Compact Patches Research Articles

Propagation mechanisms in Agave macroacantha (Agavaceae), a tropical arid‐land succulent rosette

Agave macroacantha can sexually reproduce by seeds and propagate vegetatively by aerial bulbils and ground-level basal shoots and rhizomes. It forms compact patches apparently generated by the multiplication of ground-level offshoots. We experimentally evaluated the establishment and survival of bulbils and seedlings of A. macroacantha in the Tehuacán Valley, Mexico, between 1991 and 1994 and studied comparatively the effectiveness of sexual reproduction against vegetative propagation.Seedlings showed low survival rates. Cohorts placed outside nurse plants died in less than 1 yr, while 1-10% of cohorts under nurse plants survived for more than 2 yr. Herbivores negatively affected seedling survival in non-nursed plots. In rainy years, survival rates increased. Bulbils showed higher survival rates than seedlings.The excavation of rosettes showed that most are derived from vegetative shoots, as indicated by remains of rhizomes in their base. Most rosettes had ground-level vegetative offspring totaling almost three shoots per rosette.In A. macroacantha, the establishment of seedlings and bulbils is a rare event that possibly only occurs under nurse plants in rainy years, while ground-level cloning is highly effective as a propagation mechanism. These results are consistent with the aggregated spatial pattern of the species.

Sequential degradation of proteins from the nuclear envelope during apoptosis.

We have produced new antibodies specific for the integral pore membrane protein POM121. Using these antibodies we show that during apoptosis POM121 becomes proteolytically degraded in a caspase-dependent manner. The POM121 antibodies and antibodies specific for other proteins of the nuclear envelope were used in a comparative study of nuclear apoptosis in staurosporine-treated buffalo rat liver cells. Nuclei from these cells were classified in three different stages of apoptotic progression: stage I, moderately condensed chromatin surrounded by a smooth nuclear periphery; stage II, compact patches of condensed chromatin collapsing against a smooth nuclear periphery; stage III, round compact chromatin bodies surrounded by grape-shaped nuclear periphery. We have performed double labeling immunofluorescence microscopy of individual apoptotic cells and quantitative immunoblotting analysis of total proteins from apoptotic cell cultures. The results showed that degradation of nuclear envelope marker proteins occurred in a specific order. POM121 degradation occurred surprisingly early and was initiated before nucleosomal DNA degradation could be detected using TUNEL assay and completed before clustering of the nuclear pores. POM121 was eliminated significantly more rapid compared with NUP153 (a peripheral protein located in the nucleoplasmic basket of the nuclear pore complex) and lamin B (a component of the nuclear lamina). Disappearance of NUP153 and lamin B was coincident with onset of DNA fragmentation and clustering of nuclear pores. By contrast, the peripheral NPC protein p62 was degraded much later. The results suggest that degradation of POM121 may be an important early step in propagation of nuclear apoptosis.

EFFECT OF ASPIRIN ON THE INDUCTION OF APOPTOSIS IN COLORECTAL ADENOCARCINOMA CELL-LINES

Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit experimental carcinogenesis and their use in humans has been related epidemiologically to a reduced risk of colorectal polyps and cancer, although the mechanism involved is not known. We found that aspirin triggered the death of SW948 human colorectal adenocarcinoma cells through activation of an apoptotic pathway. Exposure of SW480 and SW948 cells to 25 mu M aspirin for 5 h resulted in the detatchment of cells from the monolayer culture at 48 h. SW948 cells with continuous exposure to 25 mu M aspirin exhibited various morphological and biochemical characteristics of apoptosis, including compact patches of condensed nuclear chromatin, and DNA fragmentation. These in vitro data suggest that apoptosis may play a role in the antitumor effect of aspirin and other NSAIDs and that the induction of apoptosis may provide an attractive therapeutic target in colorectal carcinogenesis.

Numerical and experimental study of the interaction between a vortex dipole and a circular cylinder

This paper describes a study of the centred collision between a dipolar vortex and a solid circular cylinder. The flow was analysed experimentally by using dye visualizations and streak photography. Flow characteristics such as vorticity fields and the transport of passive tracers were compared with numerical simulations. Observations revealed that thin layers of vorticity, created at the cylinder wall are advected by the primary dipole halves, which, while rolling up into compact patches, give rise to the formation of two new asymmetric dipoles that move away along curved trajectories. The structure of the vorticity distribution inside the dipole, before and after the collision, has been investigated. Both the numerical and the experimental results indicate that the vorticity patches originating from the original primary dipole approximately preserve their original functional relationship ω=f(ψ), while the secondary vorticity patches show a tendency to organize into structures attaining a similar relationship.

Parkinsonite, (Pb,Mo, □)8O8Cl2, a new mineral from Merehead Quarry, Somerset

AbstractParkinsonite, ideally (Pb,Mo,□)8O8Cl2, is a new mineral from the Merehead Quarry, Cranmore, Somerset, England. It occurs as compact clusters or patches of red to purplish red bladed crystals, which have an adamantine lustre and a perfect {001} cleavage and occupy fractures and cavities in carbonate vughs in veins of manganese and iron oxide and hydroxide minerals. Associated minerals are mendipite, diaboleite, chloroxiphite, wulfenite, cerussite and hydrocerussite. Discrete crystals were not found; intergrown crystalline aggregates are the usual form of occurrence. The maximum grain size is about 300 × 100 µm, but most grains are appreciably smaller. Parkinsonite was synthesized using high purity chemicals. The measured density of the synthetic material is 7.32 g/cm3; the calculated density is 7.39 g/cm3, the difference being due to minor impurity and slight porosity in the synthetic sample. Parkinsonite is translucent. Reflectance spectra were obtained in air and in oil. Refractive indices calculated from these (at 589 nm) are for Ro, 2.58, and Re', 2.42, i.e. uniaxial negative. VHN50 is 113–133 from which the calculated Mobs hardness is 2–2.5.X-ray studies show that parkinsonite is tetragonal with space group I4/mmm, I4̄2m, I4̄m2, I4/mm, or I422 and a 3.9922(3), c 22.514(2) Å. It has a cell volume of 358.82(5) Å3 with Z = 1. The strongest six lines of the X-ray powder diffraction pattern are [d in Å (I) (hkl)] 2.823, 2.813(100) (110,008); 5.63(85) (004); 2.251(33) (116, 0.0.10); 2.988(27) (105); 3.750(15) (006); 1.994(11) (200,118). Averaged electron microprobe analyses give the empirical formula Pb6.34Mo0.89□0.77O8.02Cl1.98 on the basis of 10 atoms [O + Cl]. The name is for Reginald F. D. Parkinson, mineral collector of Somerset, UK, who first found the mineral.

Peripheral maps and synapse elimination in the cerebellum of the rat. II. Representation of peripheral inputs through the climbing fiber pathway in the posterior vermis of X-irradiated adult rats

The present study gives a detailed description of the functional characteristics and of the topographic distribution of responses mediated through the climbing fiber (CF) pathway in the cerebellum of adult rats which have been repeatedly irradiated from birth so that the Purkinje cells (PCs) in the adult remained innervated by several climbing fibers instead of one. Experiments were carried out under urethane anaesthesia. After electrical stimulation of the contralateral snout, the ipsilateral and contralateral hindlimb or forepad, and the tail, CF-EPSPs were recorded from PCs in an area extending 1000 μm laterally to the midline in the vermal part of lobules VII and VIII. The stepwise variation of CF-EPSP amplitude demonstrated the multiple innervation of the PCs by CFs in these animals. The responses of a given PC through separate CFs were analyzed separately and, using precise micromapping techniques and computer analysis, cells were located on the map of the unfolded PC layer. Taking into account the mean latency of the responses and the probability of discharge of the PCs, restricted areas of projection were found for the snout, the forepads and the tail. Zones of short-latency responses formed compact patches of approximately 1 mm 2. Their disposition was very similar to that found in normal rats. The responses evoked through the different CFs converging on a given PC were in general very homogeneous and very similar to those recorded in control rats. There was some overlap of projection zones from tail and snout and from forepads and snout. In this latter case, there was a convergence of several peripheral inputs on some of the PCs tested. No precise projection of the hindlimbs could be detected in the same lobules. These results suggest that, with the type of stimulation used, the representation of peripheral inputs through CF pathway is roughly conserved even though multiple innervation of PCs by CFs is maintained until adulthood.

Peripheral maps and synapse elimination in the cerebellum of the rat.I. Representation of peripheral inputs through the climbing fiber pathway in the posterior vermis of the normal adult rat

The present study gives a detailed description of the functional characteristics and of the topographic distribution of responses, mediated through the climbing fiber pathway and elicited by electrical stimulation of several peripheral inputs, in a circumscribed region of the posterior vermis of the rat cerebellum. Experiments were carried out on normal adult rats under urethane anaesthesia. Purkinje cells (PCs) which responded to the electric stimulation of the contralateral snout, of the ipsilateral and contralateral hindlimb or forepad, and of the tail were recorded in an area extending 1000 μm laterally to the midline in the vermal part of lobules VII and VIII. Using precise micromapping techniques and computer analysis, we located the cells on the map of the unfolded PC layer. Taking into account the mean latency of the responses and the probability of discharge of the PCs, restricted areas of projection were found for the snout, the forepads and the tail. Zones of short-latency responses form compact patches of less than 1 mm 2. There was some overlap of projection zones from tail and snout and from forepads and snout. In these zones, there was a convergence of several peripheral inputs on some of the PCs tested. No precise projection of the hindlimbs could be detected in the same lobules. These results fit well with the hypothesis already proposed that the representation of peripheral inputs through the climbing fiber pathway is fractured into a mosaic of patches, which are partly overlapping, and in which remote parts of the body are represented in adjacent areas.

The morphology and growth of Arctostaphylos uva-ursi (bearberry): an architectural analysis

A study was made of the morphology and architecture of the prostrate ericaceous shrub, Arctostaphylos uva-ursi (L.) Spreng. (bearberry) from a sand-dune area and to a lesser extent a boreal forest area. In the open where more compact patches were recognized, a largely subterranean woody frame was found to support an aerial photosynthetic mat. The mat was made up of shoot complexes defined as consisting of not more than the four youngest annual growth increments or shoots. Two kinds of shoot complexes were recognized: (i) colonizing complexes consisting of a succession of long, low dominant shoots common in the periphal or colonizing zone of a patch and (ii) maintaining complexes consisting of short, essentially upright nondominant shoots and (or) intermediate shoots designated as subdominant, chiefly in the maintaining zone of a patch. Downward reorientation of older shoot increments which were not originally horizontal was recorded. The architecture of colonizing complexes was analysed quantitatively, including such parameters as shoot length, patterns of bud release, and divergence angles of daughter shoots. Several interesting patterns were revealed. The woody frame was analysed architecturally according to such principles as orders of branching, previously applied to trees. It was found to consist essentially of an ordered system of horizontal woody frame units, recognizable segments of the structural framework organized in a much branched hierarchical sequence. Two basic types of frame units were recognized: (i) major units constructed by colonizing complexes and (ii) minor units constructed by maintaining complexes. The initiation of the architectural pattern, including the establishment of original colonizing complexes, was investigated in seedlings. The reestablishment of bearberry following disturbance was also examined.

Early and late DNA replication in respectively condensed and decondensed heterochromatin of Allium carinatum.

The structure and ultrastructure of nuclei in the S period and other phases of the mitotic cell cycle have been studied in semi- and ultrathin sections of root tips ofAllium carinatum. Significant structural differences have been found and classified by means of DNA measurements by scanning photometry of Feulgen-stained squash preparations. In G1 and early S (S1 and S2) the euchromatin forms small, compact and electron-dense patches, while the heterochromatin is condensed into a number of chromocenters of the same electron-density as the euchromatin. In middle S (S3) the euchromatic elements become larger and more thread-like. In late S (S4) the euchromatin appears in the form of thick and uniform strands as in G2, and the heterochromatin decondenses into strands of the same, or a little higher, diameter, as the euchromatin. DNA replication starts in the condensed heterochromatin (S1, becomes shifted to euchromatin (S2), continues over both eu- and heterochromatin during middle S (S3), and is restricted to decondensed heterochromatin in late S (S4). Quantitative data of various nuclear parameters are given for the different stages. The results are discussed in relation to the species-specific nuclear ultrastructure, its molecular basis, and its variation during the mitotic interphase, as well as with respect to the timing and structural expression of DNA replication.