Microspectrophotometric measurements of DNA by automated computerized scanning in cycling cells of theChrysanthemum segetum shoot apex

Summary A new technique of exploitation of the data was proposed after DNA scanning microdensitometry. By using all of the measurements obtained from the seriated sections of a single nucleus, this method made it possible to estimate six characteristic parameters during the different phases of the cell cycle in the various shoot apical cells. The cells whose rate of proliferation was the highest showed the biggest variations of their nuclear and nucleolar volumes during the cell cycle. In the axial zone, where the cells have a slow cell cycle and display the longest duration of the G₁ phase, the volume occupied by dispersed DNA was greater than in the cells of the lateral zone and of the rib meristem, where the cell cycle and the G₁ phase were short. No matter what the cell type, the proportion of the dispersed and condensed DNA varied little when the G₁ and G₂ phases were compared. In the Z phase, characterized by a decondensation of the DNA, the mean DNA amount was 3.4 C. The evolution of the nuclear density during the interphase was also estimated. It is demonstrated that the main feature of the shoot apex zonation was the decondensation of the condensed DNA in the axial zone in both the G₁ and G₂ phases.     

On the cellular localization of phosphoenolpyruvate carboxylase in Sorghum leaves

The localization of phosphoenol pyruvate carboxylase (EC 4.1.1.3.1.) in the leaf cells of Sorghum vulgare was investigated by using three techniques: the conventional aqueous and non aqueous methods gave conflicting results; the immunocytochemical techniques clearly showed that the enzyme is predominantly located in the cytoplasm of mesophyll cells.Abbreviations PEP phosphoenol pyruvate - PAG polyacrylamide gel - NADP MDH NADP malate dehydrogenase - FITC fluorescein isothiocyanate - SAB serum albumine bovine - DTT dithiothreitol - MDH malate dehydrogenase - ME malic enzyme - PBS phosphate buffer saline - PAP peroxidase anti-peroxidase     

Comparaison, à la lumière et à l'obscurité, des synthèses spécifiques d'ARN chez Euglena gracilis Z en cultures synchrones sur milieu lactate et étude du Chondriome

Summary Synchronization of Euglena gracilis (Z) on lactate medium is shown to be independent of illumination. The existence of a mitochondrial cycle in lightgrown as well as in dark-grown Euglena is demonstrated. When RNA synthesis is studied by pulse labeling with tritiated uracil in synchronously growing cells, a discontinuous RNA synthesis is found. Two peaks of preferential RNA synthesis in dark-grown cells and three peaks in light-grown cells are seen; the significance of the third peak of RNA synthesis in light-grown Euglena is discussed.     

PROTEIN SYNTHESIS BY HIGHLY AGGREGATED AND PURIFIED POLYSOMES FROM YOUNG AND ADULT RAT BRAIN

The state of aggregation and the activity of polyribosomes as well as the activity of the pH 5 enzyme fraction were studied at two stages of postnatal brain development, 9 and 50 days after birth. When the polyribosomes were prepared at 0°C in the presence of 5 mm -Mg²⁺, more than 85 per cent of the polyribosome material exhibited a sedimentation coefficient higher than 110 S. High Mg²⁺ concentrations are, therefore, unnecessary to obtain highly aggregated brain polyribosomes. The basal amino acid incorporating activity of both 9- and 50-day-old rat brain preparations is at least equal to that of rat liver. When prepared by the same procedure as above, 9-day-old rat brain polyribosomes seem to be more active (20 per cent) than those of adult brain. However, this difference in activity depends on the presence of a non-ribosomal inactive contaminant which is always present in higher amounts in adult brain preparations. When purified from this contaminant, the preparations do not differ in activity. High Mg²⁺ concentrations are also not necessary for optimal protein synthetic activity and, in fact, are inhibitory. When assayed with both types of highly aggregated polyribosomes, the pH 5 enzyme fraction from adult brain is clearly less active than that of 9-day-old rats. These results suggest that the loss of brain protein synthesis during development does not depend on the stability of the messenger RNA-ribosome complex but only on the soluble pH 5 enzyme fraction.     

Biological significance and interpretation of the corpulence index BMI (Body Mass Index)]

A study of the corpulence of young French men between the age of 18 and 20 has proved the existence of a biological constant between the height and the weight, bringing a new significance to the Body Mass Index. The elaboration of a new index BMC (BMI corrected), allows us to know with precision the underweight or overweight of any individual.     

Effects of laser radiation on rhus vernicifera laccase,type 2 Cu-depleted laccase,and stellacyanin

Laser irradiation in the 450 nm region brings about irreversible changes in the copper sites of Rhus vernicifera laccase and its type 2 Cu-depleted derivative. The absorption band at 614 nm disappears after ~ 2 hr of irradiation with a 200 mW laser beam; the amount of the paramagnetic detectable copper does not decrease, indicating no reduction of these types of copper. No apparent rearrangement of the protein backbone occurs, as ultaviolet dichroic spectra of the enzyme before and after the irradiation do not show appreciable differences. Stellacyanin is insensitive to laser radiation at any wavelength.     

Modifications of the molecular weight of membrane-bound nonspecific β-glucosidase in type 1 gaucher disease determined in situ by the radiation inactivation method

The radiation inactivation method has been used to compare the molecular weight of the nonspecific membrane-bound β-glucosidase in situ in normal human spleen and in that of two patients with Gaucher diease type 1. We report, in type 1 Gaucher spleen, the presence of a high molecular weight component (557 000) in addition to the normal low molecular weight component (97 800). The various possible hypotheses explaining this high molecular weight component are discussed.     

Schistosoma mansoni: structural and biochemical characterization of two distinct Venus Kinase Receptors

Venus Kinase Receptors (VKRs) are atypical transmembrane proteins composed of an extracellular Venus FlyTrap module linked through a single helix to a tyrosine kinase domain similar to that of insulin receptors. This structure was first described in Schistosoma mansoni, then in a selected range of invertebrates, including many insects. The preferential expression of VKRs in larvae and gonads suggested their role in development and reproduction. While a single vkr gene was consistently found in all genomes, we identified two distinct vkr genes in S. mansoni. Our data indicated that Smvkr1 and Smvkr2 are very similar in structure and likely originated from gene duplication. Both genes are expressed in all the parasite stages and encode homologous proteins with a conserved VKR structure. Recombinant SmVKR1 and SmVKR2 exhibit tyrosine kinase activities dependent on the binding of distinct small ligand molecules. SmVKR1 and SmVKR2 could represent paralogs with different functions in the parasite.     

Interembryonic regions of the uterus of the viviparous lizard Mabuya brachypoda (Squamata: Scincidae)

Analysis of the structure and physiology of the uterine incubation chambers of viviparous squamates has provided insight concerning adaptations for gestation. However, the literature addressing the biology of the interembryonic regions of the uterus is very limited, presumably because it has been assumed that this area has little role in the development and support of embryos in viviparous squamates. This study was undertaken to examine the histology of the interembryonic regions of Mabuya brachypoda, a viviparous lizard with microlecithal ova and consequently substantial matrotrophic activity. The incubation chambers are oval, distended zones of the uterus, adjacent to the interembryonic regions. The wall of the interembryonic regions includes: mucosa, formed by a cuboidal or columnar epithelium with ciliated and nonciliated cells, and a lamina propria of vascularized connective tissue containing abundant acinar glands; myometrial smooth muscle consisting of inner circular and outer longitudinal layers; and serosa. The segment of the interembryonic region adjacent to the incubation chamber forms a transitional segment that displays folds of the mucosa that protrude into the uterine lumen. The limit of the incubation chamber is well defined by the long mucosal folds of the transitional segment. Long and thin extensions of extraembryonic membranes are present in the lumen of the transitional segment, outside of the incubation chamber region. The presence of abundant uterine glands and extraembryonic membranes in the interembryonic regions during gestation suggests uterine secretory activity and histotrophic transfer of nutrients to embryos in these regions.