Photosynthesis of two Arctic macroalgae under different ambient radiation levels and their sensitivity to enhanced UV radiation

The change in optimal quantum efficiency (F _v/F _m) of the Arctic species Laminaria saccharina and Palmaria palmata was investigated in a long-term experiment in situ under different radiation levels during the summer of 1997 in the Kongsfjord (Ny-Ålesund, Spitsbergen, Norway, 78°55.5′N, 11°56.0′E). Whole plants were incubated in an open box system made of UV-transparent Perspex and exposed to solar radiation (λ>295?nm), solar radiation excluding UVB (λ?>?320?nm) and solar radiation excluding UVA?+ UVB (λ?>?400?nm). Increasing radiation levels were simulated by transplantation of the pre-adapted algae from their growth depth at 2?m to a water depth of 1?m. Sensitivity to artificially increased UV radiation was determined by exposure of algae from the three treatments to 6?h of strong UV radiation. P. palmata was relatively insensitive to increasing UV radiation and recovered very fast and almost completely in 2?h. Even plants pre-cultured in ambient radiation levels excluding UVA?+?UVB or UVB only showed no photoinhibition after exposure to extra UV radiation in the laboratory. L. saccharina was, in comparison to P. palmata, more sensitive and showed photoinhibition under solar radiation and solar minus UVB radiation after transplantation from 2 to 1?m water depth. However, after 3?weeks at 1?m depth, F _v/F _m of L. saccharina was equal in all treatments and restored to the original values at the start of the experiment. Sensitivity to extra UV radiation in the laboratory increased in time, although recovery was also fast and occurred within 20?h.     

ACCLIMATION OF PHOTOSYNTHESIS AND PIGMENTS DURING AND AFTER SIX MONTHS OF DARKNESS IN PALMARIA DECIPIENS (RHODOPHYTA): A STUDY TO SIMULATE ANTARCTIC WINTER SEA ICE COVER1

The influence of seasonally fluctuating photoperiods on the photosynthetic apparatus of Palmaria decipiens (Reinsch) Ricker was studied in a year‐round culture experiment. The optimal quantum yield (F_v/F_m) and the maximal relative electron transport rate (ETR_max), measured by in vivo chl fluorescence and pigment content, were determined monthly. During darkness, an initial increase in pigment content was observed. After 3 months in darkness, ETR_max and F_v/F_m started to decrease considerably. After 4 months in darkness, degradation of the light‐harvesting antennae, the phycobilisomes, began, and 1 month later the light harvesting complex I and/or the reaction centers of PSII and/or PSI degraded. Pigment content and photosynthetic performance were at their minimum at the end of the 6‐month dark period. Within 24 h after re‐illumination, P. decipiens started to accumulate chl a and to photosynthesize. The phycobiliprotein accumulation began after a time lag of about 7 days. Palmaria decipiens reached ETR_max values comparable with the values before darkness 7 days after re‐illumination and maximal values after 30 days of re‐illumination. Over the summer, P. decipiens reduced its photosynthetic performance and pigment content, probably to avoid photodamage caused by excess light energy. The data show that P. decipiens is able to adapt to the short period of favorable light conditions and to the darkness experienced in the field.     

Enzymatic defences against photooxidative stress induced by ultraviolet radiation in Arctic marine macroalgae

The activities of the antioxidant enzymes superoxide dismutase (SOD), glutathione reductase (GR), ascorbate peroxidase (APX) and catalase (CAT), as well as the content of the antioxidant compound ascorbic acid, were determined in five green, seven red and ten brown macroalgal species from the Kongsfjord (Spitsbergen, Svalbard, Norway). In general, higher antioxidant enzyme activities and a higher content of ascorbic acid were measured in green algae in comparison to red and brown algae. Species from the eulittoral and upper sublittoral (Acrosiphonia penicilliformis, Monostroma arcticum, Chaetomorpha linum, Chaetomorpha melagonium, Devaleraea ramentacea, Palmaria palmata) showed higher antioxidant enzyme activities compared to species from the lower sublittoral, indicating a more efficient biochemical protection in algae exposed to higher stress conditions in the field. The activity of GR was stimulated by artificial ultraviolet radiation in the green alga M. arcticum, and in the red algae Coccotylus truncatus and Phycodrys rubens after 84 h under continuous exposure. GR activity was even higher when the UV exposure was followed by incubation in darkness for 24 h, indicating a higher elimination rate of toxic oxygen radicals under these conditions. D. ramentacea, P. palmata and A. penicilliformis did not show any significant effect of UV radiation on CAT, APX and SOD activities after 8 days of culture under laboratory conditions. However, a significant reduction in activities of GR and SOD was observed in A. penicilliformis when solar UV radiation was cut off by selective filter foils in the field, indicating a lower oxidative stress in the absence of UV radiation. Overall, the ecological success of macroalgae in the eulittoral and upper sublittoral is supported by an enhanced oxygen-reactive scavenging system, allowing fast acclimation to the changes in environmental radiation conditions.     

Temperature dependence of UV radiation effects in Arctic and temperate isolates of three red macrophytes

The temperature dependence of UV effects was studied for Arctic and temperate isolates of the red macrophytes Palmaria palmata, Coccotylus truncatus and Phycodrys rubens. The effects of daily repeated artificial ultraviolet B and A radiation (UVBR: 280–320?nm, UVAR: 320–400?nm) treatments were examined for all isolates at 6, 12 and 18?°C by measuring growth, optimal quantum yield of PSII (F_v/F_m) and cyclobutane-pyrimidine dimer (CPD) accumulation. Furthermore, possible ecotypic differences in UV sensitivity between Arctic and temperate isolates were evaluated. Large species-specific differences in UV sensitivity were observed for all parameters: the lower subtidal species C. truncatus and P. rubens were highly sensitive to the UV treatments, whereas P. palmata, which predominantly occurs in the upper subtidal zone, was not affected by these treatments. Only minor differences were found between Arctic and temperate isolates, suggesting that no differences in UV sensitivity have evolved in these species. Relative growth rates were temperature-dependent, whereas species-specific UV effects on growth rates were relatively independent of temperature. In contrast, the species-specific decrease in F_v/F_m and its subsequent recovery were temperature-dependent in all species. UV effects on F_v/F_m were lower at 12 and 18?°C compared with 6?°C. In addition, UV effects on F_v/F_m decreased in the course of the experiment at all temperatures, indicating acclimation to the UV treatments. CPDs accumulated during the experiment in both isolates of P. rubens, whereas CPD concentrations remained low for the other two species. CPD accumulation appeared to be independent of temperature. The results suggest that summer temperatures occurring in temperate regions facilitate repair of UV-induced damage and acclimation to UV radiation in these algae compared with Arctic temperatures. Because the differences in UV effects on F_v/F_m, growth and CPD accumulation were relatively small over a broad range of temperatures, it was concluded that the influence of temperature on UV effects is small in these species.     

Environmental conditions influence on the physicochemical properties of wild and cultivated Palmaria palmata in the Canadian Atlantic shore

Seaweeds are a promising biomass resource that contain proteins with high potential for sustainable exploration. Palmaria palmata, one of the main red seaweeds of the Canadian coast, has a high protein content and much interest as an ingredient. Understanding the associations between environmental conditions and P. palmata color and chemical composition is of paramount importance to predict optimum harvesting conditions and thus increase its value. This study investigated the influence of environmental conditions on the composition and color of wild and cultivated P. palmata. Important changes in these parameters were found for P. palmata harvested in the subarctic Canadian transition zone, depending on the harvesting site/month. A marked increase in carbohydrates and decrease in ashes content (up to 2-fold) were observed from June to October, while photosynthetically active radiation (PAR) values have decreased. These associations suggest that wild P. palmata is shade acclimated to the Gulf of Saint Lawrence region. Maximum protein content was found for samples in June and was especially higher for samples from Grande-Rivière. Samples were intensely colored in June, possibly related to the higher protein content found in this month. Although several intricate factors seem to influence color development in this species, data from this study assist harvesting sites and period to maximise dark red color and avoid pigmentation degradation and paleness. In sum, these results may help indicate the best site/period to take commercial advantage of this species and orient future research on the multifactored relationships between environmental factors and macroalgae chemical composition and color.

     

Effects of ultraviolet radiation on photosynthesis and related enzyme reactions of marine macroalgae

 Changes in physiological parameters related to photosynthesis were studied in five macroalgal species from Spitsbergen (Monostroma arcticum, Laminaria solidungula, Alaria esculenta, Palmaria palmata, Phycodrys rubens) during a 72-h exposure to UV radiation. Maximal quantum yield of photochemistry (Fv/Fm) and maximal electron transport rate (ETRmax) were measured with a pulse-amplitude-modulated fluorometer; the activity of the Calvin cycle enzymes ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and glyceraldehyde-3-phosphate dehydrogenase (G3PDH) were estimated using a photometric test. Proteins of crude extracts were separated by SDS gel electrophoresis and changes in cellular concentrations of Rubisco were determined. Moreover, the concentration of chlorophyll a (Chl a), and protein content, were measured photometrically. In all species, Chl a content, maximal quantum yield as well as ETRmax decreased during the UV treatment. Changes in ETRmax were related to the changes in the overall activity of Rubisco. Analysis of SDS gels showed that in P. rubens, L. solidungula, M. arcticum and A. esculenta decreasing Rubisco activity partly resulted from a degradation of the enzyme. However, in A. esculenta, the formation of a high-molecular-weight polypeptide was observed. In all species, the activity of Rubisco was more strongly impaired than that of G3PDH. Exposure to UV resulted in loss of total protein only in the deepwater species L. solidungula and P. rubens. The different sensitivities to UV exposure of the species tested reflect their zonation pattern in the field. Received: 4 October 1999 / Accepted: 15 February 2000     

Plastid Replication in Vegetative Cells, Sporangia, Spores and Sporelings of Red Algae

Ultrastructural aspects of proplastid and chloroplast replicationare described as seen in sections of vegetative cells, sporangia,released spores and sporelings of the red algae Palmaria palmataand Plumaria elegans. Proplastids in apical vegetative cellsshow internal thylakoid formation from peripheral thylakoidsin both species, and proplastid formation by budding from maturechloroplasts has also been observed. Proplastid replicationby fission has been occasionally observed, and genophore divisionin the stroma of proplastids. In vegetative cells, sporangia,spores and sporelings chloroplast formation from mature plastidscan take place by elongation and fission, or by formation ofa discrete group of thylakoids which become pinched off fromthe parent chloroplast, and by irregular expansions of the parentchloroplasts with subsequent multiple fission. Plastid replication, vegetative cells, sporangia, spores, red algae     

Photosynthetic performance of Arctic macroalgae after transplantation from deep to shallow waters

Transplantation experiments conducted in the Arctic Kongsfjord (Spitsbergen) in summer 1997 investigated the effects of various types of filtered natural radiation (solar, solar without UV-B, solar without UV-A/B) on photosynthesis of various macroalgae. Two brown algal species (Laminaria solidungula, Saccorhiza dermatodea) and four red algal species (Palmaria palmata, Phycodrys rubens, Phyllophora truncata, Ptilota plumosa) were collected from deeper waters, kept in UV-transparent plexiglass tubes wrapped with different spectral cut-off filter foils and positioned at fixed depths in shallow waters for 7-9 days. At regular intervals, chlorophyll fluorescence of photosystem II (optimum quantum yield, F_v/F_m) was determined, as an indicator of photosynthetic performance. The data demonstrate that shallow-water species such as P. palmata are much less affected by natural photosynthetically active radiation (PAR) and UV radiation near the surface than extremely sensitive deep-water species such as Phyc. rubens which exhibited strong decreases in photosynthetic performance, as well as photobleaching of part of the thallus. The other species showed intermediate response patterns. In most species investigated inhibition of photosynthesis was mainly caused by the UV-B wavelengths. Interpretation of the data clearly indicates species-specific tolerances of photosynthesis to ambient solar radiation which can be explained by broad physiological acclimation potentials and/or genetic adaptation to certain (low or high) irradiances. The species-specific photosynthetic performance under radiation stress is in good accordance with the vertical distribution of the macroalgae on the shore.     

Chloroplast‐targeted bacterial RecA proteins confer tolerance to chloroplast DNA damage by methyl viologen or UV‐C radiation in tobacco (Nicotiana tabacum) plants

The nature and importance of the DNA repair system in the chloroplasts of higher plants under oxidative stress or UV radiation‐induced genotoxicity was investigated via gain‐of‐functional approaches exploiting bacterial RecAs. For this purpose, transgenic tobacco (Nicotiana tabacum) plants and cell suspensions overexpressing Escherichia coli or Pseudomonas aeruginosa RecA fused to a chloroplast‐targeting transit peptide were first produced. The transgenic tobacco plants maintained higher amounts of chloroplast DNA compared with wild‐type (WT) upon treatments with methyl viologen (MV), a herbicide that generates reactive oxygen species (ROS) in chloroplasts. Consistent with these results, the transgenic tobacco leaves showed less bleaching than WT following MV exposure. Similarly, the MV‐treated transgenic Arabidopsis plants overexpressing the chloroplast RecA homologue RECA1 showed weak bleaching, while the recA1 mutant showed opposite results upon MV treatment. In addition, when exposed to UV‐C radiation, the dark‐grown E. coli RecA‐overexpressing transgenic tobacco cell suspensions, but not their WT counterparts, resumed growth and greening after the recovery period under light conditions. Measurements of UV radiation‐induced chloroplast DNA damage using DraI assays (Harlow et al. 1994) with the chloroplast rbcL DNA probe and quantitative PCR analyses showed that the transgenic cell suspensions better repaired their UV‐C radiation‐induced chloroplast DNA lesions compared with WT. Taken all together, it was concluded that RecA‐overexpressing transgenic plants are endowed with an increased chloroplast DNA maintenance capacity and enhanced repair activities, and consequently have a higher survival tolerance to genotoxic stresses. These observations are made possible by the functional compatibility of the bacterial RecAs in chloroplasts.     

Use of enzymatic cell wall degradation for improvement of protein extraction from Chondrus crispus,Gracilaria verrucosa and Palmaria palmata

The effect of polysaccharidases (κ-carrageenase, β-agarase, xylanase, cellulase) on the protein extraction from three rhodophytes has been studied. The kinetic parameters (apparent V _m, apparent K _m) and the optimum activity conditions (pH, temperature) of each enzyme were determined by using pure substrates. All the tested enzymes possess Michaelis Menten mechanism with estimated substrate saturating concentrations of 8 000 mg l⁻¹(carrageenan) for κ-carrageenase, 8 000 mg l⁻¹ (agar) for β-agarase, 5000 mg l⁻¹ (xylane) for β-xylanase and 6 000 mg l⁻¹ (carboxymethylcellulose) for cellulase. The optimum activity conditions are pH 6.5–6.8 at 45°C for carrageenase, pH 6–6.5 at 55°C for agarase, pH 5 at 55°C for xylanase and pH 3.8 at 50°C for cellulose. Different alga/enzymes couples (κ-carrageenase/Chondrus crispus, β-agarase/Gracilaria verrucosa, β-xylanase/Palmaria palmata) were tested under the optimum activity conditions. Alga/cellulase + specific enzyme (e.g. Chondrus crispus/carrageenase + cellulase) systems were also studied at the optimum activity conditions of a specific enzyme (e.g. carageenase). The use of the only cellulose was also tested on each alga. Except for Palmaria palmata, the highest protein yields were observed with the procedures using cellulase coupled with carrageenase or agarase for an incubation period limited to 2 h. The Chondrus crispus/carrageenase + cellulose and Gracilaria verrucosa/agarase + cellulase systems gave ten-fold and three-fold improvements, respectively, in protein extraction yield as compared to the enzyme-free blank procedure. The combined action of xylanase and cellulose on protein extraction from Palmaria palmata does not significantly improve protein yield. The best overall protein yield for P. palmata is for P. palmata/xylanase with a 14-h incubation time. This study shows the interest in the use of a polysaccharidase mixture for improving protein extractibility from certain rhodophytes. This biotechnology approach, adapted from procedures for protoplast production or enzymatic liquefaction of higher plants, could be tested as an alternative method to obtain proteins from seaweeds of nutritional interest.     

Palatability of the Antarctic rhodophyte Palmaria decipiens (Reinsch) RW Ricker and its endo/epiphyte Elachista antarctica Skottsberg to sympatric amphipods

Although many macroalgae that occur throughout Western Antarctic Peninsular waters are known to produce defensive secondary metabolites that deter grazing, the rhodophyte, Palmaria decipiens is palatable to several sympatric meso- and macro-grazers. It has been hypothesized that high levels of mesoherbivory by amphipods may account for the conspicuous lack of filamentous epiphytes emerging from the thalli of marcophytes in this region. Nonetheless, Elachista antarctica is a filamentous phaeophyte found growing within, and emerging from the thallus of the rhodophyte P. decipiens. It is surprising that E. antarctica occurs exclusively in association with a palatable species of macroalgae considering the standing biomass of other chemically defended unpalatable species is very high. We tested the hypothesis that E. antarctica grows on P. decipiens due to the host's overwhelming palatability compared to that of the epiphyte. That is, the hypothesis that mesograzers prefer the host over the epiphyte, grazing around emerging filaments. Choice and no choice feeding assays with live tissues of E. antarctica and P. decipiens were conducted in three different trials with four sympatric amphipod species (Prostebbingia gracilis, Gondogeneia antarctica, Oradarea bidentata, and Paraphimedia integricauda) commonly found in association with P. decipiens. G. antarctica consumed both species but ate P. decipiens at a faster rate than the epiphyte in two of three trials. P. gracilis, O. bidentata, and P. integricauda fed on the epiphyte, E. antarctica at faster rates than upon P. decipiens. Aggressive grazing of the epiphyte by this suite of amphipods indicates that differences in palatability and differences in grazing pressure on host and epiphyte do not explain the exclusive epiphytism of E. antarctica on P. decipiens.     

UV RADIATION,PHOSPHORUS, AND THEIR COMBINED EFFECTS ON THE TAXONOMIC COMPOSITION OF PHYTOPLANKTON IN A BOREAL LAKE1

We examined how UV radiation and phosphorus (P) affect the taxonomic composition, abundance, and biomass of phytoplankton in an oligotrophic boreal lake. We exposed phytoplankton to three different solar radiation regimes (PAR + UV‐A radiation [UVAR]+ UV‐B radiation [UVBR], PAR + UVAR, and PAR only) and to five levels of P. The biomass of small chrysophytes was reduced by 350% after exposure to PAR + UVAR + UVBR compared with PAR only. No other taxa were found to be negatively affected by exposure to UVBR. Several taxa (e.g. Chry‐ sochromulina laurentiana Kling) were sensitive to UVAR, whereas others (e.g. Tabellaria flocculosa (Roth) Kutzing) were not affected by UV radiation exposure. Principal components analysis ordination separated phytoplankton that were negatively affected by UV radiation and/or positively affected by P treatments (e.g. small chrysophytes, Cryptomonas rostratiformis, T. flocculosa) from those that generally were unaffected by either treatment (e.g. desmids, some Cyanobacteria). Richness, Shannon‐Weaver diversity, and evenness were significantly higher in phytoplankton communities shielded from UVAR and UVBR. The relationship between diversity and richness was positive in all phytoplankton samples except in those exposed to UVBR. Thus, UVBR‐exposed phytoplankton communities were dominated by a few species even though the number of taxa remained relatively unchanged. Consequently, alterations in the UV environments of lakes resulting from climate warming (e.g. drought) and land‐use change (e.g. increased P export) will likely promote shifts in the community composition of lake phytoplankton.     

Effects of Macroalgal Chemical Extracts on Spore Behavior of the Antarctic Epiphyte Elachista antarctica Phaeophyceae

Most macroalgal species along the Western Antarctic Peninsula (WAP) are defended against predation, many using chemical defenses. These subtidal communities are also mostly devoid of free living filamentous algae. However, one endo/epiphyte, Elachista antarctica, is found growing exclusively out of the palatable rhodophyte Palmaria decipiens. To understand this unusual and exclusive epiphytization, we tested whether macroalgal secondary metabolites such as those responsible for deterring sympatric grazers, affect the behaviors of the epiphyte's spores. Settlement, germination, and swimming behaviors of the epiphyte's motile spores were quantified in the presence of fractionated lipophilic and hydrophilic extracts of host P. decipiens and other rhodophytes from the shallow subtidal. Host P. decipiens was the only alga tested that did not inhibit spore settlement or germination. We also examined whether extracts from these chemically rich algae affect spore swimming behaviors and found spores to be chemotactically attracted to seawater soluble extract fractions of host P. decipiens. These results indicate that chemosensory behaviors of the epiphyte's spores to metabolites associated with these chemically defended macrophytes can explain this exclusive epiphyte–host interaction.     

Biodiversity and trophic structure of invertebrate assemblages associated with understorey red algae in a Laminaria digitata bed

Although the composition of invertebrate assemblages associated with kelps has motivated several studies in the recent past, little is known about assemblages associated with smaller, understorey macroalgae in these ecosystems. Here, the composition of invertebrate assemblages living within understorey macroalgae of a kelp (Laminaria digitata) forest has been studied over two sampling dates, and the structure of the food web investigated using stable isotopes. A total of 145 species of mobile fauna, mainly amphipods and gastropods, were identified. Although differences were date-dependent, we showed that the three species considered (Palmaria palmata, Mastocarpus stellatus, Ellisolandia elongata) sheltered different associated assemblages, including high host-specificity, which suggests that the animal diversity associated with rocky shores is enhanced by a high algal diversity. Overall, a dominance of gastropods was observed for the two-dimensional, leaf-like P. palmata, while the three-dimensionally structured species (M. stellatus, E. elongata) were characterized by a dominance of amphipods. Stable isotopes highlighted different trophic structures; E. elongata-associated assemblages were most likely relying on a dominant food source, sediment organic matter, while other assemblages were based on a wider diversity of food sources (algae, sediment, suspended organic matter). Our results illustrate the need to consider the microhabitats formed by understorey macroalgae in order to thoroughly assess the diversity and understand the functioning of coastal rocky ecosystems.     

Evaluation of protein <Emphasis Type="BoldItalic">in vitro</Emphasis> digestibility of <Emphasis Type="BoldItalic">Palmaria palmata</Emphasis> and <Emphasis Type="BoldItalic">Gracilaria verrucosa</Emphasis>

Palmaria palmata and Gracilaria verrucosa are edible red seaweeds and potential protein sources for human or animal nutrition, so studies were conducted on their in vitro protein digestibility. After 30 min predigestion by pepsin followed by 6 h digestion into a cell dialysis containing porcine pancreatin, the in vitro protein digestibility of P. palmata and G. verrucosa, expressed in regard to casein digestibility, was 4.9% and 42.1%, respectively. The level of protein digestibility seems to be related to the amount of soluble fibre, which was 45.3% and 30.5%, respectively.     

DAY AND NIGHT KINETICS OF GROWTH RATE IN GREEN,BROWN, AND RED SEAWEEDS1

Growth rates in terms of area increase per 30 min were measured in flat thalli of several seaweed, species by means of computer-assisted image analysis, at 12 h light per day and a photon fluence rate of 20 μmol · m^-2· s^?1. Light fields included white fluorescent, imitated underwater, blue, green, and red light. In the green alga Ulva pseudocurvata Koeman et Hoek, blue light caused an immediate reduction of thallus area and growth rate after the onset of light, whereas green light and red light resulted in an initial peak in growth rate followed by inhibition 60 min after the onset of light. More growth was observed in darkness than in blue light in U. pseudocurvata. All brown and red algae tested, with Laminaria saccharina (L.) Lamour. and Palmaria palmata Stackh. as the main investigated species, grew faster during the day than during the night, irrespective of light quality during the main light phase. The upper intertidal red alga Porphyra umbilicalis (L.) J. Ag. achieved most of its thallus expansion per 24 h during the first 3 h of the light phase, with maximum growth rates of 2–3% increase in area per hour. Maximal growth rates were 0.7% for juvenile laminarian sporophytes and were lower than this in Palmaria palmata and other perennial red algae. The temporary growth inhibition by light in Ulva pseudocurvata suggests photomorphogenetic events, similar to the kinetics of stem elongation in higher plant seedlings after blue or red light pulses in darkness.     

EFFECTS OF UV-B-INDUCED DNA DAMAGE AND PHOTOINHIBITION ON GROWTH OF TEMPERATE MARINE RED MACROPHYTES: HABITAT-RELATED DIFFERENCES IN UV-B TOLERANCE

The sensitivity to UV-B radiation (UVBR: 280–315 nm) was tested for littoral (Palmaria palmata[L.] O. Kuntze, Chondrus crispus Stackhouse) and sublittoral (Phyllophora pseudoceranoides S. G. Gmelin, Rhodymenia pseudopalmata[Lamouroux] Silva, Phycodrys rubens[L.] Batt, Polyneura hilliae[Greville] Kylin) red macrophytes from Brittany, France. Algal fragments were subjected to daily repeated exposures of artificial UVBR that were realistic for springtime solar UVBR at the water surface in Brittany. Growth, DNA damage, photoinhibition, and UV-absorbing compounds were monitored during 2 weeks of PAR + UV-A radiation (UVAR) + UVBR, whereas PAR + UVAR and PAR treatments were used as controls. The littoral species showed a higher UV tolerance than the sublittoral species. After 2 weeks, growth of P. palmata and C. crispus was not significantly affected by UVBR, and DNA damage, measured as the number of cyclobutane-pyrimidine dimers per 10⁶ nucleotides, was negligible. Photoinhibition, determined as the decline in optimal quantum yield, was low and decreased during the course of the experiment, coinciding with the production of UV-absorbing compounds in these species. In contrast, no UV-absorbing compounds were induced in the sublittoral species. Growth rates of P. pseudoceranoides and R. pseudopalmata were reduced by 40% compared with the PAR treatment. Additionally, constant levels of DNA damage and pronounced photoinhibition were observed after the UVBR treatments. Growth was completely halted for Phycodrys rubens and Polyneura hilliae, whereas DNA damage accumulated in the course of the experiment. Because Phycodrys rubens and Polyneura hilliae showed the same degree of photoinhibition as the other sublittoral species, it appears that the accumulation of DNA damage may have been responsible for the complete inhibition of growth. The results suggest an important role of DNA repair pathways in determining the UV sensitivity in red macrophytes.     

Acclimation of a pleurocarpous moss Pleurozium schreberi (Britt.) Mitt. to enhanced ultraviolet radiation in situ

We investigated the responses of ultraviolet (UV)‐absorbing compounds, chlorophylls a and b, carotenoids and the growth responses of the pleurocarpous moss Pleurozium schreberi (Britt.) Mitt. to enhanced UV radiation in situ. The moss was exposed to a 52% elevation above the ambient level of erythemally weighted UV‐B radiation, simulating an approximate 20% reduction in the ozone column, in a dry pine forest in Sodankylä, Finland (67 °22′N, 26 °38′E), under arrays of lamps filtered with cellulose diacetate, which transmitted both UV‐B and UV‐A radiation. The moss was also exposed to elevated UV‐A radiation under control arrays of lamps filtered with Melinex polyester and to ambient radiation under arrays with no lamps in them. Effects of enhanced UV radiation on P. schreberi were recorded during the first 3 years of exposure. Enhanced UV‐B radiation did not affect the segment height growth of the moss. The annual dry mass after the second growing season was higher in the UV‐A control than in the other treatments, and dry mass decreased significantly during the third treatment year in both UV treatments compared with the ambient. The specific leaf area of the UV‐B‐treated mosses was significantly higher than the ambient control mosses during the first 2 years. An increase of UV‐absorbing compounds was found in the mosses under enhanced UV‐B radiation compared with the UV‐A control mosses during the first year. Even though the treatment effect on UV‐absorbing compounds was transient, the concentrations of these compounds correlated with the amount of UV‐A and UV‐B radiation received under the elevated UV‐B treatment. A correlation with the irradiation of previous days and preceding month of the sampling day was found. A seasonal reduction occurred in the amount of UV‐absorbing compounds from the beginning of the summer to late summer. The amount of photosynthetic pigments correlated with the amount of photosynthetically active radiation. The moss P. schreberi was thus found to tolerate increasing UV‐B radiation. Our data indicate that P. schreberi tolerates a 52% increase in erythemally weighted UV‐B radiation above ambient, responding during the first few years of exposure by increasing UV‐absorbing compounds and specific leaf area, and decreasing annual dry mass, and then acclimating to its altered radiation environment.     

Ultrastructural changes in major organelles during spermatial differentiation inBangia (Rhodophyta)

Summary The major organelles within the cells of maleBangia atropurpurea (Roth) C. Ag. filaments undergo a series of ultrastructural transformations during the production of spermatia. Initially, thylakoids within the large axial chloroplast develop a reticulate pattern commencing at the central pyrenoid region. Subsequent changes involve loss of lobes and diminution of volume through division; chloroplasts in final stages contain a few dilated, distorted thylakoids and many plastoglobuli. During differentiation the large nucleolus disappears from the nucleus and four masses of chromatin aggregate near the nuclear envelope. Furrows originating from the nuclear envelope form double membranes around each of the chromatin masses and most of the nucleoplasm is eliminated. Several types of fibrillar vesicles are formed during the process and large floridean starch reserves are utilized. Multilamellar bodies and microbody-like structures occur within the cells during certain phases of spermatiogenesis.     

INORGANIC NITROGEN AND PHOSPHORUS UPTAKE KINETICS IN PALMARIA PALMATA (RHODOPHYTA)1

The N and P uptake responses were studied in a northern Spanish population of the edible red seaweed Palmaria palmata (Linnaeus) Kuntze. The fronds were incubated at different concentrations, and the nutrient depletion in the medium was measured at successive times to calculate uptake rates. Palmaria palmata uptake response was biphasic and nonsaturable for inorganic P. This would allow the species to exploit transient pulses of high P concentration in natural and fertilized conditions. Such a response is a common feature of algae avoiding nutrient deficiency. At average concentrations measured in the ocean, the response was nonsaturable for inorganic N sources, except for ammonium in autumn and winter when it is not the major N source. In contrast to the general rule of ammonium being taken at a higher rate than nitrate, we found similar affinity for both nutrients corresponding to the minor role of ammonium as N source for field populations over the year.