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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.”

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