title: Methyl jasmonate is a more effective senescence-promoting factor in Cucurbita pepo (zucchini) cotyledons when compared with darkness at the early stage of senescence.
abstract: The effects of short-term darkening and methyl jasmonate (MeJA) on cotyledon senescence were studied 24h after transfer of intact 7-day-old Cucurbita pepo (zucchini) seedlings to darkness or spraying with 100 microM MeJA. The jasmonate inhibitory effect on chlorophyll content and chloroplast transcriptional activity was stronger compared with darkness. Further, MeJA reduced the photosynthetic rate whereas darkness did not affect photosynthesis. Neither stress factor affected the photochemical quantum efficiency of photosystem II (PSII) estimated by the variable fluorescence (F(v))/maximal fluorescence (F(m)) ratio, suggesting the existence of mechanisms protecting the functional activity of PSII at earlier stages of senescence, thus making this parameter more stable compared to others used to quantify senescence. Both stress factors caused a decrease in the content of physiologically active cytokinins, especially trans-zeatin (Z), with the jasmonate effect being much more pronounced when compared to darkness. Our results indicate that MeJA is a more potent inducer of senescence in zucchini cotyledons, at least within the relatively short period of the 24h treatment. This is likely due to its stronger down-regulatory effect on the levels of physiologically active cytokinins.
authors.affiliation: Acad M Popov Institute of Plant Physiology, Acad G Bonchev Str, Bl 21, Sofia, Bulgaria.
authors.forename: Kalina
authors.initials: K
authors.lastname: Ananieva
authors.forename: Evgueni D
authors.initials: ED
authors.lastname: Ananiev
authors.forename: Kiril
authors.initials: K
authors.lastname: Mishev
authors.forename: Katya
authors.initials: K
authors.lastname: Georgieva
authors.forename: Jiri
authors.initials: J
authors.lastname: Malbeck
authors.forename: Miroslav
authors.initials: M
authors.lastname: Kamínek
authors.forename: Johannes
authors.initials: J
authors.lastname: Van Staden
mesh_terms: D000085:Acetates / Q000378:metabolism / Q000494:pharmacology*; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism; D018548:Cotyledon / Q000187:drug effects* / Q000254:growth & development; D028464:Cucurbita / Q000187:drug effects* / Q000254:growth & development; D003517:Cyclopentanes / Q000378:metabolism / Q000494:pharmacology*; D003583:Cytokinins / Q000378:metabolism; D003624:Darkness; D018506:Gene Expression Regulation, Plant; D054883:Oxylipins; D010788:Photosynthesis / Q000502:physiology; D045332:Photosystem II Protein Complex / Q000378:metabolism; D013997:Time Factors; D014158:Transcription, Genetic
chemical_list: D000085:Acetates; D003517:Cyclopentanes; D003583:Cytokinins; D054883:Oxylipins; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; C072239:methyl jasmonate