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
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.
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
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.
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.
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®’'.
In the course of dehydration, the gas exchange and chlorophyll (Chl) fluorescence were measured under irradiance of 800 μmol m-2 s-1 in detached apple leaves, and the production of active oxygen species (AOS), hydrogen peroxide (H2O2), superoxide (O2-), hydroxyl radical (-OH), and singlet oxygen (1O2), were determined. Leaf net photosynthetic rate (PN) was limited by stomatal and non-stomatal factors at slight (2-3 h dehydration) and moderate (4-5 h dehydration) water deficiency, respectively. Photoinhibition occurred after 3-h dehydration, which was defined by the decrease of photosystem 2 (PS2) non-cyclic electron transport (P-rate). After 2-h dehydration, an obvious rise in H2O2 production was found as a result of photorespiration rise. If photorespiration was inhibited by sodium bisulfite (NaHSO3), the rate of post-irradiation transient increase in Chl fluorescence (Rfp) was enhanced in parallel with a slight decline in P-rate and with an increase in Mehler reaction. At 3-h dehydration, leaf P-rate decrease could be blocked by glycine (Gly) or methyl viologen (MV) pre-treatment, and MV was more effective than Gly at moderate drought time. AOS (H2O2 and O2-), prior to photoinhibition produced from photorespiration and Mehler reaction in detached apple leaves at slight water deficiency, were important in dissipating photon energy which was excess to the demand of CO2 assimilation. So photoinhibition could be effectively prevented by the way of AOS production. and H. S. Jia, Y. Q. Han, D. Q. Li.
Photoinhibition of photosynthesis was investigated in grapevine (Vitis vinifera L.) exposed to 2 or 4h of high irradiance (HI) (1 700-1 800 μmol m-2 s-1) leaves under field conditions at different sampling time in a day. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll fluorescence (Fv/Fm) and photosynthetic electron transport measurements. When the photochemical efficiency of photosystem 2 (PS2), Fv/Fm, markedly declined, F0 increased in both 2 (HI2) and 4 h (HI4) HI leaves sampled at midday. When various photosynthetic activities were followed on isolated thylakoids, HI4 leaves showed significantly higher inhibition of whole chain and PS2 activity than the HI2 leaves sampled at midday. Later, the leaves reached maximum PS2 efficiencies similar to those observed early in the morning during sampling at evening. The artificial exogenous electron donor Mn2+ failed to restore PS2 activity in both variants of leaves, while DPC and NH2OH significantly restored PS2 activity in HI4 midday leaf samples. Quantification of the PS2 reaction centre protein D1 and 33 kDa protein of water splitting complex following midday exposure of leaves showed pronounced differences between HI2 and HI4 leaves. The marked loss of PS2 activity noticed in midday samples was mainly due to the marked loss of D1 protein in HI2, while in HI4 it was mainly 33-kDa protein. and M. Bertamini, N. Nedunchezhian.
The effect of high irradiance (HI, photosynthetically active photon flux density of 1 300 µmol m-2 s-1) on net photosynthetic rate (PN), chlorophyll fluorescence parameters, and xanthophyll cycle components were studied in fruit tree bayberry leaves. HI induced the photoinhibition and inactivation of photosystem 2 (PS2) reaction centres (RCs), which was characterized by decreased PN, maximum yield of fluorescence after dark adaptation (Fm), photochemical efficiency of PS2 (Fv/Fm) and quantum yield of PS2 (ΦPS2), and increased reduction state of QA (1-qP) and non-photochemical quenching (NPQ). Initial fluorescence (F0) showed a decrease after the first 2 h, and subsequently increased from the third hour exposure to HI. Furthermore, a greater increase in the ratio (Fi-F0)/(Fp-F0) which is an expression of the proportion of the QB non-reducing PS2 centres, whereas a remarked decrease in the slope of Fi to Fp which represents the rate of QA reduction was observed in leaves after HI exposure. Additionally, HI caused an increase in the pool size of the xanthophyll cycle pigments and sustained elevated contents of zeaxanthin (Z), antheraxanthin (A), and de-epoxidation state (DES) at the end of the irradiation period. During HI, decreased Fm, Fv/Fm, ΦPS2, NPQ, slope of Fi to Fp, V+A+Z, and DES, and increased F0, 1-qP, ratio (Fi-F0)/(Fp-F0), and V were observed in dithiothreitol (DTT)-fed leaves compared to control ones under the same conditions. Hence photoinhibition caused by HI in bayberry was probably attributed to inactivation of PS2 RCs, and photoprotection from photodamage were mainly related to the xanthophyll cycle-dependent heat dissipation in excess photons. and Y.-P. Guo ... [et al.].
The low chlorophyll b mutant of high yield rice had a lower light-harvesting complex 2 content than the wild type. The stability of oxygen evolution side of photosystem 2 was only slightly lower. A lower photon absorption rate and a stronger xanthophyll cycle capacity of this mutant led to a higher endurance to strong irradiance and a lower photoinhibition as compared with the wild type rice. and Xinbin Dai ... [et al.].