Prolonged storage of isolated photosystem 2 (PS2)-enriched subchloroplast particles in the frozen statě leads to a decrease of the PS2 activity and to an increase of the energy transfer between chlorophyll (Chl)-proteins of the light-harvesting chlorophyll a/b (LHC)-PS2 complex. The energy transfer was less influenced than the PS2-mediated electron transport at freeze-thaw treatment of PS2 particles. The change of these parameters was not affected by the rate of freezing. The addition of cryoprotectants such as glycerol, trehalose or saccharose in the suspension medium prior to freezing preserved fo a different extent the PS2-mediated electron transport and the energy transfer between the Chl molecules of the LHC-PS2 complex.
We tested the usefulness of chlorophyll a fluorescence quenching analysis for the selection of maize parental inbred lines able to produce F1 hybrids with a high CO2 assimilation rate during growth at suboptimal temperature. Fifty inbred lines, grown at 15 °C, showed at 6 °C a broad genetic variability regarding the quantum yield of photosynthetic electron transport (ΦPS2). A decrease of ΦPS2 in sensitive lines was caused more by reduction of the efficiency of excitation energy capture by open photosystem 2 (PS2) reaction centres (Fv'/Fm') than by a drop in photochemical quenching (qP). Selected inbred lines with the highest (H) and the lowest (L) values of ΦPS2 were used for separate crossings in a diallelic arrangement. Twenty-one of H×H hybrids and 21 of the L×L hybrids were grown at 15 °C. The H×H hybrids showed at suboptimal temperature a significantly higher transport of photosynthetic electrons than the L×L hybrids at lower (400) as well as at higher [800 μmol(photon) m-2 s-1] irradiance. The mean net photosynthetic rate (PN) in H×H and L×L hybrids amounted to 8.4 and 5.8 (second leaf) and 8.5 and 7.6 μmol(CO2) m-2 s-1 (third leaf), respectively. Among the best 20 hybrids with regard to PN (values larger than the average) of second leaves, as many as 15 were derived from H lines (75 % of hybrids), whereas among the best 21 hybrids with regard to PN of the third leaves, 16 were derived from H lines (76 % of hybrids). The intensive PN of H×H hybrids was most often accompanied by less water lost via transpiration in relation to photosynthesis than in the hybrids of L lines. Hence an analysis of chlorophyll a fluorescence quenching enables the selection of inbred lines, which can produce hybrids with improved CO2 fixation and with efficient water management during growth at suboptimal temperature. and J. Kościelniak, F. Janowiak, Z. Kurczych.
The mechanistic basis for protection of exogenous ascorbate against photoinhibition at low temperature was examined in leaves of rice (Oryza sativa L.). Exposure of intact leaves to chilling temperature resulted in a drastic decrease in the speed of development of non-photochemical fluorescence quenching (NPQ). This was related to the low temperature-imposed restriction on the formation of the fast relaxing component of NPQ (qf). Feeding with 20 mM ascorbate markedly increased the rate of qf development at chilling temperature due primarily to the enhanced rate of zeaxanthin (Z) formation. On the other hand, ascorbate feeding had no influence on photosystem 2 (PS2)-driven electron flow. The reduced state of the PS2 primary electron acceptor QA decreased in ascorbate-fed leaves exposed to high irradiance at chilling temperature owing to the increased Z-associated thermal energy dissipation in the light-harvesting antenna system of PS2. Furthermore, ascorbate feeding increased the photosynthetic apparatus of rice leaves to resist photoinhibition at low temperature. The protective effect of exogenous ascorbate was fully accounted for by the enhanced xanthophyll cycle activity. and C.-C. Xu ... [et al.].
To investigate the effect of low CO2 on the expression and activity of ferredoxin-NADP+ oxidoreductase (FNR) and this enzyme-mediated cyclic electron flow around photosystem I (cyclic PSI), the activity staining, immunoblotting and initial rate of P700 + reduction were measured in high- or low-CO2-grown (H or L)-cells of wild-type Synechocystis sp. strain PCC 6803 (WT) and its ΔndhB mutant (M55). Major results were depicted as follows. (1) The protein levels and activity of FNR were remarkably stimulated in L-cells of both WT and M55 relative to that in their H-cells. (2) The rate of cyclic PSI was significantly increased in L-cells of WT, not M55, when compared to that in respective H-cells. (3) N-ethylmaleimide, an inhibitor of FNR, partially inhibited the increase in the rate of cyclic PSI induced by low CO2 in both WT and M55. These findings indicated that low CO2 enhanced the expression and activity of FNR and the cyclic PSI mediated by FNR. The contribution of FNR to cyclic PSI is shortly discussed. and Y. R. Liu, W. M. Ma, H. L. Mi.
Chloroplasts isolated from Vigna sinensis L, seedlings grown under cool íluorescent (control chloroplasts) and ultraviolet-B (UV-B)-enhanced íluorescent (UV chloroplasts) radiation, when incubated at 10, 20, 30 and 40 °C, showed large variations in the photosynthetic electron transport reactions. The overall electron transport activity in both control and UV chloroplasts incubated at 40 decreased rapidly. In contrast to this, at 30 the control chloroplasts got inactivated very rapidly during the 30 min of incubation while the UV chloroplasts showed high stability. A similar trend was also noticed at 20 “C. At 10 °C, although the rate of inactivation was slow, UV chloroplasts were more stable than control chloroplasts. A similar trend was noticed in photosystern (PS) 2 activity. In contrast to overall electron transport and PS2 reactions, PS 1 activity showed only marginal changes at all temperatures. The polypeptide profiles of chloroplasts exposed to UV-B iixadiation for 60 min at different temperatures revealed marked decreases in the level of the 23 and 33 kDa polypeptides in control chloroplasts while in UV chloroplasts these polypeptides were highly stable. In addition, UV chloroplasts contained several new polypeptides of both high and low molecular masses. The polypeptide partem indicated that higher photochemical activity of UV chloroplasts over the control chloroplasts could be due to stabilization of PS 2 core complexes by the new polypeptides induced under UV-B enhanced radiation.
The principal function of the thylakoid membrane depends on the integrity of the lipid bilayer, yet almost half of the thylakoid lipids are of non-bilayer-forming type, whose exact functions are not fully understood. Non-bilayer lipids can be extruded from the membrane in the presence of high concentrations of co-solutes. We applied 2 M sucrose to induce lipid phase separation in isolated thylakoid membranes, following consequent structural and physiological effects. Circular dichroism spectroscopy indicated significant changes in the chiral macro-arrangement of the pigment-protein complexes, which were reversed after washing out the co-solute. Similarly, merocyanine-540 fluorescence suggested reversible changes in the lipid phases. The PSII function, as tested by chlorophyll fluorescence induction transients and time-resolved fluorescence, was almost unaffected. However, the presence of sucrose dramatically increased the PSII thermostability, which can partly be explained by a direct osmolyte effect and partly by the lipid phase separation stabilizing the stacked membrane., C. Kotakis, P. Akhtar, O. Zsiros, G. Garab, P. H. Lambrev., and Obsahuje bibliografické odkazy
Anthropogenic activities are changing global precipitation regimes and result in many middle latitude arid and semiarid regions experiencing less precipitation and more extreme weather events. However, little is known about the response of active ingredient accumulation in the medicinal herb Plantago depressa Willd. Therefore, we carried out a greenhouse experiment in order to study effect of control (CK, normal water supply equal to 309 mm per four months), -30 (-WS) and +30% (+WS) of the control water supply on the photosynthesis (PN), C/N ratio, and plantamajoside accumulation in P. depressa. Our results showed that compared with the-WS and CK treatments, the +WS treatment significantly enhanced biomass, the C/N ratio, plantamajoside concentration, yield in shoots and roots, and PN, but declined the N concentration in shoots and roots. The plantamajoside concentration was positively correlated with PN, the soluble sugar content, and the C/N ratio, but negatively correlated with the N concentration. Our results suggested that, under experimental conditions, +WS increased the C/N ratio and promoted the plantamajoside accumulation of P. depressa., Z. Li, W. Bai, L. Zhang, L. Li., and Obsahuje bibliografii