Hormones
Since hormones mediate many physiological changes (Ghanem et al.2008; Albacete et al. 2008a), we profiled several root and shoot
tissues and xylem and phloem exudates of grafted plants and measured
their hormone levels (Figures 3, 4; Table S1).
Generally, NCED OE grafts had relatively few significant effects on ABA
concentration in tissues and transport pathways compared to the WT
rootstock (Figure 3a). Interestingly, the NCED OE rootstocks
significantly increased ABA concentrations in the xylem sap of a
flowering truss 180 days after transplanting, but those differences
decreased during green fruit stage and disappeared at maturity stage.
Moreover, mature fruit (juice) ABA concentration of plants grafted onto
SP12 rootstocks was more than 2-fold higher than in plants grafted on WT
rootstocks. Leaf phloem exudate ABA concentrations decreased in plants
grafted on NCED OE rootstocks (Figure 3a). SP12 rootstocks had higher
root and root xylem sap concentrations of the ABA catabolites phaseic
acid (PA) and dihydrophaseic acid (DPA) respectively, with leaves of
plants grafted on SP12 having higher DPA concentrations (Figure 3b).
Thus, rootstock NCED OE had significant effects on ABA (and metabolites)
concentrations only in some shoot tissues.
Plants grafted onto NCED OE rootstocks had lower total CKs (t -Z
and iP type) in the xylem sap of roots and flowering truss, as well as
in leaf tissue and green fruits mainly due to lower t -Z levels
(Figure 4; Table S1). The different graft combinations had similart -Z and iP concentrations in leaf xylem sap and root tissues.
However, iP type CK concentrations on leaf tissue (130 DST) and leaf
phloem exudate were 5-14-fold higher in plants grafted on NCED OE
rootstocks than on WT rootstocks, with iP the only hormone increasing in
leaf phloem exudate (Figure 4; Table S1). Thus, rootstock NCED OE
significantly affected CK concentrations in root xylem sap and shoot
tissues.
Rootstock genotype also significantly affected auxin (IAA) and ethylene
precursor (ACC) measurements. Leaf phloem exudate and root tissue ACC
concentrations were 3-25 times lower in plants grafted on NCED OE
rootstocks, while they had a higher ACC concentration in xylem sap of a
mature fruit truss (Figure 4; Table S1). Leaf phloem exudate and xylem
of mature fruit truss had up to 6-fold lower IAA concentrations when
grafted on the SP5 rootstock (Figure 4; Table S1), otherwise there were
no significant rootstock impacts on IAA levels. Similar to ABA, xylem
sap of trusses at flowering and green-fruited stages had 7.5 to 4-fold
more GA3 when grafted on NCED OE rootstocks, with these
differences disappearing at fruit maturity (Figure 4). However, leaf
xylem GA3 concentration of plants grafted on NCED OE
rootstocks was 65-80% lower than when grafted on WT rootstock.
Furthermore, root xylem JA concentration of plants grafted on SP5 was
lower, even though plants grafted on NCED OE rootstocks had leaf JA
concentrations that were more than twice that of plants grafted on WT
rootstocks at 80 DST (Table S1); however, these differences disappeared
at 130 DST (Figure 4). No significant rootstock differences in JA
concentrations occurred in other tissues at the time points analyzed
(Figure 4). The NCED OE rootstocks had few significant impacts on SA,
except for 3-10 fold lower concentrations in leaf xylem and phloem
exudates and a similar increase in ripe fruits (Figure 4, Table S1).
Thus, NCED OE rootstocks also occasionally affected tissue and transport
fluid concentrations of other acidic hormones.