Swards of cocksfoot (cvs KM2, Lutetia) and perennial ryegrass (cvs
Aurora, Vigor) were grown under full
irrigation or severe (80 d) drought in a field experiment in the South
of France. Responses of the bases of immature
leaves plus enclosed tissues were made during the drought period and after
rewatering.
By the end of the drought, water content had fallen from 3·0
to
0·8 gwater g−1dm, and osmotic
potential from −1·0
to −4·5 MPa in all cvs. Measured minerals and water-soluble
carbohydrates contributed, respectively, c 19 and
44% to osmotic potential in droughted leaf bases. The drought-sensitive
cocksfoot cv. Lutetia was characterized
by a large proportion of fructans having a low degree of polymerization
(DP=3, 4). As drought progressed,
accumulation of dehydrin transcripts and ABA were higher in leaf bases
of the sensitive cv. Lutetia than in the
resistant cv. KM2.
After rewatering, the water status of immature leaf bases returned to
control levels in 1–2 d, and then increased
further as leaves began to grow and new tissue was produced. High-DP-fructans
remained unchanged in leaf bases
of ‘Lutetia’ but were depleted by over 55%, and therefore remobilized,
in leaf bases of other cvs after 8 d.
It is concluded that enclosed immature leaf bases survive drought by tolerating
a low water status and that
changes conventionally associated with desiccation tolerance are expressed
most strongly in susceptible plants least
able to maintain their water supply.