Modalités de l'inhibition de la croissance et de la synthèse des acides nucléiques des plantules de blé par l'acide abscissique

The growth of wheat seedlings (Triticum sativum) is inhibited by abscisic acid (ABA). The inhibition increases with the concentration of ABA (from 10^-6M to 5 × 10^-5M) and is stronger in the case of coleoptiles and first leaves than in roots. In contrast, naphthaleneacetic acid (ANA), at 10^-5M, exerts its greatest inhibitory effect on the roots. The inhibitory effect of ABA on coleoptiles can be partially overcome by kinetin and to a much smaller degree by gibberellic acid. Neither of these two compounds, at 10^-5M, had any effect on the ABA-induced inhibition of root growth. The RNA and DNA contents per plant organ are considerably reduced after treatment of the seedlings with ABA, particularly in the coleoptiles and the first leaves. The incorporation of uracil-2-¹⁴C and uridine T (G) into RNA of treated seedlings is reduced in the case of coleoptiles and first leaves, but considerably enhanced in roots. The mechanism of the action of ABA is discussed in the light of these results.     

Differenciation cellulaire et composés sulfhydrylés acido-solubles de la racine de Lens culinaris Med.

Cell differentiation and acid-soluble sulfhydryl compounds in the root of Lens culinaris. Med. — The content of acid-soluble sulfhydryl compounds (SH + S-S) is determined amperometrically in tissues of the Lens root. Two distinct zones are analysed: first the meristematic one (0 to 1.6 mm from the tip) and secondly the elongating one (1.6 to 3.7 mm). Measurements concerned the first 80 hours of the root growth. SH/S-S ratio is minimum in the meristematic ZONE. Connections seem to exist between the growth rate and the amount of SH compounds in the elongating zone. These facts suggest that the increase of cytoplasmic SH is associated with the reduction of protein-disulfur-bridges, which account for t he intermicrofibrilar bindings in the cell wall. The effects of auxins (indoleacetic acid and naphtylacetic acid) treatments are also studied. They are strictly localized in the apical zone and their intensity depends upon the auxin concentration. SH-level is rising: this is due partially to a reduction of acid-soluble S-S.     

Cancer de la prostate : utilité de la TEP-TDM à la F-fluorocholine

In oncology, positron emission computed tomography (PET/CT) has become an essential tool for initial staging, response evaluation and follow-up of cancer patients. Most of the frequent tumors (lung, breast, esophagus, and lymphomas) are highly avid for ¹⁸F-fluorodeoxyglucose (¹⁸FDG), but prostate cancer has not demonstrated significant uptake of FDG. The development of new tracers labeled with ¹⁸F such as choline analogs allowed already to obtain interesting results particularly in patients with biological relapse and inconclusive conventional imaging work-up. The impact of ¹⁸F-flurocholine PET/CT on patient management needs to be validated in large studies, but many centers use already this examination in order to guide further management, including radiotherapy planning.     

Etude de quelques propriétés de la phosphofructokinase érythrocytaire de l'homme normal

Human erythrocyte phosphofructokinase was purified 150 fold by DEAE cellulose adsorption and ammonium sulfate precipitation.At pH 7,5 the enzyme exhibits allosteric kinetics with respect to ATP, fructose 6 phosphate, and Mg²⁺.ATP at high concentration acted as an inhibitor and ADP, 5′AMP, 3′,5′, AMP, acted as activators. Both effectors seemed to decrease the homotropic interactions beetween the fructose 6 phosphate molecules.The activators increased the affinity of phosphofructokinase for the substrate (F6P), the inhibitor decreased it.These ligands had no effect on the maximum velocity of the reaction except in the case of ADP.Interactions between the substrates and the effector ligands on the enzyme were considered in terms of the Monod - Changeux - Wyman model for allosteric proteins.With GTP and ITP, no inhibition was observed. At saturing concentration of GTP, ATP still inhibited phosphofructokinase.Both 3′5′ AMP and fructose 6 phosphate increased the concentration of ATP required to produce an inhibition of 50 %.Citrate, like ATP, inhibited phosphofructokinase by binding most likely at the same allosteric site. Erythrocyte phosphofructokinase is inhibited by 2–3 DPG.The study of the relation log V max = f (pH) suggested, that the active center contains at least one imidazole and one sulfhydryl group.     

Contribution à l'étude de la structure de la chromatine: I - Etude physico-chimique de la stabilité de la chromatine

Physicochemical studies of calf thymus chromatin were performed on micromicellar suspensions by thermal denaturation. These diluted suspensions were obtained, by a controlled shearing method, from a compact gel chromatin. Sedimentation and free-flow electrophoresis determined the size distribution of these particles. The most important result is a new transition on the melting profiles corresponding to a sudden increase of solution turbidity. This chromatin solution transition occurs at a higher temperature than usual DNA transition. The degree of « turbidity transitiondiminishes with micelle size but disappears when they are very mildly degraded by DNAases and when F₁ histone fraction is removed.This transition is not only size dependent but also depends on the micellar structure. This phenomenon is interpreted as an excluded volume effect by contact between compact and native regions of nucleoprotein micelles and denatured coils of DNA. Our study tried to show that the degree of turbidity transition can be a criterion of chromatin native structure.