Distribution of Protein-bound Hexosamine in Chloroplasts

Intact chloroplasts of spinach (Spinacia oleracea L.), sunflower (Helianthus annuus L.), and maize (Zea mays L.) mesophyll cells contained 0.33, 0.50, and 0.14% of bound hexosamine on a protein basis, respectively. Undifferentiated maize chloroplasts contained 0.19%. Values for chloroplast lamellae were, respectively, 0.16, 0.18, 0.12, and 0.06% and for envelope membranes they were 1.6, 2.5, 3.8, and 2.7%. Thus most of the hexosamine of chloroplasts is located in the envelope membrane.     

Changes in the Number and Composition of Chloroplasts during Senescence of Mesophyll Cells of Attached and Detached Primary Leaves of Wheat (Triticum aestivum L.)

Changes in the number and composition of chloroplasts of mesophyll cells were followed during senescence of the primary leaf of wheat (Triticum aestivum L.). Senescence was due to the natural pattern of leaf ontogeny or was either induced by leaf detachment and incubation in darkness, or incubation of attached leaves in the dark. In each case discrete sections (1 centimeter) of the leaf, representing mesophyll cells of the basal, middle, and tip regions, were examined. For all treatments, senescence was characterized by a loss of chlorophyll and the protein ribulose 1,5-bisphosphate carboxylase (RuBPCase). Chloroplast number per mesophyll cell remained essentially constant during senescence. It was not until more than 80% of the plastid chlorophyll and RuBPCase was degraded that some reduction (22%) in chloroplast number per mesophyll cell was recorded and this was invariably in the mesophyll cells of the leaf tip. We conclude that these data are consistent with the idea that degradation occurs within the chloroplast and that all chloroplasts in a mesophyll cell senesce with a high degree of synchrony rather than each chloroplast senescing sequentially.     

Effects of Water Stress and High-Temperature Stress on the Structure and Activity of Photosynthetic Apparatus of Zea Mays and Helianthus Annuus

Effects of high-temperature stress (HTS) and PEG-induced water stress (WS), applied separately or in combination, on the functional activity and ultrastructure of the photosynthetic apparatus (PSA) of maize (Zea mays L.) and sunflower (Helianthus annuus L.) plants were investigated. In maize plant tissues WS provoked the decrease in RWC by 10.9 %, HTS by 7.0 %, and after simultaneous application of the both treatments the decrease was 32.7 % in comparison with control plants. Similar but more expressed changes were observed in sunflower plants. Sunflower was more sensitive to these stresses. Net photosynthetic rate decreased significantly after all treatments, more in sunflower. In mesophyll chloroplasts after separately applied WS and HTS the number of grana and thylakoids was reduced and electron-transparent spaces appeared. At combined stress (WS+HTS) granal and stromal thylakoids were considerably affected and chloroplast envelope in many of them was partially disrupted. This revised version was published online in August 2006 with corrections to the Cover Date.     

Structural and Functional Changes of Mesophyll Cells during Leaf Growth in Two Species of Spring Ephemers

The chloroplast ultrastructure, plastid pigments, and potential photosynthesis of leaf mesophyll cells were examined during the vegetative season of two spring ephemers Scilla sibirica Haw. and Chionodoxa luciliae Boiss. The development of chloroplasts was shown to precede the appearance of photosynthesis. The earliest stage of leaf growth was marked by the synthesis of carotenoids that play a structural and organizational role in the formation of chloroplast grana and protect the photosynthetic apparatus from photodynamic destruction under high insolation and low temperature conditions. Chlorophyll synthesis was closely correlated with the dynamics of potential photosynthesis. All these structural and functional features of mesophyll cells reflect the evolutionary strategies of adaptation in spring ephemers, which enable these plants to complete their short life cycle in the environment combining low temperature and high insolation.     

Maize F<Subscript>1</Subscript> hybrid differs from its maternal parent in the development of chloroplasts in bundle sheath,but not in mesophyll cells: Quantitative analysis of chloroplast ultrastructure and dimensions in different parts of leaf blade at the beginning of its senescence

The quantitative changes of chloroplast ultrastructure and dimensions in mesophyll (MC) and bundle sheath (BSC) cells, associated with the onset of leaf senescence, were followed along the developmental leaf blade gradient of the third leaf of maize (Zea mays L.). To ascertain whether the rapidity of structural changes associated with the transition of chloroplasts from mature to senescent state is a heritable trait, the parental and the first filial generations of plants were used. The heterogeneity of leaf blade, associated with the development of maize leaf (with the oldest regions at the apex and the youngest ones at the base) was clearly discernible in the ultrastructure and dimensions of chloroplasts; however, there were differences in the actual pattern of chloroplast development between both genotypes as well as between both cell types examined. While the course of MC chloroplasts’ development at the onset of leaf senescence in maize hybrid followed that of its parent rather well, this did not apply for the BSC chloroplasts. In this case, each genotype was characterized by its own distinguishable developmental pattern, particularly as regards the accumulation of starch inclusions and the associated changes of the size and shape of BSC chloroplasts.     

Immunogold labelling indicates high catalase concentrations in amorphous and crystalline inclusions of sunflower (Helianthus annuus L.) peroxisomes

Summary Immunogold labelling and electron microscopy were used to investigate whether catalase was present in peroxisomal inclusions, the composition of which has not yet been determined in plant cells. In the mesophyll cells of sunflower (Helianthus annuus L.) cotyledons, the catalase gold label was confined to peroxisomes. At day 2 of postgerminative growth in darkness, peroxisomes were free of inclusions, and the matrix was homogeneously labelled with gold particles. Thereafter, amorphous inclusions appeared, but by day 5 of growth, conspicuous crystalline inclusions (cores) were the predominant type. This developmental change, first observed in cotyledons grown in continuous light between day 2.5 and 5, also took place in cotyledons kept in permanent darkness. Both amorphous and crystalline inclusions showed a much higher immunogold label than did the peroxisomal matrix, indicating that catalase was a component of both types of peroxisomal inclusions. In contrast to catalase, the immunogold label of glycolate oxidase was almost completely absent from cores and was confined to the peroxisomal matrix. Together with reports on the absence of other enzymes from peroxisomal inclusions in sunflower and other species (Vaughn, 1989) our results suggest that catalase is a major constituent of amorphous and crystalline peroxisomal inclusions in plants.     

Changes of Anatomical Features, Photosynthesis and Ribulose Bisphosphate Carboxylase-Oxygenase Content of Mango Leaves

Changes in anatomical and physiological features, includingchanges in amount per unit area of anthocyanin and chlorophyll,in leaves of seedling mango (Mangifera indica L. cv. Irwin)trees were determined to understand what controls the rate ofphotosynthesis (Pn) at various stages of development. The youngleaves of seedling trees contained high concentrations of anthocyanin.During enlargement of leaves, the disappearance of anthocyaninand the accumulation of chlorophyll occurred concomitantly;the anthocyanin content began to decrease markedly once theleaf area had reached a maximum. During the early period ofleaf development, the thickness of mesophyll tissue decreasedtemporarily, but when the length of the leaf reached half thatof a mature leaf, the mesophyll began to thicken again. Smallstarch grains appeared in the chloroplasts of the young leavesand chloroplast nucleoids (ct-nuclei) were distributed throughoutthe chloroplasts. When leaves matured, ct-nuclei were displacedto the periphery of chloroplasts because of the accumulationof large starch grains. Compared with young leaves, green andmature leaves contained greater concentrations of ribulose bisphosphatecarboxylase-oxygenase (RuBisCO) protein. The results of immunocytochemicalexamination of RuBisCO under the light microscope reflectedthe results of electrophoresis measurements of RuBisCO. Pn waslow during the chocolate-coloured stage of early leaf development.In green and mature leaves Pn was higher; the average Pn was7·6 mg CO₂ dm^-2 h^-1 under light at intensities above500 µmol m^-2 s^-1.Copyright 1995, 1999 Academic Press Mangifera indica L., mango leaf, chloroplast nucleoids, chloroplast ultrastructure, starch accumulation, anthocyanin, chlorophyll, DAPI staining, SDS-PAGE, immunocytochemical technique     

Genetic analysis of an electrophoretic variant for the chloroplast-associated form of Cu/Zn superoxide dismutase in sunflower (Helianthus annuus L.)

Polyacrylamide gel electrophoresis of water-soluble proteinsfrom sunflower (Helianthus annuus L.) cotyledons, followed byspecific staining for superoxide dismutase activity, discriminated,according to their electrophoretic mobility, two distinct achromaticbands for Cu/Zn superoxide dismutase. Zymograms of proteinsfrom isolated chloroplasts showed that the chloroplast-locatedCu/Zn superoxide dismutase (Cu/ZnSOD_Chl) migrated faster inthe SOD activity-stained gels. An electrophoretic variant pattern,whose mobility is lower than the control pattern, was identifiedin the ABA-deficient mutant w-1. The variant is coded by a nucleargene with two codominant alleles. Key words: Sunflower, Helianthus annuus L., ABA-deficient mutant, electrophoretic isozyme variant, superoxide dismutase     

Pollen Development and Quantitative Cytochemistry of Exine and Intine Enzymes in Sunflower, Helianthus annuus L

High resolution cytochemical methods have been used to characterizepollen development and pollen-wall structure in Helianthus annuus.Aniline-blue fluorescent material, presumably callose, was detectedin the nexine layer throughout its development. It was associatedwith acid phosphatase activity, while the outer sexine possessedintense esterase activity during the young spore period. Acidphosphatase and esterase were present in both intine and exinewall sites in contrast to their specific location in other pollentypes. Quantitative cytochemical estimates of enzyme activityduring development reveal esterase patterns typical of gametophyticsynthesis, while acid phosphatase patterns are characteristicof sporophytic origin suggesting tapetal transfer during thevacuolate period. Helianthus annuus L, sunflower, pollen development, exine enzymes, intine enzymes, quantitative cytochemistry     

甜菊叶愈伤组织诱导过程中叶绿体的超微结构变化

观察了甜菊(Stevia rebaudiana Bertoni)叶外植体愈伤组织诱导过程中叶绿体的超微结构变化。结果表明,当叶外植体转移到培养基上培养后,叶绿体的片层结构逐渐退化。在叶绿体发生退化的过程中伴有叶绿体出芽和原质体的形成。推测新产生的原质体来自叶绿体产生的芽状体。而叶绿体本身最后完全解体消失。叶绿体超微结构的这种变化与高度液泡化的叶肉细胞脱分化至分生状态是平行的。随着培养的进行,分生状态的细胞发生液泡化变为薄壁细胞时,在愈伤组织表层的细胞中,质体重新形成片层结构,而内部细胞的质体则充满淀粉粒。     

Water Stress in Sunflower (Helianthus annuus L.) 2. Effects on Leaf Cells and Leaf Area

Three water stress treatments were applied at early, mid andlate stages of vegetative development in sunflower. The effectsof these stresses on leaf area, cell frequency, number of cellsper leaf and palisade cell area were examined. Final leaf area was reduced in all stress treatments. The largestreduction occurred in leaves that were unfolding or about tounfold at the commencement of stress. At full expansion of theseleaves cell frequency had increased, cell number had decreasedand cell area had decreased. These results help to explain theeffects of stress on final leaf area, especially the reducedarea of the lower leaves that are most sensitive to water stress. Helianthus annuus L., sunflower, water stress, node number, leaf area     

<Emphasis Type="Italic">mesophyll cell defective1</Emphasis>, a mutation that disrupts leaf mesophyll differentiation in sunflower

Mutants with altered leaf morphology are useful as markers for the study of genetic systems and for probing the leaf differentiation process. One such mutant with deficient greening and altered development of the leaf mesophyll appeared in an inbred line of sunflower (Helianthus annuus L.). The objectives of the present study were to determine the inheritance of the mutant leaf trait and its morphological characterisation. The mutation, named mesophyll cell defective1 (mcd1), has pleiotropic effects and it is inherited as a monogenic recessive. The structure and tissue organization of mcd1 leaves are disrupted. In mcd1 leaves, the mesophyll has prominent intercellular spaces, and palisade and spongy tissues are not properly shaped. The mutant palisade cells also appear to be more vacuolated and with a reduced number of chloroplasts than the wild type leaves of equivalent developmental stage. The lamina thickness of mcd1 leaves is greatly variable and in some areas no mesophyll cells are present between the adaxial and abaxial epidermis. The leaf area of the mcd1 mutant is extremely reduced as well as the stem height. A deficient accumulation of photosynthetic pigments characterizes both cotyledons and leaves of the mutant. In mcd1 leaves, chlorophyll (Chl) fluorescence imaging evidences a spatial heterogeneity of leaf photosynthetic performance. Little black points, which correspond to photosystem II (PSII) maximum efficiency (F_v/F_m) values close to zero, characterize the mcd1 leaves. Similarly, the lightadapted quantum efficiency (Φ_PSII) values show a homogeneous distribution over wild type leaf lamina, while the damaged areas in mcd1 leaves, represented by yellow zones, are prominent. In conclusion, the loss of function of the MCD1 gene in Helianthus annuus is correlated with a variegated leaf phenotype characterized by a localized destruction of mesophyll morphogenesis and defeat of PSII activity.     

Effect of light on the chloroplast division cycle and DNA synthesis in cultured leaf discs of spinach

The effects of light on both the division cycle of chloroplasts and the synthesis of chloroplast DNA were investigated in cultured discs taken from the distal end of 2-centimeter spinach (Spinacia oleracea) leaves. Comparisons were made of discs cultured for a maximum of 4 days in a shaking liquid medium under continuous white light, darkness, and of discs cultured for 1 day in light following 3 days in darkness. In continuous white light the shortest generation time of chloroplasts observed in this study was 19.4 hours and the duration of spherical, ovoid, and dumbbell-shaped stages in the division cycle were 13.4, 2.8, and 3.1 hours, respectively. In darkness the generation times of chloroplasts extended to 51.5 hours. Under these conditions the duration of spherical, ovoid, and dumbbell-shaped stages were 22.8, 8.4, and 20.2 hours, respectively, suggesting that in darkness the separation of dumbbell-shaped chloroplasts may be the rate limiting step. When discs cultured in the dark were transferred to light, most dumbbell-shaped chloroplasts separated into daughter chloroplasts in less than an hour. Measurements of chloroplast DNA established that the cellular level of chloroplast DNA increased 10-fold over the 4 days of culture in continuous white light. Comparisons of the plastids of dark and light grown discs showed that the synthesis of chloroplast DNA was enhanced by light. Observations of DAPI stained dividing chloroplasts indicate that DNA partitioning can take place during the final stage of chloroplast division and that it does not precede plastid division.     

Does ABA in the Xylem Control the Rate of Leaf Growth in Soil-Dried Maize and Sunflower Plants?

Maize (Zea mays L.) and sunflower (Helianthus annuus L.) plantswere grown in large volumes of soil and leaf growth rate wasmonitored on a daily basis. Half the plants were given a soildrying treatment and when they showed a significant restrictionof growth rate (compared to both their daily growth rate beforedrying and the average growth rate of well-watered plants onthe same day), leaf water relations were measured and xylemsap was extracted using several techniques. There was a significant negative log-linear relationship betweenthe rate of leaf growth and the concentration of ABA in thexylem for both species. There was no clear relationship betweenleaf growth rate and leaf water potential or turgor for eitherspecies. Assessment of different methods for sampling xylemsap suggests that exudates collected from stem stumps or samplescollected by pressurizing the whole root system are suitablefor estimating ABA concentration in xylem, at least with largeplants of maize or sunflower, provided the first few hundredcubic millimetres of collected sap are used for the assay. Centrifugationof sections of stems resulted in dilution of ABA in the xylemsap with sap squeezed from parenchyma tissue. This is because,at least in plants subjected to mild soil drying, the concentrationof the ABA in the xylem is far higher than that in the cellsap of stem tissue. Results support the proposal that ABA plays a major role asa chemical signal involved in the root-to-shoot communicationof the effects of soil drying. The non-hydraulic restrictionof leaf growth by a chemical signal can be explained by theextra root-sourced ABA in the xylem and may be an importantcomponent of the modification of growth and development whichresults from prolonged soil drought. Key words: Soil drying, ABA, leaf growth, Zea mays L., Helianthus annuus L.     

Structure, Production and Leaf Area Dynamics: A Comparison of Lodgepole Pine and Sunflower

Populations of lodgepole pine (Pinus contorta var latifoliaEngelm) and sunflower (Heltanthus annuus L) were examined tocompare the influence of stand density on canopy structure andthe association between canopy structure and the productionof stem volume The plastic responses of canopy structure tocompetitive interactions indicated that the structural dynamicsof lodgepole pine and sunflower populations were similar, thoughthe degree of plastic response differed The influence of canopystructure on the production of stem volume, however, was fundamentallydifferent efficiency decreased as the mean crown size of lodgepolepine populations increased, but this decrease did not occurin sunflower populations This difference was attributed to thelarge accumulation of branch biomass required to display foliageeffectively in the canopies of the perennial lodgepole pine,accumulation which does not occur in the annual sunflower Lodgepole pine, Pinus contorta var latifolia Engelm, sunflower, Helianthus annuus L, leaf area, canopy structure, stand production, carbon allocation     

A Quantitative Study of Daily Variation in the Cellular Ultrastructure of Palisade Chlorenchyma from Sunflower Leaves

Stereology was used to describe cytological changes which occurin palisade cells of fully expanded leaves as part of theirnormal daily activity. These changes were evaluated by describingthe relationship between organelle volume and cell volume asratio values (i.e. percentage volumes, V_v; surface-to-volume,S_v). These ratios describe an average cell in terms of its volumecommitment to each organelle compartment. Cells were also describedin terms of actual volume (µm³) or surface area (µm²)of membrane present in an average cell. ANOVA-LSD and Mann-Whitneystatistics indicate significant changes occur in the ratio valuesof the vacuole, chloroplast, oil, starch and microbody compartmentsover the 24 h period. This indicates a re-allocation of cellspace to these compartments during this period. The S_v ratioof internal membranes of the chloroplast and mitochondria showedno significant change over 24 h indicating that there is a constantrelationship between volume and membrane surface area in theseorganelles. Significant changes occurred in average cell volumeover 24 h with maximum volume during the dark period. Sincechanges in cell volume affected the actual volume expressionof all of the organelle compartments there were diurnal variationin the actual size of these compartments, including the internalmembranes of chloroplasts and mitochondria which more than doubledin surface area. Helianthus annuus L, sunflower, cytology, stereology, quantitative microscopy, diurnal, morphometrics, ultrastructure, chlorenchyma, chloroplast, mitochondria, microbodies     

Water Stress in Sunflower (Helianthus annuus L.) 3. Responses of Cypsela Size

Six water stress treatments were applied before, during andafter anthesis of the sunflower inflorescence. The effects ofthese stresses on leaf and inflorescence size, cypsela number,pericarp and embryo weight were examined. Water stress accelerated leaf senescence and reduced leaf number.Leaf area and inflorescence diameter were reduced in some treatments.Total cypsela weight may be related to leaf area. All stresstreatments reduced pericarp weight at all positions. Embryoweight at central positions was similarly affected. Post-anthesisstress did not affect embryo weight at peripheral positions.The effects of water stress on embryo weight may involve a criticalstage in development but this differs from that envisaged forleaves. Helianthus annuus L., sunflower, water stress, cypsela, inflorescence, embryo, pericarp     

Microspectrofluorometric Measurement of Chloroplast DNA in Dividing and Expanding Leaf Cells of Spinacia oleracea

Absolute DNA amounts of individual chloroplasts from mesophyll and epidermal cells of developing spinach leaves were measured by microspectrofluorometry using the DNA-specific stain, 4,6-diamidino-2-phenyl indole, and the bacterium, Pediococcus damnosus, as an internal standard. Values obtained by this method showed that DNA amounts of individual chloroplasts from mesophyll cells fell within a normal distribution curve, although mean DNA amounts changed during leaf development and also differed from the levels in epidermal chloroplasts. There was no evidence in the data of plastids containing either the high or low levels of DNA which would be indicative of discontinuous polyploidy of plastids, or of division occurring in only a small subpopulation of chloroplasts. By contrast, the distribution of nuclear DNA amounts in the same leaf tissues in which cell division was known to be occurring showed a clear bimodal distribution. We consider that the distribution of chloroplast DNA in the plastid population shows that there is no S-phase of chloroplast DNA synthesis, all chloroplasts in the population in young leaf cells synthesize DNA, and all chloroplasts divide.     

Chloroplast Doublets and Differential Staining of the Cell Walls in Photosynthetic Tissues of Amaranthus dubius Mart

Ultrastructural studies of the leaves of Amaranthus dubius revealpresence of chloroplast doublets in mature leaf tissues. Theyalso highlight the difference in the structural organisationof the bundle sheath and the mesophyll cell walls, a featurewhich may have functional significance. Amaranthus dubius Mart., Calaloo, mesophyll, bundle sheath, chloroplast doublets, plastid fusion, plastid division, differential staining of the cell walls     

花粒期光照对夏玉米光合特性和叶绿体超微结构的影响

在大田条件下,以夏玉米品种‘登海605’为试验材料,研究花粒期不同光照强度(正常光照、开花至收获期遮阴和开花至收获期增光)对夏玉米叶片光合、荧光性能和叶绿体超微结构的影响.结果表明:与对照相比,花粒期遮阴影响叶绿体排布及内部结构发育,基粒个数和基粒片层数均有不同程度减少,叶片的净光合速率、蒸腾速率、气孔导度、叶绿素含量下降,PSⅡ反应中心的实际光化学效率和最大光化学效率降低,非光化学淬灭系数数值增加,导致产量降低;增光后叶绿体结构良好,基粒片层排列紧致、清晰且数量增加,PSⅡ反应中心的实际光化学效率增加,净光合速率、蒸腾速率、气孔导度、叶绿素含量上升,叶片光合性能增强,产量增加.即花粒期遮阴破坏了夏玉米叶片叶绿体超微结构,降低了叶片光合能力,产量下降;花粒期增光增加了叶肉细胞中叶绿体的基粒和基粒片层,导致基粒片层排列紧密有序,有利于增加作物产量潜力.