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DEVELOPMENT OF FOLIAR DIAPHRAGMS IN SPARGANIUM EURYCARPUM
Abstract
Three types of diaphragms are produced in regular sequence by the basal intercalary meristem in the leaf of Sparganium eurycarpum Engelm. (Sparganiaceae). They bridge compartments formed by the collapse and disintegration of rib meristem derivatives. The adaptive nature of diaphragms, intercalary meristems, and linear photosynthetic organs is considered for emergent aquatic plants.
Multidisciplinary analyses on ancient dental calculus revealed the possibility to reconstruct habits and diet of ancient human populations, investigate individual health status, as well as provide information on past environments. In the present study we applied both metagenomic and microscopic analysis on ancient human dental calculus in order to obtain a cross-section of the life conditions in a population of central Italy belonging to the Copper Age culture of Rinaldone (IV millennium BCE). The metagenomic profile suggested an agricultural subsistence and a dietary regimen particularly enriched in complex carbohydrates with low soluble fiber. Even bacterial functional profile seems to indicate an almost exclusive carbohydrates intake that could have favoured the occurrence of nutritional stress in the individuals. Exploring the diversity of the plant food consumed, we detected direct evidence of cereals such as wheat and/or barley, and found signals of the use of leaf vegetables, thus providing additional information on human/environment relationship. The presence of oral pathogens, even if at low abundance (<0.1%), can be related to the high consumption of carbohydrates and finds correspondence with the palaeopathological evidence. In conclusion, starting from very minute amounts of ancient dental calculus, our molecular and microscopic analysis jointly provided complementary data in support of past life condition reconstruction in ancient human populations.
Classification and phylogeny of the Nymphaeaceae are unresolved. This study provides floral anatomical data that will assist in elucidating generic interrelationships and systematic relationships to other taxa of angiosperms. The floral anatomy of Ondinea purpurea den Hartog subsp. purpurea has been examined utilizing light microscopy. The peduncle possesses stelar vascular bundle complexes and cortical vascular bundles. Cortical bundles terminate within the peduncle. Each bundle complex consists of 2 collateral bundles on the same radius, the inner bundle inverted; 2 protoxylary lacunae occur yet differ in structure and function. Progressing acropetally, the inner xylary lacunae become discrete mesarch strands surrounded centrifugally by a vascular cylinder formed by divisions and anastomosing of the bundle complexes. Together these become the massive receptacular vascular plexus. The plexus provides collateral traces to the floral organs. Each sepal receives 3 traces that separate from the plexus as 1–3 lateral traces. Petals are absent and no vestigial petal traces have been observed. Distally, the plexus forms several large strands of connate gynoecial and androecial traces termed the principal vascular bundles (PVBs). Ventral veins separate from the PVBs and the latter extend acropetally through the outer ovary wall. Branches of the ventrals and PVBs contribute to septal vascular reticula from which each ovule is supplied by one vascular bundle. Each stamen receives 1 trace from branches of the PVBs. The ventrals and PVBs terminate within the carpellary lobes. A comparative anatomical study is offered that supports the inclusion of Ondinea in the Nymphaeaceae sensu stricto.
Aerenchyma gas spaces are important for plants that survive flooding because these spaces provide an internal pathway for oxygen transport to the root zone. The objective of this study was to characterize the development of aerenchyma gas spaces in Sagittaria lancifolia L., a dominant species in freshwater wetlands adjacent to the Gulf of Mexico. Tissue at different developmental stages was collected from hydroponically grown plants, embedded in plastic, and sections were observed with a light microscope. In S. lancifolia roots, lysigeny (cell lysis) produced gas spaces that increased in volume from the root meristem to the most mature root tissue. Shoot aerenchyma occurred in the large petioles of S. lancifolia and through the blade midrib, but not in the laminar portion of the blade. In contrast to the roots, gas spaces in the petiole were formed by schizogeny (cell separation during development). Shoot initials produced cells that formed interlocking cylinders in the cortex and diaphragm cells that bridged the central portion of the cylinders. Division and expansion of both these cell types increased the diameter of the cylinders and created schizogenous gaps between diaphragm layers that produced large gas spaces in mature tissue. Therefore, aerenchyma development occurs by two different processes in S. lancifolia.
Morphogenetic pulsations in the intercalary meristem of the leaf of Typha latifolia (Typhaceae) produce regular alternating sequences of vascular and stellate-celled diaphragms separated at first by rib-meristem derivatives. The collapse of these derivatives in the region of elongation in and above the intercalary meristem, and the separation of the diaphragms from each other, produce a mature compartmentalized leaf, the compartments bridged by porous diaphragms but separated from each other by rigid vascularized partitions.
ContentsI Introduction II Schizogenous aerenchyma formation III Lysigenous aerenchyma formation IV Regulators of lysigenous aerenchyma formationV Key questions in lysigenous aerenchyma formation VI Sensing hypoxia; early events in aerenchyma formation VII Ultrastructural changes associated with lysigenous aerenchyma formation VIII Late events in cell death in aerenchyma formation IX Comparative evidence on programmed cell death in aerenchyma formation X Comparison with other abiotic initiators of cell death in plants XI Acknowledgements XII References SummaryAerenchyma – tissue containing enlarged gas spaces – occurs in many plants. It is formed either as part of normal development, or in response to stress (e.g. hypoxia). Two mechanisms of aerenchyma formation have been described; schizogeny, in which development results in the cell separation and lysigeny, in which cells die to create the gas space. While schizogenous aerenchyma provides a fascinating system for study and has been described in detail at a morphological and ultrastructural level, little is known about the molecular genetics of its formation. The ultrastructure and morphology of lysigenous aerenchyma has also been researched in detail, and considerable progress has been made in describing the cell death processes involved, particularly in relation to programmed cell death. Once again, the molecular genetics of the process are not well understood. Aerenchyma is of great importance in crop survival in waterlogging. It is also important in being a major pathway for the release of the global warming gas methane to the atmosphere in flooded soils. Understanding the regulation of its development is therefore a research priority.
The robust emergent leaves of Sparganium eurycarpum and S. americanum are supported by corner fiber masses and large bundle sheaths, but the thin floating leaves of S. fluctuans and S. minimum have only moderate bundle sheaths. In emergent types heavily photosynthetic diaphragms bearing vascular bundles are separated from each other in the leaf compartments by three lightly photosynthetic diaphragms without bundles, but in floating types only every other heavily photosynthetic diaphragm has a bundle. Palisade chlorenchyma occurs only at aerial surfaces—abaxial and adaxial in emergent leaves, but only adaxial in floating leaves. Extra photosynthetic areas are provided in emergent leaves by concentrations of chlorenchyma in limited areas on interior partitioning walls, while the remainder of the walls is translucent. Since only 25 % of the diaphragms are heavily photosynthetic, and the others essentially transparent because of their diffusely distributed chloroplasts and large intercellular spaces, a sieve effect exists which allows even the interior parts of thick emergent leaves to photosynthesize.
After the short-lived apical meristem ceases activity, a basal intercalary meristem produces all new tissues in the aerial internode of Scirpus validus Vahl. These include extensions of the original vascular system and of the original partitioning walls as well as new vascular bundles and new walls which are produced in a predictable pattern. Diaphragms begin to differentiate well within the intercalary meristem. At first their cells are indistinguishable from those that will become the aerenchyma, but they undergo segmentation and form packets of daughter cells. Such continued mitotic activity allows the diaphragms to expand with the increasing girth of the stem above the intercalary meristem. Aerenchyma cells between the diaphragms become stellate by being stretched as the cells of the vertical partitions divide and enlarge in and above the intercalary meristem.
A B S T R A C T The robust emergent leaves of Sparganium eurycarpum and S. americanum are supported by corner fiber masses and large bundle sheaths, but the thin floating leaves of S. fluctuans and S. minimum have only moderate bundle sheaths. In emergent types heavily photosynthetic diaphragms bearing vascular bundles are separated from each other in the leaf compartments by three lightly photosynthetic diaphragms without bundles, but in floating types only every other heavily photosynthetic diaphragm has a bundle. Palisade chlorenchyma occurs only at aerial surfaces-abaxial and adaxial in emergent leaves, but only adaxial in floating leaves. Extra photosynthetic areas are provided in emergent leaves by concentrations of chlorenchyma in limited areas on interior partitioning walls, while the remainder of the walls is translucent. Since only 25 % of the diaphragms are heavily photosynthetic, and the others essentially transparent because of their diffusely distributed chloroplasts and large intercellular spaces, a sieve effect exists which allows even the interior parts of thick emergent
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