Changes in dry matter and water-soluble carbohydrate components, espec
ially fructan, were examined in the basal 25 mm of expanding leaf blad
es of tall fescue (Festuca arundinacea Schreb.) to assess their roles
in plant response to water deficit. Water was withheld from vegetative
plants grown in soil in controlled-environment chambers. As stress pr
ogressed, leaf elongation rate decreased sooner in the light period th
an it did in the dark period. The decrease in growth rate in the dark
period was associated with a decrease in local relative elongation rat
es and a shortening of the elongation zone from about 25 mm (control)
to 15 mm. Dry matter content of the leaf base increased 23% during str
ess, due mainly to increased water-soluble carbohydrate near the ligul
e and to increased water-soluble, carbohydrate-free dry matter at dist
al positions. Sucrose content increased 258% in the leaf base, but esp
ecially (over 4-fold) within 10 mm of the ligule. Hexose content incre
ased 187% in the leaf base. Content of total fructan decreased to 69%
of control, mostly in regions farther from the ligule. Fructan hydroly
sis could account for the hexose accumulated. Stress caused the osmoti
c potential to decrease throughout the leaf base, but more toward the
ligule. With stress there was 70% less direct contribution of low-degr
ee-of-polymerization fructan to osmotic potential in the leaf base, bu
t that for sucrose and hexose increased 96 and 67%, respectively. Thus
, fructan metabolism is involved but fructan itself contributes only i
ndirectly to osmotic adjustment.