Water Use and Drought Response in Cultivated and Wild Apples - Abiotic Stress: Plant Responses and Applications in Agriculture - page 261

Asparagine Synthetase

5

A

4.5

d n

4

3.5

3

2.5

2

e r

1.5

1

0.5

0

con drt

Treatment

ABA Stress Protein

B

5

4.5

e d n

4

3.5

3

2.5

2

1.5

1

0.5

0

con drt

Treatment

Figure 3. Relative expression of bark genes up-regulated by drought treatment. Experiments were conducted as de‐
scribed in Methods. Test transcripts were normalized against Actin. con: well watered controls; drt: treated to 40%
saturation for two weeks. A: relative expression of asparagine synthetase gene; B: relative expression of an ABA stress
protein gene.

GMAL4002.e plants, four began to show signs of severe wilting within a few days after
reaching 40% as illustrated in Figure 7. This is consistent with WUE measurements which
indicated that this particular line was not adept at maintaining healthy water status under the
water deficit regime. Well watered GMAL4002.e controls showed no signs of wilting through‐
out the experiment. In contrast, GMAL3975.k with a WUE close to that of 'Royal Gala' showed
no signs of wilting under the well-watered regime or water deficit stress (Figure 6). These
results indicate that WUE can be used to identify apple lines that are drought sensitive, as well
as drought tolerant.