Strigolactones and karrikins modulate osmotic rearrangements in response to drought in tomato plants

Solanum lycopersicum is one of the economically most important crop in the Mediterranean basin. During the last decades, increasing drought events severely affect final yields in terms of quantity and quality. The VEG-ADAPT project aims to individuate new strategies to help plants coping with abiotic stresses, such as drought. In order to investigate hormone-based mechanisms involved in stress responses, we sprayed the canopy of tomato plants with four different hormones and hormone-like compounds, respectively abscisic acid (ABA), gibberellins (GA3), strigolactones (the artificial homologous GR24) and karrikins. Each group of ten treated plants was divided into two subgroups, five plants were exposed to moderate water stress (Ψw = -0.9 Mpa), while the remaining five were irrigated up to field capacity for the whole experimental trial. When plants reached the stress level, we re-watered them up to field capacity to fulfill recovery. Physiological parameters (water potential, stomatal conductance) were monitored during whole experiment. Treatments affected stomatal behavior under stress condition and during the following recovery. Samples collected in the final stage of the experiment (after recovery fulfillment) showed significant changes in the osmolarity values, total soluble sugar and proline contents in both leaves and roots. During our project, we used plants belonging to the wild genotype M82 and to the mutant line ccd7, strigolactones deficient. Mutant plants responded differently to drought and to the treatments. Our study will provide useful results and insights for unrevealing the role of hormone cross-talk in conferring an increased tolerance towards water stress in tomato.