Acid phosphatase activity during spore differentiation of the red algaeGigartina teedii andChondria tenuissima

The acid phosphatase activity during carposporogenesis inGigartina and tetrasporogenesis inChondria was studied using the Gomori technique. During the first steps of gonimoblast maturation ofGigartina, portions of cytoplasm are ensheathed by ER cisternae with acid phosphatase activity, giving rise to autolysosomal concentric membrane bodies. In a similar way large mucilage sacs are severed. They extrude their contents in a kind of exocytosis. Multivesicular bodies, concentrically arranged cisternae and extracytoplasmic compartments, each with acid phosphatase activity, remain in young carpospores for some time, probably as remnants of the autophagocytotic and exocytotic events. The Golgi apparatus is poorly developed in gonimoblast cells and young carpospores. It becomes a prominent cell component in maturing carpospores and then participates in cell wall formation. Only some of the dictyosomal cisternae contain acid phosphatase; these are irregularly distributed in the dictyosome. — In pre- and postmeiotic tetraspore mother cells ofChondria massive lead deposits are found in the dictyosomes and in adjacent Golgi vesicles. Finer lead precipitates occur in ER cisternae, especially in those which are sequestering starch-grain-containing portions of the cytoplasm to give rise to autolysosomes. During cell cleavage, the dictyosomes aggregate. They become devoid of acid phosphatase activity with the exception of vesicles at the trans face. Later, Golgi stacks associate and have common, Gomori positively reacting, narrow cisternae at the cis face. The Golgi apparatus derived cored vesicles do not contain lead precipitates whereas the Golgi cisternae in the final stage of tetrasporogenesis show acid phosphatase activity. Variations in acid phosphatase distribution are explained in the light of current models of membrane flow.Dedicated to Univ.-Prof. DrO. Härtel on the occasion of his 80th birthday.     

Plastid polarity and meiotic spindle development in microsporogenesis ofSelaginella

Summary Microsporogenesis inSelaginella was studied by fluorescence light microscopy and transmission electron microscopy. As in other examples of monoplastidic meiosis the plastids are involved in determination of division polarity and organization of microtubules. However, there are important differences: (1) the meiotic spindle develops from a unique prophase microtubule system associated with two plastids rather than from a typical quadripolar microtubule system associated with four plastids; (2) the division axes for first and second meiotic division are established sequentially, whereas as in all other cases the poles of second division are established before those of first division; and (3) the plastids remain in close contact with the nucleus throughout meiotic prophase and provide clues to the early determination of spindle orientation. In early prophase the single plastid divides in the plane of the future division and the two daughter plastids rotate apart until they lie on opposite sides of the nucleus. The procytokinetic plate (PCP) forms in association with the two slender plastids; it consists of two spindle-shaped microtubule arrays focused on the plastid tips with a plate of vesicles at the equatorial region and a picket row of microtubules around one side of the nucleus. Second plastid division occurs just before metaphase and the daughter plastids remain together at the spindle poles during first meiotic division. The meiotic spindle develops from merger of the component arrays of the PCP and additional microtubules emanating from the pair of plastid tips located at the poles. After inframeiotic interphase the plastids migrate to tetrahedral arrangement where they serve as poles of second division.Abbreviations AMS axial microtubule system - FITC fluorescein isothiocyanate - MTOC microtubule organizing center - PCP procytokinetic plate - QMS quadripolar microtubule system - TEM transmission electron microscope (microscopy)     

Ultrastructure of the early stages of carposporophyte development in the red algaChondria tenuissima (Rhodomelaceae,Ceramiales)

The ultrastructure of the early stages of carposporophyte development in the marine red algaChondria tenuissima has been studied. The diploid carposporophyte grows on the gametophyte. Apical gonimoblast cells develop into diploid carpospores. The basal gonimoblast cells cease to divide and undergo considerable cytoplasmic changes before they become incorporated into the expanding fusion cell. Nucleus and plastids degenerate gradually, while mitochondria remain intact. The smooth endoplasmic reticulum becomes prominent, it seems to produce small vesicles with electron dense contents. Simultaneously, numerous mucilage sacs are formed, presumably from dilating ER cisternae. The contents of the mucilage sacs are secreted by exocytosis. The pit connections between gonimoblast cells flare out. They remain as isolated bodies without connection to a wall after fusion. Secondary pit connections occur between vegetative gametophyte cells and sterile carposporophyte cells. There are three different morphological types of pit connections.     

Tentoxin effects onSorghum: The role of polyphenol oxidase

Summary In an ultrastructural and cytochemical study of tentoxin-treatedSorghum bicolor (L.) Moench, both bundle sheath and mesophyll plastids were severely affected, Plastids from chlorotic leaf areas lacked most internal membranes yet had plastid ribosomes and large fibrillar areas of plastid DNA. In recovered areas (mottled yellow and green), cells were found that had plastids of near-normal ultrastructure as well as the severely affected plastid-types found in chlorotic leaf areas. Polyphenol oxidase (PPO) cytochemistry of these mottled leaf areas indicated that all recovered mesophyll plastids had PPO whereas all the abnormal mesophyll plastids showed no activity. Because bundle sheath plastids ofSorghum have no PPO activity at any developmental stage, yet are affected by tentoxin, PPO cannot be uniquely affected by this toxin. We suggest that tentoxin may affect the transport of cytosolic proteins into the plastid.     

Fine structure of spermatogonia and primary spermatocytes in rabbits

Summary The fine structure of rabbit Spermatogonia and primary spermatocytes in meiotic prophase has been studied with different methods of preparation, including a technique for acid phosphatase activity. The spermatogonial cytoplasm is rich in free ribosomes and containes moderate amounts of vesicular, smooth-surfaced endoplasmic reticulum and mitochondria, a simple Golgi-apparatus, some micropinocytotic vesicles, and occasional multivesicular bodies, vacuoles and dense bodies with acid phosphatase activity. The large type A Spermatogonia have a prominent nucleolus and their mitochondria sometimes form clusters with a dense intermitochondrial substance, similar to that in spermatocytes.The nucleus and cytoplasm of primary spermatocytes increase markedly in volume and density during meiotic prophase. The Golgi apparatus enlarges and becomes more differentiated and finally forms small proacrosome granules. The endoplasmic reticulum produces numerous small, mainly smooth vesicles and might also be the source of a new organelle: numerous piles of narrow cisternae with opaque contents. These piles disintegrate late in prophase. The mitochondria become aggregated in clusters with dense intermitochondrial substance and their internal structure is characterized by highly dilated cristae and small particles, interpreted as mitochondrial ribosomes, in the matrix. The role of these structures in the formation of new mitochondria is discussed. The clusters of mitochondria finally disperse and their cores of dense intermitochondrial substance, possibly containing ribonucleoprotein, coalesce into a large chromatoid body similar to that in spermatids. Micropinocytosis and a few lysosomes occur in most spermatocytes. The pachytene nuclei show prominent nucleoli and a distinct sex vesicle without any synaptinemal complex.The importance for spermatid differentiation of some events taking place in the cytoplasm of primary spermatocytes is emphasized.Financial support for this study was received from the Swedish Medical Research Council.     

Ultrastructure of meiosis in the mossRhynchostegium serrulatum I. Prophasic microtubules and spindle dynamics

Summary An extensive system of microtubules develops during meiotic prophase in the mossRhynchostegium serrulatum (Hedw.)Jaeg. &Sauerb. Development of the cytoskeleton can be traced to early prophase when the nucleus is acentric and the single plastid divides into four plastids. The cytoskeletal microtubules are associated with equidistant positioning of the four plastids at the distal tetrad poles and with migration of the nucleus to a central position in the sporocyte. The cytoskeleton, which interconnects plastids and encloses the nucleus, contributes to the establishment of moss sporocyte polarity. Just prior to metaphase I evidence of the prophase cytoskeleton is lost as the bipolar metaphase I spindle develops in association with discrete polar organizers located in opposite cleavage furrows between plastids.     

The rôle of membrane-bound cytoplasmic inclusions during gametogenesis in Lilium longiflorum thunb.

In the prophase of both mega- and microsporogenesis, a sizeable proportion of the meiocyte cytoplasm becomes invested in double or multiple membrane-bround inclusions. This cytoplasm remains thus isolated from the rest of the cell until the completion of meiosis II in the female cells, or the young spore stage in those of the male. Significantly this encapsulation proceeds immediately the elimination of the major part of the ribosome population from the cytoplasm and, further, the electron microscope reveals that those ribosomes contained in these membranous inclusions remain unaffected by the lytic enzymes active elsewhere in the cytoplasm at this time. This encapsulated cytoplasm is proposed to fulfill two rôles; one, that it carries reserves necessary for postmeiotic development through from the diplophase to the haplophase environment and, two, that it permits the continuity of protein synthesis throughout meiosis I and II, a period when the major part of the protein synthetic apparatus is absent.Abbreviations MI membrane-bound inclusions - MMI multimembraned inclusions     

Ultrastructural studies on plastids of generative and vegetative cells in Liliaceae

Summary The behaviour of plastids and mitochondria during the formation and development of the male gametophyte of Chlorophytum comosum has been investigated using electron microscopy. During first pollen mitosis an intracellular polarization of plastids occurs in that the plastids are clustered in the centre of the microspore. The originating generative cell normally lacks plastids. Only in a small number of microspores have plastids been observed near the dividing nucleus of the microspore and later on in the generative cell. These observations agree with the genetic investigations of Collins (1922) on the mode of plastid inheritance which demonstrated a small amount of biparental plastid inheritance in Chlorophytum. The cytological mechanisms underlying plastid polarization during the first pollen mitosis are discussed.     

Absence of ribosomes in Capsicum chromoplasts

Ribosome development was followed by electron microscopy and gel electrophoresis of ribosomal (r)RNAs in the plastids of fully expanded fruits of Capsicum annuum L. during ripening. Chloroplasts from young Capsicum leaves were used as a structural and electrophoretic standard. Four stages were distinguished on the basis of colour changes during fruit ripening. Chloroplasts of the green fruit had a lower content of 16S and 23S rRNAs than leaf chloroplasts. They contained only a few ribosomes, some more discrete ribosomal particles, and the contrast of ribosomal structures was faint. From the outset of ripening, most of the ribosomal structures in the plastid stroma disappeared. A continuous decrease in plastid rRNAs occurred during ripening. Fully differentiated chromoplasts of the red fruit did not contain rRNAs or ribosomes. Throughout plastid development, DNA nucleoids were evident and there was only a small decrease in the DNA peak on electrophoretograms. The loss of ribosomes during the chloroplast-to-chromoplast conversion in Capsicum fruit is discussed in relation to the variations in pigments and enzymic systems in both plastid types.Abbreviations Developmental stages of leaves and fruits: A four-week-old green leaf - B green fruit - C brownish fruit - D orange fruit - E red fruit - ptRNA, DNA plastid RNA - DNA; rRNA ribosomal RNA     

Preferential degradation of plastid DNA with preservation of mitochondrial DNA in the sperm cells ofPelargonium zonale during pollen development

Summary In the present study, we studied changes in organellar DNA in the sperm cells of maturing pollen ofPelargonium zonale, a plant typical to exhibit biparental inheritance, by fluorescence microscopy after staining with 4,6-diamidino-2-phenylindole (DAPI) and by immunogold electron microscopy using anti-DNA antibody. Fluorescence intensities of DAPI-stained plastid nuclei in generative and sperm cells at various developmental stages were quantified with a video-intensified microscope photon counting system (VIMPCS). Results indicated that the amount of DNA per plastid in generative cells increased gradually during pollen development and reached a maximum value (about 70 T per plastid; 1 T represents the amount of DNA in a particle of T4 phage) in young sperm cells at 5 days before flowering. However, the DNA content of plastids was subsequently reduced to about 20% of the maximum value on the day of flowering. Moreover, the DNA content of the plastid further decreased to 4% of the maximum value when pollen grains were cultured for 6 h in germination medium. In contrast, the amount of DNA per mitochondrion did not decrease significantly around the flowering day. Similar results were also obtained by immunogold electron microscopy using anti-DNA antibody. The density of gold particles on plastids decreased during pollen maturation whereas labelling density on mitochondria remained relatively constant. The number of plastids and mitochondria per generative cell or per pair of sperm cells did not change significantly, indicating that the segregation of DNA by plastid division was not responsible for the decrease in the amount of DNA per plastid. These results indicate that the plastid DNA is preferentially degraded, but the mitochondrial DNA is preserved, in the sperm cells ofP. zonale. While the plastid DNA of the sperm cells decreased before fertilization, it was also suggested that the low DNA contents that remain in the plastids of the sperm cells are enough to account for the biparental inheritance of plastids inP. zonale.Abbreviations DAPI 4,6-diamidino-2-phenylindole - VIMPCS video-intensified microscope photon counting system     

Some observations on coleoptile cell ultrastructure in ungerminated grains of rice (Oryza sativa L)

Summary The ultrastructure of coleoptile cells of ungerminated rice grains has been examined following fixation in glutaraldehyde and osmium tetroxide. In many respects the cell structure resembles that reported for other dormant seed tissues: the cells contain protein bodies and lipid droplets, mitochondria and plastids show little internal structure but cytoplasm invaginates into many plastids; golgi cisternae cannot be discerned. Rough ER is present as cisternae surrounding protein bodies, as occasional regions of parallel layers, and in concentric whorls where it alternates with smooth paired membranes of an unknown nature. The ribosomes on the ER are at least partly arranged into regular rows. Various crystalline, presumably proteinaceous, inclusions lie in the groundplasm, plastids and nuclei.     

Ultrastructure of the vegetative cell ofBrassica napus pollen with particular reference to microbodies

Summary The ultrastructure of the vegetative cell ofBrassica napus tricellular pollen grains, just before anthesis with standard chemical fixation, is reported. The vegetative cell may be regarded as a highly differentiated and metabolically active fat-storage cell. It contains many mitochondria with a well developed internal membrane system, starchless plastids, microbodies, lipid bodies, dictyosomes and numerous vesicles thought to originate from the dictysomes. Rough endoplasmic reticulum organized in stacks of cisternae is also spatially associated with certain organelles, mainly lipid bodies, microbodies and plastids. There are also randomly distributed polyribosome areas. The microbodies are mainly polymorphic in shape and are often observed in contact with lipid bodies. The above spatial relationship implies that the microbodies may have a glyoxysomal function. In the late period of vegetative cell maturation, the microbodies are probably involved in the process of glyconeogenesis in which the conversion of lipid reserves to sugar takes place.Abbreviations VC vegetative cell - VN vegetative nucleus - SC sperm cell - M mitochondria - MB microbodies - L lipid body - P plastid - D dictyosomes     

Ultrastructural Aspects of Sporogenesis in a Fern, Pteridium aquilinum (L.) Kuhn

The meiotic process of sporogenesis in Pteridium is accompaniedby a regular cycle of ultrastructural events. These includethe dedifferentiation and redifferentiation of organelles, andthe elimination and restoration of ribosomes. Although similarin nature to corresponding stages in other land plants, sporogenesisin Pteridium provides several unique features. During prophase the plastids pass through a stage during whichno envelope can be resolved at the periphery of the stroma.They appear to survive this period and there is no evidencethat plastid lineage is broken from primary archesporium tospore. The plastid cycle is accompanied by the presence of theiron-protein complex phytoferritin. The repopulation of the spore cytoplasm with ribosomes, followingthe prophase elimination, is achieved through the agency ofnucleoloid-like bodies. These bodies, however, are not synthesizedwithin the nucleus, but form within membrane-bound regions ofthe early prophase cytoplasm. Prophase is also characterized by the development of nuclearvacuoles, expansions of the perinuclear space, which progressivelyramify through the karyoplasm prior to the dissolution of thenuclear envelope at metaphase I. The significance of these events, their similarities with, anddifferences from, comparable stages of meiosis in other plantsare discussed. Pteridium aquilinum (L.) Kuhn, bracken, meiosis, sporogenesis     

Oogenesis in Acerentomon gallicum Jonescu (Protura)

Summary At the onset of previtellogenesis, the oocytes of Acerentomon gallicum begin to grow and increase their content of organelles. The nuage material in the oocytes at first increases in amount, then declines gradually to disappear completely from oocytes that have attained 50 m in diameter. During the growth period, new dictyosomes, mitochondria and ribosomes appear. Numerous vesicles become detached from the cell membrane and subsequently fuse into cisternae, thus forming extensive complexes of the rough endoplasmic reticulum. In oocytes with diameters between 50 and 100 m the Golgi complexes show a considerable increase in activity, and many lamellar bodies arise from mitochondria that have undergone specific transformation.This work was supported by Government Problem Grant II-1.3.13     

Morphogenetic plastid migration and microtubule organization during megasporogenesis inIsoetes

Summary The large megasporocytes ofIsoetes provide an exceptional system for studying microtubule dynamics in monoplastidic meiosis where plastid polarity assures coordination of plastid and nuclear division by the intimate association of MTOCs with plastids. Division and migration of the plastid in prophase establishes the tetrahedrally arranged cytoplasmic domains of the future spore tetrad and the four plastid-MTOCs serve as focal points of a unique quadripolar microtubule system (QMS). The QMS is a dynamic structure which functions in plastid deployment and contributes directly to development of both first and second division spindles. The nucleation of microtubules at discrete plastid-MTOCs is compared with centrosomal nucleation of microtubules in animal cells where growth of microtubules involves dynamic instability.Abbreviations AMS axial microtubule system - MTOC microtubule organizing center - N nucleus - QMS quadripolar microtubule system - P plastid - PPB preprophase band of microtubules     

Ultrastructure of endopolyploid antipodals inAconitum vulparia Rchb.

Summary The ultrastructure of the antipodals ofAconitum vulparia Rchb. was studied in mature embryo sacs. Antipodal cell wall thickness varies in different parts of the cells. The antipodals resemble transfer cells with distinctly marked wall ingrowths which are particularly well developed in the chalazal part and between the antipodals. A few plasmodesmata occur in the cell wall between the antipodals and the central cell. The cytoplasm is rich in ribosomes which occur free or bound to the membranes of the well developed endoplasmic reticulum. Only in the micropylar region of the cells are some larger vacuoles found. The antipodals contain numerous mitochondria, plastids and apparently active dictyosomes. Vesicles with electron dense contents, microbodies, multivesicular bodies as well as lipid droplets and small multiple concentric cisternae are also present in the cytoplasm. The giant endopolyploid nuclei have lobed outlines, especially at the chalazal side of the nuclei.Ultrastructural features, especially the occurrence of numerous free ribosomes and the development of extensive rough endoplasmic reticulum, suggest high metabolic activity in the growing and differentiating antipodals of this species.     

Evolution of the cytoplasmic organelles during female meiosis in Pisum sativum L.

In this paper we have traced the evolution of the cytoplasmic organelles in the female germinal cell of Pisum sativum L., from the beginning of meiosis to the early stages of the maturing megaspore, in order to correlate the morphological changes with the physiological aspects of megasporogenesis.A process of intense cytoplasmic vacuolation takes place in the megaspore mother cell (MMC) during prophase I, probably proceeding from the smooth endoplasmic reticulum and dictyosomes; it results in the formation of big vacuoles, which play a role in MMC polarization. By means of this polarization most plastids and mitochondria are incorporated into the functional megaspore at the end of meiosis.There are plastid and mitochondria cycles which consist of dedifferentiation followed by redifferentiation, During these cycles a transient morphology appears, called a cup-shaped form, which we interpret as an expression of low organelle activity.The wall of the MMC thickens throughout megasporogenesis and loses its plasmodesmata during middle prophase I. The ribosome population is reduced during prophase I and then restored during the early stages of the megaspore maturing process, as shown by the quantitative study that we have carried out. The nucleolar cytoplasmic bodies play a part in this restoring process. These bodies have a special morphology and appear to be originated from the activity of the nucleolar organizing region (NOR) during nucleolar disorganization in prophase I.We think that this cytoplasmic evolution is a response to nuclear genic recombination, in order to provide the most adequate expression of the zygote genome.Abbreviations EDTA ethylene-diamine-tetracetic acid - ER endoplasmic reticulum (SER: smooth ER) - MMC megaspore mother cell - NOR nucleolar organizing region - RNP ribonucleoproteins This work has been partially supported by the Comisión Asesora para la investigación Cientifica by Técnica Projects n^o 613/02 and 613/10     

Plastid DNA in the mitochondrial genome of Oenothera: Intra- and interorganellar rearrangements involving part of the plastid ribosomal cistron

Summary Part of the plastid rRNA cistron is present in the mitochondrial genome of Oenothera. This sequence of 2081 nucleotides contains the 3 half of the plastid 23 S rRNA, the adjacent intergenic region and the 4.5 S rRNA. Secondary intramitochondrial sequence rearrangements involve this region of plastid origin and the gene encoding the putative mitochondrial small ribosomal protein S13. Sequence comparison suggests that the interorganellar transfer event occurred a long time ago. The mitochondrial sequence contains regions more homologous to the plastid DNA from tobacco than from Oenothera itself in the regions analysed, suggesting faster sequence evolution in plastids than in mitochondria of Oenothera.     

Ultrastructural studies on plastids of generative and vegetative cells inLiliaceae 3. Plastid distribution during the pollen development inGasteria verrucosa (Mill.) Duval

Summary This paper describes the development of pollen grains ofGasteria verrucosa from the late microspore to the mature two-cellular pollen grain. Ultrastructural changes and the distribution of plastids as a result of the first pollen mitosis have been investigated using light and electron microscopy. The microspores as well as the generative and the vegetative cell contain mitochondria and other cytoplasmic organelles during all of the observed developmental stages. In contrast, the generative cell and the vegetative cell show a different plastid content. Plastids are randomly distributed within the microspores before pollen mitosis. During the prophase of the first pollen mitosis the plastids become clustered at the proximal pole of the microspore. The dividing nucleus of the microspore is located at the distal pole of the microspore. Therefore, the plastids are not equally distributed into both the generative and the vegetative cell. The possible reasons for the polarization of plastids within the microspore are briefly discussed. The lack of plastids in the generative cell causes a maternal inheritance of plastids inGasteria verrucosa.