The cadmium treatment of dark-grown leaves and isolated etioplast inner membranes of wheat resulted in a decrease of the amount of the 657 nm emitting (77 K fluorescence) protochlorophyllide (PChlide) form, a simultaneous increase of the 633 nm form and the appearance of a 641.5 nm emitting form. This effect did not occur if excess NADPH was added to the isolated membranes: these samples showed spectral properties identical to those of non-treated (control) samples. Inhibition of the PChlide phototransformation was observed in the cadmium-treated leaves and membranes, the irradiation resulted in the appearance of a smáli amount of chlorophyllide (Chlide) with characteristic emission band at 678 nm. If excess NADPH was added, the inhibition did not occur and flash irradiation resulted in formation of the 694 nm Chlide form similarly as in control plants.
Chlorophyll content, photosynthetíc oxygen evolution and the activities of ATP- sulphurylase (ATP-s) (E.C. 2.7,7.4.), OAS-sulphydrylase (OAS-s) (E.C, 4.2.99.8.), nitráte reductase (NR) (E.C. 1.6.6.1.) and glutamine synthetase (GS) (E.C. 6.3.1.2), were determined in leaves of Zea mays L. Dekalb cv. Sponsor plants grown in the presence of 0, 10, 100, 250 pM Cd in order to evaluate the effect of this metal on sulphate and nitráte assimilation pathway. Cd induced a slight decrease of photosynthetíc oxygen evolution (-21 % of the control at 250 pM), whereas the enzyme activities were differently influenced: OAS-s and GS increased up to 40 and 25 % of the control, respectively, at 250 pM Cd; NR showed a 20 % stimulation at 100 pM Cd, and ATP-s was slightly inhibited. The results stress the importance of experimental conditions adopted on the response of enzyme activities to Cd and suggest that the observed increases of enzyme activities are related to a defence mechanism.
Growth, photosynthetic gas exchange, and chlorophyll fluorescence characteristics were investigated in wild type (WT) and Cd-sensitive mutant rice (Oryza sativa L.) plants using 50 µM Cd treatment for 12 d followed by a 3-d recovery. Under Cd stress, net dry mass and pigment contents were significantly lower in the mutant plants than in the WT. The mutant had lower net photosynthetic rate (P N), transpiration rate (E), and stomatal conductance (g s) than WT rice, however, it had higher intercellular CO2 concentration (C i), indicating that non-stomatal factors accounted for the inhibition of P N. Maximal photochemical efficiency of photosystem 2 (Fv/Fm), effective quantum yield of PS2 (ΦPS2), and photochemical quenching (qP) decreased much in the mutant under Cd stress. Cd content in roots and leaves of the mutant was significantly higher than those in the WT. Hence Cd toxicity was associated with the marked increases in Cd contents of plant tissue. After the recovery for 3 d, the WT rice had higher capacity to recover from Cd injury than the mutant. and J.-Y. He ... [et al.].
In the mutant CC-1047 of Chlamydomonas reinhardtii, LDS-PAGE showed that the chlorophyll-protein complex I (CPI) is almost absent. The mutant could not grow in a culture medium without organic carbon source while the wild type (WT) C. reinhardtii grew quickly. When an organic carbon source was added into the culture medium, the mutant grew almost as well as WT. The rate of photosystem 1 (PS1) electron transport (DCPIP→MV) and the rate of whole chain electron transport (H2O→MV) of chloroplasts of the CC-1047 mutant were both lower than those of WT. The photophosphorylation activity, photosynthetic O2 evolution rate, and rate of NADP+ photoreduction of CC-1047 were also much lower than the activities of WT. There were some differences in ATPase activity between the mutant and WT. Two different activation ways were used to activate the latent ATPase using methanol and dithiothreitol (DTT) as activation substrate. More methanol and DTT were required for the mutant than WT to obtain the maximum activity. Thus the photosynthetic apparatus could not operate normally when CPI was absent because of the abnormal PS1 electron transport. Meanwhile, the other adjacent complexes of the thylakoid membrane, for example, ATP synthase complex, were slightly affected. and Qing-Xiu Tang, Zhang-Lin Ni, Jia-Mian Wei.
Chromate-resistant Chlorella spp. isolated from effluents of electroplating industry could grow in the presence of 30 μM K2Cr2O7. Since photosynthesis is sensitive to oxidative stress, chromate toxicity to photosynthesis was examined in this algal isolate. Chromate [Cr(VI)] up to 100 μM was found to stimulate photosynthesis, while 90% inhibition was found, when the cells were incubated with 1 mM Cr(VI) for 4 h. Photosystem (PS) II was inhibited by 80% and PSI by 40% after such Cr(VI) treatment. Thermoluminescence studies on cells treated with 1 mM Cr(VI) for 4 h showed that S2QA - recombination peak (Q) was shifted to higher temperature, whereas S2/S3QB - recombination peak (B) was shifted to lower temperature. These shifts indicated alga stress response in order to overcome an excitation stress resulting from the inhibition of photosynthesis by Cr(VI). The nontreated Chlorella cells kept in the dark showed periodicity of four for the Q peak (4-8°C) and B peak (34-38°C) after exposure to series of single, turnover, saturating flashes. This periodicity was lost in Cr(VI)-treated cells. Higher concentrations of Cr(VI) inhibited mainly the electron flow in the electron transport chain, inactivated oxygen evolving complex, and affected also Calvin cycle enzymes in the Cr(VI)-resistant isolates of Chlorella. and S. N. Yewalkar, K. N. Dhumal, J. K. Sainis.
We investigated the effect of chromium (20-40 g m-3, 8-72 h) on the photosystem 2 (PS2) activities of Chlorella pyrenoidosa cells. By using chlorophyll fluorescence transients, thermoluminescence, oxygen polarography, and Western blot analysis for D1 protein we found that inhibition of PS2 can be accounted for by the enhanced photodestruction of the reaction centres in the cells cultivated in the presence of Cr(VI) at 25 °C in "white light" (18 W m-2). Hence photodestruction of D1 is caused by an enhanced oxidative stress and lipid peroxidation, as indicated by the appearance of a high-temperature thermoluminescence band. and Z. T. Hörcsik ... [et al.].
The effects of long-term exposure to ozone (O3, 60 mm3 m-3 for 5 h d-1) on some Calvin cycle enzymes, in particular those modulated by the thioredoxin system, were studied in two poplar clones. These clones differ in sensitivity to O3. In the I-214 clone, the first effects from O3 treatment were seen after 40 d of fumigation, while the Eridano clone showed visible symptoms of damage after only 15 d of the treatment. Specific activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (E.C. 4.1.1.39) diminished in both the clones, while specific activity of phosphoenolpyruvate carboxylase (E.C. 4.1.1.31) increased. Exposure to O3 also caused a reduction in the specific activity of ribulose-1,5-bisphosphate kinase (E.C. 2.7.1.19) in both clones. At the end of the exposure to O3, specific activity of glyceraldehyde 3-phosphate dehydrogenase (E.C. 1.2.1.13) increased in I-214 and remained similar to the control in Eridano, whereas specific activity of fructose-1,6-bisphosphate phosphatase (E.C. 3.1.3.11) was higher in Eridano and similar to the control in I-214. and E. Degl'Innocenti, L. Guidi, G. F. Soldatini.
The physiological and biochemical behaviour of rice (Oryza sativa, var. Jyoti) treated with copper (II) oxide nanoparticles (CuO NPs) was studied. Germination rate, root and shoot length, and biomass decreased, while uptake of Cu in the roots and shoots increased at high concentrations of CuO NPs. The accumulation of CuO NPs was observed in the cells, especially, in the chloroplasts, and was accompanied by a lower number of thylakoids per granum. Photosynthetic rate, transpiration rate, stomatal conductance, maximal quantum yield of PSII photochemistry, and photosynthetic pigment contents declined, with a complete loss of PSII photochemical quenching at 1,000 mg(CuO NP) L-1. Oxidative and osmotic stress was evidenced by increased malondialdehyde and proline contents. Elevated expression of ascorbate peroxidase and superoxide dismutase were also observed. Our work clearly demonstrated the toxic effect of Cu accumulation in roots and shoots that resulted in loss of photosynthesis., M. V. J. Da Costa, P. K. Sharma., and Obsahuje seznam literatury
In order to investigate the effect of day/night temperature difference (DIF) on photosynthetic characteristics of tomato plants (Solanum lycopersicum, cv. Jinguan 5) at fruit stage, an experiment was carried out in climate chambers. Five day/night temperature regimes (16/34, 19/31, 25/25, 31/19, and 34/16°C) with respective DIFs of -18, -12, 0, +12, and +18 were used and measured at mean daily temperature of 25°C. The results showed that chlorophyll (Chl) a, Chl b, net photosynthetic rate (PN), stomatal conductance (gs), maximum quantum yield of PSII photochemistry (Fv/Fm), effective quantum yield of PSII photochemistry (ϕPSII), and photochemical quenching (qp) significantly increased under positive DIF, while they decreased with negative DIF. In contrast, the Chl a/b ratio and nonphotochemical quenching (NPQ) decreased under positive DIF, while increased with negative DIF. Chl a, Chl b, PN, gs, Fv/Fm, ϕPSII, and qp were larger under +12 DIF than those at +18 DIF, while Chl a/b and NPQ showed an opposite trend., X. K. Yuan., and Seznam literatury
Spectroscopy was used to investigate the fluorescence quenching mechanism in light-harvesting complex 2 (LHC2). The 77 K fluorescence excitation spectroscopy was performed for detection of aggregation state of LHC2 treated with different concentrations of octylphenol poly(ethyleneglycol ether)10 (TX-100). Resonance Raman (RR) spectra excited with 488, 496, and 514 nm provided molecular configuration of neoxanthin, lutein 1, and lutein 2, respectively. At increased concentration of TX-100, the RR signals of xanthophylls were enhanced in the four frequency regions, which was accompanied with increase of fluorescence of chlorophyll (Chl) a. Thus the absorption of the three xanthophyll molecules was inclined to excitation wavelength, which proved that functional configurations of xanthophyll molecules in LHC2 were vital for fast transfer of excitation energy to Chl a molecules. Changes in the v4 region (C-H out-of-plane bending modes, at ∼960 cm-1 in RR spectra) demonstrated that the twist feature of neoxanthin, lutein 1, and lutein 2 molecules existed in LHC2 trimers, however, it was lost in the LHC2 macro-aggregates. In the second derivative absorption spectra of LHC2, neoxanthin absorption was not detected in LHC2 macro-aggregates, while evident absorption was found in LHC2 trimers and this absorption decreased obviously when TX-100 concentration was higher than 1 mM. Hence the neoxanthin molecule had a structural role in formation of LHC2 trimers. The RR and absorption spectra also implied that carotenoid molecules constructed the functional LHC2 trimers via their intrinsic configuration features, which enabled energy transfer to Chl a efficiently and led to lower fluorescence quenching efficiency. In contrast, these intrinsic twist configurations were lost in LHC2 macro-aggregates and led to lower energy transfer efficiency and higher fluorescence quenching efficiency. and Z. H. Hu, F. Zhou, C. H. Yang.