Danielle Laval-Martin

Pigment evolution in Lycopersicon esculentum fruits during growth and ripening

Abstract During growth and subsequent maturation, the distribution and formation of pigments in the inner pulp and in the outer region of the pericarp of ‘che

Photosynthetic properties of a DCMU resistant strain of Euglena gracilis Z.

Abstract When present during the photoheterotrophic growth of Euglena gracilis Z; DCMU, in addition to the usual inhibition of photosynthetic electron transport, induces important losses of chlorophyll and severe disorganization of chloroplast structure. After two months of growth under these conditions, however, these parameters recover their normal properties and the cells become resistant to the dose of DCMU to which they were exposed. The sensitivity of photosynthetic electron transport to increasing concentrations of DCMU was analyzed in whole cells of the wild-type and resistant strains as well as in their respective isolated chloroplasts, using oxygen evolution and fluorescence induction to measure the DCMU effects. Another photosynthetic electron transport inhibitor, ortho-1, 10-phenanthrolene (ORPHE), believed to act at the same site as DCMU, was also used to obtain dose-response curves as for DCMU, and similar results were obtained. The results suggest that the resistance, which is a function of the dose, is due neither to the acquired ability of the cells to transform DCMU into an inactive form nor to the acquisition of a permeability barrier to DCMU. It appears that DCMU resistance is caused at the level of intracellular DCMU-sensitive reactions, particularly of photosynthetic electron transport.

Characterization of diuron-resistant Euglena: Greater tolerance for various phenylurea herbicides and increased sensitivity of thylakoids to ethyl-S-dipropyl thiocarbamate

Abstract The thylakoid modifications induced by diuron confer upon the wild type strain Euglena gracilis (Z) a resistance to various phenylurea herbicides, which is inversely proportional to the size of the ‘R’ group substituents of the urea nitrogen common to all of these herbicides. There diuron-resistant cells (ZR) are also resistant to atrazine but not to the same extent. Conversely they are more sensitive to ethyl-S-dipropyl thiocarbamate (EPTC). We show that EPTC affects pigment-protein complexes by somehow causing a partial destruction of the chlorophylls. The analyses of fluorescence induction indicate that in ZR cells, the pigment-protein complexes which are less efficient in energy gathering for photosystem II (PS II) are more rapidly attacked by EPTC than the more efficient complexes. The opposite holds true for Z cells.

Analyse spectrophotometrique des chlorophylles et des pheophytines a et b en milieu hydroacetonique: Détermination des extinctions molaires

Resume Les auteurs ont determines les coefficients dabsorption specifique des chlorophylles a et b, en milieu eau-acetone. Le magnesium est dose dans chaque chlorophylle a laide dEDTA et determination du point final par voltametrie. Le noyau porphyrine est titre par le cuivre(II) dans lacide acetique anhydre avec determination du point final, simultanement par spectrophotometrie et par potentiometrie. Des resultats identiques pour ces deux titrages constituent un critere de purete des chlorophylles examinees. Dautre part, ils permettent une determination rigoureuse de labsorption molaire de lun de ces pigments, pour une longueur donde donnee.

Oxygen uptake by Euglena gracilis mitochondria and chloroplasts, stimulated by ultraviolet irradiation

Abstract Oxygen consumption by etiolated or green (treated with 5 μM DCMU) Euglena is activated by ultraviolet irradiation. This photostimulation exists in both mitochondrial and chloroplasts fractions, in which it is enhanced by 6.6 mM cyanide (a chloroplast fraction of spinach was also tested). The treatment of these subcellular fractions with sodium deoxycholate which affects electron transport chains, does not eliminate the phenomenon. Whole cells and subcellular fractions behave as do irradiated ubiquinone and plastoquinone in isopropanol-water mixtures. We propose a model in which quinone pools occupy a crossover position and could be directly light activated, with O2 as the electron acceptor, and leading to the formation of H2O2.

Analyse spectrophotometrique des chlorophylles et des pheophytines a et b en milieu hydroacetonique: Méthode cinétique de dosage

Resume En fixant le taux dhydratation et la concentration en protons dans les milieux acetoniques, on peut obtenir une difference importante entre les vitesses de pheophytinisation des chlorophylles a et b. Ces proprietes sont utilisees pour doser selectivement ces pigments par spectrophotometrie, dans les extraits hydroacetoniques de vegetaux. Les phenomenes de pheophytinisation obeissent a des lois exponentielles; leurs cinetiques peuvent etre enregistrees a une longueur donde choisie selon les concentrations relatives des chlorophylles a et b presentes dans lextrait vegetal. Le dosage de la chlorophylle a et de la chlorophylle b est effectue dans des extraits acetoniques a 10% deau. Les conditions preconisees permettent une pheophytinisation 25 a 35 fois plus rapide pour la chlorophylle a que pour la chlorophylle b. La duree du dosage nexcede pas 15 min. Les calculs des concentrations en chlorophylles et en pheophytines sont effectues a laide des extinctions molaires determinees pour le solvant utilise. Les teneurs en pigments sont ainsi obtenues avec une precision superieure a ±2%, quelles que soient les concentrations relatives en chlorophylles a et b.

Three chloroplast membrane models corresponding to different photosynthetic potentialities in the same plant

The biochemical characteristics and photosynthetic activities of chloroplast membranes of the two regions of the green tomato fruit were compared to those of the leaves which were taken as controls. Membranes may have qualitatively (and even quantitatively) identical components, such as lipids and chlorophylls, and yet have different photosynthetic abilities. Three models then are proposed.

Analysis and characterization of DCMU-resistant Euglena gracilis : III. Thylakoid modifications and dark "recovery" of photosynthesis.

Dark-grown, DCMU-adapted Euglena gracilis Z (ZR) are able to undergo light-induced chloroplast development in the presence or absence of DCMU. The differentiated chloroplasts are photosynthetically active and are resistant not only to DCMU, but also to an analog, o-phenanthrolene. When DCMU overdoses are added to ZR cells or to chloroplasts isolated from these cells, photosynthesis is partially inhibited. A brief period of darkness removes this inhibition. This recovery phenomenon is related to DCMU resistance, since it is not exhibited by non-resistant control cells. The chloroplast protein synthesis apparatus is not involved in DCMU resistance. Rather, this phenomenon is apparently related to new characteristics of thylakoids. It is shown that photosynthetic recovery by ZR cells depends on the accessibility and fluid properties of membranes. The analysis of fluorescence induction kinetics shows that changes in the environmental conformation of photosystem II units occur during recovery.

Modifications of thylakoid lipids in euglena gracilis during diuron-adaptation

Abstract The adaptation of Euglena gracilis to 25 μM diuron leading to a new resistant strain ZR results from a dedifferentiation then a redifferentiation of the photosynthetic structures and activities. The interactions between lipids and photosynthetic ability, and the biosynthetic pathways of galactolipid fatty acids were studied by following lipid changes (classes and fatty acids). During adaptation strong correlations existed between monogalactosyl diacylglycerol, digalactosyl diacylglycerol and chlorophyll for photochemistry. During the first weeks of treatment, diuron seemed to inhibit fatty acid desaturation and activated elongation. It was concluded that the mutation of the M , 32–34 K protein produced by the diuron action is accompanied by lipid changes of the thylakoid matrix.