N. Rascio

The vegetative thallus of Pterocladia capillacea (Gelidiales, Rhodophyta). I, An ultrastructural and cytochemical study

An ultrastructural study of the vegetative thallus of the red alga Pterodadia capillacea (Gmel.) Born, et Thur. has been carried out. Different kinds of cells have been recognized and described. The small cortical cells, rich in plastids, seem to be more specifically involved in photosynthesis, while the large medullary cells might essentially operate in nutrient storage. The distribution of mechanical elements has been well defined in different thallus regions. The cell wall organization and the localization of agar components in the extracellular compartment have been cytochemically analyzed.

Effects of Amitrole and Norflurazon on Carotenogenesis in Barley Plants Grown at Different Temperatures

A carotenoid deficiency can account for serious alterations of thylakoids, due to the essential roles played by these pigments in membrane protection against photo-oxidative damage (1,2). In spite of carotenoid importance in preserving the photosynthetic apparatus, information on their biosynthesis in green tissues is rather scarce, and the knowledge of carotenogenesis and its regulation mainly comes from studies on chromoplasts of ripening fruits (3,.4). Previous research on the lycopinic tigrina o 34 mutant of barley (5) and on barley plants treated with amitrole (6), a herbicide inhibiting lycopene cyclization (7), showed that plant growth temperature could affect carotenoid biosynthesis in leaf chloroplasts, suggesting the existence of thermo-modulated steps bypassing the block of mutation or herbicide. Recently, in tomato (4) and Arabidopsis (8) alternative reactions, which allow s-carotene and xanthophylls to be synthesized without involving lycopene as intermediate, have been proposed. In order to better define the relationship between temperature and carotenoid synthesis in chloroplasts, barley plants have been grown at two rather close temperatures. They have been treated with two herbicides, to analyze whether interruption of the carotenogenic pathway at distinct points would cause differentiated responses to the change in plant growth temperature. The two chemicals used were norflurazon (NF) and amitrole (AM), which inhibit phytoene desaturation and lycopene cyclization, respectively (7). In leaves of plants grown in different experimental conditions, the total and relative quantities of carotenoids synthesized and the ratios between the pigment forms were analyzed. The ultrastructural organization, chlorophyll contents and photosynthetic activity of chloroplasts were also investigated, to verify the photooxidative damage caused by the disturbed carotenoid biosynthesis.

Some observations on phycobilisomes of Pterocladiella capillacea (Gelidiaceae, Rhodophyta)

ABSTRACT Phycobilisomes (PBSs) of the red alga Pterocladiella capillacea collected in the field, were characterized both in situ and in vitro by means of a transmission electron microscope (TEM) and an image analyzer. Ultrathin sections of thalli and negatively stained PBSs after isolation revealed hemi-ellipsoidal shapes. In situ PBS dimensions were 38.5 ± 0.2 nm (height) × 38.8 ± 0.2 nm (width) × 22.6 ± 0.2 nm (thickness) in good agreement with the in vitro measurements (mean diameters of 37.6 ± 0.2 nm). These dimensions, especially the width, are smaller than those so far reported for red algae. This could depend either on the ecophysiological conditions of the thalli when harvested and/or on a staggered, symmetrically rotated and compressed disposition of biliprotein rods with respect to the allophycocyanin (APC) core. Hydroxylapatite chromatography of biliproteic extracts and SDS-PAGE electrophoresis revealed that phycoerythrin type R-(λmax 565 nm>540 nm>498 nm) is formed by α (18.6 kDa), β (19.9 kDa...

The vegetative thallus of Pterocladia capillacea (Gelidiales, Rhodophyta). II, Pit connections

Pit connections have been investigated in the vegetative thallus of the red alga Pterocladia capillacea (Gmel.) Born, et Thur. Both a polysaccharidic and a proteinaceous component have been found by cytochemical tests in these pit connections, which did not seem to be covered by a cap membrane.

Morphological, Ultrastructural and photosynthetic features of two freshwater angiosperms.

Colonization of the aquatic environment by flowering plants has required the evolution of morphological and physiological adaptative mechanisms useful to face the numerous limiting factors which can make it difficult for a macrophyte to live in water.