© 2000 Heron Publishing—Victoria, Canada
Reduction in turgid water volume in jack pine, white spruce and black spruce in response to drought and paclobutrazol
J. G. Marshall (1, 3), R. G. Rutledge (2), E. Blumwald (1) and E. B. Dumbroff (3, 4)
1. Department of Botany, University of Toronto, Toronto, Ontario M5S 3B2, Canada / 2. Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Center, 1055 du P.E.P.S., Sainte-Foy, Quebec G1V 4C7,
Canada / 3. Department of Biology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada / 4. Kennedy-Leigh Center for Horticultural Research, Faculty of Agriculture, Hebrew University of Jerusalem, P.O. Box 12, Rehovot
76100, Israel / Received May 18, 1999
Summary
Significant reductions in needle water content were observed in white spruce (Picea glauca (Moench) Voss), black spruce (Picea mariana (Mill) B.S.P.), and jack pine (Pinus banksiana Lamb.) seedlings in response to a 10-day drought, although turgor was apparently maintained. When the seedlings were re-watered
after the drought, jack pine needles regained their original saturated volume, whereas white spruce and black spruce needles
did not. Significant drought-induced reductions in turgor-loss volume (i.e., tissue volume at the point of turgor loss) were
observed in shoots of all three species, especially jack pine. Repeated exposure to 7 days of drought or treatment with the
cytochrome P450 inhibitor, paclobutrazol ((2RS,3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-pentan-3-ol), reduced seedling
height relative to that of untreated controls in all three species. The reductions in saturated and turgor-loss needle volumes
in the paclobutrazol-treated seedlings were comparable with those of seedlings subjected to a 10-day drought. The treatment-induced
reductions in shoot and needle water contents enabled seedlings to maintain turgor with tissue volumes close to, or below,
the turgor-loss volume of untreated seedlings. Paclobutrazol-treated seedlings subsequently survived drought treatments that
were lethal to untreated seedlings.
Keywords:
conifers, dehydration, needles, Picea glauca, Picea mariana, Pinus banksiana, saturated volume, shoots, turgor-loss volume.
