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3522. Photochemical activities in wheat chloroplasts incubated under irradiation and possible photoprotection by zeaxanthin
- Creator:
- Choudhury, N.K., Aslam, M., and Huffaker, R.C.
- Format:
- Type:
- model:internalpart and TEXT
- Language:
- Multiple languages
- Description:
- Chloroplasts isolated from the primary leaves of wheat seedlings lost 22 % of their chlorophyll and 35 % of the carotenoids after 4 h of incubation under a medium irradiance (MI) (400 pmol m'^ s'*, PAR). After a 3 h MI exposure, the photosystem (PS) 2 activity was completely lost while photosystem 1 (PSI) activity was reduced to 32 % of that, found initially. Chloroplasts isolated from the leaves of seedlings exposed to a high irradiance (1500 pmol m-^ s"') contained a higher concentiation of zeaxanthin (z) and lost pigments and photochemical activities at a relatively slower rate. When the z concentration in chloroplasts incubated under MI was enhanced several times by ascorbate (Asc), the losses of pigment contents and photosystem activities were significantly reduced. However, when the Asc-induced synthesis of z was inhibited by dithiothreitol, protection of the pigment contents and photochemical activities disappeared. Thus, z can photoprotect the chloroplasts during incubation under irradiation.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
3523. Photochemical and non-photochemical quenching coefficients of the chlorophyll fluorescence: comparison of variation and limits
- Creator:
- Buschmann, C.
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- pulse-amplitude-modulation
- Language:
- Multiple languages
- Description:
- There are several types of quenching coefficients currently in use which describe the decrease of the chlorophyll fluorescence: the photochemical quenching coefficients qP and q(P)rel and the non-photochemical quenching coefficients qN, q(N)rel, and NPQ. These five coefficients were calculated for a broad variety of cases of the fluorescence signals in a normal, realistic range and for determining the limits in a range with extremely low and high fluorescence values. The calculations showed that the quenching coefficients currently in use are not only numbers between 0 and 1 as one would expect when taking them as a relative measure of the quenching process. Most quenching coefficients must be regarded and interpreted carefully separated from each other. Each photochemical quenching coefficient and each non-photochemical quenching coefficient describe the same fluorescence signal in a different way. Only the relative quenching coefficients q(P)rel and q(N)rel match together and can be used to demonstrate a shift of the energy de-excitation from the photochemical to the non-photochemical route.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
3524. Photochemical and thermal phases of chlorophyll a fluorescence
- Creator:
- Samson, G., Prášil, O., and Yaakoubd, B.
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- photochemical and nonphotochemical quenching, photosystem 2, QA, and reaction center
- Language:
- Multiple languages
- Description:
- The measurement of variable chlorophyll (Chl) a fluorescence is widely used as a convenient and versatile tool in photosynthesis research. In many applications empirical correlations and simplified models of Chl a fluorescence are used with success. Nevertheless, variable Chl a fluorescence provides only indirect and complex image of processes occurring within photosynthetic membranes and such simplifications have only limited validity. In this review we elucidate some controversial and still unresolved questions about the origin and interpretation of the variable Chl a fluorescence induction and the proper use of variable Chl a fluorescence for studies of photochemical events in photosystem 2 (PS2). Although the major part of variable Chl a fluorescence reflects the photochemical closure of the PS2 reaction centers (RCs) and can be considered as a function of the redox state of the primary acceptor QA, up to 50 % of the change in the Chl a fluorescence yield can be of secondary, nonphotochemical origin. We review the possible sources of the inherent heterogeneity in the origin of variable Chl a fluorescence. We also comment on the practical implications this bears for the use of variable Chl a fluorescence. and G. Samson, O. Prášil, B. Yaakoubd.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
3525. Photochemical changes and oxidative damage in four foxtail millet varieties following exposure to sethoxydim
- Creator:
- Guo, M. J., Wang, Y. G., Dong, S. Q., Wen, Y. Y., Song, X. E., and Guo, P. Y.
- Format:
- print, bez média, and svazek
- Type:
- model:article and TEXT
- Subject:
- chlorofylová fluorescence, parametry P700, reaktivní formy kyslíku, proso, chlorophyll fluorescence, P700 parameters, reactive oxygen species, spring hybrid millet, 2, and 581
- Language:
- Multiple languages
- Description:
- In order to assess its response to the herbicide, sethoxydim (SEY), seedlings of two foxtail millet (Setaria italica) hybrids were exposed to 0.75, 1.5, 3, and 6 L(SEY active ingredient, ai) ha-1 for 7 and 15 d. Our results showed that SEY reduced photosynthesis and oxidative stress in the hybrid millet (Zhangza) at the dosage below 1.5 L(ai) ha-1 (i.e., recommended dosage), whereas it caused death of Jingu 21 at all treatment dosages. In addition, we further explored the effect of SEY on PSI and PSII; the hybrid millet showed a greater tolerance to SEY and also the ability to recover. In conclusion, the hybrid millet seems to possess certain photosynthetic protection mechanisms which could reduce or eliminate the herbicide stress by increasing nonphotochemical quenching for dissipating excessive light energy under SEY-induced oxidative stress., M. J. Guo, Y. G. Wang, S. Q. Dong, Y. Y. Wen, X. E. Song, P. Y. Guo., and Obsahuje bibliografii
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
3526. Photochemical properties of photosystem 2 in primary leaves of barley seedlings grown under various blue or red irradiances
- Creator:
- Egorova, E. A. and Bukhov, N. G.
- Format:
- bez média and svazek
- Type:
- model:article and TEXT
- Subject:
- blue radiation, chlorophyll fluorescence, photosystem 2, and red radiation
- Language:
- Multiple languages
- Description:
- Photosystem 2 (PS2)-driven electron transfer was studied in primary leaves of barley (Hordeum vulgare L.) seedlings grown under various photon fluxes (0.3-170.0 μmol m-2 s-1) of blue (BR) or red (RR) radiation using modulated chlorophyll fluorescence. The Fv/Fm ratio was 0.78-0.79 in leaves of all radiation variants, except in seedlings grown under BR or RR of 0.3 μmol m-2 s-1. The extent of the photochemical phase of the polyphasic Fv rise induced by very strong "white light" was similar in leaves of all radiation treatments. Neither radiation quality nor photon flux under plant cultivation influenced the amount of non QB-transferring centres of PS2 except in leaves of seedlings grown under BR of 0.3 μmol m-2 s-1, in which the amount of such centres increased threefold. Both BR and RR stimulated the development of photochemically competent PS2 at photon fluxes as low as 3 μmol m-2 s-1. Three exponential components with highly different half times were distinguished in the kinetics of Fv dark decay. This indicates different pathways of electron transfer from QA-, the reduced primary acceptor of PS2, to other acceptors. Relative magnitudes of the individual decay components did not depend on the radiation quality or the photon flux during plant cultivation. Significant differences were found, however, between plants grown under BR or RR in the rate of the middle and fast components of Fv dark decay, which showed 1.5-times faster intersystem linear electron transport in BR-grown leaves. and E. A. Egorova, N. G. Bukhov.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
3527. Photochemistry of Luffa cylindrica (L.) Roem under fungal biocontrol interaction
- Creator:
- Amrina, H., Shahzad, S., and Siddiqui, Z. S.
- Format:
- print, bez média, and svazek
- Type:
- model:article and TEXT
- Subject:
- fotochemie, photochemistry, fotoinhibice, lufa válcovitá, chlorophyll fluorescence transients, photoinhibition, Luffa cylindrica (L.), 2, and 581
- Language:
- Multiple languages
- Description:
- The aim of this study was to evaluate the photochemistry of Luffa cylindrica (L.) Roem in fungal biocontrol interacting treatments. Healthy plants were infected with Pythium aphanidermatum before the biocontrol application. Biocontrol agents were selected in preliminary Petri-plate experiment evaluation against causative agent P. aphanidermatum. Photosynthetic performance traits were studied. We found that P. aphanidermatum infection caused significant reduction in photosynthetic performance, pigments, and in maximum quantum yield of primary photochemistry, photochemical quenching, and electron transport rate with increase in nonphotochemical quenching as compared with non-infected control. However, application of biocontrol agents substantially improved maximum quantum yield of PSII, performance index, and total content of photosynthetic pigments in infected plants. The fluorescence intensity was used for quantifying the antagonist effect of biocontrol agents on infected plant leaves., H. Amrina, S. Shahzad, Z. S. Siddiqui., and Obsahuje bibliografii
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
3528. Photodynamic effect of 2,2'-dipyridyl and glutamic acid on wheat and vegetable marrow plants
- Creator:
- Koleva, A., Toneva, V., and Minkov, I.
- Format:
- Type:
- model:internalpart and TEXT
- Subject:
- chlorophyll synthesis, Cucurbita moschata Duch., epicotyl, hypocotyl, photodynamic herbicides, protochlorophyllide, root, shoot, and Triticum aestivum L.
- Language:
- Multiple languages
- Description:
- The possibility of simultaneously ušed chlorophyll (Chl) synthesis precursor (glutamic acid) and metal chelator (2,2'-dipyridyl) as a photodynamic inhibitor of the chlorophyll synthesis was studied. Wheat {Triticum aestivum L.) and vegetable marrow {Cucurbita moschata Duch.) leaves were treated with 2,2'-dipyridyl (2,2'- DP), and 2,2'-DP along with glutamic acid which increased the protochlorophyllide (Pchlide) content in the vegetable marrow plants to a higher extent. An irradiation of the treated leaves caused an inhibition of Pchlide reduction which was more notable in those of the dicotyledonous vegetable marrow plant.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
3529. Photoinactivation of isolated D1/D2/cytochrome b559 complex under aerobic and anaerobic conditions
- Creator:
- Allakhverdiev, S. I., Komenda, J., Feiziev, Y. M., Nedbal, L., and Klimov, V. V.
- Format:
- Type:
- model:internalpart and TEXT
- Language:
- Multiple languages
- Description:
- The preparation of Dl/D2/cytochrome 6559 complex isolated from pea (Pisum sativum h.) was photoinactivated by "white light" (140 W m‘2) at 20 and 4 "C in both the presence and absence of oxygen. The inactivation was followed by measuring the decline of the photoinduced absorbance change A/4683 (the photoaccumulation of reduced pheophytin), by measuring absorption spectra and fluorescence emission, and by polypeptide analysis. In the presence of oxygen, the ability of the DUDUcyi 6559 complex to acciunulate reduced pheophytin was lost with the halftime im of about 3 min and fluorescence quantum yield declined with ti/2 of about 30 min at both 20 and 4 ^C. The D\ and Dl polypeptides were rapidly modified at 20 °C as reflected by the presence of their large aggregates at the start of the electrophoretic gel and by a decrease of the mobility of remaining Dl and Dl monomers. This modification was substantially limited at 4 “C. Subímits of cytochrome 6559 were not modified at any temperature. When oxygen was removed, the halftime of the A/1683 decline increased by about one order of magnitude, fluorescence emission did not decline, but slightly increased, and the polypeptide pattem was only slightly affected during irradiation.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public
3530. Photoinactivation of the electron transfer through photosystem 2 as studied by time resolved flash absorption spectroscopy
- Creator:
- Eckert, H.-J., Liu, B., Eichler, H. J., and Renger, G.
- Format:
- Type:
- model:internalpart and TEXT
- Language:
- Multiple languages
- Description:
- Primary events in the photoinactivation of photosystem (PS) 2 membrane fragments by low and high "visible light" irradiance (17 to 1 700 W m'2) and UV-B irradiation (90 W m'2) were analyzed by measuiing flash-induced absorption changes at 830 nm that reflect transient formation of P680+ and Pheo*. Following results were obtained: (7) Irradiation with "visible light" under aerobic conditions affects the PS 2 electron transfer at two different sites: {a) within the PS 2 reaction centre by impairment of primary charge separation (P680 Pheo Qa P680+Pheo'QA), and (7>) on tiie PS 2 donor side by inhibition of the electron transfer from to P680+. (2) In PS 2 membrane fragments with intact 02-evolution the primary charge separation is the most sensitive target of the photoinhibition by "visible light". The UV-B irradiation, however, affects predominantly the oxygen-evolving complex or the electron transfer from the oxygen-evolving complex to Yz®’'. (5) Susceptibility of the P680 Yz segment to photoinhibition by "visible light" is drastically increased in the samples with lifetimes of Yz°* and P680+ having been signifícantly prolonged by Tris- treatment. Susceptibility of the primaiy charge separation to photoinhibition, however, is not dependent on the lifetimes of P680+ and Yz®’'.
- Rights:
- http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public