Decreases in the concentration of ozone in the stratosphere are predicted to result in more biologically damaging ultraviolet-B radiation (UVBR) reaching the Earth's surface in the near future. The consequences for plant life of this small change in the solar spectrum are currently uncertain; this is particularly true for aquatic macrophytic algae. The aim of this review is to summarize the current knowledge of UVBR effects on macrophytes, and to highlight areas for future research. An overview of published underwater UVBR measurements shows that penetration of this waveband is low in the coastal waters where most macroalgae are found. Knowledge of UVBR targets in macroalgae is poor, and biological weighting functions have yet to be established. Studies of higher plants and phytoplankton are used to illustrate the many possible targets and effects of UVBR. The role of photosynthetically active radiation in causing dynamic and chronic photoinhibition in macroalgae and the interactions of PAR with UVR are examined in detail. These interactions are central to interpretation of field measurements of photoinhibition under natural solar radiation conditions. Potential strategies and mechanisms for repair of UVBR damage are discussed. Before the long-term effects of UVBR on macroalgal production and community structure can be determined, a greater knowledge of the specific targets of UVBR in macrophytes and the mechanisms of protection and repair must be determined. The ability of macrophytes to acclimate to higher UVBR and the interaction of UVBR with other stresses, such as high PAR, temperature and desiccation, must be assessed. Studies are needed which encompass effects on all stages of the macrophyte life cycle, from recruitment to maturity.

Nostoc punctiforme is the microsymbiont of the unique fungal endocyanosis Geosiphon pyriforme. During the establishment of this endosymbiosis fungal hyphae incorporate a specific stage of the N. punctiforme life cycle, formed during differentiation from the motile hormogonium to the non-motile primordium stage. The life cycle of N. punctiforme was synchronized by first inducing hormogonium differentiation by red light illumination for 36 h, followed by applying light/dark cycles for 96 h. Different developmental stages of N. punctiforme including hormogonia, primordia and vegetative colonies were analysed by fluorescein isothiocyanate (FITC)-conjugated lectins with sugar specificity to α-D-mannose/α-D-glucose, N-acetyl-β-D-glucosamine oligomers, α-L-fucose, β-D-galactose, α-D-galactose, N-acetyl-α-D-galactosamine and sialic acid. Lectin binding properties indicate that the slime produced by the motile hormogonia contains β-D-galactosyl and α-L-fucosyl residues, which disappear during further development. There is a clear correlation between the transition from the hormogonium to the non-motile primordium stage and the appearance of a large amount of α-D-mannosyl (or α-D-glucosyl) residues in the extracellular slime. This strongly Concanavalin A (Con A)-positive compound is lost in part during later differentiation into vegetative colonies. Consequently these significant changes in the Nostoc slime, occurring at the developmental stage involved in the establishment of the Geosiphon symbiosis, could play a role in the specific recognition between the symbiosis partners.

The ultrastructure of male gametes of Ectocarpus siliculosus is described and discussed in relation to the information available on other brown algal zoids. In general, the fine structure and the organelle associations agree with those of other brown algal cells. In particular, the male gametes typically contain a single chloroplast with a pyrenoid and a prominent concave eyespot, into which the swelling of the posterior flagellum (the photoreceptor) fits. The continuity of the chloroplast endoplasmic reticulum and nuclear membrane, as well as the presence of a perinuclear Golgi consisting of several dictyosomes, is shown. The fine structure of microbodies, lipid bodies and different types of vesicles, including physodes and coated vesicles, is also discussed. Several specializations of cellular elements and their interactions are unique and have not been reported before. These features include the connection between the nuclear envelope, the Golgi and the flagellar bases mediated by fibres resembling intermediate filaments, and the organization of the Golgi as well as the association of mitochondria and a microtubular flagellar root.

The fine structure of the flagellar apparatus of male gametes of Ectocarpus siliculosus has been studied in negatively stained whole-mount preparations of isolated flagellar apparatuses and by transmission electron microscopy of embedded whole cells and flagellar apparatuses. Reconstructions from serial sections revealed a single absolute configuration and new structural details of the flagellar apparatus. A set of 5 microtubular roots is associated with the 2 flagellar basal bodies: the major anterior root consisting of 9 microtubules originates at the anterior basal body and loops through the anterior part of the cell. Cytoplasmic microtubules originate from this root at the apex of the cell and splay out in a posterior direction through the cell, thus determining cell shape. A broad microtubular band composed of a 9-membered bypassing root and a 3-membered major posterior root runs across the basal bodies. Two additional flagellar roots, the minor anterior and minor posterior rootlets, consist of a single microtubule each. The proximal end of the posterior basal body is laterally connected to the anterior basal body by a cross-striated connective (deltoid band). The basal bodies are connected to the nucleus by a small rhizoplast, and several other fibrous structures are associated with the basal bodies. The results are discussed in relation to earlier observations on flagellar apparatus organization in brown algae.

Gelidium maggsiae sp. nov. is described from plants found in shallow subtidal maërl beds off the west coast of Ireland, where it attaches to detached coralline algae by peg-like rhizoids. Rhizines are more abundant in the medullary region than in the cortex and erect axes display a prominent central row formed by the axial and periaxial filaments. Gametophytes are bisexual and protandrous and were found only in culture. Post-fertilization and cystocarp development are similar to that of G. pteridifolium and cystocarps are biloculate. Tetrasporophytes are morphologically similar to gametophytes; tetrasporangia are irregularly arranged in pod-shaped terminally inserted stichidia, borne on erect axes and arranged unilaterally. Gametangial plants reproduced under short-day (8[ratio ]16 h) conditions at 20–25°C in enriched media, but gametangial formation was independent of photoperiod when plants were kept in unenriched medium. No tetrasporophytic plants were produced from germinated carpospores, but plants originally collected in a vegetative state formed tetraspongia at 20°C, 16[ratio ]8 h. The validity of several characters previously used in species delimitation within the Gelidiales is discussed, and only cystocarp structure and the bisexual nature of the gametophyte are considered to be reliable characters.

The stress-70 protein family has previously been shown to be a useful tool for molecular phylogeny at the kingdom to family levels. Although sequences of many members of the stress-70 family are available, few genes from the Protoctista have been sequenced to date. Phylogenetic analyses of algae based on various molecules have not, as yet, provided clear results concerning relationships between major divisions. We cloned and sequenced several algal stress-70 genes in order to provide additional data and to further analyse phylogenetic relationships among algal divisions. New nuclear sequences were obtained from Guillardia theta (Cryptophyta), Ascophyllum nodosum (Heterokontophyta) and Cyanophora paradoxa (Glaucocystophyta). Phylogenetic trees of the stress-70 protein family calculated using different methods are presented. In our trees, the heterokont alga Ascophyllum nodosum is closely related to the slime mould Dictyostelium discoideum, while the nucleomorph (eukaryotic endosymbiont) of the cryptophyte Rhodomonas salina seems to be related to the chlorobiont lineage. The glaucocystophyte Cyanophora paradoxa and the nuclear sequence (host) of the cryptomonad alga Guillardia theta also seem to be closely related. The Cryptophyta and the heterokont algae have evolved from different secondary endosymbiotic events involving different hosts and probably different endosymbionts. However, until more stress-70 sequences of algal divisions become available no definitive conclusions can be drawn concerning branching of the major divisions.

DNA of Chara vulgaris thalli contains target sequences for the methylation-sensitive restriction enzymes, Sau3A, HpaII and MspI. These enzymes were used with the in situ nick-translation radioactive technique to evaluate by grain counting in autoradiograms changes in cytosine methylation during antheridial filament development and spermiogenesis. In successive generations of dividing antheridial filaments the level of DNA methylation gradually increases, then decreases slightly in the early stages of spermiogenesis. Spermatozoids display the highest level of DNA methylation.

The marine red alga known as Laurencia obtusa var. snackeyi (Weber–van Bosse) Yamada (Rhodomelaceae, Ceramiales) is characterized as follows: (1) production of 4 periaxial cells from each axial cell; (2) a few, percurrent, terete, thick main axes arising from a single discoid holdfast without stolon-like branches; (3) alternate-spiral branching; (4) presence of longitudinally oriented secondary pit-connections between contiguous superficial cortical cells; (5) absence of a palisade-like layer; (6) absence of projecting superficial cortical cells; (7) absence of lenticular thickenings in the walls of medullary cells; (8) parallel arrangement of tetrasporangia; and (9) presence of one corps en cerise per superficial cortical cell and trichoblast cell. It differs from L. obtusa (Hudson) Lamouroux in the absence of stolon-like branches with secondary attachment discs and the presence of thicker axes. The following binomial is proposed: Laurencia snackeyi (Weber–van Bosse) Masuda, stat. nov. Halogenated secondary metabolites of this species were investigated for samples from Vietnam and Malaysia. The major metabolites of the Vietnamese sample are palisadin A and aplysistatin, both sesquiterpenoids, whereas the Malaysian samples contain these compounds along with another monocyclofarnesol-derived sesquiterpenoid, 5-acetoxypalisadin B. L. snackeyi is also characterized by this set of secondary metabolites.

Examination of type material, comparative studies on vegetative characters and data from published accounts of sporangia, gametangia and spermatozoids are used here to further develop and strengthen generic and species concepts in Zonaria and Homoeostrichus. Zonaria is characterized by octosporangia which lack a stalk cell and occur among whitish paraphyses, by the presence of cortical cells in indusiate sporangial and oogonial sori, and by slightly elongate sterile cells bordering the antheridial sori. Other characters (mucilage in sporangial and oogonial sori, biflagellate sperm with a row of many tall spines along the anterior flagellum) may also be diagnostic of Zonaria but have not been demonstrated in the generitype. Eight species are retained in Zonaria. Generic placement of Zonaria stipitata, described on vegetative characters, requires confirmation. Homoeostrichus, as typified by Homoeostrichus sinclairii, is defined by the presence of brown paraphyses in nonindusiate sporangial and oogonial sori and bordering antheridial sori, a multicellular sporangial stalk, oogonia without a stalk cell, and uniflagellate spermatozoids. Zonaria harveyana and Homoeostrichus olsenii are similar in sporangial structure, but they cannot be assigned to either Zonaria or Homoeostrichus as now defined and consequently are transferred to the new genus, Exallosorus, as Exallosorus harveyanus (Pappe ex Kützing) comb. nov. and Exallosorus olsenii (Womersley) comb. nov. Exallosorus is distinguished from Zonaria and Homoeostrichus using sporangial characters: tetrasporangia have a stalk cell and are closely packed into indusiate sori which lack paraphyses and mucilage. Problems in obtaining reliable species identification for the five southern Australian species of Zonaria are partially resolved. This study demonstrates again the essential contribution of reproductive characters to the definition of taxa and supports the position that decisions to erect, subsume or transfer members of the Dictyotales should be based on more than vegetative characters.