Glucose and δ-Aminolevulinic Acid Stimulate the Dark Chlorophyll Synthesis of Rice Seedlings

This research was to examine if rice (Oryza sativa L.), a monocotyledon of angiosperm, was able to synthesize chlorophyll (Chl) in complete darkness. Five-cm-tall etiolated seedlings of rice were used as starting materials and treated with or without various concentrations of glucose and/or δ-aminolevulinic acid (ALA) in the dark. Leaves harvested at the indicated time were determined for their contents of Chl, protoporphyrin Ⅸ(Proto), Mg-protoporphyrin Ⅸ(Mg-Proto) and protochlorophyllide (Pchlide). The mole percentage of porphyrin was calculated. The Chl content in the etiolated rice seedlings slightly increased from about 2.5 μg/g to 7.5 μg/g within 12 d in the dark, but the total Chl of dark-grown rice increased from 0.36 μg/g to 3.6 μg/g. While the mole percentages of Proto, Mg-Proto and Pchlide in the dark-grown seedlings without any treatment were about 65%, 27.5% and 7.5% at the beginning, respectively, those in the light-grown seedlings were about 42.5%, 35% and 22.5%, respectively. The mole percentage of porphyrin of etiolated seedlings resumed its normal ratio within 2 d after treatment with glucose. While the Chl content of etiolated seedlings grown in culture solution with 3% and 6% glucose increased 2.5 and 4.0 folds, respectively, those with 3% and 6% glucose and 1 mmol/L ALA increased 22 and 24 folds, respectively. It is concluded that angiosperm might be able to synthesize a small amount of Chl in complete darkness, that either glucose or ALA could stimulate dark Chl synthesis in angiosperm, and that a combination of glucose and ALA exhibited an additional effect. It is still unknown and remains to be further explored what is the mechanism of the effect of glucose and ALA on the Chl synthesis of rice in the dark. Key words: angiosperm; rice; dark chlorophyll synthesis; glucose; δ-aminolevulinic acid; protoporphyrin Ⅸ; Mg-protoporphyrin Ⅸ; protochlorophyllide     

Correlation and Quantitative Trait Loci Analyses of Total Chlorophyll Content and Photosynthetic Rate of Rice （Oryza sativa） under Water Stress and Well-watered Conditions

In order to explore the relevant molecular genetic mechanisms of photosynthetic rate （PR） and chlorophyll content （CC） in rice （Oryza sativa L.）, we conducted a series of related experiments using a population of recombinant inbred lines （Zhenshan97B x IRAT109）. We found a significant correlation between CC and PR （R = 0.19＊＊） in well-watered conditions, but no significant correlation during water stress （r = 0.08）. We detected 13 main quantitative trait loci （QTLs） located on chromosomes 1, 2, 3, 4, 5, 6, and 10, which were associated with CC, including six QTLs located on chromosomes 1, 2, 3, 4, and 5 during water stress, and seven QTLs located on chromosomes 2, 3, 4, 6, and 10 in well-watered conditions. These QTLs explained 47.39% of phenotypic variation during water stress and 56.19% in well-watered conditions. We detected four main QTLs associated with PR; three of them （qPR2, qPR10, qPR11） were located on chromosomes 2, 10, and 11 during water stress, and one （qPR10） was located on chromosome 10 in well-watered conditions. These QTLs explained 34.37% and 18.41% of the phenotypic variation in water stress and well-watered conditions, respectively. In total, CC was largely controlled by main QTLs, and PR was mainly controlled by epistatic QTL pairs.     

Pigment–Protein Complexes and the Number of Reaction Centers of the Photosystems in Pea Chlorophyll Mutants

We studied fluorescent and absorption properties of the chloroplasts and pigment–protein complexes isolated by gel electrophoresis from the leaves of pea, the parent cultivar Torsdag and mutants chlorotica 2004 and 2014. Specific fluorescence peaks of chlorophyll forms in individual complexes have been determined from the absorption and fluorescence spectra of the chloroplast chlorophyll and their second derivatives at 23 and –196°C. The mutant chlorotica 2004 proved to have an increased intensity of a long-wave band of the light-harvesting complex I at both 23°C (745 nm) and –196°C (728 nm). At the same time, this mutant manifested a decreased accumulation of the chlorophyll forms making up the nearest-neighbor antenna of the PS I reaction center (at 690, 697, and 708 nm). No spectral differences have been revealed between chlorotica 2014 mutant and the parent cultivar. Gel electrophoresis revealed the synthesis of all chlorophyll–protein complexes in both mutants. At the same time, analysis of photochemical activity of PS I and PS II reaction centers and calculations of their number and the size of the light-harvesting antenna have shown that the number of reaction centers in the PS I of chlorotica 2004 mutant is reduced by a factor of 1.7 because its chlorophyll a–protein complex is disturbed by the mutation. The primary effect of chlorotica 2014 mutation remains unclear. The proportional changes in the content of photosystem complexes in this mutant suggest that they are secondary and result from a 50% decrease in chlorophyll content.     

Changes of Photosystem Ⅱ Electron Transport in the Chlorophyll-deficient Oilseed Rape Mutant Studied by Chlorophyll Fluorescence and Thermoluminescence

The photosystem Ⅱ (PSII) complex of photosynthetic membranes comprises a number of chlorophyll-binding proteins that are important to the electron flow. Here we report that the chlorophyll b-deficient mutant has de creased the amount of light-harvesting complexes with an increased amount of some core polypeptides of PSII,including CP43 and CP47. By means of chlorophyll fluorescence and thermoluminescence, we found that the ratio of Fv/Fm, qP and electron transport rate in the chlorophyll b-deficient mutant was higher compared to the wild type.In the chlorophyll b-deficient mutant, the decay of the primary electron acceptor quinones (QA-) reoxidation was decreased, measured by the fluorescence. Furthermore, the thermolumlnescence studies in the chlorophyll b deficient mutant showed that the B band (S2/S3QB-) decreased slightly and shifted up towards higher temperatures.In the presence of dichlorophenyl-dimethylurea, which is inhibited in the electron flow to the second electron acceptor quinines (QB) at the PSII acceptor side, the maximum of the Q band (S2QA-) was decreased slightly and shifted down to lower temperatures, compared to the wild type. Thus, the electron flow within PSll of the chlorophyll b-deficient mutant was down-regulated and characterized by faster oxidation of the primary electron acceptor quinine QA- via forward electron flow and slower reduction of the oxidation S states.     

Spectroscopic properties of the Chlorophyll a–Chlorophyll c 2–Peridinin-Protein-Complex (acpPC) from the coral symbiotic dinoflagellate Symbiodinium

Femtosecond time-resolved transient absorption spectroscopy was performed on the chlorophyll a–chlorophyll c ₂–peridinin-protein-complex (acpPC), a major light-harvesting complex of the coral symbiotic dinoflagellate Symbiodinium. The measurements were carried out on the protein as well on the isolated pigments in the visible and the near-infrared region at 77 K. The data were globally fit to establish inter-pigment energy transfer paths within the scaffold of the complex. In addition, microsecond flash photolysis analysis was applied to reveal photoprotective capabilities of carotenoids (peridinin and diadinoxanthin) in the complex, especially the ability to quench chlorophyll a triplet states. The results demonstrate that the majority of carotenoids and other accessory light absorbers such as chlorophyll c ₂ are very well suited to support chlorophyll a in light harvesting. However, their performance in photoprotection in the acpPC is questionable. This is unusual among carotenoid-containing light-harvesting proteins and may explain the low resistance of the acpPC complex against photoinduced damage under even moderate light conditions.     

Effects of Cadmium Stress on Leaf Chlorophyll Fluorescence and Photosynthesis of Elsholtzia argyi—A Cadmium Accumulating Plant

A hydroponic experiment was conducted to investigate the effects of cadmium (Cd) on chlorophyll fluorescence and photosynthetic parameters on a Cd accumulating plant of Elsholtzia argyi. Four weeks-seedlings of E. argyi were treated with 0 (CK) 5, 10, 15, 20, 25, 30, 40, 50 and 100 μmol L^?1 Cd for 21days. Fv/Fo, Fv/Fm, qP, ΦPSП, ETR and Fv′/Fm′ were significantly increased under low Cd (5–15 μmol L^?1 for Fv/Fo, Fv/Fm and qP, 5–10 μmol L^?1 for ΦPSП, ETR and Fv′/Fm′) stress, and these parameters were similar to control under Cd ≤ 50μmol L^?1. All above parameters were significantly decreased at 100 μmol L^?1 Cd. Compared with control, Pn was significantly (P < 0.05) increased under 5–30 μmol L^?1 Cd. However, 50 and 100 μmol L^?1 Cd significantly (P < 0.05) reduced it. Gs and Tr were substantially decreased at 50–100 and 40–100 μmol L^?1 Cd, respectively. Ci was significantly increased at 50 and 100 μmol L^?1 Cd. High Cd-induced decrease of Pn is not only connected to stomatal limitation but also to the inhibition of Fv/Fo, Fv/Fm, ΦPSП, qP, ETR and increase of NPQ. Maintain chlorophyll fluorescence and photosynthesis parameters under its Cd tolerance threshold were one of tolerance mechanisms in E. argyi.     

High-Temperature Induced Chlorophyll Fluorescence Rise in Plants at 40–50 °C: Experimental and Theoretical Approach

We studied the temperature dependence of chlorophyll fluorescence intensity in barley leaves under weak and actinic light excitation during linear heating from room temperature to 50 degrees C. The heat-induced fluorescence rise usually appearing at around 40-50 degrees C under weak light excitation was also found in leaves treated with 3-(3',4'-dichlorophenyl)-1,1-dimethylurea (DCMU) or hydroxylamine (NH(2)OH). However, simultaneous treatment with both these compounds caused a disappearance of the fluorescence rise. We have suggested that the mechanism of the heat-induced fluorescence rise in DCMU-treated leaves is different than that in untreated or NH(2)OH-treated leaves. In DCMU-treated leaves, the heat-induced fluorescence rise reflects an accumulation of Q(A) (-) even under weak light excitation due to the thermal inhibition of the S(2)Q(A) (-) recombination as was further documented by a decrease in the intensity of the thermoluminescence Q band. Mathematical model simulating this experimental data also supports our interpretation. In the case of DCMU-untreated leaves, our model simulations suggest that the heat-induced fluorescence rise is caused by both the light-induced reduction of Q(A) and enhanced back electron transfer from Q(B) to Q(A). The simulations also revealed the importance of other processes occurring during the heat-induced fluorescence rise, which are discussed with respect to experimental data.     

A Comparative Study on PSⅡ Light Harvesting Chlorophyll a/b Protein Complexes Between Spinach and Cucumber

PS Ⅱ light harvesting chlorophyll a/b protein complexes (LHC Ⅱ ) were isolated from chloroplast of spinach (Spinacia oleracea Mill. ) and cucumber (Cucumis sativus L. ). Comparative studies were made on the polymerized forms. Chl a/b ratio, spectral characteristics and polypeptide components of these two kinds of LHC Ⅱ. Experimental results showed that the LHC Ⅱ from spinach had a Chl a/b ratio of 1.33 and the LHC Ⅱ from cucumber had a Chl a/b ratio of 1.77. The spectral characteristics of the LHC Ⅱ from cucumber also indicated the enrichment of Chl b in this LHC Ⅱ . There was also obvious differences in the polypeptide components between these two kinds of LHC Ⅱ, the LHC Ⅱ of spinach contained a 27 kD and a 25 kD polypeptides, while the LHC Ⅱ of cucumber contained only a 27 kD polypeptide. This showed that the 25 kD polypeptide contained less Chl b. The analysis of the chlorophyll protein complexes showed that the monomer, dimer and trimer of the LHC Ⅱ of spinach were composed of two polypeptides, while all the polymerized forms of cucumber’s LHC Ⅱ were composed of one polypeptide.     

Chlorophyll “a” content in cells of Antarctic phytoplankton

Material was collected from the Weddell Sea and the Bransfield Strait in January/April 1989. Data on size-taxonomic composition and biomass of phytoplankton communities and Ch1 concentration were obtained to estimate the chlorophyll a (Ch1) cell content. Single cell fluorescence measured microscopically was used as a relative index of cellular Ch1 content of individual species. The relationship between the species composition of the algal communities and the ratio of phytoplankton carbonCh1 concentration (CCh1) was found. Due to changes in species composition the average CCh1 ratio in March/April (56) was half that in January/February (115). The CCh1 ratio ranged from 24 to 215 (mean=101) in the upper mixed layer and from 14 to 69 (mean=37) in the pycnocline region. The distribution of cellular Ch1 within individual species showed lower heterogeneity in the mixed layer in comparison with that in the pycnocline and below. Below the mixed layer, populations consisted partly of dead cells with very low pigment content, while other cells had greatly increased cellular Ch1. At several stations this cellular Ch1 increase led to the formation of a deep Ch1 maximum.     

Chlorophyll composition of Photosystems IIα, IIβ and I in tobacco chloroplasts

The antenna composition of the Photosystems II_α, II_β and I was studied in tobacco chloroplasts. Absorbance spectra, recorded at 4 K, were analyzed for the wild type and the mutants Su/su and Su/su var. Aurea, containing higher concentrations of the photosystems. With chloroplasts of Su/su we measured the action spectra of the three photosystems from 625 to 690 nm. Above 675 nm absorption by Photosystem I dominated. This sytem had a maximum at 678 nm and a shoulder at 660 nm. Of the long-wavelength chlorophyll a forms, absorbing at 690, 697 and 705 nm at 4 K, which are generally assigned to Photosystem I, the 697 nm form occurred in an amount of four molecules per reaction center of Photosystem I in each type of chloroplast. The Photosystem II_α spectrum was characterized by maxima at 650 and 672 nm, showing clearly the participation of the chlorophyll a and b containing light-harvesting complex. In the mutants the light-harvesting complex has a chlorophyll a to chlorophyll b ratio of more than 1; the amount of the 672 nm chlorophyll a was normal, whereas the amount of chlorophyll b was markedly decreased in the mutants relative to the wild type. The Photosystem II_β spectrum mainly consisted of a band at 683 nm.     

Light-Induced Biogenesis of Chlorophyll–Protein Complexes in Developing Wheat Thylakoids

It is shown that the apoproteins of core complexes (CC) I and II, the - and -subunits of CF₁ ATP-synthase complexes, are present in seedlings grown under intermittent light (IML). The levels of light-harvesting complex (LHC) apoproteins in the 30- to 18-kD region increase rapidly upon exposure to continuous light (CL). The newly synthesized LHC apoproteins appear to be present predominantly in monomeric forms that later assemble into higher-order oligomeric forms. During the early stages of greening of wheat seedlings, polypeptides in the 20.5-19 and 17.5-15.5 kD regions (so-called early light-induced proteins (ELIP)) are observed, but they disappear fully after 6 h. As greening proceeds, the 727-nm band in low-temperature fluorescence spectra (77 K) gradually shifts to longer wavelength (740-742 nm), which clearly demonstrates the light-driven biogenesis of LHC I and its assembly with CC I.     

Effects of Different Levels of Water Stress on Leaf Water Potential, Stomatal Resistance, Protein and Chlorophyll Content and Certain Anti-oxidative Enzymes in Tomato Plants

A greenhouse experlment was performed In order to Investigate the effects of dlfferent levels of water stress on leaf water potentlal （ψw）, stomatal resistance （rs）, protein content and chlorophyll （Chl） content of tomato plants （Lycoperslcon esculentum Mill. cv. Nlkita）. Water stress was Induced by addlng polyethylene glycol （PEG 6 000） to the nutrlent solution to reduce the osmotlc potential （ψs）. We Investlgated the behavlor of antl-oxldant enzymes, such as catalase （CAT） and superoxide dlsmutase （SOD）, durlng the development of water stress. Moderate and severe water stress （i.e. ψs= -0.51 and -1.22 MPa, respectlvely） caused a decrease In ψw for all treated （water-stressed） plants compared with control plants, wlth the reductlon belng more pronounced for severely stressed plants. In addltion, rs was slgnlflcantly affected by the Induced water stress and a decrease in leaf soluble protelns and Chl content was observed. Whereas CAT actlvlty remained constant, SOD actlvlty was increased in water-stressed plants compared wlth unstressed plants. These results Indicate the possible role of SOD as an anti-oxidant protector system for plants under water stress condltlons. Moreover, It suggests the possibllity of using this enzyme as an addltional screening crlterlon for detecting water stress in plants.     

The Influence of Surfactants on Chlorophyll Binding Status and Excitation Energy Transfer in Photosystem ￠? of Wheat (in English)

Surfactants are widely used in the purification and research of structure and function of the protein complexes in photosynthetic membrane. To elucidate the mechanism of interaction between surfactants and photosystem Ⅰ (PSⅠ), effects of two typical surfactants, Triton X-100 and sodium dodecyl sulfate (SDS) on PSⅠ, were studied at different concentrations. The results were: SDS led to the reduction of apparent absorption intensity and blue shift of absorption peaks; while Triton X-100 led to the decrease of apparent absorption intensity in red region and blue shift of the peak, but to the increase of apparent absorption intensity in blue region. The fourth derivative spectra show that the longwavelength (669 nm and 683 nm) absorbing chlorophyll a was affected greatly and their relative changes of absorbance were axially symmetrical. The presence of surfactant could make the long wavelength fluorescence emission decrease greatly and a new fluorescence peak appeared around 680 nm, it was obvious that the surfactant interceded the transfer of excitation energy from antenna pigments to reaction center. The surfactants might affect the microenvironment of proteins, even the structure of PSⅠ protein subunits and hence changed the binding status of pigments with protein subunits, or the pigments might be released from the subunits. All of these might affect the absorption and the transfer of excitation energy.     

How Do Different Watering Regimes Affect the Growth,Chlorophyll Fluorescence,Phytohormone, and Phenolic Acid Content of Greenhouse-Grown Ceratotheca triloba?

We evaluated the effect of different watering regimes on the growth, chlorophyll fluorescence, phytohormones, and phenolic acids in Ceratotheca triloba (Bernh.) Hook.f., a commonly consumed African indigenous leafy vegetable. The study was conducted in the greenhouse under different watering regimes [seven (daily); three (thrice); two (twice); one (once) day(s) per week] for a period of 2 and 4-months. In each pot (7.5 cm diameter; 150 ml volume), 50 ml of water was applied per treatment. At the end of the experiment, plant growth, chlorophyll fluorescence, phytohormones, and phenolic acids were determined. A decrease in water availability resulted in a consistent decline in plant growth after a 4-month growth period. The severity of reduced water availability was more noticeable in plants watered once a week with a 1.4-fold reduction in growth and quantum efficiency of PSII (Fv/Fm) value of 0.80. The significant decline in growth and chlorophyll fluorescence was probably due to the increased production of abscisic acid (ABA) and cytokinin (CK) content together with the detected phytohormones in plants with restricted water supply. Furthermore, plants watered once a week had a trade-off between growth and phenolic acid production, with significantly higher (threefolds) concentrations of vanillic, ferulic, caffeic, and 4-coumaric acids in 4-month-old plants. Even though C. triloba grew best in well-watered soil, the plant had the potential to adapt and survive in soils with limited water supply for longer periods of growth. These findings suggest that regulation of phytohormones and phenolic acids played an important role in improving the growth of C. triloba under limited water conditions.

     

Chlorophyll content of Plešné Lake phytoplankton cells studied with image analysis

Using image analysis, chlorophyll autofluorescence was measured in single cells of green alga Monoraphidium dybowskii and in filaments of cyanobacteria (Pseudanabaena sp. and Limnothrix sp.) in the vertical profile of small acidified mountain lake Ple?né jezero (Ple?né Lake) from May to November of 2003. Cell chlorophyll autofluorescence was converted to cell chlorophyll content using a conversion factor determined by comparing the total autofluorescence of phytoplankton in a microscope field with spectrophotometrically determined total chlorophyll concentration; the conversion factor did not differ between epilimnion (0.5 m depth) and hypolimnion (9 m depth). Vertical patterns of chlorophyll concentration and of cellular chlorophyll content depended on water column mixing: during the period of stable thermal stratification, a metalimnetic peak in total chlorophyll concentration was present and cellular chlorophyll contents in the metalimnion and hypolimnion were notably elevated compared to the surface. Monotonous vertical profiles of both total chlorophyll concentration and cell chlorophyll content were typical for the period of water column overturn. During the stratification period, hypolimnetic Monoraphidium cell chlorophyll content was on average twice as high (maximum difference 2.7-fold) compared to surface values (of 3.2–12.9 fg µm^?3), while in filamentous cyanobacteria (surface cell chlorophyll content of 2.2–13.3 fg µm^?3), the difference was much higher — six-fold on average, with an 11.6-fold maximum value. The values measured with image analysis in 2003 were compared to unpublished values of total phytoplankton biomass-specific chlorophyll concentrations obtained using manual phytoplankton biomass determination and spectrophotometric chlorophyll measurement in 1998 at the same locality. Good agreement was found in seasonal patterns and vertical profiles of chlorophyll between both seasons.     

Chlorophyll–nutrient relationships of different lake types using a large European dataset

In Europe there is a renewed focus on relationships between chemical determinands and ecological impact as a result of the Water Framework Directive (WFD). In this paper we use regression analysis to examine the relationship of growing season mean chlorophyll a concentration with total phosphorus and total nitrogen using summary data from over 1,000 European lakes. For analysis, lakes were grouped into types with three categories of mean depth, alkalinity and humic content. The lakes were also divided into broad geographic regions covering Atlantic, Northern, Central/Baltic and for some types the Mediterranean areas of Europe. Chlorophyll a was found to be significantly related to both total phosphorus and total nitrogen, although total phosphorus was almost always found to be the best predictor of chlorophyll. Different nutrient chlorophyll relationships were found for lakes according to mean depth and alkalinity, although no significant effect of geographic region or humic content was found for the majority of lake types. We identified three groups of lakes with significantly different responses. Deep lakes had the lowest yield of chlorophyll per unit of nutrient, low and moderate alkalinity shallow lakes the highest and high alkalinity lakes were intermediate. We recommend that the regression models provided for these three lake groups should be used for lake management in Europe and discuss the limitations of such models.     

Changes in Thermostability of Photosystem Ⅱ and Leaf Lipid Composition of Rice Mutant with Deficiency of Light-harvesting Chlorophyll a/b Protein Complexes

We studied the difference in thermostability of photosystem Ⅱ （PSII） and leaf lipid composition between a T-DNA insertion mutant rice （Oryza sativa L.） VG28 and its wild type Zhonghuau. Native green gel and SDS-PAGE electrophoreses revealed that the mutant VG28 lacked all light-harvesting chlorophyll a/b protein complexes. Both the mutant and wild type were sensitive to high temperatures, and the maximal efficiency of PSII photochemistry （FJ Fm） and oxygen-evolving activity of PSII in leaves significantly decreased with increasing temperature. However, the PSII activity of the mutant was markedly more sensitive to high temperatures than that of the wild type. Lipid composition analysis showed that the mutant had less phosphatidylglycerol and sulfoquinovosyl diacylglycerol compared with the wild type. Fatty acid analysis revealed that the mutant had an obvious decrease in the content of 16：1t and a marked increase in the content of 18：3 compared with the wild type. The effects of lipid composition and unsaturation of membrane lipids on the thermostability of PSII are discussed.