Due to the delayed and somewhat abnormal embryo and seed development of the 3n line, we were able to collect samples only at 14, 24, and 35
DAP (ovules) and 35 DAP and 56 DAP (embryos).
The concentration of ABA in 3n ZE was
more than double than that in the respective 2n
ZE (Fig. 4 vs. Fig. 3). However, it should be noted
that ZE of the 2n line were much more advanced
in development when compared with 3n and data
based on the chronology (DAP) of 2n and of 3n
ZE did not relate to the same growth stages. In
vivo, 2n zygotic embryos of cucumber were morphologically
completed 21 DAP (Fig. 1A) while
ZE of the 3n line were not fully developed even 35
DAP (Fig. 1B). Moreover, the concentration of
ABA in the 2n ZE on 35 DAP was already
decreasing (11 days after the peak, Fig. 3). Despite
this, if ABA is compared on a per embryo basis its
content in 2n ZE was higher than that in 3n ZE
(Table 1). In the case of ovules both the concentration
and content of ABA were always higher in
the 2n line than in the 3n (Table 1). On the other
hand, however, the concentration of ABA in the
ovary tissues of this 3n line at 35 DAP was 170%
higher (0.639 mg g1 FW) than that of the 2n line.
These data show that the level of ABA both in the
ZE and ovules of the triploid line are much lower
than in the diploid line. Since this coincides with
the period of delay and abnormalities observed
during both the ZE and seed development of the
3n line [16], it might partially be due to the low
level of ABA. It has been shown for many species
that a high level of ABA is required for proper
embryo formation, as well as, for the ‘switch on’
from the middle to late embryogenesis programme
that includes acquisition of tissue tolerance to
desiccation, and the accumulation of oil and
protein bodies and storage compounds [3].
If it is assumed that ovary tissue is a source of
ABA for the embryo, and that a high level of
ABA is required for proper embryo development
the higher concentration of ABA in the ovary
tissue of the 3n than that of the 2n (as recorded at
35 DAP) may indirectly suggest that transport of
ABA in the 3n line is slower and:or delayed
leading to the discrepancies in embryo and seed
development observed when compared with the 2n
line.