Changes in abscisic acid (ABA) within the embryo (a) and megagametophyte (b) during fluridone/GA treatments. Ungerminated seeds were analyzed before and after a 3-day soak in 100 μM fluridone and/or 50 μM GA and throughout 12 days in germination conditions (15-day total treatment time). Germinated seeds (Germ, bars) were analyzed between 7 and 9 days in germination conditions, as denoted by the double-arrowed line. Data are expressed on a ng per g DW basis and are based on 3 replicate extractions of 20 embryos or 15 megagametophytes each (±SE).
However, ABA levels in the fluridone/GA treatment remained constant
throughout the initial treatment soak in the embryo, and this was
similar to the pattern in the megagametophyte (Figure 2 ).
When seeds were placed in germination conditions, ABA levels in
embryos and megagametophytes in all treatments decreased further
until just prior to the peak in germination (that is, at 3 days in
germination conditions) (Figure 2 ).
After the peak in germination, as seed populations returned to
maintain a “dormant” state, ABA levels in embryo and
megagametophyte tissues increased in all treatments except in those
seeds treated with fluridone (Figure 2 ). .
GA 4+7 treatment of western white pine seeds led to a
more pronounced decrease in ABA levels than did the control
treatment, and its effect on ABA was similar to that elicited by
the fluridone treatment (embryo) and by the fluridone/GA treatment
(megagametophyte) until 3 days into germination conditions
(Figure 2 ).
During days 1–3, a total of 200 ng/g DW was metabolized per day;
during days 3 to 6, the catabolism rate declined to only 50 ng/g DW
per day, and it did not decrease thereafter (Figure 2a ).
Similar trends were revealed in the megagametophyte (Figure
In embryos of germinated seeds, ABA and ABA metabolite levels were
higher in seeds capable of ABA biosynthesis (control and GA) and
virtually nonexistent in germinated seeds that had been treated
with fluridone (Figure 2 and 3 ).
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