In this study, the Na+ accumulation pattern and salt tolerance of
the root was independent of the grafting process itself and scion,
indicating the importance of the selection and breeding of pumpkin
rootstock with high capacity to accumulate Na+ in the root
and decreased Na+ transport to the shoot. Similar results were also
obtained from experiments involving roses (Wahome et al., 2001)
and citrus rootstocks (Fernández-Ballester et al., 2003). In addition,
the salt-tolerant characteristic of pumpkin remained unchanged
regardless of the rootstock used. The pumpkin grafted onto cucumber
plants stored much Na+ in the stem, whereas the self-grafted
cucumber plants stored much Na+ in the leaf (data not shown).
The decreased Na+ transport from rootstock to scion, which is
required for cucumber salt tolerance, is primarily driven by the
pumpkin rootstock. In fact, the cucumber part of grafted cucumber
was not exposed to real high salt concentrations. In a recent study,
Stegemann and Bock (2009) reported that plant grafting can result
in the exchange of genetic information via either large DNA pieces
or entire plastid genomes. However, gene transfer is restricted to
the contact zone between scion and rootstock. Thus, the use of
rootstock cannot change the sensitivity of scion itself to salt stress.