The delayed luminescence (DL) of photosystem 2 (PS2) after infiltration of 7-d-old etiolated barley leaves with chlorophyllides (Chlide) a or b followed by 2.5 h dark incubation was studied. Chlide a caused a very weak DL of PS2 just at the beginning of irradiation and the intensity of this DL was not higher when the infiltration medium contained 2 mM of NADPH. Chlide b was a somewhat more efficient inducer of PS2 formation in the dark and NADPH enhanced this efficiency 4.5 times though it did not affect the amount of esterified Chlides. The photoconversion of endogenous Pchlide led to a much higher intensity of the DL in comparison with the infiltration of Chlides, while the total amount of chlorophyll (Chl) formed was almost unchanged. The use of Chlide b together with the acetone extract from green leaves, devoid of pigments, resulted in the DL intensity comparable with that observed after Pchlide photoconversion followed by 2.5 h incubation in the dark. Dark formation of active PS2 in etiolated leaves was shown for the first time. Thus the dark formation of active PS2 may require Chl b, NADPH, and some unidentified water-soluble factor(s), synthesized in the dark after a short irradiation of etiolated leaves and inherent in green leaves. and V. P. Domanskiï, L.I. Fradkin.
Distribution of NADPH-protochlorophyllide oxidoreductase (POR) in etioplast of etiolated barley leaf was studied by using Western blot analyses of etioplast fractions isolated on a sucrose gradient. When the leaf was exposed to light, POR content decreased in the etioplast inner membrane and prolamellar body sub-membrane fraction while it was simultaneously increased in the stroma. By using 77 K fluorescence spectroscopy analyzes, we found for irradiated etiolated leaf that the POR protein in the stroma was co-localized with chlorophyllide (Chlide) emitting at 678 nm. Relocalization of the POR-Chlide complex induced by irradiation suggests that POR participates in the pigment transport processes during early stages of the thylakoid membrane development. and D. Kovacevic, D. Dewez, R. Popovic.
72 to 120 h of soil flooding of barley plants (Hordeum vulgare L. cv. Alfa) led to a noticeable decrease in the rates of CO2 assimilation and transpiration, and in chlorophyll and dry mass contents. Stomatal conductance decreased following flooding without appreciable changes in the values of intercellular CO2 concentrations. A drop in the activity of ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) and of the photorespiratory enzymes phosphoglycollate phosphatase (EC 3.1.3.18) and glycollate oxidase (EC 1.1.3.1) was observed, while the activity of phosphoenolpyruvate carboxylase (EC 4.1.1.31) increased in all flooded plants. Flooding of barley plants caused an increase in proline content and in leaf acidity. and R. Y. Yordanova, L. P. Popova.
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 inhibition of photosynthetic activity by bisulphite was studied in intact leaves of abscisic acid (ABA)-treated and non-treated (control) barley plants. ABA inhibited the photosynthetic process as evidenced by lower values of chlorophyll fluorescence kinetic parameters Fv/Fm (photosystem 2 activity) and Rfd (vitality index, related to the whole photosynthetic activity) compared with ABA-non-treated plants. After bisulphite treatment, the extent of inhibition was smaller in ABA-treated plants than in the control ones indicating a protective effect of ABA. The protective action sites of ABA were the QA reduction and the Calvin cycle. and C. N. N'Soukpoè-Kossi ... [et al.].
The cytosolic and chloroplastic isoforms of glucose-6-phosphate dehydrogenase (G6PDH) were separated and purified from barley leaves (Hordeum vulgare L.). In etiolated leaves, only the cytosolic isoform was expressed. The molecular mass of the cytosolic enzyme, G6PDH1, was 112±8 kDa and that of the chloroplast enzyme, G6PDH2, was 136±7 kDa. The Km values for glucose-6-phosphate and NADP were 0.133 and 0.041 mM for G6PDH1, and 0.275 and 0.062 mM for G6PDH2, respectively. The pH optimum was 8.2 for G6PDH1 and 7.8 for G6PDH2. The enzyme is absolutely specific for NADP. NADPH is a competitive inhibitor of the G6PDH1 in respect to glucose-6-phosphate (G6P) and NADP (Ki = 0.050 and 0.025 mM, respectively). NADPH is a competitive inhibitor of the G6PDH2 in respect to NADP (Ki = 0.010 mM), but a non-competitive inhibitor in respect to the G6P. ADP, AMP, UTP, NAD, and NADH had no effect on the activity of G6PDH. ATP inhibited the G6PDH2 activity. and A. Semenihina ... [et al.].
Twelve-day-old barley seedlings were supplied with 23 μM methyl jasmonate (MeJA) or 10 μM paraquat (Pq) via the transpiration stream and kept in the dark for 24 h. Then they were exposed to 100 μmol m-2 s-1 PAR and samples were taken 1, 2, 3, and 6 h after irradiation. Treatment of seedlings with MeJA alone resulted in decreased content of chlorophyll (Chl), and net photosynthetic (PN) and transpiration rates. Pq treatment led to a decrease in Chl content and to a very strong inhibition of PN, the effects were manifested by 1 h of irradiation. Pq treatment did not affect the activity of ribulose-1,5 bisphosphate carboxylase (RuBPC, EC 4.1.1.39) but increased the activity of the photorespiratory enzymes phosphoglycolate phosphatase (PGP, EC 3.1.3.18), glycolate oxidase (GO, EC 1.1.3.1), and catalase (EC 1.11.1.6). Pre-treatment of seedlings with MeJA before exposure to Pq fully blocked the inhibitory effect of Pq on photosynthesis and protected against subsequent Pq-induced oxidative damage. and V. A. Hristova, L. P. Popova.
Senescence-induced changes in the xanthophyll cycle activity and chlorophyll (Chl) fluorescence parameters were compared in detached barley (Hordeum vulgare L.) leaf segments kept for 6 d in darkness or under continuous " white light" (90 μmol m-2 s-1). Before detachment of the leaf segments, the plants were grown at periodic regime [12 h light (90 μmol m-2 s-1)/12 h dark]. The de-epoxidation state of the xanthophyll cycle pigments (DEPS) in the leaf samples was determined immediately (the actual DEPS), after 1 h of dark-adaptation (the residual DEPS), and during 14 min of a high-irradiance (HI) exposure (500 μmol m-2 s-1) (HI-induced DEPS). In the light-senescing segments, senescence was delayed pronouncedly compared to dark-senescing ones as the Chl content, the photosystem 2 photochemistry, and electron transport processes were highly maintained. Further, the actual DEPS increased, probably due to the increased mean photon dose. The HI-induced increase in the DEPS was stimulated in the light-senescing segments, whereas it was slowed down in the dark-senescing ones. However, after the 14 min HI-exposure of the dark-senescing segments the HI-induced DEPS was not markedly lower than in the mature leaves, which indicated the maintenance of the xanthophyll cycle operation. and M. Špundová, K. Strzałka, J. Nauš.