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Phloem (/ ˈ f l oʊ. əm /, FLOH-əm) is the living tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as photosynthates, in particular the sugar sucrose, [1] to the rest of the plant. This transport process is called translocation. [2]
The phloem sugar is consumed by cellular respiration or converted into starch, which is insoluble and exerts no osmotic effect. With much of the sucrose having been removed, the water exits the phloem by osmosis or is drawn by transpiration into nearby xylem vessels, lowering the turgor pressure within the phloem. [4]
There are four primary patterns to the arrangement of protoxylem and metaxylem in stems and roots. Centrarch refers to the case in which the primary xylem forms a single cylinder in the center of the stem and develops from the center outwards. The protoxylem is thus found in the central core, and the metaxylem is in a cylinder around it. [45]
Sugars are conveyed throughout the plant in the phloem; water and other nutrients pass through the xylem. Conduction occurs from a source to a sink for each separate nutrient. Sugars are produced in the leaves (a source) by photosynthesis and transported to the growing shoots and roots (sinks) for use in growth, cellular respiration or storage.
Cross section of celery stalk, showing vascular bundles, which include both phloem and xylem Detail of the vasculature of a bramble leaf Translocation in vascular plants. Vascular tissue is a complex transporting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and ...
Complex tissues are mainly concerned with the transportation of mineral nutrients, organic solutes (food materials), and water. That's why it is also known as conducting and vascular tissue. The common types of complex permanent tissue are: Xylem (or wood) Phloem (or bast). Xylem and phloem together form vascular bundles.
Phloem loading is the process of loading carbon into the phloem for transport to different 'sinks' in a plant. Sinks include metabolism , growth, storage, and other processes or organs that need carbon solutes to persist.
An example of analysis of phloem through sieve elements was conducted in the study of Arabidopsis leaves. By studying the phloem of the leaves in vivo through laser microscopy and the usage of fluorescent markers (placed in both companion cells and sieve elements), the network of companion cells with the compact sieve tubes was highlighted. The ...