Accumulation of conjugated forms of ABA during occurred drought
and was not influenced by inhibiting phloem transport
In both species foliage ABA conjugate levels increased as drought
progressed to a maximum 10 d after peak ABA levels were measured in
leaves and when foliage ABA levels were a minimum (Figure 4). In the
angiosperm species U. californica mean foliage ABA conjugate
levels increased in both intact and girdled branches similarly from 0.2
to 2.63 µg g-1 FW prior to drought to when ABA levels
were the lowest at the end of the drought period (Figure 1 and Figure
4). Similar patterns in foliage ABA conjugate level during drought were
observed in the conifer species C. rhomboidea , increasing to a
much higher level than U. californica , from 1.5 to 23 µg
g-1 FW (Figure 4). Girdling branches and ceasing
phloem transport had no effect on the average foliage ABA level dynamics
during drought in either species (Figure 5), or on foliage ABA conjugate
levels (Figure 4). In the angiosperm species U. californica the
mean generalized additive models fitted through foliage ABA data as
Ψl declined was slightly higher over the
Ψl period at which there was a peak in foliage ABA
levels, however foliage ABA levels did decline to levels measured in
unstressed leaves once plants had reached a Ψl of -6 MPa
(Figure 5A). Mean ABA levels in girdled branches of C. rhomboideaincreased from 0.2 ± 0.1 µg g-1 FW at -0.59 MPa to
0.775 ± 0.084 µg g-1 FW at -3.16 MPa (Figure 5), this
was similar to levels of ABA in un-girdled branches (t-test, p =
0.3937).