The effect of optimal and stress temperatures on the growth kinetics of the Phaeodactylum tricornutum CCAP/1055/1 strain (a model diatom with a known genome sequence) in batch cultures was examined. The analysis of the obtained results showed two phases of culture growth. There were significant positive correlations between OD increase of chlorophyll a chlorophyll c and protein concentration at different temperatures. The F v /F m parameter achieved a maximum level on the 6 th or 7 th day and then decreased to the values registered on the first day of observation. Genetic material undergoes gradual degradation 10 days after inoculation. The size of the cells was invariable.

The importance of diadinoxanthin (Ddx) de‐epoxidation in the short‐term modulation of the temperature effect on photosynthetic membranes of the diatom Phaeodactylum tricornutum was demonstrated by electron paramagnetic resonance (EPR), Laurdan fluorescence spectroscopy, and high‐performance liquid chromatography. The 5‐SASL spin probe employed for the EPR measurements and Laurdan provided information about the membrane area close to the polar head groups of the membrane lipids, whereas with the 16‐SASL spin probe, the hydrophobic core, where the fatty acid residues are located, was probed. The obtained results indicate that Ddx de‐epoxidation induces a two component mechanism in the short‐term regulation of the membrane fluidity of diatom thylakoids during changing temperatures. One component has been termed the “dynamic effect” and the second the “stable effect” of Ddx de‐epoxidation. The “dynamic effect” includes changes of the membrane during the time course of de‐epoxidation whereas the “stable effect” is based on the rigidifying properties of Dtx. The combination of both effects results in a temporary increase of the rigidity of both peripheral and internal parts of the membrane whereas the persistent increase of the rigidity of the hydrophobic core of the membrane is solely based on the “stable effect.”

In the diadinoxanthin cycle the epoxy group is removed from diadinoxanthin and diatoxanthin is created. This conversion takes place e.g. in diatoms with the involvement of the enzyme diadinoxanthin de-epoxidase. In one of the diatom species, Phaeodactylum tricornutum (CCAP 1055/1 strain with genome sequenced) three deepoxidase genes (PtVDE, PtVDL1, PtVDL2) have been identified, but only one of them (PtVDE) corresponds to violaxanthin de-epoxidase, an enzyme which is commonly found in higher plants. In these studies, the expression of two de-epoxidase genes of another Phaeodactylum tricornutum strain (UTEX 646), which is commonly used in diatom studies, were obtained in Origami b and BL21 E. coli strains. The molecular masses of the mature proteins are about 49 kDa and 60 kDa, respectively, for VDE and VDL2. Both enzymes are active with violaxanthin as a substrate.

-The greenhouse effect results in warming the planet's surface and a higher ocean heat content. It causes changes of the water circulation frequency and turbulent mixing, delivering warm water, phytoplankton nutrients and CO2 from deeper layers of water to the water surface. All of these changes can have an impact on Earth's ecosystems. In the present study the effect of changing environmental temperature on a model diatom species, Thalassiosira pseudonana was tested under laboratory conditions. The purpose of the work was to analyze the temperature effect on fluidity and chemical composition of the thylakoid membranes. The photosynthetic activity and photosynthetic pigment contents of diatoms adapted to different temperatures were also determined. Our result show decreases of the growth rate and chlorophylls concentration in diatom cells cultured at lower temperature. It was also detected that increases of the polyunsaturated and decreases of saturated fatty acids, as well as changes in lipids:proteins ratio, resulted in stabilization of the thylakoid membranes fluidity and photosynthetic efficiency (Fv/Fm) in a physiological range of the temperature. The result show that the regulation of the concentration and interaction of fatty acids, proteins and pigments is the most important factor in the adaptation strategies of diatoms to the environmental temperature changes. Additionally, the regulation of membrane fluidity was demonstrated as important mechanism of the diatom adaptation to greenhouse effects. We also postulate that the adaptive mechanisms to temperature changes are differently expressed in the polar or hydrophobic regions of photosynthetic membranes.

The purpose of this research was to obtain recombinant violaxanthin de-epoxidases (VDEs) from two species. The first one was VDE of Arabidopsis thaliana (L.) Heynh. (WT Columbia strain) (AtVDE) which in vivo catalyzes conversion of violaxanthin (Vx) to zeaxanthin (Zx) via anteraxanthin (Ax). The second one was VDE of Phaeodactylum tricornutum Bohlin, 1897 (CCAP 1055/1 strain) (PtVDE) which is responsible for de-epoxidation of diadinoxanthin (Ddx) to diatoxanthin (Dtx). As the first step of our experiments, open reading frames coding for studied enzymes were amplified and subsequently cloned into pET-15b plasmid. For recombinant proteins production Escherichia coli Origami b strain was used. The molecular weight of the produced enzymes were estimated approximately at 45kDa and 50kDa for AtVDE and PtVDE, respectively. Both enzymes, purified under native conditions by immobilized metal affinity chromatography, displayed comparable activity in assay mixture and converted up to 90% Vx in 10 min in two steps enzymatic de-epoxidation, irrespective of enzyme origin. No statistically significant differences were observed when kinetics of the reactions catalyzed by these enzymes were compared. Putative role of selected amino-acid residues of AtVDE and PtVDE was also considered. The significance of the first time obtained recombinant PtVDE as a useful tool in various comparative investigations of de-epoxidation reactions in main types of xanthophyll cycles existing in nature are also indicated.