title: Cytokinin delays dark-induced senescence in rice by maintaining the chlorophyll cycle and photosynthetic complexes.
abstract: The phytohormone cytokinin (CK) is known to delay senescence in plants. We studied the effect of a CK analog, 6-benzyl adenine (BA), on rice leaves to understand the possible mechanism by which CK delays senescence in a drought- and heat-tolerant rice cultivar Nagina22 (N22) using dark-induced senescence (DIS) as a surrogate for natural senescence of leaves. Leaves of N22-H-dgl162, a stay-green mutant of N22, and BA-treated N22 showed retention of chlorophyll (Chl) pigments, maintenance of the Chl a/b ratio, and delay in reduction of both photochemical efficiency and rate of oxygen evolution during DIS. HPLC analysis showed accumulation of 7-hydroxymethyl chlorophyll (HmChl) during DIS, and the kinetics of its accumulation correlated with progression of senescence. Transcriptome analysis revealed that several plastid-localized genes, specifically those associated with photosystem II (PSII), showed higher transcript levels in BA-treated N22 and the stay-green mutant leaves compared with naturally senescing N22 leaves. Real-time PCR analyses showed that genes coding for enzymes associated with Chl a/b interconversion and proteins associated with light-harvesting complexes maintained higher transcript levels up to 72h of DIS following BA treatment. The pigment-protein complexes analyzed by green gel remained intact in both N22-H-dgl162 and BA-treated N22 leaves even after 96h of DIS. Thus, CK delays senescence by accumulation of HmChl and up-regulating genes in the Chl cycle, thereby maintaining the Chl a/b ratio. Also, CK treatment retains higher transcript levels of PSII-related genes, resulting in the stability of photosynthetic pigment complexes and functional stay-greenness in rice.
authors.affiliation: Centre for Cellular and Molecular Biology, Hyderabad, India.
authors.forename: Sai Krishna
authors.initials: SK
authors.lastname: Talla
authors.affiliation: Directorate of Rice Research, Rajendra Nagar, Hyderabad, India.
authors.forename: Madhusmita
authors.initials: M
authors.lastname: Panigrahy
authors.affiliation: Centre for Cellular and Molecular Biology, Hyderabad, India.
authors.forename: Saivishnupriya
authors.initials: S
authors.lastname: Kappara
authors.affiliation: Centre for Cellular and Molecular Biology, Hyderabad, India.
authors.forename: P
authors.initials: P
authors.lastname: Nirosha
authors.affiliation: Directorate of Rice Research, Rajendra Nagar, Hyderabad, India.
authors.forename: Sarla
authors.initials: S
authors.lastname: Neelamraju
authors.affiliation: Centre for Cellular and Molecular Biology, Hyderabad, India raji@ccmb.res.in rajeshwari.ramanan@gmail.com.
authors.forename: Rajeshwari
authors.initials: R
authors.lastname: Ramanan
mesh_terms: D002734:Chlorophyll / Q000378:metabolism*; D000077194:Chlorophyll A; D002851:Chromatography, High Pressure Liquid; D003583:Cytokinins / Q000378:metabolism* / Q000494:pharmacology; D003624:Darkness; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D017343:Genes, Plant; D013058:Mass Spectrometry; D053858:Metabolic Networks and Pathways / Q000187:drug effects; D020411:Oligonucleotide Array Sequence Analysis; D012275:Oryza / Q000187:drug effects / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D010788:Photosynthesis / Q000187:drug effects; D018515:Plant Leaves / Q000187:drug effects / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
chemical_list: D003583:Cytokinins; D012333:RNA, Messenger; D002734:Chlorophyll; C037184:chlorophyll b; D000077194:Chlorophyll A
keywords: Chlorophyll cycle; cytokinin; dark-induced senescence; hydroxymethyl chlorophyll; pigment–protein complex; rice; stay green.
references.citation: Planta. 2006 Aug;224(3):700-9
references.pmid: 16506064
references.citation: J Plant Physiol. 2009 Nov 1;166(16):1775-85
references.pmid: 19540618
references.citation: Plant J. 2005 May;42(4):567-85
references.pmid: 15860015
references.citation: J Plant Physiol. 2005 Nov;162(11):1226-36
references.pmid: 16323274
references.citation: Annu Rev Plant Biol. 2003;54:605-27
references.pmid: 14503005
references.citation: J Exp Bot. 2012 May;63(8):2853-72
references.pmid: 22447967
references.citation: J Biol Chem. 1996 Jan 19;271(3):1475-9
references.pmid: 8576141
references.citation: Plant J. 2009 Jan;57(1):120-31
references.pmid: 18778405
references.citation: Proc Natl Acad Sci U S A. 1984 Oct;81(19):5994-8
references.pmid: 6091129
references.citation: Plant Physiol. 2008 Oct;148(2):1082-93
references.pmid: 18715959
references.citation: Plant Cell Physiol. 2011 Dec;52(12):2200-13
references.pmid: 22051886
references.citation: Plant J. 2007 Oct;52(2):197-209
references.pmid: 17714430
references.citation: Plant Mol Biol. 1999 Sep;41(2):181-94
references.pmid: 10579486
references.citation: Biochem Biophys Res Commun. 2013 Jan 4;430(1):32-7
references.pmid: 23200839
references.citation: Annu Rev Plant Biol. 2007;58:321-46
references.pmid: 17227226
references.citation: Phytochemistry. 2004 May;65(9):1231-8
references.pmid: 15184007
references.citation: Plant Physiol. 2012 Apr;158(4):1666-84
references.pmid: 22383541
references.citation: J Integr Plant Biol. 2010 Jul;52(7):653-69
references.pmid: 20590995
references.citation: PLoS One. 2015 Jun 02;10(6):e0127831
references.pmid: 26035591
references.citation: Plant J. 2009 Sep;59(6):940-52
references.pmid: 19453447
references.citation: Plant Cell. 2004 May;16(5):1276-87
references.pmid: 15100396
references.citation: Science. 2007 Jan 5;315(5808):73
references.pmid: 17204643
references.citation: Proc Natl Acad Sci U S A. 2007 Dec 4;104(49):19631-6
references.pmid: 18048328
references.citation: J Plant Physiol. 2007 Dec;164(12):1572-82
references.pmid: 17485137
references.citation: Trends Plant Sci. 2009 Mar;14(3):155-62
references.pmid: 19237309
references.citation: J Exp Bot. 2015 Dec;66(22):7045-59
references.pmid: 26276867
references.citation: Trends Plant Sci. 2003 May;8(5):197-9
references.pmid: 12758033
references.citation: Eur J Biochem. 1994 Jan 15;219(1-2):671-9
references.pmid: 8307032
references.citation: Photosynth Res. 2002;74(2):187-93
references.pmid: 16228557
references.citation: Planta. 2010 Mar;231(4):939-49
references.pmid: 20087600
references.citation: Anal Biochem. 1991 Apr;194(1):214-22
references.pmid: 1867380
references.citation: Plant Cell. 2009 Mar;21(3):767-85
references.pmid: 19304936
references.citation: Annu Rev Plant Biol. 2006;57:55-77
references.pmid: 16669755
references.citation: Planta. 2004 Mar;218(5):886-9
references.pmid: 14652758
references.citation: Theor Appl Genet. 2002 Mar;104(4):526-532
references.pmid: 12582654
references.citation: Plant Cell. 2007 Apr;19(4):1362-75
references.pmid: 17416733
references.citation: Plant Cell Physiol. 2007 Mar;48(3):523-39
references.pmid: 17293362
references.citation: J Exp Bot. 2000 Feb;51 Spec No:329-37
references.pmid: 10938840
references.citation: Biochim Biophys Acta. 2011 Aug;1807(8):968-76
references.pmid: 21216224
references.citation: Plant Cell. 2005 May;17(5):1585-97
references.pmid: 15805480
references.citation: Prikl Biokhim Mikrobiol. 2009 Jul-Aug;45(4):389-402
references.pmid: 19764606
references.citation: Plant Physiol. 2006 Jun;141(2):776-92
references.pmid: 16603661
references.citation: Plant J. 2001 May;26(4):365-73
references.pmid: 11439124
references.citation: Plant Cell Rep. 2009 Nov;28(11):1759-65
references.pmid: 19820948
references.citation: Plant Physiol. 1949 Jan;24(1):1-15
references.pmid: 16654194