Ontogenesis of Tannin Coenocytes in Sambucus racemosa L. II. Mother Tannin Cells

Tannin coenocytes develop from mononucleate tannin mother cells.The process occurs within the whole of the first (youngest)internode and its development can be divided into three stages.In stage I the MTC is isodiametric and similar to the surroundingcells of the flank meristem, being present in the ninth celllayer from the apex surface. The nucleus becomes lanceolateand elongates, and large cytoplasmic vacuoles appear. A twofoldelongation of both the cell and nucleus continues in the secondstage, the cell-nucleus ratio indicating that it is due to theenlarged vacuole, which pushes a thin layer of cytoplasm closeto the cell wall. In this layer of cytoplasm dilated ER cisternaoccur together with small and large vacuoles, a fusion of thevacuoles increasing their volume. Such cells are diploid inspite of larger nuclear volume and rough structure of its chromatin. Sambucus racemosa L., tannin cells, development, ontogenesis     

Electrophoretic mobility of haploid cells, diploid cells, asci, and ascospores of Saccharomyces cerevisiae

The electrophoretic mobility of diploid cells, haploid cellsof different mating types, their cell walls, asci, and ascosporesof Saccharomyces cerevisiae was measured with a free-flow electrophoreticapparatus. Haploid -cells and ascospores exhibited higher mobilitythan diploid cells, haploid -cells, and asci. Similar differencesin mobility were found with isolated cell walls of the haploidand diploid cells. ² Present address: Lederle (Japan) Ltd., Kyobashi, Tokyo 104,Japan. (Received December 24, 1976; )     

The Behaviour of Nucleic Acids and Other Constituents in Protomyces inundatus Dangeard

Estimations of contents per cell of DNA and RNA were made inProtomyces inundatus. There was twice as much DNA per cell incultures derived from fusion bodies and from mycelium in thehost (Apium nodiflorum) as in those derived from unfused endospores,indicating that the former two were diploid, the latter haploid.Dry weight/cell, volume/cell, insoluble nitrogen/cell, and metaphosphate/cell,like RNA/cell, had similar values for all three types of cultures.Giant cells resulting from camphor treatment not only had twiceas much DNA/cell as normal cultures derived from unfused endospores,but all the other characteristics studied had doubled as well.In any one culture the ratio of RNA to DNA remained constantthough the absolute values decreased as the cultures aged. TheRNA to DNA ratios in P. inundatus of haploid and diploid culturesare compared to those found in yeast and other organisms.     

Association of the Generative Cell and Vegetative Nucleus in Pollen Tubes of Rhododendron

Mixed fluorescence/bright field microscopy of Rhododendron pollentubes in the first 72 h after germination reveals a lens-shapedgenerative cell which divides to give two associated spermswithin the original cell boundary. The generative cell is closelyassociated with the vegetative nucleus which precedes it in92 per cent of pollen tubes. Three-dimensional reconstruction from serial thin sections ofa pollen tube fixed 24 h after germination shows that the associationbetween the generative cell and vegetative nucleus is extremelycomplex. Elongated tails of the generative cell physically enfoldthe vegetative nucleus and penetrate into enclaves within it.The association has been clarified by use of the periodic acid-phosphotungsticacid-chromic acid technique to enhance electron contrast ofthe plasma membranes surrounding the generative cell. In thisbicellular system, the male germ unit association is apparentlyinitiated after pollen maturity but prior to generative celldivision. Pollen tube, generative cell, male germ unit, plasma membrane, vegetative nucleus, Rhododendron, Ericaceae     

Effect of Sporophytic Heterozygosity on the Male Gametophyte of the Tetraploid Potato (Solanum tuberosum L.)

Quantitative variation for pollen stainability was examinedin both tetraploid x diploid and tetraploid x tetraploid familiesof potato (Solanum tuberosum L.). The diploid parents, whichwere highly heterozygous, produced first division restitution(FDR) 2n pollen. The families used were not affected by cytoplasmic-geneticmale sterility. Significant differences between families werefound. FDR 2n pollen producing diploid clones had progenieswith a significantly higher pollen stainability than those derivedfrom crosses between tetraploid parents. This was related tothe level of heterozygosity in the sporophyte. In FDR 2n pollen,80% of the heterozygosity and a large fraction of epistasispresent in the diploid parent was transmitted to its tetraploidprogeny. This is important for the production of open pollinated,true potato seed, because pollen stainability is significantlycorrelated with fruit set (r = 0·85).Copyright 1994,1999 Academic Press FDR 2n pollen, gametophytic heterozygosity, true potato seed     

Endopolyploidy in Diploid and Tetraploid Maize (Zea mays L.)

Nuclei from different tissues such as stem, mesocotyl, nodalroot and root tip of diploid and tetraploid maize were isolated,stained with propidium iodide and passed through an EPICS-751flow-cytometer cell sorter. Variations in flow histograms wereobserved in different tissues. Stem tissues of both the diploidand tetraploid had two peaks representing G1 and G2 somaticnuclei. The remaining tissues in both the diploids and tetraploidsexhibited three peaks. The first peak observed in these tissuesrepresents G1 somatic nuclei of the lowest ploidy level. Thesecond peak represent G2 somatic nuclei of the lowest ploidylevel+G1 somatic nuclei of the next ploidy level. The thirdpeak represents G2 of the higher ploidy level+G1 somatic nucleiof the next higher ploidy level. Statistically significant differenceswere observed between the diploid and tetraploid maize tissueswith respect to nuclei distribution in the higher ploidy levelpeaks implying variation in the degree of endopolyploidy inthe diploid and tetraploid maize. The results of this studysuggest that the amount of endopolyploid observed in maize genotypeshas an effect on their overall agronomic performance under thefield conditions.Copyright 1993, 1999 Academic Press Zea mays L., maize, endopolyploidy, diploid, tetraploid, flow cytometry     

Variation of Nuclear DNA Content in the Biflorus Species of Lonchocarpus (Leguminosae)

This represents the first study of nuclear DNA content in alarge sample (135 spp.) from a tropical arboreal genus, in whicha large proportion of the species were examined (42 spp., 31.1%).Somatic chromosome numbers and 4C-DNA values for 51 taxa ofLonchocarpus are reported. All taxa were diploid with 2 n =22,but their DNA content ranged from 1.92 to 2.86 pg 4C nucleus,corresponding to a 48.95% variation in genome size. In the 74collections studied, no correlation was observed between DNAcontent and habitat altitude. Variation in nuclear DNA contentwas analysed at the level of genus, subgenus, section and subsection.Variation in genome size was also studied within some species,either among widely separated populations or among differentintraspecific taxa. Very little variation in genome size wasdetected between populations, subspecies, and varieties of thesame species. The taxonomic implications of variation in nuclearDNA content are discussed.Copyright 2000 Annals of Botany Company Lonchocarpus (Leguminosae), DNA content, chromosome number.     

The Comportment of the Vegetative Nucleus and Generative Cell in the Pollen and Pollen Tubes of Helleborus foetidus L

It has been reported that in species of Plumbaginaceae, Chenopodiaceae,Cruciferae and Amaryllidaceae a ‘male germ unit’is formed in which the two male gametes remain inter-connected,with one of the pair linked intimately to the vegetative nucleus.In two species the unit has been shown to remain intact in thepollen tube, and some accounts imply that it is polarized inits movement, the vegetative nucleus leading in the tube. Evidence given in this paper indicates that such a unit is unlikelyto be present in Helleborus foetidus L. (Ranunculaceae). Applicationof an optical sectioning technique has shown that at no timeis there a persistent linkage between the generative cell andthe vegetative nucleus in unhydrated, hydrated and germinatingpollen, nor is one present in the early pollen tube. Furthermore,no inter-connections between the two entities were seen in protoplastsfrom living, hydrated and incipiently germinating grains isolatedmechanically in an osmotically balancing medium. Following germination,the vegetative nucleus leaves the grain in advance of the generativecell in most instances, but in the samples examined the generativecell led in about 30 per cent of the tubes. Assembling a polarisedmale germ unit in these circumstances would require (a) theformation of an inter-connection between the vegetative nucleusand the generative cell or one of the gametes derived from itduring passage through the tube, and (b) where the generativecell initially leads in the tube, an exchange in relative positions.It is considered improbable that these conditions could consistentlybe met. Mature, incipiently germinating pollen of H. foetidus releasesa fibrillar component when extruded into suitable media. Websor clusters of fibrils are commonly seen to be associated withboth the vegetative nucleus and the generative cell. The possibilitythat the fibrils are composed of aggregates of microfilamentsis considered. Helleborus foetidus L., pollen germination, generative cell, vegetative nucleus, male germ unit     

Protoplast Rotation, Cell Division and Frustule Symmetry in the Diatom Navicula bacillum

Navicula bacillum frustules, like those of many other naviculoiddiatoms, exist in two forms, cis and trans, which occur in theratio 1 cis: 2 trans. During interphase the protoplast bearsa constant relation to the orientation of the hypovalve, suchthat the nucleus lies on the same side as the first-formed halfof the hypovalve. Immediately before mitosis the plastid andnucleus migrate around the cell until the nucleus lies on theopposite side from its interphase position, where it then divides.After cytokinesis the new valves form with their primary halveson the same side as the recently divided nuclei. This and the180° rotation of the protoplast during the cell cycle explainthe 1 cis: 2 trans ratio. Navicula bacillum Ehrenb., cell symmetry, diatom systematics, plastid structure, protoplast rotation     

Cytological Studies in the Laminariales

A cytological investigation of British members of the orderLaminariales has revealed the presence of a very large X-chromosomein dividing nuclei of female gametophytes and young sporophytesof Saccorhiza polyschides. This chromosome pairs with a smallY-chromosome at meiosis. A chromosome which is conspicuouslylarger than the others has also been detected in the femalegametophytes (and young sporophytes) of Laminaria spp., Chordafilum, and Alaria esculenta. There is some evidence that thisalso pairs with a smaller chromosome. Chromosome numbers determinedduring the work are as follows: Laminaria digitata, L. saccharina,L. hyperborea, L. ochroleuca, Saccorhiza polyschides, hap-loid31 and diploid 62; Alaria esculenta, haploid 28 and diploid56; Chorda filum, haploid c. 28 and diploid c. 56     

A Light Microscope Study of Carposporophyte Development in Gracilaria verrucosa (Hudson) Papenfuss

Gracilaria verrucosa is a very common marine red alga of Greekcoasts. The diploid carposporophyte which develops attachedto the female gametophyte of Gracilaria is described. The immaturecystocarps are very small while the mature ones are globose,ostiolate and are borne profusely all over the surface of thethallus. The earliest observed fusion cell is small and fusesprogressively with adjacent vegetative cells to form a largemultinucleate cell. From this fusion cell gonimoblast initialsoriginate, dividing further and giving rise to a large numberof gonimoblast cells. The resultant carposporophyte consistsof a basal-central, multinucleate cell surrounded by a conicalor hemispherical mass of gonimoblast cells. Chains or clustersof successively maturing carpospores are borne from the terminalgonimoblast cells. The liberation of mature carpospores takesplace through the ostiole of the cystocarp. The liberated carposporeslack cell walls and are naked in a mucilage mass. Gracilaria verrucosa (Hudson) Papenfuss, Gigartinales, Gracilariaceae, Rhodophyta, carposporophyte, development     

The Structure and Development of Trifolium subterraneum L. Root Nodules: I. IN PLANTS GROWN AT OPTIMAL ROOT TEMPERATURES

The structure of effective nodules on Trifolium subterraneumL. grown at a root temperature favourable for nitrogen fixationwas examined by light microscopy. Rhizobium were released intohost cells from vesicles on infection threads which were closelyassociated with the host cell nucleus. Enlargement into bacteroidforms was rapid and synchronous in similarly-aged host cells,but groups of rhizobia close to the nucleus sometimes did notdevelop into bacteroids. Rhizobium changed in shape from smallrods to more elongate and then to irregularly swollen formsbefore finally becoming coccoid. On degeneration clusters ofbacteroids became un evenly stained before coalescing at thecentre of the host cell and finally disintegrating. Small vegetativerods multiplied amongst the degenerating bacteroids and in thegreatly enlarged intercellular spaces; host cell walls becamefolded and distorted and sometimes broke before collapsing ontoeach other.     

KARYOTYPES OF FIVE SUBANTARCTIC BIVALVE SPECIES

Chromosomes of five subantarctic species were studied from mitoticmetaphases using cell suspension techniques. Among the Protobranchia,Malletiagigan-lea has a diploid chromosome number of 2n = 38with five metacentric, seven submetacentric, five sub-telocentricand one telocentric pairs, and Yoldia (Aequiyoldia) woodwardialso shows 2n = 38 but with ten metacentric, six submetacentricand three sub-telocentric pairs. Among the Lamellibranchia,the pterioidan Limatula pygmaea has 2n = 38 with six metacentric,eleven submetacentric and two sub-telocentric pairs, the veneroidanCyclocardia astar-toides has 2n = 30 with five metacentric andten telocentric pairs and the anomalodesmatan Laternula ellipticahas 2n = 40 with two metacentric, one submetacentric, two subtelocentricand fifteen telocentric pairs. Our results indicate that in all the Nuculoidea studied so far,a diploid number of 2n = 38 has been found. In addition, thekaryotypes show a close overall appearance in relative lengthswith a majority of meta-centric-submetacentric chromosomes.The species differ in the proportion of the different morphologicaltypes of chromosomes. In the Lamellibranchia, each species correspondsto a particular case within their respective orders (Pterioida,Veneroida, Anomalodesmata). (Received 22 January 1990; accepted 28 March 1990)     

Root Cap Structure in Isoetes macrospora Dur

Root meristem cells of Isoetes macrosporausually have one plastidwhich is associated with the prominent nucleus, numerous ribosomesand mitochondria, and small vacuoles. During mitosis each plastidappears to replicate so that each daughter cell contains oneplastid. The cell walls of the meristem cells are traversedby numerous plasmodesmata. Central cells of the root cap lackdistally displaced plastids but have one or more amyloplastsassociated with the nucleus. These cells also contain largeprotein deposits. Peripheral root cap cells are characterizedby being vacuolated, and by possessing a few dictyosomes andprotein deposits. They appear to be sloughed infrequently. Isoetes macrospora Dur, root cap, protein bodies, ultrastructure     

Comparison of Embryo Development in Wild and Cultivated Arachis Species

Embryo development following selfing was investigated in twowild diploid peanut species, Arachis batizocoi Krap. et Greg.(coll. K 9484) (2n = 20) and A. duranensis Krap. et Greg. nom.nud. (coll. K 7988) (2n = 20), and one cultivated tetraploidspecies, A. hypogaea L. NC-Ac 18000 (2n = 40). Rates of pegelongation and sequences of embryo development for each specieswere compared. Peg elongation rates were similar for the twowild species, but for A. hypogaea it was only one-third to one-halfthat of the diploid species. Embryos in A. hypogaea showed slightlymore rapid cell division than in the wild species. The observedvariation in reproductive development between the wild and cultivatedspecies indicate that different control mechanisms may governdevelopment in the different species and may be at least partiallyresponsible for failure to produce viable interspecific hybridsat various ploidy levels. The observations are also importantfor determining the time at which embryos of different speciesof Arachis will reach the appropriate stage of development forsuccessful culture on an artificial medium during embryo rescueprocedures. Peanut, Arachis hypogaea, wild species, embryo, peg     

Flag Leaf Anatomy of Triticum and Aegilops Species in Relation to Photosynthetic Rate

Quantitative anatomical and other measurements were made onfully expanded flag leaves of a series of diploid, tetraploidand hexaploid Triticum and Aegilops species, and photosyntheticrates per unit leaf area were measured at light saturation (P_max). Diploids had the highest P_max, hexaploids the lowest with tetraploidsbeing intermediate. The anatomical features of tetraploids andhexaploids were generally similar, but different from the diploids.The diploids had thinner leaves with less dry matter and chlorophyllper unit area. The surface area of the mesophyll cells per unitvolume of mesophyll tissue was similar for all ploidy levels,as was the ratio mesophyil cell surface area per unit leaf area.It is argued that while these anatomical features are unlikelyto account for the observed variation in Pmax, it is possiblethat other structural factors with which they are correlatedmay causally influence P_max. One such feature is the averagediffusion path length from the plasmalemma at the cell surfaceto the sites of carboxylation. Anatomy, photosynthesis, mesophyll, cell size, Triticum, Aegilops, polyploidy     

Triploidy in rainbow trout determined by computer-assisted analysis

This study was designed to assess the use of a computer-assisted system based on erythrocyte measurements as a possible alternative to flow cytometry for identifying triploid rainbow trout (Oncorhynchus mykiss). Blood smears were prepared from 26 triploid and 26 diploid specimens, as determined by flow cytometry after staining blood cells with propidium iodide. The cell and nucleus lengths of 10 erythrocytes were determined in each fish. This was followed by discriminatory analysis to distinguish between diploids and triploids based on their score profiles. Triploid trout showed significantly larger erythrocyte cell and nucleus measurements than their diploid counterparts (N=52; P<0.0001). Erythrocyte length correctly identified 100% of the fish specimens as diploid or triploid, while nucleus length was a less accurate predictor of the level of ploidy. Our findings validate the potential use of computer-assisted analysis for this purpose.     

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     

The solution to the cytological paradox of isomorphy

Cells with polyploid nuclei are generally larger than cells of the same organism or species with nonpolyploid nuclei. However, no such change of cell size with ploidy level is observed in those red algae which alternate isomorphic haploid with diploid generations. The results of this investigation reveal the explanation. Nuclear DNA content and other parameters were measured in cells of the filamentous red alga Griffithsia pacifica. Nuclei of the diploid generation contain twice the DNA content of those of the haploid generation. However, all cells except newly formed reproductive cells are multinucleate. The nuclei are arranged in a nearly perfect hexagonal array just beneath the cell surface. When homologous cells of the two generations are compared, although the cell size is nearly identical, each nucleus of the diploid cell is surrounded by a region of cytoplasm (a "domain") nearly twice that surrounding a haploid nucleus. Cytoplasmic domains associated with a diploid nucleus contain twice the number of plastids, and consequently twice the amount of plastid DNA, than is associated with the domain of a haploid nucleus. Thus, doubling of ploidy is reflected in doubling of the size and organelle content of the domain associated with each nucleus. However, cell size does not differ between homologous cells of the two generations, because total nuclear DNA (sum of the DNA in all nuclei in a cell) per cell does not differ. This is the solution to the cytological paradox of isomorphy.     

Induced single fertilization in maize

 Bicellular pollen with one vegetative nucleus and one diploid arrested generative cell (”monospermic” pollen) was induced by trifluralin treatment of diploid maize plants at 7–9 days before flowering. The arrested generative cell (seemingly a diploid sperm cell) fused with the central cell of diploid plants and produced shriveled endosperm resembling that of a 2n×4n cross in maize. Dual pollination experiments with a purple embryo marker revealed single fertilization events in which the union of one sperm cell with the egg occurs but there is no union of a second sperm cell with the central cell. Singly fertilized ovules survived at least 4 days. Furthermore, many viable triploid plants were obtained. This technique therefore appears to have the potential for manipulating ploidy level in crops and may become useful in investigating fertilization mechanisms of angiosperms. Received: 1 October 1996 / Revision accepted: 8 January 1997