Cold acclimation modifies the photosynthetic machinery and enables plants to survive at sub-zero temperatures, whereas in warm habitats, many species suffer even at non-freezing temperatures. We have measured chlorophyll a fluorescence (ChlF) and CO2 assimilation to investigate the effects of cold acclimation, and of low temperatures, on a cold-sensitive Arabidopsis thaliana accession C24. Upon excitation with low intensity (40 µmol photons m- 2 s- 1) ~ 620 nm light, slow (minute range) ChlF transients, at ~ 22 °C, showed two waves in the SMT phase (S, semi steady-state; M, maximum; T, terminal steady-state), whereas CO2 assimilation showed a linear increase with time. Low-temperature treatment (down to - 1.5 °C) strongly modulated the SMT phase and stimulated a peak in the CO2 assimilation induction curve. We show that the SMT phase, at ~ 22 °C, was abolished when measured under high actinic irradiance, or when 3-(3, 4-dichlorophenyl)-1, 1- dimethylurea (DCMU, an inhibitor of electron flow) or methyl viologen (MV, a Photosystem I (PSI) electron acceptor) was added to the system. Our data suggest that stimulation of the SMT wave, at low temperatures, has multiple reasons, which may include changes in both photochemical and biochemical reactions leading to modulations in non-photochemical quenching (NPQ) of the excited state of Chl, "state transitions," as well as changes in the rate of cyclic electron flow through PSI. Further, we suggest that cold acclimation, in accession C24, promotes "state transition" and protects photosystems by preventing high excitation pressure during low-temperature exposure.

• Klíčová slova
• 3-(3, 4-dichlorophenyl)-1, 1- dimethylurea, Chlorophyll fluorescence transients, Cold acclimation, Gas-exchange measurements, Low-temperature effect, Methyl viologen, Slow SMT fluorescence phase, State transition,
• MeSH
• aklimatizace MeSH
• Arabidopsis metabolismus   MeSH
• chlorofyl a metabolismus   MeSH
• fotosyntéza fyziologie   MeSH
• nízká teplota MeSH
• teplota MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• chlorofyl a MeSH

Diatoms are especially important microorganisms because they constitute the larger group of microalgae. To survive the constant variations of the light environment, diatoms have developed mechanisms aiming at the dissipation of excess energy, such as the xanthophyll cycle and the non-photochemical chlorophyll (Chl) fluorescence quenching. This contribution is dedicated to the relaxation of the latter process when the adverse conditions cease. An original nonlinear regression analysis of the relaxation of non-photochemical Chl fluorescence quenching, qN, in diatoms is presented. It was used to obtain experimental evidence for the existence of three time-resolved components in the diatom Phaeodactylum tricornutum: qNf, qNi and qNs. qNf (s time-scale) and qNs (h time-scale) are exponential in shape. By contrast, qNi (min time-scale) is of sigmoidal nature and is dominant among the three components. The application of metabolic inhibitors (dithiothreitol, ammonium chloride, cadmium and diphenyleneiodonium chloride) allowed the identification of the mechanisms on which each component mostly relies. qNi is linked to the relaxation of the ΔpH gradient and the reversal of the xanthophyll cycle. qNs quantifies the stage of photoinhibition caused by the high light exposure, qNf seems to reflect fast conformational changes within thylakoid membranes in the vicinity of the photosystem II complexes.

• Klíčová slova
• diatom, high light stress, photoprotection, photosynthesis, relaxation, xanthophyll cycle,
• MeSH
• časové faktory MeSH
• chlorid amonný MeSH
• chlorofyl metabolismus   účinky záření   MeSH
• dithiothreitol MeSH
• fluorescence MeSH
• fotosystém II (proteinový komplex) metabolismus   MeSH
• kadmium MeSH
• kinetika MeSH
• oniové sloučeniny MeSH
• regresní analýza MeSH
• rozsivky fyziologie   MeSH
• světlo * MeSH
• tylakoidy metabolismus   MeSH
• xanthofyly metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• chlorid amonný MeSH
• chlorofyl MeSH
• diphenyleneiodonium MeSH Prohlížeč
• dithiothreitol MeSH
• fotosystém II (proteinový komplex) MeSH
• kadmium MeSH
• oniové sloučeniny MeSH
• xanthofyly MeSH