Changes in Chloroplast Fine Structure During the Autumnal Senescence of Betula Leaves

During the ageing and senescence of leaves of the birch tree,Betula verrucosa Ehrb., from the fully expanded green stateto the yellow terminal condition, the shape of the chloroplastsalters and their volume decreases to less than one-fifth. Associatedwith these changes is an initial increase in the number of chloroplastlamellae and size of the grana but this is followed by the breakdownof the membrane systems. The chloroplast lipid globules increaseconsiderably in size but show little increase in number. Thestructure of the chloroplast membranes is described in detail.Small particles approximately 8 x 5 nm, become visible on theinner surfaces of the thylakoid membranes during chloroplastbreakdown. The chloroplasts are the first organelles to showsigns of senescence and are the last to remain after the otherorganelles have all broken down. The observations are discussedin relation to the senescence of chloroplasts of herbaceousplants and the development of chromoplasts of fruits.     

Developmental Ultrastructure of Cells and Plastids in the Petals of Wallflower (Erysimum cheiri)

An ultrastructural study of petal cells of wallflower (Erysimumcheirii) of the family Brassicaceae shows that the adaxial epidermalcells are of the conical papillate type whereas the cells ofthe abaxial epidermis are lenticular in shape. The abaxial epidermiscontains stomata, which are solitary and lack any obvious subsidiarycells. Pigmentation is apparent in both epidermal and internalmesophyll cells and results from the presence of both chromoplastsand large cytoplasmic vesicles containing pigment. These pigmentedvesicles are very obvious in preparations of fixed isolatedpetal cells. Chromoplasts are of the globular type and are presentin significant numbers in both epidermal and mesophyll cells.Division of chloroplasts in young petals prior to bud breakappears to give rise to the populations of chromoplasts observedin mature petals since there was no evidence of chromoplastdivision itself. The development of wallflower petals and theirchromoplasts is discussed in relation to development of petalsin the related species Arabidopsis thaliana. Copyright 1999Annals of Botany Company Wallflower, Erysimum cheiri, Chieranthus, petal development, chromoplasts, chloroplast differentiation.     

Ultrastructural Development of Plastids in the Epidermis and Starch Layer of Glossy Ranunculus Petals

The differentiation of chromoplasts and amyloplasts has beenfollowed in developing petals of Ranunculus acris, R. ficariaand R. repens from small bud stages through anthesis. Theseare typical of Ranunculus species with glossy yellow petals.The plastids in the adaxial epidermis of the glossy part developmany globules which enlarge and coalesce with the eventual completebreakdown of plastid structure. At anthesis only a few cytoplasmicremnants remain in the dispersed pigment in these cells whichpartially collapse with folding of the anticlinal walls. Inthe non-glossy proximal part of the petal the adaxial epidermalcells have more convex outer walls and the chromoplast developmentdoes not progress beyond a stage found in the glossy regionjust before the petal tips emerge from the bud: they have largeperipheral globules with irregular tubular lamellae betweenthem and in the central stroma. In the abaxial epidermis theplastids produce small globules and retain some grana; somehave small starch grains and differ little from the plastidsin the mesophyll. The starch layer beneath the adaxial epidermisin the glossy region is formed from a single embryonic celllayer. Amyloplasts differentiate rapidly in these cells andall plastid structure has disappeared before the flower budopens leaving the sloping palisade cells packed with starchgrains. Chromoplast, amyloplast, petal, ultrastructure, development, Ranunculus, buttercup, lesser celandine     

CHROMOPLASTS OF TOMATO FRUITS. I. ULTRASTRUCTURE OF LOW-PIGMENT AND HIGH-BETA MUTANTS. CAROTENE ANALYSES

Three pigment lines of the tomato cultivar ‘Pearson’ with isogenic backgrounds were studied to determine the relationship between certain carotenoids and the development of chromoplasts during fruit ripening. The lines were normal red (r⁺/r⁺), in which about 90% of the carotenoids in the ripe fruit is lycopene; high-beta (B/B) mutant, in which beta-carotene is the major pigment and the mature fruit color is deep orange ; and low-pigment (r/r) mutant, in which carotenoids are drastically reduced and the mature fruit is pale yellow-orange. This paper reports pigment analyses for the three lines and the ultrastructural changes in plastids of the two mutant lines. Very young, pale green fruits contain proplastids with limited lamellar structure. As the fruits reach the mature green stage, the plastids in all three lines develop into typical chloroplasts. Differences in pigment content and in ultrastructure among the lines are not apparent until ripening commences. In the low-pigment mutant carotenoids are reduced as ripening progresses and no carotenoid crystalloids are formed. As chlorophyll decreases the fruits become pale yellow. The grana become disorganized and the thylakoids appear to separate at the partitions and tend to be arrayed in lines, some still with their ends overlapping. Globules increase slightly in number. In the high-beta mutant the grana break down during ripening and globules increase greatly in size and number. Beta-carotene, presumed to be largely in the globules, crystallizes into elongated or druse type forms which may distort the globules. The crystals may affect the shape of the chromoplasts; long crystals may extend the length of the plastid to over 15 μ. Thylakoid plexes with a regular lattice structure sometimes occur in the chromoplasts of the high-beta mutant. Granules resembling aggregations of phytoferritin particles occur in the chromoplasts of both of these mutants.     

Characterisation and changes in the antioxidant system of chloroplasts and chromoplasts isolated from green and mature pepper fruits

Purification and characterisation of pepper ( Capsicum annuum L) chloroplasts and chromoplasts isolated from commercial green, red and yellow mature fruits were undertaken. Induction of the synthesis of several antioxidants in organelles isolated from mature fruits was found. The ultrastructure of organelles and the presence and activity of SOD isozymes and enzymes involved in the ASC-GSH cycle, together with the non-enzymatic antioxidant content and some oxidative parameters, were analysed. It was found that lipids, rather than proteins, seem to be a target for oxidation in the chromoplasts. The ascorbate and glutathione contents were elicited during differentiation of chloroplasts into chromoplasts in both red and yellow fruits. The activity of SOD and of components of the ASC-GSH cycle was up-regulated, suggesting that these enzymes may play a role in the protection of plastids and could act as modulators of signal molecules such as O₂^˙− and H₂O₂ during fruit maturation. The presence of an Mn-SOD in chromoplasts isolated from yellow pepper fruits was also investigated in terms of structural and antioxidant differences between the two cultivars.     

Fine Structure and Carotenoid Composition of the Fibrillar Chromoplasts of Asparagus officinalis L.

The spindle-shaped chromoplasts of the ripe fruit of Asparagusofficinalis developed from chloroplasts that lost grana andstroma lamellae and accumulated large-sized plastoglobules,most of which transformed into fibrils of exceptionally largediameter. The carotenoid concentration was high in ripe fruits(2520 µg g^–1 fresh wt) and consisted mainly of capsanthin,ß-carotene and zeazanthin. A. officinalis is onlythe third species reported to contain both capsanthin and capsorubin. The large diameter of both fibrils and their associated plastoglobulesenabled verification that flbrils pass through plastoglobules.Unlike most fibrillar chromoplasts, the plastoglobules remainedassociated with flbrils even in fully-ripe fruit, and a straightline relationship can be established between plastoglobule andfibril diameter. The presence of more than one fibril developingfrom a plastoglobule, and the occasional existence of fibrilstwisted helically around one another, is interpreted to meanthat fibril growth by lateral addition of microfibrils is unlikely. The microfibrillar ultrastructure of Asparagus flbrils was differentto that found for Capsicum fibrils, and these differences areillustrated in two models. These differences, however, do notnecessarily mean that the fibrils of each species are constructedof different protein sub-units, although the bonding betweensub-units is different.     

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     

Pigment Bodies in Fruits of Crimson and High Pigment Lines of Tomatoes

Pigment bodies in fruits of crimson (og^c), high pigment (hp),and crimson-high pigment (og^c hp) lines of tomatoes were observedby electron and light microscopy and compared with those ofnormal red lines and a yellow cultivar. During chloroplast-chromoplasttransformation, two main structurally distinct bodies are produced,their total and relative amounts apparently accounting for theentire range of colours (from very deep red to yellow) characterizingthe mature fruits of these different colour lines. The longnarrow crystalloids, believed to be lycopene, form in associationwith an extended thylakoid system; in senescing (over-ripe)fruit many of these are reduced to shorter irregular forms.The rounded globules are believed to be beta-carotene dissolvedin lipid material derived from membrane lysis. Analytical resultscorroborate microscopic observations that the effect of theog^c gene, as compared with the r⁺ gene for normal red colour,is to increase the lycopene content and lower the beta-carotenecontent. The effect of the hp gene is to increase the levelsof both pigments. The results support the view that the genescontrol the development of fruit pigments which affect chromoplastultrastructure. Lycopersicon esculentum Mill, tomato, fruit, pigment bodies, beta-carotene, lycopene     

Die Submikroskopische Entwicklung der Chromoplasten in den Blüten von Ranunculus Repens L

Summary Electron microscopic studies of the development of yellow chromoplasts in the perianth ofRanunculus repens L. show, that the structures characteristic of these yellow plastids are homogeneous osmophilic globuli up to 1500 Å in diameter which first appear in young chloroplasts or leucoplasts. They are formed between the lamellae and, while increasing in size and number, they destroy the lamellar structure until at maturity only these droplets remain lining the inner surface of the plastid membrane. It is most likely that they are formed as a result of lipophanerosis of the lamellar structures and that they represent the final stage in a monotropic plastid metamorphosis and can not revert to chloro-, or leucoplasts. This is supporting evidence for the theory of monotropic plastid transformation.Transition forms have been found, having structures characteristic of both leuco-, chloro-, and chromoplasts at the same time, thus making the usual classification into these categories no longer tenable on the basis of submicroscopic morphology.

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Mit 13 Textabbildungen

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Aus Mitteln des Schweizerischen Nationalfonds durchgeführte Untersuchung.

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O. Renner zum 75. Geburtstag gewidmet.     

Die Feinstruktur der Chromoplasten in plasmochromen Perigon-Blättern von Tulipa

Summary The chromoplasts of yellow perigon leaves of Tulipa derive from the young chloroplasts present in the bud stage. During chromoplast development and thylakoid breakdown many large plastoglobuli (diameter 80–360 nm) are formed. The function of the petal plastoglobuli as stores for the chromoplast lipids such as plastidquinones and carotenoids is discussed.     

Characterization of chromoplasts and carotenoids of red- and yellow-fleshed papaya (<Emphasis Type="Italic">Carica papaya</Emphasis> L.)

Chromoplast morphology and ultrastructure of red- and yellow-fleshed papaya (Carica papaya L.) were investigated by light and transmission electron microscopy. Carotenoid analyses by LC–MS revealed striking similarity of nutritionally relevant carotenoid profiles in both the red and yellow varieties. However, while yellow fruits contained only trace amounts of lycopene, the latter was found to be predominant in red papaya (51% of total carotenoids). Comparison of the pigment-loaded chromoplast ultrastructures disclosed tubular plastids to be abundant in yellow papaya, whereas larger crystalloid substructures characterized most frequent red papaya chromoplasts. Exclusively existent in red papaya, such crystalloid structures were associated with lycopene accumulation. Non-globular carotenoid deposition was derived from simple solubility calculations based on carotenoid and lipid contents of the differently colored fruit pulps. Since the physical state of carotenoid deposition may be decisive regarding their bioavailability, chromoplasts from lycopene-rich tomato fruit (Lycopersicon esculentum L.) were also assessed and compared to red papaya. Besides interesting analogies, various distinctions were ascertained resulting in the prediction of enhanced lycopene bioavailability from red papaya. In addition, the developmental pathway of red papaya chromoplasts was investigated during fruit ripening and carotenogenesis. In the early maturation stage of white-fleshed papaya, undifferentiated proplastids and globular plastids were predominant, corresponding to incipient carotenoid biosynthesis. Since intermediate plastids, e.g., amyloplasts or chloroplasts, were absent, chromoplasts are likely to emerge directly from proplastids.     

The greening of chromoplasts in Daucus carota L.

Summary Evidence was obtained for the transformation of chromoplasts to chloroplasts in the cortex parenchyma of carrot during exposure to light. Typical chromoplasts containing carotene crystals but no lamellar system were observed at the onset of illumination. The ensuing synthesis of chlorophyll and a lamellar system was accompanied by disappearance of the carotene crystals. Only chloroplasts were present after 48 hr in the light. The different stages of plastid development were observed using the electron microscope.     

Comparative Ultrastructure and Organization of the Prismatic Region of Two Bivalves and its Possible Relation to the Chemical Mechanism of Boring

The prismatic region of two bivalve molluscs exemplifies, inits structure and organization, one of the types of differentiatedcalcareous substrates through which boring organisms must penetrate. The oriented inorganic crystals, separated from one anotherby intercrystalline "spaces", are structurally organized intowell defined prisms. The prisms of each bivalve vary in shapeand size and are delineated from one another by electron-lucent,non-calcified regions. The demineralized organic matrix is also structurally organizedinto prisms, delineated from one another by prism sheaths, andan intraprismatic matrix structurally organized into closelypacked sheet-like compartments and subcompartments in whichthe inorganic crystals are deposited. The non-mineralized intercrystalline "spaces" between the individualinorganic crystals of the same or adjacent rows in a mineralizedsection are occupied by the walls of the intraprismalic sheet-likecompartments. Similarly, the non-calcified electronlucent regionsdelineating one mineralized prism from the next are occupiedby the thick prism sheaths. These portions of the organic matrixwhich fail to mineralize completely undoubtedly provide readypathways for the passage of solutes and solvents through thesetissues of highly ordered, densely packed, inorganic crystals.Moreover, the framework of the organic matrix, which fails tomineralize in these heavily calcified, molluscan substrates,may provide the primary, not the secondary source of chemicalattack during boring, for once the sheaths and compartmentssurrounding the crystals are broken down or solubilized, thecrystals are themselves loosened and freed for mechanical removalby shell-penetrating organisms.     

Structural changes in plastids of developing Splachnum ampullaceum sporophytes and relationship to odour production

Many mosses of the family Splachnaceae are entomophilous and rely on flies for spore dispersal. Splachnum ampullaceum produces a yellow‐ or pink‐coloured hypophysis that releases volatile compounds, attracting flies to the mature moss. The biosynthetic sources of the visual and aromatic cues within the hypophysis have not been identified, and may be either symbiotic cyanobacteria or chromoplasts that break down lipids into volatile compounds. Here, we used transmission electron microscopy and gas chromatography‐mass spectrometry (GC‐MS) to investigate the sources of these attractants, focusing on different tissues and stages of maturation. Microscopy revealed an abundance of plastids within the hypophysis, while no symbiotic bacteria were observed. During plant maturation, plastids differentiated from amyloplasts with large starch granules to photosynthetic chloroplasts and finally to chromoplasts with lipid accumulations. We used GC‐MS to identify over 50 volatile organic compounds from mature sporophytes including short‐chain oxygenated compounds, unsaturated irregular terpenoids, fatty acid‐derived 6‐ and 8‐carbon alcohols and ketones, and the aromatic compounds acetophenone and p‐cresol. The hypophysis showed localised production of pungent volatiles, mainly short‐chain fermentation compounds and p‐cresol. Some of these volatiles have been shown to be produced from lipid oxidase degradation of linolenic acid within chromoplasts. However, other compounds (such as cyclohexanecarboxylic acid esters) may have a microbial origin. Further investigation is necessary to identify the origin of fly attractants in these mosses.     

Some Structural Changes During Ripening of Mangoes (Mangifera indica var. Alphonso) by Abscisic Acid Treatment

Abscisic acid at 10^–6 M concentration enhances ripeningof mangoes. The cells in the pulp of the fruit are large andparenchymatous and lose their integrity due to cell wall hydrolysisat the ripe stage. They contain abundant polysaccharides, consistingmainly of starch, which is degraded during ripening. The chloroplastsare transformed to chromoplasts containing red or yellow carotenoidpigment. Abscisic acid treatment enhances all of these processes.Mitochondria, on the other hand, retain their structural integritythroughout the ripening process in untreated and abscisic acid-treatedmangoes. Mangoes, ripening, abscisic acid, structure     

Chromoplast development in a carotenoid mutant of maize

Summary The lethal recessive mutantlycopenic in maize is characterized by the synthesis of lycopene instead of the normal carotenoids. At normal conditions of illumination it loses chlorophyll by photo-oxidation. Seedlings of this mutant and of normal maize were grown at light intensities of 25–30 lux and 500–30,000 lux. Their plastid development was studied by electron microscopy.At low light intensities a kind of mesophyll chloroplast with elongated grana, long unpaired thylakoid segments, and sometimes prolamellar bodies is formed in mutant plants. In corresponding bleached plants the plastids are transformed into chromoplasts containing characteristic lycopene crystalloids similar to those found in tomato fruits. Various stages in this chromoplast development are described and illustrated. Also bundle-sheath plastids were found to develop into chromoplasts.It is concluded that the ultrastructure of plastids in a tissue is influenced by the nature of their pigments and that an altered carotenoid composition therefore can give rise to development of chromoplasts in plants which normally lack such organelles.     

Chromoplasts--the last stages in plastid development.

The results of investigations on the development of chromoplast fine structures in various plants are reviewed. Emphasis is placed on the specific pigment-containing structures and their development during chromoplast formation. There is a large variety of these structures, although four fundamental types can be discerned. These are plastoglobules, membranes, crystals, and tubules. During chromoplast development, various types of structure follow one after the other, or they may even be present simultaneously in the same chromoplast. Depending on the structures present in chromoplasts their pigment content also varies. It is still not clear whether the type of structure defines the pigment content of the chromoplast or vice-versa. Various possible ways of chromoplast development and dedifferentiation are discussed.     

Leaf Nucleic Acids:: II. METABOLISM DURING SENESCENCE AND THE EFFECT OF KINETIN

The nucleic acids in the green and in the senescent leaves ofthree types of plant have been studied. High and low molecularweight RNA of the chloroplast is not present in senescent leavesof Xanthium pensylvanicum, but both cytoplasmic and chloroplasticfractions are found in yellow leaves of Vicia faba and Nicotianatabacum. RNA is more rapidly degraded than DNA in the leavesof these plants when they are detached, and kinetin treatmenttemporarily arrests the loss of chlorophyll and nucleic acid.Once X. pensylvanicum leaves are yellow and senescent they cannotbe re-greened, whereas those of Nicotiana spp., and to someextent those of V. faba, can be rejuvenated. We suggest thatthe retention of chloroplast RNA in yellow leaves may be a majorfactor determining their ability to re-green and that the patternof organelle senescence prior to the first stages of leaf autolysisand dehydration is species-specific.     

Quantification of the Relative Abundance of Plastome to Nuclear Genome in Leaf and Root Tissues of Carrot (Daucus carota L.) Using Quantitative PCR

Carrot (Daucus carota L.) is an important horticultural crop with significant health benefits, providing provitamin A carotenoids in the human diet. Carotenoids primarily serve as photoprotectants in leaves during photosynthesis where they accumulate in chloroplasts. Carotenoids can also accumulate in chromoplasts, non-chlorophyll-containing plastids, in non-photosynthetic organs such as the storage roots of carrot. Therefore, plastid development is closely associated with carotenoid accumulation. The biosynthesis of chromoplasts, or more specifically the conversion of chloroplasts to chromoplasts, has been studied in a number of carotenoid-accumulating plant species, but the presence of the plastome had not been confirmed in non-pigmented carrot storage root. In this study, the plastome was confirmed to occur in similar relative abundance (plastome–nuclear genome ratio) in yellow and orange carrot storage roots while dark orange storage roots had significantly higher plastome content than white cultivated carrots. In the leaf tissue of these same plants, the relative abundance of the plastome was similar across genotypes but was lower than the ratio of plastid to nuclear genome in the root tissue of pigmented storage rooted carrot. This study is the first quantification of the ratio of plastome to nuclear genome in storage root and confirms the presence of the plastome in both pigmented and non-pigmented carrot storage root tissue.