Naturwissenschaften 6: 145–146, Komor E, Liegl I and Schobert C (1993) Loading and translocation of various cytokinins in phloem and xylem of seedlings of Ricinus communis L. Planta 191: 252–255, Kriedemann PE, Loveys BR, Possingham J and Satoh M (1976) Sink effects on stomatal physiology and photosynthesis. The translocation of assimilates. Phloem transport: flow from source to sink. Planta 132: 43–51, King RW and Zeevaart JAD (1974) Enhancement of phloem exudation from cut petioles bh chelating agents. In xylem vessels water travels by bulk flow rather than cell diffusion. There are important exceptions, however, such as self-contained portal circulations in which blood is directed to a specific area. The pressure flow hypothesis, also known as the mass flow hypothesis, is the best-supported theory to explain the movement of sap through the phloem. Please check your email for instructions on resetting your password. Phloem: Phloem is the other complex tissue found in plants, involved in the transportation of food and mineral from leaves to the growing and storing parts of the plant. Who girdled a tree, ringing the outer and inner bark in 1671 for a study. The nitrogen and sugar composition of ingested phloem sap and excreted honeydew. Tharandter Forstl Jahrb 88: 1017–1050, Hussain A, Forest JMS and Dixon AFG (1973) Changes in growth regulator content of radish seedlings, Raphanus sativus, infected with the aphid Myzus persicae. 9.2.U3 Active transport is used to load organic compounds into phloem sieve tubes at the source. Plant Physiol 76: 301–306, Setter TL, Brun WA and Brenner ML (1981) Abscisic acid translocation and metabolism in soybeans following depodding and petiole girding treatments. Radiotracer studies in which leaves are briefly exposed to 14 C-labeled carbon dioxide show that radioactive photosynthates are localized in the phloem. Phloem transport rates may be measured by pulse labeling of CO 2 and tracking the respiration stream (Högberg et al. British Society for Plant Growth Regulation, Bristol, Munns R and King RW (1988) Abscisic acid is not the only stomatal inhibitor in the transpiration stream of wheat plants. STUDY. Planta 86: 272–276, Wright STC and Hiron RWP (1969) (+)-Abscisic acid, the growth inhibitor induced in detached wheat leaves by a period of wilting. Why is phloem transport difficult to study? Gravity. In: Bopp M (ed) Plant Growth Substances 1985, pp. Plant Physiol 53: 96–103, Kluge M, Reinhard E and Ziegler H (1964) Gibberellin-aktivität von siebröhrensäften. Curr Trends Plant Biochem Physiol 8: 268, Wright STC (1969) An increase in the ‘Inhibitor-ß’ content of detached wheat leaves following a period of wilting. While an active transport inhibitor did not affect the phloem translocation of the hormone, it did cause a reduction of its uptake in leaf veins (Goldsmith et al., 1974). High concentrations of solutes in the phloem at the source lead to water uptake by osmosis. While these lipid-protein mechanisms are key to mammalian development and health, their possible importance in plants is virtually unexplored. of America, Boyce Thompson Institute, Ithaca, NY, pp 210–211, Hoad GV, Retamales JA and Whiteside RJ (1991) Identification of gibberellins in the phloem of higher plants. Bundesforschungsanstalt für Rebenzüchtung Geilweilerhof. Animals, especially chordates, have a much larger number. Ann Rev Entomol 8: 439–490, Article  Therefore, large structural investments in the xylem that improve its transport capacity reduce the need to invest in phloem structure (Hölttä et al . What does phloem transport? Plasmodesmal widening accompanies the short-term increase in symplasmic phloem unloading in pea root tips under osmotic stress. Academia Praha, Barlow CA and McCully ME (1972) The ruby laser instrument for cutting the stylets of feeding aphids. Raised hydrostatic pressure causes the contents of the phloem to flow towards sinks. Nature 224: 719, Zeevaat JAD (1977) Sites of abscisic acid synthesis and metabolism in Ricinus communis. Active and passive transport of auxin in relation to the phloem might cooperate. Thus, the typical direction of transport is downward from the primary source (leaves) to the major sink (roots). Sucrose is transported by the vascular tissue phloem from a source to a sink. 2009). Mechanism of Phloem Transport: The mechanism of long-distance transport through the sieve tube is soundly based on the internal organization of sieve tubes, without which it remains speculative. This is maintained by various plant hormonal mechanisms inside the plant. Learn more about Institutional subscriptions, Allen JRF and Baker DA (1980) Free tryptophan and indole-3-acetic acid in the leaves and vascular pathways of Ricinus communis. Phloem transport: flow from source to sink. The phloem and xylem … The phloem tissue in plants transports food materials from the leaves to different parts of the plant. Planta 120: 229–243, Phillips DA and Cleland CF (1972) Cytokoinin activity in the phloem sap of Xanthium strumarium L. Planta 102: 173–178, Purse J (1984) Phloem exudate of Perilla crispa and its effects on flowering of Perilla crispa shoot explants. Let us learn a bit more about phloem transport. Over 80 years ago, Ernest Münch (1930) proposed the now widely accepted mechanism for phl… Ann Appl Biol 75: 275–284, Hussain A, Forest JMS and Dixon AFG (1974) Sugars, organic acids, phenolic acids and plant growth regulator content of the honeydew of the aphid Myzus persicae and of its host plant Raphanus sativus. Academic Press, NY, King RW (1982) Abscisic acid in developing wheat grains and its relation to grain growth and maturation. In 1671 for a study leaves and honeydew of Salix babylonica ( 1976 ) on! 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