Karyotype analysis of Meloidogyne hapla by 3-D reconstruction of synaptonemal complexes from electron microscopy of serial sections

Meloidogyne hapla Race A (meiotic, n=17) females have 17 synaptonemal complexes (SC). The karyotype length is constant throughout pachytene, although nuclear volume increases as pachytene progresses. Each SC has at least one region in which two pairs of lateral elements run parallel to each other for a distance of 1–2 m, thus forming a double SC (dSC). Decondensed chromatin regions (DCR) occur along some SCs and represent 5% of the length of the karyotype. The DCRs may be the location of the sex-determining chromatin. Spermatocytes from males of the same meiotic parthenogenetic race (A) have SCs and cylindrical granular complexes (CGC) while males and females from a mitotic (3n=45) parthenogenetic race (B) lack such structures. The CGCs may contribute precursors necessary for the formation of SCs.     

Transition from somatic to meiotic pairing and progressional changes of the synaptonemal complex in spermatocytes of Aedes aegypti

Aedes aegypti spermatocytes were reconstructed from electron micrographs. The species has tight somatic pairing of the chromosomes, and there are therefore no classical leptotene and zygotene stages, but rather a gradual transition from somatic pairing to meiotic pairing (= pachytene). The term prepachytene has been used for the transitory stage. The first visible sign of impending meiosis was a reorganization of the chromatin, which resulted in the formation of spaces (synaptic spaces) in the chromatin, about the width of the synaptonemal complexes (SCs). Diffuse material, possibly precursor material for the SC, was present in the spaces. Later short pieces of complex were formed throughout the nucleus. Late prepachytene, pachytene, and diplotene complexes were reconstructed. Each chromosome occupied a separate region of the nucleus. The complexes became progressively shorter from prepachytene (maximum complement length 289 m) to diplotene (175 m). The thickness of the SCs increased from prepachytene to pachytene and probably decreased again during diplotene. At the beginning of diplotene the lateral elements (LEs) separated, and the single LEs became two to three times thicker than the LEs of the SC. The centromeres were at all stages attached to the nuclear membrane, whereas the telomeres were free in the nucleoplasm during pachytene and diplotene. A heterochromatic marker was present on chromosome 1 near the sex determining locus, and a diffuse marker on chromosome 3 near the nucleolus organizer region. After breakdown of the complexes, polycomplexes were present in the nucleus.     

Synaptic behaviour and recombination nodules in the human XY pair

A sample of 90 XY pairs from men with normal karyotypes has been analyzed by measuring their morphological features in electron micrographs of microspread spermatocytes. The classification of human XY types (Solari, 1980) has been given stricter definitions. Stepwise splitting of the axes is seen in types 1 and 2. The development of axial branches and lenhthening of the X axis is seen in type 3. In the two subtypes a and b of type 4 the net-like filamentous array grows in length to a maximum (average=59.7 m) in subtype b. The location of the putative Y kinetochore defines a short arm that measures 22.34% of Y axis length, and the kinetochore of the X axis defines a short arm of 38.15% of the axial length. The average number of excrescences in the X axis is 19.9 and in the Y is 4.3. The frequency of a non-homologous, distal end-joining grows steadily from type 0 to type 3. The average length of the synaptonemal complex (SC) in 51 XY pairs of types 1 and 2 is 1.33 m (SD=0.65) and it corresponds to 25.54% of the Y axis length. Thus, the average SC covers the short arm of the Y and the pericentromeric region. Maximum lengths of this SC may reach up to 81.8% of the Y axis, 30 recombination nodules (RNs) were located in 26 XY pairs, and 90% of the nodules are located in the distal half of the short arm of the Y axis. Thus, RNs are restricted to a segment much shorter than the length of the average SC. A gradient of decreasing probability of recombination may reach up to the centromeric region of the Y chromosome. Some possible consequences of these facts are discussed.     

Effect of estradiol treatment on male mice synaptonemal complexes: difference of sensitivity between neonates and adults

The effect of estrogen on pachytene spermatocytes was studied with the assistance of the synaptonemal complex analysis under electron microscopy. Male NMRI mice were injected with estradiol benzoate from birth onwards and allotted to different groups according to the dose administered: 1) three injections of either 12.5 g or 25 g or 50 g on d0, d5 and d10; 2) single injections of 50 g either on d0 or on d5 or on d10; 3) double injections of 50 g on d0 and d5; and 4) daily injection at the dose of 0.5 g/g BW from d0 to d27. Animals were sacrificed on day 28, 60 and 90. Adult male mice were treated daily with E2B (0.5 g/g BW) for one (from d30 to d60) or two months (from d30 up to d90) to test the age-related sensitivity to estrogen. A number of different SC anomalies were observed at each harvest time. Among all the anomalies, pairing failure (asynapsis) was predominant followed in decreasing order of importance by SC breakage (fragmentation of SCs), and heterotelomeric associations resulting either in quadrivalent-like figures or in trivalents. In E2B treated neonates the frequency of SC anomalies, which was less than 2% in controls, varied from 3.6 to 27% of pachytene cells regardless of the harvest time. In E2B treated adult mice, the SC anomalies were rare (<4%), but significantly different from controls in which the frequency of SC aberrations did not exceed 1% of pachytene cells. The prevalence of anomalies appeared to be independent of the TW decrease. Our observations suggest that estrogens act indirectly on SCs. Different mechanisms of action are discussed.Abbreviations BW body weight - E2B estradiol benzoate - d day - Gr(s) or gr(s) group(s) - LE(s) lateral element(s) - n number of examined mice - NAC number of abnormal cells - NPC number of cells at pachytene stage - SC(s) synaptonemal complex(es) - SD standard deviation - TW testicular weight     

A temporal study at the ultrastructural level of the developing pro-oocyte of Drosophila melanogaster

The first pro-oocyte in developing pupal germaria of females grown at 25 ° has been followed at 6 h intervals from its formation at 129 h post-ovipostion until Stage 1, to provide an unambiguous temporal order. EM autoradiographs were made of sectioned germaria, scanned at lower magnification for location of the pro-oocyte(s) within the most posterior 16-cell cyst and photographed at higher magnification to show the presence of label indicating DNA replication and synaptonemal complex indicating synapsis in the same pro-oocyte nucleus. Label, detected at 132 h and at all subsequent intervals up to and including 162 h, delimited an S-phase of 30 h and identified this period as premeiotic interphase. Extensive SCs (av. length 50 m/genome) measured in serial sections at 132 h provide irrefutable evidence that synapsis in Drosophila begins close to both pro-oocyte formation and initiation of premeiotic interphase. Measurements of SCs at 6 h intervals during interphase reveal a sharp increase between 132 and 138 h, a peak length (75 m/genome) at 144 h, a decrease and subsequent plateau ( 60 m/genome) from 150–162 h and a further drop (R~50 m/genome) at Stage 1. Maximal extension of SC at 144 h coincides with maximal genome response to heat (Grell and Day, 1974) and with midpremeiotic-S. Spherical nodules, detected at 1/genome between 138 and 150 h would, on the questionable assumption that they are the sites of recombination, provide proof of recombination during early interphase, as genetic evidence strongly implies. Evidence contrary to interpretations of fibrillar material within the nucleus as either precursor of the central region of the SC or sagittal sections of the central element of the SC, is presented. No structure corresponding to the polytene chromocenter was observed.     

The synaptonemal complexes of Caenorhabditis elegans: pachytene karyotype analysis of male and hermaphrodite wild-type and him mutants

Only five synaptonemal complexes (SC), representing the 5 autosomes, are present in wild-type, him-4 and him-8, Caenorhabditis elegans males, whereas there are six SCs, accounting for 5 autosomal bivalents and the XX bivalent, in the C. elegans hermaphrodite. The univalent X chromosome of the male is present as a heterochromatic X-body in spermatocyte pachytene nuclei. The XX bivalent in wild-type, him-4 and him-8 hermaphrodites (SC1, 2.5 m in length) represented 6% of the total karyotype length and a SC of this size is missing from the respective male karyotypes. This corresponds with the fact that the total male karyotype length is only approximately 94% that of the hermaphrodite. Associated with the central element of the SC are structures termed SC knobs that were first described in the wild-type hermaphrodite. The six SC knobs present in the wild-type hermaphrodite oocyte pachytene nuclei and the two SC knobs in the male spermatocyte pachytene nuclei are apparently randomly placed with the exception that they are never found at the ends of the SC. This is also true in him-4 and him-8 in which case there are 3 and zero SC knobs in the hermaphrodites, respectively, and one SC knob each in the male pachytene nuclei. The decrease in number of SC knobs in hermaphrodite to male represents a true sex difference. The presence or absence of the SC knobs may influence the X chromosome nondisjunction process and this effect is not localized to the region of the SC on which the SC knob is located.     

Synaptonemal complex karyotyping in spermatocytes of the Chinese hamster (Cricetulus griseus)

Relative length is a constant and distinctive characteristic for each autosomal SC, despite variations in absolute length from cell to cell. Arm ratio is distinctive for each SC except for two of the three sub-acrocentrics, and serves, together with relative length, for identification. The constancy of relative length and arm ratios indicates biological stability and lack of physical distortion in these spread preparations. There is a 11 relationship between relative lengths of autosomal SCs and mitotic autosomes; their arm ratios are also similar. These close parallels provide strikingly similar SC and somatic karyotypes. Variability was observed in sub-acrocentric arm ratios and in lengths of unpaired X and Y axes, correlated with the presence of constitutive heterochromatin. — Utilizing progressive differentiations of the X and Y chromosomes for staging, it is demonstrated that autosomal SCs decrease in length from late zygotene to mid-pachytene, and then increase at late pachytene. Within a nucleus, synchrony of length changes is maintained. It is concluded that the factors governing autosomal SC length are regular for any given bivalent from cell to cell, and may be related to those that control somatic autosome length relationships. — The X and Y axes differ quantitatively as well as qualitatively from autosomal SCs. The SC portion of the X and Y is constant in length through most of pachytene; the unpaired axes shorten and lengthen, but not in proportion to autosomal SCs. X and Y relative lengths and arm ratios vary throughout pachytene and do not maintain proportionality with somatic values. The evidence suggests, but does not prove, that the long arm of the X is paired with the short arm of the Y. — Twists occur in autosomal SCs at increasing frequencies throughout pachytene but cannot account for length changes. The number of twists per SC is directly proportional to SC length. Intertwining of SCs is random and proportional to SC length. End-to-end associations of autosomal SCs appear to be random; however, the ends of the X and Y are less often involved in such connections. — The length of axial material in all chromosomes at pachytene, expressed as an equivalent length of DNA double helix, represents 0.013% of the diploid DNA complement.     

Meiotic cytology of Saccharomyces cerevisiae in protoplast lysates

Summary This report describes cytological features of meiosis in Saccharomyces cerevisiae prepared for electron microscopy by lysis of protoplasts or nuclei on an aqueous surface. Whereas the chromatin of cells lysed before or after meiotic prophase was widely dispersed, pachytene bivalents appeared as discrete, elongate masses of compact chromatin. These bivalents were of nearly uniform thickness; they ranged in length from about 0.6 m to 4.0 m, with a median of 1.6–1.8 m. Enzymatic digestion of chromosomal DNA removed the chromatin to reveal the underlying synaptonemal complex. The lysis of partially purified nuclei was less disruptive and thereby revealed the regular association of the telomeres with fragments of the nuclear envelope. In tetraploid cells, pachytene lysates contained quadrivalents characterized by the close apposition of chromatin masses of similar length. One or more points of intimate association appear to represent sites of exchange between pairing partners. The departure of the diploid cells from pachytene was accompanied by the renewed association of spindle microtubules with the chromosomes shortly before the diplotene chromosomes decondensed. Later, the successive meiotic divisions were identified by the appearance of a single spindle for meiosis I and of two spindles for meiosis II.     

Inhibition of tumor growth in mice treated with synthetic muramyl dipeptide

Summary Treatment with synthetic MDP inhibited growth of transplantable, chemically induced tumors in syngeneic mice. The tumor-inhibitory effect was dependent on the schedule of MDP administration.Growth of SC transplants of a nonmetastasizing, MC-induced fibrosarcoma, MC11, was inhibited by local treatment with 200 g and 1,000 g MDP given SC 5–7 weeks before challenge. Treatment with lower (10 g and 100 g) doses of MDP and shorter (1–4 weeks) time intervals was not effective. Single doses of MDP (10–1,000 g) 1–3 weeks after challenge had no effect.Growth of IV-inoculated, metastasizing AAT-induced hepatoma A was inhibited by IV injections of 20 g MDP given 1 and 2 days prior to the challenge. Significant increases in the survival of hepatoma-bearing mice were observed only after injections of MDP incorporated in multilamellar liposomes.Abbreviations MDP n-acetylmuramyl-l-alanyl-d-isoglutamine - B10 C57BL/10ScSnPh mice - MC 3-methylcholanthrene - ATT o-amino-azotoluene - PBS phosphate-buffered saline     

Direct somatic embryogenesis and plantlet regeneration from cotyledonary leaves of safflower

Somatic embryos were induced directly on adaxial surface of cotyledonary leaves within 8–10 days of culture on Murashige and Skoog medium containing 5.37 to 10.74 M 1 — napthaleneacetic acid and 2.22 M benzyl adenine. Germinated embryos with shoot axes developed into complete plants after transfer onto half stength Murashige and Skoog medium containing 1.07 M 1 — napthaleneacetic acid. Histological studies suggested direct origin of somatic embryos with broad-base attachment.Abbreviations BA benzyl adenine - MS Murashige and Skoog - NAA 1-napthaleneacetic acid - RH relative humidity     

Synapsis,desynapsis, and formation of polycomplex-like aggregates in male meiosis of Pales ferruginea (diptera,tipulidae)

Meiotic prophase in Pales ferruginea spermatocytes was studied by means of 3D electron microscopical reconstruction. Chromosomes in early prophase nuclei from freshly hatched IVth instar larvae were found to be partially synapsed at several sites along the genome. The synaptic regions are distributed more or less homogeneously throughout the nucleus, i.e., they are not preferentially located. The average lengths of the synaptic regions (length of synaptonemal complex fragments, SC) were 0.62, 0.73, 0.86, and 1.0 m in four different nuclei. Unpaired axial cores were not observed, neither in nuclei with partially synapsed chromosomes nor in nuclei devoid of SC fragments. — Chromosomes in diplotene nuclei from 7–8 days old IVth instar larvae were also found to be partially synapsed, revealing SC fragments with average lengths of 1.6 and 1.95 m in two nuclei analysed. The longest SC fragments observed in diplotene were 3–6.5 m. Diplotene SCs show signs of disintegration. Unpaired axial cores do not occur. The number and the average length of SC fragments decreases towards early diakinesis. During this stage the formation of polycomplex-like aggregates (PC) begins. In later diakinesis each nucleus contains one (occasionally two) PC, while SC fragments are absent. — The observations were interpreted as follows: 1. Due to the absence of unpaired cores early prophase in Pales is difficult to relate to the typical stages of lepto- and zygotene as observed in other organisms. Synapsis seems to begin at many sites along the chromosomes. Since zipper-like alignment of cores does not occur, the entire SC structure evidently becomes assembled de novo during synapsis. 2. During desynapsis in diplotene the SCs seem to become gradually distintegrated into molecular subunits up to diakinesis. 3. The integration of SC material into PCs in diakinesis may be understood as a crystallization process from a pool of molecular subunits.     

Meiosis in Mesostoma ehrenbergii ehrenbergii (Turbellaria,Rhabdocoela)

At metaphase I during spermatogenesis in Mesostoma ehrenbergii ehrenbergii (2 × = 10), 3 bivalents and 4 univalents form. The bivalents each have a single distally localised chiasma. Electron microscope serial section reconstructions have shown that 3 short pieces of synaptonemal complex (SC) are present in pachytene nuclei in the testis. All the SC is contained in a lobe which is separated by an invagination from the main body of the nucleus. The SC pieces vary in length from approximately 2 m to 5 m, and the greatest amount found in one nucleus was approximately 13 m. It is proposed that the pieces of SC correspond to the paired regions of the 3 bivalents present at metaphase I. This system is therefore an example of localised pairing leading to localised chiasmata. Later prophase stage nuclei have also been reconstructed, in which stacks of polycomplex are present but no SC has been found. The polycomplex is thought to be an association of discarded SC sub-units.     

The contribution of size-fractionated plankton to biomass and primary production of phytoplankton in saline–alkaline ponds

Primary productivity, biomass and chlorophyll-a of size fractionated phytoplankton (<0.22 m, <3 m, <8 m, <10 m, <40 m, <64 m, <112 m and <200 m) were estimated in 6 ponds and 5 experimental enclosures. The results showed that the planktonic algae less than 10 m are important in the biomass and production of phytoplankton in saline–alkaline ponds. The production of size fractionated phytoplankton corresponding to <112 m, <10 m and <3 m in saline–alkaline ponds were 10.5 ± 6.6 , 8.6 ± 5.4 and 0.33 ± 0.1 mgC l^–1 d^–1, respectively. Mean community respiration rate was 1.80 ± 0.73, 1.69 ± 0.90 and 1.38 ± 1.12 mgC l^–1 d^–1, respectively. The average production of phytoplankton corresponding to micro- (10–112 m), nano- (3–10 m) and pico- (<3 m) were 1.61, 8.30 and 0.33 mgC l^–1 d^–1, respectively. The ratio of those to the total phytoplankton production was 15%, 79% and 3%, respectively. The mean respiration rate of the different size groups was 0.11, 0.31 and 1.38 mgC l^–1 d^–1; the ratio of those to total respiration of phytoplankton was 6%, 17% and 77%, respectively. The production of size-fractionated phytoplankton corresponding to <200 m, <10 m and <3 m in enclosures was 2.19 ± 1.63, 2.08 ± 1.75 and 0.22 ± 0.08 mgC l^–1 d^-1, respectively. Mean community respiration rates were 1.25 ± 1.55, 1.17 ± 1.42 and 0.47 ± 0.32 mgC l^–1 d^–1, respectively. The average production of phytoplankton corresponding to micro- (10–200 m), nano- (3–10 m) and pico- (<3 m) plankton was 0.11, 1.86 and 0.22 mgC l^–1 d^–1, respectively. The ratio of those to the total production of phytoplankton was 5%, 85% and 10%, respectively. The mean respiration rate of different size groups were 0.08, 0.72 and 0.46 mgC l^–1 d^–1, the ratio of those to total respiration of phytoplankton was 6%, 57% and 37%, respectively. The concentrations of chlorophyll-a of the phytoplankton in the corresponding size of micro- (10–112 m), nano- (3–10 m) and pico- (<3 m) plankton in the experimental ponds were 19.3, 98.2 and 11. 9 g l^–1, respectively. The ratio of those to the total chlorophyll-a was 15%, 76% and 9%, respectively. The concentrations of chlorophyll-a of phytoplankton micro- (10–200 m), nano- (3–10 m) and pico- (<3 m) plankton in enclosures were 1.7, 34.3 and 3.0 g l^–1, respectively. The ratio of those to the total chlorophyll-a was 4%, 88% and 8%, respectively.     

Micropropagation and ecorestoration of Vanda spathulata,an exquisite orchid

Node explants collected from flowering plants of Vanda spathulata, an endemic and exquisite orchid of Peninsular India and Sri Lanka, were cultured in Mitra medium with combinations of 4.4–88.8 m 6-benzyl adenine (BA) and 0.0–114.2 m indole-3-acetic acid (IAA). Combinations of 44.4 m BA with 17.1 or 28.5 m IAA and 66.6 mM BA with 28.5 or 40.0 m IAA induced maximum formation of 12.6 and 12.1 shoots / node, respectively, in a 6-month period. Subcultured nodal explants produced maximum of 6.1 shoots at combinations of 22.2–44.4 m 21 BA and 5.7–28.5 m IAA. Rooting of shoots occurred in medium containing 75 g l^–1 banana pulp and 5.7 m IAA within 3–9 weeks. Plantlets of 2–5 cm length possessing two to five roots established easily in community pots at 80–90% rates without hardening. Community potted plants introduced into forest segments at Ponmudi and Palode in Southern Western Ghats of India established at a rate of 50–70%.     

Development of an L6 myoblast in vitro model of moniliformin toxicosis

L6 myoblasts were used as an in vitro model to investigate the role of moniliformin and its interaction with monensin in turkey knockdown syndrome and sudden death syndromes in poultry. Cell viability and microscopic and ultrastructural alterations noted in L6 myoblasts cultured in the presence of moniliformin (0.0–0.3 g/l) were compared to those observed in parallel cultures also containing one of the following compounds: selenium (0–0.004 ng/l), thiamine (0–0.3 g/l), or pyruvate (0–0.46 g/l). Marked dilation of the RER, membranous whorls, glycogen deposition, membrane-bound cytoplasmic inclusions and necrosis were observed in myoblasts exposed to 0.03/2-0.30 g moniliformin/l medium. Supplementation of medium with thiamine and pyruvate, or selenium, provided significant protection to cells exposed to 0.0–0.3 g/l or 0.0–0.15 g moniliformin/l, respectively. Dose-dependent differences in protein and ATP production were not detected. Myoblasts grown in medium containing 0–0.15 g moniliformin/l and 7.5–50.0 M A23187, beauvericin or monensin had degrees of cytotoxicity similar to parallel cultures receiving only an ionophore. L6 myoblasts were a useful model of moniliformin toxicosis. The findings of this study suggest cytotoxicity due to moniliformin in L6 myoblasts may be due in part to oxidative damage and altered pyruvate metabolism, and that moniliformin does not predispose myoblasts to ionophore toxicosis. This study supports the results of in vivo investigations in poultry that moniliformin and monensin do not act synergistically to induce knockdown or monensin toxicosis.     

Cox-2 is needed but not sufficient for apoptosis induced by Cox-2 selective inhibitors in colon cancer cells

The role of Cox-2 in NSAID-induced apoptosis is debated. We studied the role of Cox-2 inhibition in apoptosis induced by a selective Cox-2 inhibitor, SC236 (a structural analogue of celecoxib) in two colon cancer cell lines, HT29 (expressing Cox-2 protein) and HCT116 (not expressing Cox-2 protein). Apoptosis was quantified by flow cytometry. SC236 0–75 M decreased cell numbers and induced apoptosis to identical levels in HT29 and HCT116 cells. However, SC236, concentrations >75 M reduced Cox-2 protein expression in HT29 cells and induced greater levels of apoptosis in HT29 than in HCT116 cells. In contrast, sulindac sulfide (SSD) (which inhibits Cox-1 and Cox-2) 0–200 M or sulindac sulfone (SSN) 0–500 M (without significant activity against Cox-1 or Cox-2) caused identical decreases in cell number and increases in apoptosis in HT29 and HCT116 cells. Neither SSD nor SSN altered the expression of Cox-2 in HT29 cells. To determine that the higher levels of apoptosis in HT29 cells with SC236 >75 M were related to decreased Cox-2 protein levels, we decreased Cox-2 protein expression in HT29 cells with curcumin (diferuloylmethane) and studied its effect on SC236-induced apoptosis. Curcumin augmented apoptosis induced by SC236 in HT29 cells but not in Cox-2 lacking HCT116 cells. In conclusion, selective Cox-2 inhibitors can induce apoptosis independent of Cox-2 expression. However they may selectively target cells that express Cox-2 by decreasing their Cox-2 protein expression.     

Polytene chromosome structure at the submicroscopic level

Nuclear DNA obtained by SDS treatment or phenol extraction of isolated polytene salivary gland nuclei of D. melanogaster and D. hydei was investigated electron-microscopically. All preparations contained only linear doublestranded DNA filaments of various length. The mean length of a sample of 52 DNA filaments of D. melanogaster produced by SDS treatment was 37.3 . For D. hydei a mean length of 24.2 was established on account of a sample of 51 filaments obtained by SDS treatment. In samples obtained by phenol extraction a mean length of 23.8 (26 filaments) was found. Pronase digestion following SDS treatment gave a mean length of 29.1 for D. melanogaster (46 filaments) and of 17.1 for D. hydei (57 filaments). — The mean length of DNA filaments from D. hydei sperm was 21.5 on the basis of 25 filaments measured. The length distribution of the DNA of the samples of filaments measured varied. Preparations of single-stranded DNA obtained by heat denaturation of samples of D. hydei nuclear DNA revealed very long filaments. An obvious increase in the number of filaments shorter than 30 as compared with double-stranded DNA could not be established.     

Development of the synaptonemal complex and the “recombination nodules” during meiotic prophase in the seven bivalents of the fungus Sordaria macrospora Auersw

Complete reconstruction of seven leptotene, six zygotene, three pachytene and three diplotene nuclei has permitted to follow the pairing process in the Ascomycete Sordaria macrospora. The seven bivalents in Sordaria can be identified by their length. The lateral components of the synaptonemal complexes (SC) are formed just after karyogamy but are discontinuous at early leptotene. Their ends are evenly distributed on the nuclear envelope. The homologous chromosomes alignment occurs at late leptotene before SC formation. The precise pairing starts when a distance of 200–300 nm is reached. Each bivalent has several independent central component initiation sites with preferentially pairing starting near the nuclear envelope. These sites are located in a constant position along the different bivalents in the 6 observed nuclei. The seven bivalents are not synchronous either in the process of alignment or in SC formation: the small chromosomes are paired first. At pachytene the SC is completed in each of the 7 bivalents. Six bivalents have one fixed and one randomly attached telomeres. The fixed end of the nucleolar organizer is the nucleolus anchored end. At diffuse stage and diplotene, only small stretches of the SC are preserved. The lateral components increase in length is approximately 34% between leptotene and pachytene. Their lengths remain constant during pachytene. From zygotene to diplotene the central components contain local thickenings (nodules). At late zygotene and pachytene each bivalent has 1 to 4 nodules and the location of at least one is constant. The total number of nodules remains constant from pachytene to diplotene and is equal to the mean total number of chiasmata. The observations provide additional insight into meiotic processes such as chromosome movements, initiation and development of the pairing sites during zygotene, the existence of fixed telomeres, the variations in SC length. The correspondence between nodules and chiasmata are discussed.     

Regeneration of plants from callus and embryos of ‘Royal’ apricot

Immature embryos of apricot (Prunus armeniaca L.) cv. Royal with a PF index of 25–100 were used to regenerate plants in vitro using two methods. In the first case, callus was initiated on MS medium with 4.5 M 2, 4-D plus 0.44 M BA and regeneration of shoots from the callus occurred on MS medium with 4.4 M BA plus 1.0 M 2, 4-D. In the second case, adventitious buds were directly regenerated from the cotyledons on MS medium with 4.4 M BA plus 1.0 M 2, 4-D.Abbreviations BA 6-benzyladenine - IBA dole-3-butyric acid - NAA -naphthylacetic acid - 2, 4-D 2, 4-dichlorophenoxyacetic acid - PF (embryo length/seed length) x 100     

Procedures for the axenic isolation of conchocelis and monospores from the red seaweed Porphyra yezoensis

In order to maintain axenic seedstock cultures axenically of thecommercially important red seaweed, Porphyra yezoensis, aprocedure was developed for axenic isolation and culture of conchocelis andmonospores. For axenic isolation of the conchocelis, contaminated microalgaewere most effectively removed by filtering contaminated samples through a100-m mesh after sonication. Removal of bacteria and otheralgaewas accomplished using a mixture of 5 agents (0.02% chitosan, 100 gml^–1 GeO₂, 10 gml^–1 ampicillin, 40 gml^–1 kanamycin and 200 gml^–1 streptomycin). Axenic single colonies wereisolatedfrom a semi-solid medium prepared from 1% transfer gel. After collectingmonospores from the 40–50% density layer on a percoll-gradient, removalofbacteria and fungi from the monospores was accomplished using a mixture of 5antibiotics (3.5 g ml^–1 nystatin, 2 mgml^–1 ampicillin, 400 gml^–1 kanamycin, 50 gml^–1 neomycin and 800 gml^–1 streptomycin). Axenic single juvenile blades wereisolated from a semi-solid medium prepared from 0.5% transfer gel.