Synchroma grande (Synchromophyceae, Heterokontophyta) is a marine amoeboid alga, which was isolated from a benthic habitat. This species has sessile cell stages (amoeboid cells with lorica and cysts) and non-sessile cell stages (migrating and floating amoebae) during its life cycle. The different cell types and their transitions within the life cycle are described, as are their putative functions. Cell proliferation was observed only in cells attached to the substrate but not in free-floating or migrating cells. We also characterised the phagotrophy of the meroplasmodium in comparison to other amoeboid algae and the formation of the lorica. The functional adaptations of S. grande during its life cycle were compared to the cell stages of other amoeboid algae of the red and green chloroplast lineages. S. grande was found to be highly adapted to the benthic habitat. One sexual and two asexual reproductive strategies (haplo-diploid life cycle) support the ability of this species to achieve rapid diversification and high adaptivity in its natural habitat.

Trastuzumab (Herceptin) has improved therapy of breast cancer. Only patients overexpressing ERBB2 are treated with trastuzumab, whereas its use in tumours without ERBB2 expression is useless. This led to the concept that the subgroup of trastuzumab-sensitive tumours is 'ERBB2-dependent', meaning that ERBB2 signalling is indispensable for growth of these tumours. We used a mouse model that allows anhydrotetracycline (ATc)-controlled downregulation of ERBB2 in tumour tissue. ERBB2 mRNA and protein expression were downregulated below detection limit leading to a macroscopically complete tumour remission within 14 days. Tumour remission was accompanied by a strong decrease in proliferation, a moderate increase in apoptosis, as well as dephosphorylation of ERK1/2 and AKT/PKB. These data clearly indicate ERBB2 dependence. Therefore, a high sensitivity to trastuzumab may be suspected. Surprisingly, trastuzumab caused a much weaker effect compared to ATc-induced ERBB2 downregulation, although a decrease in ERBB2 membrane localisation was induced. Only a slight decrease in proliferation and a weak transient increase in apoptosis were observed. Interestingly, tumours responded to trastuzumab by a sharp fivefold increase in phosphorylated AKT/PKB as well as a 3.5-and 5.3-fold increase in AKT1 and AKT2 mRNA levels, respectively. In conclusion, 'ERBB2 dependence' is not sufficient to define trastuzumab-responsive tumours. The suboptimal effect of trastuzumab compared to the maximally possible effect induced by ATc demonstrates a high potential for improved ERBB2 blocking therapies.

The balance of energy flow from light absorption into biomass was investigated under simulated natural light conditions in the diatom Phaeodactylum tricornutum and the green alga Chlorella vulgaris.The energy balance was quantified by comparative analysis of carbon accumulation in the new biomass with photosynthetic electron transport rates per absorbed quantum, measured both by fluorescence quenching and oxygen production. The difference between fluorescence- and oxygen-based electron flow is defined as 'alternative electron cycling'.The photosynthetic efficiency of biomass production was found to be identical for both algae under nonfluctuating light conditions. In a fluctuating light regime, a much higher conversion efficiency of photosynthetic energy into biomass was observed in the diatom compared with the green alga.The data clearly show that the diatom utilizes a different strategy in the dissipation of excessively absorbed energy compared with the green alga. Consequently, in a fluctuating light climate, the differences between green algae and diatoms in the efficiency of biomass production per photon absorbed are caused by the different amount of alternative electron cycling.

The phytoplankton community structure of a hypertrophic lake was quantitatively determined with the aid of flow cytometry. The flow cytometry signals were calibrated to obtain cell-specific information, such as the chl a content and the biovolume per cell. The reliability of this method was tested with laboratory cultures. The results of the phytoplankton structure in a hypertrophic lake with respect to chl distribution in the different algal groups obtained by flow cytometry were compared with the results from HPLC pigment fingerprinting. Both methods yield the percentage contribution of the different algal groups to total chl a. The chl a specific absorption coefficient of the phytoplankton (a(Phy)(*)) was determined via visible (VIS) spectroscopy of samples taken from a hypertrophic lake (Auensee) in 2003. The results indicated that a(Phy)(*) of the total cell suspension is dependent on the phytoplankton structure as well as on environmental factors. The linear relationship between a(Phy)(*) at 675 nm and the product of the chl a content per cell and the biovolume offered the possibility to normalize phytoplankton absorption spectra to acquire the taxon-specific a(Phy)(*). The estimated a(Phy)(*) (675 nm) values were used to normalize single cell absorption spectra at this wavelength to obtain the a(Phy)(*) between 400 and 750 nm for representatives of the major algal groups. Our measurements show that the absorption coefficient for the whole phytoplankton community varies within the season. Finally, we used the a(Phy)(*) and the chl a distribution to calculate the light absorption of each algal group in the hypertrophic lake.

The changes in thermoluminescence (TL) signals induced by short-term ozone exposure of leaves are characterized by a down-shift of the peak-temperature of the TLB-band and an increase of a TL band at 55°C. We investigated the relationship of these changes to photosystem 2 (PS2) photochemistry. The changes were not only detectable in the presence of ozone, but also after irradiation of dark-adapted leaves and after aging of irradiated detached leaf segments. The opposite effect on TL, an up-shift of the peak-temperature of the B-band and the decrease of the intensity of the band at 55°C were found after infiltration of leaves with nigericin, antimycin A, and diphenyleneiodonium chloride (DPI). Propyl gallate down-shifted the peak-temperature of the B-band. 2,5-dimethyl-1,4-benzoquinone up-shifted the peak-temperature of the B-band and decreased the intensity of the 55°C band. The intensity of the 55°C band did not change significantly in the presence of oxygen in comparison to that in nitrogen atmosphere. It decreased with time of dark adaptation (50% intensity was observed after 3 h of dark adaptation at room temperature), however, it was reactivated to its initial value (at 5 min of dark adaptation) after 1 single-turnover flash. The 55°C band was not significantly changed in the presence of DCMU. Thus the ozone-induced band at 55°C is assigned to charge recombination in PS2. Changes in the electron transport chain at the acceptor side of PS2, probably related to the cyclic electron transport around photosystem 1 and/or chlororespiration, could play an important role in the increase of the 55°C band and the down-shift of the B-band. The changes at the acceptor side indicated by TL can be an ex pression of a physiological regulatory mechanism functional under stress conditions.

We tested the Chlorophyll-a in-vivo fluorescence technique as a method to measure absolute values of primary production by the application of a bio-optical model. In this model, absolute values of gross photosynthetic oxygen evolution were calculated on the basis of Chlorophyll-a in-vivo fluorescence, such as photosystem II quantum yield and the amount of absorbed light quanta per time (Q Phar ). Simultaneous measurements of photosynthesis rates, as measured by a Clark-type electrode and estimated via the fluorescence based model, yield similar results. The P-I-curves measured by these two independent methods are nearly identical under light limitation, whereas maximal photosynthetic activities under saturating light are found to be higher using the bio-optical model. Furthermore, we determined the relationship between carbon-based biomass formation and the photosynthesis rate under low and high light. The quantity of electrons consumed for C and N assimilation is the same as the quantity of electrons produced by the photosystems under low light. Under high light, the electron production exceeds the electron consumption for N and C assimilation. We found that an oxygen production of 55-60 μmol O 2 is equivalent to the production of 1 mg dry matter. We conclude that the photosynthetic electron transport rate represents a fairly good estimated measure of newly synthesised organic matter under the applied conditions. Therefore, the use of fluorescence data in an appropriate bio-optical model is a powerful tool for measuring biomass formation in absolute terms but is restricted to replete nutrient and medium light conditions. The validity of this experimental approach for measuring primary production under stress conditions still needs to be elaborated.

A hypertrophic lake in Leipzig has been analyzed with respect to the basic limnological parameters, nutrients and phytoplankton community dynamic in the course of the year 2002. A bio-optical model was developed to assess the daily primary production based on the spectrally resolved surface irradiance, the light climate in the euphotic zone of the water column, the quantification of the light absorption by the phytoplankton and its photosynthetic efficiency measured with the help of in-vivo Chl a-fluorescence. Summing up the modeled primary production per day for the whole vegetation period it turned out that the productivity was no limited by the nutrients but by the light only. This is the first report that an adopted bio-optical modeling can be used to assess the annual primary production of a whole freshwater lake.