High photosynthetic efficiency of a rice (Oryza sativa L.) xantha mutant

Comparative analysis revealed that a xantha rice mutant (cv. Huangyu B) had higher ratios of chlorophyll (Chl) a/b and carotenoids/Chl, and higher photosynthetic efficiency than its wild type parent (cv. II32 B). Unexpectedly, the mutant had higher net photosynthetic rate (P _N) than II32 B. This might have resulted from its lower non-photochemical quenching (q_N) but higher maximal photochemical efficiency (F_V/F_M), higher excitation energy capture efficiency of photosystem 2 (PS2) reaction centres (F_V′/F_M′), higher photochemical quenching (q_P), higher effective PS2 quantum yield (Φ_PS2), and higher non-cyclic electron transport rate (ETR). This is the first report of a chlorophyll mutant that has higher photosynthetic efficiency and main Chl fluorescence parameters than its wild type. This mutant could become a unique material both for the basic research on photosynthesis and for the development of high yielding rice cultivars.     

Effects of nitrogen supply restriction on gas exchange and photosystem 2 function in flag leaves of a traditional low-yield cultivar and a recently improved high-yield cultivar of rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

The effects of nitrogen (N) supply restriction on the CO₂ assimilation and photosystem 2 (PS2) function of flag leaves were compared between two contrastive Japanese rice cultivars, a low-yield cultivar released one century ago, cv. Shirobeniya (SRB), and a recently improved high-yield cultivar, cv. Akenohoshi (AKN). Both cultivars were solution-cultured at four N supply levels from N4 (control) to N1 (the lowest). With a reduction in N-supply, contents of N (LNC), ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO), and chlorophyll (Chl) in flag leaves decreased in both cultivars. In parallel with this, the net photosynthetic rate (P _N), mesophyll conductance (g _m), and stomatal conductance (g _s) decreased. P _N was more dominantly restricted by g _m than g _s. The values of P _N, g _m, and RuBPCO content were larger in AKN than SRB at the four N supply levels. The content of Chl greatly decreased with N deficiency, but the reduction in the maximum quantum yield of PS2 was relatively small. Quantum yield of PS2 (Φ_PS2) decreased with N deficiency, and its significant cultivar difference was observed between the two cultivars at N1: a high value was found in AKN. The content ratio of Chl/RuBPCO was also significantly low in AKN. The low Chl/RuBPCO is one of the reasons why AKN maintained a comparatively high P _N and Φ_PS2 at N deficiency. The adequate ratio of N distribution between Chl and RuBPCO is the important prerequisite for the efficient and sustainable photosynthesis in a flag leaf of rice plant under low N-input.     

Enhanced antioxidant protection at the early stages of leaf expansion in ginkgo under natural environmental conditions

Photosynthetic pigments, gas exchange, chlorophyll (Chl) a fluorescence kinetics, antioxidant enzymes and chloroplast ultrastructure were investigated in ginkgo (Ginkgo biloba L.) leaves from emergence to full size. Under natural conditions, the net photosynthetic rate (P_N), contents of Chl a, Chl b and total soluble proteins and fresh and dry leaf mass gradually increased during leaf expansion. The maximum photochemical efficiency of photosystem (PS) 2 (variable to maximum fluorescence ratio, F_v/F_m) was considerably higher at the early stages of leaf development than in fully expanded leaves. During daily course, only reversible decrease in F_v/F_m was distinguished at various stages, implying that no photo-damage occurred. Absorption flux per cross section (CS) and trapped energy flux per CS were significantly lower in newly expanding leaves compared with fully expanded ones, however, dissipated energy flux per CS was only slightly lower in expanding leaves. The ratio of carotenoids (Car)/Chl decreased gradually during leaf expansion due to increasing Chl content. Moreover, activities of the antioxidant enzymes, such as superoxide dismutase, ascorbate peroxidase, catalase and peroxidase, increased at the early stages of leaf expansion. The appearance of osmiophilic granules in fully expanded leaves further proves that photo-protection is significantly strengthened at the early stages of leaf expansion.     

Fate of the porphyrin cofactors during the light-dependent turnover of catalase and of the photosystem II reaction-center protein D1 in mature rye leaves

The apoprotein of the enzyme catalase (EC 1.11.1.6) was shown to exhibit a light-dependent turnover in leaves. Present results indicate that photoinactivation of the enzyme was not accompanied by a synchronous destruction and new synthesis of its heme moiety. In rye (Secale cereale L.) leaves the catalase content was not depleted in light when porphyrin synthesis was inhibited by gabaculine. Photoinactivation of purified bovine liver or rye leaf catalase in vitro was not accompanied by concomitant damage to the heme groups. Both the incorporation of -[³H]aminolevulinic acid ([³H]ALA) into catalase-heme and its apparent turnover increased with irradiance. However, the apparent half-life of the catalase-heme was much longer than that of its apoprotein. It is probable that not only degradation but also an exchange with the free heme pool contributed to the apparent turnover of radioactivity of the catalase-heme. Part of the chlorophyll (Chl) associated with photosystem II (PS II) had a preferential light-induced turnover, and repair of PS II appeared to require new Chl synthesis also in mature green rye leaves. The activity of PS II, indicated by the ratio of variable to maximal fluorescence (F_v/F_m), rapidly declined in the presence of gabaculine in light and the reaction-center proteins D1 and D2 were depleted. When segments of mature green rye leaves were labeled with [³H]ALA and incorporation into Chl-protein complexes analysed after electrophoretic separation in the presence of Deriphat, the highest radioactivity was observed in the core complex of PS II, while PS I and the light-harvesting complex of PS II (LHC II) were unlabeled. In greening etiolated leaves highest incorporation was observed in LHC II. Both the incorporation of [³H]ALA into the PS II core complex of green rye leaves and its turnover increased with irradiance. However, the apparent half-life of the PS II-bound labeled porphyrin compounds (mainly Chl) was considerably longer than that of the reaction-center protein D1 under identical conditions.Abbreviations ALA -aminolevulinic acid - CII Core complex of PS II - Chl chlorophyll - DMSO dimethyl sulfoxide - F_v/F_m ratio of variable to maximal chlorophyll fluorescence - LHC light-harvesting complex - PAR photosynthetically active radiation We thank the Deutsche Forschungsgemeinschaft for financial support. Technical assistence by B. Kramer and Ch. van Oijen is greatly appreciated. We are grateful to Dr. Johanningmeier and Dr. Godde (Lehrstuhl für Biochemie der Pflanzen, Universität Bochum, Germany) for providing antisera against the D1 and D2 proteins and Dr. M. Schmidt (Botanisches Institut, Universität Frankfurt am Main, Germany) for valuable advice. Deriphat 160 was kindly supplied by Henkel Corp., Hoboken, N.J., USA.     

Photosynthesis and photoprotection in Nicotiana tabacum L. in vitro-grown plantlets

Nicotiana tabacum L. plantlets were cultured in vitro photoautotrophically (0% sucrose) and photomixotrophically (3% or 5% sucrose) at two irradiances (80 or 380 mumol m-2 s-1) with the aim of investigating the effect of these culture conditions on photosynthetic parameters and on protective systems against excess excitation energy. In plantlets grown photoautotrophically under higher irradiance photoinhibition was demonstrated. These plantlets had a decreased chlorophyll (Chl) a + b content and Chl a/b ratio, an increased content of xanthrophyll cycle pigments and a higher deepoxidation state, a decreased maximum photochemical efficiency of photosystem II (PS II) and actual photochemical efficiency of PS II, and an increased non-photochemical quenching. In the photoautotrophically grown plantlets and those photomixotrophically grown with 3% sucrose, the increase of growth irradiance from 80 to 380 mumol m-2 s-1 stimulated the activities of ascorbate-glutathione cycle enzymes with the exception of ascorbate peroxidase. Ascorbate peroxidase activity was not affected by the increase in growth irradiance but a significant decrease with increasing sucrose concentration was evident. The higher concentration of sucrose in the medium (5%) in combination with the higher irradiance inhibited photosynthesis (decrease in Chl a + b content and net photosynthetic rate) but no significant changes in activities of ascorbate-glutathione cycle enzymes were found. These results suggest that exogenous sucrose added to the medium improved high irradiance and oxidative stress resistance of the plantlets but the effect of sucrose is concentration dependent.     

Enhanced photosystem 2 thermostability during leaf growth of Elm (Ulmus pumila) seedlings

We examined photosynthetic activities and thermostability of photosystem 2 (PS2) in leaves of elm (Ulmus pumila) seedlings from initiation to full expansion. During leaf development, net photosynthetic rate (P _N) increased gradually and reached the maximum when leaves were fully developed. In parallel with the increase of P _N, chlorophyll (Chl) content was significantly elevated. Chl a fluorescence measurements showed that the maximum quantum yield of PS2 (ϕ_PS2), the efficiency a trapped exciton, moved an electron into the electron transport chain further than Q_A ⁻ (Ψ_o), and the quantum yield of electron transport beyond Q_A (ϕ_Eo) increased gradually. These results were independently confirmed by our low irradiance experiments. When subjected to progressive heat stress, the young leaves exhibited considerably lower ϕ_PS2 and higher minimal fluorescence (F₀) than the mature leaves, revealing the highly sensitive nature of PS2 under heat in the newly initiating leaves. Further analysis showed that PS2 structure in the newly initiating leaves was strongly altered under heat, as evidenced by the increased fluorescence signals at the position of the K step. We therefore demonstrated an inhibition in the oxygen-evolving complex (OEC) in the young leaves. This resulted in decrease in amount of the functional PS2 reaction centres and relative increase in the PS2 reaction centres with inhibited electron transport at the acceptor side under heat. We suggest that the enhanced thermostability of PS2 during leaf development is associated with improved OEC stability.     

Effects of Phytoplasma Infection on Pigments, Chlorophyll-Protein Complex and Photosynthetic Activities in Field Grown Apple Leaves

Changes in contents of pigments, chlorophyll-protein complex, and photosynthetic activities were investigated in field grown apple (Malus pumila Mill.) leaves infected by Apple Proliferation phytoplasma. The contents of chlorophyll a+b (Chl) and carotenoids (Car) markedly decreased in infected leaves. Similar results were also observed for content of total soluble proteins and ribulose-1,5-bisphosphate carboxylase activity. When various photosynthetic activities were followed in isolated thylakoids, phytoplasma infection caused a marked inhibition of whole chain and photosystem 2 (PS2) activity. Smaller inhibition of photosystem 1 (PS1) activity was observed even in severely infected leaves. The artificial exogenous electron donors, MnCl₂ diphenyl carbazide, and NH₂OH, did not restore the loss of PS2 activity in both mildly and severely infected leaves. Similar results were obtained by Chl fluorescence measurements. The marked loss of PS2 activity in infected leaves was due to the reduction of contents of chlorophyll and light-harvesting chlorophyll-protein 2 complexes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characteristics of Chlorophyll Fluorescence and Membrane-Lipid Peroxidation During Senescence of Flag Leaf in Different Cultivars of Rice

With japonica rice 98-08, indica hybrids Shanyou 63, Gangyou 881, and X07S/Zihui 100, and sub-species hybrid Peiai 64S/9311 as materials, chlorophyll (Chl) content, Chl a fluorescence parameters, and membrane lipid peroxidation in flag leaf were measured at late developmental stages under natural conditions. F_v/F_m, q_P, _PS2, and electron transport rate gradually decreased while q_N increased conversely. Excessive photon energy led to the accumulation of active oxygen (O₂ ^–), H₂O, malonyldialdehyde, and products of membrane lipid peroxidation, and resulted in reduced Chl content and early ageing subsequent to the photooxidation during flag leaf senescence. There was obvious diversification of these parameters among rice cultivars. In comparison with japonica cv. 98-08 (tolerant to photooxidation), F_v/F_m decreased in indica cv. Shanyou 63 (susceptible to photooxidation) with greater accumulation of active oxygen and a sharp drop in Chl content, which resulted in yellowish early ageing, and affected the filling and setting of rice grains. The mechanism for premature ageing in indica rice was related to irradiance and temperature at filling stages. On a sunny day at above 25 °C, the reaction centre of photosystem 2 (PS2) exhibited a dynamic change on reversible inactivation. Under the intense irradiance at noon, PS2 function in indica rice exhibited obvious down-regulation and photoinhibition. Under intense irradiance with lowered temperatures, PS2 resulted in photo-damage and early ageing, related to the degradation of PS2-D1 protein and the inhibition of endogenous protection systems such as the xanthophyll cycle and enzymes scavenging active oxygen. Hence for high-yield breeding, based on a good plant-type and utilising heterosis and tolerance of photooxidation, the selection of japonica rice or a sterile line with the japonica genotype as female is a strategy worthy of consideration.     

Effects of calcium deficiency on Coffea arabica. Nutrient changes and correlation of calcium levels with some photosynthetic parameters

Calcium deficiency was induced in hydroponically grown 1.5-years-old coffee plants with 12–14 pairs of leaves. Calcium was given in the form of Ca(NO₃)₂: 5, 2.5, 0.1, 0.01 and 0 mM. After 71 days of Ca-treatment root and shoot as well as total biomass were decreased by severe Ca-deficiency. However, a stronger decrease was observed for shoot growth as revealed by the increase in the root/shoot ratio. New leaves were affected showing decreases in the total leaf area and in Leaf Area Duration (LAD). After 91 days of deficiency, leaf protein concentration decreased (by about 45%) in the top leaves while nitrate reductase activity (NRA) and NO₃ content showed no significant changes. Total nitrogen and mineral concentrations (P, K, Ca, Mg and Na) were also determined in leaves and roots. With the decrease in calcium concentration in Ca-deficiency conditions, we observed concomitant increases in the concentrations of K⁺, Mg²⁺ and Na⁺ in leaves (maximal changes of 32% for K⁺, 96% for Mg²⁺ and 438% for Na⁺) and in roots (108% for K⁺, 86% for Mg²⁺ and 38% for Na⁺). Accordingly, the ratio between elements changed, including the ratio N/P, showing a non-equilibrium in the balance of nutrients. Significant correlations were obtained between Ca²⁺ concentration and some photosynthetic parameters. Ca-deficiency conditions would increase the loss of energy as expressed by the rise in a_E and decrease the photochemical efficiency, which confirms the importance of this element in the stabilization of chlorophyll and in the maintenance of good photochemical efficiency at PS II level.Abbreviations Chl Chlorophyll - Fv/Fm ratio of variable to maximal fluorescence - LAD leaf area duration - LHC II light harvesting complex of PS II - NRA nitrate reductase activity - PC photosynthetic capacity - PS II photosystem II - P₆₈₀ reaction center of PS II - q_N non-photochemical quenching - q_E high-energy dependent quenching - q_p photochemical quenching - SLA specific leaf area     

Effects of Phytoplasma Infection on Growth and Photosynthesis in Leaves of Field Grown apple (Malus Pumila Mill. cv. Golden Delicious)

The contents of chlorophyll (Chl), leaf biomass, and soluble proteins were markedly decreased in phytoplasma infected apple leaves. Similar results were also observed for ribulose-1,5-bisphosphate carboxylase, ¹⁴CO₂ fixation, and nitrate reductase activity. In contrast, the contents of sugars, starch, amino acids, and total saccharides were significantly increased in phytoplasma infected leaves. In isolated chloroplasts, phytoplasma infection caused marked inhibition of whole photosynthetic electron chain and photosystem 2 (PS2) activity. The artificial exogenous electron donor, diphenyl carbazide, significantly restored the loss of PS2 activity in infected leaves. Similar results were obtained when F_v/F_m was evaluated by in vivo Chl a fluorescence kinetic measurements.     

Freezing damage and frost tolerance of the photosynthetic apparatus studied with isolated mesophyll protoplasts of Valerianella locusta L.

Mesophyll protoplasts were isolated from unhardened and cold-acclimated leaves of Valerianella locusta L. and subjected to freeze-thaw treatment. To evaluate the extent and course of freezing injury, photosynthetic reactions of whole protoplasts and of free thylakoid membranes, liberated from protoplasts by osmotic lysis, were measured. In addition, the integrity of the protoplasts was determined by microscopy. The results reveal an increased frost tolerance of protoplasts isolated from acclimated leaves with respect to all parameters measured. CO₂-dependent O₂ evolution (representing net photosynthetic CO₂ fixation of protoplasts) was the most freezing-sensitive reaction; its inhibition due to freeze-thaw treatment of protoplasts was neither correlated with disintegration of the plasma membrane, nor was it initiated by inactivation of the thylakoid membranes. The frost-induced decline of protoplast integrity was not closely correlated to thylakoid damage either. Freezing injury of the thylakoid membranes was manifested by inhibition of photosynthetic electron transport and photophosphorylation. Both photosystems were affected by freezing and thawing with strongest inhibition occurring in the water-oxidation system or at the oxidizing site of photosystem II. Photophosphorylation responded more sensitively to freezing stress than electron transport, although uncoupling (increased permeability of the thylakoid membranes to protons) was not a conspicuous effect. The data are discussed in relation to freezing injury in leaves and seem to indicate that frost damage in vivo is initiated at multiple sites.Abbreviations Chl chlorphyll - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DCIP 2,6-dichlorophenolindophenol - DPC 1,5-diphenylcarbazide - Hepes 2-[4-(2-hydroxyethyl)-1-piperazinyl]-ethanesulfonic acid - MES 2-(N-morpholino)-ethanesulfonic acid - PS I photosystem I - PS II photosystem II     

Changes in Chlorophyll a Fluorescence,Lipid Peroxidation,and Detoxificant System in Potato Plants Grown under Filtered and Non-Filtered Air in Open-Top Chambers

Its high oxidant capacity and ability to generate reactive oxygen species cause ozone toxicity. We studied the effect of ambient ozone on chlorophyll (Chl) a fluorescence, antioxidant enzymes, ascorbate contents, and lipid peroxidation in potatoes grown in open-top chambers in the field. In plants grown in non-filtered air (NFA), the development of non-photochemical quenching brought about a decrease in photosystem 2 (PS2) photochemical efficiency. Also the ability of PS2 to reduce the primary acceptor Q_A was lower than in charcoal-filtered, ozone-free air (CFA). Changes in Chl fluorescence yield were associated with changes in the thylakoid membrane. Ozone altered chloroplast membrane properties, as indicated by an increase in membrane lipid peroxidation in FNA-leaves compared to CFA plants. The ascorbate pool and activities of antioxidant enzymes were used for an indication of the detoxification system state in NFA and CFA leaves, whereby ozone affects the ascorbate concentration and decreases the antioxidant enzymes activities. The capacity of both detoxifying systems together was not high enough to protect potato plants against ambient ozone concentrations which reduced the photosynthetic yield in this potato cultivar.     

Photosynthetic activity of poikilochlorophyllous desiccation tolerant plant <Emphasis Type="Italic">Reaumuria soongorica</Emphasis> during dehydration and re-hydration

Diurnal patterns of gas exchange and chlorophyll (Chl) fluorescence parameters of photosystem 2 (PS2) as well as Chl content were analyzed in Reaumuria soongorica (Pall.) Maxim., a perennial semi-shrub during dehydration and rehydration. The net photosynthetic rate (P _N), maximum photochemical efficiency of PS2 (variable to maximum fluorescence ratio, F_v/F_m), quantum efficiency of non-cyclic electron transport of PS2, and Chl content decreased, but non-photochemical quenching of fluorescence and carotenoid content increased in stems with the increasing of drought stress. 6 d after re-hydration, new leaves budded from stems. In the re-watered plants, the chloroplast function was restored and Chl a fluorescence returned to a similar level as in the control plants. This improved hydraulic adjustment in plant triggered a positive effect on ion flow in the tissues and increased shoot electrical admittance. Thus R. soongorica plants are able to sustain drought stress through leaf abscission and keep part of Chl content in stems.     

The Distinctive Pattern of Photosystem 2 Activity,Photosynthetic Pigment Accumulation,and Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Content of Chloroplasts along the Axis of Primary Wheat Leaf Lamina

Wheat (Triticum aestivum L. cv. Sonalika) seedlings were grown in Hoagland solution. Primary leaves were harvested at 8, 12, and 15 d and cut into five equal segments. Contents of photosynthetic pigments and proteins, and photosystem 2 (PS2) activity increased from base to apex of these leaves. Chlorophyll (Chl) content was maximum at 12 d in all the leaf segments, but PS2 activity showed a gradual decline from 8 to 15 d in all leaf segments. In sharp contrast, the CO₂ fixation ability of chloroplasts increased from 8 to 15 d. CO₂ fixation ability of chloroplasts started to decline from base to apex of 15-d-old seedlings, where the content of ribulose-1,5-bisphosphate carboxylase/oxygenase large subunit (RuBPCO-LSU) increased acropetally. RuBPCO-LSU content was maximum in all the leaf segments in 12-d-old seedlings. This shows a distinctive pattern of PS2, Chl, CO₂ fixation ability of chloroplasts, and RuBPCO-LSU content along the axis of leaf lamina during development and senescence. RuBPCO-LSU (54 kDa) degraded to fragments of 45, 42, 37, 19, and 16 kDa products which accumulated along the leaf axis during ageing of chloroplasts. Thus the CO₂ fixation ability of chloroplasts declines earlier than PS2 activity and photosynthetic pigment contents along the leaf lamina.     

Novel effects of methyl viologen on photosystem II function in spinach leaves

Methyl viologen (MV) is a well-known electron mediator that works on the acceptor side of photosystem I. We investigated the little-known, MV-induced inhibition of linear electron flow through photosystem II (PS II) in spinach-leaf discs. Even a low [MV] decreased the (1) average, light-adapted photochemical efficiency of PS II traps, (2) oxidation state of the primary quinone acceptor Q_A in PS II during illumination, (3) photochemical efficiency of light-adapted open PS II traps, (4) fraction of absorbed light energy dissipated constitutively in a light-independent manner or as chlorophyll (Chl) a fluorescence emission, (5) Chl a fluorescence yield corresponding to dark-adapted open reaction-center traps (F _o) and closed reaction-center traps (F _m), and (6) half-time for re-oxidation of Q_A⁻ in PS II after a single-turnover flash. These effects suggest that the presence of MV accelerates various “downhill” electron-transfer steps in PS II. Therefore, when using the MV to quantify cyclic electron flow, the inhibitory effect of MV on PS II should be taken into account.     

Alteration of Components of Chlorophyll-Protein Complexes and Distribution of Excitation Energy Between the Two Photosystems in Two New Rice Chlorophyll b-less mutants

Two new yellow rice chlorophyll (Chl) b-less (lack) mutants VG28-1 and VG30-5 differ from the other known Chl b-less mutants with larger amounts of soluble protein and ribulose-1,5-bisphosphate carboxylase/oxygenase small sub-unit and smaller amounts of Chl a. We investigated the altered features of Chl-protein complexes and excitation energy distribution in these two mutants, as compared with wild type (WT) rice cv. Zhonghua 11 by using native mild green gel electrophoresis and SDS-PAGE, and 77 K Chl fluorescence in the presence of Mg²⁺. WT rice revealed five pigment-protein bands and fourteen polypeptides in thylakoid membranes. Two Chl b-less mutants showed only CPI and CPa pigment bands, and contained no 25 and 26 kDa polypeptides, reduced amounts of the 21 kDa polypeptide, but increased quantities of 32, 33, 56, 66, and 19 kDa polypeptides. The enhanced absorption of CPI and CPa and the higher Chl fluorescence emission ratio of F685/F720 were also observed in these mutants. This suggested that the reduction or loss of the antenna LHC1 and LHC2 was compensated by an increment in core component and the capacity to harvest photon energy of photosystem (PS) 1 and PS2, as well as in the fraction of excitation energy distributed to PS2 in the two mutants. 77 K Chl fluorescence spectra of thylakoid membranes showed that the PS1 fluorescence emission was shifted from 730 nm in WT rice to 720 nm in the mutants. The regulation of Mg²⁺ to excitation energy distribution between the two photosystems was complicated. 10 mM Mg²⁺ did not affect noticeably the F685/F730 emission ratio of WT thylakoid membranes, but increased the ratio of F685/F720 in the two mutants due to a reduced emission at 685 nm as compared to that at 720 nm.     

Photosynthesis in leaves of <Emphasis Type="Italic">Nicotiana tabacum</Emphasis> L. infected with tobacco mosaic virus

In tobacco leaves inoculated with tobacco mosaic virus (TMV), changes in chlorophyll (Chl) and carotenoid contents, parameters of slow Chl fluorescence kinetics, i.e. the maximum quantum yield of photosystem (PS2) photochemistry F_v/F_m, the effective quantum yield of photochemical energy conversion in PS2 Φ₂, ratio of quantum yields of photochemical and concurrent non-photochemical processes in PS2 F_v/F₀, non-photochemical quenching (NPQ), and photochemical activities of isolated chloroplasts from systemically infected tobacco leaves were investigated. We compared two successive stages of infection, the first in the stage of vein clearing at 9^th day post inoculation (dpi) and the second at 22^nd dpi when two different regions, i.e. light- (LGI) or dark-green (DGI) islands in the infected leaf were apparent and symptoms were fully developed. These two different regions were measured separately. The Chl and carotenoid contents in infected leaves decreased with a progression of infection and were lowest in LGI in the second stage. Also the ratio of Chl a/b declined in similar manner. The maximum quantum yield of PS2 photochemistry F_v/F_m, was decreased in the following order: first stage, DGI, and LGI. The same is true for the ratio F_v/F₀. The decrease of Φ₂ in infected leaves declined as compared to their controls. On the contrary, NPQ increased in infected leaves, the highest value was found in the first infection stage. Photochemical activities of the whole electron transport chain in isolated chloroplasts dramatically declined with the progression of symptoms, the lowest value was in LGI. Similarly, but to a lesser extent, the activity of PS2 in isolated chloroplasts decreased in infected leaves. Generally, the most marked impairment of the photosynthetic apparatus was manifested in the LGI of infected leaves.     

Changes in photosynthetic apparatus during dark incubation of detached leaves from control and ultraviolet-B treatedVigna seedlings

Changes in various components of photosynthetic apparatus during the 4 d dark incubation at 25°C of detached control and ultraviolet-B (UV-B) treatedVigna unguiculata L. leaves were examined. The photosynthetic apparatus was more degraded in younger control seedlings and for a longer time UV-B treated seedlings than in the older or for a shorter time UV-B treated seedlings. This was shown by determining the losses in chlorophyll (Chl) and protein contents, variable fluorescence yield, photosystem (PS) 2, PS1 and ribulose-1,5-bisphosphate carboxylase (RuBPC) activities, and photosynthetic¹⁴CO₂ fixation. In contrast, the Car/Chl ratio increased during the dark incubation due to less expressed degradation of Car.     

Purification of highly active oxygen-evolving photosystem II from Chlamydomonas reinhardtii

A method is described for the isolation and purification of active oxygen-evolving photosystem II (PS II) membranes from the green alga Chlamydomonas reinhardtii. The isolation procedure is a modification of methods evolved for spinach (Berthold et al. 1981). The purity and integrity of the PS II preparations have been assesssed on the bases of the polypeptide pattern in SDS-PAGE, the rate of oxygen evolution, the EPR multiline signal of the S₂ state, the room temperature chlorophyll a fluorescence yield, the 77 K emission spectra, and the P700 EPR signal at 300 K. These data show that the PS II characteristics are increased by a factor of two in PS II preparations as compared to thylakoid samples, and the PS I concentration is reduced by approximately a factor ten compared to that in thylakoids.Abbreviations BSA bovine serum albumin - Chl chlorophyll - DCBQ 2,6-dichloro-p-benzoquinone - DCMU (diuron) 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DMQ 2,5-dimethyl-p-benzoquinone - EDTA ethylenediamine tetraacetic acid - EPR electron paramagnetic resonance - Hepes N-2-hydroxyethylpiperazine-N-2-ethanesulfonic acid - MES 2-[N-Morpholino]ethanesulfonic acid - OEE oxygen evolving enhancer - PS II photosystem II - SDS-PAGE sodium dedocyl sulfate polyacrylamide gel electrophoresis     

Effects of Cucumber Mosaic Virus Infection on Photosynthetic Activities of Tobacco Leaves and Chloroplasts

Changes in photosynthetic activities were studied with tobacco (Nicotiana tabacum L.) leaves and chloroplasts infected by cucumber mosaic virus (CMV) at the top, middle and bottom located leaves. Net photosynthetic rate was reduced at all three positioned leaves, with the maximum reduction occurring at the top leaves (31.9% of control). The infected chloroplasts showed a reduction in electron transport rates of the whole chain electron transport, photosystem Ⅱ (PSⅡ) and photosystem Ⅰ (PSⅠ). Since the decline in the whole chain electron transport (15.6% of control, H2O→MV) closely paralleled the decline in PSⅡ activity (20.9% of control, H2O→PBQ), the inhibition of the latter was probably responsible for the overall decrease. Chlorophyll a fluorescence measurements showed a variable reduced fluorescence yield (Fv/Fo) which indicated that PSⅡ was impaired and the CO2 assimilation was disturbed by CMV infection. Fluorescence emission spectra at 77 K indicated that energy distribution between PSⅡ and PSⅠ was affected. F686/F734 of infected leaves and chloroplasts increased and the greatest increase (331.1% of control ) was found in the top leaves. These data may conclude that the infection inhibited mainly the PSⅡ activity.