3.2. Na+ concentration
The Na+ concentrations of the shoot, root, and xylem sap
in ungrafted and self-grafted cucumber were similar (Table 2,
Figs. 1 and 2). A similar result was also obtained for ungrafted
and self-grafted pumpkin. This result implies that the grafting process
itself did not significantly affect the Na+ concentrations of the
plant tissues and xylem sap in either species. Ungrafted and selfgrafted
cucumber showed consistently higher Na+ concentrations
in the shoot, but lower Na+ concentrations in the root compared
with ungrafted and self-grafted pumpkin (Fig. 1). When the plants
were treated with 91 mM NaCl for 10 or 30 days, the Na+ concentrations
in the cucumber grafted onto pumpkin shoots decreased
by 69% or 71% compared with those of self-grafted cucumber,
whereas compared with self-grafted pumpkin, the Na+ concentrations
in pumpkin grafted onto cucumber shoot increased by 203%
or 501%, respectively (Fig. 1). In addition, the Na+ concentration
in pumpkin grafted onto cucumber shoot was higher than that
of the self-grafted cucumber plants, but this discrepancy did not
decrease the salt tolerance of pumpkin grafted onto cucumber to
a value lower than those of self-grafted cucumber plants (Table 1
and Fig. 1). This result suggests that the pumpkin is still more tolerant
to salt than cucumber, regardless of the rootstock used. The
Na+ concentrations in the root were similar in ungrafted cucumber,
self-grafted cucumber, and pumpkin grafted onto cucumber.
A similar result was obtained in ungrafted and self-grafted pumpkin.
However, the Na+ concentration in the cucumber grafted onto