The effect of copper on chlorophyll organization during greening of barley leaves

The effect of copper on chlorophyll organization and function during greening of barley was examined, using chlorophyll fluorescence and photoacoustic techniques. Copper was found to inhibit pigment accumulation and to retard chlorophyll integration into the photosystems, as evident from low temperature (77 K) fluorescence spectra. Resolution of the minimal fluorescence (F₀) into active and inactive parts, indicated a higher inactive fraction with copper treatment. This was attributed to chlorophyll molecules which failed to integrate normally, a conclusion supported by the longer fluorescence lifetime observed in copper treated plants. A lower ratio of chlorophyll a to b and fluorescence induction transients, showing accelerated Photosystem II closure, both indicate that copper treatment resulted in a larger light-harvesting antenna. Another effect of copper treatment was the suppression of oxygen evolution, indicating a decrease in photosynthetic capacity. We suggest that the non-integrated chlorophyll fraction sensitizes photodamage in the membrane, contributing to disruption of electron flow and pigment accumulation.     

Formation of the photosynthetic apparatus during greening of cadmium-poisoned barley leaves

The effect of cadmium on the formation of the photosynthetic apparatus of greening barley (Hordeum vulgare L. cv. Triangel) leaves has been investigated. Cadmium treatment of dark-grown leaves strongly reduced the extent of chlorophyll accumulation during greening. Low-temperature fluorescence emission showed, however, that neither the synthesis nor photoconversion of protochlorophyllide was inhibited, although a blue shift of the main fluorescence emission from 685 to 668 mm was found. Chlorophyll fluorescence lifetime was followed by measuring the phase-shift angle of modulated emission. Whereas this parameter normally decreases rapidly during greening, this change proceeded noticeably slower with increasing severity according to cadmium concentration. Cadmium also decreased the variable part of fluorescence induction. These results suggest that the cadmium in greening leaves, rather than interfering with chlorophyll biosynthesis, acts mainly by disturbing the integration of chlorophyll molecules into the stable complexes required for normal functional photoysnthetic activity.     

Influence of short-term osmotic stress on the photosynthetic activity of barley seedlings

Oxygen evolution and chlorophyll a fluorescence transients of two barley (Hordeum vulgare L) cultivars subjected to polyethylene glycol induced osmotic stress was examined. The relative water content of the plants was used as a measure of their water status. The results suggested that although dehydration was considerable, photosystem 2 was weakly affected by the osmotic treatment.     

Physiological effects of photosystem II-herbicides on the development of the photosynthetic apparatus

Photosystem II-herbicides (bentazone*, diuron) not only block photosynthetic electron transport, but have additional effects on the cell metabolism of Raphanus seedlings. They induce the formation of shade-type chloroplasts with a different ultrastructure and prenyllipid composition. This is shown by higher grana stacks as well as by higher chlorophyll b and lutein amounts with reference to chlorophyll a, and lower levels of the plastidic prenylquinones (plastoquinone, phylloquinone, -tocoquinone) and -carotene as compared to the controls.The two herbicides bentazone and diuron change the labelling pattern of the chloroplast pigments from ³H-mevalonic acid and 2-¹⁴C-acetate and also reduce the accumulation of anthocyanin (pelargonidin), which is a further indication of a shade-type growth response. The level of ubiquinone, an indicator for mitochondrial activity, is, however, increased.     

乙草胺对葡萄叶片光合和叶绿素荧光特性及叶绿体结构的影响

以沙培1年生巨峰葡萄为材料,研究土施乙草胺对葡萄叶片光合、叶绿素荧光特性和叶绿体结构的影响.结果表明：喷施初期(处理后第13天),上部叶片净光合速率和气孔导度显著下降,PSII最大光化学效率和实际光化学效率显著低于对照,快速叶绿素荧光诱导动力学曲线中J点和K点荧光显著上升,性能指数PI_ABS显著下降,其PSII反应中心和放氧复合体受损伤程度显著高于中部叶片,但随着处理时间的延长,受损伤的程度减轻.在喷施后期(处理后第60天),上部叶片与中部叶片各指标之间的差距变小;下部叶片对除草剂的响应滞后,PSII反应中心和放氧复合体受到较大损伤,J点和K点荧光上升及PI_ABS下降的幅度高于中、上部叶片.乙草胺处理后第60天,葡萄叶片可溶性糖和淀粉含量增加,中、上部叶片色素含量显著下降,叶绿体膜受损,叶绿体变小,片层结构模糊或间隙增大.表明土施乙草胺可传导至葡萄地上部,导致叶片光合机构损伤、PSII活性下降和光合速率降低.     

Effect of carnitine on greening barley leaves

Carnitine increases chlorophyll production in greening barley leaves. [Methyl-¹⁴C]carnitine fed to greening leaves was not utilized as a carbon sou     

Ultra-structural and functional changes in the chloroplasts of detached barley leaves senescing under dark and light conditions

Changes in the chloroplast ultra-structure and photochemical function were studied in detached barley (Hordeum vulgare L. cv. Akcent) leaf segments senescing in darkness or in continuous white light of moderate intensity (90 mumol m-2 s-1) for 5 days. A rate of senescence-induced chlorophyll degradation was similar in the dark- and light-senescing segments. The Chl a/b ratio was almost unchanged in the dark-senescing segments, whereas in the light-senescing segments an increase in this ratio was observed indicating a preferential degradation of light-harvesting complexes of photosystem II. A higher level of thylakoid disorganisation (especially of granal membranes) and a very high lipid peroxidation were observed in the light-senescing segments. In spite of these findings, both the maximal and actual photochemical quantum yields of the photosystem II were highly maintained in comparison with the dark-senescing segments.     

On the long-wavelength spectral forms of chlorophyll a in Photosystem I: Spectroscopic and immunological investigations on a greening mutant of the green alga Scenedesmus obliquus

The origin of the long-wavelength chlorophyll (Chl) absorption (_peak > 680 nm) and fluorescence emission (_peak > 685 nm) has been investigated on Scenedesmus mutants (C-2A-series, lacking the ability to synthesize chlorophyll in the dark) grown at 0.3 (LL), 10 (ML) and 240 µE s^–1 m^–2(HL). LL cells are arrested in an early greening state; consequently, Chl availability determines the phenotype. LL thylakoids are totally lacking long-wavelength Chl; nonetheless, PS I and PS II are fully functional. Gel electrophoresis and Western blots indicate that four out of seven resolved LHC polypeptides seem to require a high Chl availability for assembly of functional chlorophyll-protein complexes. The PS I core-complex of ML and HL thylakoids contains long-wavelength chlorophylls, but in the PS I core-complex of LL thylakoids these pigments are lacking. We conclude that long-wavelength pigments are only present in the PS I core in the case of high Chl availability. The following hypothesis is discussed: Chl availability determines not only the LHC polypeptide pattern, but also the number of bound Chl molecules per individual pigment-protein complex. Chl-binding at non-obligatory, peripheral sites of the pigment-protein complex results in long-wavelength Chl. In the case of low Chl availability, these sites are not occupied and, therefore, the long-wavelength Chl is absent.     

Short-term effects of aluminium at alkaline pH on the structure and function of the photosynthetic apparatus

A 24 h exposure of the salt-tolerant grass Thinopyrum bessarabicum (Savul. and Rayss) A. Love seedlings to 1 mM aluminium (Al) in nutrient solution at pH of 9.0 resulted in a significant reduction of the biomass. In control samples the mesophyll chloroplasts exhibited the usual lens shape with most grana arranged in straight or slightly curving lines, and only 6.5 % of the grana were out of order. In Al-treated plants the mesophyll chloroplasts displayed a slightly distorted shape and distended size with most grana arranged in bow-like lines, while in the central region of the organelle as many as 26.7 % of the grana were independent and out of order in relation to the long axis. The morphological changes in the chloroplast shape and grana arrangement were probably due to swelling and distension of the chloroplasts in consequence to the altered membrane permeability. The initial in vivo chlorophyll (Chl) fluorescence FO, as well as the intermediate FI and peak fluorescence FP were increased under the Al stress: this indicated a destruction of photosystem (PS) 2 reaction centres and increased reduction of QA. The (FI-FO)/(FP-FO) ratio exhibited a significant increase indicating higher proportion of PS2 centres unable to reduce QB. Changes in the chloroplast ultrastructure seemed to be the reason of photosynthetic electron transport inhibition. Yet all these changes in the photosynthetic performance and chloroplast ultrastructure were considered as indirect effects of Al treatment since Al concentration in the leaves was undetectable. Disturbances in the chloroplast ultrastructure could be caused by a reduced uptake and/or transport of other nutrients. This revised version was published online in June 2006 with corrections to the Cover Date.     

The effects of water stress on the development of the photosynthetic apparatus in greening leaves

The effects of low and high relative humidity and of polyethylene glycol-induced root water stress on chlorophyll accumulation, on formation of the lamellar chlorophyll-protein complexes, and on the development of photosynthetic activity during chloroplast differentiation were examined. Low relative humidity or polyethylene glycol-induced root water stress (stress conditions) resulted in a 3 to 4 hour lag in chlorophyll accumulation, retarded the rate of chlorophyll b accumulation, and reduced the rate of formation of the light-harvesting chlorophyll a/b protein. All of these effects could be overcome by high relative humidity (nonstress) conditions. Concomitant measurement of leaf water potential showed that under stress conditions greening leaves were subjected to initial water deficits of −8 bars which decreased to −5 bars after 3 to 4 hours of illumination corresponding to the end of the lag phase. Leaves greening under nonstress conditions did not experience leaf water deficits greater than about −5 bars. It seems that the attainment of a minimum leaf water potential of −5 bars may be critical in the control of early chloroplast development. These results demonstrate that the lag phase is not indicative of a programmed event in chloroplast development, but rather is attributable to environmental conditions prevailing during leaf development and greening.     

Photosynthesis in the basal growing zone of barley leaves

Cell proliferation, elongation, determination and differentiation mainly take place in the basal 5 mm of a barley leaf, the so-called basiplast. A considerable portion of cDNAs randomly selected from a basiplast cDNA library represented photosynthetic genes such as CP29, RUBISCO-SSU and type I-LHCP II. Therefore, we became interested in the role of the basiplast in establishing photosynthesis. (1) Northern blot analysis revealed expression of photosynthetic genes in the basiplast, although at a low level. Analysis of basiplasts at different developmental stages of the leaves revealed maximal expression of photosynthetic genes during early leaf development. The activity of these genes shows that plastid differentiation involves the development of the photosynthetic apparatus even at this early state of leaf cell expansion. (2) This conclusion was supported by the fact that chlorophylls and carotenoids are synthesized in the basiplast. The qualitative pattern of pigment composition was largely similar to that of fully differentiated green leaves. (3) The transition from proplastids to chloroplasts progressed in the basal 5 mm of the leaf, so that the number of grana lamellae per thylakoid stack increased with distance from the meristem from zero to about five. (4) Photosynthetic function was studied by chlorophyll a-fluorescence measurements. In dark-adapted 8-day-old primary leaves, the fluorescence ratio (F_P-F_o)/F_P was little decreased in basiplasts as compared to leaf blades. During steady state photosynthesis, the ratio (F_M-F_o)/F_M was high in leaf blade (0.5), but low in the sheath (0.25) and in the basiplast (0.18), indicating the existence of functional, albeit low light-adapted chloroplasts in the basiplast. (5) Further on, chlorophyll a fluorescence analysis in relation to seedling age revealed efficient photosynthetic performance in the basiplast of 3- to 6-day-old seedlings which later-on differentiates into leaf blade as compared to the basiplast of 7- to 12-day-old seedlings which develops into leaf sheath and finally ceases to grow. The leaf age dependent changes in basiplast photosynthesis were reflected by changes in pigment contents and LHCP II expression both of which also revealed a maximum in the basiplast of 4-day-old seedlings.Abbreviations bas 1 basiplast-associated gene 1 encoding a peroxide reductase - cab chlorophyll a/b binding protein - CP 29 29 kDa chlorophyll binding protein - DIG digoxigenin - EMIP epidermal major intrinsic protein - LHCP II light harvesting complex of Photosystem II - LSU large subunit of Rubisco - NPQ non photochemical chlorophyll a fluorescence quenching - PSI/PS II Photosystem I/II - PQ photochemical chlorophyll a fluorescence quenching - Rubisco Ribulose-1,5-bisphosphate carboxylase - SSU small subunit of Rubisco     

Effects of low temperature acclimation upon photosynthetic induction in barley primary leaves

Oxygen evolution and chlorophyll fluorescence were measured in cold-hardened and unhardened leaves of barley ( Hordeum vulgare L. cv. Asa) during the induction period of photosynthesis. The lag phase of light-saturated photosynthesis was increased and steady-state rates of photosynthesis were higher in cold-hardened than in unhardened barley leaves. Fluorescence was quenched more rapidly during the first minutes of induction in hardened than unhardened leaves, largely because of greater energy-dependent quenching (q_E). Also, slow fluorescence transients through the M peak were delayed and less pronounced in cold-hardened than in unhardened leaves. Based upon the combined fluorescence and oxygen evolution data it was concluded that cold-hardening delayed light activation of the energy consuming carbon reduction cycle, thereby delaying the use of ATP and NADPH formed in the light reaction. Measurements of oxygen evolution and fluorescence kinetics during photosynthetic induction under oxygenic and anoxygenic conditions suggest that oxygen photoreduction is important for additional ATP generation during both the onset of photosynthetic carbon assimilation and during steady-state photosynthesis.     

Phosphorescence of protochlorophyll(ide) and chlorophyll(ide) in etiolated and greening bean leaves

The assignment is presented for the principal phosphorescence bands of protochlorophyll(ide), chlorophyllide and chlorophyll in etiolated and greening bean leaves measured at -196°C using a mechanical phosphoroscope. Protochlorophyll(ide) phosophorescence spectra in etiolated leaves consist of three bands with maxima at 870, 920 and 970 nm. Excitation spectra show that the 870 nm band belongs to the short wavelength protochlorophyll(ide), P627. The latter two bands correspond to the protochlorophyll(ide) forms, P637 and P650. The overall quantum yield for P650 phosphorescence in etiolated leaves is near to that in solutions of monomeric protochlorophyll, indicating a rather high efficiency of the protochlorophyll(ide) triplet state formation in frozen plant material. Short-term (2–20 min) illumination of etiolated leaves at the temperature range from -30 to 20°C leads to the appearance of new phosphorescence bands at about 990–1000 and 940 nm. Judging from excitation and emission spectra, the former band belongs to aggregated chlorophyllide, the latter one, to monomeric chlorophyll or chlorophyllide. This indicates that both monomeric and aggregated pigments are formed at this stage of leaf greening. After preillumination for 1 h at room temperature, chlorophyll phosphorescence predominates. The spectral maximum of this phosphorescence is at 955–960 nm, the lifetime is about 2 ms, and the maximum of the excitation spectrum lies at 668 nm. Further greening leads to a sharp drop of the chlorophyll phosphorescence intensity and to a shift of the phosphorescence maximum to 980 nm, while the phosphorescence lifetime and a maximum of the phosphorescence excitation spectrum remains unaltered. The data suggest that chlorophyll phosphorescence belongs to the short wavelength, newly synthesized chlorophyll, not bound to chloroplast carotenoids. Thus, the phosphorescence measurement can be efficiently used to study newly formed chlorophyll and its precursors in etiolated and greening leaves and to address various problems arising in the analysis of chlorophyll biosynthesis.Abbreviations Pchl protochlorophyll and protochlorophyllide - Chld chlorophyllide - Chl chlorophyll     

Effects of four types of sodium salt stress on plant growth and photosynthetic apparatus in sorghum leaves

Sorghum variety Longza 17 was used as the experimental organism in a study of the effects of different types of sodium salt (two neutral salts, NaCl and Na₂SO₄; and two alkaline salts, NaHCO₃ and Na₂CO₃), at an equivalent Na⁺ concentration (100?mmol·L^?1) on leaf growth parameters and PSII and PSI function by using the Fast Chlorophyll Fluorescence Induction Dynamics technique and 820?nm light reflectance curves. The results showed that at Na⁺ concentration of 100?mmol·L^?1, different types of sodium salt stress significantly inhibited the growth of sorghum plants. Different types of sodium salt stress showed significant inhibition on the activities of PSII and PSI in sorghum leaves, the impact of different types of sodium salt on the activities of PSII and PSI in sorghum leaves was consistent, listed from greatest to least impact as Na₂CO₃ > NaHCO₃ > Na₂SO₄ > NaCl. The effects of alkaline salt stress on the growth and photosynthetic properties of sorghum were greater than those under the neutral salt stress, therefore, in addition to considering the impact of Na⁺ concentration in the sorghum planting area, emphasis should also be given to the influence of the degree of alkalization, especially the higher alkalinity of Na₂CO₃.     

Photooxidative damage to the photosynthetic apparatus during chilling

Short periods of chilling in the presence of light (up to 6 h: 1°C; 270 W/m²) decreased the subsequent apparent photosynthesis and chlorophyll fluorescence of leaf discs of Cucumis sativus L. cv. Kleine Groene Scherpe. The extent of the injury depended on the duration of the chilling pretreatment. After 6 h the subsequent apparent photosynthesis even reached a negative value, and it increased only slightly during the next 2 1/2 h. The decrease of apparent photosynthesis was not a consequence of increased dark respiration but was of photooxidative origin since the presence of both light and oxygen was required. Preincubation in the light for 2 h at 20°C sensitized leaf discs to subsequent photooxidation during chilling. Prompt and delayed chlorophyll fluorescence decreased simultaneously after chilling and light treatment. The corresponding decrease of photosynthesis and chlorophyll fluorescence is discussed in relation to primary photooxidative damage to the photosystems in the chloroplast membrane.     

Excitation transfer between photosynthetic units: the 1964 experiment

We review here the background and the experiments that led to the concept of excitation energy transfer among photosystem (PS) II units. On the basis of a kinetic analysis of oxygen evolution and chlorophyll a fluorescence yield, the authors showed, in 1964, that the PS II photochemical reaction involved in the formation of oxygen is not a first-order process. We concluded that excitation energy localized in a `photosynthetic unit' including a reduced primary acceptor is transferred with a high probability to neighboring PS II units. Here, the beginnings and the original data of this topic are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Haem and chlorophyll formation in etiolated and greening leaves of barley

The amounts of protochlorophyllide (P650) and protohaem were measured in ageing dark-grown barley leaves. Maximum amounts of P650 and protohaem were found in 6- to 8-day-old material after which P650 declined rapidly and protohaem more slowly. In leaves exposed to light maximum chlorophyll was produced in 6-day-old material with progressively less the older the leaves. Haem concentrations increased in seedlings of all ages exposed to light. A lag phase was observed for both chlorophyll and haem formation in leaves given a light treatment. Haem, however, showed a slight yet sig nificant decline as chlorophyll production commenced. The results indicate that chlorophyll and haem synthesis share a common pool of δ-aminolae vulinic acid (ALA). At a certain stage of development, the magnesium porphyrin pathway diverts precursors away from haem synthesis. It is only when the ALA synthesising system is well developed that the production of ALA can satisfy pathways to both haem and chlorophyll. The observed changes in haem under certain conditions suggest that, as in animal systems, haem levels may regulate porphyrin formation (chlorophylls) by controlling the supply of ALA.     

Evidence that UV-B tolerance of the photosynthetic apparatus in microalgae is related to the D1-turnover mediated repair cycle in vivo

The present study was conceived to elucidate the potential importance of the D1 turnover-mediated repair mechanism in UV-B tolerance of the photosynthetic apparatus in microalgae. To this end, the lab-identified UV-B sensitive and tolerant species of Chlorophyte and Chromophyte algae was used to examine photosynthetic response to UV-B exposure in the presence vs. the absence of streptomycin, an inhibitor of chloroplast protein synthesis. Measurements of photosynthetic O₂ evolution capacity and chlorophyll fluorescence parameters (F_v/F_m, Φ_PSII) illustrated species-specific UV-B sensitivity of the photosynthetic apparatus. Addition of the inhibitor streptomycin caused significant enhancements of UV-B-caused depression of photosynthesis in UV-B tolerant species, while little effect was observed in the sensitive species. In the tolerant species, recovery from UV-B induced 20 percnt; decline in F_v/F_m reached completion within 2 hours, much faster than that in the sensitive species. Immunoblotting revealed that exposure to UV-B radiation caused substantial degradation of the D1 protein in the sensitive Heterococcus brevicellularis, which was little enhanced by addition of the inhibitor. The same UV-B exposure lead to less D1 degradation in the tolerant Scenedesmus sp., which was significantly enhanced by addition of the inhibitor. This study shows that UV-B tolerance of the photosynthetic apparatus in microalgae was associated with a strong capacity for recovery from the UV-B-induced damage and this capacity related to the D1 turnover-mediated repair cycle, and largely determined UV-B tolerance of the photosynthetic apparatus in these organisms.     

Localization of NADPH-protochlorophyllide reductase in plastids of barley at different greening stages

The localization of protochorophyllide (Pchlide) and of NADPH-protochlorophyllide oxidoreductase (POR, EC 1.6.99.1) within (etio)chloroplasts has been investigated at selected stages of greening of barley seedlings. Pchlide pigment and POR protein contents were evaluated in different plastid membrane fractions by fluorescence spectroscopy and immunoblot analysis using a monospecific polyclonal antibody raised against the purified enzyme. Fluorescence analysis showed the presence of Pchlide in both the envelope and thylakoid membranes. During greening, the Pchlide content, expressed on a total protein basis, decreased in thylakoid membranes, whereas it increased in the envelope membranes. POR proteins were detected mainly in thylakoid membranes at early greening stages. In contrast, the weak amount of POR proteins was associated more specifically with envelope membranes of mature chloroplasts. Whatever the greening stage, thylakoid-bound Pchlide and POR proteins were more abundant in the thylakoid regions which remained unsolubilized after mild Triton treatment used as standard procedure to prepare PS II particles. This suggests the preferential association of Pchlide and POR to the appressed regions of thylakoids. This revised version was published online in June 2006 with corrections to the Cover Date.     

Photosynthetic apparatus in primary leaves of barley seedlings grown under blue or red light of very low photon flux densities

Chlorophyll (Chl) a and Chl b contents, rate of CO₂ gas exchange, quenching coefficients of chlorophyll fluorescence, and endogenous phytohormones have been studied in primary leaves of barley seedlings cultivated under blue (BL) or red (RL) light. Photon flux densities (PFD) were between 0.3 and 12 mol m^-2 s^-1. Plants grown at PFD of 0.3 mol m^-2 s^-1 demonstrated in BL tenfold and in RL threefold decreased Chl content compared to plants grown at 12 mol m^-2 s^-1. Chl a/b ratio increased from 2.3–2.5 to 4.4–4.5 in BL, not in RL, following the decrease in PFD at plant cultivation from 12 to 0.3 mol m^-2 s^-1. Plants cultivated at weak BL demonstrated severalfold decreased rate of photosynthetic CO₂ uptake, whereas decrease in PFD of RL from 12 to 0.3 mol m^-2 s^-1 caused only 20% de cline in the rate of photosynthesis. Decrease in PFD during a plant cultivation reduced the maximum quantum yield of photosynthesis in BL, not in RL leaves. Light response curves of non-photochemical and photochemical quenching of chlorophyll fluorescence calculated on the basis of absorbed quanta were not affected by PFD of RL during plant cultivation. On the contrary, both non-photochemical quenching and accumulation of Q_A ^-, reduced primary acceptor of Photosystem II, occurred at lower amounts of absorbed quanta in leaves of BL plants grown at 0.3 than at 12 mol m^-2 s^-1. Two photoregulatory reactions were suggested to exert the light control of the development of photosynthetic apparatus in the range of low PFDs. The photoregulatory reaction saturating by very low PFDs of RL was supposed to be mediated by phytochrome. Phytochrome was proposed to enhance (as related to other pigment-protein complexes of thylakoids) the accu mulation of chlorophyll- b-binding light-harvesting complex of Photosystem II (LHC II). It acts independently of the pigment mediating the second photoregulatory reaction, as evidenced by the results of experiments with plant growth under mixed blue plus red light. The contents of cytokinins and indole-3-acetic acid in a leaf were not significantly affected by either light quality and PFD thus indicating those phytohormones not to be involved into photoregulatory processes.