The Ultrastructure of Chloroplasts in Mineral-deficient Maize Leaves

The ultrastructure of mesophyll chloroplasts in full-nutrient and mineral-deficient maize (Zea mays) leaves was examined by electron microscopy after glutaraldehyde-osmium tetroxide fixation. Nitrogen, calcium, magnesium, phosphorus, potassium, and sulfur deficiencies were induced by growing the plants in nutrient culture. Distinctive chloroplast types were observed with each deficiency. Chloroplasts from nitrogen-deficient plants were reduced in size and had prominent osmiophilic globules and large grana stacks. Magnesium deficiency was characterized by the accumulation of osmiophilic globules and the progressive disruption of the chloroplast membranes. In calcium deficiency, the chloroplast envelope was often ruptured. Chloroplasts from potassium- or phosphorus-deficient plants possessed an extensive system of stroma lamellae. Sulfur deficiency resulted in a pronounced decrease of stroma lamellae, an increase in grana stacking, and the frequent occurrence of long projections extending from the body of the chloroplast. These morphological changes were correlated with functional alterations in the chloroplasts as measured by photosystem I and II activities. In chloroplasts of the nitrogen- and sulfur-deficient plants an increase in grana stacking was associated with an increase in photosystem II activity.     

ULTRASTRUCTURE OF THE LAMELLAE AND GRANA IN THE CHLOROPLASTS OF ZEA MAYS L

The fine structure of the chloroplasts of maize (Zea mays L.) has been investigated by electron microscopic examination of ultrathin sections of leaves fixed in buffered osmium tetroxide solutions. Both the parenchyma sheath and mesophyll chloroplasts contain a system of densely staining lamellae about 125 A thick immersed in a finely granular matrix material (the stroma), and are bounded by a thin limiting membrane which often appears as a double structure. In the parenchyma sheath chloroplasts, the lamellae usually extend the full width of the disc-shaped plastids, and grana are absent. The mesophyll chloroplasts, however, contain numerous grana of a fairly regular cylindrical form. These consist of highly ordered stacks of dense lamellae, the interlamellar spacing being ca. 125 A. The grana are interlinked by a system of lamellae (intergrana lamellae) which are on the average about one-half as numerous as the lamellae within the grana. In general, this appears to be due to a bifurcation of the lamellae at the periphery of the granum, but more complex interrelationships have been observed. The lamellae of the parenchyma sheath chloroplasts and those of both the grana and intergrana regions of the mesophyll chloroplasts exhibit a compound structure when oriented normally to the plane of the section. A central exceptionally dense line (ca. 35 A thick) designated the P zone is interposed between two less dense layers (the L zones, ca. 45 A thick), the outer borders of which are defined by thin dense lines (the C zones). Within the grana, the C zones, by virtue of their close apposition, give rise to thin dense intermediate lines (I zones) situated midway between adjacent P zones. A model of the lamellar structure is proposed in which mixed lipide layers (L zones) are linked to a protein layer (P zone) by non-polar interaction. Chlorophyll is distributed over the entire lamellar surface and held in the structure by van der Waals interaction of the phytol "tail" with the hydrocarbon moieties of the mixed lipide layers. The evidence in favour of the model is briefly discussed.     

小麦黄化突变体叶绿体超微结构研究

利用透射电镜对小麦自然黄化突变体及其突变亲本(西农1718)叶片细胞叶绿体的数目、形态及超微结构进行比较分析。结果发现:(1)3种不同黄化程度突变体的叶绿体分布、数目、形状及大小与突变亲本无明显差异;(2)突变体叶绿素含量为野生型58%的黄绿植株与其突变亲本叶绿体超微结构无明显差异,基质类囊体与基粒类囊体高度分化,基粒数目以及基粒片层数目较多;(3)突变体金黄和绿黄植株的叶绿素含量分别为野生型的17%、24%,其叶绿体超微结构与突变亲本明显不同,突变体的叶绿体发育存在明显缺陷,其中突变体金黄植株的叶绿体内无基粒、基质片层清晰可见,有淀粉粒,嗜锇颗粒较多,而突变体绿黄植株的叶绿体内有基粒,但明显少于突变亲本,且基粒片层较少,基质类囊体较发达。结果表明该黄化突变体叶绿体超微结构的改变,是由于叶绿素含量降低造成,推测,该黄化突变是由于叶绿素合成受阻导致的。     

水稻温敏叶绿素突变体叶片超微结构的研究

对温敏转绿型叶绿素突变体1103S和武金4B“斑马叶”性状表达过程中叶绿素含量、叶绿体超微结构的变化进行了比较研究。结果表明,在一定条件下,叶片的失绿、复绿与叶绿素含量的下降、上升变化趋势一致;叶绿体结构在失绿区表现为严重退化,基粒和基粒片层减少,淀粉粒和嗜锇粒增多;复绿后,其叶绿体结构重建和恢复     

转P_(SAG12-ipt)基因水稻叶片中叶绿体超微结构的变化

研究了转PSAG12-ipt基因水稻和对照植株发育过程中叶片中的叶绿体结构的变化。发现水稻发育到乳熟期,转基因植株叶片中的叶绿体与对照植株开始出现明显的差别。对照叶绿体中嗜锇体体积增大,数目增多,大部分基粒的类囊体膜膨胀、裂解,片层结构解体。而转基因植株叶片中的叶绿体结构变化不大,嗜锇体相对有所增加,但体积较小,大部分基粒类囊体片层结构仍然排列整齐,少数类囊体垛叠化丧失。     

FINE STRUCTURE OF CHLOROPLASTS IN “GREEN ISLANDS” AND IN SURROUNDING CHLOROTIC AREAS OF BARLEY LEAVES INFECTED BY POWDERY MILDEW

The fine structure of mesophyll chloroplasts in green islands and in adjacent chlorotic areas of barley leaves infected with Erysiphe graminis (DC.) was compared with healthy non-inoculated tissue. Chloroplasts in green islands were persistent. Green-island chloroplast grana were enlarged and fewer in number than in healthy tissue. In contrast, cells in chlorotic areas had fewer chloroplasts and their lamellae showed progressive degeneration and fragmentation. The lamellae often resembled aberrant prolamellar bodies. As lamellar degeneration progressed there was a marked increase in the amount of osmophilic material within the chloroplasts.     

冬季沙冬青细胞质中一种高电子密度结构的电镜观察

用透射电子显微镜观察了冬季沙冬青的叶肉细胞。观察表明,其细胞质中有一种电子密度很高的结构,分布广,主要位于有一定解体现象并含有较多嗜锇小球叶绿体附近,有的甚至与叶绿体被膜贴在一起,很少存在于发育良好的叶绿体附近和液泡中。其大小不同,通常为椭圆形,有时也近似圆形。表面没有包围膜,泡状结构少,常有突起。这种结构的电子密度很高,染色较均匀,冬季大量出现可能与提高植物的抗寒性有关.     

SUBMICROSCOPIC STRUCTURE AND DEVELOPMENT OF THE CHLOROPLASTS OF PSILOTUM TRIQUETRUM

Sun , C. N. (Washington U., St. Louis, Mo.) Submicroscopic structure and development of the chloroplasts of Psilotum triquetrum. Amer. Jour. Bot. 48(4): 311–315. Illus. 1961.—Aerial stems and stem tips of Psilotum triquetrum were used for the study of the fine structure and development of chloroplasts. The chloroplasts of Psilotum are ellipsoidal, with a principal axis of approximately 13 μ and a short axis of approximately 3.6 μ. They are bounded by a well-defined outer membrane which consists of 2 layers. Within the laminar system of the stroma, the lamellated grana appear as sharply defined regions. The grana are about 1–1.6 μ in diameter. They are distributed more or less uniformly throughout the entire chloroplast with the exception of a very narrow peripheral zone. Relatively large, osmiophilic globules occur in groups in the stroma. The development of the Psilotum chloroplast may be summarized as follows: (1) in the undifferentiated proplastid, vesicles occur; (2) lamellated layers are formed by the fusion of vesicles; (3) the lamellae multiply by a process of thickening and splitting; (4) the grana are differentiated within a certain area by heterogeneous deposition of material and by further cleavage of the lamellae. Osmiophilic globules are present throughout the developmental stages, and increase in number and size with increase in age of the chloroplast.     

Localization of photophosphorylation and proton transport activities in various regions of the chloroplast lamellae

Membrane fragments released by French pressure cell treatment of whole chloroplasts and isolated by differential centrifugation have been characterized structurally and with respect to phosophorylating and proton transport activities. In agreement with results of other workers, the heavy fraction released by pressure treatment was found by electron microscopy studies to be made up of mostly intact grana stacks while the light fraction was comprised of vesicles derived from the stromal lamellae. Both fractions were found to carry out rapid rates of cyclic photophosphorylation catalyzed by phenazine methosulfate (PMS). However, only the grana membranes demonstrated active proton accumulation in the presence of PMS. No light induced H⁺ uptake could be detected in the stromal lamellae fraction; and as expected, proton gradient dissipating agents such as NH₄Cl, nigericin in the presence of K⁺, and gramicidin were only slightly inhibitory to phosphorylation at concentrations which were very inhibitory in the grana membrane fraction.

Further evidence that stromal lamellae do not have active proton transport in the intact chloroplast was obtained by comparing various chloroplasts having different amounts of stromal and grana membranes. Comparative studies on young and old chloroplasts from lettuce, mesophyll and bundle sheath cell plastids from sorghum, and greening plastids from etiolated corn seedlings revealed a direct correlation between the extent of grana formation and the amount of proton transport activity. Samples which had larger amounts of stromal lamellae had high rates of ATP formation but a reduced capacity for H⁺ accumulation.     

The Development of Chloroplast Ultrastructure and Hill Reaction Activity During Leaf Ontogeny in Different Maize (Zea Mays L.) Genotypes

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.     

THE EFFECT OF LIGHT INTENSITY AND TEMPERATURE ON PLANT GROWTH AND CHLOROPLAST ULTRASTRUCTURE IN SOYBEAN

Soybean plants grown in controlled environment cabinets under light intensities of 220 w/m² or 90 w/m² (400–700 nm) and day to night temperatures of 27.5–22.5 C or 20.0–12.5 C in all combinations, exhibited differences in growth rate, leaf anatomy, chloroplast ultrastructure, and leaf starch, chlorophyll, and chloroplast lipid contents. Leaves grown under the lower light intensity at both temperatures had palisade mesophyll chloroplasts containing well-formed grana. The corresponding leaves developed under the higher light intensity had very rudimentary grana. Chloroplasts from high temperature and high light had grana consisting of two or three appressed thylakoids, while grana from the low temperature were confined to occasional thylakoid overlap. Spongy mesophyll chloroplasts were less sensitive to growth conditions. Transfer experiments showed that the ultrastructure of chloroplasts from mature leaves could be modified by changing the conditions, though the effect was less marked than when the leaf was growing.     

The Development of Chloroplast Ultrastructure and Hill Reaction Activity During Leaf Ontogeny in Different Maize (Zea Mays L.) Genotypes

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.     

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.     

THE ULTRAMICRO STRUCTURE OF STARCH-FREE CHLOROPLASTS OF FULLY EXPANDED LEAVES OF NICOTIANA RUSTICA

Weier , T. Elliot . (U. California, Davis.) The ultramicro structure of starch-free chloroplasts of fully expanded leaves of Nicotiana rustica. Amer. Jour. Bot. 48(7): 615–630. Illus. 1961.—The grana of starch-free chloroplasts of fully expanded leaves of Nicotiana rustica are distinct, compartmented, subplastid entities. They vary in size, shape, orientation and in the distinctness with which their compartments are delineated. It has not been possible to equate accurately their micro and ultramicro appearances. At the ultramicro level, the grana are connected with each other at irregular intervals by a system of anastomosing channels. The partitions forming the compartments of the grana may be coarse or very fine but are constant in appearance in any given chloroplast. The loculi enclosed by the partitions may vary in size with a granum, depending upon their location or upon the physiological activity of the chloroplast. The stroma does not penetrate the grana; it may be relatively fluid and the grana-fretwork system may move within it. A double envelope, which may have pores connecting stroma and hyaloplasm, surrounds the chloroplasts. Materials may collect between the surfaces of the envelope. There is considerable variation in the ultramicro details of chloroplast structure of Nicotiana rustica. It is not yet possible to distinguish accurately between those variations which may be of physiological significance and those which may be induced by processing.     

Short-term effects of aluminium at alkaline pH on the structure and function of the photosynthetic apparatus

A 24 h exposure of the salt-tolerant grass Thinopyrum bessarabicum (Savul. and Rayss) A. Love seedlings to 1 mM aluminium (Al) in nutrient solution at pH of 9.0 resulted in a significant reduction of the biomass. In control samples the mesophyll chloroplasts exhibited the usual lens shape with most grana arranged in straight or slightly curving lines, and only 6.5 % of the grana were out of order. In Al-treated plants the mesophyll chloroplasts displayed a slightly distorted shape and distended size with most grana arranged in bow-like lines, while in the central region of the organelle as many as 26.7 % of the grana were independent and out of order in relation to the long axis. The morphological changes in the chloroplast shape and grana arrangement were probably due to swelling and distension of the chloroplasts in consequence to the altered membrane permeability. The initial in vivo chlorophyll (Chl) fluorescence FO, as well as the intermediate FI and peak fluorescence FP were increased under the Al stress: this indicated a destruction of photosystem (PS) 2 reaction centres and increased reduction of QA. The (FI-FO)/(FP-FO) ratio exhibited a significant increase indicating higher proportion of PS2 centres unable to reduce QB. Changes in the chloroplast ultrastructure seemed to be the reason of photosynthetic electron transport inhibition. Yet all these changes in the photosynthetic performance and chloroplast ultrastructure were considered as indirect effects of Al treatment since Al concentration in the leaves was undetectable. Disturbances in the chloroplast ultrastructure could be caused by a reduced uptake and/or transport of other nutrients. This revised version was published online in June 2006 with corrections to the Cover Date.     

DEVELOPMENT OF THE DIMORPHIC CHLOROPLASTS OF SUGAR CANE

The vascular bundle sheath cells of sugar cane contain starch-storing chloroplasts lacking grana, whereas the adjacent mesophyll cells contain chloroplasts which store very little starch and possess abundant grana. This study was undertaken to determine the ontogeny of these dimorphic chloroplasts. Proplastids in the two cell types in the meristematic region of light-grown leaves cannot be distinguished morphologically. Bundle sheath cell chloroplasts in tissue with 50% of its future chlorophyll possess grana consisting of 2-8 thylakoids/granum. Mesophyll cell chloroplasts of the same age have better developed grana and large, well structured prolamellar bodies. A few grana are still present in bundle sheath cell chloroplasts when the leaf tissue has 75% of its eventual chlorophyll, and prolamellar bodies are also found in mesophyll cell chloroplasts at this stage. The two cell layers in mature dark-grown leaves contain morphologically distinct etio-plasts. The response of these two plastids to light treatment also differs. Plastids in tissue treated with light for short periods exhibit protrusions resembling mitochondria. Plastids in bundle sheath cells of dark-grown leaves do not go through a grana-forming stage. It is concluded that the structure of the specialized chloroplasts in bundle sheath cells of sugar cane is a result of reduction, and that the development of chloroplast dimorphism is related in some way to leaf cell differentiation.     

DEVELOPMENT AND CYTOCHEMISTRY OF THE THYLAKOIDAL BODY IN TOBACCO CHLOROPLASTS

Developing plastids in young tobacco leaves contain thylakoidal bodies, inclusions bound by a single membrane continuous with stroma lamellae. Both the thylakoidal body and its attached lamellae contain an enzyme that catalyzes an oxidation reaction with 3,3'-diaminobenzidine (DAB). DAB staining of the thylakoidal body and lamellae is not the result of photo-oxidation and is inhibited by potassium cyanide. The thylakoidal body disappears as plastids develop into chloroplasts and, further, the lamellar systems of the mature chloroplasts do not stain with DAB. In developing chloroplasts, it is suggested that the thylakoidal body forms by accumulation of protein which stains with DAB within primary lamellae derived from the inner plastid membrane. The ultrastructural and cytochemical evidence suggests that the thylakoidal body stores protein used later in lamellar formation.     

ELECTRON-MICROSCOPIC STUDIES ON CHLOROPLASTS FROM PHOSPHORUS-DEFICIENT PLANTS

The deficiency of phosphorus results in a series of degradative changes in the chloroplasts. These changes can be divided into 4 overlapping phases and each phase or step reflects the severity of the deficiency. The general degenerative pattern involves first the alteration of the grana-fretwork organization of the chloroplast membranes and the formation of a highly ordered, but more simplified, lamellar system. Subsequently, as the deficiency becomes more severe, the newly formed lamellar system breaks down. Concomitant with the membrane disorganization of the plastids, large osmiophilic globuli develop. These globuli probably form as a result of the gradual breakdown of the lipoprotein membranes with the lipid material accumulating in the globuli.     

Flash-induced 515 nm absorbance change in chloroplasts with various granum contents.

The 515 nm absorbance change was studied in mesophyll and bundle sheath chloroplasts of maize, which contain different amounts of grana. The amplitude of the 515 nm signal (induced by 3 micro seconds flashes repeated at 4 s intervals) has shown a correlation with the granum content of the samples. However, upon addition of N-methylphenazonium methosulphate the 515 nm signal became independent of the amount of grana: in agranal thylakoids a large pool of silent Photosystem I was activated and, as a result, the amplitude of the 515 nm signal of agranal chloroplasts increased to the level exhibited by granal chloroplasts. These data show that the 515 nm absorbance change is not limited to small closed vesicles like grana, but in the presence of suitable electron donors single lamellae of bundle sheath chloroplasts can also be active.     

Flash-induced 515 nm absorbance change in chloroplasts with various granum contents

The 515 nm absorbance change was studied in mesophyll and bundle sheath chloroplasts of maize, which contain different amounts of grana. The amplitude of the 515 nm signal (induced by 3 μs flashes repeated at 4 s intervals) has shown a correlation with the granum content of the samples. However, upon addition of N-methylphenazonium methosulphate the 515 nm signal became independent of the amount of grana: in agranal thylakoids a large pool of silent Photosystem I was activated and, as a result, the amplitude of the 515 nm signal of agranal chloroplasts increased to the level exhibited by granal chloroplasts.These data show that the 515 nm absorbance change is not limited to small closed vesicles like grana, but in the presence of suitable electron donors single lamellae of bundle sheath chloroplasts can also be active.