Molecular evidence for repeated hybridization events involved in the origin of the genus × Crepidiastrixeris (Asteraceae) using RAPDs and ITS data

We investigated the hybrid origin of × Crepidiastrixeris denticulato-platyphylla using RAPDs and ITS sequence data. The putative parents Paraixeris denticulata and Crepidiastrum platyphyllum represent separate species, irrespective of geographical origin. The occurrence of species specific RAPD markers from P. denticulata and C. platyphyllum in × C. denticulato-platyphylla established unambiguously a hybrid origin between the two taxa. This was in line with the occurrence of a combination of morphological characters such as plant habit and floret numbers. The parent taxa differed from each other by 7 nucleotide substitutions and 2 indel events in the ITS region. The hybrids showed sequence additivity and most likely represent F₁ plants, with the exception of two plants which were of possible F₂ origin, possessing either the ITS sequences of one parent only, or one predominant ITS type. The hybrids occurred in two out of three localities where the parents occurred sympatrically. This fact, together with the short life-span of the plants, suggests that × C. denticulato-platyphylla exists as a result of repeated, frequent hybridization between the parent species.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 151 , 333–343.     

Abnormal Limb Regeneration without Tumor Production in Adult Newts Directed by Carcinogens, 20-Methylcholanthrene and Benzo (α) pyrene

The effects of potent carcinogens, 20-methylcholanthrene (MC) and benzo(α)pyrene (BP), on limb regeneration were studied in adult newts. A microcrystal of these carcinogens was administered directly to the blastema of forelmibs on day 7 after amputation. The formation of the regeneration cone was delayed and the cone was shifted in abnormal polarity depending upon the site of micro-crystal administration. These carcinogens affected morphogenesis of skeletal structures of regenerating limbs. Subregeneration and superregeneration of either or both carpals and digits, absence of either or both ulna and radius, and accessory limb formation have been recorded as abnormalities caused by these carcinogens. Non-carcinogenic benzocompounds did not show such effects as those of MC and BP. The regeneration blastema of the limb appears to be resistant to carcinogenic effects of the carcinogens used since tumor formation has never been observed in our study so far.     

A UNIQUE JUNCTIONAL STRUCTURE FOUND IN BLASTULA CELLS OF THE NEWT, TRITURUS PYRRHOGASTER

The outermost cell layer of the animal half of the newt blastula ( Triturus pyrrhogaster ) was examined to investigate intercellular junctions by transmission and scanning electron microscopy. A unique structure is observed at the terminal region of the intercellular junction. The structures are cytoplasmic ridges elevated from the cell surfaces, and their inner part is filled with spaces of various sizes. It is supposed that these ridges result from the encounter of cytoplasmic folds protruding from two neighboring cells.
Below the ridges, there is a short close junctional area which is followed by a long region of intercellular space intermittently bridged by cytoplasmic projections. Microvillus-like cytoplasmic processes on the apical cell surfaces, and microfilaments and microtubules in subsurface regions are observed in this material as in many other embryonic cells of amphibians.     

Accumulation of Annulate Lamellae in the Subcortical Layer during Progesterone-induced Oocyte Maturation in Xenopus Laevis

Changes in the fine structure, the location and the number of stacks of annulate lamellae during progesterone-induced maturation of oocytes of Xenopus were determined by electron microscopy. longitudinal sections of full-grown oocytes, about 260 stacks of annulate lamellae were observed with marked concentration in the subcortical layer, particularly in the vegetal hemisphere. After exposure to. progesterone, annulate lamellae increased and accumulated further in the subcortical layer. A significant increase of annulate lamellae around the vegetal side of the germinal vesicle seen 3 h after progesterone application. In oocytes 6 h after progesterone application, an average of 320 stacks of annulate lamellae were seen in longitudinal sections and more than two-thirds of the pore complexes of annulate lamellae were localized in the subcortical layer less than 50 from the oocyte surface, the rest being distributed in the deeper ooplasm. At the time of ger- minal vesicle breakdown, all the annulate lamellae underwent complete decomposition. The results were discussed from the view point of comparative developmental biology.     

AN ANALYSIS OF DIFFERENTIATIVE CAPACITY OF PIGMENTED EPITHELIAL CELLS OF ADULT NEWT IRIS IN CLONAL CELL CULTURE

Singly dissociated cells from dorsal and ventral iris epithelia ( iris iridica ) of adult newts were cultured separately at clonal density to analyse their growth and differentiative capacity. Usually some attached cells began to proliferate on 12th day of culture, and grew with loss of melanosomes to form clonal cell colonies. Up to 30 days after inoculation, most of the clonal colonies formed typical epithelial monolayer sheets which consisted mostly of nonpigmented cells. Then, in some of those colonies, cells piled up together and form typical lens structures containing lens antigens. A month and a half after culturing, 30 to 40% of single iris cells, which had been previously marked, grew to form clonal colonies consisting of more than 100 cells. About 30% of these colonies expressed lens specificity and no significant differences in efficiency of colony formation and differentiation were detected between the dorsal cells and the ventral, suggesting that potent cells capable of transdifferentiating into lens cells are evenly distributed in all parts of the newt iris epithelium.     

Rapid synthesis of glutamine during the initial period of ammonia assimilation in roots of barley plants

After 1 hr of ammonia assimilation in barley plants, glutaminecontent in the roots increased 20 fold its original content,whereas contents of glutamic and aspartic acid decreased toa remarkable extent. These findings indicate a rapid synthesisof glutamine during the initial period of ammonia assimilationin roots. Results also suggest that glutamine synthesis fromglutamic acid initially occurring in the roots, is a primaryreaction of ammonia assimilation (Received May 11, 1971; )     

Carcinogens on Regeneration

A microcrystal (ca 5 μg) of N -methyl- N '-nitro- N -nitrosoguanidine (MNNG) or 4-nitroquinoline-1-oxide (4NQO) was directly administered to the regeneration blastema on day 7 after amputation of a forelimb in the newt in order to analyze the effect of such potent carcinogenic substances on regeneration cells. Although neither MNNG nor 4NQO arrested regeneration completely, they caused great retardation of the regeneration cone formation followed by various abnormalities in the bony structures. Abnormal regenerants could be classified into the following four categories; (1) complete absence of both ulna and radius; (2) subregeneration or superregeneration of carpals and digits; (3) multiple disorganization of skeletal elements; (4) arrest of regeneration at the stage of regeneration cone. The polarity of regenerants developed after application of MNNG or 4NQO was very often shifted, during which the regeneration cone was always formed from the site where a microcrystal of the carcinogens was administered. The secondary regeneration initiated by reamputation of the regenerating limb, which had received the carcinogens at the early blastema stage, proceeded in the same way as observed in the case of a simple amputation. This suggested local and temporal effects of the carcinogens applied. Nevertheless, tumor formation has not induced in the newt limb so far. We can learn from these data that both MNNG and 4NQO only alter behaviour of the newt regeneration cells without excerting their carcinogenic effects on them, and that the newt cells are highly resistant and stable against the above-mentioned carcinogens.     

Regeneration of the Cornea in Adult Newts: Overall Process and Behavior of Epithelial Cells

Regeneration of the cornea in adult newts was studied by means of light- and electron-microscopic techniques. We focused our analysis particularly on the behavior of epithelial cells during the initial process of wound healing after we had excised a central disk about 0.5 mm in diameter through the entire thickness of the cornea. Fine fibrous material, assumed to be fibrin, appeared within 30 min to form an acellular layer of mucous consistency which sealed the wound opening completely. The cut edge of corneal epithelium moved centripetally on this layer by coordinate movement of individual epithelial cells. Almost all cells of the remained epithelium were completely rearranged within 5 h after excision. Some desmosomes among the epithelial cells persisted during the process of cellular rearrangement. Thus, the wound opening was covered completely within 24 h by the epithelium alone without cell proliferation. Cytochalasin B or D completely inhibited movement of the corneal epithelium on the stroma in conditions in vitro, suggesting active participation of intracellular contractile microfilaments in such movement of the epithelium. Active growth of cells in the epithelium started on day 3 and the epithelium recovered its normal thickness by day 10 after excision.
After the recovery of the epithelium, keratocytes moved out from the wounded edge of the remained corneal stroma. These keratocytes actively proliferated in the wound area under the newly formed epithelium and participated in the stromal reconstitution, which proceeded gradually for more than 5 weeks.