Leaf chlorosis in oilseed rape plants (Brassica napus) grown on cadmium-polluted soil: causes and consequences for photosynthesis and growth.

Brassica napus L. (oilseed rape) was grown from seeds on a reconstituted soil contaminated with cadmium (100 mg Cd kg-1 dry soil), resulting in a marked chlorosis of the leaves which was investigated using a combination of biochemical, biophysical and physiological methods. Spectroscopic and chromatographic analyses of the photosynthetic pigments indicated that chlorosis was not due to a direct interaction of Cd with the chlorophyll biosynthesis pathway. In addition, mineral deficiency and oxidative stress were apparently not involved in the pigment loss. Leaf chlorosis was attributable to a marked decrease in the chloroplast density caused by a reduction in the number of chloroplasts per cell and a change in cell size, suggesting that Cd interfered with chloroplast replication and cell division. Relatively little Cd was found in the chloroplasts and the properties of the photosynthetic apparatus (electron transport, protein composition, chlorophyll antenna size, chloroplast ultrastructure) were not affected appreciably in plants grown on Cd-polluted soil. Depth profiling of photosynthetic pigments by phase-resolved photoacoustic spectroscopy revealed that the Cd-induced decrease in pigment content was very pronounced at the leaf surface (stomatal guard cells) compared to the leaf interior (mesophyll). This observation was consistent with light transmission and fluorescence microscopy analyses, which revealed that stomata density in the epidermis was noticeably reduced in Cd-exposed leaves. Concomitantly, the stomatal conductance estimated from gas-exchange measurements was strongly reduced with Cd. When plants were grown in a high-CO2 atmosphere (4,000 microliters CO2 l-1), the inhibitory effect of Cd on growth was not cancelled, suggesting that the reduced availability of CO2 at the chloroplast level associated with the low stomatal conductance was not the main component of Cd toxicity in oilseed rape.

Vesicles and other supramolecular systems from biocompatible synthetic glycolipids with hydrocarbon and/or fluorocarbon chains.

A series of double-tailed hydrocarbon and/or fluorocarbon glycolipids derived from galactose and glucose have been prepared. These compounds were obtained upon opening a lactono- and maltonolactone moiety by the amino group of either a glycine, glycylglycine or lysine residue. The carboxyl terminus of the glycyl and glycylglycine conjugates was further reacted with the appropriate double-tailed amine. In the case of lysine, the lactonamide conjugate was functionalized with a hydrocarbon and/or fluorocarbon fatty amine and acid, respectively. The ability of such glycolipids to disperse in water, the morphology of self-assemblies formed and the stability of the supramolecular structure obtained were shown to depend on the presence or absence and on the nature of the aminoacid spacer. Most of the compounds described were shown by conventional techniques (TEM, Cryo-TEM, LLS, etc.) to produce stable vesicular systems.

Use of triton WR-1339 in cytochemical and biochemical characterization of phytolysosomes.

A new cytochemical assay of acid phosphatase activity employing Triton WR-1339, a non-ionic detergent, has been used to demonstrate the probable origin of the phytolysosome system and of the organization of the Golgi complex in the root meristem, Cucurbita pepo. The results were controlled biochemically by differential and linear density gradient ultracentrifugation of extracts from normal and Triton-treated roots. The various fractions were characterized by electron microscopy or by assay of marker enzymes.