represents about 40% of the total activity of the tissue. 5. It is suggested that in chicken skeletal muscle the metabolism of the glycerate-2,3-P2 is regulated in a way similar to that described in mammalian skeletal muscle.     

Prenatal development of monoamine neurons in the rat]

The histofluorescence method allows the study of the prenatal development of monoamines neurons in the foetal rat brain. Certain patterns of this development can be defined: the locus niger and the raphe appears fluorescent on the 14th day, the locus coeruleus on the 15th day. These systems differentiate independently in various areas of the neural axis. Their maturation are progressive: first for the DA system, then for the NA and the 5 HT systems. The mechanisms for synthesis and storage of amines precede the complete development of the effector structures.     

Cloning and characterization of a transposable-like repeat in the heterochromatin of the darkling beetle Misolampus goudoti.

A long repeat unit of the PstI family in Misolampus goudoti (Coleoptera, Tenebrionodae) is characterized in this work. The 30 sequenced units have small differences in length (consensus 1169 bp), but very similar nucleotide composition (mean 61.1% A+T). PstI repeats contain a 36-bp-long inverted repeat at both the 5' and 3' ends, with a fully conserved 16-bp-long motif similar to those found in class II transposable elements. However, the transposable-like PstI repeats seems to be defective, since they do not encode for any protein related with transposition. Interestingly, energetically stable hairpins resembled the structure of a miniature interspersed transposable element, suggesting that the PstI satellite DNA family in M. goudoti may have originated from an ancestral active transposable element as also described in Drosophila guanche. The presence of transposable-like structure along with the non-detection of gene conversion or unequal crossing-over events suggest that transposition could be one of the putative molecular mechanisms involved in the strong amplification and (or) homogenization of these repeats. A putative transposition of PstI repeats allowing their genomic mobility also could explain why this satellite is widely distributed to all heterochromatic regions, telomeres, pericentromeric regions, and on the Y chromosome, whereas satellites of other tenebrionids lacking transposable-like structures are restricted only to pericentromeric regions.     

Carbon Fixation, Ammonium Uptake and Regeneration in an Equatorial Lake: Biological Versus Physical Control

Ammonium uptake and regeneration were measured in the euphoticzone of Petit Saut Lake, French Guyana, to examine nitrogencycling in this recently flooded equatorial forest environment.Am-monium regeneration rates were extremely high (mostly inthe range 1–6 µmol N l^–1 h^–1), and aredue to the very high grazing rates of the microzooplankton,which consumed between 56 and 95% of the phytoplankton productionin any given incubation. These regeneration rates were aboutan order of magnitude higher than the net ammonium uptake rates.This imbalance is probably due to dissolved organic nitrogenrelease during grazing. At the bottom of the euphotic zone (4–5m), photosynthetic bacteria are responsible for ammonium uptake.Diffusion-driven ammonium fluxes are an order of magnitude lowerthan biologically driven fluxes. Therefore, ammonium fluxesare dominated by biology rather than by physics in this lake.