Danielle Dupeyre

Pathway of Cytosolic Starch Synthesis in the Model Glaucophyte Cyanophora paradoxa

ABSTRACT The nature of the cytoplasmic pathway of starch biosynthesis was investigated in the model glaucophyte Cyanophora paradoxa. The storage polysaccharide granules are shown to be composed of both amylose and amylopectin fractions, with a chain length distribution and crystalline organization similar to those of green algae and land plant starch. A preliminary characterization of the starch pathway demonstrates that Cyanophora paradoxa contains several UDP-glucose-utilizing soluble starch synthase activities related to those of the Rhodophyceae. In addition, Cyanophora paradoxa synthesizes amylose with a granule-bound starch synthase displaying a preference for UDP-glucose. A debranching enzyme of isoamylase specificity and multiple starch phosphorylases also are evidenced in the model glaucophyte. The picture emerging from our biochemical and molecular characterizations consists of the presence of a UDP-glucose-based pathway similar to that recently proposed for the red algae, the cryptophytes, and the alveolates. The correlative presence of isoamylase and starch among photosynthetic eukaryotes is discussed.

First evidence for the presence of weddellite crystallites in Opuntia ficus indica parenchyma

Abstract Calcium oxalate crystallites occur very often in the plants tissues and their role is still poorly known. We report here the experimental protocol leading to the isolation of two forms of calcium oxalate crystallites differing in their hydration level in the parenchymal tissues of Opuntia ficus indica (Miller). Whereas the whewellite crystallites are habitual in all Opuntia species, the weddellite form has never been isolated from these species before, which is probably due to their small size (about 1 μm). We have identified these forms using X-ray diffraction and scanning electron microscopy.

Cellulose-Copolyamide 6,69 Blends

SYNOPSIS In a previous work [J. Polym. Sci. Polym. Phys., 32, 1437 (1994)], a technique for the preparation of cellulose-polyamide 66 (PA66) blends was proposed. It was shown that the crystallization of PA66 is responsible for the phase separation and, furthermore, for the morphology of the domains in the blends. For this reason, the use of a quasi-amorphous polyamide, i.e., a random copolymer of units 6 nd 69, instead of PA66, is now investigated. Cellulose-polyamide 669 (PA669) blends were krepared by a solution-precipitation process. A mixture of N-methylmorpholine-N-oxide and phenol (80/20 wt/wt) was used as a common solvent. Materials were precipitated whether in methanol or in water. The fibers obtained were characterized by scanning electron microscopy, mechanical spectroscopy, and tensile tests. It is shown that the morphology of these blends depends on the precipitation system and is a function of the different steps of processing of the blends. 0 1996 John Wiley & Sons. Inc.

Structural studies on V-amylose inclusion complexes

Amylose, the linear homopolymer of α-D-glucose found in native starch, can be crystallized from dilute solutions by addition of a large variety of organic guests (alcohols, lipids, aromas, etc.) [1,2]. The morphology and structure of the resulting V-type crystals depend on the nature of the complexing molecule and parameters such as degree of polymerization (DP), concentration and crystallization temperature [3].