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).