Cytokinin

Cytokininer (CK) er en klasse af plantehormoner, der fremmer celledeling, eller cytokinesis, i planterødder og skud. Cytokininer er primært involveret i cellevækst og differentiering, men påvirker også apikal dominans, aksillær knopvækst og ælde (engelsk: senescence).

Der findes to typer af cytokininer: adenin-type cytokininer repræsenteret ved kinetin, zeatin og 6-benzylaminopurin, og phenylurinstof-type cytokininer som diphenylurinstof og thidiazuron (TDZ) ^[1]. De fleste adenin-type cytokininer syntetiseres i rødder ^[2], men inderbark (kambium) og andre aktivt delende væv syntetiserer også cytokininer ^[3]. Der er ikke fundet phenylurinstofcytokininer i planter ^[4]. Cytokininer deltager i lokal- og langdistancesignalering med samme transportmekanisme som puriner og nukleosider ^[5]. Typisk transporteres cytokininer i xylem ^[2].

Cytokininer virker sammen med auxin, et andet plantevæksthormon. De to er komplementære ^[6] ^[7], men med generelt modsatrettede effekter ^[2].

Virkning

Cytokininsignalering i planter medieres af et to-komponent phosphorelay. Denne vej (engelsk: pathway) initieres af cytokininbinding til en histidinkinase-receptor i membranen af det endoplasmatiske reticulum. Dette resulterer i autophosphorylering af receptoren, hvor phosphatet derefter overføres til et phosphotransferprotein. Phosphotransferproteinerne kan derefter fosforylere type-B-responsregulatorerne (RR), som er en familie af transkriptionsfaktorer. De phosphorylerede, og dermed aktiverede, type-B RR'er regulerer transkriptionen af adskillige gener, herunder type-A RR'erne. Type-A RR'erne regulerer pathwayen negativt ^[8].

Denne artikel er helt eller delvist baseret på materiale fra den engelsksprogede Wikipedia.

Kilder og henvisninger

^ Aina O, Quesenberry K, Gallo M (2012). "Thidiazuron-Induced Tissue Culture Regeneration from Quartered-Seed Explants of Arachis paraguariensis". Crop Science. 52 (3): 555. doi:10.2135/cropsci2011.07.0367. S2CID 82510749.
^ ^a ^b ^c Campbell NA, Reece JB, Urry LA, Cain ML, Wasserman SA, Minorsky PV, Jackson RB (2008). Biology (8th udgave). San Francisco: Pearson, Benjamin Cummings. s. 827–30. ISBN 978-0-555-03883-3.
^ Chen CM, Ertl JR, Leisner SM, Chang CC (juli 1985). "Localization of cytokinin biosynthetic sites in pea plants and carrot roots". Plant Physiology. 78 (3): 510-513. doi:10.1104/pp.78.3.510. PMC 1064767. PMID 16664274.
^ Mok DW, Mok MC (juni 2001). "Cytokinin Metabolism and Action". Annual Review of Plant Physiology and Plant Molecular Biology. 52 (1): 89-118. doi:10.1146/annurev.arplant.52.1.89. PMID 11337393.
^ Sakakibara H (2006). "Cytokinins: activity, biosynthesis, and translocation". Annual Review of Plant Biology. 57 (1): 431-449. doi:10.1146/annurev.arplant.57.032905.105231. PMID 16669769. S2CID 25584314.
^ Schaller GE, Bishopp A, Kieber JJ (januar 2015). "The yin-yang of hormones: cytokinin and auxin interactions in plant development". The Plant Cell. 27 (1): 44-63. doi:10.1105/tpc.114.133595. PMC 4330578. PMID 25604447.
^ Großkinsky DK, Petrášek J (februar 2019). "Auxins and cytokinins - the dynamic duo of growth-regulating phytohormones heading for new shores". The New Phytologist. 221 (3): 1187-1190. doi:10.1111/nph.15556. PMID 30644580.
^ Hutchison CE, Kieber JJ (2002-01-01). "Cytokinin signaling in Arabidopsis". The Plant Cell. 14 (Suppl): S47-S59. doi:10.1105/tpc.010444. PMC 151247. PMID 12045269.

[1] Aina O, Quesenberry K, Gallo M (2012). "Thidiazuron-Induced Tissue Culture Regeneration from Quartered-Seed Explants of Arachis paraguariensis". Crop Science. 52 (3): 555. doi:10.2135/cropsci2011.07.0367. S2CID 82510749.

[campbell-2] Campbell NA, Reece JB, Urry LA, Cain ML, Wasserman SA, Minorsky PV, Jackson RB (2008). Biology (8th udgave). San Francisco: Pearson, Benjamin Cummings. s. 827–30. ISBN 978-0-555-03883-3.

[3] Chen CM, Ertl JR, Leisner SM, Chang CC (juli 1985). "Localization of cytokinin biosynthetic sites in pea plants and carrot roots". Plant Physiology. 78 (3): 510-513. doi:10.1104/pp.78.3.510. PMC 1064767. PMID 16664274.

[4] Mok DW, Mok MC (juni 2001). "Cytokinin Metabolism and Action". Annual Review of Plant Physiology and Plant Molecular Biology. 52 (1): 89-118. doi:10.1146/annurev.arplant.52.1.89. PMID 11337393.

[5] Sakakibara H (2006). "Cytokinins: activity, biosynthesis, and translocation". Annual Review of Plant Biology. 57 (1): 431-449. doi:10.1146/annurev.arplant.57.032905.105231. PMID 16669769. S2CID 25584314.

[6] Schaller GE, Bishopp A, Kieber JJ (januar 2015). "The yin-yang of hormones: cytokinin and auxin interactions in plant development". The Plant Cell. 27 (1): 44-63. doi:10.1105/tpc.114.133595. PMC 4330578. PMID 25604447.

[7] Großkinsky DK, Petrášek J (februar 2019). "Auxins and cytokinins - the dynamic duo of growth-regulating phytohormones heading for new shores". The New Phytologist. 221 (3): 1187-1190. doi:10.1111/nph.15556. PMID 30644580.

[8] Hutchison CE, Kieber JJ (2002-01-01). "Cytokinin signaling in Arabidopsis". The Plant Cell. 14 (Suppl): S47-S59. doi:10.1105/tpc.010444. PMC 151247. PMID 12045269.

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