Results
Chlorophyll accumulation in cucumber plants in the presence or
absence of ABA
Fig. 1 shows cucumber plants grown in the presence or absence
of ABA under sufficient-N or low-N conditions at 30 d after ABA
treatment. There was little effect on the leaf color between the
control and ABA-applied cucumber plants under sufficient-N conditions.
The cucumber plants grown in the ABA-free medium
turned yellow under low-N conditions, while the plants grown in
the medium containing ABA remained green in a dose-dependent
manner even under same conditions (Fig. 1). The levels of chlorophyll
in the cotyledons and first and second leaves of cucumber
plants grown in the presence or absence of ABA under sufficient-
N or low-N conditions were determined at 10, 20, and 30 d after
treatment. The levels of chlorophyll a and b in the cotyledons and
leaves increased slightly with the application of ABA compared
with the controls under sufficient-N conditions (Fig. 2A), while it
increased significantly with the application of ABA compared with
the controls under low-N conditions (Fig. 2B). There was almost no
difference in the level of chlorophyll in the cotyledons and leaves
when ABA 10−5M was applied at different growth periods, and
the degradation of chlorophyll a and b in the leaves was inhibited
by the application of ABA in a dose-response manner under low-
N conditions. The ratio of chlorophyll a to b in cucumber plants
grown in ABA-free medium decreased according to the cultivation
period, while the ratio in plants treated with ABA was higher even
at 30 d after treatment under low-N conditions. There was only
a slight difference between the control and ABA-applied plants
under sufficient-N conditions. We also observed that chlorophyll
b was significantly more stable in ABA-treated plants under low-N
conditions.