Relictual vegetative anatomical characters in Cactaceae: the genusPereskia

The genusPereskia, which contains numerous morphological features considered relictual in the Cactaceae, has numerous anatomical features that we consider to be relictual also. These were studied to establish a basis for determining the ways that morphogenic mechanisms and anatomical characters diversified as the family evolved. ThesePereskia features may be relictual in the family: epidermis predominantly unistratose and lacking crystals; hypodermis absent or of about three layers of weakly collenchymatous cells with druses; cortex thin and predominantly parenchyma with druses and mucilage cells but lacking cortical bundles; secondary phloem without early differentiation of sclerenchyma but with secondary sclereids developing later, either idioblastically or in clusters; ergastic substances lacking from old secondary phloem; wood with a matrix of libriform fibers (mostly septate and nucleate), scanty paratracheal parenchyma, vessels solitary or in small clusters, perforations simple, pitting circular, oval or very broad; wide-band tracheids absent; ray cells slightly thick-walled, lignified, upright, isodiametric or procumbent; all primary rays narrow; pith without medullary bundles; leaves lacking hypodermis, with only weak development of palisade mesophyll; veins of four orders, strongly distinct in size, none with fibers; vessels in leaves narrower than those in stems.     

Structural and systematic study of an unusual tracheid type in cacti

Wide-band tracheids are a specialized tracheid type in which an annular or helical secondary wall projects deeply into the cell lumen. They are short, wide and spindle-shaped, and their bandlike secondary walls cover little of the primary wall, leaving most of it available for water diffusion. Wide-band tracheids appear to store and conduct water while preventing the spread of embolisms. They may be the most abundant tracheary element in the xylem, but they are always accompanied by at least a few vessels. Typically, fibers are absent wherever wide-band tracheids are present. Wide-band tracheids occur in the primary and secondary xylem of succulent stems, leaves and roots in genera of all three subfamilies of Cactaceae but were not found in the relictual genusPereskia, which lacks succulent tissues. In the large subfamily Cactoideae, wide-band tracheids occur only in derived members, and wide-band tracheids of North American Cactoideae are narrower and are aligned in a more orderly radial pattern than those of South American Cactoideae. Wide-band tracheids probably arose at least three times in Cactaceae.     

AN INVESTIGATION OF THE MORPHOGENETIC MECHANISMS WHICH CONTROL THE DEVELOPMENT OF ZONATION IN SEEDLING SHOOT APICAL MERISTEMS

The development of zonation in the shoot apical meristems of 28 species of cacti was examined. At germination the embryonic apex may have one of three types of organization: 1) tunica/corpus; 2) tunica/central mother cells/corpus; 3) tunica/central mother cells/peripheral zone/pith-rib meristem. Apices of the third type have complete zonation and undergo little or no further structural development. Both of the other types develop the missing zones. First, the apices become mitotically active, and peripheral zone characters develop in the outer corpus. Simultaneously, or slightly later, the central mother cells differentiate if they are not yet present. The final step is the formation of the pith-rib meristem. The sequence of appearance of the zones was constant throughout all species examined, but the time of appearance of only one zone could be correlated with any other morphogenetic process: the development of peripheral zone characteristics in the outer corpus occurs with or before the beginning of leaf production. The development of zonation appears to be independent of apical size, shape, or age, either real age or plastochron age. This has been interpreted to indicate that the metabolic mechanism controlling the development of zonation in shoot apical meristems is largely autonomous and independent of other aspects of morphogenesis occurring in the seedling. Also, the fact that leaf initiation and shoot axis production can both occur before the development of either the central mother cells or the pith-rib meristem indicates that neither of these zones is essential for these two apical morphogenetic activities.     

Ontogenetic mechanisms and the evolution of Cactaceae

Abstract

The ancestors of cacti were leafy trees that had hard, woody trunks. The development of the cactus body is controlled by ontogenetic mechanisms that have evolved, and now they produce a body that is leafless, succulent and has a photosynthetic cortex. Specific changes include: bark formation is postponed and the epidermis and stomata function for many years; the outer cortex is a palisade cortex with intercellular spaces; there are cortical bundles that resemble leaf veins but which have secondary xylem and phloem. Wood development has changed dramatically such that water storage is maximized (increased ray parenchyma) and danger of water stress is minimized (increased paratracheal parenchyma, loss of fibers). Several genera have polymorphic wood: the plants produce one type of wood for several years, then later they produce a different type. It is possible that the extensive evolutionary changes have resulted from mutations in the controller regions of genes, not in the structural regions.     

Extent and Degree of Shoreline Oiling: Deepwater Horizon Oil Spill,Gulf of Mexico,USA

The oil from the 2010 Deepwater Horizon spill in the Gulf of Mexico was documented by shoreline assessment teams as stranding on 1,773 km of shoreline. Beaches comprised 50.8%, marshes 44.9%, and other shoreline types 4.3% of the oiled shoreline. Shoreline cleanup activities were authorized on 660 km, or 73.3% of oiled beaches and up to 71 km, or 8.9% of oiled marshes and associated habitats. One year after the spill began, oil remained on 847 km; two years later, oil remained on 687 km, though at much lesser degrees of oiling. For example, shorelines characterized as heavily oiled went from a maximum of 360 km, to 22.4 km one year later, and to 6.4 km two years later. Shoreline cleanup has been conducted to meet habitat-specific cleanup endpoints and will continue until all oiled shoreline segments meet endpoints. The entire shoreline cleanup program has been managed under the Shoreline Cleanup Assessment Technique (SCAT) Program, which is a systematic, objective, and inclusive process to collect data on shoreline oiling conditions and support decision making on appropriate cleanup methods and endpoints. It was a particularly valuable and effective process during such a complex spill.     

The Cytolytic Amphipathic β(2,2)-Amino Acid LTX-401 Induces DAMP Release in Melanoma Cells and Causes Complete Regression of B16 Melanoma

In the present study we examined the ability of the amino acid derivative LTX-401 to induce cell death in cancer cell lines, as well as the capacity to induce regression in a murine melanoma model. Mode of action studies in vitro revealed lytic cell death and release of danger-associated molecular pattern molecules, preceded by massive cytoplasmic vacuolization and compromised lysosomes in treated cells. The use of a murine melanoma model demonstrated that the majority of animals treated with intratumoural injections of LTX-401 showed complete and long-lasting remission. Taken together, these results demonstrate the potential of LTX-401 as an immunotherapeutic agent for the treatment of solid tumors.     

CONSTANCY OF RELATIVE VOLUMES OF ZONES IN SHOOT APICAL MERISTEMS IN CACTACEAE: IMPLICATIONS CONCERNING MERISTEM SIZE,SHAPE, AND METABOLISM

The volumes and dimensions of shoot apical meristem zones were determined for 21 species in 10 genera of the Cactaceae. If the volumes of the central-mother-cell zone (CMCZ), the peripheral zone (PZ), and the pith-rib meristem (PRM) are expressed as percentages of the total volume of the corpus, then they are remarkably constant (CMCZ = 11.1% of the volume of the corpus, PZ = 61.2% and PRM = 27.1%) regardless of the relative size of the apical meristems. The relative volume of the tunica decreases, however, as the whole apex increases. The zones have variable shapes, and whereas the PZ and PRM are always trapezoidal in longitudinal section, in apices with large volumes, these zones have a flatter, more flaring shape than they have in smaller apices. Thus large apices are flatter and less hemispherical than are small apices. The CMCZ, however, maintains a constant shape and is always relatively hemispherical regardless of its volume. A hypothesis that relates all of these shape and volume relationships as an integrated growth sequence is proposed.     

AN INVESTIGATION OF THE PHYLOGENETIC AND ONTOGENETIC VARIABILITY OF SHOOT APICAL MERISTEMS IN THE CACTACEAE

The sizes, shapes and zonations of the shoot apical meristems of 22 species of cacti were examined. This family was chosen because of its great diversity of habits; the more primitive members are nonsucculent. leafy trees and more advanced members are highly specialized “leaf-less” stem-succulents. By combining these measurements with those already in the literature, a sample of almost 70 species was obtained. Apical meristems range in size from only 80 μm in diam in some species to as much as 1.500 μm in diam in others. The shape ranges from being flat to almost hemispherical. Despite the great range in size and shape of the apical meristems, or the range in the morphologies of the leaves and stems which are produced by the meristems. all apices had the usual zonation: tunica, central mother cells, peripheral zone, and pith-rib meristem. The sizes of each of the zones. expressed either as the number of cells per zone or expressed as a percentage of the whole apex. were highly variable. The variation in apical dimensions and zone sizes occurred both phylogenetically and ontogenetically. and this has been interpreted to indicate that the morphogenetic mechanisms which control apical size and zonation are easily modified, both during the development of individual plants and during the evolution of new species.     

MEDULLARY BUNDLES AND THE EVOLUTION OF CACTI

Medullary bundles are absent from the pith of the leafy, relictual cacti (genus Pereskia) but are present in most members of subfamily Cactoideae. They are absent only from tribes Hylocereeae, Rhipsalideae, and some members of Cacteae and Notocacteae. Presence of medullary bundles tends to be correlated with presence of a broad pith, but exceptions occur. Most medullary bundles are collateral, and in all genera phloem is produced and accumulates throughout the lifetime of the bundle. Xylem definitely accumulates as medullary bundles age in some groups, but it definitely does not accumulate in others, being produced only while the bundle is young. Pith can be broad (up to 75 mm in diameter), can constitute half the shoot volume, and is long-lived, remaining alive as long as the shoot is alive. Medullary bundles appear to be adaptive in allowing this large pith to be used for storage of water and starch. Medullary bundles have fewer, narrower tracheary elements than does the stele xylem in the same region; medullary bundles probably could not carry out significant longdistance transport if a major part of the stele becomes damaged.     

SCHIZOGENY AND ULTRASTRUCTURE OF DEVELOPING LATEX DUCTS IN MAMMILLARIA GUERRERONIS (CACTACEAE)

The schizo-lysigenous latex ducts of Mammillaria guerreronis, sect. Subhydrochylus, were examined by optical and electron microscopy. These ducts are complex having a distinct outer epithelium without intercellular spaces and an inner epithelium in which schizogenous spaces arise. Schizogeny begins with formation of bulbous pockets and/or production of dark streaks in certain walls. Spaces formed by these processes ultimately contain a combination of electron dense materials, vesicles, and numerous thin, convoluted wall layers. Schizogeny may be responsible for initial formation of lumen and latex and may also separate some inner epithelial cells from the surrounding layers. Lysigeny of the inner epithelial cells contributes materials to the latex and allows enlargement of the duct. The inner epithelial cells contain mitochondria, dictyosomes, apparently functional nuclei, and numerous vesicles. The outer epithelium has fewer vesicles than the inner epithelium. Schizo-lysigeny in the members of sect. Subhydrochylus is considered to be ancestral to the strict lysigeny of the members of sect. Mammillaria. The inner and outer epithelia of M. guerreronis are thought to be homologous to the lumen and epithelium respectively of M. heyderi.