Xylem Structure and Function
نویسندگان
چکیده
The earliest land plants were short, herbaceous plants that evolved from primitive, water-living ancestors. For these plants, the change from a predominantly aquatic to a terrestrial environment was accompanied by the need for additional structural support to keep the plants upright and the need for more efficient transport of water to the aboveground parts of the plants. Larger plant sizes also increased the need for co-ordination between remote plant parts. The development of specialized vascular tissues to fulfil these requirements played an important role in the evolution and adaptation of plants to the terrestrial environment. As the early land plants filled more and more terrestrial niches, the selective advantage of increased propagule dispersal associated with increase in height, and later competition for sunlight, increased the selection pressure for plants that could grow taller than other plants. The most successful plants were able to support more weight, transport water further and sustain growth for more than one season. The dramatic result of this evolutionary process is evident in the rapid increase of plants with secondary vascular tissues and arborescent growth form in a rather short evolutionary timespan (380–350 million years ago). The stems and roots of modern plants are highly specialized conductive organs that can transport water, nutrients, photosynthetic products and chemical regulatory signals. These organs contain two types of conductive tissue: phloem and xylem. Phloem is the tissue that transports photosynthetic products and plant growth regulators (phytohormones) mainly from the leaves to the rest of the plant. Xylem is the tissue that transports water, mineral nutrients and phytohormones from the roots to the leaves and other plant organs. While herbaceous plants do contain xylem, it is a tissue that is most prominent in woody plants, especially trees. Most of our knowledge of xylem structure and function is based on woody plants. The most important functions of xylem include: (1) transport of water and mineral nutrients, (2) mechanical support and (3) storage of nutrients and water.
منابع مشابه
Structure-function constraints of tracheid-based xylem: a comparison of conifers and ferns.
The ferns comprise one of the most ancient tracheophytic plant lineages, and occupy habitats ranging from tundra to deserts and the equatorial tropics. Like their nearest relatives the conifers, modern ferns possess tracheid-based xylem but the structure-function relationships of fern xylem are poorly understood. Here, we sampled the fronds (megaphylls) of 16 species across the fern phylogeny, ...
متن کاملPhenotypic and developmental plasticity of xylem in hybrid poplar saplings subjected to experimental drought, nitrogen fertilization, and shading
Variation in xylem structure and function has been extensively studied across different species with a wide taxonomic, geographical, and ecological coverage. In contrast, our understanding of how xylem of a single species can adjust to different growing condition remains limited. Here phenotypic and developmental plasticity in xylem traits of hybrid poplar (Populus trichocarpa×deltoides) was st...
متن کاملGetting variable xylem hydraulic resistance under control: interplay of structure and function.
متن کامل
Energy Flow from Root to Shoot: A Comprehensive In silico Analysis
Background: Root to shoot connection and transfer of information seems to be taken place mostly via the transmissions of signal molecules, secondary metabolites, amino acids, hormones and proteins, through xylem sap. Examination of earlier reports is indicative of relatively high levels of conservation in xylem sap protein compositions. Apparently these protein molecules are be...
متن کاملRelationships among xylem transport, biomechanics and storage in stems and roots of nine Rhamnaceae species of the California chaparral.
Here, hypotheses about stem and root xylem structure and function were assessed by analyzing xylem in nine chaparral Rhamnaceae species. Traits characterizing xylem transport efficiency and safety, mechanical strength and storage were analyzed using linear regression, principal components analysis and phylogenetic independent contrasts (PICs). Stems showed a strong, positive correlation between...
متن کاملGene expression patterns underlying changes in xylem structure and function in response to increased nitrogen availability in hybrid poplar.
Nitrogen availability has a strong influence on plant growth and development. In this study, we examined the effect of nitrogen availability on xylogenesis in hybrid poplar (Populus trichocarpa x deltoides H11-11). Saplings of hybrid poplar were fertilized for 33 d with either high or adequate levels of ammonium nitrate. We observed enhanced radial growth, wider vessels and fibres and thinner f...
متن کامل