Salinization of water and soil has a negative impact on tomato (Solanum lycopersicum L.) productivity by reducing growth of sink organs and by inducing senescence in source leaves. It has been hypothesized that yield stability implies the maintenance or increase of sink activity in the reproductive structures, thus contributing to the transport of assimilates from the source leaves through changes in sucrolytic enzymes and their regulation by phytohormones. In this study, classical and functional physiological approaches have been integrated to study the influence of metabolic and hormonal factors on tomato fruit sink activity, growth, and yield: (i) exogenous hormones were applied to plants, and (ii) transgenic plants overexpressing the cell wall invertase (cwInv) gene CIN1 in the fruits and de novo cytokinin (CK) biosynthesis gene IPT in the roots were constructed. Although salinity reduces fruit growth, sink activity, and trans-zeatin (tZ) concentrations, it increases the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) during the actively growing period (25 days after anthesis). Indeed, exogenous application of the CK analogue kinetin to salinized actively growing fruits recovered sucrolytic activities (mainly cwInv and sucrose synthase), sink strength, and fruit weight, whereas the ethylene-releasing compound ethephon had a negative effect in equivalent non-stressed fruits. Fruit yield was increased by both the constitutive expression of CIN1 in the fruits (up to 4-fold) or IPT in the root (up to 30%), owing to an increase in the fruit number (lower flower abortion) and in fruit weight. This is possibly related to a recovery of sink activity in reproductive tissues due to both (i) increase in sucrolytic activities (cwInv, sucrose synthase, and vacuolar and cytoplasmic invertases) and tZ concentration, and (ii) a decrease in the ACC levels and the activity of the invertase inhibitor. This study provides new functional evidences about the role of metabolic and hormonal inter-regulation of local sink processes in controlling tomato fruit sink activity, growth, and yield under salinity.

Department of Plant Nutrition CEBAS CSIC Campus de Espinardo 30100 Murcia Spain

Department of Plant Nutrition CEBAS CSIC Campus de Espinardo 30100 Murcia Spain Institute of Plant Sciences Department of Plant Physiology University of Graz 8010 Graz Austria

Institute of Plant Sciences Department of Plant Physiology University of Graz 8010 Graz Austria Department of Plant and Environmental Sciences Copenhagen Plant Science Centre University of Copenhagen Højbakkegård Allé 13 DK 2630 Taastrup Denmark

Institute of Plant Sciences Department of Plant Physiology University of Graz 8010 Graz Austria Department of Plant and Environmental Sciences Copenhagen Plant Science Centre University of Copenhagen Højbakkegård Allé 13 DK 2630 Taastrup Denmark Global Change Research Centre Czech Globe AS CR v v i Drásov 470 Cz 664 24 Drásov Czech Republic

Instituto de Bioquímica Vegetal y Fotosíntesis Universidad de Sevilla CSIC 41092 Sevilla Spain

Molecular Plant Pathology Laboratory USDA ARS Beltsville MD 20705 USA

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