The Effects of Centrifugation on Asymmetric Cell Division and Differentiation of Fern Spores

We have investigated the effects of centrifugation on sporepolarity, asymmetric cell division, and rhizoid differentiationin the sensitive fern Onoclea sensibilis L. Centrifugation at10000 g for 30 min produces a random orientation of spores withstratification of the cell contents. After centrifugation atmost early stages of development, the nucleus retains its normalpattern of migration from the centre of the ellipsoidal sporeto the proximal face and then to an end of the spore, withoutregard to the orientation of stratification. This indicatesthat the polarity of the spore is stable to centrifugation.As long as the nucleus migrates to an end of the spore and asymmetriccell division occurs, the small cell differentiates into a rhizoid.The arrangement of large cytoplasmic organelles appears to haveno influence on nuclear migration, asymmetric cell division,or rhizoid differentiation. The only period during developmentwhen centrifugation blocks asymmetric cell division is immediatelypreceding and during mitosis and cytokinesis. Spores centrifugedat this stage do not complete nuclear migration, and symmetriccell division results, with neither cell differentiating intoa rhizoid. The source of the stable polarity of the spore isdiscussed. cell polarity, rhizoid differentiation, centrifugation, Onoclea sensibilis L., sensitive fern, fern spores     

Spore Germination of Ceratopteris thalictroides (L.) Brongn

Germination of the spores of Ceratopteris thalictroides wasexamined by light and scanning electron microscopy. Spores germinateby scission of the spore coat at the trilete markings. The initialcell divisions produce a proximal prothallial initial with rhizoidsthat are distal and lateral. This represents a reverse orientationof the more common situation in ferns. Evidence is presentedthat rhizoid initials divide with the most lateral of the daughtercells differentiating into a rhizoid. Rhizoids are long andunbranched. The uniseriate protonema is transient with bi-dimensionalgrowth established quite early. About a week following germination,the gametophyte is broad at the basal region and narrow at theanterior region. Further growth of cells in the basal regionis by elongation and the anterior region broadens to producean elongate-ovate gametophyte.     

Apical Structure of Actively Growing Fern Rhizoids Examined by DIC and Confocal Microscopy

The development and cytology of gametophyte primary rhizoidsof the fern Dryopteris affinis was examined using actively growingmaterial. During development an apical cytoplasmic ‘ accumulation’forms and is associated with active tip growth. This accumulationdeteriorates as terminal differentiation and cessation of growthapproaches. During early development the nucleus moves fromthe rhizoid cell base into the newly extending rhizoid. Later,during the active elongation phase, the nucleus takes up a relativelystable location approx. 100 µm behind the extending apex.Towards terminal differentiation the nucleus lags further behindthe tip. In actively growing rhizoids four distinct zones weredistinguished: a richly cytoplasmic ‘cap’; an apicalregion with tubular vacuolar intrusions; a region distinguishedby a peripheral sheath of cytoplasm and fine irregular cytoplasmicstrands connecting to the nucleus; and the main subapical vacuole.Confocal microscopy of gametophytes stained with fluorescentvital dyes, not previously used to examine fern rhizoid structure,confirmed that the tubular vacuolar system extends well intothe apical cytoplasm, and that the network of fine cytoplasmicstrands leads back from the apical cytoplasm to the nucleus.It also revealed that mitochondria are distributed throughoutthe rhizoid and are not excluded from the extreme apex. Membranestaining by FM 4-64 suggested a high density of membrane vesicleswithin the cytoplasm of the extreme apex. Uptake of this endocytosismarker into endomembranes also suggested rapid plasma membraneturnover in the rhizoid. This study highlights the similarityin the developmental stages and appearance of D. affinis rhizoidsto angiosperm root hairs and their much less distinct apicalzonation compared to pollen tubes. Copyright 2000 Annals ofBotany Company Rhizoid, root hair, confocal imaging, vital stains.     

Negative Phototropism in the Rhizoid of Bryopsis plumosa

Negative phototropism in the rhizoid of Bryopsis plumosa wasanalyzed. The growth zone of the rhizoid was confined to theapical hemisphere, as is typical of tip growth. Upon unilateralillumination, the rhizoid bent away from the light source witha "bulging" manner. The photoreceptive site for phototropismwas also restricted to the apical hemisphere. The action spectrumfor this negative phototropism was determined from fluence-responsecurves that were obtained after fixing the duration of illuminationat 60 min and varying the fluence rate between 0.1 and 3.0 Wm^-2. The action spectrum had a large peak at 467 nm and smallerpeaks at 378 and 414 nm, resembling the action spectra of certainother blue-light responses. (Received November 29, 1995; Accepted May 29, 1995)     

Rhizoid differentiation in Spirogyra II. Photoreversibility of rhizoid induction by red and far-red light

The optimum light conditions for rhizoid formation in Spirogyrawere determined. Red light was significantly effective on rhizoidformation while green, blue and violet lights had less effect.The dose-effect curve of red light was investigated and theminimum energy needed to saturate the effect was 8.1 Kergs.cm_–2.The effect of red light was completely reversed by subsequentirradiation with far-red light. The doseeffect curve of far-redlight was also obtained. The repeatedly reversible photoresponseswith red and far-red light strongly suggest that the photoreceptorof the rhizoid formation system is phytochrome. The existenceof phytochrome in the Spirogyra cell was also demonstrated spectrophotometrically.The half time for the escape reaction from the reversal effectof far-red light was 2hr. There may be no pigment other thanphytochrome mediating the photoreaction. (Received December 14, 1972; )     

Phototropism in a red alga, Griffithsia pacifica

In the red alga, Griffithsia pacifica, shoot portions of a plantare positively phototropic and rhizoids are negatively phototropic.We have studied the phototropic response of rhizoids which elongateby tip growth. For 45 min after the beginning of unilateralillumination a rhizoid grows straight, then phototropic curvaturebegins and continues rapidly until the rhizoid is growing awayfrom the light. Curvature is 70–80% complete after 3 hr.If the unilateral stimulus is given for a short time (15 min),curvature again begins at 45 min. However, within an additional30–45 min the rhizoid stops growing away from the lightand wanders back towards its original direction of growth. Phototropismis elicited by light of wavelengths from 350 nm to 500 nm; inlight of wavelengths above 550 nm, little, if any, responseoccurs. ¹Present address: Division of Natural Sciences, University ofCalifornia, Santa Cruz, California 95064, U.S.A. (Received December 10, 1976; )     

Action Spectrum in the Ultraviolet Region for Phototropism of Bryopsis Rhizoids

The phototropic response of the rhizoid of the marine coenocyticgreen alga Bryopsis plumosa to ultraviolet light (250–350nm) was investigated. The rhizoid exhibited negative bendingthat was due to bulging upon absorption of light in the UV region,as well as in the visible region, of the spectrum. The negativebending might not be a result of the inhibition of growth onthe irradiated side of the apical hemisphere by UV irradiationbecause growth inhibition was observed after bending had reacheda maximum within one to two hours. The action spectrum obtainedfrom fluence rate-response curves had a pronounced peak at 260nm and a small peak at 310 nm. The quantum effectiveness at260 nm was about five times that in the visible region. Phenylaceticacid (PAA), a potent inhibitor of flavin photoreactions, inhibitedthe phototropic response to both UV light and blue light withoutany obvious effect on tip growth. The inhibition of the phototropicresponse to blue light by PAA was partially overcome by rinsingthe alga with riboflavin-containing medium, which result suggeststhe involvement of flavins in the phototropism of Bryopsis rhizoids. (Received February 6, 1995; Accepted June 19, 1995)     

Effects of Gibberellic Acid on the Rhizome and Rhizoids of the Algal Coenocyte, Caulerpa prolifera, in Culture

Treatment of the large coenocyte Caulerpa prolifera with a hormonallevel of GA₂ resulted in increased elongation of the rhizomeand more frequent initiation of rhizoids when the hormone wasadded to the Erdschreiber culture medium. No effect of GA₂ wasfound on the rate of initiation or elongation of blades. Theseresults suggest that the recently discovered gravimorphogeneticeffect on rhizoid development is mediated by endogenous gibberellin. Caulerpa prolifera, coenocyte, green alga, gibberellic acid     

Action spectrum of negative phototropism in Boergesenia forbesii

The rhizoid of Boergesenia forbesii, a gigantic unicellulargreen alga, exhibited negative phototropism. The bending processat 32?C followed Weber-Fechner's law and Bunsen- Roscoe's law.The minimum light energy inducing the phototropic bending was30 J.m^–2 at 467 nm and 32?C. The action spectrum of thisnegative phototropism had two distinct peaks at 380 and 443nm, with shoulders at 430 and 470 nm and a trough around 410run. Light of wavelengths longer than 502 nm was ineffective.The structure of the spectrum agrees well with that reportedfor the positive phototropism of Avena coleoptiles and otherplant parts. (Received February 24, 1979; )     

Spore Germination Patterns in the Ferns, Cyathea and Dicksonia

Cell division patterns during germination of spores of Cyatheaaustralis, C. cooperi and Dicksonia antarctica were examinedby light microscopy of sectioned materials and by the scanningelectron microscope. In C. australis and C. cooperi the rhizoidwas traced to a small cell formed by an asymmetric divisionof the spore by a wall parallel to its equatorial plane. Incontrast, the rhizoid was formed by a division of the sporeparallel to its polar axis in D. antarctica. In spores of bothgenera, a second division wall oriented in a plane perpendicularto the first gave rise to the protonemal cell. Certain aspectsof germination described here in spores of Cyathea and Dicksoniaare in conflict with the published accounts of spore germinationin these genera. Cyathea, Dicksonia, spore germination, cell division pattern     

Vacuolation in Nitella flexilis (Characeae)

In Nitella flexilis, a species belonging to the section Anarthrodactylaeof the genus Nitella (Characeae), some mature cells, with theexception of those of the nodal complex and the rhizoid, shownumerous spherical vacuoles occupying the entire central regionof the cell. These vacuoles are fairly uniform in size measuring30–40 µm in diameter. Evidence is presented frominvestigations with the light and electron microscopes suggestingthat some mature cells of a certain group of Nitella speciesmay not have a huge central vacuole. Vacuolation in young cellsof the apex apparently begins by progressive dilation of theendoplasmic reticulum. The Golgi complex may also be involvedin vacuolation. The necessity for re-examination of certainbiological activities in the giant internode cell is explored.     

Growth and phototropic bending in Boergesenia rhizoid

The rhizoid of Boergesenia forbesii. a coenocytic green alga,exhibited typical tip growth. The growth stopped at temperatureslower than 15?C and was promoted by red light but inhibitedby blue light (430 nm). The rhizoid showed negative phototropicbending caused by blue light, and the mode of bending was the"bulging" type. The dioptric effect was not involved in thisnegative phototropism. The phototropicbending process was modifiedgreatly by temperature. At low temperature (18?C), bending didnot occur but the phototropic effect could be accumulated andstored. The accumulated effect appeared as a bending in thedark when the temperature was raisedto 25?C. This accumulatedphototropic effect, designated "stored bending", attenuatedat a half-life of 1.5 hr at 18?C in the dark. (Received February 24, 1979; )     

DIE WIRKUNG VON PHYTOHORMONEN AUF KEIMUNG UND ENTWICKLUNG VON FARNPROTHALLIEN IV. DIE WIRKUNG VON UNTERSCHIEDLICHEN GIBBERELLINE UND VON ALLO-GIBBERINSAURE AUF DIE AUSLOSUNG DER ANTHERIDIENBILDUNG BEI ANEMIA PHYLLITIDIS L. UND EINIGEN POLYPODIACEEN

The relative activities of seven gibberellins have been testedin their ability to induce antheridia in prothallia of Anemiaphyllitidis. The spectrum of activities differs from the spectradescribed for other gibberellin reactions. Allogibberic acidproved to be highly active in the Anemia test. Additionallyit causes a change in the polarity of the germinating spore.Under the influence of this compound the primary rhizoid istransformed into an additional chloronema. In high concentrationsof allogibberic acid more than 80% of the prothallia developinto those "twins". Out of the polypodiaceous ferns only fewspecies respond to gibberellin application. The relations between chemical structure and activity of differentgibberellins are discussed. (Received January 17, 1966; )     

Changes in Intracellular Distribution of Thiol Groups During the Development of Acetabularia mediterranea

A cytochemical study of intracellular thiol distribution inAcetabularia mediterranea intact cells was performed using thefluorescent thiol-labelling agent monobromobimane (mBBr). Differentdevelopmental stages were examined during the vegetative phaseand generative phase of the algal life cycle up to cyst maturation.Important changes in thiol localization have been found to coincidewith turning-points ofAcetabularia development. During the rapid growth phase, overall thiol content steadilyincreased along the stalk, being maximal shortly before capdifferentiation. At this stage, the thiol distribution patternparalleled that of cap morphogenesis essential processes: thiolsbeing accumulated at the apex where morphogenesis is going tobe expressed. High thiol contents were also present in the rhizoidal partof the alga throughout the vegetative phase. At the onset ofthe generative phase, important alterations in rhizoid thioldistribution coincided with the presumptive time of nucleardivision. Overall thiol content strongly decreased and thiolsbecame highly concentrated in definite zones localized in thecentral area of the rhizoid. Later on, during the sequence of morphogenetic events leadingto cyst differentiation, changes in thiol localization and relativecontent were observed in the cap rays. Positioning of secondarynuclei into the cap coincided with a high increase in thiolcontent in the entire cap. During the process of cyst formation,thiol content slightly decreased and thiols were localized incyst domains. Thiol distribution was also studied during regenerative processesafter merotomy. A spatio-temporal coincidence was shown withcell wall regeneration. Key words: Acetabularia, thiols, development, bromobimanes     

Dilated Endoplasmic Reticulum Cisternae in Differentiating Xylem of Minor Veins of Mimosa pudica L. Leaf

The differentiating tracheary elements in the xylem of minorveins in Mimosa pudica L. contain, as is usual, complete nucleateprotoplasts. Within the latter, dictyosomes with associatedvesicles and endoplasmic reticulum (ER) are prominent components.The ER cisternae show an uncommon feature of developing voluminousdilations accumulating finely fibrous material. Similar dilatedER cisternae occur in parenchyma cells associated with the trachearyelements. Most of the dilated cisternae are elongated, taperingat both ends, and almost circular in transections. They varyin size. The largest measured was 10 µm long and 3 µmwide. In the tracheary elements the cisternae break down asthe protoplast disintegrates. For a time, mature cells containfibrous material, apparently the product of the dilated cisternae,at least in part. In the parenchyma cells the dilated cisternaeare released into the vacuoles after the associated trachearyelements reach maturity. They become structurally modified anddisintegrate. The timing in the appearance and disintegrationof the dilated ER cisternae suggests that these structures havesome function with reference to the differentiation of trachearyelements in the xylem.     

Gametophytic and Sporophytic Regeneration from Bud Scales of the FernPlatycerium bifurcatum(Cav.) C.Chr.In Vitro

Regeneration fromPlatycerium bifurcatumscalesin vitrowas observedfor the first time. Regeneration was obtained from scales detachedfromin vitrogrown juvenile shoots. Regeneration began as rhizoidsor as a proliferation of one or more scale cells into undifferentiatedoutgrowths distinguishable from adjacent cells by their shapeand colour. Outgrowths developed into adventitious buds, aposporousgametophytes, or remained undifferentiated. Numerous outgrowthsformed rhizoids on their surfaces. Aposporous gametophytes producedgametangia. Sucrose enhanced scale viability and regeneration,and promoted rhizoid development on outgrowths, but sucroseconcentrations greater than 0.1% tended to inhibit apospory. Platycerium bifurcatum(Cav.) C.Chr.; staghorn fern; scale; regeneration; organogenesis; sucrose; apospory     

Saponin-induced release of single cells from filaments and rhizoid differentiation in<Emphasis Type="Italic"> Spirogyra</Emphasis>

Some species of Spirogyra living in streams can anchor to the substratum by differentiating a rhizoid from a terminal cell of a filament. Rhizoid differentiation occurs in the light but not in the dark. When a filament of Spirogyra sp. competent for rhizoid differentiation was incubated in a medium containing 0.1% saponin, terminal cells were released one by one, forming single cells. Single cells effectively differentiated to be rhizoids when saponin in the incubation medium was removed. The single-cell system developed in the present study seems suitable for analysis of gene expression during rhizoid differentiation of Spirogyra.     

The Life-History of Marginariella urvilliana (Ach. Rich.) Tandy

In Marginariella urvilliana gametes are produced in the thirdyear and then annually for several years. On germination ofthe egg a single primary rhizoid is formed. Its early subdivisioninto four main branches is unusual amongst the Fucaceae. Growthof both the main axis and of the receptacles is carried outby a three-sided apical cell. The oogonia develop earlier thanthe antheridia. Nuclear divisions are completed within the conceptacle,often several weeks before extrusion of oospheres. The liberatedoosphere is held in a tubular stalk until after fertilizationand the sporeling has begun to develop. Marginariella has affinities with the other endemic submergedAustralasian fucoids, and together these form a rather isolatedgroup, probably rightly included within the Fucaceae.     

BIOADHESION IN CAULERPA MEXICANA (CHLOROPHYTA): RHIZOID‐SUBSTRATE ADHESION1

The attachment of the psammophytic alga Caulerpa mexicana Sond. ex Kütz., a coenocytic green alga, to crushed CaCO₃ particles was examined utilizing the scanning electron microscope and fluorescently tagged antivitronectin antibodies. Plants attached to the substrate through morphologically variable tubular rhizoidal extensions that grew from the stolon. In this study, we describe two means of attachment: (i) the rhizoid attachment to limestone gravel by thigmoconstriction, where tubular extensions of the rhizoid wrapped tightly around the substrate and changed morphology to fit tightly into crevices in the limestone, and (ii) through adhesion pads that formed in contact with the limestone granules. Flattened rhizoidal pads were observed to secrete a fibrillar material that contained vitronectin‐like proteins identified through immunolocialization and that facilitated binding of the rhizoid to the substrate.