Growth of individual leaves
Leaves L1 to L15 of well-watered plants unfolded and
expanded in a uniform, sequential pattern (Fig. 3). Water
stress disrupted this pattern such that expansion was nearly
halted during stress. Although it resumed after rewatering,
the development of stressed plants was delayed, and individual
leaf areas at full expansion were less than controls.
The disruption was also apparent in terms of relative expansion
rate (RER), especially during the stress period (Fig. 4).
The impacts of stress on the patterns of growth depended on
the developmental stage at which stress was imposed.
Leaves L1 to L5 (Group 1) had unfolded and entered the
phase of rapid expansion (>5 cm2 d1) when soil water
content approached the stress set point on day 2–3; in
these leaves, stress slowed or halted expansion, and
although it resumed after rewatering, final areas were
17–44 % less than controls (Fig. 3). In leaves L6 to L11
(Group 2), which had not yet begun the final phase of rapid
expansion when the plants first experienced stress (day 3),
the resumed expansion after rewatering approximated to
a sigmoid pattern (Fig. 3), and RER recovered to values
approaching controls (Fig. 4). Nevertheless, leaf expansion
was substantially delayed, and final areas were 14–34%less
than controls. The full expansion of leaves L12 to L15
(Group 3), which were at an early stage when water deficit
was imposed, was delayed by 4–6 d, but final leaf area did
not differ from controls.