Changes in Hill reaction activity (HRA) and ultrastructure of mesophyll cell (MC) chloroplasts were studied during the ontogeny of third leaf of maize plants using polarographic oxygen evolution measurement, transmission electron microscopy, and stereology. The chloroplast ultrastructure was compared in young (actively growing), mature, and senescing leaves of two different inbreds and their reciprocal F1 hybrids. Statistically significant differences in both HRA and MC chloroplast ultrastructure were observed between different stages of leaf ontogeny. Growth of plastoglobuli was the most striking characteristic of chloroplast maturation and senescence. The chloroplasts in mature and senescing leaves had a more developed system of thylakoids compared to the young leaves. Higher HRA was usually connected with higher thylakoid volume density of MC chloroplasts. and J. Kutík ... [et al.].
The light response changes of oxygen evolutíon in the isolated spinách (Spinacia oleracea L.) thylakoids associated with the photoinhibition, influenced by the temperature and radical protection, were determined. Photoinhibition was performed at 20 ®C with or without an addition of antioxidant mixture consisting of glutathione, ascorbate, superoxide dismutase and catalase, oř, altematívely, at 0 oC without the antioxidants. Beside the effects on decline of atrazine binding sites and variable room temperature fluorescence, the three variants of photoinhibition differed with respect to their effects on the yield of oxygen evolutíon. Quantum yield of oxygen evolutíon (<{>02) flecline preceded Úie decrease of electron transport capacity at the beginning, while similar low values were found at the end of the treatment. In the presence of antioxidants the electron transport capacity remained high, whereas marked decline of (|»o^ occurred with the equally treated thylakoids. Comparable deviating behaviour of (t»Oj and the electron transport capacity was not found following photoinhibition at 0 oC; both were affected to the same degree, regardless if ferricyanide or the Qg- independent electron acceptor siUcomolybdate were ušed. With isolated thylakoids the quotient FyF,„, which is often ušed as a measure for photochemical efficiency of open photosystem 2 reaction centres in whole plant studies, did not decline to the same extent as (|)Oj under the dififerent photoinhibitoiy conditions applied. The main conclusion is that in thylakoid photoinhibition the independent mechanisms are associated with the changes of both the and electron transport capacity, and that the (j>02-related mechanism is inhibited at 0 oC.
Wheat (Triticum aestivum L. cv. Sonalika) seedlings were grown in Hoagland solution. Primary leaves were harvested at 8, 12, and 15 d and cut into five equal segments. Contents of photosynthetic pigments and proteins, and photosystem 2 (PS2) activity increased from base to apex of these leaves. Chlorophyll (Chl) content was maximum at 12 d in all the leaf segments, but PS2 activity showed a gradual decline from 8 to 15 d in all leaf segments. In sharp contrast, the CO2 fixation ability of chloroplasts increased from 8 to 15 d. CO2 fixation ability of chloroplasts started to decline from base to apex of 15-d-old seedlings, where the content of ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit (RuBPCO-LSU) increased acropetally. RuBPCO-LSU content was maximum in all the leaf segments in 12-d-old seedlings. This shows a distinctive pattern of PS2, Chl, CO2 fixation ability of chloroplasts, and RuBPCO-LSU content along the axis of leaf lamina during development and senescence. RuBPCO-LSU (54 kDa) degraded to fragments of 45, 42, 37, 19, and 16 kDa products which accumulated along the leaf axis during ageing of chloroplasts. Thus the CO2 fixation ability of chloroplasts declines earlier than PS2 activity and photosynthetic pigment contents along the leaf lamina. and F. Dilnawaz ... [et al.].
The history of the journals "Photosynthetica" and "Photosynthesis Research" is traced from its beginning. Their development is related to the history of several publishers (Dr W. Junk Publishers, Martinus Nijhoff, Kluwer Academic Publishers). This account is based on recollections and records of the authors, Ad C. Plaizier, and René Marcelle (the first Editor-in-Chief of Photosynthesis Research). and Govindjee, Z. Šesták, W. R. Peters.
Short-term (2 h) treatment with 10 µM abscisic acid decreased stomatal conductance and net photosynthetic rate, and increased carbonic anhydrase activity in pea seedlings. The treatment with 10 µM methyl jasmonate did not significantly affect these parameters. and G. N. Lazova, M. I. Kicheva, L. P. Popova.
Pisum sativum (L.) plants were grown under "white" luminescent lamps, W [45 µ mol(quantum) m-2 s-1] or under the same irradiation supplemented with narrow spectrum red light-emitting diodes (LEDs), RE [λmax = 660 nm, Δλ = 20 nm, 40 µmol(quantum) m-2 s-1]. Significant differences in the chlorophyll (Chl) a fluorescence parameters, degree of State 1-State 2 transition, and the pigment-protein contents were found in plants grown under differing spectral composition. Addition of red LEDs to the "white light" resulted in higher effective quantum yield of photosystem 2 (PS2), i.e. F'v/F'm, linear electron transport (ϕPS2), photochemical quenching (qP), and lower non-photochemical quenching (qN as well as NPQ). The RE plants were characterised by higher degree State 1-State 2 transition, i.e. they were more effective in radiant energy utilisation. Judging from the data of "green" electrophoresis of Chl containing pigment-protein complexes of plants grown under various irradiation qualities, the percentage of Chl in photosystem 2 (PS2) reaction centre complexes in RE plants was higher and there was no difference in the total Chl bound with Chl-proteins of light-harvesting complexes (LHC2). Because the ratio between oligomeric and monomeric LHC2 forms was higher in RE plants, we suggest higher LHC2 stability in these ones. and N. M. Topchyi ... [et al.].
Annual plants transport a large portion of carbohydrates and nitrogenous compounds from leaves to seeds during the phase of reproductive growth. This study aimed to clarify how reproductive growth affects photosynthetic traits in leaves and matter transport within the plant in the annual herb Chenopodium album L. Plants were grown in pots and either reproductive tissues or axillary leaves were removed at anthesis. Matter transport was evaluated as temporal changes in dry mass (as a substitute of carbohydrates) and nitrogen content of aboveground organs: leaves, axillary leaves, stems and reproductive tissues. Photosynthetic capacity (light-saturated photosynthetic rate under ambient CO2 concentration), nitrogen, chlorophyll and soluble protein content were followed in the 20th leaf that was mature at the start of the experiment. Removal of reproductive tissues resulted in accumulation of dry mass in leaves and axillary leaves, and accumulation of nitrogen in stem as nitrogen resorption from leaves and axillary leaves proceeded with time. Removal of axillary leaves proportionally reduced dry mass and nitrogen allocation to reproductive tissues, thus affecting the quantity but not quality of seeds. Removal treatments did not alter the time course of photosynthetic capacity, nitrogen, chlorophyll or soluble protein content during senescence in the 20th leaf, but changed the photosynthetic capacity per unit of leaf nitrogen according to demand from reproductive tissues. Together, the results indicate that reproductive tissues affected carbon and nitrogen economy separately. The amount of carbon was adjusted in leaves through photosynthetic capacity and carbohydrate export from them, and the amount of nitrogen was adjusted by transport from stem to reproductive tissues. The plant's ability to independently regulate carbon and nitrogen economy should be important in natural habitats where the plant carbon-nitrogen balance can easily be disturbed by external factors.
The peptide surfactants are amphiphilic peptides which have a hydrophobic tail and a hydrophilic head, and have been reported to stabilize and protect some membrane proteins more effectively than conventional surfactants. The effects of a class of peptide surfactants on the structure and thermal stability of the photosynthetic membrane protein lightharvesting complex II (LHCII) in aqueous media have been investigated. After treatment with the cationic peptide surfactants A6K, V6K2, I5K2 and I5R2, the absorption at 436 nm and 470 nm decreased and the absorption at 500-510 nm and 684-690 nm increased. Moreover, the circular dichroism (CD) signal intensity in the Soret region also decreased significantly, indicating the conformation of some chlorophyll (Chl) a, Chl b, and the xanthophyll molecules distorted upon cationic peptide surfactants treatment. The anionic peptide surfactants A6D and V6D2 had no obvious effect on the absorption and CD spectra. Except for A6D, these peptides all decreased the thermal stability of LHCII, indicating that these peptides may reconstitute protein into a less stable conformation. In addition, the cationic peptide surfactants resulted in LHCII aggregation, as shown by sucrose gradient ultracentrifugation and fluorescence spectra. and S. Liu, Y. Qiu, D.-Y. Yu
The study investigated the effects of different CaCl2 concentrations (2, 5, and 10 mM) on photosynthetic enzymatic activities, photosynthesis, and chlorophyll fluorescence of tung tree seedlings under drought conditions. Plants were sprayed with either CaCl2 or distilled water until run-off. Irrigation was then withheld to induce drought stress. The strength of drought stress was evaluated by relative leaf water content and soil water content, which was 27.3 and 9.5% on day 0 and day 12, respectively. Drought stress decreased activities of ribulose-1,5-bisphosphate carboxylase/oxygenase and phosphoenolpyruvate carboxylase, chlorophyll (a+b) content, net photosynthetic rate, stomatal conductance, transpiration rate, electron transport rate, the maximal quantum yield of PSII photochemistry, and effective quantum yield of PSII in tung tree seedlings. The CaCl2 pretreatments alleviated the negative effect of drought stress to some degree on all the parameters mentioned above., Z. Li, X. F. Tan, K. Lu, Z. M. Liu, L. L. Wu., and Obsahuje bibliografii
Chemical modification of purifíed phosphoenolpyravate carboxylase (PEPC) from the crassulacean acid metabolism plant Crassula argentea Thunb. with the histidyl reagent diethylpyrocarbonate (DEPC) resulted in a transient increase in activity followed by a decrease of activity with time. This biphasic response was observed when the modifíed enzyme was assayed at both low (sub-K,^ and saturating substráte (phosphoenolpyruvate, PEP) concentrations. There was an approximate 25- fold difference in the apparent rate constants for the activation and inhibition phases. This is in contrast to what we háve observed under similar conditions for the C4 enzyme from Zea mays L. for which only inhibition of activity occurs. Spectral studies indicated that up to 7 of the potential 20 histidine residues per subunit were modifíed, at least 3 of which were necessary for activity. The biphasic response of the Crassula enzyme was dependent on the concentration of DEPC. Progressively less inactivation was observed when modifying the enzyme with lower concentrations of DEPC. Chemical modification of PEPC with 75 pM DEPC resulted in a form of the enzyme with a lower K^, and higher This was concomitant with the modification of 4 histidines per subímit. Changes in the response of the enzyme to allosteric effectors were also observed; with modification the enzyme was desensitized to malate inhibition and glucose-6-phosphate activation. The Kj of the modifíed enzyme for malate increased over 15-fold. This was consistent with fluorescence binding studies using the extrinsic conformationalprobe S-anilino-l-naphthalenesulfonate which indicated the elimination of binding of malate and increased binding of the substráte to PEPC. Protection studies showed that malate desensitization was delayed by the presence of malate during modification. Malate also slowed the initial rate of histidine modifícation as measured spectrophotometrically. Thus histidine plays a role in the malate site of Crassula PEPC.