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.     

The effect of ultraviolet radiation on photosynthesis and ultraviolet-absorbing substances in the endemic Arctic macroalga Devaleraea ramentacea (Rhodophyta)

In field studies conducted at the Kongsfjord (Spitsbergen), the effect of filtered natural radiation conditions (solar without ulraviolet [UV]-A+UV-B, solar without UV-B, solar) on photosynthesis and the metabolism of UV-absorbing mycosporine-like amino acids (MAAs) in the marine red alga Devaleraea ramentacea have been studied. While solar treatment without UV-A+UV-B did not affect photosynthesis during the course of a day, solar without UV-B and the full solar spectrum led to a strong inhibition. However, after offset of the various radiation conditions, all algae fully recovered. Isolates collected from different depths were exposed in the laboratory to artificial fluence rates of photosynthetic active radiation (PAR), PAR+UV-A, and PAR+UV-A+UV-B. The photosynthetic capacity was affected in accordance with the original sampling depth, i.e. shallow-water isolates were more resistant than algae from deeper waters, indicating that D. ramentacea is able to acclimate to changes in irradiance. Seven different UV-absorbing MAAs were detected in this alga, namely mycosporine-glycine, shinorine, porphyra-334, palythine, asterina-330, palythinol, and palythene. The total amount of MAAs continuously decreased with increasing collecting depth when sampled in mid June, and algae taken in late August from the same depths contained on average 30–45% higher MAA concentrations, indicating a seasonal effect as well. The presence of increasing MAA contents with decreasing depth correlated with a more insensitive photosynthetic capacity under both UV-A and UV-B treatments. Populations of D. ramentacea collected from 1 m depth, with one fully exposed to solar radiation and the other growing protected as understorey vegetation underneath the kelp Laminaria saccharina, exhibited quantitatively different MAA compositions in the apices. The exposed seaweeds contained 2.5-fold higher MAA values compared with the more shaded algae. Moreover, the exposed isolates showed a strong tissue gradient in MAAs, pigments, and proteins. The green apices contained 5-fold higher MAA contents than the red bases. Transplantation of D. ramentacea from 2 m depth to the surface induced the formation and accumulation of MAAs after 1 week exposure to the full solar spectrum. Control samples which were treated with the solar spectrum without UV-A+B or with solar without UV-B showed unchanged MAA contents, indicating a strong UV-B effect on MAA metabolism. All data well supported the suggested physiological function of MAAs as natural UV sunscreens in macroalgae.     

Seasonal Growth and Photosynthetic Performance of the Antarctic Macroalga Desmarestia menziesii (Phaeophyceae) Cultivated under Fluctuating Antarctic Daylengths

Growth, photosynthesis, dark respiration and pigment contents were monitored in adult sporophytes of the Antarctic brown alga Desmarestia menziesii J. Agardh grown under fluctuating Antarctic daylength conditions. Growth rates were closely coupled to daylength variations with values varying from 0.05% d^?1 in winter condition (July-August) to 0.5% d^?1 in early summer (December). Photosynthetic pigments had maximum values of 1.8 mg g^?1 FW (chlorophyll a), 0.4 mg g^?1 FW (chlorophyll c) and 0.9 mg g^?1 FW (fucoxanthin) in summer. These changes were also closely related to individual size and biomass of the plants. Net photosynthesis (P_max), on a fresh weight basis, showed a clear seasonal pattern with highest rates of 25μmol O₂ g^?1 FW h^?1 in October and minima close to 9μmol O₂ g^?1 FW h^?1 in April. Dark respiration was high in spring (13μmol O₂ g^?1 FW h^?1) approximately coinciding with growth peaks. Likewise, photosynthetic efficiency (α) and the initial saturating light point of photosynthesis (l_k) increased significantly in spring [1.3 μimol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 and 26μmol photons m^?2 s^?1, respectively]. In the case of α, no significant differences between fresh weight and Chl a based rates were found. The results of the present study are the first that demonstrate seasonality of physiological parameters in D. menziesii sporophytes and confirm also that phenology and physiology of macroalgae can be simulated in the laboratory. On the other hand this study adds new elements to the explanation of the life strategy of D. menziesii, in particular that algal growth and photosynthesis occur under a programmed seasonal pattern.     

Developing indices of relative abundance for monitoring cave and ground wētā (Orthoptera) in southern beech forest,New Zealand

We sampled populations of forest-floor dwelling cave and ground wētā using footprint tracking tunnels and spotlight transect counts in southern beech forest, New Zealand. Samples were compared to estimates of wētā density based on mark–recapture estimates from 25?m² enclosures. Both activity indices captured variability in cave wētā in time and space, were strongly correlated with each other, and have the potential for monitoring cave wētā activity levels. Comparisons between indices and cave wētā density estimates were equivocal, as recapture rates were too low to calculate high-resolution density estimates. We also found that cave wētā counts had a curved relationship increasing with temperature, and a negative relationship with increasing shrub and woody debris cover. Based on these preliminary results, tracking tunnels could be a viable method of monitoring cave wētā as they appear more efficient than transect counts and are relatively inexpensive. However, further calibration trials are needed to determine if indices mirror robust population density estimates.     

Seasonal changes in C, N and major organic compounds and their significance to morpho-functional processes in the endemic Antarctic brown alga Ascoseira mirabilis

The seasonal and intra-thallus variations in the contents of C, N, proteins and amino acids, as well as in the storage carbohydrates mannitol and laminaran, were measured in the endemic Antarctic brown alga Ascoseira mirabilis between September and February and related to seasonal changes in dark respiration and photosynthesis. Carbon contents between 31 and 37% DW were relatively constant throughout these months and no variations were detected among thallus regions. Nitrogen contents, by contrast, were higher in September/October (3.1% DW) and decreased in January and February (1.8% DW). In general, the basal regions had the lower N contents. Proteins reached maximum values of 13% DW in November and February and were inversely correlated to photosynthesis (net P_max). The amino acid content was also higher in October and November (maxima close to 10% DW), but low between December and February (close to 5% DW), probably related to a seasonal pattern of N allocation in the alga. The storage carbohydrates mannitol and laminaran exhibited inverse seasonal changes: low mannitol values close to 5% DW in September were coupled with high laminaran contents varying between 7 and 15% DW. The existence of high laminaran contents in the distal blade region during September and February suggests that this compound was effectively accumulated in this region. The low P/R ratios in spring and the existence of a significant relationship between mannitol content and seasonal photosynthetic activity in the basal region appear to support the hypothesis of a possible utilization of carbohydrates to power growth in A. mirabilis. Received: 7 November 1996 / Accepted: 28 August 1997     

Adaptive response of human lymphocytes for the repair of radon-induced chromosomal damage

In human lymphocytes low doses of X-rays can decrease the number of chromatid deletions induced by subsequent high doses of sparsely ionizing X-rays. Because of the concern with the carcinogenic effects of low doses of -particles from radon in homes, experiments were carried out to see if low doses of X-rays could also decrease the yield of chromosomal aberrations induced by subsequent exposure to radon. Human peripheral blood lymphocytes were irradiated with low doses of X-rays (2 cGy) at 48 h of culture, exposed to radon at 72 h of culture, and analyzed for the presence of chromatid aberrations at subsequent intervals. The frequency of chromatid aberrations induced by radon alone increased with time after exposure, indicating exaggerated differences in the stage sensitivity of cell cycle stages to high-LET radiation. Furthermore, the numbers of aberrations per cell did not follow a Poisson distribution but were over dispersed, as might be expected since high-LET radiations have a high relative biological effectiveness compared with low-LET radiations. Nevertheless, lymphocytes exposed to 2 cGy of X-rays before radon exposure contained approximately one-half the number of chromatid deletions compared with lymphocytes treated with radon alone and analzed at the same time. Thus, the putative chromosomal repair mechanism induced by low doses of sparsely ionizing radiation is also effective in reducing chromosomal aberrations induced by radon, which hitherto had been thought to be relatively independent of repair processes.     

Photosynthesis,dark respiration and light independent carbon fixation of endemic Antarctic macroalgae

Summary The light saturated photosynthesis, dark respiration and light independent carbon fixation of macroalgal species endemic to the Antarctic were measured. Five brown algae. Ascoseira mirabilis, Desmarestia anceps, D. antarctica, Phaeurus antarcticus, Himantothallus grandifolius and the red alga Palmaria decipiens were included. Rates of these three parameters at 0°C were very similar to those measured in other studies on temperate algae at higher temperature. This indicates a high degree of physiological adaptation to the Antarctic environment within these species. A comparison was made of polarographic and chemical means of measuring oxygen flux during photosynthesis and dark respiration at low temperature. There was a good correlation between measurements of oxygen evolution and carbon fixation, although apparent photosynthetic quotient values were in most cases high.Abbreviations HEPES N-(Hydroxyethyl) piperazine-N-(2 ethane-sulphonic acid) - RuBP D-ribulose 1,5-bisphosphate Contribution No. 415 from the Alfred-Wegener-Institut für Polaru. Meeresforschung     

Dimethylsulphoniopropionate (DMSP) accumulation in green macioalgae from polar to temperate regions: interactive effects of light versus salinity and light versus temperature

Summary The effect of photon fluence rate on the ß-dimethylsulphoniopropionate (DMSP) content of salt-stressed eulittoral green macroalgae from different geographic regions was determined. At 55 mol photons m^–2s^–1 DMSP increased continuously with increasing salinities up to 68 in Ulothrix implexa, Ulothrix subflaccida, Enteromorpha bulbosa and Acrosiphonia arcta from Antarctica, while the Subantarctic/cold-temperate Ulva rigida and the temperate Blidingia minima showed a large rise in intracellular DMSP concentration only under gentle hypersaline treatment (51). At the highest salinity tested the DMSP content of the latter species declined. In contrast, the capacity to form DMSP in the dark under hypersaline conditions was very low in all species. In addition, the DMSP content of the Antarctic species was determined after one year cultivation at 0°C under photon fluence rates of 2, 30 and 55 mol m^–2s^–1. All isolates increased their DMSP concentration with increasing irradiance. In contrast to previous experiments done at 10°C, these species exhibited up to 5 fold higher DMSP values at 0°C under most photon fluence rates. The data support the idea of a light-dependent DMSP biosynthesis, and also demonstrate the stimulating effect of low water temperatures on the DMSP content of Antarctic green macroalgae. Apparently, in these plants DMSP may function as a cryoprotectant.Contribution No. 547 of the Institute for Polar and Marine Research, Bremerhaven     

Seasonality of brown macroalgae from Antarctica—a long-term culture study under fluctuating Antarctic daylengths

Summary The seasonal development of the endemic Antarctic Desmarestiales Himantothallus grandifolius, Phaeurus antarcticus, Desmarestia anceps, of a ligulate Desmarestia sp., of the Antarctic cold-temperate Adenocystis utricularis (Dictyosiphonales) and of the endemic Antarctic Ascoseira mirabilis (Ascoseirales) was monitored in a 2-year culture study under fluctuating daylengths mimicking the daylength conditions on King George Island (Antarctica). Temperature was kept constant at 0° C and nutrient levels were maintained at 0.6 moles m^–3 nitrate and 0.025 moles m ^–3 phosphate. Sporophytes were initiated between (April-) June and July in all Desmarestiales. This event was controlled either by induction of gametophyte fertility (in H. grandifolius and D. anceps) or by induction of spore formation (in Desmarestia sp. and P. antarcticus). Young sporophytes of all species showed a growth optimum from September to December (-February). Desmarestia sp. and P. antarcticus produced spores and degenerated subsequently after one year of culture at 3 mol photons m^–2 s^–1 or after 22 months of culture at 2 mol m^–2 s^–1. In D. anceps spores were released without degeneration of the mother plants after 20 and 19 months of culture at 3 and 10 olm^–2 s^–1, respectively. In H. grandifolius spore formation was not observed. Adult one year old plants of the latter two perennial species showed growth optima between September and November. Microthalli of A. utricularis were the dominant life phase of this alga in winter. Macrothalli started to develop from June onwards at 3 mol m^–2 s^–1 or from August to September at 2 mol m^–2 s^–1. Growth rates of macrothalli cultivated at 9 mol m^–2 s^–1 showed a growth optimum from September to November. The macrothalli released spores from January to February. Macrothalli cultivated at 3 mol m^–2 s^–1 maximally grew in January. They became fertile after almost 2 years of culture at 3 mol m^–2 s^–1 and remained vegetative at 2 mol m^–2 s^–1. A. mirabilis exhibited a prominent growth optimum from August to October, at photon fluence rates between 2 and 47 mol m^–2 s^–1. A second optimum was evident from January to March in plants cultivated at 9 mol m^–2 s^–1. The results closely correspond to available field data and indicate that the phenology of the studied species can be controlled in the laboratory solely by simulating Antarctic daylengths conditions. The light requirements for growth were very low in microthalli and in juvenile macrothalli and growth was mostly light saturated at 4–12 mol m^–2 s^–1. Few-celled sporophytes of H. grandifolius and D. anceps tolerated at least 8 and 11 months of darkness. The minimum light demands for completion of the life cycle are 31.4 mol m^–2 year^–1 in Desmarestia sp., P. antarcticus and probably also in the 2 perennial Desmarestiales; 47.1 mol m^–2 year^–1 are needed in A. utricularis and probably also in A. mirabilis. These values predict a lower distribution limit of the investigated species at 53±23 m or 48±21 m in clear offshore waters and at 28±5 m or 26±5 m, respectively, in inshore fjords of the Antarctic Peninsula region.Contribution No. 281 of the Alfred-Wegener-Institut für Polar-u. Meeresforschung     

Tonoplast fine structure and osmotic regulation in Porphyra umbilicalis

In Porphyra, an intertidal red alga, the fine structure of the tonoplast was studied by freeze-fracture electron microscopy. It was shown that density and size of intramembraneous particles on the protoplasmic fracture face vary with external osmotic potential. The frequency of particles grouped in size classes (calculated per cell) increases with increasing osmotic stress and shows a maximum in 3 to 4 x artificial seawater medium ASP₁₂. It is concluded that the intensity of tonoplast transport, which probably is enhanced with increasing osmotic stress from 1 to 4 x media, is most likely correlated with a change in membrane fine structure of the tonoplast.