© 2008 The Author(s).
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RESEARCH PAPER |
Hormonal changes in relation to biomass partitioning and shoot growth impairment in salinized tomato (Solanum lycopersicum L.) plants
1Departamento de Nutrición Vegetal, Centro de Edafología y Biología Aplicada del Segura (CEBAS), Consejo Superior de Investigaciones Científicas (CSIC), Campus Universitario de Espinardo, E-30100, Espinardo, Murcia, Spain
2Groupe de Recherche en Physiologie Végétale, Université catholique de Louvain (UCL), Croix du Sud 5, boîte 13, B-1348 Louvain-la-Neuve, Belgium
3Departamento de Biología Vegetal-Fisiología Vegetal, Facultad de Biología, Universidad de Murcia, Campus Universitario de Espinardo, E-30100, Espinardo, Murcia, Spain
4The Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK
To whom correspondence should be addressed: E-mail: alfocea{at}cebas.csic.es
Following exposure to salinity, the root/shoot ratio is increased (an important adaptive response) due to the rapid inhibition of shoot growth (which limits plant productivity) while root growth is maintained. Both processes may be regulated by changes in plant hormone concentrations. Tomato plants (Solanum lycopersicum L. cv Moneymaker) were cultivated hydroponically for 3 weeks under high salinity (100 mM NaCl) and five major plant hormones (abscisic acid, ABA; the cytokinins zeatin, Z, and zeatin-riboside, ZR; the auxin indole-3-acetic acid, IAA; and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid, ACC) were determined weekly in roots, xylem sap, and leaves. Salinity reduced shoot biomass by 50–60% and photosynthetic area by 20–25% both by decreasing leaf expansion and delaying leaf appearance, while root growth was less affected, thus increasing the root/shoot ratio. ABA and ACC concentrations strongly increased in roots, xylem sap, and leaves after 1 d (ABA) and 15 d (ACC) of salinization. By contrast, cytokinins and IAA were differentially affected in roots and shoots. Salinity dramatically decreased the Z+ZR content of the plant, and induced the conversion of ZR into Z, especially in the roots, which accounted for the relative increase of cytokinins in the roots compared to the leaf. IAA concentration was also strongly decreased in the leaves while it accumulated in the roots. Decreased cytokinin content and its transport from the root to the shoot were probably induced by the basipetal transport of auxin from the shoot to the root. The auxin/cytokinin ratio in the leaves and roots may explain both the salinity-induced decrease in shoot vigour (leaf growth and leaf number) and the shift in biomass allocation to the roots, in agreement with changes in the activity of the sink-related enzyme cell wall invertase.
Key words: Abscisic acid, 1-aminocyclopropane-1-carboxylic acid, indole-3-acetic acid, plant hormones, salt stress, sodium chloride, tomato (Solanum lycopersicum L.), zeatin, zeatin-riboside
* AA and MEG contributed equally to this work.
Present address: Department of Horticulture-Seed Biology, Oregon State University, OR 97331, Corvallis, USA.
Received 19 June 2008; Revised 11 September 2008 Accepted 15 September 2008
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