Plastid Structure Research Articles

Plastid development and ferritin content of stigmas of the legumesAcacia, Lotus andTrifolium

Inclusions of ferritin have been observed in plastids from the stigma and stylar tissues of several legumes. The ferritin particles occurring in the stroma of plastids appear as paracrystalline clusters inAcacia or as fingerprint-like patterns inLotus andTrifolium. InAcacia, developmental studies indicate there is a transition in plastid structure from chloroplasts in the meristematic stigma cells, through amyloplasts, amoeboid amyloplasts to oleoplasts in mature stigmas. Following pollination,Acacia stigma cells may undergo holocrine secretion, with cytoplasmic contents becoming electron dense and undergoing autolysis. The ferritin along with other cellular constituents is available for uptake during the heterotrophic nutrition of the pollen tubes.

Structure and Development of Plastids in Epidermal Cells of African Violet (Saintpaulia ionantha Wendl.) in Culture

Structure and Development of Plastids in Epidermal Cells of African Violet (Saintpaulia ionantha Wendl.) in Culture

Plastid DNA Levels in Albino and Green Leaves of the «albostrians» Mutant of Hordeum vulgare

Summary The levels of plastid DNA (pt DNA) in both the green and albino leaves of the barley mutant «albostrians» (Hordeum vulgare, Mutant 4205) are the same. The albino leaves of this plant are similar in size to green leaves and contain numerous undifferentiated plastid structures. They have previously been shown to contain no plastid ribosomes, (Borner et al., 1976). These plastids contain a single pt DNA nucleoid while fully differentiated chloroplasts in green leaves each contain a number of small, peripherally located nucleoids. We conclude that both the replication of pt DNA and the formation of simple undifferentiated plastids does not require plastid protein synthesis, is controlled by nuclear DNA, and is mediated by the cytoplasmic protein synthesizing system. We suggest that during differentiation pt DNA is redistributed through the plastid matrix. The implications of these observations in relation to the standing of the concept that plastids are semi-autonomous, self-replicating organelles is discussed.

Effects of nuclear gene mutations on the structure and function of plastids in pea

Two chlorophyll-deficient mutants of Pisum sativum L. were investigated to elucidate the effect of mutations of nuclear genes on the synthesis and function of the light-harvesting chlorophyll a/b protein (LHCP). Both mutants, a chlorotic as well as a chlorophyll b-less mutant, exhibited chloroplasts differentiated into grana and stroma regions, but, for the most part, grana formation was reduced and the number of lamellae per granum was decreased. The major LHCP-apoprotein was reduced in the thylakoid membranes of the chlorotic mutant and was missing (or very greatly reduced) in the membranes of the chlorophyll b-less mutant. The polyadenylated RNA of both mutants was isolated from young green leaves and translated in a wheat germ cell-free system. Using immunoprecipitation, it was demonstrated that both mutants contained the mRNA for the LHCP-apoprotein and that this message is taken up into polysomes, as shown by read-through translation. From these experimental data it is concluded that transcription and translation of the major protein of the light-harvesting complex are not affected by these genetic defects. A close correlation between the amount of chlorophyll b and the amount of LHCP incorporated into the membrane was observed.

Chloroplast elongation factor Tu: Evidence that it is the product of a chloroplast gene in Euglena

The chloroplast protein synthesizing factor responsible for the binding of aminoacyl-tRNA to ribosomes (EF-Tu chl) has been identified in extracts of Euglena gracilis. This factor is present in low levels when Euglena is grown in the dark and can be induced more than 10-fold when the organism is exposed to light. The induction of the chloroplast EF-Tu by light is inhibited by streptomycin, an inhibitor of protein synthesis on chloroplast ribosomes, indicating that protein synthesis within the chloroplast itself is required for the induction of this factor. The induction of the chloroplast EF-Tu by light is also inhibited by cycloheximide, a specific inhibitor of protein synthesis on cytoplasmic ribosomes. The effect of cycloheximide probably results from the inhibition of chloroplast ribosome synthesis which requires the synthesis of many proteins by the cytoplasmic translational system. Chloroplast EF-Tu cannot be induced by light in an aplastidic mutant (strain W 3BUL) of Euglena which has neither significant plastid structure nor detectable chloroplast DNA. These data strongly suggest that the genetic information for chloroplast EF-Tu resides in the chloroplast genome and that this protein is synthesized within the organelle itself.

Structure and development of plastids in hypsophylls of Euphorbia pulcherrima and Bouganwillea sp.

The fine structure of plastids in hypsophyll at different stages of development and pigmentation has been followed in two short-days plants: Euphorbia pulcherrima and Bouganwillea.In Euphorbia the young chloroplasts observed in the embryonal green hypsophyll change into plastids of small dimensions when contained in the red expanded hypsophyll. Moreover in the green leaves, where red colour is afterwards superimposing, chloroplasts are undergoing a degenerative process. In Bouganwillea the plastid ultrastructure is changing from a young embryonal feature to a moderately developed state, while in the fully expanded hypsophyll degenerated chloroplasts are present together with a population of plastids characterized by numerous large globules and few residual membranes. The unlike chloroplasts behaviour observed in the two different hypsophylls is discussed keeping in consideration pigment synthesis and hypsophyll derivation.In Bouganwillea phloem tubes characteristic P-plastids have been observed and have confirmed the importance of this plastid as a systematic character of Caryophyllales.

Freeze-fracture architecture and polypeptide composition of thylakoid membranes from euploid Ricinus cells.

The freeze-fracture architecture and polypeptide composition of thylakoid membranes of euploid cells of Ricinus communis L. were examined. Electron microscopic examination of the chloroplasts of 1N 2N and 4N cells revealed little variation in the size of chloroplasts, lamellar structure and internal organization of plastids, despite increases in plastid numbers per cell observed to accompany the increase in nuclear ploidy. Thylakoid membranes from euploid cells were also similar in their freeze-fracture morphology. Two basic types of intramembranous particles were observed on the fracture faces of thylakoid membranes of euploid cells. The endoplasmic fracture (EF) face of experimentally unstacked thylakoid membranes of 1N, 2N and 4N cells contain 2 size categories of particles (115-121 A and 164-166 A), whereas the protoplasmic fracture (PF) face of these membranes contain a single size category of particles (85-88 A). The distribution and size of the EF- and PF-face particles were found to be similar among membranes from cells of the 3 ploidy levels. Analysis of the polypeptide composition of thylakoid membranes from 1N, 2N and 4N cells revealed no difference in the relative proportion of the constituent polypeptides of these membranes. The possible factors involved in the regulation of the development of thylakoid structure and composition in the presence of altered nuclear genome size are discussed.

ULTRASTRUCTURAL CHANGES OF PLASTIDS IN FLAX EMBRYOS CULTIVATED IN VITRO

SUMMARYThe ultrastructure of plastids in the cells of flax cotyledons was investigated at three stages during embryogenesis and germination: (1) immature 14‐day old green embryos excised from seeds, (2) 24‐day old embryos which yellowed following a 10‐day cultivation in vitro and (3) 34‐day old embryos which grew for 20 days on the medium and after a temporary loss of pigment regreened and germinated. For comparison, the ultrastructure of chloroplasts from the mature leaves was also investigated.The chloroplasts of 14‐day old embryos are characterized by a well‐developed system of both the grana and the intergranal lamellae and stroma which contains starch grains and phytoferritin. During cultivation in vitro the dimensions of plastids decrease and the internal structure of the chloroplasts undergoes disintegration. In the stroma of plastids of the 24‐day old embryos, lamellae of different length, vesicles and electron‐dense, membrane‐bound bodies and numerous plastoglobulin can be identified and amoeboid plastids occur in the cells. During continued cultivation the dimensions of plastids again increase and in them again differentiation of the system of grana and intergranal lamellae can be observed. The structure of plastids in the 34‐day old embryos is in good agreement with the structure of those in the mature, assimilating leaves of flax. The results indicate that the basic developmental pathway takes place in the same plastids of the flax embryos once during the embryogenesis and once during germination.

Protoplasts as a Means of Studying Chloroplast Development in Vitro

Protoplasts obtained enzymically from etiolated primary leaves of oat were illuminated in vitro, and the process of etioplast chloroplast transformation followed. Chloroplast development proceeded up to 6 hours of incubation in the light (20 C). During this period, complete photosynthetic light and dark reactions were constituted, in addition to prolamellar body-degrading protease activity.In parallel, electron microscopic investigations showed a pronounced decrease in prolamellar body area from 89.5 square micrometers at 0 hours to 40.6 square micrometers at 6 hours, whereas the length of the thylakoid membranes (prothylakoids, thylakoids) increased from 21 micrometers at 0 hour to about 293 micrometers at 6 hours. This was accompanied by the formation of grana (bi- and polythylakoids).A comparison of plastid structure and function, developed within isolated protoplasts and those of organelles greened in intact leaves up to 6 hours, showed that there was only a slight lag in development of plastids illuminated in vitro to those illuminated in vivo. However, times of in vitro illumination longer than 6 hours resulted in signs of deterioration and the lack of further development, except for photosystem I activities.

Factors in chloroplast differentiation.

It is evident that light plays the predominant role in differentiation of the chloroplasts. The development of chloroplast structure is, however, greatly affected by additonal factors, particularly hormones, nutritional state, and water stress. In the present chapter the most important factors and their effects will be discussed. A rather extensive discussion will be devoted to the effects exerted by hormones and nutrient state, because rather few such compilations are found in the literature. Comparative studies of photosynthesis and plastid structure are important to reveal the mechanism of photosynthesis, since differentiation of chloroplast structures can be shown to be well correlated with the ontogenesis of various parts of the photosynthetic apparatus.

Evidence for the nuclear location of the gene for chloroplast elongation factor G

The chloroplast protein synthesis factor responsible for the translocation step of polypeptide synthesis on chloroplast ribosomes (chloroplast elongation factor G [EF-G]) has been detected in whole cell extracts and in isolated chloroplasts from Euglena gracilis. This factor can be detected by its ability to catalyze translocation on 70 S prokaryotic ribosomes such as those from E. coli. Chloroplast EF-G is present in low levels when Euglena is grown in the dark and can be induced more than 20-fold when the organism is grown in the light. The induction of this factor by light is inhibited by cycloheximide, a specific inhibitor of protein synthesis on cytoplasmic ribosomes. However, inhibitors of chloroplast protein synthesis such as streptomycin or spectinomycin have no effect on the induction of this factor by light. Furthermore, chloroplast EF-G can be partially induced by light in an aplastidic mutant (strain W 3BUL) which has neither significant plastid structure nor detectable chloroplast DNA. These data strongly suggest that the genetic information for chloroplast EF-G resides in the nuclear genome, and that this protein is synthesized on cytoplasmic ribosomes prior to compartmentalization within the chloroplasts.

PLASTID DEVELOPMENT IN THE PRIMARY LEAF OF PHASEOLUS VULGARIS: VARIATIONS BETWEEN DIFFERENT TYPES OF CELL

SummaryDuring the period of cellular differentiation, plastids in all cells throughout the primary leaf of Phaseolus vulgaris undergo the same sequence of structural changes. However plastids in different types of cell can, at an early stage, be distinguished from each other quantitatively, i.e. in size, in the amount of starch accumulated, and, later, in the extent of their thylakoid systems. These quantitative differences depend in part on the position of the cell within the lamina and in part on the type of cell involved, and they persist throughout development. Further modifications in plastid structure affect only a few specialized types of cell. These later modifications in plastid structure take place only as the cells become fully differentiated.Plastid division occurs in two separate phases, during seed development on the parent plant and during germination. It is probable that differing rates of plastid division and cell division in epidermal, palisade and mesophyll cells during early stages of germination are responsible for the characteristically different numbers of plastids present in each type of cell in the mature leaf.

Interactions entre le chloramphénicol et la 6-benzylaminopurine au cours du verdissement de cotylédons de concombre

Etiolated cotyledons of cucumber (Cucumis sativus L.) were incubated for 15 h in the dark followed by 72 h in the light in the presence of 10−6 g/ml 6-benzylaminopurine (6-BAP) or 10−4 g/ml chloramphenicol (CHL). These compounds were applied either permanently or only during the dark period, the first 6 h in the light, or the following 66 h in the light. In all cases 6-BAP stimulates both chlorophyll synthesis and plastid differentiation and increases the area of appressed thylakoids. CHL decreases the rate of chlorophyll synthesis only if given during the whole incubation period (dark + light). However, CHL always inhibits the development of the stroma thylakoids and increases both the number of stacked thylakoids per grana and the size of these thylakoids. During the first 6 h in the light, the structure and pigment content of plastids submitted to 6-BAP and CHL (or conversely) appear to be regulated by the compound applied in the dark period. The changes observed in the following light period (after 6 h) depend on the compound present during this period. These results, and those obtained with the two compounds acting simultanously, indicate that the action of these molecules is localized at different cellular levels. The modes of interaction between 6-BAP and CHL are discussed with reference to a biometrical analysis of some structural parameters of plastids.

A SUGGESTED CYCLE OF PLASTID DEVELOPMENTAL INTERRELATIONSHIPS

SUMMARYIt is suggested that developmental changes in plastid structure follow a cyclic pathway which may involve the dedifferentiation of mature chloroplasts to proplastids and the subsequent redifferentiation of proplastids to mature chloroplasts. The proposal of a cyclic plastid relationship revives the earlier concept of Schimper. This has generally been discarded in favour of a unidirectional concept which discounts dedifferentiation as a normal process. Justification of the cyclic concept depends largely on the verification that plastid dedifferentiation and re differentiation do indeed take place. Evidence for this comes not only from the literature, but also from personal observations.

Changes in plastid structure, pigmentation and photosynthesis of the conchocelis stage of Porphyra leucosticta (Rhodophyta, Bangiophyceae) in response to low light and darkness

Abstract Plastids of Porphyra leucosticta conchocelis phase undergo structural alterations after filaments are placed in the dark or at light intensities below the compensation point. These transformations involve formation of tubular units by fragmentation and dilation of thylakoids, each tube having a diameter of 35 nm. On the surface of the tubes are four equally-spaced rows of tightly-packed phycobilisomes. Tubulation occurs most extensively around the pyrenoid and at the ends of the thylakoidal rows, and the number of tubes increases as time of dark incubation is extended. Another change resulting from dark treatment is a loss of osmium staining by plastoglobuli. Photosynthetic capacity slowly decreases after transferring filaments to the dark, such that after 3 weeks, rates are about 50% of those observed in light-grown plants. Phycoerythrin and carotenoid contents do not change with dark incubation but chlorophyll a approximately doubles. Filaments placed in NO3-deficient medium for 2 weeks lose mu...

Spontaneous High-level BUdR Tolerance of the Unorganized Crown-gall Tumour

Summary One phenovariant of crown-gall tumour tissue derived from a haploid plant of Nicotiana tabaeum was able to grow on minimal medium supplemented with 10−3 M of 5-bromodeoxyuridine. This BUdR-tolerance seems to be correlated with the degree of oncogenic transformation induced by Agrobacterium tumefaciens. BUdR-tolerance of the least organized tumour tissue is most probably of a constitutive character and is not the result of selection of incident mutations. Cultivation in the presence of BUdR resulted only in a decrease of chlorophyll content (bleaching effect). Electron microscopic examinations showed degenerative changes of plastid structures in this case. Measurements of 3H-incorporation into tissue DNA fractions in the course of incubation with 3H-BUdR revealed that uptake of BUdR into cells of BUdR tolerant tumour tissue was not affected.

The Fine Structure of Plastids in Various Tissues in the Leaf Blade of Rice

The Fine Structure of Plastids in Various Tissues in the Leaf Blade of Rice

Prolamellar body transformation with increasing cell age in the maize leaf

The fine structure of the plastids in the leaf's basal meristem and in the leaf tissues 2 cm immediately above has been studied in maize leaves of different ages. In the young leaves the proplastids of the basal meristem differentiate, in the tissues within 2 cm above the meristem, into chloroplasts containing two or more prolamellar bodies, indipendently whether the tissues have been fixed 11 hours after a period of illumination or of darkness. In the oldest leaves, in the tissues immediately above the basal meristem, no prolamellar body is present in the plastids, and the proplastids differentiate directly into chloroplasts, without passing through an “etio-chloroplast” stage.

Ultrastructure of meristematic epidermal cells of maize root under water deficit conditions

Structural components of meristematicZea mays primary root epidermal cells were observed after osmotic stress of the nutrient medium (12.5 atm.) and after rehydration. After non-lethal osmotic stress (24 hours), aggregation of nuclear chromatin, parallel ER arrangement, and reduction of mitochondrial cristae were found. Increased number of Golgi cisternae indicated vesicle production inhibition, and microtubules were absent in treated cells, although plastid structure remained unchanged. After lethal osmotic stress (48 hours), fragmentation of cytoplasmic membranes and a more severe structure damage of all cellular components occurred. Structure of the nucleus, mitochondria, Golgi apparatus and microtubules reappeared in the cells after rehydration. The only new feature of these cells was occurrence of smooth ER, which may indicate that the ER system has acquired a different function in regenerated cells.

Correlations between photosynthetic enzymes, CO2-fixation and plastid structure in an albino mutant of Zea mays L.

An albino seedling of Zea mays L. was investigated for its potential for CO2-assimilation. In the mesophyll the number, dimensions and fine structure of chloroplasts are drastically reduced but to a lesser extent in the bundle sheath. Chlorophyll concentration is zero and carotenoid concentration almost zero. Albinism also exerts a strong influence on the stroma of bundle sheath chloroplasts; ribulose-1.5-biphosphate carboxylase (EC 4.1.1.39) activity and glyceraldehyde-3-phosphate dehydrogenase (NADP) (EC 1.2.1.13) activity is not detectable. The C4-enzymes phosphoenolpyruvate carboxylase (EC 4.1.1.31) and malate dehydrogenase (decarboxylating) (EC 1.1.1.40) and the non-photosynthetic linked enzymes malate dehydrogenase (NAD) (EC 1.1.1.37), aspartate-2-oxoglutarate aminotransferase (EC 1.1.1.37), aspartate-2-oxoglutarate aminotransferase (EC 2.6.1.1.) and glyceraldehyde-3-phosphate dehydrogenase (NAD) (EC 1.2.1.1.) are present in the albino seedling with activities comparable to those in etiolated maize seedlings. The potential for CO2 fixation of the albino seedlings exceeds that of comparable dark seedlings considerably. The results are discussed with regard to enzyme localization of the C4 pathway of photosynthesis.