Ulf Karsten

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

SummaryThe 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 μmol 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 μmol 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.

Growth pattern andβ-dimethylsulphoniopropionate (DMSP) content of green macroalgae at different irradiances

Growth rates and intracellularβ-dimethylsulphoniopropionate (DMSP) concentrations of five green algal species collected from different geographic regions in 1986 and 1989 were determined under four photon flux rates. InUlothrix implexa, U. subflaccida andAcrosiphonia arcta from Antarctica, growth was light-saturated at lower irradiances than in temperateUlva rigida from Southern Chile andBlidingia minima from Germany. The DMSP content ofUlothrix implexa, A. arcta andUlva rigida was directly correlated with the light factor: with increasing irradiance, algal DMSP level increased. In contrast, inUlothrix subflaccida andB. minima DMSP concentrations gradually decreased up to a photon flux rate of 30µmol m−2 s−1, then increased markedly under the highest photon flux rate tested. In non-growing, dark-incubatedA. arcta DMSP content was reduced by 35%, while the DMSP pool of all other species remained unchanged, at the level of pre-culture conditions. Under full darkness all plants exhibited a significantly higher DMSP concentration compared with algae grown at low photon flux rates of 2 to 30µmol m−2 s−1. These data show a correlation between growth pattern and DMSP biosynthesis, and may point to a species-specific minimum amount of light energy necessary for DMSP accumulation.

Mannitol in the red algal genus Caloglossa (Harvey) J. Agardh

Summary Analytical data on the occurrence of the polyhydric alcohol mannitol in the red algal genus Caloglossa (Ceramiales, Delesseriaceae) were obtained by 13 C NMR and HPLC techniques. Six species were isolated in different geographic regions and kept in laboratory cultures. In all isolates intracellular mannitol concentrations ranging from 25.4 to 579.3 mmol kg -1 DW were measured. In field material of Caloglossa leprieurii from New South Wales, Australia the mannitol content appears to be influenced by salinity of the natural habitat: plants from freshwater (0 % 0 ) contained 3.2 mmol kg -1 DW, plants from estuarine (26–35 % 0 ) and marine (35 % 0 ) habitats exhibited 40 and 202.6 mmol kg -1 DW respectively. Cultured material of Caloglossa apomeiotica was subjected to osmotic stresses ranging from 5.3–70 % 0 . The mannitol content linearly increased with increasing salinities. The possible function of mannitol as a compatible solute in Caloglossa is discussed. The occurrence of these high mannitol concentrations and the absence of typical red algal carbohydrates are discussed with reference to the chemotaxonomy of the genus.

Incomplete turgor pressure regulation in the terrestial red alga, Bostrychia scorpioides (Huds.) Mont.

Abstract The red alga, Bostrychia scorpioides , was subjeced to osmotic stresses ranging from hypoosmotic (535 mOsm kg −1 ) to hyperosmotic conditions (1440 mOsm kg −1 ). The ionic concentrations of Na + , K + , and Cl − as well as the hexitols d -sorbitol and d -dulcitol increased with increasing salinity. Other ions (Mg 2+ , Ca 2+ , sulphate and phosphate) did not change in their concentrations with salinity. Turgor pressure, however, was not regained and decreased with increasing salinity. The alga is able to tolerate incomplete turgor regulation, which may be a prerequisite to survive long term dessiccation, a stress condition occurring frequently in the upper supralittoral zone, the natural habitat of this alga.

The intertidal red alga Bostrychia simpliciuscula Harvey ex J. Agardh from a mangrove swamp in Singapore: acclimation to light and salinity

Abstract The growth of the mangrove red alga Bostrychia simpliciuscula Harvey ex J. Agardh was studied in relation to a gradient of salinities (5–70 ppt) and photon fluences rates (2.5–60 μmol m −2 s −1 ). The photosynthesis-irradiance ( PI ) curve and the effect of salinity on the intracellular d -sorbitol and d -dulcitol concentrations were also examined. Bostrychia simpliciuscula grew under all salinities tested with a preference for brackish water conditions. The growth versus light pattern and the PI curve indicate an adaptation to shaded habitats. This alga synthesised and accumulated d -sorbitol in parallel with increasing salinities over the whole range of 5–60 ppt, while d -dulcitol was only involved in the osmotic acclimation between 15 and 45 ppt. The abundance of B. simpliciuscula under the extreme environmental conditions predominant in mangrove swamps of southeast Asia can be explained by these physiological properties.

The effect of salinity on growth, photosynthesis and respiration in the estuarine red algaBostrychia radicans mont

The estuarine red alga,Bostrychia radicans, was subjected to osmotic stresses ranging from hypo-osmotic (9.9‰) to hyperosmotic conditions (37.4‰). The growth rate decreased with increasing salinities and showed a maximum in a mesohaline medium, while the photosynthetic rate and the chlorophyll a content increased under hyper-osmotic conditions. The rate of respiration remained constant over the salinity range tested.B. radicans revealed typical characteristics of “shade plants” having a low light compensation point at 3–4 μE m−2 s−1 correlated with a low photon flux density of 70–100 μE m−2 s−1 for saturation of photosynthesis. These physiological properties may explain the success ofB. radicans in estuarine habitats.

The Effect of Salinity Changes upon the Physiology of Eulittoral Green Macroalgae from Antarctica and Southern Chile. I. Cell Viability, Growth, Photosynthesis and Dark Respiration*

Summary The salinity tolerance of the eulittoral green macroalgae Ulothrix implexa , Ulothrix subflaccida , Enteromorpha bulbosa and Acrosiphonia arcta from Antarctica was determined. Cell viability, growth, photosynthesis and dark respiration were used as criteria. A Subantarctic-cold temperate Ulva rigida from southern Chile was also included in this study. Cells of U. implexa , E. bulbosa and A. arcta showed considerably broader salinity tolerance than cells of U. subflaccida and U. rigida . All investigated species grew well under a wide range of salt treatments. With the exception of U. implexa , growth rates of all other species were inhibited at the lowest salinity tested. After incubation under extreme hypersaline conditions all species responded with a strong reduction in growth. The photosynthesis and dark respiration responses were similar to those of growth. These very plastic physiological properties under different salinities are similar between Antarctic and temperate plants. The successful spreading of green macroalgae in the eulittoral zone of all continents including cold Antarctica and cold-temperate southern Chile may thus be explained.

The distribution of D-sorbitol and D-dulcitol in the red algal genera Bostrychia and Stictosiphonia (Rhodomelaceae, Rhodophyta)—a re-evaluation

The subfamily Bostrychioideae contains the genera Bostrychia and Stictosiphonia, which differ from each other in a number of morphological characters. Quantitative data are provided on the distribution of the isomeric hexitols D-sorbitol and D-dulcitol in nine of 11 known Bostrychia and in three of six known Stictosiphonia species. D-sorbitol was found in all algae investigated. D-dulcitol was missing in all Stictosiphonia investigated, in one isolate of B. radicans, and in B. tenuissima. While the occurrence of both polyols characterizes most members of the genus Bostrychia, the occurrence of D-sorbitol alone cannot be used to differentiate between the two genera.