title: Involvement of source-sink relationship and hormonal control in the response of Medicago ciliaris - Sinorhizobium medicae symbiosis to salt stress.
abstract: In order to explore the relationship between leaf hormonal status and source-sink relations in the response of symbiotic nitrogen fixation (SNF) to salt stress, three major phytohormones (cytokinins, abscisic acid and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid), sucrose phosphate synthase activity in source leaves and sucrolytic activities in sink organs were analysed in two lines of Medicago ciliaris (salt-tolerant TNC 1.8 and salt-sensitive TNC 11.9). SNF (measured as nitrogenase activity and amount of N-fixed) was more affected by salt treatment in the TNC 11.9 than in TNC 1.8, and this could be explained by a decrease in nodule sucrolytic activities. SNF capacity was reflected in leaf biomass production and in the sink activity under salinity, as suggested by the higher salt-induced decrease in the young leaf sucrolytic activities in the sensitive line TNC 11.9, while they were not affected in the tolerant line TNC 1.8. As a consequence of maintaining sink activities in the actively growing organs, the key enzymatic activity for synthesis of sucrose (sucrose phosphate synthase) was also less affected in the mature leaves of the more tolerant genotype. Ours results showed also that the major hormone factor associated with the relative tolerance of TNC 1.8 was the stimulation of abscisic acid concentration in young leaves under salt treatment. This stimulation may control photosynthetic organ growth and also may contribute to a certain degree in the maintenance of coordinated sink-source relationships. Therefore, ABA may be an important component which conserves sucrose synthesis in source leaves.
authors.affiliation: Laboratoire de Plantes Extrêmophiles, CBBC, BP 901 2050 Hammam-Lif Tunisia. imen_ben_salah@yahoo.fr
authors.forename: Imène
authors.initials: I
authors.lastname: Ben Salah
authors.forename: Nahida
authors.initials: N
authors.lastname: Jelali
authors.forename: T
authors.initials: T
authors.lastname: Slatni
authors.forename: Margaret
authors.initials: M
authors.lastname: Gruber
authors.forename: A
authors.initials: A
authors.lastname: Albacete
authors.forename: Cristina
authors.initials: C
authors.lastname: Martínez Andújar
authors.forename: V
authors.initials: V
authors.lastname: Martinez
authors.forename: F
authors.initials: F
authors.lastname: Pérez-Alfocea
authors.forename: C
authors.initials: C
authors.lastname: Abdelly
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism; D000598:Amino Acids, Cyclic / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D003583:Cytokinins / Q000378:metabolism; D029902:Medicago / Q000187:drug effects* / Q000382:microbiology* / Q000502:physiology; D009586:Nitrogen Fixation / Q000187:drug effects; D010937:Plant Growth Regulators / Q000378:metabolism*; D018515:Plant Leaves / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D020579:Sinorhizobium / Q000187:drug effects* / Q000502:physiology; D012965:Sodium Chloride / Q000494:pharmacology*; D013312:Stress, Physiological / Q000502:physiology*; D013395:Sucrose / Q000378:metabolism; D013559:Symbiosis / Q000187:drug effects*
chemical_list: D000598:Amino Acids, Cyclic; D003583:Cytokinins; D010937:Plant Growth Regulators; D002734:Chlorophyll; C023863:1-aminocyclopropane-1-carboxylic acid; D012965:Sodium Chloride; D013395:Sucrose; D000040:Abscisic Acid