Chlorophyll Biosynthesis

Four-day-old etiolated cucumber seedlings (Cucumis sativus L.) were transferred to cool-white-fluorescent light (15 µmol m -2 s -1 ) for 1 h and 24 hours and etiochloroplasts and chloroplasts were isolated from developing cotyledons. Plastids were fractionated to stroma, envelope and thylakoid or inner membranes and the pigment contents of all these different fractions were analysed. In intact cucumber chloroplast protochlorophyllide was present in significant amounts whereas protoporphyrin IX and Mg-protoporphyrin plus its monoester were present only in very small quantities. Out of the total chloroplastic protochlorophyllide pool 1.0 % was partitioned to envelope membranes and 99.0 % was partitioned to thylakoids. Stroma had only trace amounts of protochlorophyllide. In contrast to chloroplasts, etiochloroplasts had, besides protochlorophyllide, significant amounts of other chlorophyll biosynthetic intermediates. In etiochloroplasts, protoporphyrin IX primarily partitioned to inner membranes (59.1 %) followed by stroma (37.7 %) and envelope (3.21 %). The content of Mg-protoporphyrin IX plus its monoester in different subplastidic fractions was 74.4 % for inner membranes, 22.58 % for stroma and 3.02 % for envelope. Protochlorophyllide primarily partitioned to inner membranes (95.79 %), followed by envelope (4.15 %) and, to a negligible extent (0.06 %), into stroma. The sub-plastidic distribution of chlorophyll biosynthetic intermediates in etiochloroplasts was, therefore, different than that of chloroplasts. The significance of differential distribution of chlorophyll biosynthetic intermediates among thylakoids, envelope and stroma in developing and mature plastids is discussed in relation to chloroplast biogenesis.

Chlorophyll biosynthesis in plants is subjected to modulation by various environmental factors. To understand the modulation of the chlorophyll (Chl) biosynthesis during greening process by salt, 100-200 mM NaCl was applied to the roots of etiolated rice seedlings 12 h prior to the transfer to light. Application of 200 mM NaCl to rice seedlings that were grown in light for further 72 h resulted in reduced dry matter production (-58%) and Chl accumulation (-66%). Ionic imbalance due to salinity stress resulted in additional downregulation (41-45%) of seedling dry weight, Chl and carotenoid contents over and above that of similar osmotic stress induced by polyethylene glycol. Downregulation of Chl biosynthesis may be attributed to decreased activities of Chl biosynthetic pathway enzymes, i.e. 5-aminolevulinic acid (ALA) dehydratase (EC-2.4.1.24), porphobilinogen deaminase (EC-4.3.1.8), coproporphyrinogen III oxidase (EC-1.3.3.3), protoporphyrinogen IX oxidase (EC-1.3.3.4), Mg-protopor...

Four-day-old etiolated cucumber seedlings (Cucumis sativus L.) were transferred to cool-white-fluorescent light (15 µmol m -2 s -1 ) for 1 h and 24 hours and etiochloroplasts and chloroplasts were isolated from developing cotyledons. Plastids were fractionated to stroma, envelope and thylakoid or inner membranes and the pigment contents of all these different fractions were analysed. In intact cucumber chloroplast protochlorophyllide was present in significant amounts whereas protoporphyrin IX and Mg-protoporphyrin plus its monoester were present only in very small quantities. Out of the total chloroplastic protochlorophyllide pool 1.0 % was partitioned to envelope membranes and 99.0 % was partitioned to thylakoids. Stroma had only trace amounts of protochlorophyllide. In contrast to chloroplasts, etiochloroplasts had, besides protochlorophyllide, significant amounts of other chlorophyll biosynthetic intermediates. In etiochloroplasts, protoporphyrin IX primarily partitioned to inner membranes (59.1 %) followed by stroma (37.7 %) and envelope (3.21 %). The content of Mg-protoporphyrin IX plus its monoester in different subplastidic fractions was 74.4 % for inner membranes, 22.58 % for stroma and 3.02 % for envelope. Protochlorophyllide primarily partitioned to inner membranes (95.79 %), followed by envelope (4.15 %) and, to a negligible extent (0.06 %), into stroma. The sub-plastidic distribution of chlorophyll biosynthetic intermediates in etiochloroplasts was, therefore, different than that of chloroplasts. The significance of differential distribution of chlorophyll biosynthetic intermediates among thylakoids, envelope and stroma in developing and mature plastids is discussed in relation to chloroplast biogenesis.

Protochlorophyllide oxidoreductase is an important photo-enzyme in angiosperms that needs light as a substrate for the synthesis of chlorophylls. Therefore, angiosperms cannot green in dark although several algae and lower green plants can synthesize chlorophyll in dark due to the presence of light-independent protochlorophyllide oxidoreductase (LIPOR). In response to climate change, during the great oxygenation event light-dependent protochlorophyllide oxidoreductase (LPOR) evolved due to the O 2 -induced selection pressure that inactivated the oxygen-sensitive LIPOR. Increased O 2 concentration, changing light quality and quantity at different depths of ocean, gene reorganization during several endosymbiotic events, selective LIPOR gene loss and multiple duplication events played a major role in the evolution and diversification of LPOR and its isoforms in phototrophs. Phylogenetic studies indicate that LPOR genes have been overwhelmingly horizontally transferred between phototrophs and also non phototrophic organisms. Presence of LPOR in non-photosynthetic organisms, Mycobacterium and certain fungi suggests that LPOR may have some other reductive functions in these organisms.

Stroma, envelope and thylakoid membranes were prepared from chloroplasts isolated from leaves of Beta vulgaris. Out of total plastidic protochlorophyllide, envelope membranes contained 1.5%, thylakoids had the maximum 98.48% and stroma had a trace fraction of 0.02%. Distribution of the Mg-protoporphyrin IX and its monoester was 89.0% in thylakoids, 10.0% in stroma and 1.0% in envelope. A substantial fraction (33.77%) of plastidic protoporphyrin IX was partitioned into stroma. Envelope contained 0.66% and thylakoids had 65.57% of the total plastidic protoporphyrin IX pool. The proportion of monovinyl and divinyl forms of protochlorophyllide was almost similar in intact plastid, thylakoids, and outer and inner envelope membranes suggesting a tight regulation of vinyl reductase enzyme. The significance of differential distribution of chlorophyll biosynthetic intermediates among thylakoids, envelope and stroma is discussed.

Tomato (Solanum lycopersicum Mill.) is one of the widely cultured vegetables under protected cultivation, in which insufficient light is one of the major factors that limit its growth, yield, and quality. Chlorophyll b (Chl b) is exclusively present in the light-harvesting complex (LHC) of photosystems, while its synthesis is strictly regulated in response to light conditions in order to control the antenna size. Chlorophyllide a oxygenase (CAO) is the sole enzyme that converts Chl a to Chl b for Chl b biosynthesis. Previous studies have shown that overexpressing CAO without the regulating domain (A domain) in Arabidopsis overproduced Chl b. However, the growth characteristics of the Chl b overproduced plants under different light environmental conditions are not well studied. Considering tomatoes are light-loving plants and sensitive to low light stress, this study aimed to uncover the growth character of tomatoes with enhanced production of Chl b. The A domain deleted Arabidopsis ...

Chlorophyll-a (chla) is a source of water pollution. Monitoring the quality of water in reservoirs is necessary to take any action for protecting the water quality. Traditional methods of sampling are usually costly and time consuming. Also they need skillful labors and some areas are out of reach or sampling at those areas is dangerous. Remote sensing technology could solve problems of high cost, time consuming and unavailability of traditional sampling methods. Landsat 7 imagery is a suitable resource of data because it has been using since a long time ago and could be used to analyze past events. This research aims to investigate the possibility of eutrophication assessment in Acbatan reservoir (pool) using remote sensing images. Field data of the study such as chla were collected in 2010. To reach this aim first the Top of Atmosphere (TOA) reflectance of imagery was calculated for each band. Then the relationship between concentration of chla and reflectance values was determined. Different conversions were applied on reflectance values at the next step to find the best regression equation for estimating the concentration of chla. The best model for estimating the concentration of chla was based on the band ratios. The values of R 2 Adj and SE are 0.91 and 0.04 respectively for this model. Based on the results of this research Landsat 7 is capable of reflecting the eutrophication problem in a small reservoir (pool) as Acbatan.

Plant development is regulated by external and internal factors such as light and chloroplast development. A revertant of the Arabidopsis thaliana (L.) Heyhn. chloroplast biogenesis mutant snowy cotyledon 3 (sco3–1) was isolated partially recovering the impaired chloroplast phenotype. The mutation was identified in the Phytochrome B (PhyB) gene and is a result of an amino acid change within the PAS repeat domain required for light-induced nuclear localisation. An independent phyB-9 mutation was crossed into sco3–1 mutants, resulting in the same partial reversion of sco3–1. Further analysis demonstrated that SCO3 and PhyB influence the greening process of seedlings and rosette leaves, embryogenesis, rosette formation and flowering. Interestingly, the functions of these proteins are interwoven in various ways, suggesting a complex genetic interaction. Whole-transcriptome profiling of sco3–1phyB-9 indicated that a completely distinct set of genes was differentially regulated in the dou...

Role of porphyrin-binding by Gun4 protein 2 Background: The Gun4 protein stimulates activity of Mg-chelatase and it is important for chlorophyll biosynthesis. Results: Mechanism of porphyrin-binding by Gun4 was proposed and a Gun4 mutant characterized in detail. Conclusion: Gun4 controls substrate-channeling into chlorophyll biosynthesis. Significance: For the first time in silico, in vitro and in vivo data were integrated to explain the function of Gun4 protein.

Plant development is regulated by external and internal factors such as light and chloroplast development. A revertant of the Arabidopsis thaliana (L.) Heyhn. chloroplast biogenesis mutant snowy cotyledon 3 (sco3-1) was isolated partially recovering the impaired chloroplast phenotype. The mutation was identified in the Phytochrome B (PhyB) gene and is a result of an amino acid change within the PAS repeat domain required for light-induced nuclear localisation. An independent phyB-9 mutation was crossed into sco3-1 mutants, resulting in the same partial reversion of sco3-1. Further analysis demonstrated that SCO3 and PhyB influence the greening process of seedlings and rosette leaves, embryogenesis, rosette formation and flowering. Interestingly, the functions of these proteins are interwoven in various ways, suggesting a complex genetic interaction. Whole-transcriptome profiling of sco3-1phyB-9 indicated that a completely distinct set of genes was differentially regulated in the double mutant compared with the single sco3-1 or phyB-9 mutants. Thus, we hypothesise that PhyB and SCO3 genetically suppress each other in plant and chloroplast development.

Flowering plants (angiosperms) can grow at extreme altitudes, and have been observed growing as high as 6,400 metres above sea level1,2; however, the molecular mechanisms that enable plant adaptation specifically to altitude are unknown. One distinguishing feature of increasing altitude is a reduction in the partial pressure of oxygen (pO2). Here we investigated the relationship between altitude and oxygen sensing in relation to chlorophyll biosynthesis—which requires molecular oxygen3—and hypoxia-related gene expression. We show that in etiolated seedlings of angiosperm species, steady-state levels of the phototoxic chlorophyll precursor protochlorophyllide are influenced by sensing of atmospheric oxygen concentration. In Arabidopsis thaliana, this is mediated by the PLANT CYSTEINE OXIDASE (PCO) N-degron pathway substrates GROUP VII ETHYLENE RESPONSE FACTOR transcription factors (ERFVIIs). ERFVIIs positively regulate expression of FLUORESCENT IN BLUE LIGHT (FLU), which represses th...

In spite of multiple studies elucidating the regulatory pathways controlling chlorophyll biosynthesis and photosynthetic activity, little is known about the molecular mechanism regulating cold-induced chlorosis in higher plants. Herein the characterization of the maize inbred line A661 which shows a cold-induced albino phenotype is reported. The data show that exposure of seedlings to low temperatures during early leaf biogenesis led to chlorophyll losses in this inbred. A661 shows a high plasticity, recovering resting levels of photosynthesis activity when exposed to optimal temperatures. Biochemical and transcriptome data indicate that at suboptimal temperatures chlorophyll could not be fully accommodated in the photosynthetic antenna in A661, remaining free in the chloroplast. The accumulation of free chlorophyll activates the expression of an early light inducible protein (elip) gene which binds chlorophyll to avoid cross-reactions that could lead to the generation of harmful reactive oxygen species. Higher levels of the elip transcript were observed in plants showing a cold-induced albino phenotype. Forward genetic analysis reveals that a gene located on the short arm of chromosome 2 regulates this protective mechanism.

Tomato (Solanum lycopersicum Mill.) is one of the widely cultured vegetables under protected cultivation, in which insufficient light is one of the major factors that limit its growth, yield, and quality. Chlorophyll b (Chl b) is exclusively present in the light-harvesting complex (LHC) of photosystems, while its synthesis is strictly regulated in response to light conditions in order to control the antenna size. Chlorophyllide a oxygenase (CAO) is the sole enzyme that converts Chl a to Chl b for Chl b biosynthesis. Previous studies have shown that overexpressing CAO without the regulating domain (A domain) in Arabidopsis overproduced Chl b. However, the growth characteristics of the Chl b overproduced plants under different light environmental conditions are not well studied. Considering tomatoes are light-loving plants and sensitive to low light stress, this study aimed to uncover the growth character of tomatoes with enhanced production of Chl b. The A domain deleted Arabidopsis ...

In the present studies, we have found a fragment of amino acid sequence, called TFT motif, both in light-dependent protochlorophyllide oxidoreductase (LPOR) and in the L subunit of dark-operative (light-independent) protochlorophyllide oxidoreductases (DPOR). Amino acid residues of this motif shared similar physicochemical properties in both types of the enzymes. In the present paper, physicochemical properties of amino acid residues of this common motif, its spatial arrangement and a possible physiological role are being discussed. This is the first report when similarity between LPOR and DPOR, phylogenetically unrelated, but functionally redundant enzymes, is described.

Chlorophyll (Chl) biosynthesis in chill (7°C)- and heat (42°C)-stressed cucumber (Cucumis sativus L. cv poinsette) seedlings was affected by 90 and 60%, respectively. Inhibition of Chl biosynthesis was partly due to impairment of 5-aminolevulinic acid biosynthesis both in chill- (78%) and heat-stress (70%) conditions. Protochlorophyllide (Pchlide) synthesis in chill- and heat-stressed seedlings was inhibited by 90 and 70%, respectively. Severe inhibition of Pchlide biosynthesis in chill-stressed seedlings was caused by inactivations of all of the enzymes involved in protoporphyrin IX (Proto IX) synthesis, Mg-chelatase, and Mg-protoporphyrin IX monoester cyclase. In heat-stressed seedlings, although 5-aminolevulinic acid dehydratase and porphobilinogen deaminase were partially inhibited, one of the porphyrinogen-oxidizing enzymes, uroporphyrinogen decarboxylase, was stimulated and coproporphyrinogen oxidase and protoporphyrinogen oxidase were not substantially affected, which demonst...

Crowth and photosynthesis of wheat (Triticum aestivum 1. cv Super DwarO plants grown onboard the space shuttle Discovery for 10 d were examined. Compared to ground control plants, the shoot fresh weight of space-grown seedlings decreased by 25%. Postflight measurements of the O, evolution/photosynthetic photon flux density response curves of leaf samples revealed that the C0,-saturated photosynthetic rate at saturating light intensities in space-grown plants declined 25% relative to the rate in ground control plants. l h e relative quantum yield of C0,-saturated photosynthetic O, evolution measured at limiting light intensities was not significantly affected. In space-grown plants, the light compensation point of the leaves increased by 33%, which likely was dueto an increase (27%) in leaf dark-respiration rates. Related experiments with thylakoids isolated from space-grown plants showed that the light-saturated photosynthetic electron transport rate from H,O through photosystems I1 and I was reduced by 28%. These results demonstrate that photosynthetic functions are affected by the microgravity environment.

Cucumber (Cucumis sativus L., cv Poinsette) plants were sprayed with 20 millimolar 5-aminolevulinic acid and then incubated in the dark for 14 hours. The intact chloroplasts were isolated from the above plants in the dark and were exposed to weak light (250 micromoles per square meter per second). Within 30 minutes, photosystem 11 activity was reduced by 50%. The singlet oxygen (102) scavengers, histidine and sodium azide (NaN3) significantly protected against the damage caused to photosystem II. The hydroxyl radical scavenger formate failed to protect the thylakoid membranes. The production of 102 monitored as N,N-dimethyl p-nitrosoaniline bleaching increased as a function of light exposure time of treated chloroplasts and was abolished by the 102 quencher, NaN3. Membrane lipid peroxidation monitored as malondialdehyde production was also significantly reduced when chloroplasts were illuminated in the presence of NaN3 and histidine. Protochlorophyllide was the most abundant pigment accumulated in intact chloroplasts isolated from 5-aminolevulinic acid-treated plants and was probably acting as type 11 photosensitizer.

The cucumber (Cucumis sativus L.) plants were sprayed with 20 mM 5-aminolevulinic acid or distilled water (control) and incubated in dark for 14 hr. The thylakoid membranes prepared from the intact chloroplasts, isolated from the above plants in dark, were illuminated with low light intensity (100 W/m2) for 30 min. Due 10 photodynamic reactions, the photochemical function of photosystem II was damaged by 50% in treated thylakoids whereas it was only slightly (8%) affected in control thylakoids. The photosystem I was, however, not affected. The exogenous electron donors, MnCI2, diphenyl carbazide and NH20H failed to restore the photosystem II activity suggesting that the photodynamic damage had taken place very close to photosystem II reaction center. Singlet oxygen scavenger, histidine, could protect the photosystem II activity while superoxide radical scavengers, superoxide dismutase and 1, 2-dihydroxybenzene-3, 5-disulphonic acid disodium salt, and hydroxyl radical scavenger, formate, failed to protect the same.

Chlorophyll b is synthesized by the oxidation of a methyl group on the B ring of a ttrapyrrole molecule to a formyl group by chlorophyllide a oxygenase (CAO). The full length CAO, from Arabidopsis thaliana was overexpressed in tobacco (Nicotiana tabacum) that grows well at light intensities much higher than those tolerated by Arabidopsis. This resulted in an increased synthesis of glutamate semialdehyde, 5-aminolevulinicacid, Mg-porphyrins and chlorophylls. Overexpression of CAO resulted in increased chlorophyll b synthesis and a decreased chlorophyll a/b ratio in low-light-grown as well as in high-light-grown tobacco plants; this effect was, however, more pronounced in high-light. The increased potential of the protochlorophyllide oxidoreductase activity and chlorophyll biosynthesis compensated for the usual loss of chlorophylls in high light. Increased chlorophyll b synthesis in CAO-overexpressed plants was accompanied not only by an increased abundance of light-harvesting chlorop...

The reverse transcriptase polymerase chain reaction (RT-PCR) is an extremely sensitive technique for detecting RNA transcripts. Real-time RT-PCR using fluorescent dyes and instruments such as the Roche Lightcycler allows real-time kinetic quantification of transcript levels. Here we report a method for the relative quantification of RNA transcripts using real-time RT-PCR that gives results comparable to Northern blotting utilizing 10-100 fold less RNA. We have also optimized a method for the rapid and efficient extraction of RNA from Chlamydomonas reinhardtii. The method is more rapid than other methods tested, allows simultaneous processing of multiple samples, and yields reproducible quantities of total RNA from a fixed number of cells. In addition the purified total RNA is of high quality and polyA-mRNA can be easily isolated. Using these methods we found that the pattern of changes in RNA transcript levels of the magnesium chelatase (Mg-chelatase) genes, chlH, chlD and chlI, of ...

Plastids are specialized organelles found in plants, which are endowed with their own genomes, and differ in many respects from the intracellular compartments of organisms belonging to other kingdoms of life. They differentiate into diverse, plant organ-specific variants, and are perhaps the most versatile organelles known. Chloroplasts are the green plastids in the leaves and stems of plants, whose primary function is photosynthesis. In response to environmental changes, chloroplasts use several mechanisms to coordinate their photosynthetic activities with nuclear gene expression and other metabolic pathways. Here, we focus on a redox-based regulatory network composed of thioredoxins (TRX) and TRX-like proteins. Among multiple redox-controlled metabolic activities in chloroplasts, tetrapyrrole biosynthesis is particularly rich in TRX-dependent enzymes. This review summarizes the effects of plastid-localized reductants on several enzymes of this pathway, which have been shown to und...

The adaptive responses of the greening process of plants to temperature stress were studied in cucumber (Cucumis sativus L. cv. Poinsette) seedlings grown at ambient (25°C), low (7°C) and high (42°C) temperatures. Plastids isolated from these seedlings were incubated at dierent temperatures and the net syntheses of various tetrapyrroles were monitored. In plastids isolated from control seedlings grown at 25°C, the optimum temperature for synthesis of Mg-protoporphyrin IX monoester or protochlorophyllide was 35°C. Temperature maxima for Mg-protoporphyrin IX monoester and protochlorophyllide syntheses were shifted to 30°C in chill-stressed seedlings. The net synthesis of total tetrapyrroles was severely reduced in heat-stressed seedlings and the optimum temperature for Mg-protoporphyrin IX monoester or protochlorophyllide synthesis shifted slightly towards higher temperatures, i.e. a broader peak was observed. To further study the temperature acclimation of seedlings with respect to the greening process, tetrapyrrole biosynthesis was monitored at 25°C after pre-heating the plastids (28± 70°C) isolated from control, chill-and heat-stressed seedlings. In comparison to 28°C-pre-heated plastids the percent inhibition of protochlorophyllide synthesis in 40°C-pre-heated plastids was higher than for the control (25°C-grown) in chill-stressed seedlings and lower than for the control in heat-stressed seedlings. Maximum synthesis of total tetrapyrroles and protoporphyrin IX was observed when chloroplasts were heated at 50°C, which was probably due to heatinduced activation of the enzymes involved in protoporphyrin IX synthesis. Prominent shoulders towards lower or higher temperatures were seen in chill-stressed or heat-stressed seedlings, respectively. The shift in optimum temperature for tetrapyrrole biosynthesis in chill-and heat-stressed seedlings was probably due to acclimation of membranes possibly undergoing desaturation or saturation of membrane lipids. Proteins synthesized in response to temperature-stress may also play an important role in conferring stress-tolerance in plants.

A homology model of NADPH:protochlorophyllide (Pchlide) oxidoreductase A (POR; E.C. 1.3.33.1) of barley is developed and verified by site-directed mutagenesis. PORA is considered a globular protein consisting of nine α-helices and seven β-strands. The model predicts the presence of two functionally distinctive Pchlide binding sites where the pigment is coordinated by cystein residues. The pigment bound to the first, high-affinity Pchlide binding site is used for the formation of the photoactive state of the enzyme. The pigment bound to the second, low-affinity Pchlide binding site is involved in the PORA:PORB interaction, allowing for resonance energy transfer between the neighboring PORs in the complex. In the in vitro reconstituted light-harvesting POR:Pchlide complex (LHPP), light absorbed by PORA-bound Pchlide b is transferred to PORB-bound Pchlide a . That induces the conversion of Pchlide a to chlorophyllide (Chlide) a . This energy transfer eliminates the possibility of Pchli...

Cytochromes are important components of photosynthetic electron transport chain. Here we report on genetic transformation of Cytochrome c 6 (UfCyt c 6) gene from Ulva fasciata Delile in tobacco for enhanced photosynthesis and growth. UfCyt c 6 cDNA had an open reading frame of 330 bp encoding a polypeptide of 109 amino acids with a predicted molecular mass of 11.65 kDa and an isoelectric point of 5.21. UfCyt c 6 gene along with a tobacco petE transit peptide sequence under control of CaMV35S promoter was transformed in tobacco through Agrobacterium mediated genetic transformation. Transgenic tobacco grew normal and exhibited enhanced growth as compared to wild type (WT) and vector control (VC) tobacco. Transgenic tobacco had higher contents of photosynthetic pigments and better ratios of photosynthetic pigments. The tobacco expressing UfCyt c 6 gene exhibited higher photosynthetic rate and improved water use efficiency. Further activity of the water-splitting complex, photosystem II quantum yield, photochemical quenching, electron transfer rate, and photosynthetic yield were found comparatively higher in transgenic tobacco as compared to WT and VC tobacco. Alternatively basal quantum yield of non-photochemical processes in PSII and non-photochemical quenching were estimated lower in tobacco expressing UfCyt c 6 gene. As a result of improved photosynthetic performance the transgenic tobacco had higher contents of sugar and starch, and exhibited comparatively better growth. To the best of our knowledge this is the first report on expression of UfCyt c 6 gene from U. fasciata for improved photosynthesis and growth in tobacco.

Role of porphyrin-binding by Gun4 protein 2 Background: The Gun4 protein stimulates activity of Mg-chelatase and it is important for chlorophyll biosynthesis. Results: Mechanism of porphyrin-binding by Gun4 was proposed and a Gun4 mutant characterized in detail. Conclusion: Gun4 controls substrate-channeling into chlorophyll biosynthesis. Significance: For the first time in silico, in vitro and in vivo data were integrated to explain the function of Gun4 protein.

Tomato and cucumber seedlings were grown in a growth chamber to evaluate the effects of different cycles of light–dark exposure conditions (T0 (control treatment) (1 cycle of 24 h distributed in 18 h of light exposure and six hours of dark), T1 (two cycles of 12 h distributed in nine hours of light exposure and three hours of dark) and T2 (three cycles of eight hours distributed in six hours of light exposure and two hours of dark) on growth, nutrient status, pigment concentration and physiological changes. Total dry weight showed different behaviors in both species, since in tomato the total dry weight remained unchanged under varying light–dark cycles, whereas in cucumber seedlings there was a clear decrease compared to the control treatment. In both species, plants grown under T2 showed the best water content. Nitrogen, P and K content—as well as partitioning in the different organs of the plants—displayed different patterns under varying cycles of light–dark conditions in both s...

This research compared the chlorophyll biosynthetic and degradation pathways, pigment-protein complexes, and thylakoid morphology of a mature oval-pointed cecidomyiid gall and the infected leaf of host plant Machilus thunbergii Sieb & Zucc (Lauraceae). The mature gall always possesses far less photosynthetic pigment than the infected leaf. The content of anthocyanin and tannin of the gall are much higher than in the infected leaf. Both the mole percent of porphyrin and the ratio of pheophytin/chlorophyllide are much different between the gall and infected leaf, suggesting their chlorophyll biosynthetic and degradation pathways are much different. While the infected leaf may take the degradation pathway of chlorophyll®pheophytin®pheophorbide as the major route, the cicedomyiid gall may take chlorophyll®chlorophyllide®pheophorbide as the major route. The infected leaf still possesses the CPI and CPII pigment-protein complexes fractionated by Thornber system, or the A1, AB1, AB2, AB3 p...

In the present studies, we have found a fragment of amino acid sequence, called TFT motif, both in light-dependent protochlorophyllide oxidoreductase (LPOR) and in the L subunit of dark-operative (light-independent) protochlorophyllide oxidoreductases (DPOR). Amino acid residues of this motif shared similar physicochemical properties in both types of the enzymes. In the present paper, physicochemical properties of amino acid residues of this common motif, its spatial arrangement and a possible physiological role are being discussed. This is the first report when similarity between LPOR and DPOR, phylogenetically unrelated, but functionally redundant enzymes, is described.

Barley (Hordeum vulgare) has been widely used as a model crop for studying molecular and physiological processes such as chloroplast development and photosynthesis. During the second half of the 20th century, mutants such as albostrians led to the discovery of the nuclear-encoded, plastid-localized RNA polymerase and the retrograde (chloroplast-to-nucleus) signalling communication pathway, while chlorina-f2 and xantha mutants helped to shed light on the chlorophyll biosynthetic pathway, on the light-harvesting proteins and on the organization of the photosynthetic apparatus. However, during the last 30 years, a large fraction of chloroplast research has switched to the more “user-friendly” model species Arabidopsis thaliana, the first plant species whose genome was sequenced and published at the end of 2000. Despite its many advantages, Arabidopsis has some important limitations compared to barley, including the lack of a real canopy and the absence of the proplastid-to-chloroplast ...

Chlorophyll (Chl) b is synthesized by oxidation of a methyl group on the B ring of the porphyrin molecule to a formyl group by chlorophyllide (Chlide) a oxygenase (CAO). The overexpression of Arabidopsis thaliana full length CAO (AtCAO) in tobacco (Nicotiana tabacum) resulted in an increased Chl synthesis and a decreased Chl a/b ratio in low-light-grown (LL) as well as in highlight grown (HL) tobacco plants, where the effect was more pronounced. In HL-plants, increased [Chl b] resulted in efficient capture of solar energy and enhanced (40%-80%) electron transport rates at both limiting and saturating light intensities.

To study if etiolation symptoms exist in plants grown under natural illumination conditions, under-soil epicotyl segments of light-grown pea (Pisum sativum) plants were examined and compared to those of hydroponically dark-grown plants. Light-, fluorescence-and electron microscopy, 77 K fluorescence spectroscopy, pigment extraction and pigment content determination methods were used. Etioplasts with prolamellar bodies and/or prothylakoids, protochlorophyll (Pchl) and protochlorophyllide (Pchlide) forms (including the flash-photoactive 655 nm emitting form) were found in the (pro)chlorenchyma of epicotyl segments under 3 cm soil depth; their spectral properties were similar to those of hydroponically grown seedlings. However, differences were found in etioplast sizes and Pchlide:Pchl molar ratios, which indicate differences in the developmental rates of the under-soil and of hydroponically developed cells. Tissue regions closer to the soil surface showed gradual accumulation of chlorophyll, and in parallel, decrease of Pchl and Pchlide. These results proved that etioplasts and Pchlide exist in soil-covered parts of seedlings even if they have a 3-4-cm long photosynthetically active shoot above the soil surface. This underlines that etiolation symptoms do develop under natural growing conditions, so they are not merely artificial, laboratory phenomena. Consequently, dark-grown laboratory plants are good models to study the early stages of etioplast differentiation and the Pchlide-chlorophyllide phototransformation.

The key regulatory enzyme of chlorophyll biosynthesis in higher plants, the light-dependent NADPH:protochlorophyllide oxidoreductase (POR), is a nuclear-encoded plastid protein. Its post-translational transport into plastids is determined by its substrate. The.precursor of POR (pPOR) is taken up and processed to mature size by plastids only in the presence of protochlorophyllide (Pchlide). In etioplasts, the endogenous level of Pchlide saturates the

We explored the interaction between radiation of different wavelength and jasmonic acid (JA) or brassinosteroids (BR) on leaf senescence-induced oxidative stress. Three approaches were used: 1) jasmonic acid insensitive1-1 (jai1-1) and brassinosteroid-deficient [dumpy (dpy)] mutants were treated with red (R) or far-red (FR) radiation; 2) phytochromedeficient aurea (au) and high pigment-1 (hp-1) (radiation exaggerated response) mutants were treated with methyl jasmonate (MeJA) or epibrassinolide (epiBL); and 3) double mutants au jai1-1 and au dpy were produced. Leaf chlorophyll content, lipid peroxidation, and antioxidant enzyme activities were determined. After senescence induction in detached leaves, we verified that the patterns of chlorophyll degradation of hormonal and photomorphogenic mutants were not significantly different in comparison with original cv. Micro-Tom (MT). Moreover, there was no significant change in lipid peroxidation measured as malondialdehyde (MDA) production, as well as catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) activities in the hormonal mutants. Exogenous BR increased CAT and APX activities in MT, au, and hp-1. As concerns the double mutants, severe reduction in H 2 O 2 production which was not accompanied by changes in MDA content, and CAT and APX activities was observed during senescence in au dpy. The results suggest that JA and BR do not participate in light signaling pathway during leaf senescence-induced oxidative stress.

Chlorophyll b is synthesized by the oxidation of a methyl group on the B ring of a ttrapyrrole molecule to a formyl group by chlorophyllide a oxygenase (CAO). The full length CAO, from Arabidopsis thaliana was overexpressed in tobacco (Nicotiana tabacum) that grows well at light intensities much higher than those tolerated by Arabidopsis. This resulted in an increased synthesis of glutamate semialdehyde, 5-aminolevulinicacid, Mg-porphyrins and chlorophylls. Overexpression of CAO resulted in increased chlorophyll b synthesis and a decreased chlorophyll a/b ratio in low-light-grown as well as in high-light-grown tobacco plants; this effect was, however, more pronounced in high-light. The increased potential of the protochlorophyllide oxidoreductase activity and chlorophyll biosynthesis compensated for the usual loss of chlorophylls in high light. Increased chlorophyll b synthesis in CAO-overexpressed plants was accompanied not only by an increased abundance of light-harvesting chlorop...

Crystalline inclusions occur in the cytoplasm of healthy cells in many plant species and represent protein storage structures or the accumulation of fraction-I protein or enzymes. The inclusions are of various sizes and shapes and have been found in cell constituents such as spherosomes, mitochondria and plastids (Marinos, 1967; Martelli and Russo, 1977; Newcomb, 1967). Crystalloids have often been observed in the plastids of bean leaves treated with hypertonic solutions or poisonous gases (Shumway et al., 1967; Gunning et al., 1968; Wrischer, 1973). There are cases in which ordinary crystalline cell contituents are much more abundant in diseased than in healthy cells. Esau (1975) related the higher number of the intraplastidial protein crystals, found in yirus infected cells in spinach, as compared to healthy cells, to an effect of the causal agent on the metabolism and sugar translocation in leaves. The results of cytological studies carried out to determine numerical and morpholo...

To study if etiolation symptoms exist in plants grown under natural illumination conditions, under-soil epicotyl segments of light-grown pea (Pisum sativum) plants were examined and compared to those of hydroponically dark-grown plants. Light-, fluorescence-and electron microscopy, 77 K fluorescence spectroscopy, pigment extraction and pigment content determination methods were used. Etioplasts with prolamellar bodies and/or prothylakoids, protochlorophyll (Pchl) and protochlorophyllide (Pchlide) forms (including the flash-photoactive 655 nm emitting form) were found in the (pro)chlorenchyma of epicotyl segments under 3 cm soil depth; their spectral properties were similar to those of hydroponically grown seedlings. However, differences were found in etioplast sizes and Pchlide:Pchl molar ratios, which indicate differences in the developmental rates of the under-soil and of hydroponically developed cells. Tissue regions closer to the soil surface showed gradual accumulation of chlorophyll, and in parallel, decrease of Pchl and Pchlide. These results proved that etioplasts and Pchlide exist in soil-covered parts of seedlings even if they have a 3-4-cm long photosynthetically active shoot above the soil surface. This underlines that etiolation symptoms do develop under natural growing conditions, so they are not merely artificial, laboratory phenomena. Consequently, dark-grown laboratory plants are good models to study the early stages of etioplast differentiation and the Pchlide-chlorophyllide phototransformation.

Senescence is a ubiquitous characteristic in the biological world. From an ontogenetic perspective, senescence is now established as a developmental and genetic program acquired during evolution (Wojciechowska et al., 2018). Like in other organisms, senescence in plants is genetically programmed (Nam, 1997; van Doorn and Woltering, 2004; Wojciechowska et al., 2018). In plants, senescence is a prelude to cell (organ) death, and during this process metabolites and macromolecules released are salvaged for utilization by the plant for growth. Generally, senescence occurs prior to programmed cell death (PCD), since symptomatic leaf yellowing can be reversed based on the timing of senescence while PCD is a terminal, irreversible program. It has been suggested that the term "PCD" in plants should be restricted to the specific stage of intrinsic senescence program when it has reached a "point of no return" and leaf yellowing is no longer reversible (Mattoo and Handa, 2003). Programmed cell death in plants was described as a sequential process that included apoptosis-like necrosis and autophagy (van Doorn et al., 2011). Autophagy under normal growth conditions favors turnover of cellular components for maintaining homeostasis,

Cell-free extracts prepared from the leaves of etiolated red kidney bean (Phaseolus vulgaris) seedlings contain an enzyme which degrades Mg protoporphyrin monoester (Mg Proto ester). The activity is O2~iependent, heatlabile, and has a pH optimum at 7.5. The enzyme has been partially purified by gel filtration on Sephadex G-25. It is suggested that this enzyme may play a role in porphyrin turnover.

The process of chloroplast biogenesis requires a multitude of pathways and processes to establish chloroplast function. In cotyledons of seedlings, chloroplasts develop either directly from proplastids (also named eoplasts) or, if germinated in the dark, via etioplasts, whereas in leaves chloroplasts derive from proplastids in the apical meristem and are then multiplied by division. The snowy cotyledon 2, sco2, mutations specifically disrupt chloroplast biogenesis in cotyledons. SCO2 encodes a chloroplast-localized protein disulphide isomerase, hypothesized to be involved in protein folding. Analysis of co-expressed genes with SCO2 revealed that genes with similar expression patterns encode chloroplast proteins involved in protein translation and in chlorophyll biosynthesis. Indeed, sco2-1 accumulates increased levels of the chlorophyll precursor, protochlorophyllide, in both dark grown cotyledons and leaves. Yeast two-hybrid analyses demonstrated that SCO2 directly interacts with the chlorophyll-binding LHCB1 proteins, being confirmed in planta using bimolecular fluorescence complementation (BIFC). Furthermore, ultrastructural analysis of sco2-1 chloroplasts revealed that formation and movement of transport vesicles from the inner envelope to the thylakoids is perturbed. SCO2 does not interact with the signal recognition particle proteins SRP54 and FtsY, which were shown to be involved in targeting of LHCB1 to the thylakoids. We hypothesize that SCO2 provides an alternative targeting pathway for light-harvesting chlorophyll binding (LHCB) proteins to the thylakoids via transport vesicles predominantly in cotyledons, with the signal recognition particle (SRP) pathway predominant in rosette leaves. Therefore, we propose that SCO2 is involved in the integration of LHCB1 proteins into the thylakoids that feeds back on the regulation of the tetrapyrrole biosynthetic pathway and nuclear gene expression.

Chlorophyll-a (chla) is a source of water pollution. Monitoring the quality of water in reservoirs is necessary to take any action for protecting the water quality. Traditional methods of sampling are usually costly and time consuming. Also they need skillful labors and some areas are out of reach or sampling at those areas is dangerous. Remote sensing technology could solve problems of high cost, time consuming and unavailability of traditional sampling methods. Landsat 7 imagery is a suitable resource of data because it has been using since a long time ago and could be used to analyze past events. This research aims to investigate the possibility of eutrophication assessment in Ecbatan reservoir using remote sensing images. Field data of the study such as chla were collected in 2010. To reach this aim first the Top of Atmosphere (TOA) reflectance of imagery was calculated for each band. Then the relationship between concentration of chla and reflectance values was determined. Different conversions were applied on reflectance values at the next step to find the best regression equation for estimating the concentration of chla. The best model for estimating the concentration of chla was based on the band ratios. The values of R 2 Adj and SE are 0.91 and 0.04 respectively for this model. Based on the results of this research Landsat 7 is capable of reflecting the eutrophication problem in a small reservoir as Ecbatan.

The realization of manned missions for space exploration requires the development of Bioregenerative Life Support Systems (BLSSs) to make human colonies self-sufficient in terms of resources. Indeed, in these systems, plants contribute to resource regeneration and food production. However, the cultivation of plants in space is influenced by ionizing radiation which can have positive, null, or negative effects on plant growth depending on intrinsic and environmental/cultivation factors. The aim of this study was to analyze the effect of high-LET (Linear Energy Transfer) ionizing radiation on seed germination and seedling development in eye bean. Dry seeds of Dolichos melanophthalmus DC. (eye bean) were irradiated with two doses (1 and 10 Gy) of C- and Ti-ions. Seedlings from irradiated seeds were compared with non-irradiated controls in terms of morpho-anatomical and biochemical traits. Results showed that the responses of eye bean plants to radiation are dose-specific and dependent ...

Chlorophyll (Chl) b is synthesized by oxidation of a methyl group on the B ring of the porphyrin molecule to a formyl group by chlorophyllide (Chlide) a oxygenase (CAO). The overexpression of Arabidopsis thaliana full length CAO (AtCAO) in tobacco (Nicotiana tabacum) resulted in an increased Chl synthesis and a decreased Chl a/b ratio in low-light-grown (LL) as well as in highlight grown (HL) tobacco plants, where the effect was more pronounced. In HL-plants, increased [Chl b] resulted in efficient capture of solar energy and enhanced (40%-80%) electron transport rates at both limiting and saturating light intensities.

Chlorophyll b is synthesized by the oxidation of a methyl group on the B ring of a ttrapyrrole molecule to a formyl group by chlorophyllide a oxygenase (CAO). The full length CAO, from Arabidopsis thaliana was overexpressed in tobacco (Nicotiana tabacum) that grows well at light intensities much higher than those tolerated by Arabidopsis. This resulted in an increased synthesis of glutamate semialdehyde, 5-aminolevulinicacid, Mg-porphyrins and chlorophylls. Overexpression of CAO resulted in increased chlorophyll b synthesis and a decreased chlorophyll a/b ratio in low-light-grown as well as in high-light-grown tobacco plants; this effect was, however, more pronounced in high-light. The increased potential of the protochlorophyllide oxidoreductase activity and chlorophyll biosynthesis compensated for the usual loss of chlorophylls in high light. Increased chlorophyll b synthesis in CAO-overexpressed plants was accompanied not only by an increased abundance of light-harvesting chlorop...

Chlorophyll b is synthesized by the oxidation of a methyl group on the B ring of a tetrapyrrole molecule to a formyl group by chlorophyllide a oxygenase (CAO). The full-length CAO from Arabidopsis (Arabidopsis thaliana) was overexpressed in tobacco (Nicotiana tabacum) that grows well at light intensities much higher than those tolerated by Arabidopsis. This resulted in an increased synthesis of glutamate semialdehyde, 5-aminolevulinic acid, magnesium-porphyrins, and chlorophylls. Overexpression of CAO resulted in increased chlorophyll b synthesis and a decreased chlorophyll a/b ratio in low lightgrown as well as high light-grown tobacco plants; this effect, however, was more pronounced in high light. The increased potential of the protochlorophyllide oxidoreductase activity and chlorophyll biosynthesis compensated for the usual loss of chlorophylls in high light. Increased chlorophyll b synthesis in CAO-overexpressed plants was accompanied not only by an increased abundance of light-harvesting chlorophyll proteins but also of other proteins of the electron transport chain, which led to an increase in the capture of light as well as enhanced (40%-80%) electron transport rates of photosystems I and II at both limiting and saturating light intensities. Although the quantum yield of carbon dioxide fixation remained unchanged, the lightsaturated photosynthetic carbon assimilation, starch content, and dry matter accumulation increased in CAO-overexpressed plants grown in both low-and highlight regimes. These results demonstrate that controlled up-regulation of chlorophyll b biosynthesis comodulates the expression of several thylakoid membrane proteins that increase both the antenna size and the electron transport rates and enhance carbon dioxide assimilation, starch content, and dry matter accumulation.