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1.
Morphological,histochemical and ultrastructural indicators of maize and barley leaf senescence 总被引:1,自引:0,他引:1
In this study we report on morphological and histochemical indicators of maize and barley leaf senescence. We determined how
the traits such as distribution of stomata and hairs, presence of epicuticular wax, staining of tissues with toluidine blue,
change with leaf age and within the leaf blade. We identified regions of young, non-mature leaves as exhibiting juvenile phase,
regions with features typical for mature and fully differentiated leaves-as an adult phase and regions with traits of age
damage as a senescing phase. Ultrastructural analysis of these regions of leaves gives a clear picture of the time development
of the senescence process. Appearance of morphological and histological indicators of senescence in certain regions of leaf
is correlated with ultrastructural changes of mesophyll cells of the same regions. We have thus found a relatively simple
method of estimating the stage of senescence both in maize and barley. 相似文献
2.
Summary. Leaf senescence is a highly coordinated process which involves programmed cell death (PCD). Early stages of leaf senescence
occurring during normal leaf ontogenesis, but not triggered by stress factors, are less well known. In this study, we correlated
condensation of chromatin and nuclear DNA (nDNA) fragmentation, two main features of PCD during early senescence in barley
leaves, with the appearance of nitric oxide (NO) within leaf tissue. With the help of the alkaline version of the comet assay,
together with measurements of nDNA fluorescence intensity, we performed a detailed analysis of the degree of nDNA fragmentation.
We localised NO in vivo and in situ within the leaf and photometrically measured its concentration with the NO-specific fluorochrome
4-amino-5-methylamino-2′,7′-difluorofluorescein. We found that both nDNA fragmentation and chromatin condensation occurred
quite early during barley leaf senescence and always in the same order: first nDNA fragmentation, in leaves of 6-day-old seedlings,
and later chromatin condensation, in the apical part of leaves from 10-day-old seedlings. PCD did not start simultaneously
even in neighbouring cells and probably did not proceed at the same rate. NO was localised in vivo and in situ within the
cytoplasm, mainly in mitochondria, in leaves at the same stage as those in which chromatin condensation was observed. Localisation
of NO in vascular tissue and in a large number of mesophyll cells during the senescence process might imply its transport
to other parts of the leaf and its involvement in signalling between cells. The fact that the highest concentration of NO
was found in the cytoplasm of mesophyll cells in the earliest stage of senescence and lower concentrations were found during
later stages might suggest that NO plays an inductive role in PCD.
Correspondence: A. Mostowska, Department of Plant Anatomy and Cytology, Institute of Experimental Biology of Plants, University
of Warsaw, Miecznikowa 1, 02-096 Warsaw, Poland. 相似文献
3.
Aspects of programmed cell death during leaf senescence of mono- and dicotyledonous plants 总被引:6,自引:0,他引:6
Summary Leaf senescence is a highly regulated stage in the plant life cycle, leading to cell death, recently examined as a type of
the programmed cell death (PCD). One of the basic features of PCD is the condensation of nuclear chromatin which is caused
by endonucleolytic degradation of nuclear DNA (nDNA). In our investigations, we applied the technique of the single-cell electrophoresis
system (“comet assay”) in order to determine the type of nDNA fragmentation during leaf senescence. The comet assay, a sensitive
method revealing nonrandom internucleosomal damage that is specific for PCD, is especially useful for the detection of nDNA
degradation in isolated viable cells. Simultaneously, we analyzed the mesophyll cell ultrastructure and the photosynthetic-pigment
concentration in the leaves of two species,Ornithogalum virens andNicotiana tabacum, representing mono- and dicotyledonous plants which differ in the pattern of leaf differentiation. These investigations demonstrated
that, in both species, the comet assay revealed nDNA degradation in yellow-leaf protoplasts containing chloroplasts that showed
already changed ultrastructure (swelled or completely degraded thylakoids) and cell nuclei with a significant condensation
of chromatin. There was no nDNA degradation in green-leaf protoplasts containing differentiated chloroplasts with numerous
grana stacks and nuclei with dispersed chromatin. The analysis of intermediate developmental stage showed that the degradation
of nDNA precedes condensation of nuclear chromatin. Thus the comet assay is a very useful and sensitive method for early detection
of PCD. Moreover, results of our studies indicate that leaf senescence involves PCD. 相似文献
4.
Kordyum E Adamchuk N 《Journal of gravitational physiology : a journal of the International Society for Gravitational Physiology》1997,4(2):P77-P78
Photosynthesis is known to provide nearly all the carbon and chemical energy needed for plant growth, it depends on many environmental factors and alternates when these factors fluctuate. The degree of the chloroplast membrane system development can be, to a certain extent, an indicator of the organelles' photosynthetic activity. To-date, changes in chloroplast size and ultrastructure as well as starch and pigment content in leaf mesophyll cells in microgravity have been found in variety of the angiosperm species investigated in this respect. However, available data are very limited and contradictory. Taking into account the importance of studying the photosynthesis process to elucidate the possibilities of plant physiological adaptation in altered gravity that is the basis for working out the technologies of space planting in controlled ecological life-support systems, we conducted the investigations of ultrastructure and state of the photosynthetic apparatus in Arabidopsis thaliana leaf mesophyll cells at the different stages of plant development under clinorotation. 相似文献
5.
W. R. Fagerberg 《Protoplasma》1984,119(1-2):21-30
Summary Changes in the relative volume of palisade cells (Vv) allocated to various organelle compartments during postemergent leaf development was measured using stereological techniques. The surface to volume ratios (Sv) of the chloroplast and mitochondrial membranes were also measured at each stage. Three leaf stages were sampled, each was defined based on lamina length (10, 45, and 150 mm). The last stage represented a fully expanded leaf. Chloroplast and nuclear compartment Vv values changed significantly in the early stages when cells were actively dividing. Mitochondrial and vacuolar compartment Vv values showed significant changes in the latter stages during cell expansion. The oil vesicle and microbody compartments showed no significant change in Vv value during the developmental process. The surface to volume ratios of the chloroplast membranes increased significantly throughout all stages of the leaf development while mitochondrial cristae Sv values did not change. Organelle replication rates appeared to be independent of changes in cell volume with each organelle exhibiting a specific replication activity pattern. The results of this study suggest two possible mechanisms for the control of cell structural development involving both intrinsic and extrinsic factors. 相似文献
6.
Changes in the Number and Composition of Chloroplasts during Senescence of Mesophyll Cells of Attached and Detached Primary Leaves of Wheat (Triticum aestivum L.) 总被引:11,自引:5,他引:6
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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. 相似文献
7.
大麦和玉米叶片叶绿体中Rubisco及其活化酶的免疫金标记定位 总被引:2,自引:0,他引:2
运用免疫金标记电镜技术研究了禾本科C3植物大麦(Hordeum vulgare L.)和C4植物玉米(Zea mays L.)叶片中Rubisoo及其活化酶(RCA)的细胞定位,结果表明:两种植物叶片解剖结构及叶绿体超微结构差别明显.在大麦叶细胞中,只有一种叶肉细胞叶绿体,Rubisoo和RCA主要分布于叶绿体的间质中.在玉米叶细胞中,存在着维管束鞘细胞和叶肉细胞两种类型叶绿体,Rubisco主要分布于鞘细胞叶绿体的基质中,但在叶肉细胞叶绿体中亦有少量特异性标记;RCA在鞘细胞叶绿体和叶肉细胞叶绿体的基质中都有分布.两种植物叶绿体结构及光合作用关键酶定位的不同,体现了C3植物和C4植物在光合器结构与功能上的差异. 相似文献
8.
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. 相似文献
9.
1. By means of cell separation method, we studied the differentiation of the leaf cells of wheat, Nongda 183 and the development of the chloroplasts in the mesophyll. cells. 2. The differentiation of the cells of the first leaf can be divided into 3 stages. Beginning from the leaf primordium to the fully expanded leaf, the cells are in the stage of division and expansion. When the fully expanded leaf becomes deep green in color, the leaf cells are in the prime of life. When the leaf begins to show yellowish colored spots to its complete withering, the cells are in the stage of senescence. Accompanying these stages, the external form and the internal structure of the cells change also. 3. In the early stage of cell division and expansion, one can observe many 0.5μ × 3.4μ mitochondria-like protoplastids which go through various morphological changes to become chloroplasts. 4. The mesophyll cells of the leaf begin to show the signs of senescence sooner than the epidermal cells and the cells of the vascular bundle. The latter last the longest in the life span of the leaf. 相似文献
10.
11.
Summary Primary leaves of intact bean plants (Phaseolus vulgaris) were treated with benzyladenine (BA) at different stages of growth. Changes in the ultrastructure of chloroplasts and the contents of chlorophyll, carotenoid, and protein (soluble and insoluble) in leaves with different treatments were followed and compared. When BA was applied from an early stage, it increased the chloroplast size and the number of grana per chloroplast without any pronounced effect on the grana size. When BA treatment was stopped at the early stage, these effects remained for a while and then diminished. When BA treatment was begun at a late stage, such marked effects were not observed, suggesting that only young leaves could respond to BA in that manner. However, the late treatment efficiently prevented the process of the last stage of leaf senescence characterized by disintegration of thylakoids with concomitant increase in the plastoglobule size. Chlorophyll, carotenoid, and insoluble protein contents per leaf followed similar changes in chloroplast length and the number of grana per chloroplast section. 相似文献
12.
The equilibrium density of chloroplasts from barley (Hordeum vulgare L. cv. Hassan) was analyzed by sucrose gradient centrifugation. Natural and detachment-induced leaf senescence were associated
with a decrease in density and an increase in heterogeneity of the chloroplast population. Treatments (with growth regulators
and light) which retarded or accelerated senescence, respectively, retarded or accelerated chloroplast density decrease. Accelerators
as well as retardants of senescence decreased the heterogeneity of the chloroplast population. 相似文献
13.
Specific association of a small protein with the telomeric DNA-protein complex during the onset of leaf senescence in Arabidopsis thaliana 总被引:5,自引:0,他引:5
Telomeres and their changes in length throughout the life span of cells have been intensively investigated in different organisms. Telomere length is assumed to control replicative senescence in mammalian cells. However, only very few data are available on the developmental dynamics of plant telomeres. Here, changes of telomere length and DNA-protein structure of Arabidopsis thaliana telomeres were analysed in different stages of development, with the main focus resting on the transition from pre-senescent to senescent leaves. The lengths of the telomeres, ranging from ca. 2.0 to 6.5 kb, do not significantly change during plant development indicating that telomere length is not involved in differentiation and replicative senescence nor in post-mitotic senescence of A. thaliana. In dedifferentiated cultured cells a slight increase in length can be determined. The nucleoprotein structure of the telomeric DNA was investigated by gel mobility shift assays, with synthetic oligonucleotides and nuclear protein extracts derived from four defined stages of post-mitotic leaf senescence. In all four stages, a highly salt-resistant DNA-protein complex was formed with the double-stranded as well as with the single-stranded G-rich telomeric DNA. An additional DNA-protein complex was identified in nuclear protein extracts isolated from plants in the transition stage from pre-senescence to senescence. The protein components of the DNA-protein complexes were analysed on native PAGE and SDS-PAGE gels. A protein of 67 kDa (ATBP1) bound to the telomeric DNA in all developmental stages. An additional protein of merely 22 kDa (ATBP2) was associated via protein-protein interaction with ATBP1 to form a higher-order complex exclusively during the onset of senescence. DNA interaction of this higher-order protein complex seems to be restricted to double-stranded telomeric DNA. The defined period of ATBP1/ATBP2 complex formation with the telomeric DNA probably indicates that ATBP2 is involved in the onset of post-mitotic leaf senescence by either disturbing an established or establishing an additional function exhibited by the telomeres in the interphase nuclei. 相似文献
14.
Summary Previously, we showed that all greening mesophyll cells in the coleoptiles of rice (Oryza sauva L. cv. Nippon-bare) follow the identical program of senescence, which features the early degradation of chloroplast DNA (cpDNA) and subsequent nuclear condensation and disorganization. Following the coleoptile study, we analyzed the senescence-associated changes in the blade of the second leaf of rice at the tissue and cellular levels. Under the experimental conditions, the second leaf started to elongate rapidly 2 days after sowing and emerged on day 3. The blade of the second leaf completed its growth on day 4, although the sheath continued to grow until day 7. The amount of soluble protein and chlorophyll (Chl) per blade reached a maximum on day 7, and then declined. When blades were divided into three parts (the tip, mid-region, and base), levels of both soluble protein and Chl in the tip segment peaked earlier and decreased at a faster rate than in the other parts, demonstrating a longitudinal gradient of senescence from the tip to the base of the blade. In cross sections through the center of the tip and base segments, all the mesophyll cells senesced synchronously. They passed through the following steps in order: (i) degradation of cpDNA, (ii) decrease in the size of the chloroplast with degeneration of the chloroplast inner membranes, and (iii) condensation and disorganization of the nuclei. Although some differences were shown between the coleoptile and the second leaf in the timing and rate of each event, the order of those senescence-related events was conserved, suggesting an identical program of senescence exists in rice leaves.Abbreviations Chl
chlorophyll
- cpDNA
chloroplast DNA
- cpnucleoid
chloroplast nucleoid
- DAPI
4,6-diamidino-2-phenylindole
- DiOC7
3,3-dihexyloxacarbocyanine iodide
- VB
vascular bundle
- VIMPCS
video-intensified microscope photon-counting system 相似文献
15.
Shading-induced changes in the leaf mesophyll of plants of different functional types 总被引:1,自引:0,他引:1
L. A. Ivanova L. A. Ivanov D. A. Ronzhina V. I. P’yankov 《Russian Journal of Plant Physiology》2008,55(2):211-219
Changes in the structural characteristics of mesophyll induced by shading were investigated in ten species of wild plants of diverse functional types. In all plant types, shading reduced leaf thickness and density by 30–50% and total surface of mesophyll, by 30–70%. The extent and mechanisms of mesophyll structural rearrangement depended on the plant functional type. In the ruderal plants, integral parameters of mesophyll, such as the surface of cells and chloroplasts and mesophyll resistance, changed threefold predominantly because of changes in the dimensions of the cells and chloroplasts. In these plants, shading reduced the volume of chloroplasts by 30%, and the chloroplast numbers per cell declined. The competitor plants showed a twofold increase in mesophyll resistance due to a decrease in the number of photosynthesizing cells per leaf area unit. Moreover, these plants maintained constant dimensions of mesophyll cells, ratios mesophyll surface/mesophyll volume and chloroplast surface/cell surface. In stress-tolerant plants, diffusion resistance of mesophyll remained the same irrespective of the growing conditions, and mesophyll rearrangement was associated with inversely proportional changes in the dimensions of the cells and cell volume per chloroplast. Noteworthy of these plants were relatively constant chloroplasts number per cell, per leaf area unit and total surface area of chloroplasts. The nature of relationship between the mesophyll diffusion resistance and structural parameters of leaf mesophyll differed in plants of diverse functional types. 相似文献
16.
Changes in Hill reaction activity (HRA) and ultrastructure of mesophyll cell (MC) chloroplasts were studied during the ontogeny of third leaf of maize plants using polarographic oxygen evolution measurement, transmission electron microscopy, and stereology. The chloroplast ultrastructure was compared in young (actively growing), mature, and senescing leaves of two different inbreds and their reciprocal F1 hybrids. Statistically significant differences in both HRA and MC chloroplast ultrastructure were observed between different stages of leaf ontogeny. Growth of plastoglobuli was the most striking characteristic of chloroplast maturation and senescence. The chloroplasts in mature and senescing leaves had a more developed system of thylakoids compared to the young leaves. Higher HRA was usually connected with higher thylakoid volume density of MC chloroplasts. 相似文献
17.
Ramularia collo-cygni causes leaf spots on barley (Hordeum vulgare), a disease of growing economical importance. Scanning electron microscopy was used to study the life cycle of the fungus
on barley during the vegetation period and in winter. The infectious stage started with conidium germination on the surface
and the penetration into the leaf via the stomatal pore where the hyphae grew within the cells that became necrotic. The conidiophores
emerged through the stomatal pore. On older leaves, however, they frequently emerged apart from it and the results suggested
a pushing apart of adjacent cell walls of the epidermal cells. An assessment of the amount of conidium formation of one heavily
infested barley plant resulted in 4.05 × 106 conidia per plant. For the first time, conidiophores, conidium production and germination of conidia were also observed in
winter on barley and on maize leaves. 相似文献
18.
19.
Changes in Hill reaction activity (HRA) and ultrastructure of mesophyll cell (MC) chloroplasts were studied during the ontogeny
of third leaf of maize plants using polarographic oxygen evolution measurement, transmission electron microscopy, and stereology.
The chloroplast ultrastructure was compared in young (actively growing), mature, and senescing leaves of two different inbreds
and their reciprocal F1 hybrids. Statistically significant differences in both HRA and MC chloroplast ultrastructure were
observed between different stages of leaf ontogeny. Growth of plastoglobuli was the most striking characteristic of chloroplast
maturation and senescence. The chloroplasts in mature and senescing leaves had a more developed system of thylakoids compared
to the young leaves. Higher HRA was usually connected with higher thylakoid volume density of MC chloroplasts.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
20.
Realization of programmed cell death in senescence represents an activation/inactivation of the respective gene. Enzymatic methylation of nuclear DNA with the creation of 5methylcytosine is one of the mechanisms, which can regulate gene activity in animal and plant cells. 5Azacytidine (5azaC) acts as an inhibitor of DNA methylation, and induces expression of a range of some genes including genes responsible for senescence. Fragmentation of nuclear DNA is one of the hallmarks of programmed cell death in apoptosis pathway in plant cells. The influence of 5azaC (100 microg/ml) on nuclear DNS amount and its fragmentation in the first leaf cells of barley was studied. It was shown that in the first leaf cells of barley seedlings there is an apoptosis pathway of programmed cell death. It was also observed that nuclear DNA fragmentation under the 5azaC influence is strongly inhibited, and the DNA amount in the first leaf increases. Synthesis and destruction of chlorophyll also play a significant role in programmed cell death in plants. It was shown that under the 5azaC influence, the absorption spectrum of a pigment does not change in leaves and coleoptiles in the light, whereas in the dark condition, these pigments are not created under the 5azaC influence. 相似文献