The short-term acclimation (10-d) of Norway spruce [Picea abies (L.) Karst] to elevated CO2 concentration (EC) in combination with low irradiance (100 μmol m-2 s-1) resulted in stimulation of CO2 assimilation (by 61 %), increased total chlorophyll (Chl) content (by 17 %), significantly higher photosystem 2 (PS2) photochemical efficiency (Fv/Fm; by 4 %), and reduced demand on non-radiative dissipation of absorbed excitation energy corresponding with enhanced capacity of photon utilisation within PS2. On the other hand, at high cultivation irradiance (1 200 μmol m-2 s-1) both Norway spruce and spring barley (Hordeum vulgare L. cv. Akcent) responded to EC by reduced photosynthetic capacity and prolonged inhibition of Fv/Fm accompanied with enhanced non-radiative dissipation of absorbed photon energy. Norway spruce needles revealed the expressive retention of zeaxanthin and antheraxanthin (Z+A) in darkness and higher violaxanthin (V) convertibility (yielding even 95 %) under all cultivation regimes in comparison with barley plants. In addition, the non-photochemical quenching of minimum Chl a fluorescence (SV0), expressing the extent of non-radiative dissipation of absorbed photon energy within light-harvesting complexes (LHCs), linearly correlated with V conversion to Z+A very well in spruce, but not in barley plants. Finally, a key role of the Z+A-mediated non-radiative dissipation within LHCs in acclimation of spruce photosynthetic apparatus to high irradiance alone and in combination with EC was documented by extremely high SV0 values, fast induction of non-radiative dissipation of absorbed photon energy, and its stability in darkness. and I. Kurasová ... [et al.].
The effects of different spectral region of excitation and detection of chlorophyll (Chl) a fluorescence at room temperature on the estimation of excitation energy utilization within photosystem (PS) 2 were studied in wild-type barley (Hordeum vulgare L. cv. Bonus) and its Chl b-less mutant chlorina f2 grown under low and high irradiances [100 and 1 000 µmol(photon) m-2 s-1]. Three measuring spectral regimes were applied using a PAM 101 fluorometer: (1) excitation in the red region (maximum at the wavelength of 649 nm) and detection in the far-red region beyond 710 nm, (2) excitation in the blue region (maximum at the wavelength of 461 nm) and detection beyond 710 nm, and (3) excitation in the blue region and detection in the red region (660- 710 nm). Non-photochemical quenching of maximal (NPQ) and minimal fluorescence (SV0), determined by detecting Chl a fluorescence beyond 710 nm, were significantly higher for blue excitation as compared to red excitation. We suggest that this results from higher non-radiative dissipation of absorbed excitation energy within light-harvesting complexes of PS2 (LHC2) due to preferential excitation of LHC2 by blue radiation and from the lower contribution of PS1 emission to the detected fluorescence in the case of blue excitation. Detection of Chl a fluorescence originating preferentially from PS2 (i.e. in the range of 660-710 nm) led to pronounced increase of NPQ, SV0, and the PS2 photochemical efficiencies (FV/FM and FV'/FM'), indicating considerable underestimation of these parameters using the standard set-up of PAM 101. Hence PS1 contribution to the minimal fluorescence level in the irradiance-adapted state may reach up to about 80 %. and M. Štroch ... [et al.].
The review deals with thermal dissipation of absorbed excitation energy within pigment-protein complexes of thylakoid membranes in higher plants. We focus on the de-excitation regulatory processes within photosystem 2 (PS2) that can be monitored as non-photochemical quenching of chlorophyll (Chl) a fluorescence consisting of three components known as energy-dependent quenching (qE), state-transition quenching (qT), and photoinhibitory quenching (qI). We summarize the role of thylakoid lumen pH, xanthophylls, and PS2 proteins in qE mechanism. Further, both the similarity between qE and qI and specific features of qI are described. The other routes of thermal energy dissipation are also mentioned, that is dissipation within photosystem 1 and dissipation through the triplet Chl pathway. The significance of the individual de-excitation processes in protection against photo-oxidative damage to the photosynthetic apparatus under excess photon supply is stretched. and M. Štroch, V. Špunda, I. Kurasová.
The present study was conducted to examine changes in photosynthetic pigment composition and functional state of the thylakoid membranes during the individual steps of preparation of samples that are intended for a separation of pigmentprotein complexes by nondenaturing polyacrylamide gel electrophoresis. The thylakoid membranes were isolated from barley leaves (Hordeum vulgare L.) grown under low irradiance (50 μmol m-2 s-1). Functional state of the thylakoid membrane preparations was evaluated by determination of the maximal photochemical efficiency of photosystem (PS) II (FV/FM) and by analysis of excitation and emission spectra of chlorophyll a (Chl a) fluorescence at 77 K. All measurements were done at three phases of preparation of the samples: (1) in the suspensions of osmotically-shocked broken chloroplasts, (2) thylakoid membranes in extraction buffer containing Tris, glycine, and glycerol and (3) thylakoid membranes solubilized with a detergent decyl-β-D-maltosid. FV/FM was reduced from 0.815 in the first step to 0.723 in the second step and to values close to zero in solubilized membranes. Pigment composition was not pronouncedly changed during preparation of the thylakoid membrane samples. Isolation of thylakoid membranes affected the efficiency of excitation energy transfer within PSII complexes only slightly. Emission and excitation fluorescence spectra of the solubilized membranes resemble spectra of trimers of PSII light-harvesting complexes (LHCII). Despite a disrupted excitation energy transfer from LHCII to PSII antenna core in solubilized membranes, energy transfer from Chl b and carotenoids to emission forms of Chl a within LHCII trimers remained effective. and V. Karlický ... [et al.].
The response of barley (Hordeum vulgare L. cv. Akcent) to various photosynthetic photon flux densities (PPFDs) and elevated [CO2] [700 μmol (CO2) mol-1; EC] was studied by gas exchange, chlorophyll (Chl) a fluorescence, and pigment analysis. In comparison with barley grown under ambient [CO2] [350 μmol (CO2) mol-1; AC] the EC acclimation resulted in a decrease in photosynthetic capacity, reduced stomatal conductance, and decreased total Chl content. The extent of acclimation depression of photosynthesis, the most pronounced for the plants grown at 730 μmol m-2 s-1 (PPFD730), may be related to the degree of sink-limitation. The increased non-radiative dissipation of absorbed photon energy for all EC plants corresponded to the higher de-epoxidation state of xanthophylls only for PPFD730 barley. Further, a pronounced decrease in photosystem 2 (PS2) photochemical efficiency (given as FV/FM) for EC plants grown at 730 and 1 200 μmol m-2 s-1 in comparison with AC barley was related to the reduced epoxidation of antheraxanthin and zeaxanthin back to violaxanthin in darkness. Thus the EC conditions sensitise the photosynthetic apparatus of high-irradiance acclimated barley plants (particularly PPFD730) to the photoinactivation of PS2. and I. Kurasová ... [et al.].