Constitutive gibberellin response in grafted tomato modulates root-to-shoot signaling under drought stress.

Plants are sessile organisms that must perceive and respond to various environmental constraints throughout their life cycle. Among these constraints, drought stress has become the main limiting factor to crop production around the world. Water deprivation is perceived primarily by the roots, which efficiently signal the shoot to trigger drought responses in order to maximize a plant's ability to survive. In this study, the tomato (Solanum lycopersicum L.) mutant procera (pro), with a constitutive response to gibberellin (GA), and its near isogenic line cv. Micro-Tom (MT), were used in reciprocal grafting under well-watered and water stress conditions to evaluate the role of GA signaling in root-to-shoot communication during drought stress. Growth, oxidative stress, gene expression, water relations and hormonal content were measured in order to provide insights into GA-mediated adjustments to water stress. All graft combinations with pro (i.e. pro/pro, MT/pro and pro/MT) prevented the reduction of growth under stress conditions without a reduction in oxidative stress. The increase of oxidative stress was followed by upregulation of SlDREB2, a drought-tolerance related gene, in all drought-stressed plants. Scions harboring the pro mutation tended to increase the abscisic acid (ABA) content, independent of the rootstock. Moreover, the GA sensitivity of the rootstock modulated stomatal conductance and water use efficiency under drought stress, indicating GA and ABA crosstalk in the adjustment of growth and water economy.

Cadmium stress antioxidant responses and root-to-shoot communication in grafted tomato plants.

Many aspects related to ROS modulation of signaling networks and biological processes that control stress responses still remain unanswered. For this purpose, the grafting technique may be a powerful tool to investigate stress signaling and specific responses between plant organs during stress. In order to gain new insights on the modulation of antioxidant stress responses mechanisms, gas-exchange measurements, lipid peroxidation, H2O2 content, proline, superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), ascorbate peroxidase (APX) and guaiacol peroxidase (GPOX) were analyzed in Micro-Tom grafted plants submitted to cadmium (Cd). The results observed revealed that higher amounts of Cd accumulated mainly in the roots and rootstocks when compared to leaves and scions. Macronutrients uptake (Ca, S, P and Mg) decreased in non-grafted plants, but differed among plant parts in all grafted plants. The results showed that the accumulation of proline observed in scions of grafted plants could be associated to the lower MDA contents in the scions of grafted plants. In the presence of Cd, non-grafted plants displayed increased CAT, GR, GPOX and APX activities for both tissues, whilst grafted plants revealed distinct trends that clearly indicate signaling responses from the rootstocks, allowing sufficient time to activate defense mechanisms in shoot. The information available concerning plants subjected to grafting can provide a better understanding of the mechanisms of Cd detoxification involving root-to-shoot signaling, opening new possibilities on strategies which can be used to manipulate heavy metal tolerance, since antioxidant systems are directly involved in such mechanism.