Discussion
Roots sense a complex soil environment and change their architecture and function to optimize resources and restore plant functional equilibrium. Rootstock-specific SlNCED1 overexpression altered root ABA biosynthesis, shoot phenotypes and enhanced stress-tolerance, likely via multiple mechanisms including altered root-to-shoot signalling (Dodd, 2005; Pérez-Alfocea et al . 2010). NCED OE rootstocks increased vegetative and reproductive growth, with enhanced xylem ABA concentrations in flower trusses and ABA catabolites (PA and DPA) in root, xylem sap and leaves (Figure 3) and diminished root system development (Figure 1; Table 1), although changes in root xylem ABA were more evident in younger vegetative stages (Figure S1). Thus root ABA biosynthesis and catabolism is not only enhanced, but ABA is exported to the shoots, although did not accumulate in most tissues analyzed. There are multiple changes in other hormone groups in many different tissues (Figure 4; Table S1), suggesting that SlNCED1 plays a complex role in regulating growth. Thus, it is necessary to understand how NCED OE in the roots alters shoot phenotype through both local and systemic responses affecting root gene expression and root-shoot communication in the plant.