Starch Accumulation In Chloroplasts Research Articles

Sink-source imbalance triggers delayed photosynthetic induction: Transcriptomic and physiological evidence.

Sink-source imbalance causes accumulation of nonstructural carbohydrates (NSCs) and photosynthetic downregulation. However, despite numerous studies, it remains unclear whether NSC accumulation or N deficiency more directly decreases steady-state maximum photosynthesis and photosynthetic induction, as well as underlying gene expression profiles. We evaluated the relationship between photosynthetic capacity and NSC accumulation induced by cold girdling, sucrose feeding, and low nitrogen treatment in Glycine max and Phaseolus vulgaris. In G. max, changes in transcriptome profiles were further investigated, focusing on the physiological processes of photosynthesis and NSC accumulation. NSC accumulation decreased the maximum photosynthetic capacity and delayed photosynthetic induction in both species. In G. max, such photosynthetic downregulation was explained by coordinated downregulation of photosynthetic genes involved in the Calvin cycle, Rubisco activase, photochemical reactions, and stomatal opening. Furthermore, sink-source imbalance may have triggered a change in the balance of sugar-phosphate translocators in chloroplast membranes, which may have promoted starch accumulation in chloroplasts. Our findings provide an overall picture of photosynthetic downregulation and NSC accumulation in G. max, demonstrating that photosynthetic downregulation is triggered by NSC accumulation and cannot be explained solely by N deficiency.

Whirly1 enhances tolerance to chilling stress in tomato via protection of photosystem II and regulation of starch degradation.

In plants, the chilling response involves decreased photosynthetic capacity and increased starch accumulation in chloroplasts. However, the mechanisms that modulate these processes remain unclear. We found that the SlWHY1 gene is significantly induced by chilling stress (4°C) in tomato. Three SlWHY1 overexpression (OE) lines grew better than the wild type (WT) under chilling stress; the OE plants retained intact photosynthetic grana lamellae and showed enhanced hydrolysis of starch. By contrast, RNAi lines that inhibited SlWHY1 were more affected than the corresponding WT cultivar. Their grana lamellae were damaged and starch content increased. The psbA gene encodes the key photosystem II (PSII) protein D1. We show that SlWHY1 binds to the upstream region (A/GTTACCCT/A) of SlpsbA and enhances the de novo synthesis of D1 in chloroplasts. Additionally, SlWHY1 regulates the expression of the starch-degrading enzyme α-amylase (SlAMY3-L) and the starch synthesis-related enzyme isoamylase gene (SlISA2) in the nucleus, thus modulating the starch content in chloroplasts. We demonstrate that SlWHY1 enhances the resistance of tomato to chilling stress by maintaining the function of PSII and degrading starch. Thus, overexpression of WHY1 may be an effective strategy for enhancing resistance to chilling stress of chilling-sensitive crops in agricultural production.

The Omp85-type outer membrane protein p36 of Arabidopsis thaliana evolved by recent gene duplication.

Proteins of the Omp85 family are involved in the insertion of β-barrel shaped outer membrane proteins in bacteria and mitochondria, and-at least-in the transfer of preproteins across the chloroplast outer envelope. In general these proteins consist of up to five N-terminal "polypeptide transport associated" (POTRA) domains and a C-terminal, membrane embedded β-barrel domain. In Arabidopsis thaliana two plastidic gene families coding for Omp85-like proteins exist, namely the Toc75-III and the Toc75-V/Oep80 sub-family. The latter is composed of three genes, of which two do not contain POTRA domains. These are annotated as P39 and P36. However, P36 resulted from a very recent gene duplication of P39 and appears to be specific to Arabidopsis thaliana. Furthermore, we show that P39 is specifically expressed in vein tissues, while P36 is expressed at early and late developmental stages. T-DNA insertion in P36 causes a mild phenotype with reduced starch accumulation in chloroplasts of sepals pointing towards a yet to be described plastid function.

Comparative Proteomics of Thellungiella halophila Leaves from Plants Subjected to Salinity Reveals the Importance of Chloroplastic Starch and Soluble Sugars in Halophyte Salt Tolerance

Thellungiella halophila, a close relative of Arabidopsis, is a model halophyte used to study plant salt tolerance. The proteomic/physiological/transcriptomic analyses of Thellungiella plant leaves subjected to different salinity levels, reported herein, indicate an extraordinary ability of Thellungiella to adapt to large concentrations of exogenous saline by compartmentalizing Na(+) into cell vacuoles and accumulating proline and soluble sugars as organic osmolytes. Salinity stress stimulated the accumulation of starch in chloroplasts, which resulted in a greatly increased content of starch and total sugars in leaves. Comparative proteomics of Thellungiella leaves identified 209 salt-responsive proteins. Among these, the sequences of 108 proteins were strongly homologous to Arabidopsis protein sequences, and 30 had previously been identified as Thellungiella proteins. Functional classification of these proteins into 16 categories indicated that the majority are involved in carbohydrate metabolism, followed by those involved in energy production and conversion, and then those involved in the transport of inorganic ions. Pathway analysis revealed that most of the proteins are involved in starch and sucrose metabolism, carbon fixation, photosynthesis, and glycolysis. Of these processes, the most affected were starch and sucrose metabolism, which might be pivotal for salt tolerance. The gene expression patterns of the 209 salt-responsive proteins revealed through hierarchical clustering of microarray data and the expression patterns of 29 Thellungiella genes evaluated via quantitative RT-PCR were similar to those deduced via proteomic analysis, which underscored the possibility that starch and sucrose metabolism might play pivotal roles in determining the salt tolerance ability of Thellungiella. Our observations enabled us to propose a schematic representation of the systematic salt-tolerance phenotype in Thellungiella and suggested that the increased accumulation of starch, soluble sugars, and proline, as well as subcellular compartmentalization of sodium, might collectively denote important mechanisms for halophyte salt tolerance.

Chilling-induced ultrastructural changes to mesophyll cells of Arabidopsis grown under short days are almost completely reversible by plant re-warming

Exposure of plants to chilling (low temperatures above freezing) limits growth and development in all environments outside the lowest latitudes. Cell ultrastructure and morphometric studies may allow associations to be made between chilling-induced changes at the ultrastructural level, molecular events and their physiological consequences. We examined changes in the shape, size and membrane organization of the organelles of mesophyll cells in Arabidopsis thaliana (Col 0), a cold-resistant species, after subjecting 6-week-old plants grown at normal growth temperatures to chilling (2.5-4°C; 14-h dark/10-h light cycle) for 6, 24 and 72 h and after a re-warming period of 50 h. No ultrastructural differences were seen in the first 6 h of chilling but after 24 h we observed swollen and rounded chloroplasts with larger starch grains and dilated thylakoids compared to control plants. By 72 h, chilling had resulted in a large accumulation of starch in chloroplasts, an apparent crowding of the cytosol and a lower abundance of peripheral reticulum than in the controls. The average area per chloroplast in cell sections increased after 72-h chilling while the number of chloroplasts remained the same. Ring-shaped and other morphologically aberrant mitochondria were present in significantly higher abundance in plants given 72 h chilling than in the controls. Plant re-warming for 50 h reduced chloroplast size to those of the controls and returned mitochondria to standard morphology, but peripheral reticulum remained less abundant than in plants never given a cold treatment. The near full return to normal ultrastructure upon plant re-warming indicates that the morphological changes may be part of acclimation to cold.

The effect of heterologous VHb expression to the functioning of stress-related genes in hybrid aspen lines exposured to biotic stress

Background The hemoglobin produced by Vitreoscilla bacterium, VHb, is capable to promote the respiratory activity and ATP production under hypoxic conditions [1]. In micro-organisms grown under oxygen-limited conditions, the heterologous vhb expression improves the production of primary and secondary compounds, growth as well as stress tolerance [2,3]. VHb has also been shown to protect plants against deleterious effects of nitric oxide (NO), the important signalling molecule produced during pathogen challenges [4]. We have previously studied the vhb expressing hybrid aspen lines (Populus tremula L. x tremuloides Michx.) under elevated UV-B illumination and showed that the VHb lines had increased secondary metabolite production and also enhanced accumulation of starch in chloroplasts when grown in standard greenhouse conditions [5]. In order to reveal the effect of VHb on the expression of stressrelated genes in hybrid aspen exposed to biotic stress, we conducted experiments with pathogenic fungus and larvae of insect herbivore.

The effect of experimental warming on leaf functional traits, leaf structure and leaf biochemistry in Arabidopsis thaliana.

BackgroundThe leaf is an important plant organ, and how it will respond to future global warming is a question that remains unanswered. The effects of experimental warming on leaf photosynthesis and respiration acclimation has been well studied so far, but relatively little information exists on the structural and biochemical responses to warming. However, such information is very important to better understand the plant responses to global warming. Therefore, we grew Arabidopsis thaliana at the three day/night temperatures of 23/18°C (ambient temperature), 25.5/20.5°C (elevated by 2.5°C) and 28/23°C (elevated by 5°C) to simulate the middle and the upper projected warming expected within the 21st century for this purpose.ResultsThe 28/23°C treatment significantly reduced the life span, total biomass and total weight of seeds compared with the other two temperatures. Among the three temperature regimes, the concentrations of starch, chlorophyll, and proline were the lowest at 28/23°C, whereas the total weight of seeds, concentrations of chlorophyll and proline, stomatal density (SD), stomatal conductance (gs), net CO2 assimilation rate (A) and transpiration rate (E) were the highest at 25.5/20.5°C. Furthermore, the number of chloroplasts per cell and mitochondrial size were highest at 25.5/20.5°C and lowest at 28/23°C.ConclusionsThe conditions whereby the temperature was increased by 2.5°C were advantageous for Arabidopsis. However, a rise of 5°C produced negative effects, suggesting that lower levels of warming may benefit plants, especially those which belong to the same functional group as Arabidopsis, whereas higher levels of warming may produce negative affects. In addition, the increase in A under moderately warm conditions may be attributed to the increase in SD, chlorophyll content, and number of chloroplasts. Furthermore, starch accumulation in chloroplasts may be the main factor influencing chloroplast ultrastructure, and elevated temperature regulates plant respiration by probably affecting mitochondrial size. Finally, high SOD and CAT activities may enable plants grown at elevated temperatures to exhibit relatively high tolerance to temperature stress, thus alleviating the harmful effects of superoxide anion radicals and hydrogen peroxide.

Expression of Vitreoscilla haemoglobin in hybrid aspen (Populus tremula × tremuloides)

We describe the first ever expression of Vitreoscilla haemoglobin (VHb) in an economically important boreal woody plant hybrid aspen (Populus tremula x tremuloides). VHb has mainly been expressed in biotechnologically important unicellular organisms of both prokaryotic and eukaryotic origin. VHb expression, in this study, was analysed under different greenhouse cultivation conditions and under elevated UV-B illumination. Microscope analyses of leaves grown under optimized conditions revealed significant differences both in cell structure and size when the transgenic VHb lines were compared with the control lines. VHb lines displayed a higher relative volume of mitochondria and a significantly enhanced accumulation of starch in chloroplasts, all of which pointed towards changes in cellular energy production. Under elevated UV-B illumination, the differences between VHb lines became evident. Some specific VHb lines had elevated levels of total flavonoids, individual quercetin, kaempferol- and myricetin-derivatives relative to controls and other transgenic lines. This observation may reflect the availability of extra energy resources for secondary metabolite production and possibly an enhanced protection ability of these transgenic lines against UV-B illumination. Thus, all these findings point to changes in the energy metabolism of VHb lines. In the cultivation conditions tested this observation did not, however, result in a general improvement of elongation growth.

Photosynthetically active suspension cultures of potato spindle tuber viroid infected tomato cells as tools for studying viroid ? host cell interaction

Photosynthetically active callus and cell suspension cultures were established from uninfected Lycopersicon peruvianum plants and from uninfected and potato spindle tuber viroid (PSTVd) infected plants of Lycopersicon esculentum cv. Rutgers. Viroid infection was maintained in photoheterotrophic culture on media containing 3% sucrose, but during continuous photo-mixotrophic culture in low sucrose media (1% sucrose), the level of PSTVd accumulation decreased. Photoautotrophic cell suspensions could be established with uninfected, but not with viroid infected tomato cells. As compared to uninfected cells, PSTVd infected cells grew slowly, were morphologically different in size and shape, and formed tight cell aggregates. Electronmicroscopy showed that starch accumulation in chloroplasts, deformation of the chloroplast envelope and irregular plasmalemmasomes at the cell membrane were associated with PSTVd infection.

Effects of ozone on starch accumulation in Norway spruce (Picea abies)

Fumigation with 100 μg/m3 and 200 μg/m3 ozone in closed-top fumigation chambers induced starch accumulation in chloroplasts of Norway spruce. This accumulation was probably due to a partial inhibition of the starch translocation at night. The intensity of the effect was dependent on the season and the age of the needles. The accumulation was reversed in winter. It is therefore unlikely that such an effect has much significance for plant health.

Salt tolerance in the halophyte Suaeda maritima (L.) Dum. The influence of the salinity of the culture solution on leaf starch and phosphate content

Abstract. The starch concentration in mature leaves of the halophyte Suaeda maritima increased from 4.7 to 7.3 mg mg−1 chlorophyll when sodium chloride (680 mol M−3) was added to the solution in which the plants were grown. This effect of salinity on the starch: chlorophyll ratio was greater in young than in old leaves. Electron micrographs showed the starch to be in the chloroplasts and this was confirmed by measurements on isolated chloroplasts. Total phosphorus concentration (mg mg−1 chlorophyll) in leaves of all ages from plants of S. maritima decreased on salinization of the growth medium suggesting an inverse relationship between phosphorus and starch concentrations. However, although leaf starch concentration varied with leaf age, phosphorus concentration did not. The cause of starch accumulation in chloroplasts at salinities which are optimal for growth (340 mol m−3) remains unclear.

Plasmolysis of Glycine max mesophyll cells: the use of octylguanidine and its implications in protoplast isolation

Soybean ( Glycine max Merr cv. ‘Ransom’) mesophyll cells were difficult to plasmolyze when placed in mannitol. Plasmolysis behavior depended largely on plant age and cell type. Difficulty in plasmolyzing mesophyll cells increased with plant age. Cells of the the second palisade layer were more difficult to plasmolyze than those of the first layer and spongy parenchyma. No plasmolysis occured in cells from podding stage plant material (16 weeks old). Brief treatment of cells with 0.3 mM octylguanidine (OG) in 0.4 M mannitol decreased plasmamembrane adherence to the cell wall and enhanced plasmolysis in all cell types except starch filled palisade cells of the second layer of 16-week-old material. Light starvation of tissue and OG treatment or 0.75 M CaCl 2 as plasmolyticum improved plasmolysis in cells of the second palisade layer of leaves of 10–16-week-old plants. These observations indicate that plasmolysis of soybean mesophyll cells is difficult due to either strong adherence of the plasma membrane to the cell wall, and/or mechanical resistance to protoplast contraction as a consequence of starch accumulation in chloroplasts. Our observations on the plasmolytic behavior of mesophyll cells and the high protoplast yield at microscale isolation in situ suggest that plasmolysis using OG will result in higher protoplast yield and quality.

Starch accumulation in bundle sheath chloroplasts during the leaf development of C3 and C4 plants of the Gramineae

Nonphotosynthetic starch accumulation in chloroplasts is examined by light microscopy during the leaf development of several C3 and C4 grasses and compared between mesophyll and bundle sheath cells. In Oryza sativa, Phragmites communis (C3 grasses), and Cynodon dactylon (C4 grass), bundle sheath chloroplasts accumulate large amounts of starch in the early stages of the leaf development, while in other grasses, both mesophyll and bundle sheath chloroplasts accumulate only small amounts of starch. It is suggested that bundle sheath chloroplasts of starch-accumulating species, regardless of their photosynthetic characteristics, are specialized in the accumulation and supply of storage starch during the leaf development.