title: Senescence progression in a single darkened cotyledon depends on the light status of the other cotyledon in Cucurbita pepo (zucchini) seedlings: potential involvement of cytokinins and cytokinin oxidase/dehydrogenase activity.
abstract: Darkness mediates different senescence-related responses depending on the targeting of dark treatment (whole plants or individual leaves) and on the organs that perceive the signal (leaves or cotyledons). As no data are available on the potential role of darkness to promote senescence when applied to individual cotyledons, we have investigated how darkness affects the progression of senescence in either a single or both individually darkened cotyledons of young 10-day-old Cucurbita pepo (zucchini) seedlings. Strong acceleration of senescence was observed when both cotyledons were darkened as judged by the damage in their anatomical structure, deterioration of chloroplast ultrastructure in parallel with decreased photosynthetic rate and photochemical quantum efficiency of PSII. In addition, the endogenous levels of cytokinins (CKs) and IAA were strongly reduced. In a single individually darkened cotyledon, the structure and function of the photosynthetic apparatus as well as the contents of endogenous CKs and IAA were much less affected by darkness, thus suggesting inhibitory effect of the illuminated cotyledon on the senescence of the darkened one. Apparently, the effect of darkness to accelerate/delay senescence in a single darkened cotyledon depends on the light status of the other cotyledon from the pair. The close positive correlation between CK content and the activity of CK oxidase/dehydrogenase (CKX; EC 1.4.3.18/1.5.99.12) suggested that CKX was essentially involved in the mechanisms of downregulation of endogenous CK levels. Our results indicated that CKX-regulated CK signaling could be a possible regulatory mechanism controlling senescence in individually darkened cotyledons.
authors.affiliation: Acad. M. Popov Institute of Plant Physiology, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., Bl. 21, Sofia 1113, Bulgaria.
authors.forename: Kalina
authors.initials: K
authors.lastname: Ananieva
authors.forename: Evguéni D
authors.initials: ED
authors.lastname: Ananiev
authors.forename: Snejana
authors.initials: S
authors.lastname: Doncheva
authors.forename: Katya
authors.initials: K
authors.lastname: Georgieva
authors.forename: Nikolina
authors.initials: N
authors.lastname: Tzvetkova
authors.forename: Miroslav
authors.initials: M
authors.lastname: Kamínek
authors.forename: Václav
authors.initials: V
authors.lastname: Motyka
authors.forename: Petre
authors.initials: P
authors.lastname: Dobrev
authors.forename: Silvia
authors.initials: S
authors.lastname: Gajdosová
authors.forename: Jiri
authors.initials: J
authors.lastname: Malbeck
mesh_terms: D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000648:ultrastructure; D018548:Cotyledon / Q000166:cytology / Q000378:metabolism*; D028464:Cucurbita / Q000378:metabolism*; D003583:Cytokinins / Q000378:metabolism*; D003624:Darkness; D007210:Indoleacetic Acids / Q000378:metabolism; D046529:Microscopy, Electron, Transmission; D010088:Oxidoreductases / Q000378:metabolism*; D010788:Photosynthesis; D045332:Photosystem II Protein Complex / Q000378:metabolism
chemical_list: D003583:Cytokinins; D007210:Indoleacetic Acids; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D010088:Oxidoreductases; C019984:cytokinin oxidase