The Ultrastructure of Phaseolus vulgaris Chloroplasts

A comparison of bean chloroplasts after being fixed in potassiumpermanganate, osmium, and formaldehyde coupled with negativestaining shows that the general organization of the chloroplastis similar in all cases. However, the mature chloroplasts ofbean vary considerably in the extent and orientation of theinternal membranes—the grana and the interconnecting membranesbetween the grana. The interconnecting membranes are thin, branching,flexuous structures. This is illustrated by serial sectionsand by cross- and face-view sections of osmium- fixed chloroplastsand the best model, which allows for a considerable flexibilityin the orientation of the grana and also describes the thininterconnecting membranes between the grana, is the grana-fretworksystem proposed by Weier (1961). Furthermore, the comparative studies show that the internalregions of grana are separated from the stroma and that thegrana-fretwork systems appear to be a continuous membrane system.This membrane is single along the frets, end compartments, andgranal margins. It is double in the partitions of the granabut separated by a component, possibly a cementing material,which does not stain. It is suggested that this membrane isstructurally similar in the chloroplasts of higher plants, butthat its overall organization may vary from one plant to another.     

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

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.     

Fatty Acids in Chloroplasts and Leaves

The fatty acid composition of green and white leaf tissue inAcer negundo, Zea mais, and Ilex aquifolium, of green and yellowtissue in Ligustrum ovatifolium and of etiolated and green tissuein Vicia faba has been determined. The mesophytic green leavesexamined show a general similarity in fatty acid composition,characterized by a high concentration of non-conjugated octadecatrienoicacid. Chloroplasts were isolated from Vicia and Acer and containan even higher concentration of this acid and only traces ofnon-conjugated octadecadienoic acid. Conjugated diene and trieneacids occur in traces in chioroplasts, but are also found innon-green leaf tissue. The fats of non-green leaves are in generalmore saturated than those from green tissue but vary considerablyin composition. The relationship between fat composition andplastid development is discussed.     

Ultrastructure and Dimensions of Chloroplasts in Leaves of Three Maize (Zea mays L.) Inbred Lines and their F1 Hybrids Grown Under Moderate Chilling Stress

Influence of moderate chilling stress on vascular bundle sheath cell (BSC) and especially mesophyll cell (MC) chloroplasts of mature maize leaves was studied by electron microscopy and stereology. Plants of two inbred lines of maize, differing in their photosynthetic activity, and their F₁ hybrids were cultivated during autumn in heated or unheated glasshouse. Generally, chilling temperatures resulted mainly in the decrease in stereological volume density (VD) of both granal and intergranal thylakoids of MC chloroplasts, while the ratio of granal to all thylakoids (granality) was less affected. The VD of peripheral reticulum and plastoglobuli usually increased after cold treatment of plants. The volume of MC chloroplasts usually increased under chilling stress, the shape of the chloroplasts changed only slightly. The ultra-structure of chloroplasts differed between individual genotypes; chilling-stressed hybrid plants showed positive heterosis particularly in the granal thylakoids' VD of MC chloroplasts.     

Ultrastructure of Mesophyll Cells and Pigment Content in Senescing Leaves of Maize and Barley

Leaf senescence is a genetically regulated stage in the plant life cycle leading to death. Ultrastructural analysis of a particular region of the leaf and even of a particular mesophyll cell can give a clear picture of the time development of the process. In this study we found relations between changes in mesophyll cell ultrastructure and pigment concentration in every region of the leaf during leaf senescence in maize and barley. Our observations demonstrated that each mesophyll cell undergoes a similar senescence sequence of events: a) chromatin condensation, b) degradation of thylakoid membranes and an increase in the number of plastoglobules, c) damage to internal mitochondrial membrane and chloroplast destruction. Degradation of chloroplast structure is not fully correlated with changes in photosynthetic pigment content; chlorophyll and carotenoid content remained at a rather high level in the final stage of chloroplast destruction. We also compared the dynamics of leaf senescence between maize and barley. We showed that changes to the mesophyll cells do not occur at the same time in different parts of the leaf. The senescence damage begins at the base and moves to the top of the leaf. The dynamics of mesophyll cell senescence is different in leaves of both analyzed plant species; in the initial stages, the process was faster in barley whereas in the later stages the process occurred more quickly in maize. At the final stage, the oldest barley mesophyll cells were more damaged than maize cells of the same age.     

Ultrastructure of Chloroplasts and Their Storage Inclusions in the Primary Leaves of Mesembryanthemum crystallinum Affected by Putrescine and NaCl

The effects of salinity (300 mM NaCl), putrescine (Put), and the combination of two agents on the structure of chloroplasts and storage deposits were studied in the third leaf pair of a facultative halophyte Mesembryanthemum crystallinum. Within 6 days, the common ice plants responded to NaCl and Put treatments by diminished chloroplast volumes and swollen grana. Different effects of the experimental treatments were primarily manifested in the chloroplast storage inclusions. Under the salinity conditions, the starch content dropped down almost threefold as compared to untreated plants (control), whereas the number of plastoglobules did not change. Put and Put + NaCl treatments further decreased the starch content per unit section area; in contrast, the plastoglobule area per chloroplast section increased eightfold and tenfold in Put and Put + NaCl treatments, respectively. The morphology and electronic density of plastoglobules changed in all treatments. In both Put treatments there ware no destructive changes in the chloroplasts, and therefore the authors presume that the increase in the numbers plastoglobules was related to the redirection of cell metabolism towards the products of the higher reduction potential. The ferritin deposits in the chloroplasts were observed in all treatments they were more abundant in the vascular parenchyma cells, especially under salinity. The ability of the common ice plants to accumulate large Fe quantities in their chloroplasts and the characteristic pectin-filled pockets, which were observed earlier, and intercellular spaces are probably related to the genetically determined traits of plant adaptation to salinity and water deficit.     

Lipid Synthesis and Ultrastructure of Isolated Barley Chloroplasts

The cell organelle contents of chloroplast preparations made from barley leaves with salt and sucrose isolation media at pH 6 and 8 were determined and compared with the acetate incorporating activity of these preparations. A chloroplast preparation obtained with 0.5 m sucrose at pH 8 gave the highest number of intact chloroplasts (with envelope and stroma), the lowest number of contaminating mitochondria, and the highest activity in light dependent acetate incorporation into lipids. In the preparations observed, the light induced lipid synthesizing capacity correlates well with the percentage of intact chloroplasts. It is suggested that the intact chloroplasts are responsible for the light induced lipid synthesis of the preparations and that the synthesizing enzymes are localized in the chloroplast stroma. Acetate is mainly incorporated into palmitic and oleic acids. The low yield of intact chloroplasts and of light induced lipid synthesis in preparations isolated at pH 6 seem to result from the action of galactolipid lipase(s).     

The Transport of Photosynthetic Products from the Chloroplasts of Tobacco Leaves

Tobacco leaves were fractionated by the non-aqueous method afterphotesynthesis for short periods in ¹⁴CO₂ and with or withoutsubsequent photosynthesis in ¹²CO₂ or respiration in the dark.Phosphate esters became labelled only slowly in the non-chloroplastparts of the leaf; glycine and serine which became rapidly labelledin the non-chloroplast leaf fraction appear to be concernedin the transport of newly assimilated carbon from the chloroplast.     

Early Development and Ultrastructure of the Major Veins and Their Sheath Tissues in the Maize Leaves

The report described the ultrastructural changes that occurred in the major veins and their associated bundle sheaths (BS) of the maize ( Zea mays L. ) leaf blade in the process of their differentiation from three adjacent cells in the middle layer of the ground meristem, the minimal number of cells involved with the initiation of a procambial strand and the associated BS. The inner cell underwent two successive unequal periclinal divisions: a smaller cell that later differentiated into the adaxial BS cell precursor, and a larger one that divided once again periclinally yielding an abaxial BS cell precursor and a centrally located procambial initial cell. One of the two lateral cells immediately adjacent to either side of the inner cell also divided periclinally; these derivatives, along with another lateral cell of the original three-celled unit formed the precursor cells of the lateral BS. Prior to the initiation of protophlcem differentiation, all of the procambial cells showed ultrastructural characteristics basically similar to the procambial initial. They possessed a prominent nucleus with electron-dense aggregates of heterochromatin, a dense cytoplasm rich in ribosomes, proplastids and mitochondria; also a thin wall containing numerous plasmodesmata. In many cases, only short pieces of rough endoplasmic reticulum cistemae and a few small sized vacuoles were present. In adclifton, evidence of cytoplasmic disintegration leading to new vacuole formation was noted in the process of proeambium development. It was observed that certain endoplasmic reticulum was engaged in the sequestration and lysis of cytoplasm. No apparent uhrastmctuml difference was found between the BS cell precursors and the procambial initials, that was, the distinction between the procambium and the surrounding BS cells occurred gradually after vein initiation, The major ultrastmctural changes which occurred during the differentiation of the meristematic BS cells into the vacuolated cells were (1) a proplastid to chloroplast transformation going through a prolamellar body stage, and (2) the appearance of the multi-concentric membrane complex which might play a role in the degradation of some ribosomes and other cytoplasmic components during the differentiation of BS cells.     

Modulation of NADP-Malate Dehydrogenase Activity in Maize Mesophyll Chloroplasts

When intact mesophyll chloroplasts of Zea mays var Kelvedon Glory were illuminated, activation of NADP-malate dehydrogenase occurred. Activity declined rapidly on darkening. Light activation of the enzyme was very much greater in the presence of pyruvate (~10- to 20-fold) than with the electron acceptors 3-phosphoglycerate or oxaloacetate present (~2-fold). Following preillumination in the presence of pyruvate, addition of 3-phosphoglycerate, oxaloacetate, or nitrite substantially diminished the activity of NADP-malate dehydrogenase. In these circumstances, with pyruvate and 3-phosphoglycerate present, activity could be restored by the addition of nigericin or dihydroxyacetone phosphate. Nigericin also restored activity with both oxaloacetate and pyruvate present. The effect of nitrite was more marked in the presence of low concentrations of DCMU.

These observations are discussed in terms of the dependence of enzyme activity upon the redox state of ferredoxin and electron carriers; the redox state of the latter was estimated by analysis of the DCMU-induced relaxation kinetics of chlorophyll fluorescence quenching in the presence of different substrates.

     

Effect of Manganese Deficiency on Chloroplasts of Lemon Leaves

Manganese deficiency in chloroplasts of Eureka lemon leaves resulted in 23% and 40% increase of chloroplast nitrogen and protein, respectively, on a chlorophyll unit basis. Acrylamide gel electrophoresis carried out on extracts of these chloroplasts disclosed also qualitative differences between the normal and deficient leaves. Calculated on chloroplast N basis there is an increase of 17% in the chloroplast protein under Mn deficiency. This increase apparently indicates a more intense protein synthesis in the Mn deficient chloroplasts. Hill activity of the –Mn leaves was about one-third of the analog control leaves. Manganese infiltration into detached but intact leaves restored the activity in the –Mn leaves up to 70% of the control. Lemon leaves affected by other macro- and micro- nutrient deficiencies did not respond to the manganese infiltration; therefore, the use of this infiltration method is suggested for the evaluation of the manganese nutrition status of citrus and probably other higher plants.     

The Role of Phosphoenolpyruvate in Proton/Pyruvate Cotransport into Mesophyll Chloroplasts of Maize

Phosphoenolpyruvate (PEP) was transported together with H⁺ inC₄ mesophyll chloroplasts. Medium alkalization and stromal acidificationdue to pyruvate uptake into maize mesophyll chloroplasts inthe light were partially inhibited by adding PEP. Thus, theH⁺ taken up by H⁺/pyruvate cotransport into mesophyll chloroplastsis released together with PEP in vivo. (Received August 5, 1994; Accepted October 3, 1994)     

衰老叶片和叶绿体中H_2O_2的累积与膜脂过氧化的关系

在自然衰老和ABA处理的叶片和叶绿体中活性氧H_2O_2均比对照明显增高。外加H_2O_2刺激水稻叶绿体膜脂过氧化作用。叶绿体的丙二醛含量随H_2O_2浓度、光照时间、光照强度及叶绿体完整性而变化。AsA、GSH、SOD、甘露醇和过氧化氢酶对外源H_2O_2引起的膜脂过氧化有缓解作用,Fe~(2+)有刺激作用。而H_2O_2对叶绿体过氧化损伤主要是转化为OH之故。     

The EfFect of B9 upon the Structure of Leaves and Chloroplasts in Peanut plant

When peanut plants (Arachis hypogaea L.) were treated with aqueous solution of Bo (2000 ppm) by spraying application, the cells of the assimilating tissue were enlarged and the thickness of the leaves were increased. B9 promoted the development of the chloroplast, so that the number of chloroplast, grana and the lamella were increased. As a result, the volume of the “container” of chlorophyll was enlarged. In addition, the chlorophyll content of file leaves also increased after B9 treatment, there fore the leaves turned dark green.