Potted 1·5-year-old apricot plants (Prunus armeniaca L.), growing under polycarbonate glasshouse
conditions with a cooling system, were subjected to two successive water stress/recovery periods until
pre-dawn leaf water potential (Ψpd) reached values between −2·0 and −2·5 MPa, during summer
1996. Control plants were irrigated daily to maintain the soil matric potential at c. −20 kPa. Water
stress limited plant growth and induced a significant reduction in leaf area, caused by mature leaf
abscission. The parallel behaviour of leaf turgor potential and epinasty in stressed plants indicated
that these movements are turgor-dependent. Osmotic adjustments of 0·27 and 0·60 MPa were
observed at the end of the first and second stress period, respectively. Relative apoplastic water
content (RWCa) values were high, ranging from 27 to 42%, and were not affected by water stress.
The rapid decrease in leaf conductance (gl) from the beginning of the stress periods, together with the
delay in stomatal reopening after rewatering the plants, indicated that stomatal behaviour was not
a simple passive response to water deficits. Net photosynthesis decreased only at the end of both stress
periods and recovered quickly. These observations indicate that leaf productivity may be affected
only slightly by short-term water stress. The results indicate that drought resistance in apricot is based
mainly on avoidance mechanisms, such as stomatal control, epinasty and limitation of transpiration
by reducing leaf area. However, some tolerance characteristics, including osmotic adjustment, high
RWC a and low leaf osmotic potential at turgor loss point (Ψtlp) values were observed.