Pollen Wall Development of Xiphidium coeruleum (Haemodoraceae) and its Systematic Implications

The development of the pollen grain wall in Xiphidium coeruleum(Haemodoraceae) was studied using TEM and cytochemical stainingtechniques. Microsporocyte ontogeny initiates with the degradationof the cellulosic cell wall and subsequent deposition of a thickcallosic cell wall. Following callose deposition, successivemeiosis occurs, resulting in a tetragonal tetrad of microspores.during meiosis, the cell walls of the tapetum break down, releasingthe syncytial periplasmodium. Irregular non-sporopollenous globularbodies are deposited in this peripheral periplasmodium, whichis rich in ER, golgi bodies, vesicles, and characteristic starchplastids. Within the microspore cytoplasm, vesicles, golgi bodies,and plastids are plentiful during the early tetrad stage. Atthis time the plasma membrane of the microspore develops characteristicevaginations. An extracellular membrane, the ‘white line’,is secreted outside the microspore plasma membrane, followedby callose wall degradation. Bead-like deposits of exine orprimexine are deposited at points along the ‘white line’simultaneously on inner and outer surfaces and opposite theoriginal plasma membrane evaginations. The bead-like exine depositscontinue to grow during the release of the microspores and developinto laterally appressed, rod-shaped ektexinous elements havinga tangentially oriented commissure, the vestige of the original‘white line’. The mature intine is two-layered,the outer exintine containing radially oriented vesicular structures,which are apparently derived from plasma membrane extensions.Exine development in Xiphidium is similar to ‘nexine 1’development in Lilium and may have evolved from an ancestraltectate-columellate condition by the loss of the sexine. Walldevelopment in members of the Zingiberales is strikingly similarto that reported here for the Haemodoraceae—evidence ofa possible relationship between the two taxa. Xiphidium coeruleum, Haemodoraceae, pollen, tapetum, development, exine     

Commitment of Mitotic Cells to Meiosis during the G2 Phase of Premeiosis

In the developing anther, archesporial cells that proliferateby mitotic division are converted into meiotic cells duringthe premeiotic interphase. Experiments with explanted microsporocytesof Lilium and Trillium were made to obtain evidence for theconversion of mitotic to meiotic cells during the premeioticperiod. Explanted premeiotic cells were cultured through thedivision cycle at relatively high division frequencies and showeda variety of division types with respect to chromosomal events.The type of division depended on the premeiotic stage at whichthe cells were explanted. Cells in the G₁, S and early G² phasesunderwent mitotic division and formed a diad or binucleate monad.Cells explanted at the late G₂ phase were cultured throughoutthe normal meiotic cycle, which resulted in typical tetrad configuration. In microsporocytes explanted during the main part of the G₂interval, centromere behavior was meiotic, but chromosome pairingand chiasma formation were disturbed. Thus, she G₂ intervalwas shown to be critical for the commitment of mitotic cellsto meiotic division. Detailed analysis showed that the intracellularchanges that commit the cells to meiosis begin shortly aftercompletion of premeiotic DNA synthesis and that these changesare progressive and cumulative. (Received February 2, 1982; Accepted May 24, 1982)     

Microsporogenesis in Taxus baccata L.: The Formation of the Tetrad and Development of the Microspores

Following meiosis II in Taxus microsporangia a small proportionof the tetrads regularly degenerated. Despite frequent inequalityin the frequency of ribosomes between the spores of a tetrad,partial degeneration within a tetrad was never observed. Theinitial wall of the young spores was found to resemble the wallof the mother cell in containing a fibrillar layer, and thetwo walls may possess similar isolating properties. The symmetryof the tetrad was regularly iso-bilateral. The formation ofthe sporoderm began as the spores were released into the loculusby the rapid dissolution of the wall of the mother cell. Osmiophilicdroplets emerged from the spore protoplast and entered the wall.The fibrillar layer ceased to be recognizable and the dropletscoalesced to form an outer layer on which up to six sporopolleninlamellae, probably of tapetal origin, were deposited. The accretionof a single layer of sporopollenin droplets, in no recognizablepattern, gave rise to the outer verrucose part of the exine.Cytochemical tests showed that the tapetum was rich in acidphosphatases from the beginning of meiosis. Towards the endof its degeneration the tapetum intruded into the loculus andcould therefore be regarded as partly invasive. Taxus baccata, microsporogenesis, tetrad symmetry, sporoderm     

Callose Deposition During Megagametogenesis in Two Species of Oenothera

Callose deposits are present both in degenerating megasporesof the heteropolar tetrad in Oenothera hookeri and in degeneratingembryo sacs of the homopolar developing tetrad in O biennis.They are partially continuous with the cell wall and partiallyenclosed in the degenerating cytoplasm and show electron opaquebands within a less electron opaque material Vesicles calledcallose grains are present in the degenerating cytoplasm ofthe embryo sac in O biennis These show an electron opaque fibnllaror granular core surrounded by a halo of low electron opacity Similarities in fine structure between callose deposits of femalegametophytes which follow the degenerating pathway of development,and callose plugs present in pollen tubes during their growth,are discussed. Oenothera, evening primrose, megagametogenesis, megasporogenesis, callose, ultrastructure     

Reproduction in Seagrasses: Pollen Development in Thalassia hemprichii, Halophila stipulacea and Thalassodendron ciliatum

The general features of pollen morphogenesis in three marinemonocotyledons, Thalassia hemprichii, Halophila stipulacea andThalassodendron ciliatum, are described in this paper. Thalassia disperses spherical trinucleate pollen grains. Inthis genus simultaneous cytokinesis generally produces an isobilateraltetrad of microspores, but linear and T-shaped configurationsalso occur, together with configurations intermediate betweenisobilateral and T-shaped. Partitioning is followed by a phaseof cellular degeneration affecting one or two, never more, membersof the tetrad. Subsequent development of the surviving, functionalmicrospores does not differ essentially from the pattern ofmorphogenesis in terrestrial flowering plants. Halophila disperses strings of four reniform trinucleate pollengrains contained in a mucilaginous moniliform tube. These ariseby successive transverse partitioning of an elongate mothercell and the linear unit so formed is maintained throughoutpollen development. The tetrad tube substance originates inthe tapetal periplasmodium and deposition begins soon aftermeiosis. Thalassodendron disperses filiform trinucleate pollen grains.The characteristic form of the pollen in this genus is attainedduring post-meiotic growth and differentiation, as in othergenera belonging to the same family. This contrasts with thesituation in seagrasses belonging to the Zosteraceae where thefiliform shape is established before meiosis. Precocious divisionof the microspore nucleus in Thalassodendron launches the binucleatepollen phase soon after the spores separate from the tetrad.The division precedes the vacuolate period; again, this is afeature of the family. In Thalassia the tapetal periplasmodium is progressively transformedinto thecal slime. In Thalassodendron and Halophila the periplasmodialresidue forms a superficial coating on the pollen wall and tetradtube. These products could be implicated in attachment and recognitionof the pollen at the stigma surface. Thalassia hemprichii, Halophila stipulacea, Thalassodendron ciliatum, seagrasses, pollen development     

A Persisting Cellulosic Wall of Microspore Mother Cells during Microsporogenesis in Allium tuberosum Rottl. and Cyclamen persicum Mill

Light microscopic studies were carried out on the anthers ofAllium tuberosum Rottl. and Cyclamen persicum Mill. Callosedeposition is initiated within the primary wall round each microsporemother cell during early prophase of meiosis I and is of maximumthickness at the tetrad stage. The original cellulosic wall,contrary to earlier reports for other species, persists aroundthe microspore mother cells until the late tetrad stage in bothspecies. In C. persicum, it dissolves to release the callose-encasedtetrads, and in A. tuberosum, il dissolves simultaneously withcallose at the time of release of microspores. Allium tuberosum Rottl., Cyclamen persicum Mill., microsporogenesis, microspore mother cell     

Pollen Wall Development in Gibasis (Commelinaceae)

The development of the one and-inline of the pollen wall aredescribed for Gibasis karwinsk yana and G. venustula. Duringthe tetrad stage the appearance of electron-opaque depositionsor tri-partite plates at discrete sites between the plasma membraneof the spore and the inward surface of the callose special wallare the first indications of exine development. The sulcus rapidlydifferentiates being composed of discrete exine granules ona thin foot layer. Probacula in non-apertural areas developin an electron-opaque granular layer situated between the plasmamembrane, which is highly convoluted, and the callose specialwall. A foot layer is formed from electron-opaque lamellae atthe plasma membrane. Exine pattern is clearly established withinthe tetrad. After release of the spores from the tetrad an intimate associationis rapidly developed between the plasma membrane of the periplasmodialtapetum and the newly-formed exine. Compacted electron-opaquematerial is found at the interface between membrane and theexine and vesicular material is added from the tapetum. Theincrease in volume that occurs in both spore and anther is accompaniedby considerable vacuolation. Intine development begins just prior to pollen grain mitosisand continues rapidly at the aperture. The thin foot layer becomesdiscontinuous. Further intine deposition takes place after mitosisand a bilayer is apparent in mature grains. The matrix of thislayer contains conspicuous electron-opaque platelets. The exineof the mature spore stains less intensely than in the youngspore and the interbacula spaces are filled with material fromthe degenerate tapetum. Gibasis karwinskyana, Gibasis venustula, Commelinaceae, exine, intine, tapetum, pollen wall, ultrastructure     

Anther-filament Extension in Lilium: Potassium lon Movement and Some Anatomical Features

The growth of the anther filaments in the Lilium bud is essentiallyexponential after a length of 5 mm is reached, when the celldivision rate declines and growth is by cell extension, particularlyof cells in the central part of the filament. During the periodof extension, fresh vascular tissue is formed and xylem continuityis conserved up to the time of anther dehiscence, in contrastto the Graminae where the filament extends much more rapidly.The expansion of the lily filament depends in part on the continuoustransfer of potassium ions from the receptacle throughout theperiod of growth. Although starch to sugar conversion may bean important source of osmoticum as the cells expand, regulationof K⁺ ion movement would be likely to provide a more sensitiveand faster method of regulation of cell osmoticum. Anther filament, extension growth, filament, ion movement, Lilium, lily, potassium, stamen filament, turgidity, vasculation, xylem     

Mechanism of Pollination in Gladiolus: Roles of the Stigma and Pollen-tube Guide

Gladiolus has a dry type of stigma. Compatible pollen grainsalight and germinate on the receptive surface of the papillae,penetrate the cuticle and grow towards the style through a sub-cuticularpollen-tube guide of mucilage. This is secreted from epidermalcells of the stylodium and style canal. The cuticle, which coversthe pollen tube guide mucilage, is continuous through the stylecanal to the ovary. The wet stigma of Lilium also has cuticulartissue running through the style canal, covering the mucilage.     

Structural Analysis of a recA-like Gene in the Genome of Arabidopsis thaliana

A recA-like gene was identified in the genome of Arabidopsisthaliana by means of PCR using primers designed on the basisof previously reported amino acid sequences of eukaryotic RecA-likeproteins. The structure of the gene, termed ArLIM15, was investigatedby comparing the primary structure of the genomic DNA with thatof the corresponding cDNA. The open reading frame, which wassplit into 15 exons, was established to have the capacity forencoding a 37.3-kDa polypeptide. The amino acid sequence ofthe putative product of ArLIM15 showed a high degree of similaritytothat of LIM15 in the monocotyledonous plant Lilium, includinga 93% identity, and to those of other recA-like genes in yeastsand vertebrates with identities of 69–71%. Phylogeneticanalysis indicated ArLIM15 to be much closer to meiosis-specificLIM15 and DMC1 in Saccharomyces cerevisiae than to RAD51 inS. cerevisiae and its homologues on an evolutionary scale.     

Isolated Megaspore Tetrads of Stauropteris burntislandica

A new type of fossil spore tetrad, Didymosporites scotti gen.et sp. nov. is described from the Dinantian and Namurian (Carboniferous)of Ireland, Scotland, and England. The spores always occur inthe form of a tetrad composed of two large (presumably fertile)and two minute (presumably abortive) spores, all with cutinizedwalls. Reasons are given for regarding these as the megasporesof the coenopterid fern Stauropteris burntislandica; their distributionindicates a far wider range in time and space than that previouslyknown for this species. Their occurrence as adhering tetradssuggests that Stauropteris burntislandica 'shed' its megasporesstill enclosed in the sporangiumIan interesting analogy withboth Lepidocarpon and the seeds of Pteridosperms.     

The loculus content and tapetum during pollen development in Lilium

 The ratio of loculus volume to the volume of the entire anther began to increase from the microspore mother cell stage and reached 32.3% at anthesis. The content of the loculus was examined in Lilium during pollen development and two waves could be distinguished. From the premeiotic stage until the vacuolated microspore stage, the loculus consisted of neutral polysaccharides, pectins and proteins. These substances originated from tapetal activity from the premeiotic stage until the young microspore stage. Dictyosomes and rough endoplasmic reticulum seemed to be involved in tapetal secretion, although, in some mitochondria, vesicles progressively developed as early as premeiosis and increased until the young microspore stage, which could reveal their involvement in the secretion process. At this stage, numerous cytoplasmic vesticles containing material similar to the locular material fused with the plasma membrane of the tapetum so that vesicle content was in contact with the loculus. It seems that tapetal and callose wall degradation at the late tetrad stage may also have contributed to the production of material in the loculus. From pollen mitosis to anthesis, the anther loculus contained mainly the pollenkitt which was synthesized in the tapetum between the young microspore stage and the vacuolated microspore stage. At the young microspore stage, proplastids divided and developed into elaioplasts and smooth endoplasmic reticulum (SER) increased dramatically. Pollenkitt had a double origin: some droplets were extruded directly from the plastid stroma through the plastid envelopes; the others were unsaturated lipid globules, which presumably derived from the interaction between SER saccules and plastids. Received: 2 September 1997 / Revision accepted: 12 March 1998     

Interactions between Developing Citrus Fruits and their Supportive Vascular System

The developing fruit is a strong sink, which demands large amountsof assimilates. A correlation between grapefruit (Citrus ParadisiMacf., var. Marsh seedless) fruit size and its pedicel crosssectional area (CSA) can be demonstrated, suggesting a closeinteraction between them. The presence of fruits seems to determinethe developmental pattern of the vascular tissues within thebranches on which the fruits are borne. The pedicel normally terminates its diametric growth prior tothe linear phase of fruit growth. Fruit thinning (90%) and trunkgirdling, performed in order to minimize carbohydrate limitations,result in dramatic increases in fruit growth rate and pedicelCSA. Partial girdling of the pedicel causes a transient decreasein fruit growth. An increase in specific mass transport (SMT)through the existing vascular routes is the immediate response,due to the instantaneous upsurge of carbohydrate supply to individualfruit. Nevertheless, the rapid development of new vascular tissueshas been the major factor responsible for the long term enhancement,or recovery, of fruit growth, suggesting that limitation intransport capacity does occur. The cause and effect relationships between fruit and vasculardevelopment are discussed.Copyright 1995, 1999 Academic Press Source, sink, fruit growth, vascular development, transport limitation, specific mass transport (SMT), carbohydrate availability, competition, Citrus     

Development of the Embryo Sac in Amitostigma kinoshitae (Makino) Schltr. (Orchidaceae)

The embryo sac of Amitostigma kinoshitae was studied. The ovuleis anatropous, bitegmic, and tenuinucellate. The inner integumentalone forms a micropyle. The megaspore of a tetrad nearest tothe chalaza develops into an eight-nucleate embryo sac of thetypical Polygonum-type. Double fertilization takes place normally.     

Tapetal Organization During Sporogenesis in Psilotum nudum

Stages in the differentiation of the tapetum of Psilotum nudumare described. Two concurrently occurring components of thetapetum can be recognized. A plasmodial tapetum with associatedfunctional nuclei develops within the sporangial loculus duringthe early stages of differentiation, appears to remain viablefor several months, that is during the entire period of sporogenesis,and undergoes reorganization on three occasions. During MeiosisI groups of spore mother cells are enclosed in clear areas withinthe plasmodium: by the end of Meiosis II each tetrad is isolatedin a plasmodial chamber; and, finally, mature spores are enclosedwithin individual tapetal chambers. Typically enlarged cellsare present during the development of a cellular, parietal tapetum.A sporopollenin-containing layer or tapetal membrane characteristicof a secretory tapetum develops on the inner tangential walland lines the surface of the loculus. This tapetal membranepersists even after dehiscence of the sporangium. These observationsare discussed in relation to previously published conflictingdata and may be relevant to the arguments concerning the relationshipof the Psilotaceae to the Filicales. Psilotum nudum, light microscopy, parietal tapetum, plasmodial tapetum, tapetal membrane, tapetal reorganization, sporogenesis, sporopollenin     

A light and electron microscopy analysis of the events leading to male sterility in Ogu-INRA CMS of rapeseed (Brassica napus)

Ogura cytoplasmic male sterility (CMS) occurs naturally in radishand has been introduced into rapeseed (Brassica napus) by protoplastfusion. As with all CMS systems, it involves a constitutivelyexpressed mitochondrial gene which induces male sterility tootherwise hermaphroditic plants (so they become females) anda nuclear gene named restorer of fertility that restores pollenproduction in plants carrying a sterility-inducing cytoplasm.A correlative approach using light and electron microscopy wasapplied to define what stages throughout development were affectedand the subcellular events leading to the abortion of the developingpollen grains upon the expression of the mitochondrial protein.Three central stages of development (tetrad, mid-microsporeand vacuolate microspore) were compared between fertile, restored,and sterile plants. At each stage observed, the pollen in fertileand restored plants had similar cellular structures and organization.The deleterious effect of the sterility protein expression startedas early as the tetrad stage. No typical mitochondria were identifiedin the tapetum at any developmental stage and in the vacuolatemicrospores of the sterile plants. In addition, some strikingultrastructural alterations of the cell's organization werealso observed compared with the normal pattern of development.The results showed that Ogu-INRA CMS was due to premature celldeath events of the tapetal cells, presumably by an autolysisprocess rather than a normal PCD, which impairs pollen developmentat the vacuolate microspore stage, in the absence of functionalmitochondria. Key words: Brassica napus, cell death, light and electron microscopy, mitochondria, plastids, pollen development, Ogu-INRA cytoplasmic male sterility, transgenic-restored plants, tapetum Received 30 September 2007; Revised 11 December 2007 Accepted 20 December 2007     

The Morphology and Development of Tripospora tripos (Cooke) Lindau

The development of the stroma, microconidial locule, and ascigerouslocule of Tripospora tripos are described. The first structureto appear on the leaf after infection is a stromal mass composedof mainly fungal pseudoparenchyma. Within this is differentiateda microconidial locule Bulges of purely stromal tissue appearon this original stromal mass and these ultimately form theascigerous locules A wall, separately formed in the stroma,is not produced around the asci; the ascocarp arises as a loculein a stroma. There is a disintegration of tissue within thelocule into which a number of fascicles of unitunicate ascigrow. As such a combination of unitunicate asci with an ascostromaticascocarp is unusual, and since other related species share thesame developmental characteristics, a new developmental typeis proposed.     

The Inductive Role of Bacterial Symbionts in the Morphogenesis of a Squid Light Organ

SYNOPSIS. The association of the sepiolid squid Euprymna scolopeswith its marine luminous bacterial symbiont Vibrio fischeriis an emerging model system to study the initiation and developmentof bacterial symbioses in higher animals, in particular theinfluence of bacteria on the ontogenic development of symbiotic-specifichost tissues. Experiments comparing the development of juvenilesquid infected with symbiotic V. fischeri with that of uninfectedjuveniles suggest postembryonic development of the light organrequires cell-cell interactions with the bacterial symbionts.The presence of symbiotic bacteria induces specific morphologicalchanges by affecting such fundamental processes as cell deathand cell differentiation. The surface of the juvenile organis largely composed of ciliated cells that appear to facilitateinfection of the light organ. These cells begin to undergo celldeath within hours of infection with symbiotic V. fischeri.Within three days the epithelial cells that form the bacteriacontainingcrypts of the light organ increase in size; these cells do notappear mitotically active, and may represent a terminally differentiatedstate. The light organs of uninfected juvenile E. scolopes,however, do not exhibit any of these early postembryonic developmentalevents but remain in a state of arrested morphogenesis.     

Intrachloroplast Localization of 65Zn and 63Ni in a Zn-tolerant Plant, Ocimum basilicum Benth

Intrachloroplast localization studies of ⁶⁵Zn and ⁶³Ni weremade in a Zn-tolerant plant Ocimum basilicum var. purpurascensBenth. in order to investigate the mechanism and specificityof metal tolerance. The isotopes were supplied in solution tothe roots 14 d before fractionation. It was observed that ⁶⁵Znactivity was comparatively greater in the chloroplast envelopemembranes and stroma than the ⁶³Ni; and ⁶³Ni was largely foundin the lamellar and stroma fractions. Further analysis of lamellaerevealed that photosystem II (PS II) particles were richer inradioactivity than photosystem I (PS I) particles. The photochemicalevents of photosynthesis were less affected in Zn-treated plantsthan in the Ni-treated plants. The changed levels of the electrontransport chain intermediates including cytochromes, plastocyaninand ferredoxin provide supporting evidence for the localizationstudies. The activity of carbonic anhydrase, a zinc metalloprotein,was increased in Zn-treated plants with increase in nutrientZn concentration, indicating the binding of zinc to a proteinmoiety in the chloroplasts.     

Composition, Degradation and Utilization of Endosperm During Germination in the Oil Palm (Elaeis guineensis Jacq.)

The insoluble carbohydrate and lipid fractions, and -D-galactosidase,ß-D-mannosidase and isocitrate lyase activities werestudied in the various tissues of oil palm (Elaeis guineensisJacq.) kernels prior to and during germination. In ungerminatedkernels insoluble carbohydrate and lipid constituted 36 and47% of endosperm dry weight respectively. During germinationthe thick endosperm cell walls became markedly thinner, concurrentwith a significant decrease in the percentage of insoluble carbohydrateand an increase in -galactosidase and ß-mannosidaseactivity in both degraded and residual endosperm. The proportionof lipid in degraded endosperm also increased significantly.The insoluble carbohydrate appears to be a galactomannan locatedin the secondary walls of the endosperm. No galactomannan wasdetected in oil palm embryos or haustoria. Isocitrate lyasewas present in, and confined to, tissues of the haustorium ofgerminating kernels. The enzyme was not active in endospermat any stage of germination, nor was it active in embryos beforeor at the end of imbibition. The results suggest that galactomannan is the second largestcomponent of oil palm endosperm and that it is utilized morerapidly than lipid during the early stages of germination. Thefact that isocitrate lyase activity is confined to the haustoriumsuggests that in Elaeis gluconeogenesis, the conversion of triglycerideto carbohydrate, takes place entirely within the cotyledon ofthe seed. Elaeis guineensis, galactomannan, galactosidase, germination, isocitrate lyase, mannosidase, oil palm