Occurrence of Localized Intense Cation Uptake Sites in the Vascular Rings of Red Beet Storage Tissue 2

Development and decline of cation uptake capacity in discs takenfrom the vascular and parenchyma rings of storage tissue ofred table beet (Beta vulgaris L.) were observed during 12 dof ageing. Uptake capacity for Na⁺ and Rb⁺ showed a steady risereaching maximums by the fourth to fifth days of ageing. Thereafter,there was a steady decline in the uptake rates. Vascular ringtissues were able to develop a greater uptake capacity for bothNa⁺ and Rb⁺ than the tissues of parenchyma rings. This difference,which was more pronounced for Rb⁺ than for Na⁺ uptake, is attributedto a combination of variations in cell density and differencesin the acquisition and retention of the cation uptake capacity.Respiration of tissue discs showed no significant rise duringageing, nor were there significant differences in the respirationof vascular and parenchyma tissues. Vascular tissues containedsignificantly more betacyanin than parenchyma tissues; and theyretained their pigment, as well as their acquired cation uptakecapacity, for a longer period during the ageing process. Key words: Cation uptake, Red beet, Vascular rings, Ageing     

An Autoradiographic Study of Bacterial DNA in Lycopersicon esculentum

³H-DNA from Escherichia coli has been fed to cut shoots of Lycopersiconesculentum. Autoradiographic studies have shown the bacterialDNA to be localized in the nuclei, plastids, and mitochondriaof cells in the phloem, cambium, parenchyma, collenchyma, andepidermis. Two populations of cells were detectable, namely, those withnuclei in which the ³H-DNA was localized, and those which failedto incorporate ³H-DNA into their nuclei. This may, in part,be due to the degree of availability of the DNA in these tissues,cambium, parenchyma, and collenchyma.     

The division of pleomorphic plastids with multiple FtsZ rings in tobacco BY-2 cells

Plastids, an essential group of plant cellular organelles, proliferate by division to maintain continuity through cell lineages in plants. In recent years, it was revealed that the bacterial cell division protein FtsZ is encoded in the nuclear genome of plant cells, and plays a major role in the plastid division process forming a ring along the center of plastids. Although the best-characterized type of plastid division so far is the division with a single FtsZ ring at the plastid midpoint, it was recently reported that in some plant organs and tissues, plastids are pleomorphic and form multiple FtsZ rings. However, the pleomorphic plastid division mechanism, such as the formation of multiple FtsZ rings, the constriction of plastids and the behavior of plastid (pt) nucleoids, remains totally unclear. To elucidate these points, we used the cultured cell line, tobacco (Nicotiana tabacum L.) Bright Yellow-2, in which plastids are pleomorphic and show dynamic morphological changes during culture. As a result, it was revealed that as the plastid elongates from an ellipsoid shape to a string shape after medium renewal, FtsZ rings are multiplied almost orderly and perpendicularly to the long axis of plastids. Active DNA synthesis of pt nucleoids is induced by medium transfer, and the division and the distribution of pt nucleoids occur along with plastid elongation. Although it was thought that the plastid divides with simultaneous multiple constrictions at all the FtsZ ring sites, giving rise to many small plastids, we found that the plastids generally divide constricting at only one FtsZ ring site. Moreover, using electron microscopy, we revealed that plastid-dividing (PD) rings are observed only at the constriction site, and not at swollen regions. These results indicate that in the pleomorphic plastid division with multiple FtsZ rings, the formation of PD rings occurs at a limited FtsZ ring site for one division. Multiplied FtsZ rings seem to localize in advance at the expected sites of division, and the formation of a PD ring at each FtsZ ring site occurs in a certain order, not simultaneously. Based on these results, a novel model for the pleomorphic plastid division with multiple FtsZ rings is proposed.     

Structure and Organization of the Vascular System in the Rhizome of Drynarioid Ferns

Form and structure of the vascular cylinder of the rhizome of14 species belonging to six genera of drynarioid ferns are described.The study reveals that drynarioid ferns fall into two categories:the Drynaria group (Drynaria, Photinopteris), which is probablythe more primitive, exhibits the alternate two-ranked leaf arrangementand this could have led through suppression to the one-rankedcondition occurring in the Aglaomorpha group (Aglaomorpha, Drynariopsis,Pseudodrynaria, Merinthosorus, Thayeria). It seems that rhizomemorphology provides characters which help to separate differentspecies into the two distinct groups and indicates some phylogenetictrends. The most characteristic feature of the rhizome of drynarioidfern is seen in Thayeria, where some of the leaves on the dorsalsurface of the rhizome are dormant and some of them developon a prominent short, stout phyllopodium. Pteridophyta, Polypodiaceae, rhizome, vascular system, drynarioid ferns     

The assembly of the FtsZ ring at the mid-chloroplast division site depends on a balance between the activities of AtMinE1 and ARC11/AtMinD1

Chloroplast division comprises a sequence of events that facilitatesymmetric binary fission and that involve prokaryotic-like stromaldivision factors such as tubulin-like GTPase FtsZ and the divisionsite regulator MinD. In Arabidopsis, a nuclear-encoded prokaryoticMinE homolog, AtMinE1, has been characterized in terms of itseffects on a dividing or terminal chloroplast state in a limitedseries of leaf tissues. However, the relationship between AtMinE1expression and chloroplast phenotype remains to be fully elucidated.Here, we demonstrate that a T-DNA insertion mutation in AtMinE1results in a severe inhibition of chloroplast division, producingmotile dots and short filaments of FtsZ. In AtMinE1 sense (overexpressor)plants, dividing chloroplasts possess either single or multipleFtsZ rings located at random intervals and showing constrictiondepth, mainly along the chloroplast polarity axis. The AtMinE1sense plants displayed equivalent chloroplast phenotypes toarc11, a loss-of-function mutant of AtMinD1 which forms replicatingmini-chloroplasts. Furthermore, a certain population of FtsZrings formed within developing chloroplasts failed to initiateor progress the membrane constriction of chloroplasts and consequentiallyto complete chloroplast fission in both AtMinE1 sense and arc11/atminD1plants. Our present data thus demonstrate that the chloroplastdivision site placement involves a balance between the opposingactivities of AtMinE1 and AtMinD1, which acts to prevent FtsZring formation anywhere outside of the mid-chloroplast. In addition,the imbalance caused by an AtMinE1 dominance causes multiple,non-synchronous division events at the single chloroplast level,as well as division arrest, which becomes apparent as the chloroplastsmature, in spite of the presence of FtsZ rings.     

COMPARATIVE LEAF STRUCTURE OF SEVERAL SPECIES OF HOMOSPOROUS LEPTOSPORANGIATE FERNS

The structure of the mature leaves of 13 species from 9 families of homosporous leptosporangiate ferns was examined by light and electron microscopy. In 11 species (Adiantum pedatum L., Athyrium angustum Roth., Cyathea dregei Sm., Lygodium palmatum Sw., Mohria caffrorum (L.) Desv., Oleandra distenta Kuntae, Pellaea calomelanos (Sw.) Link, Pityrogramma calomelanos (L.) Link var. austro-americana (Domn.) Farw., Trichomanes melanotrichum Schlechtend., Vittaria guineensis Desv., and Woodwardia orientalis Sw.) the lamina veins are collateral; in two (Phlebodium aureum and Platycerium bifurcatum), bicollateral as well as collateral veins are present. The vascular bundles in the midribs of C. dregei and those in the petioles and midribs of Phlebodium and Platycerium are concentric. All of the vascular bundles in the homosporous leptosporangiate ferns studied are delimited by a tightly arranged cylinder of endodermal cells with Casparian strips. Within the veins without parenchymatic xylem sheaths, some sieve elements commonly abut tracheary elements with hydrolyzed primary walls. The majority of vascular parenchyma cells contact both sieve elements and tracheary elements, although some parenchyma cells are associated with only one type of conducting cell. Transfer cells (parenchyma cells with wall ingrowths) occur in the veins of 6 species examined. Most of the vascular parenchyma cells, however, have no distinctive structural characteristics. The sieve elements of the homosporous leptosporangiate ferns are very similar structurally and each consists of a plasmalemma, a parietal, anastomosing network of smooth endoplasmic reticulum (ER), and variable numbers of refractive spherules, plastids and mitochondria. The sieve elements of L. palmatum also contain plasmalemma tubules. The parenchymatic cells of the leaf (mesophyll, endodermal and vascular parenchyma cells) are united by desmotubule-containing plasmodesmata. The sieve elements are connected to each other by sieve pores and to parenchymatic cells by pore-plasmodesma connections. The sieve-area pores contain variable amounts of membranous material, apparently ER membranes, but do not occlude them. These membranes commonly are found in continuity with the parietal ER of the lumen. Based upon the relative frequencies of cytoplasmic connections between cell types, the photosynthates may move from the mesophyll to the site of phloem loading via somewhat different pathways in different species of homosporous leptosporangiate ferns.     

Plastid Tubules in the Sporogenous Lineage of the Moss Timmiella barbuloides (Bryophyta): An Ultrastructural Study

Tubular inclusions are ubiquitous in the sporogenous plastidsof the moss Timmiella barbuloides (Brid.) Moenk. They have anouter diameter of 26–40 nm and a central lumen of 10–15nm, and occur either singly or in groups of up to 15 parallelelements in the peripheral stroma. The tubules are associatedwith the central isthmus in dividing plastids but lie closeto the extremities during the growth phase. These positionalchanges suggest roles in plastid division, growth and the maintenanceof shape. Bryophytes, mosses, Timmiella barbuloides, sporogenous cell lineage, plastid tubules, ultrastructure     

Intercalary Growth in the Aerial Shoot of Eleocharis acuta R. Br. Prodr.: I. Structure of the Growing Zone

The numbers and distribution of cell division and the cell lengthshave been determined for the various tissues in the intercalarymeristem of Eleocharis acuta R. Br. Prodr. Cell divisions aremost numerous in the chlorenchyma tissue and fewest in the plateparenchyma. In all tissues examined except the plate parenchyma,cell length is inversely correlated with numbers of cell divisions.The cell divisions which occur in the vascular tissue in theintercalary meristem are regarded as being a part of the intercalarygrowth and not as a normal development of a procambium. Maturexylem and phloem are seen to be present in the larger vascularbundles right through the meristematic zone, and the xylem trachiedsare shown to be conductive. The transverse strands connectingadjacent vascular bundles are considered to be important inthe conduction of water.     

In vivo Observations of Plastid and Cell Division in Raphid Diatoms and Their Relevance to Diatom Systematics

Premitotic rearrangements of the protoplast, cytokinesis andpostmitotic rearrangements were followed in vivo in Naviculapupula Küitz. and N. bacillum Ehrenb. The plastids andnuclcus perform translational movements before cytokinesis,taking up well-defined positions on opposite sides of the cell.Following this the plastid divides by constriction and the cellcleaves in two. Cytokinesis takes 5–8 min and is effectedby a contractile ring. This is circular, except where constrainedby the cell wall. Parts of the ring appear to be functionalbefore cleavage begins. The two volutin granules persist duringcell division and are segregated one to each daughter cell.The granules are associated with the tonoplast and contractilering until late in cleavage, when they are released into thevacuoles. After value formation, the plastid, which has beenchanging in shape since before mitosis, rotates through 90°.A new volutin granule is formed in each daughter cell. The segregationof the granules, the tilt of the dividing nucleus and the rotationof the plaslid are chiral. The positions and shapes taken bythe organelles during the cell cycle suggest the presence ofintracellular recognition and attachment sites, which existfor specific periods. The taxonomic value of cell cycle eventsis discussed. Navicula, cell cycle, cell division, diatom systematics, plastid division, plastid rotation, volutin granules     

Gland Cells in Resin Canal Epithelia in Guayule (Parthenium argentatum) in Relation to Resin and Rubber Production

Schizogenous resin canals develop in the pith and cortex ofthe primary stem tissue in guayule (Parthenium argentatum Gray).In secondary tissue concentric rings of resin canals are producedfrom derivatives of the vascular cambium. Both resin and rubberaccumulate in the epithelial cells of the canals. These havethe characteristics of gland cells. Resin is secreted into thecanals and rubber accumulates in the surrounding parenchymacells as well as the gland cells, especially in winter. Younggland cells contain modified plastids and smooth tubular endoplasmicreticulum. These organelles probably accommodate the compartmentalizedsteps of the isoprenoid biosynthetic pathway leading to theproduction of isopentenyl pyrophosphate. As these ultrastructuralcharacteristics only exist in young gland cells of the currentseason's growth they seem to be the sole source of the precursorsfor both resin and rubber formation. Parthenium argentatum, guayule, resin canals, gland cells, plastids, smooth endoplasmic reticulum, rubber, resin, epithelial cells, ultrastructure     

Oogenesis in the Apogamous Fern Pteris cretica

The events that characterize egg formation and maturation inPteris cretica were investigated using transmission electronmicroscopy and electron microscope microprobe analysis. Theydid not differ significantly from those described for sexuallyreproducing ferns. The significance of these findings is discussedin relation to current theories concerning phase change in ferns. Pteris cretica, fern, apogamy, agamospory, transmission electron microscopy, oogenesis     

The distribution of protochlorophyllide and chlorophyll within seedlings of the lip1 mutant of Pea

The distribution of protochlorophyllide (Pchlide) and NADPH-Pchlideoxidoreductase (POR) was characterized in the epicotyls androots of wild-type pea (Pisum sativum L. cv. Alaska) and lip1,a mutant with light-independent photomorphogenesis caused bya mutation in the COP1 locus. The upper part of the dark-grownlip1 mutant epicotyls had a high Pchlide content that decreaseddownward the organ. The elevated Pchlide level in lip1 seedlingswas a result of the differentiation of more proplastids intoPchlide-containing plastids. The cortex cells in the lip1 epicotylwere filled with such plastids in contrast to the cortex cellsof wild-type seedlings. The mutant also developed Pchlide-containingplastids in the roots, indicating the suppressing effect ofthe COP1 locus on development of plastids in the correspondingtissues in dark-grown wild-type plants. The distribution ofPchlide-containing plastids in dark-grown lip1 mutant stem androot was similar to the distribution of chloroplasts in irradiatedwild-type plants. Both wild-type and lip1 epicotyls containedmostly short wavelength Pchlide fluorescing at 631 nm withonly a small shoulder at 654 nm, which was transformedto a minute amount of chlorophyllide (Chlide) by flash irradiation.In contrast, with continuous irradiation a considerable amountof Chlide was formed especially in the lip1 epicotyls. Immunoblotsindicated the presence of POR, as a 36 kDa band, in epicotylsof both dark-grown wild-type and lip1 mutant seedlings. However,lip1 stem tissue had a higher content of POR than the wild-typepea. The high content of POR was unexpected as lip1 lacked boththe 654 nm fluorescing Pchlide form and the regular PLBs.In light, a significant amount of chlorophyll was formed alsoin the roots of the lip1 seedlings. ³ Corresponding author: E-mail, mahdi.seyedi@molbio.gu.se; Fax,+46-31-773-2626.     

Root Gravitropism in a Cultivar of Zea mays Whose Columella Cells Contain Starch-deficient Amyloplasts

Starch occupies 4.2 per cent of the volume of plastids in calyptrogencells in primary roots of Zea mays L. cv. vp-7 wild type. Plastidsin calyptrogen cells are distributed randomly around large,centrally located nuclei. The differentiation of calyptrogencells into columella cells is characterized by cellular enlargementand the sedimentation of plastids to the bottom of the cells.Although sedimented plastids in columella cells do not containsignificantly more starch than those in calyptrogen cells, primaryroots are graviresponsive. The onset of root gravicurvatureis not associated with a significant change in the distributionof plastids in columella cells. These results indicate thatin this cultivar of Z. mays (1) the sedimentation of plastidsin columella cells is not based upon their increased densityresulting from increased starch content alone, (2) starch-ladenamyloplasts need not be present in columella cells for rootsto be graviresponsive, and (3) the onset of root gravicurvaturedoes not require a major redistribution of plastids in columellacells. Columella cell, gravitropism (root), plastids, root cap, Zea mays     

Structure and Histochemistry of Stomata and Epidermal Cells in Five Species of Polypodiaceae

The epidermal structure of the five species of ferns, Arthromeriswallichiana (Spr.) Ching., Drymoglossum piloselloides (Prest.),Drynaria quercifolia (L.) J. Smith, Lepisorus nudus (Hook.)Ching. and Pyrrosia nuda (Gies.) Ching., has been investigated.Fifteen types of stomatal structures have been identified ofwhich copolo-desmocytic and coperi-desmocytic are new types.Four more possible stomatal structures: ccpolo-peri-, codesmo-polo-,codesmo-peri- and duplodesmocytic, are suggested. Localizationof starch, insoluble polysaccharides, protein and lipids hasbeen examined histochemically in the guard cells, subsidiarycells and epidermal cells. In Drynaria starch plastids and plastidscontaining both starch and protein are present in guard cells.Starch plastids are present in the subsidiary cells of all speciesexcept in Arthromeris, whereas, they are present in epidermalcells of only Drymoglossum and Lepisorus. Granular or amorphousinsoluble polysaccharides (other than starch) are present inguard cells of all the species, in the subsidiary cells of Arthromeris,Drynaria and Pyrrosia, and in the epidermal cells of Pyrrosia.Except in Pyrrosia lipids are present in the guard cells. Subsidiarycells of Drynaria and the epidermal cells of Arthromeris andDrynaria show lipid bodies. The presence of plasmodesmata andectodesmata is demonstrated in the epidermal cells of Drymoglossum.     

Localization of Thermo-Osmotically Active Partitions in Young Leaves of Nuphar lutea

The submerged roots and rhizomes of the aquatic vascular macrophyteNuphar lutea (L.) Sm. are aerated, at least in part, by pressurizedventilation. Depending on temperature differences of up to 5K between the inside of young, just-emerged leaves and the surroundingair, pressure differences of 79 to 100 Pa higher than atmosphericare detectable inside the lacunuous spongy parenchyma of theleaf blades. The pressurization is a consequence of structuralfeatures of leaf tissues separating the air filled spaces ofthe spongy parenchyma from the atmosphere. These tissues areacting as thermo-osmotic partitions. Whereas the dimensionsof the stomatal openings (about 5·6 x 2·4 µm)and of the intercellular spaces of the palisade parenchyma (diametersabout 15 µm) are too large, those of the monolayers ofcells separating the palisade and the spongy parenchyma (diameters:0·7–1·2 µm) are small enough to impedefree gaseous diffusion. This inner non-homogeneous partitioninggives rise to the so-called Knudsen diffusion, a physical phenomenonleading to pressurization of the warmer air inside the spongyparenchyma. The rising pressure difference is strong enoughto establish an air flow through the aerenchyma of the wholeplant and out of the most porous older leaves in which a temperatureinduced pressurization is never detectable. These thermo-osmoticallyactive leaves enhance the influx of air to the rhizome and thediffusion path for oxygen to the roots is shortened to the distancebetween rhizome and root tips. Therefore, pressurized ventilationin Nuphar is seen to be of considerable ecological importancefor plant life in anaerobic environments. Key words: Aeration, leaf anatomy, thermo-osmosis of gases, Nuphar lutea     

Composition and fine structure of minor veins inTetragonia leaf

Summary Mesophyll containing the minor veins from leaves ofTetragonia expansa Murr. was examined in preparation for a study of effects of beet yellows virus on the leaf tissues of this plant. The sieve elements throughout the minor veins exhibit the characteristics commonly found in this type of cell in dicotyledons. The cells are connected with one another by sieve plates and with contiguous parenchyma cells by branched plasmodesmata. Mature sieve elements are enucleate and lack ribosomes. No tonoplast was discerned in these cells. Mitochondria, plastids, and sparse endoplasmic reticulum are retained in mature cells. The plastids, which contain a massive fibrous ring of proteinaceous material, resemble the sieve element plastids ofBeta. The P-protein in the sieve elements is occasionally composed of tubules; more commonly it is represented by loose helices. The tracheary elements have scalariform secondary thickenings. In regions free of these thickenings, the primary wall largely disintegrates; only some loosely arranged fibrils remain. The mesophyll and vascular parenchyma cells contain the various organelles characteristic of living plant cells but vary in degree of vacuolation and in density of cytoplasm. Some vascular parenchyma cells have particularly dense protoplasts. They contain numerous ribosomes and their background matrix consists of a dense population of fine fibrils. Occasional vascular parenchyma cells contain the tubular spiny cell component first recognized inBeta. This work was supported in part by National Science Foundation grant GB-5506.     

Observations on Companion Cells and Specialized Phloem Parenchyma Cells of Nelumbo nucifera Gaertn

The phloem of very young petioles of Nelumbo nucifera Gaertn.(Nelumbium speciosum Willd.) was studied with the light microscope.The elongated, mature sieve elements contain slime, plugs, strands,and numerous plastids. Some sieve elements remain nucleatedfor a brief period even after the sieve plates are well developed.The companion cells numbering 8–14 undergo disintegrationbefore the elongation of the ontogenetically related sieve elementis completed. They are uninucleate to begin with but later becomebinucleate and finally degenerate and obliterate. The variousstages in their ontogeny and disintegration are described. Ofthe very few specialized phloem parenchyma cells present, someare associated with sieve elements. They have slime body-likestructures, and plastid-like bodies which group together andeventually disintegrate.     

DEVELOPMENTAL ANATOMY AND HISTOCHEMISTRY OF LIGHT-INDUCED CALLUS FORMATION BY DIÖON EDULE (ZAMIACEAE) SEEDLING ROOTS IN VITRO

Light exposure caused massive areas of callus to develop from primary roots of aseptically cultured Diöon edule seedlings. Callus initiation and continued growth was due to cortical cell hypertrophy and subsequent periclinal cell division. Callus initiation occurred in the subdermal cortex and developed radially and centripetally from the locus of initiation. Callus formation encompassed virtually all of the cortex, but did not incorporate any of the vascular tissues. With very large calluses, sectors of internal periderm arose between the developing callus and the remaining quiescent cells of the inner cortex. Most of the callus cells were typical, vacuolate parenchyma with cellulose walls, and large, multilobed amyloplasts. Callus also contained idioblasts with globular deposits of polyphenols. Adjacent cortical cells were typical parenchyma with peripheral cytoplasm, but contained small plastids with little starch accumulation.     

Ultrastructural Aspects of the Nectary Spur of Limodorum abortivum (L) Sw. (Orchidaceae)

The ultrastructure of the nectary spur of Limodorum abortivum(L) Sw. was examined before and after anthesis. In cross sectionthe nectary spur shows an internal epidermal layer of thin-walledcells bordering the secretory cavity and 10–12 layersof parenchyma cells. The ultrastructure of the secretory cellssuggests the involvement of ER, Golgi and plastids in nectarsecretion. The nectar accumulated in the sub-cuticular spaceis released into the nectariferous cavity by rupture of theouter layer of the cuticle. Limodorum abortivum (L) Sw., Orchidaceae, nectary spur, nectar secretion, ultrastructure, anthesis, endoplasmic reticulum, dictyosomes, plastids     

Dynamic morphologies of pollen plastids visualised by vegetative-specific FtsZ1–GFP in Arabidopsis thaliana

The behaviour and multiplication of pollen plastids have remained elusive despite their crucial involvement in cytoplasmic inheritance. Here, we present live images of plastids in pollen grains and growing tubes from transgenic Arabidopsis thaliana lines expressing stroma-localised FtsZ1–green-fluorescent protein fusion in a vegetative cell-specific manner. Vegetative cells in mature pollen contained a morphologically heterogeneous population of round to ellipsoidal plastids, whilst those in late-developing (maturing) pollen included plastids that could have one or two constriction sites. Furthermore, plastids in pollen tubes exhibited remarkable tubulation, stromule (stroma-filled tubule) extension, and back-and-forth movement along the direction of tube growth. Plastid division, which involves the FtsZ1 ring, was rarely observed in mature pollen grains.