ABSTRACT
The interactive effects of an 8 h exposure to UV radiation and altered temperatures on the ultrastructure and germination of zoospores of the sublittoral brown alga Laminaria hyperborea (Gunn.) Foslie were investigated for the first time. Spores were exposed to four temperatures (2, 7, 12 and 17 degrees C) and three light regimes (PAR, PAR + UV-A, PAR + UV-A+UV-B). Freshly-released spores of L. hyperborea lack a cell wall and contain a nucleus with fine granular nucleoplasm and a nucleolus, one chloroplast, several mitochondria, dictyosomes and an endoplasmatic reticulum. Further, several kinds of so-called adhesive vesicles, lipid globuli and physodes containing UV-absorbing phlorotannins are embedded in the cytoplasm. No eye-spot is present. Physodes were found but they were rare and small. After an 8 h exposure to UV-B, the nucleoplasm had a mottled structure, chloroplasts contained plastoglobuli, the structure of the mitochondria changed from crista- to sacculus-type and germination was strongly inhibited at all temperatures. UV-A only had an impact on the ultrastructure at the highest temperature tested. The strongest effects were found at 17 degrees C, where germination was reduced to 35%, 32% and 9% after exposure to PAR, PAR+UV-A and PAR + UV-A + UV-B, respectively. This study indicates that UV-B radiation has strong damaging effects on the physiology and ultrastructure of zoospores of L. hyperborea. The results are important for developing scenarios for the effect of enhanced UV radiation and increasing temperatures caused by global climate changes.
Subject(s)
Laminaria/ultrastructure , Spores/ultrastructure , Temperature , Ultraviolet Rays , Laminaria/growth & development , Laminaria/radiation effects , Spores/growth & development , Spores/radiation effectsABSTRACT
The N-terminus of the major polypeptide component of the light-harvesting complex (LHC) from the brown alga Laminaria saccharina is blocked. Two partial sequences, one near the N-terminus and the other near the C-terminus, have been obtained by chemical cleavage with acetic acid and N-chlorosuccinimide. Four peptides were separated after trypsin digestion of the thylakoid membranes. One fragment is not phosphorylated, is not blocked, and has been sequenced. Purification on a reversed-phase column showed two forms of the LHC protein: the more hydrophobic form appears to be bound to photosystem I. These results are compared with LHC from other Chromophytes and the CAB family of green plants.
Subject(s)
Carotenoids/analogs & derivatives , Chlorophyll/chemistry , Chloroplasts/ultrastructure , Laminaria/chemistry , Photosynthetic Reaction Center Complex Proteins/chemistry , Xanthophylls , Amino Acid Sequence , Aspartic Acid/metabolism , Carotenoids/chemistry , Carotenoids/metabolism , Chlorophyll/metabolism , Chlorophyll A , Chloroplasts/chemistry , Intracellular Membranes/chemistry , Laminaria/ultrastructure , Light-Harvesting Protein Complexes , Molecular Sequence Data , Peptide Fragments/chemistry , Peptide Fragments/metabolism , Phosphorylation , Photosynthetic Reaction Center Complex Proteins/metabolism , Photosystem I Protein Complex , Proline/metabolism , Sequence Analysis , Succinimides , Trypsin/metabolismABSTRACT
Thin sections of tissue preparations from a green alga, Ulva lactuca (Ulvophyceae), and brown alga, Laminaria digitata (Pheophyceae) showed the presence of coated pits and coated vesicles in these 2 species. A discontinuous sucrose gradient after subcellular fractionation of the tissue homogenate resulted in an enriched coated vesicle fraction. Electron microscopy of negatively stained samples revealed the presence of coated vesicles of diameter ranging from 40-125 nm, together with large sheets of polygonal nets of clathrin. Electrophoresis of the CV purified fraction revealed various polypeptide components. Two of them, a 175 kDa and a 70 kDa, exhibited a positive response to bovine brain anticlathrin antibodies raised in goat or in rabbit. A third component of 30-40 kDa also gave a faint positive response. These 3 components corresponded to the clathrin heavy and light chains already described in higher plants. Clathrin was released from the CV algal preparations by treatment with 2M urea in Tris buffer, pH 8.5. Interestingly, in Ulva lactuca, the proportion of clathrin relative to the other proteins from the CV decreased with plant growth. Biochemical analysis of the purified CV revealed the presence of all the major phospholipids characterized in mammalian CV. The ratio of protein over lipid was also in the same range as that calculated for mammalian CV. Carbohydrate analysis demonstrated a high proportion of N-acetylgalactosamine and N-acetylglucosamine in both algal CV whereas these sugars were not detectable in the crude homogenate. These results demonstrate the presence of clathrin and coated vesicles in 2 species of algae.(ABSTRACT TRUNCATED AT 250 WORDS)
