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.