Effect of UV-B (1.9 W m-2) alone or in combination with supplemental "white light". WL (20 W m-2) exposure was studied on the energy transfer process of intact phycobilisomes isolated from Spirulina platensis. Exposure of UV-B or supplemental irradiation induced a decrease in room temperature fluorescence intensity and caused a shift towards shorter wavelengths. The low temperature fluorescence measurements showed that UV-B impairs energy transfer from phycocyanin to allophycocyanin B and the extent of damage may be reduced by the exposure to supplemental WL. and S. Rajagopal, Prasanna Mohanty, S. D. S. Murthy.
Seedlings of winter rape were cultured in vitro on media containing 24-epibrassinolide, EBR (100 nM) and cadmium (300 µM). After 14 d of growth, fast fluorescence kinetics of chlorophyll (Chl) a and contents of photosynthetic pigments and Cd in cotyledons were measured. Cd was strongly accumulated but its content in cotyledons was 14.7 % smaller in the presence of EBR. Neither Cd nor EBR influenced the contents of Chl a and b and carotenoids. Cd lowered the specific energy fluxes per excited cross section (CS) of cotyledon. The number of active reaction centres (RC) of photosystem 2 (RC/CS) decreased by about 21.0 % and the transport of photosynthetic electrons (ET0/CS) by about 17.1 %. Simultaneously, under the influence of Cd, the activity of O2 evolving centres (OEC) diminished by about 19.5 % and energy dissipation (DI0/CS) increased by about 14.6 %. In the cotyledons of seedlings grown on media without Cd, EBR induced only a small increase in the activity of most photochemical reactions per CS. However, EBR strongly affected seedlings cultured with cadmium. Specific energy fluxes TR0/CS and ET0/CS of the cotyledons of plants Cd+EBR media were about 10.9 and 20.9 % higher, respectively, than values obtained for plants grown with Cd only. EBR also limited the increase of DI0/CS induced by Cd and simultaneously protected the complex of OEC against a decrease of activity. Hence EBR reduces the toxic effect of Cd on photochemical processes by diminishing the damage of photochemical RCs and OECs as well as maintaining efficient photosynthetic electron transport. and A. Janeczko ... [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.].
Seedlings of tropical leguminous tree Samanea saman (Jacq.) Merrill were exposed for 7 d to acidic mist (AM, induced by H2SO4) of pH 5.6, 4.0, and 2.0. AM significantly reduced seedling growth (root and shoot length, leaf density, leaf area, fresh and dry mass accumulation) and photosynthetic activities. In thylakoids isolated from leaves treated at pH 4.0 and 2.0 a decrease in the activities of photosystem (PS) 2 and whole chain electron transport was observed, but PS1 activity did not change. When the seedlings were subsequently sprayed with triacontanol (TRIA), the AM effect was partially or completely reversed indicating that TRIA can protect from AM effects. The artificial electron donors, di-phenylcarbazide (DPC) and hydroxylamine (NH2OH), markedly restored the loss of PS2 activity in AM (pH 2.0) treated leaves. This is the first report of alleviating the AM by TRIA in tropical tree seedlings. and K. Muthuchelian, V. Meenakshi, N. Nedunchezhian.
Infiltration of methyl viologen (MV, source of O2-) and Na-diethyldithiocarbamate (DDC, inhibitor of SOD) into wheat leaves resulted in the accumulation of active oxygen species and photo-oxidative damage to photosynthetic apparatus under both moderate and high irradiance. Exogenous antioxidants, ascorbate (ASA) and mannitol, scavenged active oxygen efficiently, protected the photosynthetic system from MV and DDC induced oxidative damage, and maintained high Fv/Fm [maximal photochemical efficiency of photosystem 2 (PS2) while all PS2 reaction centres are open], Fm/F0 (another expression for the maximal photochemical efficiency of PS2), ΦPS2 (actual quantum yield of PS2 under actinic irradiation), qP (photochemical quenching coefficient), PN (net photosynthetic rate), and lowered qNP (non-photochemical quenching coefficient) of the leaves kept under high irradiance and oxidative stress. Phenolic compounds used in these experiments, catechol (Cat), resorcinol (Res), and tannic acid (Tan), had similar anti-oxidative activity and protective effect on photosynthetic apparatus as ASA and mannitol. The anti-oxidative activity and the protective effect of phenolic compounds increased with increase in their concentration from 100 to 300 g m-3. The number and the position of hydroxyl group in phenolic molecules seemed to influence their antioxidative activity. and Hui Jie Zhao, Qi Zou.
Previously, our data indicated that both cAMP and MAP kinase signaling play important roles in microalgal physiology as well as in lipid or carotenoid biosynthesis. In order to understand downstream genes of these signaling pathways, we employed proteomics approach. Both signal pathways were first altered with specific signaling inhibitors or modulators. Treatment of specific inhibitors changed microalgal size and increased lipid contents. With the microalgal cells after treatments of specific signaling inhibitor or modulators, we performed the proteomics analysis to identify downstream genes responsible for these phenotypes. Interestingly, multiple photosynthesis genes were identified, particularly proteins associated with PSII. Our data suggested that MAP kinase and cAMP signaling affect the photosynthesis, thereby leading to microalgal lipid or carotenoid biosynthesis., C. Lee, J.-K. Rhee, D. G. Kim, Y.-E. Choi., and Obsahuje seznam literatury
Localization of protochlorophyll(ide) (Pchlide) forms and chlorophyllide (Chlide) transformation process were studied by using comparative analyses of de-convoluted 77 K fluorescence spectra of barley etioplast stroma and different membrane fractions obtained by sucrose gradient centrifugation. Non-photoactive 633 nm Pchlide form was mainly located in the envelope-prothylakoid membrane mixture while the photoactive 657 nm Pchlide was dominant pigment in the prolamellar body membrane and in the soluble etioplast fraction (stroma). When these fractions were exposed to a saturating flash, conversion of photoactive Pchlide into 697 nm Chlide was preferential in the prolamellar body and in the stroma, while the 676 nm Chlide was dominant pigment form in the envelope-prothylakoid fraction. These spectral characteristics are considered to reflect molecular composition and organization of the pigment-protein complexes specific for each etioplast compartment. and D. Kovacevic, D. Dewez, R. Popovic.
Because the transformation of protochlorophyllide (Pchlide) to chlorophyllide (Chlide) is an irradiation-dependent process, it is at the heart of the photosynthetic membrane biogenesis, turnover, and adaptation to changes of the environment. I review here the new data published during the year 2004 on Pchlide reduction to Chlide.
The aim of our study was to investigate the role of protons in regulating energy distribution between the two photosystems in the thylakoid membranes. Low pH-induced changes were monitored in the presence of a proton blocker, N,N′-dicyclohexylcarbodiimide (DCCD). When thylakoid membranes were suspended in a low-pH reaction mixture and incubated with DCCD, then a decrease in the fluorescence intensity of photosystem II (PSII) was observed, while no change in the intensity of photosystem I (PSI) fluorescence occurred according to the measured fluorescence emission spectra at 77 K. Since low pH induced distribution of energy from PSII to PSI was inhibited in the presence of DCCD, we concluded that pH/proton concentration of the thylakoid membranes plays an important role in regulating the distribution of the absorbed excitation energy between both photosystems., T. Tongra, S. Bharti, A. Jajoo., and Obsahuje bibliografii