ABA catabolism to phaseic acid requires rehydration for activation
The rewatering of drought stressed plants activated the catabolism of ABA to PA (Figure 3). In the angiosperm species U. californicarewatering whole plants from a Ψl of -6 MPa, when foliage ABA levels were the lowest of the entire drought period, resulted in a reduction in foliage ABA levels over four days from 1.62 ±0.35 µg g-1 FW to 0.297 ±0.025 µg g-1 FW (Figure 3). This reduction in foliage ABA levels in U. californica corresponded to an increase in foliage PA levels from 0.42 ±0.08 µg g-1 FW to 1.08 ±0.076 µg g-1 FW in the 24 h after rewatering (Figure 3). In the conifer species C. rhomboidea rewatering whole plants from a similar initial Ψl at the angiosperm U. californica restored water status and also drove a decline in foliage ABA levels from 0.54 ±0.15 µg g-1 FW to 0.16 ±0.03 µg g-1 FW in 48 h (Figure 3). Like in the angiosperm species, PA levels in C. rhomboidea increased from 0.057 ±0.03 µg g-1 FW to 0.4 ±0.13 µg g-1 FW (Figure 3).