Thylakoid System Research Articles

Acclimation of Adult Lolium multiflorum Leaves to Changes in Irradiance: Effect on Leaf Photosynthesis and Chloroplast Ultrastructure

Summary Photosynthetic and morphological features were examined in fully expanded leaves of plants transferred either from low to high or high to low light conditions and compared to control leaves maintained under constant high or low light. In both control conditions, net maximum photosynthetic rate, stomatal and intracellular conductances declined about one week following full leaf expansion suggesting the onset of leaf senescence. Plants transferred from low to high light at the time of full expansion of experimental leaf (3rd) showed an increase in all photosynthetic parameters within 2–3 days, a plateau (5–7 days) and then a decline. In the reciprocal transfer from high to low light, a dramatic decrease in photosynthetic characteristics occurred after 4 days, progressively levelling off to control low light values. Low-light control chloroplasts showed a typical dense thylakoid system versus a more reduced network in the high light counterpart. A transfer from low to high light induced a reduction in the relative lamellar content thus readjusting to a typical high-light plastid morphology, while in the reciprocal transfer renewed thylakoid growth or rearrangement led to a dense lamellar system comparable to that in control low light plastids. Thus photosynthetic parameters and chloroplast ultrastructure keep pace with or can be readjusted by prevailing light conditions even in fully differentiated leaves.

Cotyledonal chloroplasts in the hypogeal seeds of clementine

Clementine (Citrus nobilisxCitrus aurantium amara pumila) is a chloroembryophyte with green quiescent embryos and hypogeal germination. The cotyledonal chloroplasts have been studied during germination in the dark and under two different irradiances 120 and 240 μmol·m(-2)·s(-1) throughout a period of three weeks. The plastids of the outer adaxial and inner regions develop differently. In the light, the former differentiate a photosynthetically active thylakoid system with an ultrastructural organization and a polypeptide composition resembling that of leaf chloroplasts. The "inner" chloroplasts maintain an organization reminiscent of chloroplasts of the quiescent embryo and never get beyond the photosynthesis/respiration compensation point; their differentiation pattern appears essentially the same under the two different irradiances. These observations and the germination in the dark indicate that the above differentiation is not strictly photodependent. The greening ability of the cotyledons provides, on occasion, an additional photosynthetic supply to this plant.

Modulation by a high citrate concentration of kinetic parameters and of functional stability of two immobilized thylakoid systems

This article deals with aspects of the reciprocal interaction between the activity of chloroplast membranes and their microenvironment. The artificial matrices used in the present work to immobilize thylakoids (albumin-glutaraldehyde matrix, polyurethane foam) can be regarded as weak ion exchangers. Thus, the distribution of the solute between the matrix surface and the external solution should, at least in part, be governed by a Donnan equilibrium. The influence of a high ionic strength medium (750mM potassium citrate) on the kinetic parameters (K(p1) V(m)) and on the stability of the photosynthetic activity of immobilized chloroplast membranes has been studied. The results show similarities in behavior of the two supports studied in that, for both, a high concentration of salt (citrate) increases the apparent affinity for ferricyanide and allows a better transformation of this electron acceptor in CSTR experiments.

Photoautotrophic cell suspension cultures of periwinkle (Catharanthus roseus (L.) G. Don): Transition from heterotrophic to photoautotrophic growth

Chlorophyllous, heterotrophic periwinkle (Catharanthus roseus (L.) G. Don) cells were capable of sustained photoautotrophic growth in sugar-free B5 medium containing naphthaleneacetic acid and kinetin when provided with a CO2-enriched atmosphere. An increase in cell fresh weight, first observed approximately 2 weeks after transfer from heterotrophic to photoautotrophic conditions, coincided with the development of maximum chlorophyll content and photosynthetic activity. Electron micrographs revealed that chloroplasts of cells cultured photoautotrophically in continuous light contained large starch granules and exhibited a less extensive thylakoid system than did periwinkle mesophyll chloroplasts. Photoautotrophic cells did not accumulate vindoline or dimeric alkaloids.

Influence of lead on Chlamydomonas reinhardii danegard (volvocales, chlorophyta): Accumulation, toxicity and ultrastructural changes

Cell suspensions of Chlamydomonas reinhardii obtained from continuous cultures were exposed under batch culture conditions to various concentrations of lead. Photosynthetic oxygen evolution, chlorophyll content, dry weight and lead accumulation were determined. Exposure to 1 μM Pb in the medium for 3 hr caused a marked reduction in net photosynthesis. A reduction of approximately 50% ( ed 50) was obtained with 5 μM Pb. Exposure of the alga for 24 hr to 20 μM Pb was lethal. The amounts of lead accumulated within 24 hr by algae exposed to external metal concentrations of 1, 5, and 20 μM Pb were 26.3, 99.1, and 339.3 μM Pb/g of dry weight, respectively. Contaminated algal material, obtained by exposure to lead at the toxic level of 5 μM, was examined by transmission electron microscopy. Lead caused drastic ultrastructural damage: the thylakoid systems of the chloroplast were disarranged and showed a fingerprint-like appearance. Stigmata were missing or only partially present. Changes were observed in nuclear and mitochondrial structure. The number of lipid bodies was increased whereas starch granules were generally absent. Using the EDX technique we found deposits of lead in the cell wall, the chloroplast, the remaining part of the stigma, and the vacuole.

Quantitative fluorescence microscopy on dynamic changes of plastid nucleoids during wheat development

Dynamic change of plastid nucleoids (pt nucleoids) was followed by fluorescence microscopy after staining with 4′6-diamidino-2-phenyl indole (DAPI). The fluorescence image was quantified with a supersensitive photonic microscope system based on photon counting and image analysis. The results showed that small pt nucleoids located in the center of proplastids in the dry seed increased in size after imbibition and formed highly organized ring structures in the dark, which divided into ca. 10 pieces within 3 days. Corresponding to this morphological change, DNA content of a plastid multiplied 7.5 fold. Total increase in DNA content of pt nucleoids per cell was 34 times as that of dry seed, as plastid multiplied 4.6 times in the average during this period. Upon light illumination small pt nucleoids having basic genome size were separated from divided pt nucleoids, suggesting a relationship with the formation of thylakoid system. The significance of the procedure established in this study is discussed in analysing the dynamic changes of intracellular small genomes.

Primary Role of the Cytoplasmic Membrane in Thermal Acclimation Evidenced in Nitrate-Starved Cells of the Blue-Green Alga, Anacystis nidulans

The lipid phase transition of the cytoplasmic membrane and the chilling susceptibility were studied in nitrate-starved Anacystis nidulans cells. Nitrate starvation resulted in the disappearance of the thylakoid membrane system, without any effect on chilling susceptibility. The chilling susceptibility of the algal cells depended on the growth temperature. Temperatures of lipid phase transitions of the cytoplasmic membranes were detected by chilling-induced spectral changes in the carotenoid region, in vivo. These values were identical to those of cultures containing intact thylakoid systems. Our results suggest that cytoplasmic membrane plays a determinative role in the thermal acclimation of the alga cells.

Thylakoid formation from coiled lamellar bodies during carposporogenesis in Faucheocolax attenuata Setch. (Rhodophyta, Rhodymeniales).

Chloroplast development during carposporogenesis in the parasitic red alga Faucheocolax attenuata Setch. was studied by electron microscopy. Proplastids are usually found in the peripheral cytoplasm of young carpospores and are characterized by the presence of portions of a peripheral thylakoid and coiled lamellar bodies that range in size up to 0.5 micron. One type of coiled lamellar body occurs in the peripheral region of the proplastid and is continuous with the peripheral thylakoid, while the other type is found in the central portion of the stroma. These coiled lamellae separate and expand, adding membranes to both thylakoid systems, thereby functioning as thylakoid-forming bodies. As each coiled lamella unravels, it forms an undulated double-membraned structure having the same width as a thylakoid. After substantial expansion, the developing thylakoids begin to straighten and assume a parallel orientation to each other, thus becoming mature thylakoids. Small coiled lamellae often persist in mature carpospore chloroplasts, and are utilized in additional thylakoid formation during carpospore germination.

Formation of Polar Lipids and Isoprenoid Compounds in Heat-Treated 70S Ribosome-Deficient Rye Leaves

Summary The chloroplast-specific glycolipids monogalactosyldiacylglycerol, digalactosyldiacylglycerol, sulfoquinovosyldiacylglycerol and the prenylquinones α-tocopherol, plastoquinone-9 and phylloquinone were formed in the 70S ribosome-deficient leaf tissue of rye seedlings grown at a non-permissive temperature of 32°C. In light 32°-grown 70S ribosome-deficient leaves were chlorotic. Etiolated 32°-grown leaves contained about 50% of the protochlorophyll(ide) content of control leaves from permissive growth conditions (22°C). As in chloroplasts, monogalactosyldiacylglycerol and digalactosyldiacylglycerol were the predominating polar lipids in isolated bleached ribosome-deficient plastids. Sulfoquinovosyldiacylglycerol and the phospholipids phosphatidylcholine, phosphatidylglycerol and phosphatidylinositol were also present. The 32°-grown 70S ribosome-deficient leaves contained the same molecular species of monogalactosyldiacylglycerol and digalactosyldiacylglycerol as 22°-grown control leaves. As under permissive conditions linoleic and linolenic acid were the prevailing fatty acids of the galactolipids from 70S ribosome-deficient leaves. All enzymes of the biosynthesis of protochlorophyll(ide) and of the chloroplast glycolipids and prenylquinones must be synthesized on cytoplasmic 80S ribosomes. In accord with the reduction of the thylakoid system the ratio of monogalactosyldiacylglycerol to digalactosyldiacylglycerol was lower in 70S ribosome-deficient than in normal green leaves. In etiolated leaves grown at either 32°C or 22°C the amounts of the glycolipids and prenylquinones did not differ markedly. However, in light the glycolipid and prenylquinone contents remained almost as low in the bleached 70S ribosome-deficient leaves as in darkness, while several-fold increases accompanied greening of normal leaves in light. The data suggest that the light-mediated increase of glycolipids and prenylquinones depends on the availability of chlorophyll. The contents of steroidal saponins in oat leaves were slightly higher in light than in darkness and showed no specific relationship to the presence of etioplasts. They did not notably differ in 22°- or 32°-grown leaves.

Freeze-Fracture Ultrastructure of Thylakoid Membranes in Chloroplasts from Manganese-Deficient Plants

Leaves from spinach (Spinacia oleracea L. cv Hybrid 102) plants grown in Mn-deficient nutrient solution were characterized by chlorosis, lowered chlorophyll a/b ratio and reduced electron transport. There were characteristic changes in room temperature fluorescence induction kinetics with increased initial yield (F(o)) and decreased variable fluorescence (F(v)). The fluorescence yield after the maximum fell rapidly to a level below F(o). The shape of the rise from F(o) to the maximum was altered and the size of photosystem II units increased, as measured by half-rise time of F(v) in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. The Mn-deficient leaves were harvested before necrosis, when thin section electron microscopy revealed no disorganization of the thylakoid system. Thylakoid membranes were examined by freeze-fracture electron microscopy. The effect of Mn-deficiency was the specific loss of three-quarters of the particles from the endoplasmic fracture face of appressed thylakoids (EFs). Mn-deficient leaves were restored to near normal 2 days after application of exogenous Mn to the nutrient solution. It is concluded that the loss of most, but not all, functional photosystem II reaction centers from grana, with no alteration in light-harvesting complex or photosystem I, is responsible for the fluorescence and functional properties observed. The response of thylakoids to Mn deficiency shows that there is a fundamental difference in composition and function of stacked and unstacked endoplasmic fracture particles. The stacked endoplasmic fracture particle probably contains, in close association, the photosystem II reaction center and also the Mn-containing polypeptide, the 3-(3,4-dichlorophenyl)-1,1-dimethylurea-binding protein, and all electron transport components in between.

Seasonal Changes in the Chloroplast Ultrastructure in Abutilon Mosaic Virus (AbMV) infected Abutilon spec. (Malvaceae)

AbstractVarious kinds of pathological effects of the Abutilon Mosaic Virus (AbMV) in seasonal dependency have been observed on the macroscopic as well as on the microscopic level. The annual rhythmic fluctuation of light caused by the varying length and intensity of light incidence is directly correlated with the realization of symptoms, leading to an intensification of the leaf mosaic and to an increase in the light leaf areas during the summer. These macroscopic observations are correlated with an annual change in the plastid fine structure in the mesophyll of the lightest areas of the leaf. The grana‐stroma‐organization of the plastids is completely eliminated through a reduction and disorganization in the thylakoid system during the spring and summer, restored in the autumn, and preserved over the winter. This change in the plastid fine structure is limited to the leaf mesophyll. The plastids of the leaf stem, like the plastids of non‐infected plants, do not display any change in their fine structure.

Three-dimensional ultrastructure of a unicellular cyanobacterium.

The first complete three-dimensional ultrastructural reconstruction of a cyanobacterium was accomplished with high-voltage electron microscopy and computer-aided assembly of serial sections. The precise arrangement of subcellular features within the cell body was very consistent from one cell to another. Specialized inclusion bodies always occupied specific intracellular locations. The photosynthetic thylakoid membranes entirely surrounded the central portion of the cytoplasm, thereby compartmentalizing it from the rest of the cell. The thylakoid membranes formed an interconnecting network of concentric shells, merging only at the inner surface of the cytoplasmic membrane. The thylakoids were in contact with the cytoplasmic membrane at several locations, apparently to maintain the overall configuration of the thylakoid system. These results clarified several unresolved issues regarding structure-function relationships in cyanobacteria.

PLASTIDS IN THE ROOTS OF PHASEOLUSVULGARIS

SUMMARYIn roots of Phaseolus vulgaris plastid development takes place from the apical meristem both upwards into the root proper and downwards into the root cap. The maximum state of plastid development seems to be achieved in the cortical cells of that part of the primary root associated with mature root hairs. However in these cortical cell plastids the thylakoid system is very limited in extent and no true prolamellar bodies are formed. Farther from the apex of the root proper, in the zone of mature lateral roots, the plastids appear to have undergone dedifferentiation and to have lost whatever thylakoids they once contained. Both the rate of plastid development and the patterns of production of ancillary plastid structures, including starch and membrane–bound bodies, vary in different cell files. The differential distribution of these and other plastid features are summarized in the accompanying diagrams.

Oxygen exchange associated with electron transport and photophosphorylation in spinach thylakoids

O 2 uptake in spinach thylakoids was composed of ferredoxin-dependent and -independent components. The ferredoxin-independent component was largely 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) insensitive (60%). Light-dependent O 2 uptake was stimulated 7-fold by 70 μM ferredoxin and both uptake and evolution (with O 2 as the only electron acceptor) responded almost linearly to ferredoxin up to 40 μM. NADP + reduction, however, was saturated by less than 20 μM ferredoxin. The affinity of O 2 uptake for for O 2 was highly dependent on ferredoxin concentration, with K 1 2 (O 2) of less than 20 μM at 2 μM ferredoxin but greater than 60 μM O 2 with 25 μM ferredoxin. O 2 uptake could be suppressed up to 80% with saturating NADP + and it approximated a competitive inhibitor of O 2 uptake with a K i of 8–15 μM. Electron transport in these thylakoids supported high rates of photophosphorylation with NADP + (600 μmol ATP/mg Chl per h) or O 2 (280 μmol/mg Chl per h) as electron acceptors, with ATP 2 e ratios of 1.15–1.55. Variation in ATP 2 e ratios with ferredoxin concentration and effects of antimycin A indicate that cyclic electron flow may also be occurring in this thylakoid system. Results are discussed with regard to photoreduction of O 2 as a potential source of ATP in vivo.

Light-induced absorbance changes of carotenoids in brown algae

Light-induced absorbance changes were studied for brown algae with 23 species and a pronounced absorbance change around 563 nm was found in all algae examined. 3-(3,4-dichlorophenyl)-1,1-dimethylurea and gramicidin J suppressed the initial rate and the magnitude of the absorbance change. Carbonylcyanidem-chlorophenylhydrazone did not affect the initial rate but decreased the maximum level of the change. All thalli and the chloroplasts tested had an absorption band at around 540 nm due to fucoxanthin which accounted for about 70–90% of the total carotenoids in brown algae. It is proposed that the 563 nm-change is caused by the red shift of fucoxanthin responding to the light-induced change in the membrane potential of the thylakoid system.

DIFFERENTIATION OF THE PHOTOSYNTHETIC APPARATUS IN PHYLLITIS SCOLOPENDRIUM (L.) NEWMAN

SUMMARY Chloroplast development in both coiled and uncoiling croziers of Phyllitis scolopendrium has been studied. An interesting stage of chloroplast ontogenesis appears to be that characterized by the presence of very long thylakoid stacks. It resembles the final stage of organization attained by the chloroplasts of many green algae at maturity even if, in P. scolopendrium, it represents only an intermediate stage in thylakoid system ontogenesis. Growing the plants in the dark has a pronounced effect on the morphogenesis of the frond and on plastid differentiation. In both dark- and light-grown plants we could observe, even if in different amounts, prolamellar body-like structures interconnected with the thylakoids. The presence of such structures is discussed, especially in view of the fact that ferns are able to synthesize chlorophylls in the dark.

The Ultrastructure of Carposporogenesis in Gigartina teedii (Roth) Lamour. (Gigartinales, Rhodophyceae): Auxiliary Cell, Cystocarpic Plant

Summary The auxiliary cell and the tissues of the female gametophyte (cystocarpic plant) have been studied during carposporogenesis in Gigartina teedii by light and electron microscopy and histochemistry. During the formation of gonimoblast cells, the auxiliary cell has an irregular shape and is multinucleated. It contains dense cytoplasm, few dictyosomes, numerous mitochondria, starch grains and plastids in a proplastid state. A covering layer of cells, derived from medullary filaments, is formed around the gonimoblast. It thickens and forms a medullary pericarp of haploid origin. The medullary pericarp cells are characterized by many conspieuous vacuoles (mucilage sacs), few dictyosomes, mitochondria and by plastids with a reduced thylakoidal system. These cells are also multinucleate. The inner medullary pericarp cells are less vacuolized, and are connected both with the gonimoblast cells and with peripheral elongated cells of the medullary pericarp. There are isodiametric cells with a rich, dense cytoplasm, numerous mitochondria and lipid droplets, microbodies and a few plastids with reduced thylakoidal structure. In addition there are elongate medullary pericarp cells between the gonimoblast cells. All these cells seem to serve as the nutritive tissue of the developing gonimoblast. During carposporogenesis the cortical cells surrounding the cystocarp divide repeatedly. The dictyosomes become hypertrophied and many vesicles containing polysaccharides (periodic acid silver-methenamine method) are formed from the Golgi apparatus. The wall of the epidermal cells does not give a positive PAS-reaction. This is in contrast to their apical cap formed by the contents of Golgi vesicles. The cell walls of the epidermal cells stains, however, with ruthenium red. The “cuticle” is about 5 μm thick and has a multilayered structure. The results of staining reactions suggest that it contains proteins and polysaccharides.

The Ultrastructure of Carposporogenesis in Gigartina teedii (Roth) Lamour. (Gigartinales, Rhodophyceae): Gonimoblast Cells and Carpospores

Carpospore differentiation has been studied in Gigartina teedii using light and electron microscopy and histochemistry. Young gonimoblast cells possess a rich and dense protoplasmic content, but contain few organelles. The chloroplasts are present in a proplastid state and usually possess only a single peripheral thylakoid. Mature gonimoblast cells are highly vacuolate. Carpospore development may be separated into 3 stages. The youngest (stage I) is characterized by dictyosomes with a straight profile, formation of fibrous vesicles, and the presence of mucilage sacs, dense ER-associated bodies, microbodies and twisted structures within the mitochondrial matrix. Formation of the internal thylakoid system commences in the chloroplasts, while concomitantly the first small-sized starch grains appear in the cytoplasm. The primary mucilage of mucilage sacs is rich in sulfated polysaccharides and probably serves in spore liberation. The second stage (stage II) is characterized by the disappearance of the mucilage sacs, dense ER-associated bodies, microbodies and twisted structures of mitochondria. The dictyosomes retain a straight profile, exhibit extreme hypertrophy and continue to secrete fibrous vesicles. The inflated fibrous vesicles derived from dictyosomes of stage I and II migrate to the periphery of the cytoplasm and are responsible for most of the cell wall deposition to form the thick carpospore wall. During the final stage (stage III) the dictyosomes assume a semicircular profile and produce cored vesicles with a glycoproteinrich content, which probably functions as an adhesive after spore liberation. The older carpospores are also characterized by having large quantities of starch, rough ER, and numerous large fibrillar vacuoles which are derived from the Golgi-cored vesicles. The mucilaginous component of the cell wall and the intercellular matrix of Gigartina teedii carpospores seem to be rich in sulfated polysaccharides.

The contact activity of difenzoquat in two United Kingdom spring wheat cultivars

SummaryThe contact action of difenzoquat was investigated on seedlings of spring wheat (Triticum aestivum L.) cultivars tolerant (Maris Butler) and susceptible (Sicco) to the translocated etTect of the herbicide on the apical meristem. Applied as a spray the chemical caused an increase in electrolyte leakage before the development of visible damage. Chlorophyll levels were also reduced and both effects were greater on Maris Butler than Sicco.Droplets of difenzoquat caused similar ultrastructural effects on the two cultivars. These included swelling of the chloroplasts with subsequent disorganization of the thylakoid system accompanied by disruption of other cellular components. Similar effects have been reported with paraquat and it is suggested that the contact action of difenzoquat is due to a weak paraquat type activity.

THE ESTABLISHMENT OF THE PLASTID THYLAKOID SYSTEM

SummaryMaking use of serial thin sections of conventionally fixed tissue we have constructed a model of the thylakoid system in a pre‐granal, dividing chloroplast. The three‐dimensional configuration of this plastid is compared with the thylakoid configurations seen in 1μm thick sections of the zinc iodide‐osmium impregnated tissue which were examined with a high voltage electron microscope. A comparison has also been made between the differential staining characteristics of the various membranous invaginations, vesicles and tubules which are frequently associated with the plastid envelope and which may play a part in development of the thylakoid system.