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 adaptation of barley (Hordeum vulgare L. cv. Akcent) plants to low (LI, 50 µmol m-2 s-1) and high (HI, 1000 µmol m-2 s-1) growth irradiances was studied using the simultaneous measurements of the photosynthetic oxygen evolution and chlorophyll a (Chl a) fluorescence at room temperature. If measured under ambient CO2 concentration, neither increase of the oxygen evolution rate (P) nor enhancement of non-radiative dissipation of the absorbed excitation energy within photosystem 2 (PS2) (determined as non-photochemical quenching of Chl a fluorescence, NPQ) were observed for HI plants compared with LI plants. Nevertheless, the HI plants exhibited a significantly higher proportion of QA in oxidised state (estimated from photochemical quenching of Chl a fluorescence, qP), by 49-102 % at irradiances above 200 µmol m-2 s-1 and an about 1.5 fold increase of irradiance-saturated PS2 electron transport rate (ETR) as compared to LI plants. At high CO2 concentration the degree of P stimulation was approximately three times higher for HI than for LI plants, and the irradiance-saturated P values at irradiances of 2 440 and 2 900 µmol m-2 s-1 were by 130 and 150 % higher for HI plants than for LI plants. We suggest that non-assimilatory electron transport dominates in the adaptation of the photosynthetic apparatus of barley grown at high irradiances under ambient CO2 rather than an increased NPQ or an enhancement of irradiance-saturated photosynthesis. 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.