Activity Of Chloroplasts Research Articles

Effect of galvanotaxic graphene oxide on chloroplast activity: Interaction quantified with Biolayer-Interferometry coupled confocal microscopy

The knowledge on the effect of graphene oxide (GO) on plants are limited to germination, growth, and toxicity. Since, chloroplast generates sugar by the reduction of CO2 with the optical stimulation through a series of electron transport chain and GO being the 2D material with electron transport property, it is reasonable to check their interaction. Here, the effect of GO without and with amine conjugation (AGO) having opposite charges were allowed to interact with chloroplast. The uptake is documented by using biolayer interferometry coupled with confocal imaging. The ex vivo chloroplast activity with GO and AGO has been tested and found that the GO treatment shows 1.3 times more activity than control. In contrast, AGO function as efficient electron conductor and cause imbalance in the redox beyond the capacity of the antioxidant rich chloroplast solute. Finally, in vivo toxicity has been evaluated in the spinach plants, which highlights the chance of AGO application as herbicide to remove any unwanted plants.

Cas9/gRNA-mediated genome editing of yeast mitochondria and Chlamydomonas chloroplasts.

We present a new approach to edit both mitochondrial and chloroplast genomes. Organelles have been considered off-limits to CRISPR due to their impermeability to most RNA and DNA. This has prevented applications of Cas9/gRNA-mediated genome editing in organelles while the tool has been widely used for engineering of nuclear DNA in a number of organisms in the last several years. To overcome the hurdle, we designed a new approach to enable organelle genome editing. The plasmids, designated “Edit Plasmids,” were constructed with two expression cassettes, one for the expression of Cas9, codon-optimized for each organelle, under promoters specific to each organelle, and the other cassette for the expression of guide RNAs under another set of promoters specific to each organelle. In addition, Edit Plasmids were designed to carry the donor DNA for integration between two double-strand break sites induced by Cas9/gRNAs. Each donor DNA was flanked by the regions homologous to both ends of the integration site that were short enough to minimize spontaneous recombination events. Furthermore, the donor DNA was so modified that it did not carry functional gRNA target sites, allowing the stability of the integrated DNA without being excised by further Cas9/gRNAs activity. Edit Plasmids were introduced into organelles through microprojectile transformation. We confirmed donor DNA insertion at the target sites facilitated by homologous recombination only in the presence of Cas9/gRNA activity in yeast mitochondria and Chlamydomonas chloroplasts. We also showed that Edit Plasmids persist and replicate in mitochondria autonomously for several dozens of generations in the presence of the wild-type genomes. Finally, we did not find insertions and/or deletions at one of the Cas9 cleavage sites in Chloroplasts, which are otherwise hallmarks of Cas9/gRNA-mediated non-homologous end joining (NHEJ) repair events in nuclear DNA. This is consistent with previous reports of the lack of NHEJ repair system in most bacteria, which are believed to be ancestors of organelles. This is the first demonstration of CRISPR-mediated genome editing in both mitochondria and chloroplasts in two distantly related organisms. The Edit Plasmid approach is expected to open the door to engineer organelle genomes of a wide range of organisms in a precise fashion.

Photochemical activity of chloroplasts of isogenic lines (E genes) of soybean (Glycine max (L.) Merr.) under different periods of red-light irradiation

The effect of different periods of red-light (RL, 660 nm) irradiation of plants on the biomass, leaf area, chlorophyll content, level of the Hill reaction and photophosphorylation in short-day (SD) and photoperiodical neutral (PhPN) lines of soybean have been studied in vegetation experiments. The objects of study were the isogenic lines (E genes) of soybean (Glycine max (L.) Merr.), Clark variety. The SD (E1E2E3) and PhPN lines (e1e2e3) were used. The plants were grown in a vegetation chamber in the soil culture (black soil). Plants of SD and PhPN lines were grown in 9 vessels of three liters volume. 10–12 plants were grown in each vessel. The constant growing conditions were provided during the experiment: temperature – 20–24/17–20°С (day/night), soil moisture – 60–70 % of the total soil moisture content, intensity of illumination – 20 klx, photoperiod duration – 10 hours. After 4–5 weeks of vegetation (after the second true leaf formation), plants of each line in three vessels were irradiated for 30 minutes with low intensity red light at the beginning (experiment 1) or in the middle of the dark period (experiment 2). The light diodes emitting in the region of 630±10 nm were used for plant irradiation. Other plants in three vessels of each line, which were not illuminated by the red light, were used as a control group. It was shown that under the short day the SD line in the control group passed to flowering 43±1.8 days after germination and PhPN line – 44±2.2 days after germination. The red-light irradiation, both before the beginning and in the middle of night, caused a delay of the transition to flowering in the SD line by 5±1 and 7±2.2 days, respectively. In the PhPN line, changing flowering period due to RL was not established. In the SD line, activation of the phytochromes by RL before the dark period caused an increase of the biomass, leaf area, total chlorophyll content, reduction of potassium ferrocyanide and photophosphorylation by isolated chloroplasts per chlorophyll of one leaf. While interruption of the night by RL caused decrease of these parameters and Hill reaction intensity per 1 mg of chlorophyll. The effect of RL on the studied parameters in the PhPN soybean line has not been detected.

Chloroplasts and Plant Immunity: Where Are the Fungal Effectors?

Chloroplasts play a central role in plant immunity through the synthesis of secondary metabolites and defense compounds, as well as phytohormones, such as jasmonic acid and salicylic acid. Additionally, chloroplast metabolism results in the production of reactive oxygen species and nitric oxide as defense molecules. The impact of viral and bacterial infections on plastids and chloroplasts has been well documented. In particular, bacterial pathogens are known to introduce effectors specifically into chloroplasts, and many viral proteins interact with chloroplast proteins to influence viral replication and movement, and plant defense. By contrast, clear examples are just now emerging for chloroplast-targeted effectors from fungal and oomycete pathogens. In this review, we first present a brief overview of chloroplast contributions to plant defense and then discuss examples of connections between fungal interactions with plants and chloroplast function. We then briefly consider well-characterized bacterial effectors that target chloroplasts as a prelude to discussing the evidence for fungal effectors that impact chloroplast activities.

The Sustainable Reasons of Controversy over the Mechanisms for the Stomatal Opening

Depending on the diversities of the plant species, the mechanisms of the stomatal opening are thought to be different. First, Paphiopedilum insigna var. sanderae do not have chloroplasts in the guard cells. However, the stomata of this plant function as normal. Plants lacking the chloroplasts in the guard cell imply that the chloroplasts in guard cells are not related to stomatal opening. The guard cells without chloroplasts cannot be the source cells of the photosynthetic products, and the guard cells must be act as the sink cells. Second, the distinctive features of guard cells are specialized cell walls, which are considerably thickened to 5 µm. In contrast, the thickness of mesophyll cell walls is less than 100 nm. In the guard cells, most of the photosynthetic products may be used for the production of cell walls. The low photosynthetic activities of chloroplasts in the guard cell cannot be sufficient to maintain the structures and functions of the guard cell walls. Third, 40~60 chloroplasts in the guard cell of Lilium longiflorum which is belong to angiosperm were found in the first time. Lilium longiflorum of the relationship with mesophyll cells cannot be completely excluded, but it is assumed that guard cell chloroplasts in Lilium longiflorum may play an important role for the stomatal opening.

PH-dependent cell\u2013cell interactions in the green alga Chara

Characean internodal cells develop alternating patterns of acid and alkaline zones along their surface in order to facilitate uptake of carbon required for photosynthesis. In this study, we used a pH-indicating membrane dye, 4-heptadecylumbiliferone, to study the kinetics of alkaline band formation and decomposition. The differences in growth/decay kinetics suggested that growth occurred as an active, autocatalytic process, whereas decomposition was due to diffusion. We further investigated mutual interactions between internodal cells and found that their alignment parallel to each other induced matching of the pH banding patterns, which was mirrored by chloroplast activity. In non-aligned cells, the lowered photosynthetic activity was noted upon a rise of the external pH, suggesting that the matching of pH bands was due to a local elevation of membrane conductance by the high pH of the alkaline zones of neighboured cells. Finally, we show that the altered pH banding pattern caused the reorganization of the cortical cytoplasm. Complex plasma membrane elaborations (charasomes) were degraded via endocytosis, and mitochondria were moved away from the cortex when a previously acid region became alkaline and vice versa. Our data show that characean internodal cells react flexibly to environmental cues, including those originating from neighboured cells.

Synthesis of quinolyl-pyrrole derivatives as novel environment-sensitive fluorescent probes

We synthesized novel environment-sensitive fluorophores using a unique fluorogenic core quinolyl-pyrrole (QP, 2-(1H-pyrrol-2-yl)quinoline). QP was obtained from isatins and 2-acetylpyrrole by Pfitzinger quinoline synthesis. Derivatization at the quinoline and pyrrole rings was carried out using the Sonogashira–Hagiwara cross coupling and Vilsmeier–Haack reactions, respectively. The obtained dyes showed strong fluorescence solvatochromism, but their absorption spectra remained nearly unchanged. The introduction of a dimethylaminophenylethynyl moiety at the quinoline side of the QP resulted in a change in the fluorescence color from blue to red within a narrow relative permittivity range of roughly 2–10, demonstrating that the substitution strengthened the sensitivity of the dye to the low polarity environment. The dye also reflected voltage changes across liposomal membranes, showing a 3.7-fold enhanced fluorescence intensity when tested under the same conditions as di-4-ANEPPS, a popular voltage sensitive dye, which only changed its fluorescence intensity by a factor of 1.2. The voltage sensitivity of the dye was calculated to be 2.3%/mV, much larger than that of di-4-ANEPPS (0.13 – 0.18%/mV). These dyes may be utilized for the studies on the activities of neurons or chloroplasts.

Responses of the chloroplast glyoxalase system to high CO2 concentrations.

Sugar metabolism pathways such as photosynthesis produce dicarbonyls, e.g. methylglyoxal (MG), which can cause cellular damage. The glyoxalase (GLX) system comprises two enzymes GLX1 and GLX2, and detoxifies MG; however, this system is poorly understood in the chloroplast, compared with the cytosol. In the present study, we determined GLX1 and GLX2 activities in spinach chloroplasts, which constituted 40% and 10%, respectively, of the total leaf glyoxalase activity. In Arabidopsis thaliana, five GFP-fusion GLXs were present in the chloroplasts. Under high CO2 concentrations, where increased photosynthesis promotes the MG production, GLX1 and GLX2 activities in A. thaliana increased and the expression of AtGLX1-2 and AtGLX2-5 was enhanced. On the basis of these findings and the phylogeny of GLX in oxygenic phototrophs, we propose that the GLX system scavenges MG produced in chloroplasts during photosynthesis.

Effects of Chilling on the Structure, Function and Development of Chloroplasts.

Chloroplasts are the organelles that perform energy transformation in plants. The normal physiological functions of chloroplasts are essential for plant growth and development. Chilling is a common environmental stress in nature that can directly affect the physiological functions of chloroplasts. First, chilling can change the lipid membrane state and enzyme activities in chloroplasts. Then, the efficiency of photosynthesis declines, and excess reactive oxygen species (ROS) are produced. On one hand, excess ROS can damage the chloroplast lipid membrane; on the other hand, ROS also represent a stress signal that can alter gene expression in both the chloroplast and nucleus to help regenerate damaged proteins, regulate lipid homeostasis, and promote plant adaptation to low temperatures. Furthermore, plants assume abnormal morphology, including chlorosis and growth retardation, with some even exhibiting severe necrosis under chilling stress. Here, we review the response of chloroplasts to low temperatures and focus on photosynthesis, redox regulation, lipid homeostasis, and chloroplast development to elucidate the processes involved in plant responses and adaptation to chilling stress.

Dawn regulates guard cell proteins in Arabidopsis thaliana that function in ATP production from fatty acid beta-oxidation.

Based on the nature of the proteins that are altered in abundance, we conclude that guard cells switch their energy source from fatty acid metabolism to chloroplast activity, at the onset of dawn. During stomatal opening at dawn, evidence was recently presented for a breakdown and liquidation of stored triacylglycerols in guard cells to supply ATP for use in stomatal opening. However, proteome changes that happen in the guard cells during dawn were until now poorly understood. Bad accessibility to pure and intact guard cell samples can be considered as the primary reason behind this lack of knowledge. To overcome these technical constraints, epidermal guard cell samples with ruptured pavement cells were isolated at 1h pre-dawn, 15min post-dawn and 1h post-dawn from Arabidopsis thaliana. Proteomic changes were analysed by ultra-performance-liquid-chromatography-mass-spectrometry. With 994 confidently identified proteins, we present the first analysis of the A. thaliana guard cell proteome that is not influenced by side effects of guard cell protoplasting. Data are available via ProteomeXchange with identifier PXD009918. By elucidating the identities of enzymes that change in abundance by the transition from dark to light, we corroborate the hypothesis that respiratory ATP production for stomatal opening results from fatty acid beta-oxidation. Moreover, we identified many proteins that were never reported in the context of guard cell biology. Among them are proteins that might play a role in signalling or circadian rhythm.

SlARF10, an auxin response factor, is involved in chlorophyll and sugar accumulation during tomato fruit development.

The photosynthesis of green tomatoes contributes to fruit growth and carbon economy. The tomato auxin response factor 10 (SlARF10) belongs to the ARF family and is located in nucleus. In this study, we found that SlARF10 was highly expressed in green fruit. Overexpression of SlARF10 in fruit produced a dark-green phenotype whilst knock-down by RNAi produced a light-green phenotype. Autofluorescence and chlorophyll content analyses confirmed the phenotypes, which indicated that SlARF10 plays an important role in chlorophyll accumulation. Overexpression of SlARF10 positively affected photosynthesis in both leaves and fruit. Furthermore, SlARF10-overexpression lines displayed improved accumulation of starch, fructose, and sucrose in fruit, whilst SlARF10-RNAi lines showed decreased accumulation of starch and sucrose. Regulation of SlARF10 expression altered the expression of AGPase starch biosynthesis genes. SlARF10 positively regulated the expression of SlGLK1, POR, CBP1, and CBP2, which are related to chlorophyll metabolism and regulation. Electrophoretic mobility shift assays confirmed that SlARF10 directly targets to the SlGLK1 promoter. Our results thus indicate that SlARF10 is involved in chlorophyll accumulation by transcriptional activation of SlGLK1 expression in tomato fruit, and provide insights into the link between auxin signaling, chloroplast activity, and sugar metabolism during tomato fruit development.

The cDNA Structures and Expression Profile of the Ascorbate Peroxidase Gene Family During Drought Stress in Wild Watermelon

Ascorbate peroxidase (APX) plays an important role in detoxifying reactive oxygen species under environmental stress. Although previous work in drought-tolerant wild watermelon has shown an increase in chloroplast APX enzyme activity under drought, molecular entities of APX have remained uncharacterized. In this study, structure and transcriptional regulation of the APX gene family in watermelon were characterized. Five APX genes, designated as CLAPX1 to CLAPX5, were identified from watermelon genome. The mRNA alternative splicing was suggested for CLAPX5, which generated two distinct deduced amino acid sequences at their C-terminus, in resemblance to a reported alternative splicing of chloroplast APXs in pumpkin. This observation suggests that two isoenzymes for stromal and thylakoid-bound APXs may be generated from the CLAPX5 gene. Phylogenetic analysis classified CLAPX isoenzymes into three clades, i.e., chloroplast, microbody, and cytosolic. Physiological analyses of wild watermelon under drought showed a decline in stomatal conductance and CO2 assimilation rate, and a significant increase in the enzyme activities of both chloroplast and cytosolic APXs. Profiles of mRNA abundance during drought were markedly different among CLAPX genes, suggesting distinct transcriptional regulation for the APX isoenzymes. Up-regulation of CLAPX5-I and CLAPX5-II was observed at the early phase of drought stress, which was temporally correlated with the observed increase in chloroplast APX enzyme activity, suggesting that transcriptional up-regulation of the CLAPX5 gene may contribute to the fortification of chloroplast APX activity under drought. Our study has provided an insight into the functional significance of the CLAPX gene family in the drought tolerance mechanism in this plant.

Changes of antioxidant enzyme activities in chloroplast of ‘717’ poplar under NaCl treatment

In order to study the salt tolerance of ‘717’ hybrid poplar under salt treatment, we studied the changes of antioxidant enzyme activities in chloroplasts treated with 0, 25,75mmol/L Knack. The results showed that: (1) Knack treatment can increase the content of hydrogen peroxide (H2O2) and malondialdehyde (MDA) in chloroplast. The H2O2 increased the highest at 1d, and reached 39.5%. The content of MDA in chloroplast increased by 38.3% at the low concentration of day 5, and increased to 74.4% at day 10 after high concentration of Knack treatment. (2) The activity of acerbate peroxidase (APX) in chloroplast increased at low concentration and decreased at high concentration. The activity of peroxidase (POD) in chloroplast was not significantly changed at low concentration, but at high concentration, the POD activity decreased by up to 35% at day 1. The activity of glutathione reductive (GR) in chloroplast was increased by 15.9% under low Knack treatment. Increased by 53.6% at 1 d on high concentration of Knack. (3) Knack treatment, the activities of ascorbic acid (As A) and (reduced glutathione) GSH in chloroplast were increased. At low concentration, the activity of ASA in chloroplast increased by 43.8% at 10 d, and the content of GSH was an increase of 72.2% at 10 d. In the high concentration of Knack treatment, the activity increased significantly. In conclusion, the low concentration of Knack (25mmol / L) could promote the activity of antioxidant enzymes in chloroplast of 717 and maintain the growth, while the antioxidant enzyme activity was inhibited when the Knack was treated with high concentration (75mmol / L). Hydrogen peroxide and MDA content increased, the cells were subjected to Knack stress.

Dynamin-Like Proteins Are Potentially Involved in Membrane Dynamics within Chloroplasts and Cyanobacteria.

Dynamin-like proteins (DLPs) are a family of membrane-active proteins with low sequence identity. The proteins operate in different organelles in eukaryotic cells, where they trigger vesicle formation, membrane fusion, or organelle division. As discussed here, representatives of this protein family have also been identified in chloroplasts and DLPs are very common in cyanobacteria. Since cyanobacteria and chloroplasts, an organelle of bacterial origin, have similar internal membrane systems, we suggest that DLPs are involved in membrane dynamics in cyanobacteria and chloroplasts. Here, we discuss the features and activities of DLPs with a focus on their potential presence and activity in chloroplasts and cyanobacteria.

The role of chloroplasts in plant pathology.

Plants have evolved complex tolerance systems to survive abiotic and biotic stresses. Central to these programmes is a sophisticated conversation of signals between the chloroplast and the nucleus. In this review, we examine the antagonism between abiotic stress tolerance (AST) and immunity: we propose that to generate immunogenic signals, plants must disable AST systems, in particular those that manage reactive oxygen species (ROS), while the pathogen seeks to reactivate or enhance those systems to achieve virulence. By boosting host systems of AST, pathogens trick the plant into suppressing chloroplast immunogenic signals and steer the host into making an inappropriate immune response. Pathogens disrupt chloroplast function, both transcriptionally-by secreting effectors that alter host gene expression by interacting with defence-related kinase cascades, with transcription factors, or with promoters themselves-and post-transcriptionally, by delivering effectors that enter the chloroplast or alter the localization of host proteins to change chloroplast activities. These mechanisms reconfigure the chloroplast proteome and chloroplast-originating immunogenic signals in order to promote infection.

Effects of rare earth and acid rain pollution on plant chloroplast ATP synthase and element contents at different growth stages

Combined rare earth and acid rain pollution has become a new environmental problem, seriously affecting plant survival. The effects of these two kinds of pollutants on plant photosynthesis have been reported, but the micro mechanisms are not very clear. In this research, we studied the effects of lanthanum [La(III), 0.08, 1.20 and 2.40 mM] and acid rain (pH value = 2.5, 3.5 and 4.5) on the ATPase activity and gene transcription level and the functional element contents in rice leaf chloroplasts. The results showed that the combined 0.08 mM La(III) and pH 4.5 acid rain increased the ATPase activity and gene transcription level as well as contents of some functional elements. But other combined treatments of acid rain and La(III) reduced the ATPase activity and gene transcription level as well as functional element contents. The change magnitude of the above indexes at rice booting stage was greater than that in seedling stage or grain filling stage. These results reveal that effects of La(III) and acid rain on ATPase activity and functional element contents in rice leaf chloroplasts are related to the combination of La(III) dose and acid rain intensity and the plant growth stage. In addition, the changes in the ATPase activity were related to ATPase gene transcription level. This study would provide a reference for understanding the microcosmic mechanism of rare earth and acid rain pollution on plant photosynthesis and contribute to evaluate the possible environmental risks associated with combined La(III) and acid rain pollution. One sentence summaryThe effects of La(III) and acid rain on activity and gene transcription level of rice chloroplast ATPase and contents of functional elements were different at different growth stages.

Pathways for external alkalinization in intact and in microwounded Chara cells are differentially sensitive to wortmannin

ABSTRACTProton flows across the plant cell membranes play a major role in electrogenesis and regulation of photosynthesis and ion balance. The profiles of external pH along the illuminated internodal cells of characean algae consist of alternating high- and low-pH zones that are spatially coordinated with the distribution of photosynthetic activity of chloroplasts underlying these zones. The results based on confocal laser scanning fluorescence microscopy, pH microsensors, and pulse-amplitude-modulated chlorophyll microfluorometry revealed that the coordination of H+ transport and photosynthesis is disrupted by the 2 different environmental cues (low light and wounding) and by a chemical, wortmannin interfering with the inositol phospholipid metabolism. On the one hand, the transition from moderate to low irradiance diminished the peaks in the profiles of photosystem II (PSII) quantum efficiency but did not remove the pH bands. On the other hand, the microwounding of the internode with a glass micropipette, impacting primarily the cell wall, resulted in a rapid local alkalinization of the external medium (by 2–2.5 pH units) near the cell surface, thus mimicking the appearance of natural pH bands. Despite their seeming similarity, the alkaline bands of intact cells were eliminated by wortmannin, whereas the wound-induced alkalinization was insensitive to this drug. Furthermore, the attenuation of natural pH bands in wortmannin-treated cells was accompanied by the enhancement in spatial heterogeneity of PSII efficiency and electron transport rates, which indicates the complexity of chloroplast–plasma membrane interactions. The results suggest that the light- and wound-induced alkaline areas on the cell surface are associated with different ion-transport systems.

Molecular characterization of the acquisition of longevity during seed maturation in soybean.

Seed longevity, defined as the ability to remain alive during storage, is an important agronomic factor. Poor longevity negatively impacts seedling establishment and consequently crop yield. This is particularly problematic for soybean as seeds have a short lifespan. While the economic importance of soybean has fueled a large number of transcriptome studies during embryogenesis and seed filling, the mechanisms regulating seed longevity during late maturation remain poorly understood. Here, a detailed physiological and molecular characterization of late seed maturation was performed in soybean to obtain a comprehensive overview of the regulatory genes that are potentially involved in longevity. Longevity appeared at physiological maturity at the end of seed filling before maturation drying and progressively doubled until the seeds reached the dry state. The increase in longevity was associated with the expression of genes encoding protective chaperones such as heat shock proteins and the repression of nuclear and chloroplast genes involved in a range of chloroplast activities, including photosynthesis. An increase in the raffinose family oligosaccharides (RFO)/sucrose ratio together with changes in RFO metabolism genes was also associated with longevity. A gene co-expression network analysis revealed 27 transcription factors whose expression profiles were highly correlated with longevity. Eight of them were previously identified in the longevity network of Medicago truncatula, including homologues of ERF110, HSF6AB, NFXL1 and members of the DREB2 family. The network also contained several transcription factors associated with auxin and developmental cell fate during flowering, organ growth and differentiation. A transcriptional transition occurred concomitant with seed chlorophyll loss and detachment from the mother plant, suggesting the activation of a post-abscission program. This transition was enriched with AP2/EREBP and WRKY transcription factors and genes associated with growth, germination and post-transcriptional processes, suggesting that this program prepares the seed for the dry quiescent state and germination.

The Effect of Two Amino acid Residue Substitutions via RNA Editing on Dark-operative Protochlorophyllide Oxidoreductase in the Black Pine Chloroplasts

Dark-operative protochlorophyllide oxidoreductase (DPOR) is a key enzyme to produce chlorophyll in the dark. Among photosynthetic eukaryotes, all three subunits chlL, chlN, and chlB are encoded by plastid genomes. In some gymnosperms, two codons of chlB mRNA are changed by RNA editing to codons encoding evolutionarily conserved amino acid residues. However, the effect of these substitutions on DPOR activity remains unknown. We first prepared cyanobacterial ChlB variants with amino acid substitution(s) to mimic ChlB translated from pre-edited mRNA. Their activities were evaluated by measuring chlorophyll content of dark-grown transformants of a chlB-lacking mutant of the cyanobacterium Leptolyngbya boryana that was complemented with pre-edited mimic chlB variants. The chlorophyll content of the transformant cells expressing the ChlB variant from the fully pre-edited mRNA was only one-fourth of the control cells. Co-purification experiments of ChlB with Strep-ChlN suggested that a stable complex with ChlN is greatly impaired in the substituted ChlB variant. We then confirmed that RNA editing efficiency was markedly greater in the dark than in the light in cotyledons of the black pine Pinus thunbergii. These results indicate that RNA editing on chlB mRNA is important to maintain appropriate DPOR activity in black pine chloroplasts.

Erratum to: Connectivity between electron transport complexes and modulation of photosystem II activity in chloroplasts.

In chloroplasts, photosynthetic electron transport complexes interact with each other via the mobile electron carriers (plastoquinone and plastocyanin) which are in surplus amounts with respect to photosystem I and photosystem II (PSI and PSII), and the cytochrome b 6 f complex. In this work, we analyze experimental data on the light-induced redox transients of photoreaction center P700 in chloroplasts within the framework of our mathematical model. This analysis suggests that during the action of a strong actinic light, even significant attenuation of PSII [for instance, in the result of inhibition of a part of PSII complexes by DCMU or due to non-photochemical quenching (NPQ)] will not cause drastic shortage of electron flow through PSI. This can be explained by “electronic” and/or “excitonic” connectivity between different PSII units. At strong AL, the overall flux of electrons between PSII and PSI will maintain at a high level even with the attenuation of PSII activity, provided the rate-limiting step of electron transfer is beyond the stage of PQH2 formation. Results of our study are briefly discussed in the context of NPQ-dependent mechanism of chloroplast protection against light stress.