Chloroplasts Of Mesophyll Cells Research Articles

Cutinsomes of Malus Mill. (Rosaceae) leaf and pericarp: genesis, localization, and transport

New data were obtained on specific bionanostructures, cutinsomes, which are involved in the formation of cuticles on the surface of leaf blades and pericarp of Malus domestica Borkh (Malus Mill., Rosaceae)introduced to the mountains at the altitudes of 1200 and 1700 m above sea level. Cutinsomes, which are electron-dense structures of spherical shape, have been identified by transmission electron microscopy. It was demonstrated that plastids can be involved in the synthesis of their constituent nanocomponents. The greatest number of nanoparticles was observed in the granal thylakoid lumen of the chloroplasts in palisade mesophyll cells and pericarp hypodermal cells. The transmembrane transport of cutinsomes into the cell wall cuticle proper by exocytosis has been visualized for the first time. The plasma membrane is directly involved in the excretion of nanostructures from the cell. Nanoparticles of cutinsomes in the form of necklace-like formations line up in a chain near cell walls, merge into larger conglomerates and are loaded into plasmalemma invaginations, and then, in membrane packing, they move into the cuticle, which covers both outer and inner cell walls of external tissues. The original materials obtained by us supplement the ideas about the non-enzymatic synthesis of cuticle components available in the literature and expand the cell compartment geography involved in this process.

Chimeric deletion mutation of rpoC2 underlies the leaf-patterning of Clivia miniata var. variegata.

The deletion mutated rpoC2 leads to yellow stripes of Clivia miniata var. variegata by down regulating the transcription of 28 chloroplast genes and disturbing chloroplast biogenesis and thylakoid membrane development. Clivia miniata var. variegata (Cmvv) is a common mutant of Clivia miniata but its genetic basis is unclear. Here, we found that a 425bp deletion mutation of chloroplast rpoC2 underlies the yellow stripes (YSs) of Cmvv. Both RNA polymerase PEP and NEP coexist in seed-plant chloroplasts and the β″ subunit of PEP is encoded by rpoC2. The rpoC2 mutation changed the discontinuous cleft domain required to form the PEP central cleft for DNA binding from 1103 to 59aa. RNA-Seq revealed that 28 chloroplast genes (cpDEGs) were all down-regulated in YSs, of which, four involved in chloroplast protein translation and 21 of photosynthesis system (PS)I, PSII, cytochrome b6/f complex and ATP synthase are crucial for chloroplast biogenesis/development. The accuracy and reliability of RNA-Seq was verified by qRT-PCR. Moreover, the chlorophyll (Chl) a/b content, ratio of Chla/Chlb and photosynthetic rate (Pn) of YS decreased significantly. Meanwhile, chloroplasts of the YS mesophyll cells were smaller, irregular in shape, contain almost no thylakoid membrane, and even proplastid was found in YS. These findings indicate that the rpoC2 mutation down-regulated expression of the 28 cpDEGs, which disturb chloroplast biogenesis and its thylakoid membrane development. Thus, there are not enough PSI and II components to bind Chl, so that the corresponding areas of the leaf are yellow and show a low Pn. In this study, the molecular mechanism of three phenotypes of F1 (Cmvv ♀ × C. miniata ♂) was revealed, which lays a foundation for the breeding of variegated plants.

Dynamic association of the plastid localized cysteine synthase complex is vital for efficient cysteine production, photosynthesis, and grana thylakoid formation in transgenic tobacco.

Cysteine biosynthesis is essential for translation and represents the entry point of reduced sulfur into plant metabolism. The two consecutively acting enzymes serine-acetyltransferase (SAT) and O-acetylserine-thiol-lyase catalyze cysteine production and form the cysteine synthase complex (CSC), in which SAT is activated. Here we show that expression of active SAT in plastids of tobacco (PSA) causes substantial cysteine accumulation. Remarkably, enhanced cysteine production in plastids entirely abolished grana stack formation, impaired photosynthesis capacity, and decreased the number of chloroplasts in mesophyll cells of PSA lines. Transgenic tobacco lines expressing active SAT in the cytosol (CSA) accumulated comparable amounts of thiols but displayed no phenotype. To dissect the consequences of CSC formation from enhanced SAT activity in tobacco plastids, we expressed an enzymatically inactive SAT that can still form the CSC in tobacco plastids (PSI). The PSI lines were indistinguishable from PSA lines, although the PSI lines displayed no increase in plastid-localized SAT activity. Neither PSA lines nor PSI lines suffered from an oxidized redox environment in plastids that could have been causative for the disturbed photosynthesis. From these findings, we infer that the association of the plastid CSC itself triggers a signaling cascade controlling sulfur assimilation and photosynthetic capacity in leaves.

Nondestructive circadian profiling of starch content in fresh intact Arabidopsis leaf with two-photon fluorescence and second-harmonic generation imaging

Plant chloroplasts conduct photosynthesis to convert solar energy into sugars for the carbon source essential for cell living and growth during the day. One fraction of photosynthetic products is stored in chloroplasts by forming starch granules to continue the provision of carbon energy during the night. Currently, profiling the starch temporal pattern requires either: (i) sacrificing the leaves, or (ii) generating transgenic plants at the risk of changing the metabolisms by incorporating a genetically modified granule-bound starch synthase (GBSS). In this paper, we demonstrated a nondestructive method using two-photon fluorescence (TPF) and second-harmonic generation (SHG) imaging to quantify starch granules within chloroplasts of fresh intact leaves across a day-night cycle. We did so using two Arabidopsis lines having normal and excess starch contents: wild-type (Columbia-0) and starch excess 1 (sex1). The starch granules were visualized by SHG imaging, while the chloroplasts in mesophyll cells were visualized by TPF imaging. Our results provided micron scale spatial resolution of starch distribution within leaves and showed starch circadian patterns consistent with those profiled by enzymatic assays in previous studies. We demonstrated that TPF-SHG imaging is a potential tool for revealing the real-time heterogeneity of starch circadian rhythm in leaf cells, without the need for destructive sample preparation.

Chloroplastic photoprotective strategies differ between bundle sheath and mesophyll cells in maize (Zea mays L.) Under drought.

Bundle sheath cells play a crucial role in photosynthesis in C4 plants, but the structure and function of photosystem II (PSII) in these cells is still controversial. Photoprotective roles of bundle sheath chloroplasts at the occurrence of environmental stresses have not been investigated so far. Non-photochemical quenching (NPQ) of chlorophyll a fluorescence is the photoprotective mechanism that responds to a changing energy balance in chloroplasts. In the present study, we found a much higher NPQ in bundle sheath chloroplasts than in mesophyll chloroplasts under a drought stress. This change was accompanied by a more rapid dephosphorylation of light-harvesting complex II (LHCII) subunits and a greater increase in PSII subunit S (PsbS) protein abundance than in mesophyll cell chloroplasts. Histochemical staining of reactive oxygen species (ROS) suggested that the high NPQ may be one of the main reasons for the lower accumulation of ROS in bundle sheath chloroplasts. This may maintain the stable functioning of bundle sheath cells under drought condition. These results indicate that the superior capacity for dissipation of excitation energy in bundle sheath chloroplasts may be an environmental adaptation unique to C4 plants.

Physiological Mechanism of Exogenous 5-Aminolevulinic Acid Improved the Tolerance of Chinese Cabbage (Brassica pekinensis L.) to Cadmium Stress

The 5-aminolevulinic acid (ALA), a new type of plant growth regulator, can relieve the toxicity of cadmium (Cd) to plants. However, its mechanism has not been thoroughly studied. In the study, the roles of ALA have been investigated in the tolerance of Chinese cabbage (Brassica pekinensis L.) seedlings to Cd stress. The results showed that Cd significantly reduced the biomass and the length of the primary root of seedlings but increased the malondialdehyde (MDA) and the hydrogen peroxide (H2O2) contents. These can be effectively mitigated through the application of ALA. The ALA can further induce the activities of antioxidant enzymes in the ascorbate-glutathione (AsA-GSH) cycle under Cd stress, which resulted in high levels of both GSH and AsA. Under ALA + Cd treatment, the seedlings showed a higher chlorophyll content and photosynthetic performance in comparison with Cd treatment alone. Microscopic analysis results confirmed that ALA can protect the cell structure of shoots and roots, i.e., stabilizing the morphological structure of chloroplasts in leaf mesophyll cells. The qRT-PCR results further reported that ALA downregulated the expressions of Cd absorption and transport-related genes in shoots (HMA2 and HMA4) and roots (IRT1, IRT2, Nramp1, and Nramp3), which resulted in the low Cd content in the shoots and roots of cabbage seedlings. Taken together, the exogenous application of ALA alleviates Cd stress through maintaining redox homeostasis, protecting the photosynthetic system, and regulating the expression of Cd transport-related genes in Chinese cabbage seedlings.

Salt tolerance in relation to elemental concentrations in leaf cell vacuoles and chloroplasts of a C4 monocotyledonous halophyte.

Halophytes accumulate and sequester high concentrations of salt in vacuoles while maintaining lower levels of salt in the cytoplasm. The current data on cellular and subcellular partitioning of salt in halophytes are, however, limited to only a few dicotyledonous C3 species. Using cryo‐scanning electron microscopy X‐ray microanalysis, we assessed the concentrations of Na, Cl, K, Ca, Mg, P and S in various cell types within the leaf‐blades of a monocotyledonous C4 halophyte, Rhodes grass (Chloris gayana). We also linked, for the first time, elemental concentrations in chloroplasts of mesophyll and bundle sheath cells to their ultrastructure and photosynthetic performance of plants grown in nonsaline and saline (200 mM NaCl) conditions. Na and Cl accumulated to the highest levels in xylem parenchyma and epidermal cells, but were maintained at lower concentrations in photosynthetically active mesophyll and bundle sheath cells. Concentrations of Na and Cl in chloroplasts of mesophyll and bundle sheath cells were lower than in their respective vacuoles. No ultrastructural changes were observed in either mesophyll or bundle sheath chloroplasts, and photosynthetic activity was maintained in saline conditions. Salinity tolerance in Rhodes grass is related to specific cellular Na and Cl distributions in leaf tissues, and the ability to regulate Na and Cl concentrations in chloroplasts.

Two major metabolic factors for an efficient NADP-malic enzymetype C4 photosynthesis.

Compared to the large number of studies focused on the factors controlling C3 photosynthesis efficiency, there are relatively fewer studies of the factors controlling photosynthetic efficiency in C4 leaves. Here, we used a dynamic systems model of C4 photosynthesis based on maize (Zea mays) to identify features associated with high photosynthetic efficiency in NADP-malic enzyme (NADP-ME) type C4 photosynthesis. We found that two additional factors related to coordination between C4 shuttle metabolism and C3 metabolism are required for efficient C4 photosynthesis: (1) accumulating a high concentration of phosphoenolpyruvate through maintaining a large PGA concentration in the mesophyll cell chloroplast and (2) maintaining a suitable oxidized status in bundle sheath cell chloroplasts. These identified mechanisms are in line with the current cellular location of enzymes/proteins involved in the starch synthesis, the Calvin–Benson cycle and photosystem II of NADP-ME type C4 photosynthesis. These findings suggested potential strategies for improving C4 photosynthesis and engineering C4 rice.

Singlet Oxygen Leads to Structural Changes to Chloroplasts during their Degradation in the Arabidopsis thaliana plastid ferrochelatase two Mutant.

During stress, chloroplasts produce large amounts of reactive oxygen species (ROS). Chloroplasts also contain many nutrients, including 80% of a leaf's nitrogen supply. Therefore, to protect cells from photo-oxidative damage and to redistribute nutrients to sink tissues, chloroplasts are prime targets for degradation. Multiple chloroplast degradation pathways are induced by photo-oxidative stress or nutrient starvation, but the mechanisms by which damaged or senescing chloroplasts are identified, transported to the central vacuole and degraded are poorly defined. Here, we investigated the structures involved with degrading chloroplasts induced by the ROS singlet oxygen (1O2) in the Arabidopsis thaliana plastid ferrochelatase two (fc2) mutant. Under mild 1O2 stress, most fc2 chloroplasts appeared normal, but had reduced starch content. A subset of chloroplasts was degrading, and some protruded into the central vacuole via 'blebbing' structures. A 3D electron microscopy analysis demonstrated that up to 35% of degrading chloroplasts contained such structures. While the location of a chloroplast within a cell did not affect the likelihood of its degradation, chloroplasts in spongy mesophyll cells were degraded at a higher rate than those in palisade mesophyll cells. To determine if degrading chloroplasts have unique structural characteristics, allowing them to be distinguished from healthy chloroplasts, we analyzed fc2 seedlings grown under different levels of photo-oxidative stress. A correlation was observed among chloroplast swelling, 1O2 signaling and the state of degradation. Finally, plastoglobule (PG) enzymes involved in chloroplast disassembly were upregulated while PGs increased their association with the thylakoid grana, implicating an interaction between 1O2-induced chloroplast degradation and senescence pathways.

Transcriptomic analyses reveal variegation-induced metabolic changes leading to high L-theanine levels in albino sectors of variegated tea (Camellia sinensis)

Camellia sinensis cv. ‘Yanling Huayecha’ (YHC) is an albino-green chimaeric tea mutant with stable genetic traits. Here, we analysed the cell ultrastructure, photosynthetic pigments, amino acids, and transcriptomes of the albino, mosaic, and green zones of YHC. Well-organized thylakoids were found in chloroplasts in mesophyll cells of the green zone but not the albino zone. The albino zone of the leaves contained almost no photosynthetic pigment. However, the levels of total amino acids and theanine were higher in the albino zone than in the mosaic and green zones. A transcriptomic analysis showed that carbon metabolism, nitrogen metabolism and amino acid biosynthesis showed differences among the different zones. Metabolite and transcriptomic analyses revealed that (1) downregulation of CsPPOX1 and damage to thylakoids in the albino zone may block chlorophyll synthesis; (2) downregulation of CsLHCB6, CsFdC2 and CsSCY1 influences chloroplast biogenesis and thylakoid membrane formation, which may contribute to the appearance of variegated tea leaves; and (3) tea plant variegation disrupts the balance between carbon and nitrogen metabolism and promotes the accumulation of amino acids, and upregulation of CsTSⅠ and CsAlaDC may enhance L-theanine synthesis. In summary, our study provides a theoretical basis and valuable insights for elucidating the molecular mechanisms and promoting the economic utilization of variegation in tea.

Supraoptimal Iron Nutrition of Brassica napus Plants Suppresses the Iron Uptake of Chloroplasts by Down-Regulating Chloroplast Ferric Chelate Reductase.

Iron (Fe) is an essential micronutrient for plants. Due to the requirement for Fe of the photosynthetic apparatus, the majority of shoot Fe content is localised in the chloroplasts of mesophyll cells. The reduction-based mechanism has prime importance in the Fe uptake of chloroplasts operated by Ferric Reductase Oxidase 7 (FRO7) in the inner chloroplast envelope membrane. Orthologue of Arabidopsis thaliana FRO7 was identified in the Brassica napus genome. GFP-tagged construct of BnFRO7 showed integration to the chloroplast. The time-scale expression pattern of BnFRO7 was studied under three different conditions: deficient, optimal, and supraoptimal Fe nutrition in both leaves developed before and during the treatments. Although Fe deficiency has not increased BnFRO7 expression, the slight overload in the Fe nutrition of the plants induced significant alterations in both the pattern and extent of its expression leading to the transcript level suppression. The Fe uptake of isolated chloroplasts decreased under both Fe deficiency and supraoptimal Fe nutrition. Since the enzymatic characteristics of the ferric chelate reductase (FCR) activity of purified chloroplast inner envelope membranes showed a significant loss for the substrate affinity with an unchanged saturation rate, protein level regulation mechanisms are suggested to be also involved in the suppression of the reduction-based Fe uptake of chloroplasts together with the saturation of the requirement for Fe.

The expansion of mesophyll cells is coordinated with the division of chloroplasts in diploid and tetraploid Arabidopsis thaliana.

Cell expression is coordinated with chloroplast division in diploid and tetraploid Arabidopsis thaliana, polyploidy promoted the expansion of mesophyll cells and chloroplast division in A. thaliana. Cell development and differentiation are always accompanied by cell expansion and chloroplast division in plants, but the relationship between them is still relatively unknown. To confirm the relationship between cell expansion and chloroplast division during the leaf development process of diploid and tetraploid Arabidopsis thaliana, we systematically analyzed the expansion of mesophyll cells and the division of chloroplasts through cytological observation and gene-expression characteristics. As a result, in diploid and tetraploid A. thaliana, there were two peaks in both mesophyll cell expansion and chloroplast division during the leaf development process. Tetraploid A. thaliana mesophyll cells were larger and contained more chloroplasts than diploid A. thaliana mesophyll cells, which indicated that cell division and cell expansion were coordinated with chloroplast division in A. thaliana and that polyploidy further promoted mesophyll cell expansion and chloroplast division.

Photosynthetic performance of quinoa (Chenopodium quinoa Willd.) after exposure to a gradual drought stress followed by a recovery period

Drought is an abiotic scourge, one of the major environmental stress factors that adversely affect plant growth and photosynthesis machinery through a disruption of cell organelles, arrangement thylakoid membranes and the electron transport chain. Herein, we probed the effect of drought stress on photosynthetic performance of Chenopodium quinoa Willd. Beforehand, plants were subjected to water deficit (as 15% Field Capacity, FC) for one (D-1W) or two weeks (D-2W), and were then re-watered at 95% FC for 2 weeks. Light and electron microscopy analysis of leaves showed no apparent changes in mesophyll cell organization and chloroplast ultrastructure after one week of drought stress, while a swelling of thylakoids and starch accumulation were observed after the prolonged drought (D-2W). The latter induced a decrease in both PSI and PSII quantum yields which was accompanied by an increase in F0 (minimum fluorescence) and a decline in Fm (maximum fluorescence). Drought stress influenced the fluorescence transients, where the major changes at the OJIP prompt FI level were detected in the OJ and IP phases. Prolonged drought induced a decrease in chl a fluorescence at IP phase which was readjusted and established back after re-watering and even more an increase was observed after 2 weeks of recovery. The maximum quantum yield of primary photochemistry (φPo) was unaffected by the different drought stress regimes. Drought induced an increase in the ABS/RC and DI0/RC ratios which was concurrent to a stable φPo (maximum quantum yield of PSII primary photochemistry). A substantial decrease in PI(ABS) was detected especially, during severe drought stress (D-2W) suggesting a drop in the PSII efficiency and the level of electron transport through the plastoquinone pool (PQ pool) towards oxidized PSI RCs (P700+). The immunoblot analysis of the main PSII proteins revealed considerable changes in the D1, D2, CP47, OEC, PsbQ and LHCII proteins under drought. These changes depend on the stress duration and recovery period. The main message of this investigation is the elevated recovery capacities of PSII and PSI photochemical activities after re-watering.

Differential localization of flavonoid glucosides in an aquatic plant implicates different functions under abiotic stress.

Flavonoids may mediate UV protection in plants either by screening of harmful radiation or by minimizing the resulting oxidative stress. To help distinguish between these alternatives, more precise knowledge of flavonoid distribution is needed. We used confocal laser scanning microscopy (cLSM) with the "emission fingerprinting" feature to study the cellular and subcellular distribution of flavonoid glucosides in the giant duckweed (Spirodela polyrhiza), and investigated the fitness effects of these compounds under natural UV radiation and copper sulphate addition (oxidative stress) using common garden experiments indoors and outdoors. cLSM "emission fingerprinting" allowed us to individually visualize the major dihydroxylated B-ring-substituted flavonoids, luteolin 7-O-glucoside and luteolin 8-C-glucoside, in cross-sections of the photosynthetic organs. While luteolin 8-C-glucoside accumulated mostly in the vacuoles and chloroplasts of mesophyll cells, luteolin 7-O-glucoside was predominantly found in the vacuoles of epidermal cells. In congruence with its cellular distribution, the mesophyll-associated luteolin 8-C-glucoside increased plant fitness under copper sulphate addition but not under natural UV light treatment, whereas the epidermis-associated luteolin 7-O-glucoside tended to increase fitness under both stresses across chemically diverse genotypes. Taken together, we demonstrate that individual flavonoid glucosides have distinct cellular and subcellular locations and promote duckweed fitness under different abiotic stresses.

Активность антиоксидантных ферментов в хлоропластах мезофилла и обкладки сосудистых пучков кукурузы (Zea mays L.), под воздействием солевого стресса

Antioxidant defense systems have been studied in the mesophyll (MC) and bundle sheath cell (BSC) chloroplasts of maize (Zea mays L.) leaves cultivated in an artificial climate chamber under various concentrations (0%, 1%, 2%, 3%) of NaCl. The amounts of some of the main products of lipid peroxidation malondialdehyde (MDA) and reactive oxygen species hydrogen peroxide (H2O2) as well as activities of superoxide dismutase (SOD) and ascorbate peroxidase (APO) were determined in MC and BSC chloroplasts. BSC chloroplasts were found to be more tolerant to salt stress compared with MC chloroplasts. The MDA amount increased in both chloroplasts. H2O2 was found to be localized mainly in MC chloroplasts at various NaCl concentrations. The SOD and APO activities increased in both chloroplasts of the plants exposed to salt stress.

Changes in leaf blade morphology and anatomy caused by clomazone and saflufenacil in Setaria viridis, a model C4 plant

Clomazone and saflufenacil are herbicides extensively used worldwide to weed control. We studied the effects of these two herbicides on morphoanatomical parameters of Setaria viridis. Plants were sprayed with four concentrations of each herbicide (clomazone: 500, 1000, 1500 and 2000 g of active ingredient (ai) ha−1 and saflufenacil: 49, 98, 147 and 196 g ai ha−1) besides control (without spraying) 20 days after transplantation. The experimental design was completely randomized with five replicates per treatment. Pigment content, visible injuries, morphological and ultrastructural changes were evaluated. No signs of tolerance to either of the tested herbicides were observed. Clomazone caused a decrease in photosynthetic pigment content over time, mostly in young leaves, leading to an “albino” like appearance. There was a reduction in the number of grana in the chloroplasts of mesophyll cells (MC) in necrotic areas. Saflufenacil reduced chlorophyll content, impairing energy absorption in the antenna complex. Injuries to foliar tissues, such as necrosis and depigmentation, were visible as early as 24 h after herbicide application. Bundle sheath chloroplasts (BSC) and MC were completely deformed. The data support the use of S. viridis as a model plant for studies on herbicide effects in C4 monocots.

Three-dimensional ultrastructural change of chloroplasts in rice mesophyll cells responding to salt stress.

Excess salinity inhibits the metabolism of various systems and induces structural changes, especially in chloroplasts. Although the chloroplast body seems to swell under salinity stress as observed by conventional transmission electron microscopy, previous studies are limited to 2-D data and lack quantitative comparisons because specimens need to be sliced into ultrathin sections. This study shows three-dimensionally the structural changes in a whole mesophyll cell responding to salinity stress by serial sectioning with a focused ion beam scanning electron microscope (FIB-SEM) and compares the differences in chloroplast structures based on reconstructed models possessing accurate numerical voxel values. Leaf blades of rice plants treated with 100 mm NaCl or without (control) for 4 d were fixed chemically and embedded in resin. The specimen blocks were sectioned and observed using the FIB-SEM, and then the sliced image stacks were reconstructed into 3-D models by image processing software. On the transverse sections of rice mesophyll cells, the chloroplasts in the control leaves appeared to be elongated meniscus lens shaped, while those in the salt-treated leaves appear to be expanded oval shaped. The 3-D models based on serial sectioning images showed that the chloroplasts in the control cells spread like sheets fitted to the shape of the cell wall and in close contact with the adjacent chloroplasts. In contrast, those in the salt-stressed cells curled up into a ball and fitted to cell protuberances without being in close contact with adjacent chloroplasts. Although the shapes of chloroplasts were clearly different between the two treatments, their volumes did not differ. The 3-D reconstructed models of whole rice mesophyll cells indicated that chloroplasts under salt stress conditions were not swollen but became spherical without increasing their volume. This is in contrast to findings of previous studies based on 2-D images.

The effects of exogenous organic acids on the growth, photosynthesis and cellular ultrastructure of Salix variegata Franch. Under Cd stress

We studied the effects of three organic acids (citric acid, tartaric acid and malic acid) on the biomass, photosynthetic pigment content and photosynthetic parameters of Salix variegata under Cd stress and observed the ultrastructure of mesophyll cells in each treatment. Cd stress significantly reduced photosynthesis by reducing the content of pigments and disrupting chloroplast structure, which consequently decreased the biomass. However, respective addition of three organic acids greatly increased the biomass of S. variegata under Cd stress. Among them, the effect of malic acid or tartaric acid on shoot and total biomass accumulation was greater than that of citric acid. The alleviation of biomass probably related with the photosynthetic process. Results revealed that treatment with each organic acid enhanced the net photosynthesis rate under Cd stress. Malic acid promoted plant growth and biomass by increasing the chlorophyll content and mitigating damage to the photosynthetic apparatus resulting from Cd stress. Tartaric acid had little impact on the photosynthetic pigment content, but it was important in mitigating the ultrastructural damage of plants caused by Cd. Addition of citric acid significantly increased the carotenoid as well as the number and volume of chloroplasts in mesophyll cells, while the mitigation of structural damage in the photosynthetic apparatus was weaker than that in tartaric acid or malic acid treatment. It is concluded that application of tartaric acid or malic acid is effective in increasing the growth potential of S. variegata under Cd stress and thus can be a promising approach for the phytoremediation of Cd-contaminated soil.

Seasonal movement of chloroplasts in mesophyll cells of two Picea species.

Cold acclimation in evergreen conifers of temperate zone is associated with seasonal structural changes of mesophyll cells. Photoprotective reactions include the movement of chloroplasts from summer position when they are located along the cell walls to winter arrangement with their aggregation in one part of the cell. Special spatial arrangement of mesophyll in Picea species with chloroplasts located along the two opposite cell walls causes the very specific pattern of chloroplast movement. To reveal the intracellular apparatus involved in the seasonal organelle position changes, 3D reconstruction of mesophyll cell structure was applied. Two Picea species, P. obovata and P. pungens, from two geographic regions were studied in a 3-year course. The involvement of small transparent vacuoles in the development of cytoplasmic strands penetrating through the central vacuole and connecting two opposite lateral sides of the cell was shown. The nucleus and cytoplasmic organelles including chloroplasts move inwards the strand forming the cytoplasmic conglomerate enclosed by the vacuole at the cell center. Two Picea species have distinct differences in spatial organization of winter mesophyll cells and in structural events leading to its formation. Analysis of Picea species from two geographic regions over 3years of monitoring reveals dependence of seasonal organelle movement on the dynamics of temperature decline in autumn.

Fine mapping of a novel yellow-green leaf 14 (ygl14) mutant in rice

As the primary organ for photosynthesis, the leaf color is crucial for plant growth and development. In this study, we isolated a yellow green leaf 14 (ygl14) mutant from Xinong 1B, an indica restorer line of rice (Oryza sativa L.), which was treated with ethyl methane sulfonate. The mutant not only showed a yellow-green leaf phenotype for the entire life cycle, the flag leaf is significantly longer and the total leaf area is increased, which resulted in an increase in photosynthetic area. Leaf pigment (chlorophyll and carotenoids) contents were significantly lower in ygl14 than those in the wild type (WT). Compared with WT, stomatal conductance, photosynthetic rate, and transpiration rate of ygl14 were significantly reduced, whereas the intercellular CO2 concentration was significantly increased. Anatomical observation revealed that a portion of the chloroplasts in mesophyll cells of ygl14 were structurally impaired compared with those of WT. YGL14 was fine-mapped to a 70.7 kb region on chromosome 5, covered includes 15 open reading frames, no other yellow-green leaf related mutants have ever been reported within this region in rice. Quantitative real-time PCR analysis showed that the expression levels of genes associated with chlorophyll metabolism and photosynthesis were significantly altered in the ygl14 mutant. These results provide a foundation for cloning and functional analysis of the yellow-green leaf gene YGL14.