The Fine Structure of Avocado Plastids

Ultrastructural studies of both young and harvest-ripe avocadofruits have established that the skin and outer green layersof flesh contain chloroplasts with an extensive thylakoid system.Etioplasts occur in the yellow flesh adjacent to the stone.The pale-green flesh contains plastids, intermediate betweenchloroplasts and etioplasts, which have prominent prolamellarbodies from which radiate grana. When segments of both the yellow and pale-green flesh of maturefruit (7 cm diam.) are cultured in the light their prolamellarbodies do not disperse although there is a change in their crystallinity.The palegreen tissues of immature (4 mm and 2 cm diam.) fruitsalso contain etioplasts but on culturing these differentiateinto chloroplasts. Both chlorophyll content and the ratio ofchlorophyll a to b varied in the different tissues of youngand mature fruits.     

Plastid Ontogeny in the Corolla Cells of Digitalis purpurea L. cv. Foxy

Initially the corolla plastids of Digitalis purpurea containsmall grana with negatively stained thylakoids. Degenerationof the grana, loss of chlorophyll and the transient accumulationof starch accompany corolla expansion Starch disappears by thetime the anthers dehisce and granular and amorphous phytoferrtindeposits become prominent in the stroma Concomitant with theseparation of the stigmatic lobes the thylakoid system is reducedto a central membranous network enveloping the phytofemtm aggregatesJust prior to corolla abscission the stroma becomes packed withplastoglobuh Although this developmental sequence closely resemblesthat for chromoplasts in yellow and red flowers, fruits andautumn leaves there is no synthesis of carotenoid pigments inthe corollas of Digitalis purpurea At maturity the plastidsare therefore best described as elaioplasts. Digitalis purpurea L., foxglove, corolla, plastids, elaioplasts, phytofemtin, ultrastructure, X-ray microanalysis     

The effects of inhibitors of protein synthesis on the differentiation of plastids in etiolated bean seedlings

Summary It has been shown that inhibitors of protein synthesis do not influence the breakdown of the crystal-lattice-like structure of the prolamellar bodies in the plastids when etiolated plants are exposed to light. The formation of grana and the greening of leaves are however considerably inhibited, depending on the concentration of the inhibitor used.     

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.     

金叶连翘叶片色素含量和解剖结构研究

金叶连翘不同冠层的成熟叶片呈现为不同颜色。以朝鲜连翘深绿色叶为对照,观察金叶连翘冠层上、中、下位叶色,测定其叶片大小和叶绿素a、叶绿素b、总叶绿素及类胡萝卜素含量,同时观察分析叶片横切面解剖结构,旨在阐明叶片色素含量和解剖结构对叶色的影响。研究表明:上层黄色、中层黄绿色、下层浅绿色,黄、黄绿、浅绿色叶总叶绿素含量分别是对照组的0.51%、4.44%和66.47%,均极显著低于对照(P <0.01),但黄绿叶的叶绿素a/b比值显著升高(P <0.05),黄、黄绿叶的总叶绿素/类胡萝卜素比值极显著降低(P <0.01)。黄、黄绿叶的叶绿体发育停滞于单片层时期,类囊体分化程度低,浅绿叶类囊基粒片层肿胀;黄叶细胞器降解,栅栏组织细胞形状难以辨别,黄绿叶上表皮细胞凸起。金叶连翘属于总叶绿素及叶绿素b合成减少型突变体,表现为叶绿素严重缺失,类胡萝卜素相对含量升高;其叶绿体发育停滞,类囊体结构异常,是金叶连翘叶片呈现不同颜色的主要因素,与其叶片解剖显微结构无关。     

THE ULTRASTRUCTURE OF DEVELOPING LATEX DUCTS IN MAMMILLARIA HEYDERI (CACTACEAE)

Electron microscopy was used to investigate early development of latex ducts in Mammillaria heyderi (Cactaceae). Numerous vesicles (secondary vacuoles) form from invaginations of the plasmalemma near sites of wall thinning, from endoplasmic reticulum (ER), and from vesiculate grana of degenerate plastids. Dictyosomes, though they occur in young duct cells, do not seem to be responsible for the formation of vesicles. Cytoplasmic vesicles may contain fibrillar, globular, or crystalline materials, or may be devoid of any type of particulate matter. They may be responsible for storage of numerous laticiferous components. Lysosomal materials could be stored in some vesicles and contribute to the degradation of the protoplast. Some nuclei contain condensed chromatin and are subject to deformation and collapse. Mitochondria and lipid bodies are common in young duct cells but ER is rare. When ducts form in young tissues, plastids in the lumen do not produce starch grains or extensive membranous networks. The plastids eventually degenerate to become a part of latex. If ducts form in older, established tissues having mature plastids, the plastids undergo extreme modification.     

Effects of Different Light Qualities on Structure of Chloroplasts and Photosynthetic Physiological Properties in Panax ginseng

The ultrastructure of chloroplasts and the photosynthetic physiological properties of Panax ginseng C. A. Mey. grown under different light qualities with same light transmission rate (25 % of sun light) were investigated. The results showed that the thylakoid membranes of Panax ginseng chloroplasts are well deve lopted, and the number of grana and granal lame llae under green and violet film are more than that under red and blue film. The content of chlorophyll in the same area of leaves and the absorption spectra area of chlorophylls and leaves under violet and green film are higher than those under other films. All the photosynthetic rates are very low, and their sequence from high to low are violet, green, red and blue . Green film is advantageous to the accumulation of chlorophylls and the development of thylakoid membranes and red film is advantageous to the accumulation of chlorophyll b. Blue film reduced granal thylakoid staking and decreased the photosynthetic rate. A superior trend of the photosynthetic physiologic properties as well as the structure of chloropiasts of Panasc ginseng leaves under violet film,being composed with red and blue film is significant.     

AN ULTRASTRUCTURAL STUDY OF CHLOROPLAST STRUCTURE AND DEDIFFERENTIATION IN TISSUE CULTURES OF STREPTANTHUS TORTUOSUS (CRUCIFERAE)

Cells of Streptanthus tortuosus callus tissue contain chloroplasts when cultured in a liquid medium in the light. Similar cells grown in the dark contain proplastids that fail to develop prolamellar bodies but do contain a complex of loosely-associated membranes. When green, light-grown cultures are cut into small pieces and subcultured to a fresh culture medium, they become bleached even though maintained under the same illumination. The fine structure of the chloroplasts and the chlorophyll content of the cells indicate a dedifferentiation of the chloroplasts to a proplastid state during the early culture period. The changes in the ultrastructure of the plastids are paralleled by a dedifferentiation of the vacuolate cells to a less differentiated, meristematic state. Subsequent growth in the light results in a re-formation of chloroplasts and an increase in the chlorophyll content of the cells. The period of chloroplast redevelopment is associated with the re-formation of large central vacuoles in the cultured cells. Invaginations of the inner membrane of the plastid envelope occur at all stages of plastid development and are not lost during the period of grana degeneration. The proplastids formed from the dedifferentiation of the chloroplasts contain a large number of these invaginations and the redevelopment of grana is associated with a change in the electron density of the invaginating membranes. The degradation of the chlorophyll-containing membranes of the grana occurs during a period of rapid cytoplasmic synthesis induced by the fresh supply of nutrients in the culture medium. These results suggest that the high levels of nutrients may act directly on the chloroplasts and cause their dedifferentiation or that the rapid cell growth induced by the nutrients may cause a degradation of the membrane proteins in the grana of the chloroplasts and an incorporation of the released amino acids into non-plastid components of the cytoplasm.     

Significance of structural variation in thylakoid membranes in maintaining functional photosystems during reproductive growth

Structural variation in the stroma‐grana (SG) arrangement of the thylakoid membranes, such as changes in the thickness of the grana stacks and in the ratio between grana and inter‐grana thylakoid, is often observed. Broadly, such alterations are considered acclimation to changes in growth and the environment. However, the relation of thylakoid morphology to plant growth and photosynthesis remains obscure. Here, we report changes in the thylakoid during leaf development under a fixed light condition. Histological studies on the chloroplasts of fresh green Arabidopsis leaves have shown that characteristically shaped thylakoid membranes lacking the inter‐grana region, referred to hereafter as isolated‐grana (IG), occurred adjacent to highly ordered, large grana layers. This morphology was restored to conventional SG thylakoid membranes with the removal of bolting stems from reproductive plants. Statistical analysis showed a negative correlation between the incidences of IG‐type chloroplasts in mesophyll cells and the rates of leaf growth. Fluorescence parameters calculated from pulse‐amplitude modulated fluorometry measurements and CO₂ assimilation data showed that the IG thylakoids had a photosynthetic ability that was equivalent to that of the SG thylakoids under moderate light. However, clear differences were observed in the chlorophyll a/b ratio. The IG thylakoids were apparently an acclimated phenotype to the internal condition of source leaves. The idea is supported by the fact that the life span of the IG thylakoids increased significantly in the later developing leaves. In conclusion, the heterogeneous state of thylakoid membranes is likely important in maintaining photosynthesis during the reproductive phase of growth.     

Electron microscope studies on the morphogenesis of plastids

Comparisons of the ultrastructure of plastids in three kinds of variegated leaves of tomato plants were made. No difference in the structure and development of chloroplasts in normal green leaves and in the green tissue of variegated leaves was found. The albescent tissues of chromosomal genetic variegated leaves contained only aberrant plastids, which were amoeboid or cup-shaped and had large vacuoles in the stroma. Ribosomes were absent from all plastids in this kind of variegated leaves. Three types of plastids, i.e. chloroplasts containing grana, chloroplasts lacking grana, and plastids lacking internal membranes, were present in the pale green tissues of the variegated leaves of extrachromosomal genetic tomato mutants. Depending on the distribution of these plastids, five cell types were observed in these tissues. Ribosomes were present in all plastids in this type of variegated leaves. In the albescent tissues of variegated leaves induced by streptomycin treatment, two kinds of plastids were observed, one containing giant grana and the other lacking organized internal membranes. A common feature of plastids in this albescent tissue was the presence of light stainable ribosomes. It was suggested that the development of variegated leaves may be caused by blocking an early stage of plastid development. This work was carried out in the Department of Botany, University of California, Davis, by Grant-GB-11906 from National Science Foundation of U.S.A.     

Über das Vorkommen kleiner netzartiger Strukturen in den Plastiden

Summary In the chlorotic leaves of the Oenothera hybrid Oe. (lamarckiana x hookeri) velans· ^h hookeri with lamarckiana plastids the differentiation of the chloroplasts is disordered in different ways because of a disharmony between genom and plastom. Some of the plastids possess numerous vesicles and plastoglobuli but only a few isolated grana instead of the normal thylakoid system. Furthermore, the plastids contain lattice-like structures consisting of fibrils with a thickness of approximately 5 to 11 nm. These networks are connected with thylakoids, vesicles or plastoglobuli. They are interpreted as fragments of prolamellar bodies. Sometimes prolamellar bodies are distinctly recognizable in the chloroplasts even though the thylakoid system is rather well differentiated.     

Effect of Elevated CO2 Concentration on the Starch Grain Accumulation in Chloroplasts from Soybean Leaves at Different Nodes

Soybean ( Glycine max (L.) Merr. ) plants were grown under ambient and elevated CO2 (plus 350 μL/L) concentration in cylindrical open-top chamber to examine their effects on the ultra- structure of chloroplasts. The upper, lower and mid-node leaves were harvested after 7 days full expansion under different CO2 concentrations and ultrathin section were prepared for transmission electron microscopy. In general, the average content of starch grains and thylakoid membranes in the chloroplasts under the elevated CO2 concentration were always higher than the control. Under higher CO2 concentration, there were smaller and less starch grains in the chloroplasts from upper-node leaves than those from mid-node leaves. The shape of their starch grains changed from elliptical to oval,and their thylakoid membranes and grana remained normal. At lower-node leaves, one or two oval, or three timer starch grains accumulated in the chloroplasts. In the mid-node leaves,however, some chloroplasts under higher CO2 concentration had rather large tim elliptical starch grains which could consequently cause disruption of grana and stroama thylakoids in the chloroplasts, whereas in other chloroplasts, the thylakoid membranes and grana were not deformed as the starch grains were smaller and elliptical. On the other hand, under higher CO2 concentration, the stacking degree of thylakoid membranes and starch grains accumulation in the mid-node leaves were significantly higher than those in the lower-node leaves,and slightly higher than the upper-node leaves. These results, in agreement with the chlorophyll contents and photosynthetic rate which reported by other authors in the past, indicated that the ultrastmcture response of the chloroplasts from different leaf nodes of soybeen under elevated CO2 coneentration were different. The seed yield of soybean at different nodes was decreased gradually from mid-nodes towards both upper- and lower-nodes. The greatest effect of elevated CO2 eoneentrafion on seed yeild was at the mid-node leaves. The variation of seed yields of soybean at different nodes under elevated CO2 concentration was in eoneert with the change in the ultrastmcture of chloroplasts and in turn the change in their photosynthetic rates of leaves at different nodes.     

高CO_2浓度对大豆不同叶位叶片叶绿体淀粉粒积累的效应

对高CO_2浓度下生长的大豆(Glycine max(L.)Merr.)不同叶位的叶片进行了电镜观察,揭示出大豆不同叶位叶片的叶绿体对倍增的CO_2浓度反应不一。其显著的超微结构差异特征是:1.叶位居中的叶片叶绿体积累的淀粉粒不仅很大,而且最多,有的叶绿体中的淀粉粒可达20个,几乎充满着叶绿体的基质空间。2.下位叶叶绿体的淀粉粒积累较多,通常为2～5个;3.上位叶叶绿体所含淀粉粒既小又少,虽然有的叶绿体中也积累有3～4个淀粉粒,但大多数叶绿体中所含淀粉粒仅有1～2个。以上结果联系到大豆中位叶的光合作用速率较高及对籽粒产量起作用最大来讨论是很有意义的。     

Effect of cytokinins on plastid development and photosynthetic polypeptides during organogenesis ofPinus ponderosa Dougl. cotyledons culturedin vitro

InPinus ponderosa Dougl., application of the cytokinins, benzyladenine and 2-isopentenyl adenine, to excised cotyledons, promoted thein vitro formation of meristematic centers which led to bud and shoot production. Meristematic cells showed plastids with poorly developed thylakoid membranes and rudimentary grana, whereas cells in non-meristematic tissues and in growth regulator free medium, had chloroplasts with well developed inner membranes, and more thylakoid membranes and grana than plastids of meristematic cells. Chlorophyll and six polypeptides associated with photosynthesis were present in lower concentrations in cytokinin-treated cotyledons than in those cultured in growth regulator free medium. Both benzyladenine and 2-isopentenyl adenine are effective in inhibiting the accumulation of at least two photosynthetic polypeptides in the first 24 h in culture. The ability of cotyledons to respond in this way to cytokinins is lost after three days in culture in growth regulator free medium prior to treatment with cytokinin.     

Pigment composition and plastid structure in leaves of carotenoid mutants of maize

Summary In monogenic, recessive chloroplast mutants of maize which contain chlorophylls, and lycopene or -carotene but no normal carotenoids, great variability in the size of plastids was associated with a number of ultrastructural abnormalities. In the mutant accumulating lycopene some plastids contain dense bundles of lamellae, whereas the chloroplasts of the -carotene mutant show poor thylakoid development. Neither of the mutants was able to form normal grana.A comparison of chlorophyll/carotenoid ratios in different chloroplast fractions of normal and mutant leaves showed that plastids of small size and delicate structure contain relatively less chlorophyll than fully differentiated chloroplasts.     

Plastid inheritance in Job's tears,Coix lacryma-jobi L.

Summary The yellow striping in Job's tears showed nonchromosomal maternal inheritance of the trait producing green, yellow lethal and striped seedlings in the offspring in widely different ratios whenever the striped plant was used as female parent.Plastids in yellow regions of the striped plant were of various sizes and colours ranging from normal to minute size and light yellow or pale green to transparent ones. They were even absent in some cells. The plastids in the leaves of the yellow lethals were usually pale green.While the histological studies indicate the probability that the genetic determinants affecting plastids were in the cytoplasm, the possibility that all the abnormal plastid types could be different expressions of the same original mutation that occurred in the plastids, together with the extensive data on the breeding behaviour of the striped plant, is strongly in favour of the concepts of plastid mutation and autonomy.     

Genetically Programmed Chloroplast Dedifferentiation as a Consequence of Plastome-Genome Incompatibility in Oenothera

Comparision of chloroplast from plants with one of four plastome types (I, II, III, IV) in the nuclear background of Oenothera elata strain Johansen addressed the effects of plastome-genome incompatibility with respect to leaf pigmentation, plastid ultrastructure, chlorophyll a/chlorophyll b ratio, and photosynthetic electron transport. Previous observations of plastomes I, II, and IV in this nuclear background have revealed no indications of incompatibility, but the studies reported here demonstrate that chloroplasts of plastome IV have subtle alterations in their photosynthetic abilities, in particular, deficiencies in photosystem II. The well-characterized "hybrid bleaching" of plants with the AA genotype and plastome III involves leaves that become bleached in the center while remaining green at the tips, edges, and veins. Electron transport assays performed on fractionated bleached and green tissue from the same plants show photosynthetic defects in both the green and bleached regions, although defects in the latter are more severe. Ultrastructural studies show that chloroplasts in the bleached areas enlarge, thylakoid membranes become swollen and vesiculated, and production of new thylakoids is blocked, with chloroplasts appearing to undergo a programmed senescence. A time course revealed that the senescence is actually a reversible dedifferentiation. Alterations in the composition of medium to which AA/III seedlings were transferred showed that the presence of auxin can prevent the development of the typical incompatibility response, with leaf tissue remaining green rather than bleaching. It is proposed that differences in concentrations of plant growth regulators may be responsible for the persistence of normal chloroplasts near the vascular tissue and leaf blade edges and that seasonal fluctuations in auxin levels could explain the periodic bleaching that occurs in older plants.     

Gain and loss of photosynthetic membranes during plastid differentiation in the shoot apex of Arabidopsis

Chloroplasts of higher plants develop from proplastids, which are undifferentiated plastids that lack photosynthetic (thylakoid) membranes. In flowering plants, the proplastid-chloroplast transition takes place at the shoot apex, which consists of the shoot apical meristem (SAM) and the flanking leaf primordia. It has been believed that the SAM contains only proplastids and that these become chloroplasts only in the primordial leaves. Here, we show that plastids of the SAM are neither homogeneous nor necessarily null. Rather, their developmental state varies with the specific region and/or layer of the SAM in which they are found. Plastids throughout the L1 and L3 layers of the SAM possess fairly developed thylakoid networks. However, many of these plastids eventually lose their thylakoids during leaf maturation. By contrast, plastids at the central, stem cell-harboring region of the L2 layer of the SAM lack thylakoid membranes; these appear only at the periphery, near the leaf primordia. Thus, plastids in the SAM undergo distinct differentiation processes that, depending on their lineage and position, lead to either development or loss of thylakoid membranes. These processes continue along the course of leaf maturation.     

ULTRASTRUCTURAL AND PHYSIOLOGICAL DIFFERENCES IN SOYBEANS WITH GENETICALLY ALTERED LEVELS OF PHOTOSYNTHETIC PIGMENTS

Soybeans displaying incomplete dominance for leaf pigmentation possess chloroplasts with characteristic shape and organization of photosynthetic membranes. The chloroplasts of light green plants lack grana typical of dark green or a field type (Beeson) but normally possess doubled thylakoids. Achlorophyllous lethal yellow plants have thylakoids reduced to single spiralled membranes. The yellow plants lack a waxy cuticle over the leaf surface which is characteristic of all other soybeans examined, and they lack catalase activity in microbodies. Photosynthetic rates in the light green plants are at least as high as in the fully pigmented ones and photorespiration levels are not significantly different. Thus, in light green plants greater efficiency of enzymatic processes in photosynthesis apparently offsets the inhibitory activities associated with photorespiration. Single allele alterations from dark green to light green and light green to lethal yellow appear to alter a variety of structures and functions.