The Anatomy of Contractile Roots in Eucomis L'H?rit

The anatomical changes in the different tissues during rootcontraction were studied in two species of Eucomis (Liliaceae).It is evident that the shortening of the root is brought aboutby radial and tangential broadening and longitudinal shorteningof the perivascular cortical cells. This tissue is hence calledcontractile parenchyma. As a result of this contraction thecell walls of the exodermis, endodermis, pericycle, phloem andpith become buckled longitudinally while the annular and spiralthickenings of the xylem are pressed together.     

Root Cell Ultrastructure in Developing Aerenchyma Tissue of Three Wetland Species

Patterns of root cortex cell development and ultrastructurewere analysed in Sagittaria lancifolia L., Thalia geniculataL. and Pontederia cordata L. using scanning and transmissionelectron microscopy (SEM, TEM). In all three species, cortexcells were arranged in radial columns extending from the endodermisto the hypodermis/epidermis. During gas space formation, thecortex cells elongated parallel to the root radius and shrankin the plane perpendicular to the radius leaving long and thinrows of cortex cells extending from the endodermis to the epidermis.Although the cortex cells appeared collapsed in tissue withwell-developed gas spaces, TEM revealed that the cortical cellsas well as the epidermal cells maintained intact membranes andmany normal organelles. Formation of root cortex tissue withwell-developed gas spaces does not require cell death in thesespecies. Living cortex cells in root tissue with mature gasspaces could provide a symplastic pathway for transport betweenthe root stele and the living epidermal cells. Copyright 2000Annals of Botany Company Sagittaria lancifolia, Thalia geniculata, Pontederia cordata, aerenchyma, root, wetland, development     

Root Contraction in Hyacinthus orientalis

Root contraction is effected in many species by redirected growthof parenchyma cells, supplemented in some cases by other processes.In Hyacinthus, root contraction is associated with the growthof inner cortical cells, which after becoming fully elongatedin the normal growth of the root, then expand radially and contractlongitudinally. The contraction is, however, a growth process,since it occurs in turgid tissue and is partly reversible byplasmolysis. Moreover, the radial walls of the cells concernedincrease in area and the cells increase in volume. The changes in cell shape associated with contraction involvechanges in cell-wall structure which, in so far as they aredetectable by polarization microscopy, are described and discussedin the light of current views on cell-wall growth.     

ROOT CONTRACTION IN FREESIA (IRIDACEAE)

The contractile roots of the horticultural variety Freesia hybrida Bailey (Iridaceae) were determined to contract via a growth/collapse mechanism. Contraction is initiated by a radial growth of middle and outer cortical parenchyma cells which is morphologically evident by an expanded diameter of the root. No concomitant decrease in length of the actively growing cells was observed. Shortening of the root is caused by axial tension produced by the radial growth of cells contiguous with nonexpanded cells distally. Centripetal collapse of expanded cells, coupled with passive shortening of inner cortical parenchyma and stelar tissues, releases axial tension slowly, returning the shortened root to equilibrium. Inner cortical parenchyma cells shorten in an accordion-like manner facilitated by partial dissolution of middle lamellar material.     

Effects of K$(86Rb) Transport and the Net H$ Efflux on Electrical Properties along Bean (Phaseolus mungo) Roots

The three-phase electric potential distribution along two-day-oldintact Phaseolus roots was investigated in relation to cellgrowth and K^$ and H^$ transports using tracer K^$(⁸⁶Rb) and pHexperiments. The activity of a radial electrogenic componentlocated between the cortical cells and the external solutionwas high in the elongating region and in the completely maturedregion. The activity of another radial electrogenic componentlocated between the cortical cells and the stele was maximalin the elongating region. Both potassium uptake from the externalsolution into the cortical cells and H^$ excretion took placemainly in these regions. (Received November 9, 1983; Accepted June 21, 1984)     

Thigmomorphogenesis: Changes in Cell Division and Elongation in the Internodes of Mechanically-perturbed or Ethrel-treated Bean Plants

Examination of first internodes of young Phaseolus vulgarisL. plants which have been subjected to mechanical perturbationshows decreased elongation and increased radial growth. Thedecreased elongation can be attributed to both reduced cellelongation of epidermal and cortical cells and a reduced numberof cells in the vascular and pith tissues. The increased radialenlargement is due to increased cortical cell expansion andincreased secondary xylem production resulting from increasedcambial activity. All of these responses are observable withina few hours of a single mechanical perturbation. Treatment ofplants with ethrel mimics all of these effects of mechanicalperturbation. Phaseolus vulgarisL, Kidney bean, thigmomorphogenesis, mechanical perturbation, ethrel, (2-chloroethyl phosphonic acid), cell division, internode elongation     

Some Observations on Infection of Arachis hypogaea L. by Rhizobium

The infection process in Arachis hypogaea by rhizobia differsfrom that normally found in Trifolium spp. in that no infectionthreads are formed. The root hairs, which are long (up to 4mm), septate, and often with large basal cells, occur only atthe sites of emerging lateral roots. Infection occurs only wherethe root hairs have large basal cells. Rhizobia cause curlingand deformation of the root hairs (as in Trifolium spp.) butenter the root at the junction of the root hair and the epidermaland cortical cells. The bacteria are distributed intercellularlyvia the middle lamellae and enter the cortical cells throughthe structurally altered cell wall, often close to the hostcell nucleus. The root hairs and large basal cells become infectedin the same way. Within the cortical cells of the emerging lateralroot the rhizobia multiply rapidly and the invaded cells dividerepeatedly to form the nodule tissue. Bacteriod formation occursonly when the host cell ceases to divide.     

Variation in the Structure and Response to Flooding of Root Aerenchyma in some Wetland Plants

The structure and response to flooding of root cortical aerenchyma(air space tissue) in a variety of wetland (flood-tolerant)species was investigated and compared with some flood-intolerantspecies. In some species aerenchyma consisted of enlarged schizogenousintercellular spaces and in others aerenchyma formation involvedlysigeny. Two types of lysigenous aerenchyma were distinguished.In the first the diaphragms between lacunae were arranged radiallyand consisted of both collapsed and intact cells. In the secondtype, which was confined to the Cyperaceae, the radial diaphragmscontained intact cells, and stretched between them were tangentially-arrangeddiaphragms of collapsed cells. Flooding in sand culture generally increased root porosity (airspace content) although there were exceptions. The flood-intolerantspecies Senecio jacobaea produced aerenchyma but did not survivelong-term flooding. Among the flood-tolerant species, Filipendulaulmaria did not produce extensive aerenchyma even when flooded.Eriophorum angustifolium and E. vaginatum produced extensiveaerenchyma under drained conditions which was not increasedby flooding. In Nardus stricta root porosity was increased bylow nutrient levels as well as by flooding. Aerenchyma, root cortex, wetland plants, waterlogging, flooding-tolerance, Ammophila arenaria, Brachypodium sylvalicum, Caltha palustris, Carex curia, Eriophorum vaginatum, Filipendula ulmaria, Glyceria maxima, Hieracium pilosella, Juncus effusus, Myosotis scorpioides, Nardus stricta, Narthecium ossifragum, Phalaris arundinacea, Senecio jacobaea, Trichophorum cespitosum     

Amitosis and Endocytogenesis in the Fruit of Malus sylvestris

Cyto-histological investigations on the initiation and developmentof a non-pathogenic physiological ‘cork spot’ necrosisin the outer cortex of the fruit of Malus sylvestris Mill. ‘YorkImperial’ revealed two distinct aberrancies, namely, amitoticnuclear division and intracellular or endogenous proliferationswithout hyperplasia per se The incipient necrotic conditionbecomes evident internally about 3 weeks after fruit set asminute isolated, discoloured, amorphous spots of disorganizedruptured cells within otherwise healthy cortical tissue Thedisorganization continues slowly with adjoining cells becomingsimilarly necrotic After the lysis of the initial cork spotcells, about 1 month later, sporadic cellular changes occurin various healthy vacuolated cortical cells contiguous to andencompassing the necrotic tissues. The nuclei increase in sizeand volume as they assume distinctive positions in preparationfor amitotic nuclear divisions. The enlarged nucleus or macronucleus,containing one or several nucleoli, divides by a distinct cleavagedeveloping from a constriction perpendicular to its longitudinalaxis The division results in the amitotic formation of two daughtermicronuclei that usually become separated by the formation ofa cell wall. No evidence of cell plate formation was observedand the method of cell wall formation could not be determined.Repeated amitotic divisions of the micronuclei result in anintracellular or endocytogenetic proliferation of parenchymatouscells that are invariably confined within the original mothercell until its wall ruptures The endogenous proliferations arereleased into lacunae or intercellular spaces, eventually becomedisorganized, and disintegrate, with the accumulated residualincrements resulting in an overall ‘cork spot’ appearance. Malus sylvestris Mill., apple, amitosis, endocytogenesis, multinucleate cells, macronuclei, micronuclei     

Locomotion of Fundulus Deep Cells during Gastrulation

SYNOPSIS. Mechanism of locomotion of deep cells of Fundulusheteroclitus was studied in vivo during gastrulation with theaid of time lapse cinemicrography (Nomarski differential interferencecontrast optics), scanning electron microscopy of cells knownto be moving at the time of fixation, and cell culture. Theseare our findings. 1) Deep cells usually move rapidly, at about10–15 µ/min, regardless of whether they move byblebbing or spreading. Evidence suggests that this high speedis associated with weak adhesion of the trailing edge: it remainsrounded, without large retraction fibers, and it advances continuouslywith advance of the leading edge, not sporadically, as it wouldif it adhered strongly. 2) In contrast, when stationary cellsin close contact separate, they remain connected by retractionfibers, suggesting strong punctate adhesions. 3) Locomotionby shortening of a long lobopodium is really a form of spreadingmovement; the tip of a lobopodium always spreads. Also, sincespeed of shortening decreases with continuance, it may dependprimarily on elastic recoil rather than active contraction.4) Fundulus deep cells appear to move in two ways: a) protrusionof blebs, followed by much cytoplasmic flow; b) protrusion oflamellipodia, accompanied by filopodia and frequent cell shortening.5) Filopodia were not found except at the leading edge of aspreading lamellipodium and often spread themselves; perhapsfilopodia and lamellipodia are interconvertible. 6) A lamellipodialmargin may form undulations in vivo that move backward likeruffles in vitro. 7) At all times, whether stationary or moving,the surface of deep cells is smooth, raising unanswered questionsconcerning the source of surface for their rapid protrusiveactivity.     

Arrangement of Cortical Microtubules in Avena Coleoptiles and Mesocotyls and Pisum Epicotyls

Cortical microtubules (MTs) in coleoptiles and mesocotyls ofAvena sativa and epicotyls of Pisum sativum were examined byimmunofluorescence. In elongating Avena coleoptiles whose elongationis less localized, the orientations of cortical MTs of parenchymaand adaxial epidermal cells, and abaxial epidermal cells aretransverse, and oblique or longitudinal, respectively, and doesnot differ between the upper, middle and lower parts. The transverseMTs in parenchyma and adaxial epidermal cells turns to obliqueor longitudinal ones after elongation stops. The obliquity ofMTs in abaxial epidermal cells also tends to become steeperas elongation comes to a stop. In Avena mesocotyls and Pisumepicotyls whose elongation is localized, the orientation ofcortical MTs of cortical cells in the elongating region is relativelytransverse. The epidermis has intermingling cells of transverseor oblique MTs. In the non-elongating region, MT orientationbecomes steeper both in the cortex and epidermis. The present results indicate that whatever the degree of localizationof the elongation, the obliquity of MTs in these organs is steeperin epidermal than in inner tissue cells and becomes steeperas elongation stops in both tissues. (Received October 26, 1987; Accepted April 19, 1988)     

The Endophytic System of Arceuthobium minutissimum, the Indian Dwarf Mistletoe

The Indian dwarf mistletoe, Arceuthobium minutissimum Hook f.is the most diminutive dicotyledonous stem parasite on Pinusexcelsa. The endophytic system is well developed, having a largenumber of anastomosing strands in the cortex and sinkers penetratingthe medullary rays in wood. The cortical strand is protostelicwith the central tracheary elements, the vessels, surroundedby paren-chymatous cells. An earlier report of absence of vesselsseems to be erroneous. The growth of the cortical strands iseffected by an apical cell. The sinkers typically associatedwith the rays of host, are composed of parenchymatous cellsand tracheary elements including vessels. They make contactswith the cells of the ray through pits present in the trachearyelements. The sinkers cause hypertrophy and even fusion of twoor more rays to form a composite medullary ray. The tracheidsof the host tissue also become stunted and contorted in shape.These observations are in agreement with those of other investigatorson American host species for Arceuthobium.     

Dynamic Organization of Microtubules in Guard Cells of Viciafaba L. with Diurnal Cycle

Stomatal movement is regulated by changes in the volume of guardcells, thought to be mainly controlled by an osmo-regulatorysystem. In the present study, we examined the additional involvementof cytoskeletal events in the regulation of stomatal movement.Microtubules (MTs) in guard cells of Viciafaba L., grown undersunlight, were observed during the day and night by immunofluorescencemicroscopy. Cortical MTs began to be organized in a radial arrayat dawn and increased in numbers in the morning following theincrease in the stomatal aperture size. Thereafter, MTs becamelocalized near the nucleus and began to be destroyed from theevening to midnight, following the decrease in stomatal aperturesize. These diurnal changes in MT organization were observedeven two days after transfer from natural light condition tototal darkness, and were accompanied by corresponding changesin stomatal aperture. The increase in stomatal aperture sizein the early morning was inhibited by 50 µM propyzaraide,which destroys cortical MTs in guard cells, whereas the decreasein aperture size in the evening was suppressed by 10 µMtax-ol, which stabilizes cortical MTs. These results suggestthat radially-organized cortical MTs of guard cells may controldiurnal stomatal movement. (Received September 3, 1997; Accepted November 5, 1997)     

Induction of a 'Periderm-like' Tissue in Excised Roots of the Fern Ophioglossum petiolatum Hook

Basal applications of plant growth regulators to excised rootsof Ophioglossum induce modifications in the outer cortical cells.Benzyladenine initiates periclinal divisions in these outercells producing a ‘periderm-like’ tissue while 2,4-Dcauses cell enlargement only. Walls of the outer cells of the‘periderm-like’ tissue are resistant to sulphuricacid and stain with Sudan IV and presumably are suberized.     

The Orientation and Localization of Cortical Microtubules in Differentiating Conifer Tracheids during Cell Expansion

Arrays of cortical microtubules (MTs) on radial walls in differentiatingtracheids of Taxus cuspidata were randomly oriented when primarywalls formed. The orientation of MTs changed progressively fromlongitudinal to transverse as cells expanded. During formationof primary walls, MTs in differentiating tracheids disappearedlocally at sites of future intertracheal bordered pits. In furtherdifferentiated tracheids, circular bands of MTs were observedaround the edges of developing bordered pits. (Received July 17, 1996; Accepted November 11, 1996)     

Changes in the Arrangement of Microtubules and Microfibrils in Differentiating Conifer Tracheids During the Expansion of Cells

The arrangements of microtubules and the cellulose microfibrilsof radial walls in tracheids of Abies sachalinensis Mastersduring the expansion of cells were examined by immunofluorescenceand field-emission scanning electron microscopy. The radialdiameter of tracheids increased to three to four times thatof cambial initial cells. Microfibrils on the innermost surfaceof primary walls of conifer tracheids at early stages were notwell ordered and most of the microfibrils were oriented longitudinally.As each cell expanded, microfibrils in the process of depositionwere still not well ordered but their orientation changed fromlongitudinal to transverse. When cell expansion ceased, microfibrilswere well ordered and oriented transversely. Cortical microtubulesshowed a change in orientation similar to that of the microfibrils.These results indicate that the orientation of cortical microtubulesis correlated with that of microfibrils as they are being laiddown and with cell morphogenesis in conifer tracheids.Copyright1995, 1999 Academic Press Microfibril, microtubule, tracheid, cell expansion, Abies sachalinensis Masters, field-emission scanning electron microscopy, immunofluorescence microscopy     

Influence of intercellular tissue connections on airway muscle mechanics

Contraction ofsmooth muscle in visceral organs is modified by structures external tothe muscle. Within muscle tissue itself, connective tissue plays animportant role in force transference among the contractile cells.Connections arranged radially can affect contractile mechanics bylimiting tissue expansion at short lengths. Previous work suggests thatincreased stiffness at extreme shortening is due to such radialconstraints. Two approaches to further study of these effects arereported. To increase radial constraints, very thin Silastic bands wereplaced loosely about strips of canine trachealis muscle at rest length.The strips were allowed to shorten under light afterloads, expandinguntil restrained by the bands. Subsequent removal of the bands allowed increased shortening, with less increase in stiffness at short lengths.Related isometric effects were observed. To reduce constraints, musclestrips were partially digested with collagenase. Compared with controlconditions, this treatment permitted further shortening, with lessincrease in stiffness at short lengths. These results emphasize therole of extracellular structures in determining mechanical function ofsmooth muscle.

     

Non-geotropic Growth Curvatures in the Striga Radicle

When seedlings of the root parasite Striga asiatica Benth. (=S. lutea Lour.) are grown in0 the absence of the host the radiclegrows to a length of about 4 mm. On emergence the radicle showsa strong curvature which is brought about by a failure of cellextension on one side. The inhibited cells generally remainun-extended throughout the life of the seedling. Neither thesodium salt of indole-3-acetic acid nor Inhibitor-ß(which is present in the seeds), induced permanent inhibitionsto the radicle cells when applied externally, as did the endogenouscurvature factor. 2: 3: 5-tri-iodobenzoic acid reduced curvatureby promoting extension of the normally inhibited cells.     

Neuroepithelial stem cell proliferation requires LIS1 for precise spindle orientation and symmetric division

Mitotic spindle orientation and plane of cleavage in mammals is a determinant of whether division yields progenitor expansion and/or birth of new neurons during radial glial progenitor cell (RGPC) neurogenesis, but its role earlier in neuroepithelial stem cells is poorly understood. Here we report that Lis1 is essential for precise control of mitotic spindle orientation in both neuroepithelial stem cells and radial glial progenitor cells. Controlled gene deletion of Lis1 in vivo in neuroepithelial stem cells, where cleavage is uniformly vertical and symmetrical, provokes rapid apoptosis of those cells, while radial glial progenitors are less affected. Impaired cortical microtubule capture via loss of cortical dynein causes astral and cortical microtubules to be greatly reduced in Lis1-deficient cells. Increased expression of the LIS/dynein binding partner NDEL1 restores cortical microtubule and dynein localization in Lis1-deficient cells. Thus, control of symmetric division, essential for neuroepithelial stem cell proliferation, is mediated through spindle orientation determined via LIS1/NDEL1/dynein-mediated cortical microtubule capture.     

Morphology and Microtubule Organization in Arabidopsis Roots Exposed to Oryzalin or Taxol

In roots of Arabidopsis thaliana, we examined the effects oflow concentrations of microtubule inhibitors on the polarityof growth and on the organization of microtubule arrays. Intact6 d old seedlings were transplanted onto plates containing inhibitors,and sampled 12 h, 24 h and 48 h later. Oryzalin, a compoundthat causes microtubule depolymerization, stimulates the radialexpansion of roots. The amount of radial swelling is linearlyproportional to the logarithm of the oryzalin concentration,from the response threshold, 170 nM, to 1 µM. Cells inthe zone of division were slightly more sensitive to oryzalinthan were cells in the zone of pure elongation. Radial swellingis also stimulated by taxol, a compound that causes microtubulepolymerization. Taxol at 1 µM causes little swelling,but at 10µM causes extensive radial swelling of cellsin the elongation zone, and does not affect cells in the divisionzone. To examine the microtubules in these roots, we used methacrylatesections with immunofluorescence microscopy. At all concentrationsof oryzalin, cortical arrays are disorganized and depleted ofmicrotubules, and the microtubules themselves often appear fragmented.These effects increase in severity with concentration, but areunmistakable at 170 nM. In taxol, cortical arrays appear tobe more intensely stained than those of controls. At 10 µM,many cells in growing regions of the stele have longitudinalmicrotubules, whereas many cells in the cortex appear to havetransversely aligned microtubules. Taxol affects microtubulesin cells of division and elongation zones to the same extent,despite the observed difference in growth. We conclude thatthe precise, spatial pattern of cortical microtubules may notbe primarily responsible for controlling growth anisotropy;and that control over growth anisotropy may differ between dividingand non-dividing cells. (Received December 6, 1993; Accepted June 7, 1994)