Sap

Sapis afluidtransported inxylemcells (vessel elements or tracheids) orphloem sieve tube elementsof aplant.These cells transport water andnutrientsthroughout the plant.

Sap is distinct fromlatex,resin,orcell sap;it is a separate substance, separately produced, and with different components and functions.

Insect honeydewis called sap, particularly when it falls from trees, but is only the remains of eaten sap and other plant parts.^[1]

Types of sap

Saps may be broadly divided into two types: xylem sap and phloem sap.

Xylem sap

Xylem sap (pronounced/ˈzaɪləm/) consists primarily of a watery solution ofhormones,mineral elementsand othernutrients.Transport of sap in xylem is characterized by movement from therootstoward theleaves.^[2]

Over the past century, there has been some controversy regarding the mechanism of xylem sap transport; today, most plant scientists agree that thecohesion-tension theorybest explains this process, but multiforce theories that hypothesize several alternative mechanisms have been suggested, including longitudinal cellular and xylemosmotic pressure gradients,axial potential gradients in the vessels, and gel- and gas-bubble-supported interfacial gradients.^[3]^[4]

Xylem sap transport can be disrupted bycavitation—an "abrupt phase change [of water] from liquid to vapor"^[5]—resulting in air-filled xylem conduits. In addition to being a fundamental physical limit on tree height, two environmental stresses can disrupt xylem transport by cavitation: increasingly negative xylem pressures associated withwater stress,and freeze-thaw cycles in temperate climates.^[5]

Phloem sap

Phloem sap (pronounced/ˈfloʊɛm/) consists primarily ofsugars,hormones, and mineral elements dissolved in water. It flows from wherecarbohydratesare produced or stored (sugar source) to where they are used (sugar sinks).^{[citation needed]}Thepressure flow hypothesisproposes a mechanism for phloem sap transport,^{[citation needed]}although other hypotheses have been proposed.^[6]Phloem sap is thought to play a role in sending informational signals throughout vascular plants. According toAnnual Review of Plant Biology,

Loading and unloading patterns are largely determined by theconductivityand number ofplasmodesmataand the position-dependent function ofsolute-specific,plasma membrane transport proteins.Recent evidence indicates that mobile proteins andRNAare part of the plant's long-distance communication signaling system. Evidence also exists for the directed transport and sorting ofmacromoleculesas they pass through plasmodesmata.^[6]

Many insects of theorder Hemiptera(the half-wings), feed directly on phloem sap, and make it the primary component of their diet. Phloem sap is "nutrient-rich compared with many other plant products and generally lacking in toxins and feeding deterrents, [yet] it is consumed as the dominant or sole diet by a very restricted range of animals".^[7]This apparent paradox is explained by the fact that phloem sap is physiologically extreme in terms of animal digestion, and it is hypothesized that few animals take direct advantage of this because they lack two adaptations that are necessary to enable direct use by animals. These include the existence of a very high ratio ofnon-essential/essential amino acidsin phloem sap for which these adapted Hemiptera insects containsymbiotic microorganismswhich can then provide them with essential amino acids; and also insect "tolerance of the very high sugar content andosmotic pressureof phloem sap is promoted by their possession in the gut ofsucrase-transglucosidaseactivity, which transforms excess ingested sugar into long-chainoligosaccharides."^[7] A much larger set of animals do however consume phloem sap by proxy, either "through feeding on thehoneydewof phloem-feeding hemipterans. Honeydew is physiologically less extreme than phloem sap, with a higher essential/non-essential amino acid ratio and lower osmotic pressure, "^[7]or by feeding on thebiomassof insects that have grown on more direct ingestion of phloem sap.

Human uses

Maple syrupis made from reducedsugar maplexylem sap.^[8]The sap often is harvested from the sugar maple,Acer saccharum.^[9]

In some countries (e.g.,Lithuania,Latvia,Estonia,Finland,Belarus,Russia) harvesting the early spring sap ofbirchtrees (so called "birch juice") for human consumption is common practice; the sap can be used fresh orfermentedand containsxylitol.^[10]

Certain palm tree sap can be used to makepalm syrup.^{[citation needed]}In theCanary Islandsthey use theCanary Island date palmwhile in Chile they use theChilean wine palmto make their syrup calledmiel de palma.^{[citation needed]}

References

^"How to Remove Tree Sap From a Car".HowStuffWorks.20 August 2019.Retrieved23 December2020.
^Marschner, H (1983). "General Introduction to the Mineral Nutrition of Plants".Inorganic Plant Nutrition.Encyclopedia of Plant Physiology. Vol. 15 A. Springer. pp. 5–60.doi:10.1007/978-3-642-68885-0_2.ISBN 978-3-642-68887-4.
^Zimmerman, Ulrich (2002). "What are the driving forces for water lifting in the xylem conduit?".Physiologia Plantarum.114(3): 327–335.doi:10.1034/j.1399-3054.2002.1140301.x.PMID 12060254.
^Tyree, Melvin T. (1997)."The cohesion-tension theory of sap ascent: current controversies".Journal of Experimental Botany.48(10): 1753–1765.doi:10.1093/jxb/48.10.1753.
^^a ^bSperry, John S.; Nichols, Kirk L.; Sullivan, June E; Eastlack, Sondra E. (1994)."Xylem Embolism in ring-porous, diffuse-porous, and coniferous trees of Northern Utah and Interior Alaska"(PDF).Ecology.75(6): 1736–1752.Bibcode:1994Ecol...75.1736S.doi:10.2307/1939633.JSTOR 1939633.Archived fromthe original(PDF)on 2017-08-10.Retrieved2018-12-18.
^^a ^b Turgeon, Robert; Wolf, Shmuel (2009). "Phloem Transport: Cellular Pathways and Molecular Trafficking".Annual Review of Plant Biology.60(1): 207–21.doi:10.1146/annurev.arplant.043008.092045.PMID 19025382.
^^a ^b ^c Douglas, A.E. (2006)."Phloem-sap feeding by animals: problems and solutions".Journal of Experimental Botany.57(4): 747–754.doi:10.1093/jxb/erj067.PMID 16449374.
^Saupe, Stephen."Plant Physiology".College of Saint Benedict and Saint John's University.Retrieved3 April2018.
^Morselli, Mariafranca; Whalen, M Lynn (1996)."Appendix 2: Maple Chemistry and Quality".In Koelling, Melvin R; Heiligmann, Randall B (eds.).North American Maple Syrup Producers Manual.Bulletin. Vol. 856. Ohio State University. Archived fromthe originalon 29 April 2006.Retrieved20 September2010.
^Suzanne Wetzel; Luc Clement Duchesne; Michael F. Laporte (2006).Bioproducts from Canada's Forests: New Partnerships in the Bioeconomy.Springer. pp. 113–.ISBN 978-1-4020-4992-7.Archivedfrom the original on 23 November 2017.Retrieved6 April2013.

External links

Media related toPlant sapat Wikimedia Commons

[1] "How to Remove Tree Sap From a Car".HowStuffWorks.20 August 2019.Retrieved23 December2020.

[marschner1983-2] Marschner, H (1983). "General Introduction to the Mineral Nutrition of Plants".Inorganic Plant Nutrition.Encyclopedia of Plant Physiology. Vol. 15 A. Springer. pp. 5–60.doi:10.1007/978-3-642-68885-0_2.ISBN 978-3-642-68887-4.

[3] Zimmerman, Ulrich (2002). "What are the driving forces for water lifting in the xylem conduit?".Physiologia Plantarum.114(3): 327–335.doi:10.1034/j.1399-3054.2002.1140301.x.PMID 12060254.

[tyree1997-4] Tyree, Melvin T. (1997)."The cohesion-tension theory of sap ascent: current controversies".Journal of Experimental Botany.48(10): 1753–1765.doi:10.1093/jxb/48.10.1753.

[sperry1994-5] Sperry, John S.; Nichols, Kirk L.; Sullivan, June E; Eastlack, Sondra E. (1994)."Xylem Embolism in ring-porous, diffuse-porous, and coniferous trees of Northern Utah and Interior Alaska"(PDF).Ecology.75(6): 1736–1752.Bibcode:1994Ecol...75.1736S.doi:10.2307/1939633.JSTOR 1939633.Archived fromthe original(PDF)on 2017-08-10.Retrieved2018-12-18.

[turgeon2009-6] Turgeon, Robert; Wolf, Shmuel (2009). "Phloem Transport: Cellular Pathways and Molecular Trafficking".Annual Review of Plant Biology.60(1): 207–21.doi:10.1146/annurev.arplant.043008.092045.PMID 19025382.

[douglas2006-7] Douglas, A.E. (2006)."Phloem-sap feeding by animals: problems and solutions".Journal of Experimental Botany.57(4): 747–754.doi:10.1093/jxb/erj067.PMID 16449374.

[8] Saupe, Stephen."Plant Physiology".College of Saint Benedict and Saint John's University.Retrieved3 April2018.

[morselli-9] Morselli, Mariafranca; Whalen, M Lynn (1996)."Appendix 2: Maple Chemistry and Quality".In Koelling, Melvin R; Heiligmann, Randall B (eds.).North American Maple Syrup Producers Manual.Bulletin. Vol. 856. Ohio State University. Archived fromthe originalon 29 April 2006.Retrieved20 September2010.

[WetzelDuchesne2006-10] Suzanne Wetzel; Luc Clement Duchesne; Michael F. Laporte (2006).Bioproducts from Canada's Forests: New Partnerships in the Bioeconomy.Springer. pp. 113–.ISBN 978-1-4020-4992-7.Archivedfrom the original on 23 November 2017.Retrieved6 April2013.

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