Breakdown of Meiosis in a Tetraploid Clone from Dichanthium-Bothriochloa Complex

The paper describes the details of meiosis in a tetraploid clone(collection number 260) from Dichanthium-Bothriochloa complex.Meiosis is reported to have broken down very early in prophaseI. Pollen mother cells are reported to be present in the formof plasmodial mass or syncyte with several nuclei in each ofthem. Each syncyte, presumably, gave rise to one pollen grainwithout undergoing division. Consequently, each pollen grainhad one to several nuclei. A brief note on morphology and taxonomy of the collection isalso added. Although the spikelet morphology indicated it tobe a natural hybrid Bothrio-chloa grahamii x B. intermedia,in other morphological characters, it resembled Dichanthiumannulatum. It was concluded, therefore, that it was a productof continuous natural introgression.     

Pollen Dimorphism--Origin and Significance in Pollen Plant Formation by Anther Culture

Pollen dimorphism during the ripening of Nicotiana tabacum antherstakes the form of differentiation at the binucleate pollen stageinto normal (N) grains, characterized by their high frequency,larger size, densely–staining cytoplasm and high starchcontent and into smaller (S) grains characterized by their variableand low frequency and weakly–staining cytoplasm. Mostof the S grains show distinctive vegetative and generative nuclei(A grains); a small number have two vegetative–type nuclei(B grains). Evidence is presented that when excised anthersare cultured, pollen plants arise only from S grains. It issuggested that the differentiation into N and S grains arisesby an abnormal second meiotic division in the pollen mothercells. Nicotiana tabacum, tobacco, pollen dimorphism, anther culture     

Influence of Irradiated Pollen on Embryo and Endosperm Development in Kiwifruit

Development of seeds following pollination with irradiated pollenwas studied inActinidia deliciosa(kiwifruit) ‘Hayward’.Pollinations were carried out using two different sources ofpollen (‘Tomuri’ and ‘Matua’) irradiatedwith gamma rays at doses of 700 and 900 Gy. Non-irradiated crosseswere used as controls. Pollen irradiation had little effectonin vitropollen germination. Irradiated pollen affected seedset and seed content, and induced the formation of parthenogeneticembryos. In comparison to the control, the embryo growth ratewas slower and the endosperm contained very low amounts of storageproducts. Seed set was significantly reduced following bothdoses of irradiation. Two types of seeds were observed: (1)seeds with endosperm only; and (2) seeds with both embryo andendosperm. The proportion of seeds containing endosperm onlywas almost ten-fold higher than those containing both embryoand endosperm. Embryo production by gamma-irradiated pollenwas genotype- and dose-dependent. The induction of parthenogenesiswas higher following gamma ray doses of 900 Gy than 700 Gy,which suggests the ‘Hertwig Effect’; the best efficiencywas obtained with ‘Tomuri’ pollen. Ploidy levelof parthenogenetic embryos was evaluated by nuclear size (area)with the use of image analysis. There was a large differencein embryo nuclei size between control and parthenogenetic embryos(mean size 90.8 and 49.1 µm², respectively). It is concludedthat parthenogenetic embryos represent trihaploids.Copyright1998 Annals of Botany Company. Actinidia deliciosa, kiwifruit, pollen irradiation, induced parthenogenesis.     

RNA and Protein Synthesis in Germinating Pine Pollen

The results of autoradiographic experiments demonstrate that,as with the pollen of most other species, both the generativeand vegetative nuclei of Loblolly Pine (Pinus taeda) activelyengage in RNA synthesis from the very early stages of pollengermination. Unlike most other species, however, this newlysynthesized RNA includes rRNA. Evidence is provided for theimportance of this newly synthesized RNA in the process of continuedpollen tube growth. One and two-dimensional gel electrophoretic analysis revealsa number of both qualitative and quantitative differences amongthe proteins synthesized during the early stages of germinationand the later stages of pollen tube growth. One of the mostnotable of these is a 36 kD protein, the synthesis of whichpredominates during the later stages of pollen germination.A similar pattern of 36 kD protein synthesis is observed whenmRNA extracted from pollen at each of these stages is translatedin vitro. Key words: Pinus, pollen tube growth     

Pollen Tube Development and Characteristics of the Protein Emission in Conifers

When ripe, viable pollen of Pinus contorta, Pinus nigra, Piceasitchensis, Abies alba and Cedrus deodara is germinated on asuitable artificial substrate, the process of pollen tube growthbegins 12–36 h later, according to the species. The tubeemerges at the leptoma, a structurally specialized site in thepollen wall, and the early tube wall is continuous with thetwo microfibrillar intine strata within the grain. Later inpollen tube development, when cytoplasmic zonation has beenestablished, only the inner of these two wall layers is differentiated. Cytochemical methods show that, during hydration and throughoutthe period of tube growth in culture, proteins are releasedfrom the pollen grains; before germination most conspicuouslyfrom the leptoma, subsequently from the tube itself. The emissioncontains a number of hydrolytic enzymes and a non-catalyticmoiety. Gel-electrofocusing reveals that the hydrolases releasedfrom germinating Pinus contorta pollen include several acidphosphatase and esterase isozymes, and that there are differencesbetween the composition of the emission and the spectrum ofsoluble proteins extracted from the pollen grains before germination.Analysis by immunodiffusion demonstrates that two componentswith antigenic characteristics present in the quiescent pollengrains are represented in the emission. The possible utilityof the released components in the biology of conifer reproductionis discussed. Pinus contorta, Pinus nigra, Picea sitchensis, Abies alba, Cedrus deodara, lodgepole pine, Austrian pine, Sitka spruce, European silver fir, deodar, pollen tube, pollen germination, protein release, isoelectric focusing     

Rapid Assessment of Microspore and Pollen Development Stage in Wheat and Maize Using Dapi and Membrane Permeabilization

The use of the DNA-specific fluorochrome DAPI has been extended to stage assessment of fresh pollen in wheat and maize. Membrane permeabilization by Triton X-100 incorporated in the staining solution allows access of the fluorochrome to nuclear DNA. At all stages of gametophytic development, the nuclei can be sharply visualized. Starch does not interfere with the fluorochrome so that it is possible to study the second pollen grain mitosis and sperm differentiation. With its rapidity and reliability, this technique represents an efficient tool for routine staging or investigation of the nuclear status of the pollen grains     

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     

Role of Sucrose in Microspore Embryo Production in Brassica napus ssp. oleifera

Dun well, J. M. and Thurling, N. 1985. Role of sucrose in microsporeembryo production in Brassica napus ssp. oleifera.—J.exp. Bot. 36: 1478–1491. One cultivar of winter oil seed rape (Brassica napus ssp. oleifera)and three cultivars of spring rape were used in a study of theeffects of sucrose on microspore survival and embryo inductionin cultured anthers. A preliminary study on the winter cultivar(Fiona) revealed that the osmotic pressure of the supernatantof anther homogenates was equivalent to a solution of 17% sucrose.A study of microspore survival and embryo induction in thiscultivar on media containing either 8 %, 12%, 16% or 20% sucroserevealed the highest survival (after 16 d) and the greatestnumber of anthers with induced embryos (after 42 d) occurredon the highest sucrose concentration. A subsequent study on three spring cultivars (Willi, Duplo andTower) examined microspore survival at 8 d and embryo induction(42 d) on media containing either 8 % or 16 % sucrose and againrevealed much higher survival and induction at the higher concentration.The variation in response between the cultivars was also reducedby culture at the higher sucrose concentration. The beneficialeffect of the 16% level occurred regardless of the growth environmentof the donor plants and of the stage of pollen development atthe start of culture. However, macroscopic embryos emerged onlyfrom anthers on the 8 % sucrose concentration, suggesting thattransfer of anthers from a high to a normal sucrose concentrationduring culture would ensure that full advantage was taken ofthe much higher initial survival on the higher concentration Key words: Brassica napus, sucrose, microspore embryo production     

Anatomy of Watermelon Embryo Sacs Following Pollination, Non-pollination or Parthenocarpic Induction of Fruit Development

There is little information on the fate of embryo sacs in plantovules if pollination is prevented. In this study embryo sacsfrom watermelon were observed over a 13 day period followingflowering with (a) normal pollination, (b) non-pollination and(c) induction of parthenocarpic fruit development with naphthaleneacetic acid. Following pollination, and prior to fertilizationapproximately 2 days later, the embryo sacs completed developmentand consisted of two synergids with prominent filiform apparatus,an egg cell, a central cell with two polar nuclei and threeantipodal cells. Sperm nuclei were observed within the embryosac at 2 days and by 4 days the endosperm was proliferating.In the non-pollination treatment the embryo sac was still intactafter 4 days although the antipodal nuclei were becoming hardto distinguish. By 7 days only the two synergids and the eggcell were still well defined, the polar nuclei appeared in somepreparations to be fused, and the antipodals had degenerated.By 10 days the embryo sac was a structure-less watery mass.In parthenocarpic fruit the fate of the embryo sac was similarto that in non-pollinated fruit except that final breakdownwas delayed past 10 days. Maturity of the majority of embryo sacs in an ovary appearedto be contemporaneous with penetration of the pollen tube, andon the basis of the anatomical results it seems possible thatembryo sacs could be fertilized up to 2 days beyond the normaltime. Citrullus lanatus, watermelon, embryo sac, anatomy, pollination, parthenocarpy     

Plant Regeneration from Isolated Microspore of Indica Rice

Isolated microspores of rice (Oryza saliva L.) cultivars, IR36and IR43, belonging to the recalcitrant indica subspecies werecultured. Two types of microspores were observed after isolationfrom the fresh anthers and from pre-cultured anthers—onetype consisted of vacuolated, larger-sized grains, while theother was composed of microspores of smaller sizes with densecytoplasm. Within few days in culture, all the smaller sizedgrains were dead, and only the large grains were viable andproduced pollen embryos. After 30 days from culture, microcalliwere transferred to semisolid modified Murashige and Skoog mediumcontaining 1 mg/liter each of kinetin and naphthaleneaceticacid and kept under continuous light at 25?C. IR36 showed onlycell division while IR43 gave 32 green plants from these experiments. (Received January 18, 1990; Accepted July 4, 1990)     

Flow Cytometric Determination of Relative Nuclear DNA Contents in Bicellulate and Tricellulate Pollen

Nuclear DNA content in mature pollen was measured with a flowcytometer Pollen of Lilium longiflorum, Dendranthema grandiflora(syn Chrysanthemum monfolium) and Zea mays was chopped and stainedwith the DNA fluorochrome DAPI DNA levels, expressed as arbitraryC values, were compared with those of nuclei isolated from leafor root material of the same plants In mature tricellulate pollen the generative cell is dividedafter second pollen mitosis into two sperm cells Tricellulatepollen from maize and chrysanthemum gave rise to one large 1Cpeak and, only in the case of chrysanthemum, a much smallerone at the 2C level These results suggest that the haploid nucleiof the vegetative as well as both sperm cells in tricellulatepollen are arrested in the G₁ stage of nuclear division Thesmall 2C peak in the case of chrysanthemum probably arose froma fraction of pollen with the sporophytic chromosome number(2n pollen) In contrast to this, mature bicellulate lily pollengave rise to two identical peaks at the 1C and the 2C levelFrom this result it was concluded that in bicellulate pollen,the 1C peak is caused by the signal of the haploid vegetativenucleus arrested in the G₁ stage of nuclear division, whereasthe 2C peak originates from the haploid generative nucleus whichhas already undergone DNA synthesis and is arrested in G₂ Lilium longiflorumThunb, lily, Dendranthema grandiflora Tzelev (syn Chrysanthemum morifolium Ramat ), chrysanthemum, Zea maysL, maize, male gametophytic cells, vegetative cells, generative cells, sperm cells, unreduced pollen, sporophytic cells, relative nuclear DNA contents, replication stage     

Light Microscope Study of Pollen Tube Growth, Fertilization and Early Embryo and Endosperm Development in the Avocado Varieties Fuerte and Hass

Pollen tube growth, fertilization and early embryo and endospermdevelopment were studied using light microscopy in the avocadovarieties Fuerte and Hass. The ovule was penetrated by a pollen tube by 24 h after pollination.On reaching the ovary, the pollen tube grew along the surfaceof the inner ovary wall. It then grew around the funicle, throughthe micropyle in the inner integument and between the papillatecells at the apex of the nucellus. It entered the embryo sacvia a synergid. Sperm nuclei were present in the embryo sacat 48 h after pollination and fusion of the polar and spermnuclei took place before fusion of the egg and sperm. The endospermnucleus was the first to divide and cell wall formation occurredfollowing division. The first division of the zygote occurredat 5 or 6 days after pollination. In the variety Fuerte less than 20 per cent of the 1- and 2-day-oldembryo sacs had been penetrated by a pollen tube although tubeswere often observed in the integument or nucellus. In the varietyHass over 60 per cent of the embryo sacs were penetrated. Inwas concluded that low yields of the variety Fuerte may be partlyattributable to the failure of the pollen tube to penetratethe embryo sac. Persea americana Mill, avocado, pollen tube, fertilization, embryo, endosperm     

Microsporogenesis, Pollination, Pollen Germination and Male Gametophyte Development in Taxus brevifolia

Taxus brevifolia(Nutt.), commonly known as Pacific or westernyew, is a conifer native to the Pacific northwest of North America.Contrary to other Taxus species, T. brevifolia staminate strobiliare usually located on 2-year-old foliage although they mayoccur on foliage from 1 to 5-years-old. This delayed staminatestrobilus development may be an adaptation to the low lightenvironment where T. brevifolia grows. Microsporogenesis occurredin the autumn preceding pollination. Successive divisions producedisobilateral tetrads visible as early as mid-October. Over-winteringstaminate strobili usually contained separate microspores. In1996 to 1999, pollination occurred in March and April in twonatural forest sites on southern Vancouver Island, British Columbia,Canada. The low amounts of airborne pollen and prolonged pollinationperiod indicated low pollination success within T. brevifolia.Female receptivity was measured by the presence of a pollinationdrop. Protandry up to 18 d was observed. In vitro pollen germinationwas moderate to good, ranging from 65 to 88% depending on thetree and year. DAPI fluorescence staining showed successfulmale gametophyte development in vitro. The microspore dividedforming a tube nucleus and generative cell within 3 d of culture.The generative cell then divided forming a sterile nucleus andspermatogenous nucleus after 17 d. The spermatogenous nucleusacquired a cell wall then divided forming two equal sperm after24 d. Copyright 2000 Annals of Botany Company Taxus brevifolia, Pacific yew, microsporogenesis, pollination, pollen germination, male gametophyte development     

To Repeat the Effects of Hormones on the Early Microspore Developments of Wheat in Vitro in Anther Culture

1. The normal development of pollen cells can be transformed by the exoision itself of anther culture: The second mitotic division of pollen grains has been prevented; The frequency of anomalous division of pollen grains was higher than that present in anthers in vive; The generative nuclei after the first mitosis were more or less globular in form and in their subsequent developments most of them do not become spindly-shape which is particular to the generative cells in vive. In the meantime, they show a weak staining reaction with Feulgen reagent. 2. The higher concentrations of hormones were found to enhance the frequency of abnormal division obviously. Of anthers cultured on the four N6 media added with various concentration ratios of IAA to Kinetin 2:10, 10:2, 2:12, and 12:2 mg/l. The mean percentages of abnormal pollen grains were 34.02%, 35.28%, 34.27% and 36.65% respectively. 3. The higher hormone level may promote the formation of multicellular pollen grains obviously. When the IAA concentration was raised up to 12 mg/l, the mean multieellular pollen grain yields per anther increased to 13.3 unit, while the control without hormone was only 4 unit.     

Abortive Meiosis in Plasmodial Pollen Mother Cells of Helianthemum

The anthers of two garden varieties of Helianthemum containnot only normal pollen mother cells but also a large proportionof plasmodia with varying numbers of nuclei of varying nuclearcomplements. These abnormal cells probably resulted from a splitspindle associated with a failure of wall formation during severalpremeiotic mitoses. Chromosome pairing at meiosis is higherthan might be expected and in abnormal tissues such as theseit provides evidence for ‘somatic pairing’ havingtaken place during the premeiotic mitoses. Meiosis stops atthe end of the first division in the plasmodia and althoughit is completed in the normal pollen mother cells viable pollenis never produced.     

Anther Culture of Lolium temulentum, Festuca pratensis and Lolium x Festuca Hybrids. II. Anther and Pollen Development In Vivo and In Vitro

The various pathways of pollen development were investigatedin cultured anthers of Lolium temulentum, Festuca pratensisand the L. multiflorum x F. pratensis hybrid ‘Elmet’.In all three, development from the vegetative cell was the predominantpathway of pollen callus development. However, there were characteristicdifferences in the behaviour of the generative cell. In L. temulentumit remained attached to the pollen wall and degenerated, whereasin F. pratensis it divided. In ‘Elmet’ it detachedfrom the pollen wall and remained undivided. Both polarizedand unpolarized partitioned calluses were observed. Developmentof the fusion product of the vegetative and generative nucleiwere also observed in anthers of L. temulentum. Anomalous grainswere not found to be major source of pollen calluses. Sections of anthers of L. temulentum were used to investigatethe origin of S pollen grains, the small pale-staining grainswhich denote pollen dimorphism. Such grains form out of contactwith the tapetum and are therefore determined before or duringmeiosis (i.e. before harvest of anthers for culture). Sectionswere also used to demonstrate the influence of the durationof pretreatment on the development of the middle layer of theanther wall. Festuca pratensis, Lolium temulentum, Lolium x Festuca, anther culture, haploid, microspore, pollen     

Structure and Development of Stomata in Some Leptosporangiate Ferns

The structure and development of stomata are described for 17species of leptosporangiate ferns. In these species the maturestomata are anomocytic, diacytic, Pyrrosia(applied), tetracytic,suspended, or floating type. Stomata are present on both surfacesof floating as well as sub merged leaves of Azolla and Marsilea.In a few species twin stomata, arrested development, and persistentstomatal initials are present Floating stomata result from disintegrationof the anticlinal suspending wall in Pleopeltis, and by detachmentand displacement in Azolla pinnata. The development of stomatais haplocheilic, syndetocheilic, or syndetohaplocheilic. InCyathea spinulosa the guard cell nuclei divide amitoticallyand the resulting two daughter nuclei occupy the opposite polesof the guard cells     

Early Microspore Divisions and Subsequent Formation of Microspore Calluses at High Frequency in Anthers of Hordeum vulgare L.

The products of first microspore mitosis were studied in anthersof Hordeum vulgare. These anthers were obtained either directlyfrom plants at the binucleate stage or from tillers which hadbeen estimated visually as containing pollen at the mid-uninucleatestage and then pretreated by being clipped off at ground leveland allowed to stand in water for 2 d. In microspores from thelatter plants ten-fold increases in the failure of nuclear differentiation,alteration of the axis of division, or both were observed. Highfrequencies of further microspore response in individual antherswere subsequently induced through culture of the spikes fromthe pretreated tillers in agitated liquid medium. A five toten-fold increase in the percentage of anthers producing macroscopiccallus was observed in these spikes when compared with the controls.It is suggested that nucleo-cytoplasmic disturbances in themicrospores, brought about through the pretreatment period,stimulated the further divisions which eventually resulted inmicrospore callus formation. Microspore calluses were produced most often following an equalfirst division, although when mitosis resulted in differentiatednuclei further divisions of the vegetative nucleus also resultedin callus production. Haploid, diploid, polyploid, and mixaploidmicrospore calluses were produced but no evidence was obtainedto link haploid production with any particular developmentalpathway. Macroscopic calluses which emerged from the culturedanthers were probably mixtures of cell populations derived fromseveral or many different gametic genotypes.     

Ontogenesis of Tannin Coenocytes in Sambucus racemosa L. I. Development of the Coenocytes from Mononucleate Tannin Cells

Tannin coenocytes in shoots of Sambucus racemosa L. developfrom mono-nucleate tannin cells which can be distinguished amongthe cells of the first internode, and which keep on growing.After karyokinesis without cytokinesis bi-nucleate tannin cellsoccur which yield a synchronous karyokinesis leading to 4 nucleiin the tube. The number of nuclei in the coenocyte is 2ⁿ wheren equals the number of karyokineses that have occurred. Sometimesthe number of nuclei is different and one nucleus is bigeerthan the rest indicating that a previous fusion of nuclei hasoccurred. The distribution of nuclei in the coenocyte supportsthe possibility of fusion of chromosome sets at the moment ofnuclear envelope dispersion. Sambucus racemosa L., coenocytes, synchronous karyokinesis, development     

Partially Fertile Line with Apospory Obtained from Tissue Culture of Male Sterile Plant of Sorghum (Sorghum bicolor L. Moench)

A partial restoration of male fertility has been revealed inthree among 20 regenerants from callus cultures obtained fromthe panicle fragments of the sorghum plant with cytoplasmicmale sterility. Induced fertility is retained under self-pollinationfor eight generations. The pollen fertility level in every generationvaries in different plants (0-70%) and depends on the environmentalfactors, rather than on plant genotype. A high positive correlation(r = 0·90; P < 0·01) has been revealed betweenthe pollen fertility level and the total rain precipitationduring the microgametophytogenesis. Cytoembryological investigationof this line has shown the presence of structures similar toaposporous embryo sacs (ESs), which have developed in the ovulesalong with the sexual ESs. The ovules with aposporous formationshave been observed almost in all of the studied plants in severalgenerations, however, their frequency varied (2-53%). Parthenogeneticproembryos and endosperm nuclei without signs of pollen tubepenetration have been found in some of such ESs. The natureof the instability observed in a number of generations in maleand female generative structures is discussed.Copyright 1995,1999 Academic Press Cytoplasmic male sterility, fertile revertants, apomixis, somaclonal variability, Sorghum bicolor L. (Moench)