We assessed the effect of the exposure to full sunlight (5, 35, and 120 min, i.e. T5, T35, and T120) on fluorescence parameters of two young tropical trees, Swietenia macrophylla, a gap-demanding species, and Minquartia guianensis, a shade tolerant species. Fluorescence parameters (F0, Fm, Fv/Fm) were recorded before treatments and after the transition to low irradiance (LI). Recovery from photoinhibition (measured as Fv/Fm) was monitored for 24 h at LI. In Swietenia, an almost complete restoration of the Fv/Fm values occurred in T5 and T35 plants, when a rise in F0 was observed after the transition to LI. This was inferred as indicative of dynamic photoinhibition. T120 led to a decline in F0 in Minquartia, but not in Swietenia. The plants of both species were unable to recovery from photoinhibition after 24 h at LI, when F0 declined or remained unchanged. This was interpreted as indicative of chronic photoinhibition. Compared with Swietenia, Minquartia was more susceptible to photoinhibition, as indicated by lower Fv/Fm values. and D. P. Dias, R. A. Marenco.
The degree of photoinhibition of sun and shade grown leaves of grapevine was determined by means of the ratio of variable to maximum chlorophyll (Chl) fluorescence (Fv/Fm) and electron transport measurements. The potential efficiency of photosystem 2 (PS2), Fv/Fm, markedly declined under high irradiance (HI) in shade leaves with less than 10 % of F0 level. In contrast, Fv/Fm ratio declined with about 20 % increase of F0 level in sun leaves. In isolated thylakoids, the rate of whole chain and PS2 activity in HI shade and sun leaves was decreased by about 60 and 40 %, respectively. A smaller inhibition of photosystem 1 (PS1) activity was also observed in both leaf types. In the subsequent dark incubation, fast recovery was observed in both leaf types that reached maximum PS2 efficiencies similar to non-photoinhibited control leaves. The artificial exogenous electron donors DPC, NH2OH, and Mn2+ failed to restore the HI-induced loss of PS2 activity in sun leaves, while DPC and NH2OH were significantly restored in shade leaves. Hence HI in shade leaves inactivates on the donor side of PS2 whereas it does at the acceptor side in sun leaves, respectively. Quantification of the PS2 reaction centre protein D1 and the 33 kDa protein of water splitting complex following HI-treatment of leaves showed pronounced differences between shade and sun leaves. The marked loss of PS2 activity in HI leaves was due to the marked loss of D1 protein of the PS2 reaction centre protein and the 33 kDa protein of the water splitting complex in sun and shade leaves, respectively. and M. Bertamini, K. Muthuchelian, N. Nedunchezhian.
Photoinhibition of photosynthesis was investigated in Vitis berlandieri and Vitis rupestris 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 PS2, Fv/Fm, markedly declined, F0 increased significantly in leaves of V. berlandieri, while F0 did not increase in V. rupestris leaves. Isolated thylakoids of leaves of V. berlandieri showed significant inhibition of whole chain and PS2 activities at midday. A smaller inhibition was observed for V. rupestris. 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 species, while DPC and NH2OH significantly restored PS2 activity in V. rupestris 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 V. berlandieri and V. rupestris leaves. The marked loss of PS2 activity noticed in midday samples was mainly due to the marked loss of D1 protein in V. berlandieri while in V. rupestris it was the 33 kDa protein. and M. Bertamini, N. Nedunchezhian.
Photoinhibition under irradiance of 2 000 µmol m-2 s-1 (HI) was studied in detached control (C) and water deficit (WD) leaves of grapevine (Vitis vinifera L.) plants. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll (Chl) fluorescence (Fv/Fm) and electron transport measurements. The potential efficiency of photosystem (PS) 2, Fv/Fm, marginally declined under HI in WD-leaves without significant increase of F0. In contrast, Fv/Fm ratio declined markedly with significant increase of F0 in C-leaves. In isolated thylakoids, the rate of whole chain and PS2 activity under HI were more decreased in C-than WD-leaves. The artificial exogenous electron donors diphenyl carbazide, NH2OH, and Mn2+ failed to restore the HI-induced loss of PS2 activity in both C-and WD-leaves. Thus HI operates at the acceptor side of PS2 in both leaf types. Quantification of the PS2 reaction centre protein D1 following HI exposure of leaves showed pronounced differences between C-and WD-leaves. The marked loss of PS2 activity under HI of C-leaves was due to the marked loss of D1 protein of the PS2 reaction centre. and M. Bertamini ... [et al.].
Exposure of plants to irradiation, in excess to saturate photosynthesis, leads to reduction in photosynthetic capacity without any change in bulk pigment content. This effect is known as photoinhibition. Photoinhibition is followed by destruction of carotenoids (Cars), bleaching of chlorophylls (Chls), and increased lipid peroxidation due to formation of reactive oxygen species if the excess irradiance exposure continues. Photoinhibition of photosystem 2 (PS2) in vivo is often a photoprotective strategy rather than a damaging process. For sustainable maintenance of chloroplast function under high irradiance, the plants develop various photoprotective strategies. Cars perform essential photoprotective roles in chloroplasts by quenching the triplet Chl and scavenging singlet oxygen and other reactive oxygen species. Recently photoprotective role of xanthophylls (zeaxanthin) for dissipation of excess excitation energy under irradiance stress has been emphasised. The inter-conversion of violaxanthin (Vx) into zeaxanthin (Zx) in the light-harvesting complexes (LHC) serves to regulate photon harvesting and subsequent energy dissipation. De-epoxidation of Vx to Zx leads to changes in structure and properties of these xanthophylls which brings about significant structural changes in the LHC complex. This ultimately results in (1) direct quenching of Chl fluorescence by singlet-singlet energy transfer from Chl to Zx, (2) trans-thylakoid membrane mediated, ΔpH-dependent indirect quenching of Chl fluorescence. Apart from these, other processes such as early light-inducible proteins, D1 turnover, and several enzymatic defence mechanisms, operate in the chloroplasts, either for tolerance or to neutralise the harmful effect of high irradiance. and N. K. Choudhury, R. K. Behera.
To investigate the photoprotection of energy dissipation and water-water cycle, a C3 euhalophytic herb, Suaeda salsa L., was exposed either to chilling temperature (4°C) accompanied by moderate irradiance (600 μmol m-2 s-1) (CM) and/or to chilling temperature (4°C) accompanied by low irradiance (100 μmol m-2 s-1) (CL). During chilling stress, both the maximal photochemical efficiency of PSII (Fv/Fm) and the oxidizable P700 decreased in S. salsa leaves either under CM or CL, which indicated the severe photoinhibition. Relative to Fv/Fm, the oxidizable P700 decreased markedly under CL, which indicated that PSI was more sensitive to CL treatment than PSII. Initial fluorescence, number of closed PSII centers, and nonphotochemical quenching increased under CM, but more markedly under CL in S. salsa leaves. Activity of superoxide dismutase and ascorbate peroxidase was higher under CM than that under CL. The production of reactive oxygen species (ROS) decreased first and then increased under both treatments, but the content of O2.- and H2O2 was higher under CL than that under CM after 12 h of chilling stress. These results suggested that photoinhibition in S. salsa might be related to the accumulation of reactive oxygen species (ROS) induced by excess energy. The water-water cycle could not dissipate energy efficiently under CL, which caused the great accumulation of ROS., N. Sui., and Obsahuje bibliografii
The amphibious plant species of intermittent aquatic habitats thrive both submerged and emerged. In order to outline the adaptive characters of these two life forms photochemical efficiency of photosystem 2, leaf contents of chlorophyll (Chl) a and b, carotenoids (Car), anthocyanins (Ant), and UV-B absorbing compounds (UV-B abs), and root aerenchyma and arbuscular mycorrhizal (AM) colonisation were studied in Glyceria fluitans, Gratiola officinalis, Ranunculus lingua, Teucrium scordium, Sium latifolium, Sparganium emersum, and Veronica anagallis-aquatica. Water level fluctuations did not exert a severe effect on photon harvesting efficiency. Submerged specimens had higher contents of Car and Ant whereas higher contents of UV-B abs were found in emerged specimens indicating efficient protection against the harmful effects of solar radiation. Roots of all species studied had extensive aerenchyma and were colonised by AM fungi, which were significantly more abundant in emerged specimens. This is the first report on AM symbiosis in S. latifolium and S. emersum. and N. Šraj-Kržič ... [et al.].
The redox interaction of exogenous cytochrome c550 (Cyt) with PSII isolated from spinach was studied. Illumination of PSII particles in the presence of Cyt led to: (1) Cyt photooxidation by PSII reaction center (demonstrated at the first time), (2) Cyt photoreduction via O2- photoproduced on the acceptor side of PSII, and (3) Cyt photoreduction by reduced electron carriers of PSII. A step-by-step removal of components of water-oxidizing complex was accompanied by the appearance of Cyt photooxidation, an increase in the superoxide dismutase (SOD)-dependent Cyt photoreduction (related to O2- formation), and a decrease in the SOD-independent Cyt photoreduction. Re-addition of PsbO protein diminished the
Cyt-induced restoration of electron transfer in PSII. Addition of diuron led to inhibition of these photoprocesses, while exogenous Mn2+ inhibited only the Cyt c photooxidation. The results can be important for correct measurements of O2- photoproduction in PSII and for elucidation of the role of cytochrome c550 in cyanobacterial PSII., A. A. Khorobrykh, D. V. Yanykin, V. V. Klimov., and Obsahuje bibliografické odkazy
With untransformed rice cv. Kitaake as control, the characteristics of carbon assimilation and photoprotection of a transgenic rice line over-expressing maize phosphoenolpyruvate carboxylase (PEPC) were investigated. The PEPC activity in untransformed rice was low, but the activity was stimulated under high irradiance or photoinhibitory condition. PEPC in untransformed rice contributed by about 5-10 % to photosynthesis, as shown by the application of the specific inhibitor 3,3-dichloro-2-(dihydroxyphosphinoylmethyl)propenoate (DCDP). When maize PEPC gene was introduced into rice, transgenic rice expressed high amount of maize PEPC protein and had high PEPC activity. Simultaneously, the activity of carbonic anhydrase (CA) transporting CO2 increased significantly. Thus the photosynthetic capacity increased greatly (50 %) under high CO2 supply. In CO2-free air, CO2 release in the leaf was less. In addition, PEPC transgenic rice was more tolerant to photoinhibition. Treating by NaF, an inhibitor of phosphatase, showed that in transgenic rice more phosphorylated light-harvesting chlorophyll a/b-binding complexes (LHC) moved to photosystem 1 (PS1) protecting thus PS2 from photo-damage. Simultaneously, the introduction of maize PEPC gene could activate or induce activities of the key enzymes scavenging active oxygen, such as superoxide dismutase (SOD) and peroxidase (POD). Hence higher PS2 photochemical efficiency and lower superoxygen anion (O2.-) generation and malonyldiadehyde (MDA) content under photoinhibition could improve protection from photo-oxidation. and D. M. Jiao, X. Li, B. H. Ji.
Chlorophyll (Chl) fluorescence decay measurements were performed on higher plant leaves to investigate the photoprotective mechanisms under in vivo conditions. Measurements on leaves with different amounts of zeaxanthin pointed out that zeaxanthin is necessary for most of the observed nonphotochemical energy quenching, that has to be activated by a transthylakoid ΔpH. An additional sustained energy quenching component was clearly resolved in leaves with high amounts of zeaxanthin. The changes of the Chl fluorescence decay parameters did not correlate with a photoprotective energy dissipation in the reaction centre of photosystem 2 (P680), nor with a ΔpH-mediated, zeaxanthin-independent aggregation of the antenna complexes; no indications for a state 1/state 2 transition of the main light-harvesting complex LHC2 were found.